GeoPRISMS NSF Awards – extended abstracts


FY16FY15FY14FY13FY12FY11

Jaime Barnes & John Lassiter
NSF Award 1455432

Fluid-mobile and volatile element (Cl, B, and Li) cycling through the forearc: Case study of cold and thermal spring geochemistries from the Hikurangi accretionary prism, New Zealand

Jaime Barnes (jdbarnes@jsg.utexas.edu), John Lassiter

A subduction zone is an area where two tectonic plates collide and the denser plate (also called a subducting slab, consisting of seafloor sediments, oceanic crust, and underlying mantle) is forced to sink into the mantle beneath the more buoyant plate. Hydrous minerals in the slab break down when exposed to the high temperatures encountered at depth, releasing fluids ultimately involved in the creation of arc magmas and explosive arc volcanoes. In addition, these fluids are also thought to influence seismic slip behavior and the manifestation of earthquakes. Therefore, determining the sources and amount of fluids released at depth within a subduction is critical for understanding volcanic and earthquake behavior along plate margins.

Particular elements (for example, lithium, chlorine, and boron) are highly fluid-mobile, thereby making them excellent tracers of fluid source. These fluids impart diagnostic geochemical signatures to overlying material that can be used to trace mass transfer through subduction zones. This work will geochemically characterize cold and thermal spring waters from the Hikurangi (New Zealand subduction zone) accretionary prism to trace fluid sources along the fore-arc and quantify volatile flux through the fore-arc. Fluid sources to the fore-arc will be determined by examining variations in elemental concentrations (and ratios) and isotopic compositions. The data will be used to evaluate causal links between fluid sources and earthquake mechanics, such as shallow slow slip events. The Hikurangi margin is the ideal locality for this study due to the numerous exposed fore-arc springs, which allow a rare glimpse into the shallow part of the subduction zone, and the previously documented along arc variability in subduction parameters (e.g., amount of subducting sediment) and seismic slip behavior. Geochemical evidence for increased (or more shallow) dehydration reactions in the northern portion of the margin compared to the southern portion would support a link between dehydration reactions and shallow slow slip events.

Robert King & Rebecca Bendick
NSF Award 1551753, 1551823 

Collaborative Research: A community velocity field for East Africa

Robert King (rwk@chandler.mit.edu), Rebecca Bendick (bendick@mso.umt.edu)

The break-up of Africa along the East African Rift System has long served as the type example of how stable continents fall apart in tectonic cycles. As a result, many geophysical and geologic studies have measured and analyzed different sections of the very long rift system in detail, including studies using GPS geodesy to measure the speed, direction, and distribution in space of the ongoing separation of most of Africa (Nubia) from its eastern part (Somalia). However, few, if any, of these previous studies took a comprehensive view over the whole rift and continent, in order to explore how different sections of the rift link together, interact with one another, or influence neighboring parts of the continent outside of the rift valleys. Such a comprehensive view is necessary to better understand the whole continent and, indeed, how other continents split apart in the past or will in the future. The broad process of rifting forms the basis of plate tectonic theory, and also influences the distribution of earthquakes, volcanoes, geothermal resources, mineral resources, and topography in both time and space.

This experiment addresses two pieces of the task of building such a continent-scale view of rifting. First, it includes compiling all known geodetic observations in Africa and surrounding regions from 22 different research groups representing 10 countries. These data will then be combined into a single large-scale velocity field, thus minimizing any uncertainties in relative velocities (and strain rates) arising from variations in reference frame definitions, processing strategies, or network geometries. Second, it includes re-measurements of high-value sites with limited or poor past measurement histories, including a campaign network spanning the Turkana Depression of the Kenya-Ethiopia borderlands, where two parallel active rift structures in Kenya relay to a single rift in Ethiopia. Both of these efforts are directed at providing the highest possible quality present-day tectonic velocity field for the whole African Rift System at the continent scale, as a basic research product and as an open-access kinematic framework for many other diverse research efforts directed at the African system and rifting in general.

Nathan Bangs
NSF Award 1457221

Investigation of the hydrogeologic role of faults in the downgoing plate through comparison of Central America, Cascadia, Nankai, and Alaska subduction zones

Nathan Bangs (nathan@ig.utexas.edu)

Part 1 – The award will fund a GeoPRISMS postdoctoral Fellowship for two years of training at the University of Texas, Institute for Geophysics (UTIG). The proposed work seeks to quantitatively determine the structure and water content in the faults within the select segments of the subducting plates. This will allow the assessment of the effects of subducting water on subduction zone processes. The study will use existing 2D and 3D multichannel seismic data from Central America, Cascadia, Nankai, and Alaska subduction zones. The results will provide a better understanding of the geohazard potential in subduction zones, which is particularly relevant for the Pacific Northwest region where large magnitude earthquakes have occurred on the Cascadia megathrust in recent history. The postdoctoral fellow is an early-career female scientist. The results of the study will be presented at workshops and conferences and will contribute to the high school curriculum development program at UTIG.

Part 2- Funds are provided for a postdoctoral fellow to conduct amplitude preserved seismic prestack depth migration, 2D waveform modeling of fault plane reflections, and fluid flow modeling of the 2D multichannel seismic data at Nicaragua, Cascadia, Nankai, and Alaska subduction zones to explore the limits on the water content of the fault zones in the oceanic plate seaward of the trench. From these results she will begin to quantitatively assess the hydration state of incoming plate at different subduction zones. The seismic attribute analysis of decollement, near-basement sediment, and basement crustal rocks, and the waveform modeling of the faults in the down-going plate beneath the slope in Nankai and Costa Rica 3D datasets will allow the assessment of fluid exchange between the hydrologic systems of upper and lower plate. The post-doctoral fellow will identify water expulsion along faults in the down- going plate as it migrates upward into the upper plate. The results from this study will contribute to answer the two key questions in the GeoPRISMS Subduction Cycles and Deformation science plan: “How are volatiles, fluids, and melts stored, transferred, and released through the subduction system?” and “How do volatile release and transfer affect the rheology and dynamics of the plate interface, from the incoming plate and trench through to the arc and backarc?”

Broader Impacts: The proposed work will provide a better understanding of the geohazard potential in subduction zones, which is particularly relevant for the Pacific Northwest region where large magnitude earthquakes have occurred on the Cascadia megathrust in recent history. The project will support the postdoctoral training of an early-career female scientist. The results of the study will be presented at workshops and conferences and will contribute to the high school curriculum development program at UTIG.

Peter Kelemen
NSF Award 1457293

Collaborative Research: Focused Study of Aleutian Plutons and their Host Rocks: Understanding the building blocks of continental crust

Peter Kelemen (peterk@ldeo.columbia.edu)

Arc magmatism is the most important process that generates the continental crust today and likely throughout Earth’s history. However, average continental crust composition is andesitic and calc-alkaline, while average arc lava composition is basaltic and tholeiitic. The largely unexposed and unsampled plutonic part of the arcs, on the other hand, may be more similar to the continental crust. Therefore, understanding the genesis of plutonic rocks is a key to understanding continental crust formation and evolution via arc magmatism, a key science goal for the GeoPRISMS initiative. The Aleutian arc is uniquely well-suited for such a study, because of the extensive exposures of plutonic rocks, unmatched in any other intra-oceanic arc. In the Aleutian arc, most felsic plutonic rocks have compositions that overlap estimates for the bulk continental crust. Our pilot study found that Eocene-Miocene plutonic rocks and Holocene volcanic rocks show distinctly different elemental and isotopic signatures, which indicate that they were derived from distinct parental magmas. This difference could reflect temporal variation of the mantle under the region, or fundamentally different mechanisms that form plutons and lavas – perhaps strongly calc-alkaline magmas, with high H2O contents, tend to degas in the mid-crust, causing a rapid increase in viscosity and crystallinity, therefore they tent to stall and form plutons; while hotter, drier, tholeiitic basalts have lower viscosity and readily erupt to form lavas.

As it is crucial to understand the extent and origin of the compositional difference between central Aleutian lavas and plutons through time and space, this project will map and sample plutonic rocks exposed on the central Aleutians and their coeval volcanic host rocks. A subset of the most promising samples will be measured for major element, trace element and isotopic compositions (Sr, Nd, Hf, Pb). The ages of the plutons and/or the lavas will be constrained using U-Pb zircon geochronology and 40Ar/39Ar geochronology analyses of plagioclase phenocrysts and the groundmass. These preliminary results and the samples acquired in this study will help to answer fundamental questions of continental crust formation, and shed light on the formation mechanisms of plutons and volcanics in arcs.

Ronald Cole
NSF Award 1456630

RUI: Magmatic Evolution Leading Up to the Modern Aleutian Arc on the Alaska Peninsula

Ronald Cole (ron.cole@allegheny.edu)

Alaska contains the largest number of active volcanoes in the United States and is one of the most volcanically active regions in the world. Most of the volcanoes in Alaska form a belt that includes the Aleutian Islands and extends landward onto the Alaska Peninsula, ending across the Cook Inlet from Anchorage. The Alaska Peninsula hosts more than 20 volcanoes with historic activity, five with major eruptions in the past 25 years and includes the world’s largest eruption of the 20th century. This project will investigate the growth of the volcanic system on the Alaska Peninsula and evaluate the factors that influence the composition and behavior of volcanoes in this region. The results of this project will contribute to ongoing work of the U.S. Geological Survey and Alaska Volcano Observatory for understanding volcanic behavior in a region where there are roughly 30,000 people per day transported in commercial aircraft over the volcanoes and where eruptions can have severe impact on Anchorage (Alaska’s largest population center) and along the Kenai Peninsula. The Alaska Peninsula is also one of the nation’s most important mineral resource regions; this project will provide an improved regional framework that will be useful for future detailed studies to delineate economic mineral deposits. Scientific advances made through this project will also contribute to the public-outreach mission of Lake Clark and Katmai National Parks, where several of the volcanoes of this study are located. This project will additionally provide high-level STEM training for undergraduate students. The project is highly cost-effective because it uses publically-available sample collections of the U.S. Geological Survey, building on past investments in federal funding.

Southern Alaska is one of the best places in the world to investigate long-term magmatism and crustal growth along a convergent margin, as recognized by the GeoPRISMS community who selected the Alaska/Aleutian subduction zone as the highest priority site for the Subduction Cycles and Deformation (SCD) initiative. This two-year project will benefit the GeoPRISMS community with an unprecedented synoptic study to evaluate temporal and along-strike geochemical trends for Eocene through Quaternary igneous rocks on the Alaska Peninsula. Data will include major and trace element, whole rock Nd-Sr-Hf and zircon Hf-isotopes, and 40Ar/39Ar and zircon U/Pb dating on volcanic and plutonic rocks. The results of this research will provide new constraints on the continental portion of Aleutian arc including: i) along-arc trends in magma chemistry and relationships with sediment flux and regional tectonics, ii) geochemical products of subduction over time and how these influence the composition of new continental crust, and iii) the timing of subduction initiation and relationship to Pacific-wide versus local tectonic processes. This work is in concert with the GeoPRISMS SCD initiatives to “focus on long-term margin evolution and material transfer” and “the growth and evolution of volcanic arcs and continents” and can be integrated with other projects (i.e., geophysical studies of the southern Alaska margin) to yield advances in understanding the regional controls on convergent margin magmatism.

Eric Mittelstaedt
NSF Award 1456664

Emplacement of regularly spaced volcanic centers in the East African Rift: Melt production or melt extraction?

Eric Mittelstaedt (emittelstaedt@uidaho.edu)

Volcanoes and volcanic activity present significant natural hazards, but they are poorly understood. The principal goal of this project is to constrain the proccess that regulate the timing, location, and volumes of volcanism at the Earth’s surface, specifically within continental rifts, but more broadly in any region undergoing tectonic extension. Observations at continental rifts, such as the East African Rift, find changes in the style of volcanism from widely, irregularly spaced volcanic centers in areas with small amounts of extension to surprisingly regularly spaced, uniform volcanoes in significantly extended regions. We propose that the changes in volcanic style may be controlled by a balance between the location of faults and fractures near the surface and the variability of magma production beneath the crust, in the Earth’s mantle. To determine the role of these two processes and how those roles may change with extension, will will use both numerical simulations and analogue laboratory models to develop mathematical tools that will inform our understanding of the drivers of volcanic activity in these areas.

As continental rifts evolve, volcanic centers within rift valleys often develop a characteristic spacing, or wavelength, such as observed in the Red Sea Rift and within the Afar depression, the Main Ethiopian Rift (MER), and the Kenya (Gregory) Rift of the East African Rift System (EARS). The surprisingly regular spacing of the volcanic centers within the EARS is attributed to lithosphere thickness, pre-existing fault systems, and mantle processes. However, little quantitative assessment of these hypotheses has been undertaken and few studies attempt to include the visco-elastic-plastic rheology of the lithosphere. The primary goal of this work is to use data from coupled numerical and laboratory experiments along with observations from the East African Rift System (EARS) to quantitatively assess the contribution of both melt production and melt extraction processes on the distribution of volcanic activity along the three main branches of the actively spreading EARS. We will perform two groups of coupled laboratory and numerical experiments; the first will simulate Rayleigh-Taylor type instabilities within the partially molten mantle (melt production), and the second will simulate the importance of pre-existing fractures and volcano loading on surface volcanism (melt extraction). Numerically, we will use a 3D marker-in-cell, finite difference code to initially match the laboratory experiments and then expand the parameter range beyond that possible in the laboratory. Both sets of experiments will vary rift opening rate, lithospheric thickness, pre-exiting fractures, and volcanic loading. Finally, we will develop predictive scaling laws that relate volcano spacing and volume to the above parameters. These scaling laws will permit the use of surface observations to estimate the relative importance of melt production below the lithosphere versus melt extraction through the lithosphere in both the EARS and other continental rifts.

Jeffrey Freymueller
NSF Award 1457361

Interseismic Slip Deficit at the Edge of a Locked Patch: Shumagin Islands, Alaska

Jeffrey Freymueller (jeff.freymueller@gi.alaska.edu)

Alaska is a premier location for studying what controls variations in seismic activity along a margin where tectonic plates converge. This is because the width of the seismic zone is known to differ between segments along the Alaskan subduction zone. The Alaska Peninsula segment includes the transition from a wide, locked region on the plate interface to a dominantly creeping section. The fact that a chain of islands runs across this segment provides an ideal setting for measuring deformation, and these data will be used to determine the distribution of recent slip (or lack thereof) along the plate boundary fault. This is the first time that a detailed view of how the seismogenic zone varies from a locked to a creeping section will be obtained. The findings will inform assessment of earthquake and tsunami hazards, both in relation to the Alaska Peninsula and along the US west coast due to trans-Pacific tsunamis. Investigators will conduct public lectures and work with a teacher in the school district of the local community of Sand Point, Alaska, in the Shumagin Islands. Lesson materials will be developed on the topics of earthquakes and tsunamis in Alaska, subduction and its impact on their local environment.

GPS measurements will be made at sites that have not been surveyed since the 1990s, providing new highly precise plate velocities. Most of the sites have been measured once, and the new measurements will come >20 years after the first, resulting in velocity uncertainties that should be <0.5 mm/yr. These data will be used to estimate the distribution of locked and creeping parts of the plate interface fault, and spatial changes in the seismogenic zone will be compared with spatial changes in seismicity and properties of the downgoing plate. Results will address how abrupt the along-strike transition is, from the wide locked region of the Semidi segment to the much narrower and/or creep-dominated locked region of the Shumagin segment. The structure within the partially locked region of the Shumagin segment will be addressed through modeling. The study will also investigate potential correlation between observed slip variations and features on the overriding or downgoing plates, the reflection character of the plate interface itself, seismicity patterns, or other geologic observations.

Terry Plank & Diana Roman
NSF Awards 1456814, 1456939

Collaborative Research: From the Slab to the Surface: Origin, Storage, Ascent, and Eruption of Volatile-Bearing Magmas

Terry Plank (tplank@ldeo.columbia.edu), Diana Roman (droman@dtm.ciw.edu)

On any given day, approximately 15-30 volcanoes worldwide are either in eruption or show strong signs of unrest (e.g., anomalously high rates of seismic activity, ground deformation, or gas emissions). Volcanic activity, including high-altitude eruptions of ash or emission of large volumes of gas, poses a significant hazard to people and property in the United States and worldwide. This is particularly true in Alaska, with over 10,000 passengers a day flying over 35 historically active volcanoes on North America/Asia flight routes. Although significant progress has been made in recent decades in understanding the physical processes occurring in the upper portions of the Earth’s crust that lead directly to volcanic activity and associated unrest, there is a fundamental lack of understanding of how these shallow crustal processes link to and are controlled by the large-scale crustal tectonics and deep mantle melting that are ultimately responsible for arc volcanism. Specifically, although it is well understood that the amount of water and other volatiles dissolved in a magma plays a key role in its generation, ascent, and eruption, it is unclear why some arc volcanoes erupt ‘wetter’ magmas than others. Identifying large scale controls on magma volatile contents is thus critical for accurate forecasting of the frequency, volume, and explosivity of volcanic eruptions.

Here, we propose an integrated geochemical-geophysical study of the Unimak-Cleveland corridor of the Aleutian volcanic arc, which encompasses six volcanoes that have erupted in the past 25 years with a wide range of magmatic water contents. This relatively small corridor also exhibits a range of deep and upper-crustal seismicity, apparent magma storage depths, and depths to the subducting tectonic plate. Our goal is to link two normally disconnected big-picture problems: 1) the deep origin of magmas and volatiles, and 2) the formation and eruption of crustal magma reservoirs, which we propose to do by establishing the depth(s) of crustal magma reservoirs and pre-eruptive volatile contents throughout the corridor. The integrated study components include analysis of volcano- seismic events and magmatic volatile analysis. Existing seismic data catalogs contain ~ 14,000 events, and some samples of volcanic eruption products are already in hand. The existence of two actively erupting volcanoes in the corridor further motivates collection of simultaneous seismic, gas (in collaboration with the USGS Alaska Volcano Observatory) and tephra samples during eruption, that reflect active evolution of the magmatic system.

Kerry Key & Ninfa Bennington
NSF Awards 1456710, 1456749

Collaborative Research: Magnetotelluric and Seismic Investigations of Arc Melt Generation, Deliver and Storage Beneath Okmok Volcano

Kerry Key (kkey@ucsd.edu), Ninfa Bennington (ninfa@geology.wisc.edu)

Part 1 – The investigators will conduct a magnetotelluric (MT) survey at Okmok volcano in the Aleutian arc in order to characterize the magmatic system beneath the volcano. New onshore passive seismic and MT data and offshore MT data will be collected to test hypotheses regarding the role of slab fluids in arc melt generation, melt migration within the crust, and the crustal magmatic plumbing and storage system beneath an active caldera. The project will support a female early career investigator several graduate and undergraduate students providing the latter hands-on research at sea. Data from this project is planned to be incorporated into undergraduate Earth Sciences courses and presentations.

Part 2 – The Aleutian volcanic arc is a GeoPRISMS primary investigation site that is tectonically active region considered to be ideal for studying arc magmatism. Okmok, an active volcano located in the central Aleutian arc, is only about 100 km from Dutch Harbor making it a logistically advantageous for an amphibious onshore and offshore geophysical imaging of the arc?s magmatic system. Okmok is also selected due to its known volcanic activity, the presence of a crustal magma reservoir, as inferred from previous studies, and the volcanic hazard it presents, as evidenced by the lack of warning prior to 2008 eruption. It has hosted 2 caldera-forming eruptions (CFE) and is representative of volcanoes both within the Aleutian arc and worldwide that experience long periods of effusive eruptions punctuated by much larger explosive CFE. The project will test hypotheses on the role fluids play in melting the mantle wedge and how melts ascend through the corner flow regime of the mantle wedge. It will also test competing hypotheses about melt migration and storage within the upper mantle and crust and how this impacts explosive CFE. Data collected by this project will be used to map seismic velocity and electrical conductivity variations within the arc, providing unique constraints on temperature, mineralogy and fluid content. These constraints will be used to study the mantle melt flux, its possible storage at the base of the crust, the distribution of partial melt/magma bodies in the mid-upper crust, and the thermal and mechanical properties of the upper crust beneath the caldera.

Broader Impacts: The proposed work would help improve our understanding of magma storage and transport and its implications on volcanic hazards at Okmok volcano. A female early career investigator and three graduate students (1 Scripps; 2 UW-Madison) would be supported. Seven undergraduate students would be supported (partially through funds from this project and via Scripps NSF REU supported SURF program) to participate in onshore/offshore fieldwork. Data from this project will be incorporated into undergraduate Earth Sciences courses and presentations will be given at local K-12 schools and via live webinars to a few Alaskan schools. A short course on MT methods will be given at UW-Madison and a computer display for this project will be created for the UW Geology Museum?s Active Earth display.

Rebecca Bendick & Robert King
NSF Awards 1347192, 1347282

Collaborative Research: Active kinematics of lithospheric extension along the East African Rift

Rebecca Bendick (bendick@mso.umt.edu), Robert King (rwk@chandler.mit.edu)

This 1-year, collaborative proposal is aimed at creating a community solution for tectonic velocities throughout the East African region. This region hosts the foremost example of continental rifting, where Africa stretches and splits into a two pieces, Somalia and Nubia in the East African Rift and beyond. Observations of the speed and pattern of continental break-up serve as a framework for other geosciences research on continental rifting, including in volcanology, petrology, geochemistry, and solid earth-climate interactions. They also offer the possibility of general results for the material properties of continents and the basic physics of how plates are formed, move, and change. Beyond the science, mapping patterns of surface deformation in East Africa informs earthquake and volcano hazard assessments and development of geothermal energy and water resources. A final contribution of this project is to foster data sharing and community model building among academic institutions throughout the U.S. and East Africa.

Specific initiatives we propose include: 1) formally combine GPS results from all available prior studies, along with any other available GPS data in the region for a fully self-consistent, continent-scale solution and to identify future needs and data acquisition strategies, 2) maintain existing geodetic assets developed over the past 6 years to extend GPS time series to reduce rate uncertainties, 3) extend or establish agreements (Memoranda of Understanding) with host-country partners (Ethiopia, Eritrea, Kenya, Tanzania, Mozambique, Zambia, and Malawi) for future joint initiatives, 4) measure a first epoch on nine campaign GPS sites in the Turkana Depression, and 5) develop a framework for data sharing and data product development to serve the broader African Rift scientific community.

Matthew Jackson, Elizabeth Cottrell & Katherine Kelley
NSF Awards 1347377, 1347248, 1347330

Collaborative Research: The role of oxygen fugacity in calc-alkaline differentiation and the creation of continental crust at the Aleutian arc

Matthew Jackson (jackson@geol.ucsb.edu), Elizabeth Cottrell (cottrelle@si.edu), Katherine Kelley (kelley@gso.uri.edu)

This proposal seeks to examine the role of oxygen variations in the origin of the calc-alkaline magmas that erupt at subduction-related volcanoes (arc volcanoes). In particular, the PIs seek to determine how oxygen varies during differentiation and degassing, and see how it varies along strike of the Aleutian arc as a function of material derived from the subducted slab. The work will also include an experimental study of the relationship and interplay between H2O and fO2 during magma formation, a critical question with implications for the formation of continental crust. The PIs note that the Aleutian arc features local and regional variations in numerous geochemical features, but lacks the complexities introduced when magmas move through continental crust. The proposed work includes novel (micro XANES) analysis of the ferrous/ferric ratio in glasses (a proxy for oxygen content), especially glass inclusions in mineral. Water, CO2 and major and trace elements (including Cl and S) will also be analyzed. The PIs also propose an experimental program in which fO2 is varied at constant water content. The experimental glasses will be analyzed using the same techniques as described for the natural glasses. Broader impacts include a new interactive exhibit at the Smithsonian that will include an on-line component. Material from the exhibits will be incorporated into undergraduate curricula. There will be undergraduate mentoring through REU and/or senior thesis, as well as mentoring of grad students and a post-doc.

Katie Keranen, Donna Shillington & Demian Saffer
NSF Awards 1347262, 1347312, 1347343

Collaborative Research: The Aleutian megathrust from trench to base of the seismogenic zone; integration and synthesis of laboratory, geophysical and geological data

Kathleen Keranen (keranen@cornell.edu), Donna Shillington (djs@ldeo.columbia.edu), Demian Saffer (dsaffer@geosc.psu.edu)

Earth’s largest and most destructive earthquakes and tsunamis are generated along subduction megathrusts. The portion of these plate tectonic boundary faults that ruptures in earthquakes is known as the seismogenic zone. Recent observations of high slip that propagates to the near surface, and new discoveries of anomalously slow slip events, have raised fundamental questions about widely held hypotheses that explain seismogenic zone behavior. In particular, the seismogenic zone of many subduction faults appears to be ‘patchy’, with some regions that fail suddenly in large earthquakes and others that slide by stable, aseismic creep. Additionally, in certain depth ranges, typically at the shallow and deep fringes of the seismogenic zone, slow slip events and earthquakes with anomalous low frequency energy have been observed at many margins. Current knowledge of the fault zone conditions and processes that cause these different modes of slip is limited, largely because quantitative constraints on in situ conditions in the subsurface are scarce. As a result, the associated earthquake and tsunami hazards are similarly poorly constrained. This project will combine high quality regional geophysical studies from the Aleutian subduction margin with laboratory experimental measurements on relevant rock and sediment, to calibrate the geophysical data and quantify in situ pore fluid pressure and stress along the subduction megathrust. Ultimately by providing quantitative estimates of the subsurface conditions along the plate boundary from the trench through the seismogenic zone, this study will test hypothesized mechanisms for the wide range of earthquake behavior.

To accomplish this, the study will integrate laboratory data from modern oceanic sediment and exhumed metapelites with existing, multi-resolutional geophysical data to improve our understanding of in situ conditions and processes along the plate boundary megathrust from the trench to ~30-40 km depth. The project will address the following questions: 1) What are the in situ conditions, materials, and properties along the subduction megathrust that are sensed by low Vp, high Vp/Vs ratio, and high reflectivity? To what extent do seismic data image weak metasedimentary material vs. high-porosity channels or patches at near-lithostatic pressure and low effective stress? 2) How do the properties of the plate boundary change with depth and along-strike, and how do they relate to seismicity and upper plate deformation? These two overarching questions will be addressed by: (1) extracting detailed constraints on geophysical properties of the megathrust (Vp, Vp/Vs, reflectivity) from active and passive source datasets from the trench to depths of ~30-40 km; (2) defining elastic and hydrologic properties of sediment and rock relevant to the in situ subduction interface at the Alaska margin, via lab experiments on IODP cores from offshore Alaska and samples from exhumed fault zones on Kodiak Island; (3) integrating the geophysical and laboratory components to test hypotheses about the roles of material properties and state variables on geophysical signatures along the subduction thrust; and (4) investigating the correlation of megathrust properties with earthquake locations via precise relocation of microseismicity. The work will leverage several existing high-quality geophysical datasets, a suite of already collected samples, and DSDP/IODP cores and data. As a whole, this coordinated study will vastly improve our understanding of the conditions and materials along the megathrust, their relationship to seismicity, and serve as a template for similar studies at other margins.

Susan DeBari & Cathy Busby
NSF Awards 1347794, 1347901

Collaborative Research: The Rosario Segment of the Cretaceous Alisitos Oceanic Arc (Baja California, Mexico): An Outstanding Field Analog to the Izu Bonin Arc

Susan DeBari (susan.debari@wwu.edu), Cathy Busby (cathy.busby@ucsb.edu)

This collaborative research project will interface closely with the IODP projects in the Izu-Bonin-Mariana (IBM) arc by fully characterizing what is probably its best field analog on Earth: the Rosario segment of the Alisitos arc. DeBari has been deeply involved in the IBM proposals, and Busby is co-chief scientist on IODP Expedition 350. Exhumed rocks from arc crustal sections have the unique ability to inform studies of active subduction zones by “ground-truthing” the assumptions that go into models, experiments, and interpretive geophysics and geochemistry. Some of the questions we will ask, highly complementary to the IBM work, are: How is arc middle crust constructed? What is the relationship and proportion between volcanic and plutonic rocks in juvenile arc crust? What is the tempo of constructing arc crust? How does arc crust composition change with time? Is there any older crust that makes up significant parts of the Alisitos arc? What can we learn about convergent margin mineralization by comparing the Alsitos arc to the Izu Bonin arc? How does the crustal structure of the Alisitos arc compare with seismic velocity profiles in modern arcs? Can surface and borehole heat flow measurements in modern arcs be related to features preserved in the geologic record of ancient arcs?

This research furthers the careers of two female scientists (DeBari at WWU and Busby at UCSB) and their respective graduate students. Training of these graduate students is collaborative so that both students will become skilled at the integration of field geology, petrology and geochronology. Scientific interaction between US scientists at WWU and UCSB and international colleagues at UNAM in Mexico will broaden the perspectives of all participants, and enhance research and training outcomes. The proposed project is of interest to the broader science community, as it addresses some of the foremost questions in the NSF GeoPRISMS science plan on the growth and evolution of continental crust through study of island arcs (http://www.geoprisms.org/science-plan.html#science-plan), as well as research envisioned by the GeoPRISMS ExTerra initiative (http://www.geoprisms.org/scd/exterra.html). One of the main products, a web-based ?Island Arc Crust Virtual Field Model?, will be used by scientists as a reference model for IBM drilling outcomes, and in curriculum for both undergraduate and graduate students. A field workshop in the Alisitos arc, ideally held in conjunction with Expeditions 350-352 post-expedition meetings and before IBM-4 drilling begins, will provide invaluable context for IBM drilling participants.

The Rosario segment of the Cretaceous Alisitos arc in Baja California is an outstanding field analog for the Izu-Bonin-Mariana (IBM) volcanic arc. The IBM arc is under intense study by the International Ocean Drilling Program (IODP) as an in-situ example of present-day formation of nascent continental crust. Earth is the only planet in the solar system with extensive felsic (Si-rich, Mg-poor) continental crust. The rocky planets and the Moon have basaltic (Mg-rich) crusts formed early in the history of the solar system. The volume of continental crust on Earth has grown over time due to plate tectonic processes, dominantly because of accretion of felsic to intermediate volcanic arcs at convergent margins. However, the processes that produce this felsic to intermediate crust are not well characterized in situ. The Rosario segment has superior three-dimensional exposures of an upper- to middle-crustal section through an extensional oceanic arc. Previous mapping of this 60-km-long segment of the Alisitos arc, done in the 1990?s (Busby et al., 2006), will provide a framework for the proposed study; however, that study focused mainly on field descriptions of the volcanic rocks, with limited geochronology, and no geochemistry. The proposed study will determine in detail the relationships between rock types at all stratigraphic levels in the arc, using field, geochemical, and geochronological data. This collaborative research project will interface closely with IODP Expeditions 350-352 (in 2014) and a fourth ambitious proposal to drill to the arc middle crust (IODP Proposal 698 at site IBM-4, awaiting scheduling. These data will be used to construct an ?Island Arc Crust Virtual Field Model? to be used by scientists as a reference model for IBM drilling outcomes.

Chris Marone & Demian Saffer
NSF Awards 1347344

Runaway Slip: Understanding Nucleation of Subduction Megathrust Earthquakes and Slow Slip Precursors

Chris Marone (cjm38@psu.edu), Demian Saffer (demian@psu.edu)

Subduction zone earthquakes where ‘runaway slip’ allows faulting to rupture from depth all the way up to the seafloor can cause enormous tsunamis that devastate coastal population centers. Not all subduction zone earthquakes develop runaway slip- details of a particular fault’s frictional behavior dictate what happens. This study will conduct laboratory experiments to determine how different types of fault rock respond to applied forces. Results could improve understanding of whether some subduction zones are more, or less, likely to generate megathrust earthquakes.

Current understanding of the mechanical response to shear stress of fault rock is limited by the lack of measurements on relevant natural samples at in-situ conditions. Laboratory shear measurements will document friction at in-situ pressures and temperatures using natural fault zone material. A transition in clay structure is thought to play an important role, along with mineral fabric and pore fluid pressure. A series of experiments on both crushed samples and intact wafers will be conducted. Start and end microstuctural and geochemical analyses will quantify the shearing impacts. Interpretation will focus on the nucleation phase of megathrust earthquakes. A female postdoctoral scientist will lead the study and the results will contribute to advancing knowledge within the GeoPRISMS program initiative ‘Subduction Cycling and Deformation’.

Dave Chadwell
NSF Award 1249876

Constraining Slip Distribution of the Cascadia Subduction Zone Offshore Central Oregon with Seafloor Geodesy

C. D. Chadwell (cchadwell@ucsd.edu)

This project seeks to initiate geodetic measurements of plate motion in the Cascadia subduction zone. Three sites off the Oregon coast, one on the incoming plate to measure relative plate motion and two on the continental slope to measure motions related to fault motions and deformation will be monitored for horizontal displacement at the cm scale. These will be the first offshore monitors of upper-plate Cascadia motion and fault behavior. This work will lead to a better understanding of earthquake and tsunami risk in Cascadia. It implements a new autonomous approach to data collection. It places permanent benchmarks on the seafloor so that monitoring can continue into the indefinite future. Transponders will be recovered and reused and become part of instrument pool that can be used to extend these studies in the future.

Robert Harris
NSF Award 1249552

Thermal Structure of the Cascadia Subduction Zone, Grays Canyon Discovery Corridor, Washington

Robert Harris (rharris@coas.oregonstate.edu)

Heatflow measurements using a 3.5 m probe will be added to a scheduled experiment “Thermal structure of the cascadia subduction zone on the WA margin (PIs Johnson & Solomon, OCE-1144164). The probe temperature and thermal conductivity measurements will enhance the ~1 m depth heatflow determinations the main experiment will obtain. Improved assessment of possible bottom water temperature variation will be documented by deviations from linearity in the uppermost thermal gradient measured by the probe. One day of shiptime to conduct heat probe work is confirmed, a second day is requested if ship schedule allows. Postcruise numerical modeling of these data aims to constrain temperature structure extending down to the subducting plate interface, which is related to deep seismicity patterns.

Taryn Lopez
NSF Award 1250148

GeoPRISMS Postodoctoral Fellowship: Geochemical constraints on the source, flux, migration, and seismic signature of volcanic fluids, Katmai Volcanic Cluster, Alaska

Taryn Lopez (tlopez@gi.alaska.edu)

Fluid movement in the subsurface of active volcanoes is frequently thought to produce abundant seismicity (i.e. earthquakes); however the actual type of fluid, including magma, volcanic gases, or hydrothermal waters, and the implications of the fluid movement cannot currently be constrained from seismic data. Knowledge of the type of fluid/s in the subsurface is critical for both forecasting volcanic eruption and estimating the explosivity of the impending eruption. Through comparison of high temporal resolution measurements of volcanic gas composition and seismicity, it may be possible to identify the type of fluid associated with unique seismic signatures. The ability to identify magma movement from seismic data will enable scientists to better determine the likelihood and/or timing of impending eruptions.

In this project, geochemical measurements of volcanic fluids and complementary seismic data from three historically-active Alaskan volcanoes will be used to: (1) determine the source (i.e. subducted slab, mantle, crust) and flux of volcanic gases, (2) determine proportions of magmatic and hydrothermal fluids within the subsurface, and (3) distinguish trends in gas composition and/or flux that correlate with seismic signatures of fluid movement. Gas composition will be combined with total gas flux to help elucidate subduction and magma generation processes. Daily measurements of gas composition and flux will be compared with seismic data collected over a two-month period to help determine the type of fluid movement associated with certain seismic signals. This project will answer fundamental science questions applicable to GeoPRISMS objectives, specifically regarding the storage, transfer, and release of volcanic fluids, and the relationship between subduction and surface processes.

Peter van Keken, Bradley Hacker & Geoff Abers
NSF Awards 1249353, 1249486, 1249703

Collaborative Research: The role of fluids in intermediate-depth seismicity and wedge anisotropy: Case studies for Cascadia and Alaska, with a comparison to Japan

Peter van Keken (keken@umich.edu), Bradley Hacker (hacker@geol.ucsb.edu), Geoff Abers (abers@cornell.edu)

The main goal of this study is to determine whether the presence of fluids within Earth’s mantle is a controlling factor determining where earthquakes occur within subduction zones, specifically along the fault that enables the down-going tectonic plate to slip deeper into surrounding viscous mantle. The fact that this seismicity is located within the crust at ‘cool’ subduction zones, such as Alaska and Tohoku, versus in the mantle at ‘warm’ subduction zones, such as Cascadia and Nankai, suggests that fluids play an important role. Directional dependence of seismic wave propagation speeds will be assessed, so that possible bias in earthquake locations can be accounted for. Simultaneously, information about deformation within the viscously flowing mantle will be obtained. Ratios of shear and compressional wave velocities will suggest where fluids are present or not. These constraints will guide computer modeling of mantle flow and temperature in the subduction zones. These results will be linked to petrologic models of mineral phase change associated with plate dehydration that introduce fluids near the plate interface and lead to the generation of arc volcanism.

In-depth collaboration by three geoscientists- a geodynamist, petrologist, and seismologist, serves as a model of interdisciplinary Earth System research. Graduate and undergraduate students will receive training in the use of state-of-the-art methods in their sub-discipline as well as learning how to address interplay with evolving results from complementary sub disciplines. The international collaboration with Japanese scientists provides access to the best instrumented and well-studied Japanese subduction system. The study leverages ongoing work in the NSF GeoPRISMS and EarthScope Programs at Cascadia and that planned for Alaska.

Elizabeth Johnson & Esteban Gazel
NSF Awards 1249438, 1249412

Collaborative Research: Virginia’s Volcanoes: a Window into Eastern North America Mantle Processes

Elizabeth Johnson (johns2ea@jmu.edu), Esteban Gazel (egazel@vt.edu)

The recent magnitude 5.8 earthquakes in Mineral, VA, impacted major metropolitan areas on the East Coast of the U.S. and sparked a need to better understand the geologic characteristics the of Eastern North America Margin (ENAM). A group of more than 100 volcanic bodies approximately 47-49 million years old exposed in Virginia and West Virginia are the youngest known eruptions on the East Coast of the U.S. These magmas and the fragments of rock they collected from the crust and mantle during their ascent and eruption are the only direct samples of the crust and the mantle in recent geologic times. The results from this study will be used in conjunction with data from the EarthScope Transportable Array of seismometers currently being deployed along the East Coast as well as other seismic studies to create a comprehensive picture of the state of the crust and mantle underneath the Eastern U.S., providing context for the potential of future seismic hazards. This project will support graduate and undergraduate research at Virginia Tech and James Madison University. The proximity of the field site to both universities makes field characterization and sampling highly accessible. A field trip for middle and high school students and an outreach course through the Lifelong Learning Institute will be developed in addition to course materials for general education. An exhibit will be created for the Museum of Geociences at Virginia Tech. Data from this research will be shared with the public, the GeoPRISMS and EarthScope communities.

Few constraints currently exist on the composition and structure of the asthenosphere and lithosphere under the ENAM. Geochemical and petrologic data are critical for interpretation of seismic data in the region and understanding the long-term, continued evolution of the rift-to-drift transition for ENAM, as well as for rift margins worldwide. A swarm of Eocene volcanic bodies exposed in Virginia and West Virginia are the youngest known magmatism in the Eastern U.S. and are the only petrologic window into Cenozoic processes in the mantle and lower crust in ENAM. We hypothesize that: 1) The Eocene magmas were generated through adiabatic melting of shallow asthenosphere (e.g., lithospheric delamination, edge-driven convection, or effects from deep subduction), 2) Melting is related to the lithospheric response to the breakup of Pangaea and/or Farallon subduction that continued under this passive margin at least through the Eocene. We will test these hypotheses with an array of geochemical, spectroscopic, and petrologic observations and modeling. Geochronology of the melts and basement xenoliths will evaluate melting processes, constrain the structure and evolution of the lithosphere, and evaluate the age of the volcanic activity relative to the age of the xenoliths. The EarthScope Transportable Array is currently being deployed along the East Coast through 2013 and the location of our project lies within the ?Richmond Transect? proposed for concentrated seismic studies. Our data will produce a vertical cross-section deep into the ENAM that will provide important constraints on basement and mantle composition, lithospheric and asthenospheric structures, and volatile contents for large-scale geodynamic and seismic studies.

Bernard Hallet & Peter Koons
NSF Awards 1250130, 1249909

Collaborative Proposal: Modeling Sediment Production from Glaciers off south-central Alaska during Quaternary Climate Oscillations

Bernard Hallet (hallet@u.washington.edu), Peter Koons (Peter.Koons@maine.edu) and S. Birkel

The PIs will model the production, transport, and deposition of glacial sediments at the Alaska-Aleutian subducting margin during the last 125,000 years. The Cordilleran Ice Sheet and crustal response to ice loading will be modeled using the University of Maine Ice Sheet Model (UMISM). USISM solutions will be related to existing sediment datasets and glacial power erosion laws to determine temporal and spatial patterns of erosion and sediment distribution. Suspended sediment samples and field measurements of rock strength will be collected and integrated with the modeling efforts.

Broader Impacts:The societal impacts of the study ultimately include a better understanding of earthquake hazards along this active margin. The project will involve graduate and undergraduate students. Data and models will be simplified for online experimental learning modules targeted at K12/general audiences. Model results will be made available through the U Maine web server.

Peter van Keken
NSF Award 1339783

GeoPRISMS Office Support

Peter van Keken (keken@umich.edu)

GeoPRISMS program that conducts interdisciplinary activities that integrate the Earth and Ocean Sciences communities. The overarching themes of research are 1) the origin and evolution of the continental crust; 2) fluids, melts and their interactions; 3) tectonic-sediment-climate interactions; 4) geochemical cycles; and 5) plate boundary deformation and geodynamics. The guiding principles to study these main themes are 1) the use of interdisciplinary communities; 2) the study of active systems; 3) use of experiment, theory and computation; 4) crossing the shorelines; and 5) use of focus sites. Research at the main initiatives (Rift Initiation and Evolution; Subduction Cycles and Deformation) combine large scale amphibious deployments and smaller marine or terrestrial field studies at Cascadia, Eastern US, Alaska-Aleutians, East Africa and New Zealand. The field studies are augmented with thematic and global studies.

Funds are provided for the GeoPRISMS Office including deliberations of a Steering and Oversight Committee and an Education Advisory committee. The Office will provide structure for the GeoPRISMS community to facilitate community planning, organizes planning and synthesis meetings, and supports the community management structure by organizing meetings of the steering and educational committees. The Office will also support education and outreach activities, provides direct links between the GeoPRISMS community and national infrastructure facilities (such as EarthScope), and facilitates international collaboration.

Broader Impacts: The office will provide a central vehicle for the dissemination of the planning, execution, and documentation of the main scientific projects. The Office will also provide outreach to scientists working in hazards and economical resources and promote teaching, training, and learning through its education and outreach activities that include a distinguished lecturer program, mini-lessons and webinars, a student and community forum, a postdoctoral fellowship program, and graduate student symposia that are held during GeoPRISMS workshops.

Harm Van Avendonk et al., the ENAM CSE team
NSF Awards 1348454, 1348124, 1347024, 1347310, 1348228, 1348934, 1347498, 1348342

Collaborative Research: A community seismic experiment targeting the pre-, syn-, and post-rift evolution of the Mid Atlantic US margin

Harm Van Avendonk (harm@ig.utexas.edu), Matt Hornbach (mhornbach@smu.edu), Steve Harder (harder@utep.edu), Maureen Long (maureen.long@yale.edu), Brandon Dugan (dugan@rice.edu), Paul Wiita (wiita@chara.gsu.edu), Donna Shillington (djs@ldeo.columbia.edu), Dan Lizarralde (danl@whoi.edu)

The structure and evolution of the Eastern North America margin are the focus of this GeoPRISMS community seismic experiment. The data obtained will form a fundamental framework to address several aspects of the Program’s Rift Initiation and Evolution initiative: how tectonic, magmatic, erosional and depositional processes interact; the role of mantle dynamics in ongoing deformation along this passive margin; the impact of ancient regional structure on long-term evolution that shapes present-day distribution of geologic activity.

A year-long ocean bottom seismometer array (OBSIP- 30 instruments) will extend onshore station coverage (EarthScope Transportable Array, ~30 sites relevant) across Cape Hatteras. Additional transects of densely-spaced seismometers will record seismic waves that travel across the coastline, documenting more detailed structure from the continental slope through the coastal plain. Multi-channel seismic reflection data will be openly available upon completion of a training workshop that will conduct basic processing. Similarly, seismic refraction data will be distributed for a second training workshop. Data for investigations using natural seismic events will also be openly available via the IRIS Data Management Center. Station spacing and array aperture target crust and upper mantle imaging. The experiment design builds on existing data to address current scientific questions, emphasizing both deeper structure, which will illuminate driving forces for ongoing evolution, and modernizing shallow structural constraints, to better document surface response records and their relationship to the history of glacial, sea level, depositional, and magmatic loading.

Paul Wiita, Scott King & Maureen Long
NSF Awards 1251329, 1250988, 1251515

Collaborative Research: Mantle Dynamics, Lithospheric Structure, and Topographic Evolution of the Southeastern US Continental Margin

Paul Wiita (wiitap@tcnj.edu), Scott King (sdk@vt.edu), Maureen Long (maureen.long@yale.edu)

The surface geology of the eastern United States is extraordinary in its complexity. This complexity reflects a wide range of tectonic processes that have operated in the region over the past billion years, including episodes of subduction and rifting associated with two complete cycles of supercontinent assembly and breakup. A record of these processes is preserved in the geological units and topography we see at the surface today. It is unknown, however, how the crust and mantle lithosphere have responded to these tectonic forces over time, and whether and how the geological units preserved at the surface relate to deeper structures. The persistence of Appalachian topography through time remains a major outstanding problem in the study of landscape evolution. There is an ongoing interplay among erosion, topography, rock type, and mantle flow at depth that controls the structures we see at the surface today. However, understanding the complex role played by each of these factors requires better constraints on the history of topographic change and its relationship to the deep structure and dynamics of the mantle. Our project, known as the Mid-Atlantic Geophysical Integrative Collaboration (MAGIC), aims to address these fundamental questions about the geophysical evolution of the eastern United States by studying surface processes, crustal and lithospheric structure, and deep mantle flow across Virginia, West Virginia, and Ohio.

MAGIC involves a collaborative effort among seismologists, geodynamicists, and geomorphologists. We are undertaking a two-year deployment of 28 broadband seismometers in a dense linear transect from the Atlantic coast to the continental interior. In combination with EarthScope USArray Transportable Array (TA) stations our experiment geometry will provide an opportunity to image isotropic and anisotropic crust and mantle structure from the coast to the continental interior in unprecedented detail, using techniques such as shear wave splitting, receiver function analysis, and tomographic inversions. The dense linear array allows us to target small-scale crustal and lithospheric variations for imaging. Our geodynamical modeling effort focuses on quantitatively testing several different hypotheses for the pattern of mantle flow by using 3-D, time-dependent, numerical models to make testable predictions about mantle anisotropy and surface topographic change, which will be tested against results from the seismology and geomorphology components of the project. The geomorphology component of the project uses quantitative stream profile data and cosmogenic isotopes to understand the history of erosion rates and topographic change throughout the Appalachian region. Insights into uplift history and the approach to equilibrium among lithology, topography, and erosion (and their spatial variation) will be compared to inferences on the mantle flow field and deep crustal and lithospheric structure gained from the geodynamics and seismology components of the project. Insight from all three efforts will be combined to obtain a vertically integrated picture of tectonic processes from the surface through the crust and mantle lithosphere to the asthenosphere and deeper mantle. The education and outreach component of this project focuses on the involvement of undergraduates in scientific research, opportunities for graduate students to mentor and advise undergraduate students, and forging ties with colleges and universities (including many primarily undergraduate institutions) in our study region that are not currently involved with the EarthScope initiative.

Ken Creager et al., the iMUSH team
NSF Awards 1144568, 1144455, 1144353, 1444275

Collaborative Research: Illuminating the architecture of the greater Mt. St. Helens magmatic systems from slab to surface

Kenneth Creager (kcc@uw.edu), Olivier Bachmann, Heidi Houston, John Vidale, Alan Levander (alan@esci.rice.edu), Adam Schultz (adam@coas.oregonstate.edu), Paul Bedrosian, Geoff Abers (abers@cornell.edu)

To better understand volcanic activity, it is fundamental to get an accurate representation of magma generation zones and storage regions in the Earth?s crust and upper mantle. Illuminating the architecture of the plumbing system beneath volcanoes will allow scientists to determine (1) at which depths and conditions magmas are generated, and (2) the shapes and sizes of pathways and reservoirs along which magma travels towards the surface. Such knowledge will allow scientists to make more informed predictions on the durations of volcanic crises and on the total volume of erupted material during eruptive episodes.

This project focuses on the Mount St. Helens volcanic edifice, (WA, USA), whose explosive eruption in 1980 attracted world?s attention, and was the first volcano to be thoroughly monitored with modern instruments. Mount St. Helens provides an ideal setting to apply state-of-the-art geophysical and geochemical techniques to image its subterranean roots: It is active, easily accessible, and has a well recorded past history. The project will use several different methods (active and passive source seismic tomography and scattered wave imaging, magnetotelluric imaging, petrology and geochemistry), involving a large collaborative team, to image the volcano?s plumbing system with unprecedented resolution from the subducting plate to the surface. The results will be informative for many other volcanoes around the world, particularly those located along the infamous Pacific Ring of Fire.

Neal Blair
NSF Award 1144483

The Subduction Margin Carbon Cycle: A Preliminary Assessment of the Distribution Patterns of Multicycle Carbon

Neal Blair (n-blair@northwestern.edu)

The role of recycled fossil C in elemental budgets and organic C behavior on active margins is not known beyond the mid-slope. Fossil C would be expected to persist longer in surface environments than younger materials because of its low reactivity. Its persistence would influence the global C and O2-cycles, product formation during deep burial, and the interpretation of sedimentary organic geochemical records. This exploratory study of the three GeoPRISMS Subduction Cycles and Deformation (SCD) primary focus sites, the Alaskan, Cascadia and Hikurangi Margins, has the specific objective of developing a preliminary assessment of the distribution of multicycle C at the sites. Samples will come primarily from archives held by the National Institute of Water and Atmospheric Research of New Zealand and the Deep Sea Drilling Project/Ocean Drilling Project repositories in the US. In addition, sample collection and analysis is proposed for the planned Integrated Ocean Drilling Program expedition to the Alaskan margin in 2013. Analyses of samples will include Raman and FTIR microscopy, stable carbon and radiocarbon isotopic measurements, and elemental (H/C) determinations. The survey to be generated by this project will be a first look at multicycle C across several active margin environments beyond the mid-slope. The baseline information will be used to plan future C-cycling and paleoenvironmental studies.

Broader Impacts: This project and participation in the GeoPRISMS program will be valuable educational and professional experiences for the graduate student involved. Supplemental REU funding will be sought to engage an undergraduate in the research. A GIS-based education tool for the high school study of the global C-cycle will be developed in collaboration with Northwestern?s Office of STEM Education Partnerships.

Emily Brodsky
NSF Award 1144695

GeoPRISMS Posdoctoral Fellowship: Systematic search and characterization of very low frequency earthquakes and offshore tremor in Cascadia using the Amphibious Array

Emily Brodsky (brodsky@pmc.ucsc.edu)

The study will undertake a systematic search for very low frequency earthquakes (VLFE), along the entire margin of Cascadia subduction zone, from the trench to the down-dip edge of the transition zone. The sources of VLFEs will be located and characterized to better understand the physics of fault slip, particularly at the edges of the locked zone. The study will better characterize the nature of seismic radiation and their spatiotemporal variability along the fault zone in the crust. It is also holed that it will improve our understanding of the full spectrum of the seismic radiation during slow slip episodes, physical mechanism governing slow earthquakes, and their relationship with regular seismicity. It may also shed light on the implications of the slow seismic activities on the nucleation of large damaging earthquakes. The study will form an early career research project for a new postdoc under the mentorsuip of the PI.

Broader impacts include support of career development of a new young investigator. The study will examine the seismicity of a subduction zone that can potentially produce great damaging earthquakes. It reflects some of the major goals of the NSF-GeoPRISMS and the Cascadia Initiative, and makes good use of the Amphibious Array. Results from this study may help in planning focused interdisciplinary experiments, and guide the selection of target areas for future research.

Dave Chadwell
NSF Award 1144493

Potential contributions of Seafloor Geodesy to understanding slip behavior along the Cascadia Subduction Zone

Dave Chadwell (cchadwell@ucsd.edu)

The purpose of the study is to determine the optimum placement of seafloor geodetic monuments along the Cascadia Subduction Zone and the frequency and duration of horizontal and vertical seafloor geodetic measurements required to resolve the character of slip along the offshore portion of the thrust fault. Presently, onshore geodesy has determined that the locked region lies almost entirely offshore, however these data lack proximity and poorly resolve details of the stick-slip behavior near the deformation front and the location of the boundary from full stick slip to some component of stable sliding. This one-year project to assimilate existing models of fault geometry, locking behavior along the fault, onshore GPS data, and field-proven precisions of horizontal and vertical seafloor geodesy into an elastic/visco-elastic model. Using this model construction, various placements of seafloor geodetic monuments will be simulated and the resolving power estimated to determine the minimum required array configuration along Cascadia to constrain regional-scale slip behavior on the thrust fault. The project contributes directly to the first two science goals in the GeoPRISMS Science plan on Subduction Cycles and Deformation: What governs the size, location and frequency of great subduction zone earthquakes and how is this related to the spatial and temporal variation of slip behaviors observed along subduction faults? And how does deformation across the subduction plate boundary evolve in space and time, through the seismic cycle and beyond?

The broadest impact of this study will be to provide a guide towards using seafloor geodesy to better quantify the earthquake and tsunami risk associated with a large rupture of the thrust fault within the Cascadia subduction zone. Seafloor geodetic measurements could be collected all along the CSZ as a needed constraint to models of megathrust slip that are mostly constrained by the sub-aerial GPS vectors from the Plate Boundary Observatory, a part of Earthscope. Results of this study will help guide this data collection.

Brian Jicha & Suzanne Kay
NSF Awards 1144494, 1144499

Collaborative Research: A 21st Century Reconnaissance of Aleutian Arc Inception

Brian Jicha (bjicha@geology.wisc.edu), Brad Singer, Suzanne Kay (smk16@cornell.edu)

The Alaska/Aleutian Arc is the most geologically active region in North America with abundant large earthquakes and eruptions from more than 50 active volcanoes. Determining precisely how and when the Aleutian Arc began to form is one of the key elements for understanding the origin of the Bering Sea-Alaska-North Pacific region as well as how several circum-Pacific volcanic zones are related to one another. Our understanding of how volcanism initiated in the Aleutian Arc is clouded due in large part to the scarcity of data that bear on the ages of the earliest volcanic rocks in the Aleutian Islands. The proposed reconnaissance investigation of Aleutian Arc inception involves sampling and determining the ages of the oldest records of volcanism. The aim is to define when Aleutian arc volcanism started and highlight potential linkages with the initiation of volcanism elsewhere in the Pacific and the rapid change in the relative motions of oceanic plates that occurred 52 million years ago. In addition, the proposed research will generate basic information regarding how and why the Aleutian arc poses significant volcanic and earthquake hazards to the population in Alaska and around the Pacific Rim.

The proposed research will employ state-of-the-art 40Ar/39Ar and U-Pb geochronology, along with geochemical, and isotopic analysis of the dated rocks. The focus is on subaerial outcrops on Amatignak, Ulak, and Kiska islands, which hold the greatest potential for exploration into the early history of the Aleutians. New geochronologic and geochemical data will precisely constrain when the Aleutian arc inception began, what the compositions of the eruptive products were, and how they evolved through the earliest history of the arc. This information will also be used to evaluate the existing tectonic models of Aleutian arc inception and Pacific Plate motion during the middle Eocene. This project will forge a new collaboration between scientists at UW-Madison, Cornell University, and the University of Alaska-Fairbanks/USGS that may benefit the GeoPRISMS program for its duration. Our findings will be used immediately to determine where future efforts to examine the Aleutian Arc and its fore-arc structures via submersible ROVs, dredging, and geophysical imaging should concentrate to best address questions of subduction zone initiation.

Paul Johnson
NSF Award 1144164

Thermal Structure of the Cascadia Subduction Zone on the Washington Margin

Paul Johnson (johnson@ocean.washington.edu), E. Solomon

To obtain an accurate estimate of conductive heat flux from the Cascadia accretionary prism, the PIs plan redundant methods to obtain both thermal and fluid flux measurements along a 2.5 D profile of the margin at a single latitude. In this profile they will use thermal blankets suitable for impenetrable sub-stratum, continuous fluid flow meters, multi-core deployments for sediment pore-water chemistry and thermal gradient measurements, and Jason-II heat flow probes. The heat flow and fluid flux data will be obtained at 10 specific equally-spaced depth intervals, along the margin from 2900 m to 500 m depths. The heat flow profile would also coincide spatially with other large-scale NSF programs planned for the Washington corridor at 47°N, including the OBSIP (Ocean Bottom Seismometer) focused deployment site, Endurance Array moorings for OOI, high resolution EM302 bathymetry surveys, and an Open Access 3-D MCS volume using the LANGSETH. The goal would be to obtain data of sufficient quality that downward projection of the surficial thermal gradients to the CSZ décollement and igneous basement can be made with reasonable confidence.

The Open Data Access strategy developed by the MCS community is the new paradigm for geophysical data that has wide community interest, and we plan to follow that model. The planned heat flow, fluid flux and companion geophysical data will be made publically available (via GeoPRISM and UW web sites) in preliminary form, within 3 months of the end of the cruise. The project will also incorporate UW graduate and undergraduate students, as well as students from other institutions in the cruises and equipment development. The Grays Canyon area is within the treaty fishing zone of the Quinault Indian Nation, and the PIs plan to include students and teachers from the Tahola High School and Cascadia Community College in the field program.

Peter Kelemen & Matthieu Rioux
NSF Awards 1144759, 1144648

Collaborative Research: Plutons as ingredients for continental crust: Pilot study of the differences between intermediate plutons and lavas in the intra-oceanic Aleutian arc

Peter Kelemen (peterk@ldeo.columbia.edu), S. Goldstein, S. Hemming, Matthew Rioux (rioux@eri.ucsb.edu)

Felsic plutonic rocks formed in arcs are buoyant with respect to mantle peridotite over the entire range of relevant pressures and temperatures. They tend to remain at the Earth?s surface, to form the fundamental building blocks of continental crust. In the Aleutians, most felsic plutonic rocks have compositions that overlap estimates for the bulk composition of the continental crust, and that are distinctly different from spatially associated lavas. Understanding the genesis of Aleutian felsic plutonic rocks is a key to understanding continental genesis and evolution via arc magmatism, a key science goal for the MARGINS and GeoPRISMS Initiatives. The PIs will address the following questions: (1) Do Aleutian plutonic rocks have an isotopically distinct source composition, compared to nearby lavas? If they do, this is vitally important since it is commonly assumed that erupted basalts are representative of the magmatic flux from the mantle into arc crust. If not, we will evaluate how they can be explained as the result of different differentiation processes operating on the same parental melt. (2) Has there been compositional variation in the Aleutian arc over time? Do differences between plutonic and volcanic rocks represent temporal evolution of the arc, or different modes of magma transport and emplacement for different magma compositions? And (3) are high viscosity felsic magmas preferentially emplaced in plutons, while low viscosity, mafic magmas preferentially form lavas? What biases does this introduce, when lavas are presumed to be representative of arc magmatic processes and compositions?

Broader Impacts: The Aleutian arc poses numerous hazards to society. Understanding subduction processes helps to predict, avoid, and/or mitigate the hazardous consequences of volcanic eruptions, landslides and earthquakes. During this project, a graduate student will be trained in research, and will likely be able to help design and participate in a larger field research program based on this pilot project.

Adam Kent
NSF Award 1144555

The explosive volcanic history of the Central Oregon Cascades: Probing the changing state of the Neogene Cascade arc

Adam Kent (adam.kent@geo.oregonstate.edu), R. Duncan, A. Grunder

Subduction zones ? volcanically active regions where one tectonic plate is pushed beneath another ? are home to most of the Earth?s explosive volcanic eruptions. In large part this is because the magmas that are produced and erupted in subduction zones tend to be both richer in water and in silica, both of which increase the propensity for eruptions to be explosive. The Cascade margin, running from Mount Lassen in northern California to southern British Columbia is host to a number of well-known volcanoes such as Mount Hood, Mount St Helens and Mount Rainier as well as numerous other volcanic edifices, and much of the region is also heavily populated. Explosive eruptions have occurred in the recent history of the Cascades, examples include Mount St Helens in 1980 and the prehistoric eruption of Mount Mazama at Crater Lake ~7700 years ago. However, although these younger eruptions are well documented, less is known about the long-term explosive record of the Cascade subduction zone over longer timescales, and the forces that influence such explosive behavior.

This project will help establish the long-term eruptive history of the Cascades in Central Oregon over the last 15 million years, by looking at volcanic rocks preserved within the Deschutes and Simtustus Formations of central Oregon. Many examples of ash fall and ash flow deposits that result from large explosive eruptions are preserved in these sequences, and they can be used to estimate the frequency, composition, age and size of large explosive eruptions in this section of the subduction zone. This research will use a combination of approaches, including field, geochronological, geochemical and petrological studies and will enable us to study changes in eruption rate, eruption size and chemical and isotopic composition through time and to compare this to the more recent behavior of the subduction zone.

Peter Lonsdale, Martin Grove & David Kimbrough
NSF Awards 1144558, 1144392, 1144367

Collaborative Research: Dating Submerged Continental Crust Beneath the Southern Gulf of California, and a Synthesis of the Magmatic and Tectonic History of This MARGINS Focus Site

Peter Lonsdale (pfl@mpl.ucsd.edu), Martin Grove (mjgrove@stanford.edu), David Kimbrough (dkimbrough@geology.sdsu.edu)

The PIs propose to measure and interpret U-Pb crystallization ages of a varied suite of volcanic and plutonic rocks recovered from water depths of 300-3500m at several hundred sites on the submerged and previously unsampled rifted continental crust that underlies most of the southern Gulf of California. Many samples were collected along traverses up fault scarps and across volcanic features by a remotely operated vehicle; 50 dredge hauls also recovered igneous rock. All relevant samples have been petrographically described and geochemically analyzed. These samples record a long and complex magmatic history in this region, which in the past 20 Myr has changed from a volcanic arc to a subaerial intra-continental rift, been flooded by a marine incursion, and developed a chain of axial basins growing by seafloor spreading. Radiometric dates are needed to define this history, and to test hypotheses that up till now have been solely derived from still-subaerial outcrops at the margins of the rift. Existing dating show striking discordance between the age estimates, hinting at interesting cooling histories with likely tectonic implications. Targeted zircon (U-Th)/He and K-feldspar 40Ar/39Ar thermochronologic analyses and modeling will constrain thermal histories, thereby contributing to understanding rift tectonics including continental uplift and subsidence in the gulf rift.

The work will very likely deepen our understanding of rifting history of the southern Gulf of California. Funding will also provide research opportunities for graduate students, foster collaboration with Mexican scientists and the results will be used in ongoing education and outreach programs, such as SDSU’s K-8 project.

Yang Shen
NSF Award 1144771

Developing a comprehensive model of subduction and continental accretion at Cascadia

Yang Shen (yshen@uri.edu)

Cascadia is a prime site to understand subduction dynamics and continental accretion, because it has one of the youngest subducting slabs in the world and a wide range of tectonic units. A variety of scientific questions can be addressed at Cascadia: What controls the subduction zone segmentation? What is the role of water transport in the subduction zone? Where does melting occur and how does magma migrate in the mantle and crust? And how does oceanic lithosphere accrete to the continent? Paleoseismic records show that Cascadia has a history of generating ~M9 megathrust earthquakes, so research is needed to improve the assessment of seismic and tsunami hazards from megathrust earthquakes.

This project develops and implements an advanced seismological method to construct a comprehensive, high-resolution velocity model of the crust and upper mantle for the entire Cascadia subduction zone. The velocity model provides a detailed structural framework and new understanding of the subduction processes. The structural correlations of a well-resolved model help address whether serpentinization of the forearc mantle varies substantially along strike and how it is related to the subduction of sediments, pre-existing features on the slab, and melt production beneath the volcanic arc. The project tests whether the recurrence of episodic tremor and slow slip events is related to properties of the overriding plate or the subducting oceanic plate. The new crustal model helps in understanding how accretion of oceanic lithosphere contributes to continental growth and subduction evolution. Accurate and high-resolution characterization of the crust and upper mantle structure is also critical to refining seismic and tsunami hazard assessment in Cascadia.

Matt Pritchard & James Gaherty
NSF Awards 1049611, 1049620

Collaborative Research: Faulting Processes During Early Stage Rifting: Analysis of an Unusual Earthquake Sequence in Northern Malawi

Matt Pritchard (mp337@cornell.edu), James Gaherty (Gaherty@ldeo.columbia.edu), S. Nooner, Donna Shillington

Intellectual Merit: This project is to analyze earthquake data collected after a large earthquake sequence occurred in the Malawi section of the East African Rift zone. InSAR data from the area will also be analyzed to determine how the region was affected by the earthquakes. The goal of the proposed work is to obtain a better understanding of the deformation associated with the inception and early stages of rifting of a continent.

Broader Impacts: This project has a large component of international collaboration. The PIs have a strong relationship with the Malawi Geological Survey department and will host Malawi colleagues in the U.S. so they can learn earthquake relocation techniques. The PIs will also travel to Malawi to speak with various groups, and help to install the software needed for seismic analysis.

Kyle Straub & B. Sheets
NSF Awards 1049387, 1049582

Collaborative Research: Reconstructing ancient passive margin dynamics by relating geomorphic and stratigraphic surfaces: a combined laboratory and field study

Kyle Straub (kmstraub@tulane.edu), B. Sheets (sheets@u.washington.edu)

Funds are provided to carry out a lab and field investigation of statistics describing the stratigraphic architecture of passive continental margins and their relationship to geomorphic surfaces. The overall objective of the project is to improve our ability to invert the stratigraphic record for paleo surfaces dynamics and topography. The continental margin record contains features such as bars, channels and channel networks, yet we cannot precisely reconstruct the relationship between these preserved deposits and geomorphic processes that produce them. Thus, the research plan is to use flume models to measure and identify scaling relationships in channelized, distributive systems with a focus on deltaic and deep water systems. The goal is determine how stratigraphic discontinuities are formed and to see if the mechanism of formation can be deduced from statistical descriptions of surface morphology. The ultimate objective is be able to infer the dynamic origin of fossilized erosional surfaces, using relationships derived from the experimental flume models.

The stated broader impacts include student training. The work also has practical value in understanding how coastal systems grow, as well as in resource extraction from the deltaic and deep-water systems. The results could have important implications in how we interpret stratigraphic surfaces in the field.

Greg Hirth
NSF Award 1049582

Experimental Constraints on the Rheology and Seismicity of Subducting Lithosphere and the Slab-Wedge Interface

Greg Hirth (Greg_Hirth@brown.edu), D. Goldsby

To understand the spatial and temporal distribution of earthquakes in subduction zones, as well as the processes responsible for the wide spectrum of fault slip behaviors on the slab/wedge interface, it is important to constrain the rheological properties of altered lithosphere, how they evolve during dehydration reactions, the rheology of reaction products, and the feedbacks between metamorphic reactions and transport properties of the downgoing slab. Primarily motivated by surface heat flow measurements in subduction zones, current mantle wedge corner flow models use various boundary conditions to impose decoupling between the subducting slab and overlying mantle wedge. One hypothesis is that a layer of weak serpentinite (a hydrated magnesian silicate) above the slab accommodates the majority of the deformation. Serpentine has also been hypothesized to play an important role in the origin of the double seismic zone observed in numerous subduction settings, and on the origin of intermediate and deep seismicity along the slab. In other settings, dehydration of lawsonite (a hydrated calcium-aluminum silicate) has been hypothesized to promote seismicity. In this case, seismicity is interpreted to result from high pore fluid pressures that arise during dehydration, and subsequent embrittlement of the rock. Examining the frictional behavior of fault materials over a wide range of sliding velocities is essential for understanding the dynamics of stress evolution and slip during earthquakes. Geophysical observations suggest that sheet-structure minerals (e.g., serpentine, talc and other clays) may control the strength and frictional behavior of creeping sections of faults. Previous friction experiments on serpentinite document velocity-strengthening behavior at plate-tectonic displacement rates, consistent with this hypothesis. However, high velocity friction experiments on serpentinite document dramatic weakening and dehydration at slip velocities above ~ 0.1 m/s. Our experiments demonstrate an approximately 1/V dependence of friction on velocity above a characteristic weakening velocity Vw ~ 0.1 m/s, consistent with theoretical predictions for flash heating and subsequent weakening of asperity (uneven) contacts. Extrapolation of these results to mantle conditions suggests that slow-slip events and/or slow earthquakes could be nucleated by seismic ruptures into serpentinized regions. Primarily motivated by new results from experiments in our lab that both challenge and inform some of these hypotheses, we propose to study (a) the rheological properties of antigorite at high pressure and temperature; (b) the role of dehydration reaction kinetics on the mechanical evolution of serpentinites and blue-schists; (c) the rheology of slab dehydration reaction products at conditions appropriate for intermediate depth earthquakes and (d) the frictional properties of serpentinites at seismic and infra-seismic slip rates.

Parts of the project will form the basis of a Ph.D. thesis for a Brown University student and the senior thesis chapter for Helen Doyle and another undergraduate student. The results of the experiments will provide constraints for a wide range of scientists with interests in the diverse fields of metamorphism, geodynamics, seismology, the physics of earthquakes, and fluid transport, crossing the boundaries between the new GEOPRISMS initiatives. We will make all of our results available including digital records of all raw data files – via on-line supplements and our lab websites.

Juli Morgan
NSF Award 1046795

GeoPRISMS Office Support – Building Beyond MARGINS

Juli Morgan (morganj@rice.edu)

Funds are provided to support the GeoPRISMS Office at Rice University from October 2010 through September 2013. The GeoPRISMS Program provides a framework for developing an integrated understanding of the origin and evolution of continental margins through focused studies that cross the shoreline. the Program maps a pathway of scientific investigation, guided by the MARGINS Decadal Review Committee and the MARGINS Successor Planning Workshop. The program will include: (1) two broad Initiatives focusing research into Rift Initiation and Evolution and Subduction Cycles and Deformation, (2) five overarching scientific themes that cross-cut tectonic categories, (3) interdisciplinary teams carrying out observational, experimental, and modeling studies, and (4) implementation of science objectives through focus-site and thematic-based studies. GeoPRISMS research will also see increased attention on US margins and facilities such as EarthScope and the Cascadia Amphibious Array. This science initiative will be guided by the GeoPRISMS Steering and Oversight Committee (GSOC), which will provide support, evaluation and oversight for the program, and will form the principal link to the broader scientific community. The GeoPRISMS Office will provide the organizational support for the community activities, which will feed back into the “science plans”. The Office will organize planning and coordination efforts through support of the GSOC and related committees, and through promotion of planning meetings and workshops.

Broader Impacts. Primary functions of the GeoPRISMS Office will be the support of scientific infrastructure through workshops, and dissemination of scientific results through publications. GeoPRISMS also has practical application to resource management and availability, and understanding and mitigating geohazards. Education and outreach will be a major activity of the Office, developing resources and providing opportunities for K-12 to early career scientists, including Distinguished Lecture Series, GeoPRISMS mini-lessons for undergraduate courses, postdoctoral fellowships, and Best Student Paper awards.

Demian Saffer
NSF Award 1049591

MARGINS Post-Doctoral Fellowship Research: Evolution of Sediment Physical Properties in the Nankai Subduction Zone and Implications for the Updip Limit of Seismogenesis

Demian Saffer (dsaffer@geosc.psu.edu)

Funds are provided for a post-doctoral study of deformation and slip behaviors in subduction systems by an experimental approach combined with seismic data and microstructure observations. The PIs will conduct friction experiments on smectite and illite at elevated temperature and measure the acoustic wave velocities on sediment core samples at different stress states. Results of the friction experiments will be used to further test the hypothesis of smectite-illite transition for updip limits of seismicity. The measurements of acoustic wave velocities at different stress states will allow the PIs to estimate the in-situ stress states and pore pressure in subduction systems by incorporating with seismic data. Samples and data from the IODP NanTroSEIZE transect area will be used to investigate the in situ stress and pore pressure conditions.

Broader Impacts – The award will support a young female researcher as a MARGINS/GeoPRISMS postdoctoral fellow. The proposed research aims to understand the evolution of slip behavior at the upper limit of the seismogenic zone and the deformation mechanisms in subduction zone fault systems and accretionary prisms. The focal points of the proposed study are also aligned with key questions of the Subduction Cycles and Deformation initiative within the new GeoPRISMS program. Understanding the mechanics and in situ conditions of faulting deformation at subduction plate boundaries has both scientific and social significance in terms of earthquake prediction and disaster prevention.

Magali Billen
NSF Award 1049660

Postdoctoral Fellowship: 3D Numerical Models of the Dynamic Generation of Outer Rise Faults

Magali Billen (mibillen@ucdavis.edu)

Intellectual Merit: This project is to model the developments of faults during the bending of the tectonic plate as it approaches a subduction zone. Two dimensional and three dimensional numerical models will be developed using a finite element code. The results of the modeling will be compared to observations of fault patterns observed at subduction zones, mainly the Central America trench where there are plentiful data. Understanding plate strength and how the plate behaves is crucial in geodynamics as convection and energy dissipation on the Earth are mainly driven and caused by subducting oceanic plates.

Broader Impacts – This project is to support a postdoctoral researcher and the results will be shared with the MARGINS community and the broader geologic community

Ellen Syracuse
NSF Award 1049533

MARGINS: Seismic Evidence for Hydration of the Central American Slab: Guatemala Through Costa Rica

Ellen Syracuse (syracuse@geology.wisc.edu), Chris Thurber

Intellectual merits. The cycling of fluids into and out of subduction zones plays an integral role in the formation of volcanic arcs. The Central American subduction zone is an ideal location for studying the effects of fluid on the arc and underlying mantle wedge and subducted slab due to its varying inputs and outputs. Existing geochemical studies indicate wide variability in degree of slab hydration along this arc, with maximum and minimum slab contributions to magma generation localized beneath Nicaragua and Costa Rica, respectively. Geochemical studies suggest that slab fluid contributions are also present beneath El Salvador and Guatemala, but diminish to the northwest. Geophysical studies are consistent with a high degree of slab serpentinization and fluid release beneath Nicaragua, versus comparatively little beneath Costa, but otherwise the rest of the arc is poorly characterized geophysically – primarily because the slab is not well-resolved beneath El Salvador and Guatemala. The present study will utilize all available seismic data to extend the velocity model developed for Costa Rica and Nicaragua into the northwestern section of the arc, allowing regional analysis of the relation between seismic structure and fluid distribution. Data reported to the International Seismic Centre will be combined with additional data from local seismic networks from Guatemala through Costa Rica, which has never been integrated to study the entire Central American subduction zone. This study will obtain a more extensive seismic image of the slab and mantle wedge within the Central American subduction zone through the use of a double difference velocity tomography and relocation method.

Broader Impacts. The proposed project will primarily support the professional development of a young female scientist (Syracuse), who has not has prior NSF support. Syracuse will participate in the UW-Madison DELTA program for Integrating Research, Teaching, and Learning. DELTA supports current and future faculty in science, technology, engineering and math in their improvement of student learning.