Alaska Amphibious Community Experiment draft plan open for comment
A proposal for a community amphibious seismological experiment in Alaska is being prepared for the GeoPRISMS deadline, to address high-priority scientific problems across the Alaska margin. The plan addresses the high scientific priorities of the Amphibious Array Futures Workshop report as they address the GeoPRISMS and EarthScope Science plans in a region of great earthquakes and abundant volcanism, as outlined on this webpage. A draft experiment plan including rationale and a deployment map are now posted to this web site.
That plan is open for community feedback through July 10, 2016. We encourage all interested parties to review the draft deployment plan and map, and provide any feedback. Send your feedback to the form on the project web page, under Leave A Reply. All feedback comments will be publically posted to this web page shortly after posting. If you wish to keep your comments confidential, please indicate that clearly at the beginning of your comment text and the moderator will communicate your comment to the PI group. Please use the web page mechanism for any comments to the plan rather than emailing the PI’s directly.
Alaska Amphibious Community Experiment (AACE)
Draft plan and request for public comment, June 30, 2016
A proposal for a community amphibious seismological experiment in Alaska is being prepared for the GeoPRISMS deadline, to address high-priority scientific problems across the Alaska margin. The plan addresses the high scientific priorities of the Amphibious Array Futures Workshop report as they address the GeoPRISMS and EarthScope Science plans in a region of great earthquakes and abundant volcanism, as outlined on the project web page. The PI team is listed there as well.
The plan presented here attempts to address these scientific priorities within the framework outlined in the March 2016 Dear Colleague Letter (NSF-16061) inviting proposals for such an experiment. We outline the draft deployment plan and rationale below and on the accompanying deployment map. This community experiment proposal is due at the July 26, 2016 GeoPRISMS deadline. At present we are seeking cost estimates from OBSIP on various components, and may adjust the plan somewhat depending on those estimates.
In keeping with the community nature of this project we are now soliciting community feedback, through July 10, 2016 at which time we will finalize the budgets and proposal. Send your feedback to the form on the project web page, under Leave A Reply. All feedback comments will be publically posted to this web page shortly after posting. If you wish to keep your comments confidential, please indicate that clearly at the beginning of your comment text and the moderator will communicate your comment to the PI group. Please use the web page mechanism for any comments to the plan rather than emailing the PI’s directly.
We do not expect to be able to deploy significantly more stations than described below, so it is most valuable to receive input about the particular choices of deployment scheme. The main limitations to keep in mind are the small number of instruments (25) available for deployment in shallow water (<200 m), the importance of integration with the TA described in the Dear Colleague Letter, and the importance of accomplishing objectives in a single 1-1.5 year deployment. We are particularly interested in thoughts about tradeoff between areal coverage and station density, for example over the thrust zone or in the outer rise.
Some of the major design criteria include:
- Sampling of the megathrust at sufficient density to locate thrust-zone seismicity;
- Sampling across major segment boundaries capturing both locked and creeping sections of the megathrust;
- Staggered transects in at two locations with contrasting inputs and megathrust behavior that allow imaging of the entire subduction system from outer rise to far backarc;
- Coverage of the outer rise sufficient to image serpentinization, e.g. via ambient noise;
- Optimize ability to integrate with existing data sets, for example active-source lines.
The deployment plan is outlined as follows.
- The experiment is limited to a single deployment to minimize costs and number of support cruises, covering two consecutive summers and the intervening winter, starting spring 2018 when ships become available.
- Only 25 instruments would be capable of operating in shallow (<200m) water, using existing Trawl Resistant Mount instruments and modifying a limited number of deep-water instruments.
- The experiment is concurrent with the Alaska Transportable Array (TA) and maximizes integrated use of TA instruments, so naturally focuses on the easternmost part of the subduction system. A transect crossing Kodiak and Katmai nicely integrates with onland TA stations 1000 km behind the arc. A transect near the creeping fault near the Shumagin Islands utilizes several Alaska Peninsula and island stations, and at low resolution benefits from stations on the east coast of the Bering Sea.
- We anticipate being able to deploy 85 broadband OBS’s, including the 25 TRM’s. Where possible those near the thrust zone may include absolute pressure gages for recording potential creep events and on-scale recording of moderate-to-large earthquakes.
- We are exploring the use of short-period OBS’s in the deep-water parts of the forearc. Should they result in significant cost savings, we could deploy ten in this region in place of five of the deep-water OBS’s.
- We are exploring the costs of a limited number of accelerometers added to OBS’s.
- On shore we would deploy a limited number of broadband stations, particularly along the two primary transects on Kodiak, across and north of the Katmai volcanic field, and perhaps near the Alaska Peninsula. To control costs and logistical uncertainty all stations should be reachable by plane or boat; helicopters will not be used due to cost and logistical uncertainty in Aleutian weather.
- The land station geometry is notional at present, while access and permissions are being evaluated.
We are envisioning a series of educational opportunities as well, including open applications for participation in cruises and onshore fieldwork, a data-oriented post-cruise short course for scientists new to these data types, outreach to communities within the deployment region, and a web page with regular updates on field progress. We welcome suggestions for maximizing the broader impacts of this program.
The attached map shows stations, color-coded by type, as indicated by the map legend.
On March 16, NSF released a Dear Colleague Letter (DCL; NSF16-061) encouraging proposals for community-driven shoreline-crossing seismological arrays along the Alaska subduction margin. The concept follows directly from the success of the Cascadia Initiative community experiment, and is targeted toward subduction-related problems of relevance to GeoPRISMS and EarthScope science plans. The Alaska experiment would take advantage of the Alaska component of the Earthscope Transportable Array currently being deployed, in a region of great earthquakes and abundant volcanism. A workshop in October, 2014 provided scientific rationale for such successors to the Cascadia Amphibious Array, as outlined in a report released in February 2015. Much of that report emphasized the seismogenic megathrust and volatile cycling through the subduction factory as the two major science targets that require broad, shoreline-crossing observations in subduction zones. Both targets could be optimally addressed by studies of the Alaska margin. The DCL specifically invites community experiment proposals to be submitted to the July 15, 2016 GeoPRISMS deadline.
In response to the DCL, many of the 2015 Amphibious Array Report authors have formed an ad hoc steering committee to nucleate a community proposal to deploy onshore and offshore seismometers across the Alaska Margin. The proposed community experiment would focus on the regions off the Alaska Peninsula and farther east, where the on-land Transportable Array exists, extending onshore and offshore a far as necessary to achieve primary scientific goals. We are also offering to serve as a clearinghouse for parallel submissions for other sorts of observations that could be well integrated with the Seismic Array. The DCL and a subsequent FAQ encourages one 15-18 month OBS deployment beginning in summer 2018 that focuses on seismic observations. Two such deployments might also be considered if required to attain specific scientific goals. Concurrent with the OBS deployment, we anticipate a densification of on-land seismometers to supplement the TA. No restriction on the number of land or OBS instruments exists beyond what is available in the pool; the OBS pool includes of 20 trawl-resistant seismometers that can be deployed in shallow water (http://www.obsip.org/).
To begin this effort, and make this an open process, we are taking several steps:
- A webinar has been scheduled for April 25, 2016 to introduce the community to the exciting scientific opportunities that this DCL offers and to outline general strategies for achieving them. The video of the webinar is now available on Youtube.
- Ideas for specific deployment strategies are being solicited. A web-based form (see tab form) provides an easy mechanism for communicating science targets and deployment plans. After some review, submissions are likely to be posted in a manner accessible from this web page.
- Volunteers interested in joining the PI team are requested. This web page provides a place to submit a statement of interest, and upload a bio. Following the DCL, PI’s will be supported for participation in data collection only and not for data analysis through this mechanism, although scientists are encouraged to write separate proposals for subsequent data analysis.
This is an exciting opportunity to collect what should be one of the seminal data sets from an active subduction zone.
A webinar (April 25, 2016) introduced the community to the exciting scientific opportunities that this DCL offers and to outline general strategies for achieving them. Watch the record of the webinar below.
Presenters: Susan Schwartz, Geoff Abers, Emily Roland, Rob Evans, Doug Wiens, Jeff Freymueller
Ideas for specific deployment strategies are being solicited. This form provides an easy mechanism for communicating science targets and deployment plans. After some review, submissions are likely to be posted in a manner accessible from this web page.
If you are interested in joining the PI team please submit a statement of interest, and upload a bio. Following the DCL, PI’s will be supported for participation in data collection only and not for data analysis through this mechanism, although scientists are encouraged to write separate proposals for subsequent data analysis.
Peter Haeussler – USGSI strongly endorse the idea of deploying an amphibious array off of Alaska in the so-called “megathrust megaswath” region. The number of historical earthquake ruptures, and the range in slip behavior in the region, combined with the numerous earthquakes would make this region of great interest. My white paper submitted to the “Future of the Amphibious Array” meeting in 2014 at Snowbird, Utah, outlines the idea of “A proposed ‘megathrust megaswath’ OBS deployment in southern Alaska”, and encompasses the suggested “Deployment 1” in the AAF workshop report. I recognize that there may not be enough funds to instrument the entire proposed ‘megaswath’ region, but I do think that straddling the freely slipping part of the megathrust in the Shumagin Islands region is an important component of any experiment design. I personally favor extending the megaswath westward across the oceanic/continental transition for Deployment 2, rather than re-deploying in a separate region spanning the Amlia fracture zone, but I could be swayed otherwise. I also think it would be wise to equip some of the more seaward seismometers with strong motion accelerometers, to be able to measure large earthquakes and remain on scale. In addition to the general benefits of an on-scale recording, I think this information would be of great interest to researchers trying to understand the generation of submarine landslides above megathrusts.
Aubreya Adams – Colgate UniversityI am especially interested in the questions related to along strike variability in earthquake cycles/locking and melt production, and think these questions would be best addressed by a 2-leg deployment spanning the Shumagin and Semidi segments. I also suggest that the training component of the Cascadia Initiative, involving student and early career researchers, be extended to the the proposed Alaskan experiment.
Paul Johnson, Joan Gomberg, Susan Hautala, Marie Salmi As a collaborative research group (UW and USGS), we have been active in processing the temperature, pressure and seismic data from the first 3 years of the Cascadia Initiative OBS data sets. Our examination of the temperature data, from the Paroscientific quartz temperature sensors on the APGs), showed that 6 of the 68 LDEO OBSs that had temperature sensors showed temperature anomalies that we are interpreting as influence from nearby sediment-laden gravity flows. These interpretations are consistent with our initial analysis of the companion pressure and seismic sensor data from the same instruments. Because of the potential impact on the OBS external environment by sediment flows – generated both by local and distant seismic triggers, we are proposing to continue this analysis using the marine OBS component of the Alaska Subduction Zone experiment discussed by the present Webnar group. Our addition to the Alaska Community Experiment would be on a non-interfering add-on basis, requiring only the addition of small Antares or MAVS sensors to the OBSs, similar to what has been done on the New Zealand margin. Our proposal would distinct from, but integrated with, the current proposal to deploy the marine component of the Transportable Array on the Alaskan margin.
Spahr Webb – Columbia University (LDEO) The Shumagin and Semidi segments show a transition from fully coupled to nearly or fully uncoupled behavior (based on GPS observations), so a deployment south of the Aleutian peninsula should elucidate coupling processes and would be relevant to understanding seismic hazard. Ongoing planning seems to be moving in a very sensible direction with 1) plans for OBS deployments from early one summer with a recovery late in the following summer, with an interlude to refurbish the OBS during the winter, 2) an emphasis on shielded OBSs in shallow water (<400m). The shields have been shown to provide significantly lower noise levels by shielding the sensors from current. Significant trawling is conducted across the much of shelf, so heavy shields will be required to avoid OBS losses. The abundant seismicity of the margin will enable excellent imaging of structures within a short period of time, however it also poses a problem for current OBS fleets in that large nearby events will cause the seismic sensors to clip. APGs (and low gain hydrophones) could help with this problem, but a subset of the OBSs should be equipped with strong motion sensors if possible. A strong effort to develop shielding for deep water OBSs should be undertaken as soon as possible given the obvious advantage of shielding in shallow water. Significant tidal currents are present at the seafloor in deep water. Unfortunately, tidal currents are strong south of Alaska (but similar to northern Cascadia). I would also like to see an experiment in the Amlia fracture zone region (as described in the Alaska planning meeting report), although this site could be done in later years after Earthscope leaves Alaska.
Cindy Ebinger – University of Rochester Recent studies in extensional arcs and magmatic rifts reveal multiple feedbacks between faulting processes and crustal magma intrusion and eruption, with strong implications for eruption prediction and EQ hazard assessment. Yet, few observations exist in compressional magmatic arcs to investigate feedbacks between stress, faults, and crustal intrusion and eruption. The recent comparison of geophysical data from the southern Andes (Uturuncu) by Pritchard and Gregg reveals massive magma-rich zones in the mid- to lower crust beneath this arc system, yet pathways and triggers for intrusion remain poorly understood. The rapid convergence and high volcano activity levels in the Aleutian arc, and the presence of the TA in the region provide a unique and time-sensitive study locale. Existing GPS and seismicity data suggest considerable shortening across the arc in the Kodiak and Semidi segments, related in large part to plate coupling variations along the length of the trench. My suggestion is to deploy a local net seaward of Katmai volcano in the Kodiak segment that ruptured in 1964, and instruments around Chiginagak or Aniakchak in the Semidi segment. The denser array will enable detection of microseisms and larger EQs that provide constraints on the distribution and kinematics of crustal deformation, and that will enable some imaging of crustal magma reservoirs. Crustal anisotropy measurements provide additional constraints. This work will complement recent studies of Okmok, Akutan, and Makushin. I will contact Cliff Thurber, Ellen Syracuse, Stephanie Prejean, and Mike West if there’s hope of pulling this off.
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