Abstract
We evaluated the long-term strain rate by using continuous global navigation satellite system data of GEONET and compared it with seismicity activation between 1996 and 2017 near Iriomote Island, south Ryukyu arc. We analyzed the seismicity by using the epidemic-type aftershock sequence model to detect the timing when the seismicity had changed. The results revealed that the long-term shear strain rate had increased on around 2002 and around 2013, and this was accompanied by an increase in seismicity in both 2002 and 2013. The change in the shear strain rate in 2002 could be explained by the crustal movement induced by the 2002 afterslip in the area west of Iriomote Island. The change in the shear strain rate in 2013 could be explained by the post-seismic crustal movement induced by the dike intrusion that occurred during the earthquake swarm in the Okinawa Trough in April 2013. These findings suggest that the long-term seismicity near Iriomote Island is strongly affected by changes in the crustal strain rate, which have occurred in the past in response to dike intrusions in the Okinawa Trough and slow earthquakes in the Ryukyu Trench.
Highlights
Faulting during a slow earthquake changes the stress distribution and can induce surrounding seismicity
Almost the entire region in the area southwest of Iriomote Island was positive with the different frictional coefficients. These results suggest that the effect of the difference of frictional coefficient was small for the ∆difference in Coulomb failure stress (CFS) in the area southwest of Iriomote Island
The seismicity in the S region was found to be related to the long-term shear strain rate
Summary
Faulting during a slow earthquake changes the stress distribution and can induce surrounding seismicity. In the Boso region, central Japan, earthquake swarms have been generated repeatedly when slow slip events (SSEs) occurred in the subducting Pacific plate (Ozawa et al 2007). The moment magnitude of the studied SSEs was ~ Mw 6.5, whereas the maximum magnitude of the swarm was Mw ~ 4 (Ozawa et al 2007). This finding suggests that the plate interface mainly slips aseismically, whereas small seismic patches ruptured during the slip of the Mw 6.5 aseismic events. The seismicity of the swarm accompanying the SSEs had notable characteristics in that the background
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