[SCG53-P14] A comparison of the stress evolutions due to Boso slow slip events and the accompanying earthquake swarms
Keywords:subduction zone, GNSS, tilt changes, earthquake swarm, slip process
We select three locations on the subducting plate interface in and around the Boso SSE source area where the earthquake activity during the SSEs in 2007, 2011, and 2014 are relatively high. Source slip processes for the three SSEs estimated based on GNSS displacements and tilt change records (Hirose et al., 2014) are assumed and the time-dependent stress changes caused by the slip processes are calculated with Okada's (1992) expression for a homogeneous elastic half-space. The Hi-net routine earthquake catalog (Obara et al., 2005) is used for measuring the earthquake activities.
There are many earthquake clusters where shear stress increases during the SSEs, but there are also a few clusters where shear stress decreases. For the earthquake clusters with stress increase, the maximum in shear stressing rate precedes the largest seismicity rate for a few days at most of these locations. In addition, an earthquake activity in a cluster begins when the share stress change reaches a similar level at most of these locations. These lines of evidence suggest that the stress is one of the most important factors that govern an earthquake activity, but also suggest that there may be other controlling factors since some of the clusters activate during stress decrease.
We should note that the calculated stresses likely include large uncertainties because the spatial resolution in the geodetic inversion for the SSE source slip processes are limited but heavily affects the stress calculation.
Acknowledgments: The GNSS data were provided by Geospatial Information Authority of Japan.