Periodic Occurrence of the Slow Slip Events Off Kyushu Island, Southwest Japan, Based on Spatial Gradients of Displacement Rate Field and Activities of Small Repeating Earthquakes

Date: 4/24/2019

Time: 11:15 AM

Room: Cascade II

Periodic changes in the interplate locking in the northeast Japan subduction zone were revealed based on the activity of small repeating earthquakes and the change in the spatial gradient of horizontal displacement rate field. Speaking of the southwest (SW) Japan subduction zone, large earthquakes such as Tokai, Tonankai, and Nankai earthquakes repeatedly occur that rupture the plate interface fault between the Philippine Sea plate and the continental plate (Eurasia or Amurian plate). Long- and short-term slow slip events on the plate interface are also found in the SW Japan subduction zone and the relationship between the occurrence of the SSEs and the generation process of the mega-thrust earthquakes are under discussion. In this study, we focused on the spatio-temporal change in the interplate locking along the plate boundary in SW Japan based both on the geodetic and seismic data. We applied the monitoring method for spatial and temporal variation of the degree of the interplate locking proposed by Iinuma [2018] to the southwest Japan. The spatial gradient of the surface displacement rate field in each swath region that is configured along the direction normal to the Nankai Trough for time windows such as one and two years being shifted by one week. The also utilized the activities of small repeating earthquakes that occur east off Kyushu Island to estimate the average cumulative slip within several sub-areas assuming the underlying slow slip is similar in each area. The results show that temporal changes in the spatial gradients of surface displacement rates and in the cumulative slip estimated from the small repeating earthquakes mostly coincide. The temporal changes show 5 to 6 peaks within ~14 years suggesting quasi-periodic occurrence of SSEs on the plate boundary. These SSEs are located to the south of the locked areas for previous large interplate earthquakes and suggesting non-stationary slow–slip behavior in this area.

Presenting Author: Takeshi Iinuma

Authors