GeoPRISMS - EarthScope Planning Workshop
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We are pleased to report on the outcome of the most recent GeoPRISMS planning meeting, the GeoPRISMS-EarthScope Planning Workshop for the Alaska Primary Site, held over a 2.5-day period in Portland, OR this past week. Approximately 150 people were in attendance. Substantial discussion took place both in break-outs and in plenary session, leading to a consensus plan for GeoPRISMS science in Alaska.
The primary elements of the science implementation plan are a geophysical transect along the oceanic part of the arc in combination with complementary focused studies of the Alaska Peninsula and Cook Inlet areas.
The geophysical transect along the oceanic arc is envisioned as the "back-bone" which provides a framework for focused studies at point locations encompassing varied aspects of the arc, fore-arc, trench and incoming plate. The chief focal point on the transect is the Amlia Fracture Zone area, where a strong contrast in trench sediment thickness and subducting plate age are linked to distinctive magma chemistry in the arc. This location may also mark a change in seismogenic character. Additional focal points in the Adak and Unalaska areas provide unique opportunities to characterize the birth and evolution of the arc, through geochemical and geochronological studies of plutonic and volcanic rocks produced early in the arc's history. Volcanoes of the Unalaska area (e.g., Okmok, Akutan, Shishaldin) also provide ideal targets, located on the backbone transect, for slab-to-surface geophysical imaging of the largest and most active volcanic centers in the Alaska-Aleutian subduction system.
The Alaska Peninsula features dramatic along-strike changes in the seismogenic zone, spanning megathrust rupture areas in different parts of their cycles, and is the best location for combining onshore and offshore studies to investigate the causes of these changes. This area allows for focused investigation of segments characterized by creep, segments characterized by wide locked regions, and the boundaries between them. It offers the best opportunity to examine links between seismicity and forearc surface process and variable subduction inputs (e.g., fan sediment, seamounts, Aja Fracture zone). The Alaska Peninsula includes the most productive volcanoes of the continental part of the arc, including both large dominantly basaltic centers and smaller dominantly andesitic centers.
The Cook Inlet area is the continental end-member of the subduction zone, which experienced a watershed megathrust event in 1964, and is dominated in the Quaternary by glacial and other surface processes that direct sediment into the subduction zone and forearc. The clearest evidence in Alaska for large slow slip events and transient changes in the extent of the seismogenic zone come from this region. Cook Inlet and the Alaska Peninsula are also areas with substantial opportunities for synergy with EarthScope and the Alaskan Volcano Observatory, which maintains active monitoring of volcanoes in these regions.
Alaska was chosen as GeoPRISMS Primary Site because of the distinct along-arc changes in volcanism, seismicity, forearc structure, and subducting sediment thickness. Participants recognized that specific synoptic studies that address these spatial changes along the entire arc as opposed to specific target areas were needed. These studies could include geodesy, paleoseismology, surface processes and along-arc sediment transfer, arc geochemistry and geochronology, and passive seismic monitoring.
We would like to thank the meeting attendees for their participation in the process of reaching a consensus on the GeoPRISMS science plan for Alaska. Also, a special thanks to all of the speakers, break-out group leaders, and white paper authors for their contributions in making the workshop such a success. Finally, we want to recognize the enthusiastic participation of the graduate students and post-docs - their input is greatly appreciated.
A number of important tasks lie ahead. The conveners and break-out leaders plan to prepare a comprehensive workshop report for distribution by November 2011, and an updated draft of the GeoPRISMS Alaska science implementation plan by January 2012. The implementation plan will be made available for public comment prior to final release. It will serve as a guide for proposals submitted for the next NSF GeoPRISMS solicitation, July 1, 2012.
Jeff Freymueller (University of Alaska-Fairbanks)
Peter Haeussler (USGS, Anchorage)
John Jaeger (University of Florida)
Donna Shillington (Lamont-Doherty Earth Observatory)
Cliff Thurber (University of Wisconsin-Madison)
Gene Yogodzinski (University of South Carolina)