Descr: This proposed project will image the subducted plate, upper plate, and intervening deformation in the region between the Alaska coastline and BEAAR. Here subduction passes through and past the 1964 rupture zone. We will: (1) seismically image the top of the downgoing plate through and below the thrust zone. 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 over 150 km depth. (2) Image geodetically and with seismicity the deformation currently associated with the plate interface where it ruptured in the planet’s second largest known earthquake. Modeling of deformation, when integrated with imaging of structure, will elucidate the nature of the locked zone, the origin of asperities, and the structural controls on interplate thrust processes. We will also be able to test more fully 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. The experiment consists of a deployment of 30 broadband seismographs at dense spacing, supplemented by short-period seismographs in places where higher-resolution seismicity would provide most information, and GPS measurements of across this zone. Because of the short working period in Alaska, we plan to prepare sites the first summer with limited instrument deployment, deploy most instruments the beginning of the second summer, recover seismic equipment the end of the third summer, leaving a year for analysis. Many of the seismicity and GPS sites are collocated, so there are cost savings to simultaneously conducting geodetic and seismic field work.
