The Relationship Between Slow Earthquake Activity and Frictional Property on the Plate Boundary Around Japan

Session: From Aseismic Deformation to Seismic Transient Detection, Location and Characterization
Type: Oral
Date: 4/29/2020
Time: 04:45 PM
Room: 230 + 235
Description: 

On the subducting plate boundaries, slow earthquakes are distributed mainly in the downdip and updip vicinities of seismogenic zones of megathrust earthquakes and we expect some relationships between both earthquakes. They are characterized by spatial variation of their activity reflecting the heterogeneity of the frictional condition on the plate boundary. We focus on very low frequency earthquakes (VLFEs) which are one type of slow earthquakes and whose signal has predominant period of 20－50 s, because they have the potential to clarify detailed spatiotemporal slip behaviors in the updip and downdip sides of the seismogenic zone.

Around Japan, the Philippine sea plate and the Pacific plate subducts from the Nankai Trough and the Japan and Kuril Trenches, respectively. Along the Japan and Kuril Trenches, Baba et al. (2019) detected VLFEs comprehensively by the matched-filter technique. They set virtual source grids on the plate boundary and used synthetic template waveforms based on a 3D velocity model. The focal mechanisms are consistent with the geometry of the plate boundary and the plate motion. To compare all VLFE activities across Japan, we detected VLFEs along the Nankai Trough by the same method as Baba et al. (2019) by using seismograms of NIED F-net from 2003 to 2019.

The distribution of shallow VLFE activity rate is more heterogeneous along trench axes and clearly shows an anti-correlation relationship with the spatial distribution of interplate coupling rate, whereas the variation of deep VLFE activity rate is small and deep VLFEs are distributed only in weak coupled areas. This suggests that the along-strike heterogeneity of frictional property is stronger in the shallow part than in the deep part. And shallow VLFEs are mainly hosted within low seismic velocity anomalies, thus slow earthquakes can be encouraged by decreased effective stress due to high pore fluid pressure within regions with weak interplate coupling. Our results suggest that slow earthquake activity is an indicator illuminating interplate slip behavior surrounding the seismogenic zone.

Presenting Author: Satoru Baba

Authors