Numerical Modeling of Long- and Shallow Slow Slip Events Including Shallow Region in Hyuganada and Western Nankai, Japan

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

Deep long-term slow slip events (SSEs) are newly found in the Hyuganada and western Nankai region in recent years (e.g., Kobayashi, 2014; Ozawa. 2017). Shallow SSEs are also recently reported with low-frequency tremor and very low-frequency earthquakes (e.g., Araki et al., 2017; Nakano et al., 2018). In our previous study, we have numerically reproduced recurring deep long- and short-term SSEs in the Shikoku region (Matsuzawa et al., 2013), considering the actual distribution of slow earthquakes and configuration of subducting plate. We aim to reproduce deep long- and short-term SSEs and shallow SSEs in a single numerical model applying a similar approach in Matsuzawa et al. (2013).

We adopt a rate- and state-dependent friction law (RS-law) with cutoff velocities. We assume that (a-b) value in the RS-law is negative within the SSE region, and positive outside the region. Deep short-term SSE region is modeled based on the actual distribution of low frequency tremor. Deep long-term SSE region is assumed based on the geodetic observation. We also assumed low cutoff velocity at the depth shallower than 9 km to reproduce shallow SSEs. Low effective normal stress is assumed at the depth of SSEs. Temporal evolution of slip velocity is numerically simulated, introducing elastic response and realistic configuration of the plate interface.

In our simulation, shallow episodic SSEs off Ashizuri are reproduced. This suggests that the configuration of plate interface can characterize the occurrence of shallow SSEs. In terms of deep long-term SSEs in Hyuganada, a simple extension of the long-term SSE region in the Bungo Channel cannot reproduce the segments of observed SSEs. Narrowed long-term SSE region in the dip direction between Bungo and southern Hyuganada can reproduce the segments of SSEs. Our model comprehensively reproduces various SSEs, including newly found long-term SSEs which seem to occur commonly in the subduction zone of southwestern Japan. Moreover, when our model is simply applied to the Cascadia region, long-term SSEs are also predicted.

Presenting Author: Takanori Matsuzawa

Authors