Multidisciplinary Observations of Onshore Subduction (MOOS)

MOOS Seismic Array Map - Alaska

The MOOS experiment seeks to understand the structure and dynamics of subduction in the region of the 1964 Alaska earthquake, one of the three largest recorded (Mw 9.2), where terrane collision is actively occurring.

Multidisciplinary Observations of Onshore Subduction
a.k.a.
More Observations Of Subduction
a.k.a.
MOOS

PI’s:   Geoff Abers (Lamont-Doherty Earth Observatory); Doug Christensen (University of Alaska Fairbanks); Jeff Freymueller (University of Alaska Fairbanks)

The MOOS experiment seeks to understand the structure and dynamics of subduction in the region of the 1964 Alaska earthquake, one of the three largest recorded (Mw 9.2), where terrane collision is actively occurring.  The collision of thickened crust with subduction zones significantly modifies subduction.  It can lead to net growth of continents, drive much of subduction-related tectonism, and may also have a profound effect on the size, coupling, and rupture characteristics of large intraplate earthquakes. The present accretion of an exotic terrane, the Yakutat terrane, with the Alaska subduction system represents one of the few examples of this process currently active.  In this region, the collision occurs at the largest rupture asperity known, part of the great 1964 Alaska earthquake, and mountains have grown both along the Alaska coast and far inland.   Thickened crust has been imaged at the top of the subducting receiver functions from the BEAAR (Broadband Experiment Across the Alaska Range) IRIS-PASSCAL experiment, beneath Mt McKinley to 130 km depth. MOOS continues the BEAAR transect updip, in the region between the Alaska coastline and the Alaska Range, crossing the Kenai Peninsula, Anchorage area, and Prince William Sound. The experiment consists of a deployment of 34 broadband seismographs at dense spacing, provided by the IRIS-PASSCAL Instrument Center, and GPS measurements of surface deformation across this zone.  Sparse permanent seismic and geodetic (PBO) stations provide regional control. Seismograph deployment began with 4 pilot stations in summer 2006, with the remaining 30 seismographs deployed in summer 2007.  Half the instruments are removed in 2008 and the remainder in summer 2009.  As of Summer 2008, data recovery exceeds 90%.

 Integration with previous studies will provide the longest continuous transect of a subduction zone yet available, over 700 km across strike, following a slab from the trench to coast to where last seen at 150 km depth.  In parallel, a combination of geodesy and seismicity is used to image deformation currently associated with the plate interface, where it ruptured in the 1964 earthquake.  Modeling of deformation, when integrated with the imaging, elucidates the nature of the locked zone, the origin of the largest asperity, and the structural controls on interplate thrust processes.  These results are used to test ideas for the origins of intermediate-depth earthquakes, by sampling at high resolution the transition at the down-dip end of the thrust zone in seismicity, strain, and structure.

This project is funded by the NSF Geophysics Program, and supported by the IRIS-PASSCAL Instrument Center.

Location

Alaska
United States