EAGER: Upper-plate Response to a Great Eathquake: Integrating Deformation from Seismic to Geologic Timescales

As was clearly demonstrated in the 2011 Mw 9.0 Tohoku (Japan) earthquake and tsunami, earthquakes that occur along subduction zone plate boundaries can be both among the largest and most devastating natural events on Earth. One key to anticipating what regions of subduction zones are most vulnerable to these mega-thrust events is to estimate the magnitude and location of un-released plate motion that accumulates prior to a major earthquake. Current subduction zone models assume a relatively simple link between observed deformation on the upper plate above the subduction interface and this slip deficit on the plate interface; however it is becoming clear that the actual distribution of co-seismic slip on the plate interface and the resulting upper plate response is substantially more complex. In order to map the accumulation of unreleased seismic moment, it is necessary to better understand how to map the observations of pre-, co- and post-earthquake deformation (made on land away from the plate interface) to the actual processes of slip accumulation and release on the plate boundary fault itself. This project will utilize a very rich data set of observed crustal deformation (GPS, geologic mapping, seismicity), observed on time scales ranging from geologic (millions of years) to earthquake cycle (hundreds-to-thousands of years) to earthquake rupture (minutes-to-seconds) in the vicinity of the Tohoku event. By combining geologic time-scale and seismic cycle time-scale observations conceptual models of subduction zone strain evolution can be improved. With a better understanding of how the upper plate in a subduction zone acts as a deformational filter, using observations of upper plate deformation the research team will be able to develop substantially improved estimates of plate boundary slip deficits, post-seismic loading of active structures on the upper plate (which may becomes seismically activated in response the main earthquake), and a better sense of seismic potential of subduction boundaries.

This project is an attempt to bridge a substantial gap in current subduction science - the gap between tectonic observations on geologic time-scales and current geophysical/geodetic observations of deformation through the earthquake cycle. Outcomes from this research will move subduction science toward better informed estimates of earthquake potential, maximum magnitudes that could be expected, and improved estimates of locations of maximum energy (moment) release during major earthquakes - all key components in reducing human vulnerability to major subduction zone earthquake hazards.