GeoPRISMS Postdoctoral Scholar Program


Current GeoPRISMS Postdoctoral Scholars. From left to right: Tamara Jeppson (Texas A&M University), Megan Newcombe (Columbia University), and Shuoshuo Han (University of Texas at Austin)

(May 16, 2018) Important revisions from solicitation NSF 18-559:

  • Postdoctoral proposals now only require two letters of reference
  • Postdoctoral Fellows are now called Postdoctoral Scholars

The GeoPRISMS Postdoctoral program is aimed at providing opportunities for early-career scientists to solidify research skills, build a track record, and establish peer relationships. NSF’s GeoPRISMS Program provides support for postdoctoral researchers to conduct up to two years of multi-disciplinary research at institutions of higher education in the United States. The intention is to encourage individuals, typically within five years after award of their Ph.D., to diversify their expertise relative to that used in their thesis research.

  icon-chevron-right Learn more about the current and former GeoPRISMS Posdoctoral Scholars

The GeoPRISMS Postdoctoral Program is designed so that recipients can choose the research environment most beneficial for their scientific development and that of the GeoPRISMS Program. To this end, applicants are encouraged to establish a relationship with a proposed advisor (mentor) well in advance of proposal submission.

It is expected that candidates will write their own proposals for submission, except where otherwise required. There is no fixed dollar amount for a postdoctoral proposal; rather, the budget should be for the candidate’s direct work only and should be appropriate to the postdoctoral research project, including salary commensurate with the experience of the candidate, institutional standards and local cost of living.

NSF enables career-life balance through a variety of mechanisms. Support to address dependent care issues may be available for awardees. For more information, please see https://www.nsf.gov/career-life-balance/.

GeoPRISMS Postdoctoral proposals are subject to the same submission and review criteria as other proposals for GeoPRISMS funding. Submissions should state, in the Project Description, that the proposal is for a GeoPRISMS Postdoctoral Award and must be submitted by the institution to which an award would be made. In addition to the standard NSF proposal requirements, applicants should also include, in a Supplementary Document: a short abstract of your dissertation research and planned publications (not to exceed one single-spaced page); any fellowships, scholarships, teaching, and other positions relevant to your field held since entering college/university; any academic honors you have received relevant to your major field of study; and a statement of your long-term career goals and a description of the ways the GeoPRISMS Postdoctoral Scholar award will lead to development of long-term collaborative activities in GeoPRISMS science.

The proposal should also be supported by two (2) letters of reference which must be uploaded by the applicant directly as Supplementary Documents. It is anticipated that one of your referees will be your Ph.D. thesis adviser, and another the sponsoring/collaborating scientist at the proposed host institution. The latter reference should state that your proposed mentor and institution are willing to host you and can accept the GeoPRISMS Scholar award.


GeoPRISMS/MARGINS Posdoctoral Scholars: Biographies

Shuoshuo Han – University of Texas at Austin

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

NSF Award 1559298

Fluid plays a key role in the subduction zone processes, and most of the fluid is from the downgoing oceanic plate. Faults in the oceanic plate are instrumental in facilitating
deep plate hydration near the trench and in providing pathways for fluid migration during subduction. However, the internal structure and hydraulic conductivity of these
faults and their variation over time and space have not been examined and quantified.

At Lamont-Doherty Earth Observatory, Columbia University, working with Suzanne Carbotte, I started my PhD research at the fast spreading mid-ocean ridge East Pacific Rise. Using 3D multi channel seismic reflection data, I imaged a group of melt lenses beneath the ridge flanks and assessed the contribution of off-axis magmatism to crustal accretion. From this project, I became familiar with the structure and formation process of the oceanic crust. Then I participated in the Juan de Fuca Ridge- to-Trench project, during which I imaged the detailed structure of the Juan de Fuca plate from its formation at the Juan de Fuca ridge to prior to subduction at the Cascadia subduction zone. In particular, I characterized the faulting deformation in this young oceanic plate and found deep-cutting faults formed offshore Oregon in response to subduction bending, but are absent offshore Washington. This more extensive bend-faulting deformation offshore Oregon correlates with the higher degree of plate hydration determined from coincident seismic refraction data, and has important implications for seismicity at the Cascadia subduction zone. Through this project, I got interested in understanding how fluid is transported into the deeper part of the oceanic plate through faults, and this motivated my GeoPRISMS postdoc study.

Now at the Institute for Geophysics at the University of Texas at Austin, I am working with Nathan Bangs to investigate the hydrogeological role of faults in the downgoing oceanic plate. The reflections from the fault planes in the oceanic crust and uppermost mantle, although only observed in a few locations so far, provide windows for us to probe the internal structure of these faults. Through waveform modeling and inversion of the fault plane reflections, I constrain the impedance, and from these I estimate the porosity and water content within the fault zones. I also use depth imaging to characterize the distribution and larger-scale geometry of these faults. By comparing downgoing plates of different subduction zones, I hope to understand the dependence of fault structure on parameters such as plate age, bending curvature, and fault offset, and explore the limit of plate hydration through these faults. In addition, using accurate seismic velocity determined from depth imaging, I examine the consolidation state of sediments above the oceanic plate, another major fluid source, so that I can have a fuller view of the fluid input into subduction zones.

 icon-envelope han [at] ig.utexas.edu


Tamara Jeppson – Texas A&M University

Experimental investigations on the deformation behavior of sediment in the shallow region of the Nankai, Sumatra, and Aleutian subduction zones

NSF Award 1654486

In general, the seismogenic zone is characterized by unstable slip while aseismic zones are characterized by stable slip. In the last decades, however, the discovered new modes of slip and observations of shallow coseismic slip to the trench have blurred the distinction between seismic and aseismic and suggest subduction zones are more complex than this simple model. Because the deformation behaviors of sediments have a strong influence on fault stability, magnitude of co-seismic slip, and a spectrum of slip behaviors in the shallow regions of subduction zones, characterizing and quantifying the full range of visco-elasto-plastic deformation behaviors of subduction zone sediments is essential to understand earthquake and fault mechanics in this environment.

I obtained my Bachelor of Science degrees in geology and physics from Utah State University. There I worked with Dr. James Evans on constraining the relationship between deformation and alteration observed in fault rocks and borehole geophysical measurements using data from the San Andreas Fault Observatory at Depth. I also worked with Dr. Anthony Lowry to determine if slow slip events occurred on the Wasatch Fault. As a result of these projects I became interested in understanding variations in the physical properties of fault zone rocks and their role in different fault slip behaviors. I continued to pursue this interest while working on my Master’s and Doctoral degrees with Dr. Harold Tobin at the University of Wisconsin – Madison. There my research focused on characterizing the seismic velocity structure of plate boundary faults at multiple scales. My work on drill core samples from the Japan Trench frontal prism lead to a collaboration with Dr. Eric Dunham’s group at Stanford University and early results from that collaboration suggest that the presence of a compliant accretionary prism can lead to a significant increase in shallow coseismic slip and seafloor displacement.The results of my graduate research illustrated a need to better characterize the physical properties and deformation behaviors of the sediments that are present within the shallow region of subduction zones. Now at Texas A&M I am working with Dr. Hiroko Kitajima to define elastic, plastic and viscous deformation behaviors of shallow subduction zone materials by performing high-pressure and high-temperature consolidation and creep experiments on samples of incoming sediment obtained during ocean drilling projects at the Nankai, Aleutian, and Sumatra subduction zones. This work will address fundamental questions about and advance knowledge of strain accumulation, fault coupling, and slip behaviors in shallow subduction zones by providing new insights on sediment deformation at in-situ conditions over time and the mechanisms of earthquakes and co-seismic slip that occur in the shallow portion of plate boundary faults.

 icon-envelope tjeppson [at] tamu.edu


Megan Newcombe – Columbia University

Magma ascent and eruption in the Aleutian Arc

NSF Award 1551868

The links between precursory signals of volcanic eruptions (as inferred from seismic and geodetic data) and eruptive style are poorly understood. Factors that are thought to play a role in controlling the vigor of a volcanic eruption include the volatile content of the magma, the depth of vapor-melt segregation, the ascent and mass transfer rate of the magma in the volcanic conduit, and the thermal history of the magma. These parameters are difficult to measure directly; however, they can be inferred a posteriori from analyses of erupted materials, and this is the main goal of my GeoPRISMS postdoctoral project at the Lamont-Doherty Earth Observatory.

My interest in basaltic volcanism began during my undergraduate degree at the University of Cambridge, during which I had the opportunity to sample pillow-rim glasses in central Iceland. I analyzed olivine-hosted melt inclusions from the Icelandic glasses and I studied the extent to which their compositions could be influenced by post-entrapment diffusion. I then moved to Caltech for my PhD, where I transitioned to the study of basaltic volcanism on the Moon. I conducted experiments to determine the solubility and diffusivity of water in lunar basalt. Also during my PhD, I characterized chemical zonation in olivine-hosted melt inclusions and I developed a technique that uses this zonation to constrain the syneruptive thermal histories of the inclusions. One aspect of my GeoPRISMS postdoctoral work is the application of this method to explosive basaltic eruptions to determine whether their magmas increase or decrease in temperature during ascent through the conduit.

Over the course of my GeoPRISMS postdoctoral fellowship, I have measured gradients of water and other chemical species in erupted crystals and glasses from Aleutian arc
volcanoes. These chemical gradients are signatures of magma ascent, degassing, and cooling. I am developing techniques for interpreting such chemical gradients that can be used to provide constraints on the ascent rates and thermal histories of magmas in the minutes to hours prior to their eruption. The ultimate goal of this approach is to provide a physical framework in which to place real-time volcano monitoring data.

 icon-envelope newcombe [at] ldeo.columbia.edu


 

2Lopez_Karymsky_2012Taryn Lopez – University of Alaska Fairbanks

NSF Award 1250148

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

Changes in the chemical composition and flux of volcanic gases released at the surface of volcanoes can provide insight into subsurface volcanic conditions, such as the approximate magma degassing depth, the presence (or absence) of a shallow water system, and/or relative conduit permeability. Additionally, the chemical and isotopic composition of volcanic gases can be used to determine the source of these volatiles at depth. This knowledge is critical for understanding subduction processes, forecasting volcanic eruptions, and estimating the explosivity of impending eruptions.

I obtained my Bachelor of Science degree in Geology at the University of Wisconsin Eau Claire. I then went on to pursue a Masters degree in Volcanology at Michigan Tech University. My advisor at Michigan Tech, Matt Watson, was a spectroscopist whose main area of study was remote sensing of volcanic emissions. He taught me that volcanic gas geochemistry could be used to understand subsurface volcanic processes and this idea has since been the main motivation of my research. My master’s research correlated the sulfur speciation and temperature of volcanic emissions from Cerro Negro Volcano, Nicaragua, where we used a combination of direct sampling and remote sensing techniques. Following completion of my M.S. degree, I went on to pursue my Ph.D. at the University of Alaska Fairbanks, due to its direct involvement with the Alaska Volcano Observatory (AVO) and opportunity for students to participate in daily volcano monitoring and eruption response. My Ph.D. research focused on using repeated volcanic gas measurements throughout varying stages of volcanic unrest to understand both surface activity and subsurface processes at three active volcanoes within the North Pacific: Redoubt (Alaska), Bezymianny (Kamchatka, Russia) and Karymsky (Kamchatka, Russia).

Through regular discussions with my AVO colleagues while pursuing my Ph.D., I gained a strong appreciation for the added value of integrating volcanic gas data with complementary petrologic, geochemical and geophysical datasets to obtain a more complete understanding of volcanic processes. During this time period I was surprised to learn that volcano seismicity is often interpreted to be caused by subsurface fluid movement; however, the actual type of fluid (i.e. magma, gas/volatiles, or hydrothermal waters) is often not well constrained, and these interpretations are often not supported by complementary volcanic gas measurements. This curiosity inspired my current GeoPRISMS postdoctoral project. The aims of this project are to use geochemical measurements of volcanic fluids and complementary seismic data from three historically-active Alaskan volcanoes within the Katmai Volcanic Cluster to: (1) determine the source (i.e. subducted slab, mantle, crust) and flux of volcanic gases, (2) identify 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.

Taryn Lopez is now Research Assistant Professor at the University of Alaska Fairbanks Geophysical Institute


Abhijit Gosh  –  University of California Santa Cruz

NSF Award 1144695

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

Subduction zones worldwide pose great seismic hazard, as they repeatedly produce large damaging earthquakes and associated tsunamis. Large earthquakes nucleate at the locked zone of the fault, spanning approximately 10 to 40 km in depth. Such fast earthquakes are believed to be the main observable mode of stress release for major plate boundary faults. But recent discovery of slow earthquakes in the transition zones forces earth scientists to rethink this paradigm. Such slow earthquakes are believed to load the up-dip locked zone, taking it closer to the next large megathrust earthquake. I study earthquakes, both fast and slow, using seismology as the main tool to understand the dynamics of earthquakes and faulting.

I did my undergraduate in structural geology. I earned my first Masters Degree in Geology from the University of Calcutta, India. While doing that, I got interested in earthquakes and faults. I got my second Masters Degree in the Earth and Atmospheric Sciences from Georgia Tech, where I studied earthquake statistics to infer variations in plate coupling in the Middle America Trench. In my PhD at the University of Washington, I focused on slow earthquakes and tremor in the Cascadia Subduction Zone, and San Andreas Fault. I developed new array techniques to image slow earthquakes with unprecedented resolution. I used this technique to image slow earthquakes captured by multiple seismic arrays that we designed and installed in Cascadia. I helped to resolve a long-standing scientific debate in Cascadia by showing that the majority of the tremor, the seismic signature of slow quakes, is occurring at the plate interface and likely a result of shear slip on the subduction fault. Furthermore, I showed that the behavior of tremor is complex and varies with distinct, identifiable patterns over timescales of minutes to months. My works suggest that the interaction between the stress field and rheological and/or geometrical asperities on the fault plane may control the evolution of slow quakes.

In the GeoPRISMS Postdoctoral proposal, I plan to integrate land-based and offshore seismic data collected under the Cascadia Initiative to scan the seismicity from the trench offshore to the base of the down-dip transition zone, up to ≈100 km inland from the coast. In the process, I will systematically search for exotic elusive events like, very low frequency earthquakes and offshore tremor. The goal is to take a holistic approach to better understand the full spectrum of fault slip behavior, and how it governs the subduction zone dynamics.

Abhijit Gosh is now Assistant Professor at the University of California Riverside


Hiroko Kitajima – Pennsylvania State University

NSF Award 1049591

Evolution of Sediment Physical Properties in the Nankai Subduction Zone and Implications for the Updip Limit of Seismogenesis

Both the updip and downdip limits of seismicity are thought to be controlled by temperature. For the updip limit, it has been hypothesized that change in slip behavior from aseismic creep to seismic slip is affected by smectite-illite transition associated with an increase in temperature. However, the updip limit of seismicity may be controlled by an interaction between multiple mechanical and chemical processes including deformation, sedimentation, metamorphism, fluid flow, dissolution, cementation, and solute transport. Along with temperature, stress states and strain rates are important factors that control deformation and slip behaviors.

As a part of my Ph.D. research at Texas A&M University, working with Frederick Chester and Judith Chester, I investigated mechanical and hydraulic properties of marine sediments along different loading paths to simulate the range of stress conditions in accretionary subduction systems. I deformed sediment core samples recovered from relatively shallow portions of the Nankai Trough accretionary prism during the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE). The deformation test results revealed that most prism sediment samples are overconsolidated and that consolidation state of sediments is an important factor in determining deformation modes (brittle or ductile deformation) and permeability evolution. I have also conducted high-speed rotary-shear friction experiments on fault materials to understand frictional behaviors of natural faults at coseismic slip rates. At such slip rates, dynamic weakening occurs in association with frictional heating, and I realized the significance of temperature on frictional behaviors.

Now at the Pennsylvania State University, I am working with Demian Saffer and Chris Marone, where I will measure acoustic wave velocities on sediment core samples at different stress states. By incorporating measured data with seismic data, I will estimate the in-situ stress states and pore pressure in subduction systems. The estimation of in-situ stress states can be verified by coring and logging from deeper portions of the accretionary prism in future stages of the NanTroSEIZE. I will also conduct friction experiments on smectite and illite at elevated temperature to document their behaviors and to test the hypothesis for the updip limit of seismicity. I am grateful for the GeoPRISMS/MARGINS postdoctoral fellowship program.

Hiroko Kitajima is now Assistant Professor at Texas A&M University


John Naliboff – UC Davis

NSF Award 1049660

3-D numerical models of the dynamics of outer rise faults

The dynamic processes of the lithosphere and convecting mantle are largely governed by buoyancy driven stresses and the solid Earth’s rheological structure. These solid Earth processes operate over a diverse spectrum of spatial and temporal scales, and include frictional sliding along faults, propagation of seismic energy through elastic media and viscous creep in ductile portions of the Earth. In order to correctly link brittle and ductile processes to observations of surface deformation, plate motion and mantle flow it is critical to have independent estimates of the solid Earth’s rheological structure and the buoyancy forces available to drive deformation.

During my PhD at the University of Michigan, I focused on the origins of the lithospheric stress field using numerical simulations of lithospheric deformation and mantle flow. The results of my PhD work suggest that rheology may play a large role in the transmission and distribution of stress through the lithosphere. As a MARGINS postdoctoral fellow I plan to continue examining the role of rheology on lithospheric dynamics with Dr. Magali Billen at UC Davis.

The primary focus of my work will center on the dynamics of normal faulting along the bending-induced topographic bulge seaward of trenches in subduction zones (“outer rise”). Normal faulting in the outer rise regions of subduction zones reflects the extensional stress state generated by bending of the downgoing oceanic lithosphere that may produce new faults in the oceanic lithosphere or reactivate pre-existing faults generated at mid-ocean ridges. A number of recent high-resolution seismic studies have revealed the depth, spacing, dip and offset of these faults at multiple subduction zones, in addition to clear examples of when new faults are formed or pre-existing faults are reactivated. Using high-resolution 2-D and 3-D numerical models, I hope to test how viscous flow laws, brittle yielding parameters, strain-induced weakening and fluid-related weakening affect the formation and evolution of outer rise fault patterns. In addition to providing additional constraints on the rheology of the oceanic lithosphere, these numerical simulations will provide further insight into the large-scale dynamics of subduction zones and the transmission of stress over different wavelengths and timescales in subduction systems.

John Naliboff is now Assistant Project Scientist at UC Davis