Time-dependent Inversion of slow slip events and associated seismicity in Lower Cook Inlet, Alaska

Abstract:

We identified two long-term slow slip events (SSEs) in Lower Cook Inlet, Alaska (1992.0-2004.8 and 2009.85-2011.81) by inverting the GPS site velocities. We estimated slip distributions during four time periods (period 1: 1992.0-2004.8, period 2: 2004.8-2009.85, period 3: 2009.85-2011.81, period 4: 2011.81-2014.87) covering the SSEs and periods with no SSEs. Both SSEs located in the depth range of 40-60 km, at the downdip end of the locked zone. Observed velocities near Prince William Sound are systematically under predicted for all time periods which adds to the overall misfit. In order to obtain a comprehensive view of the time evolution of slip distributions on the plate interface, time dependent modeling of slip deficit on the plate interface in Lower Cook Inlet needs to be estimated from GPS time series directly by using TDEFNODE (McCaffrey et al. 2009).

The inverted time-dependent slip behaviors allow us to track the corresponding stress changes and associate them with seismic activity and non-tectonic tremor in Lower Cook Inlet. We will use our slip models to calculate the Coulomb stress change induced by the time-dependent slip on Alaska-Aleutian subduction zone plate interface. We are interested to see whether the observations of the seismicity in Lower Cook Inlet are consistent with stress triggering outside the slowly slipping region. We will test whether the temporal evolution of earthquakes are explained by increased stressing caused by SSEs, implying that the earthquakes are triggered. If this hypothesis can be tested, it can lead to a useful method to quantify the increasing the potential hazard during SSEs since the triggered earthquakes have the potential to be large and destructive ones.