Numerical modeling of slow slip events in Nankai and Cascadia, considering plate configuration and tremor distribution

Wednesday, 24 February 2016: 11:20 AM
Takanori Matsuzawa, National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan, Bunichiro Shibazaki, International Institute of Seismology and Earthquake Engineering,Building Research Institute, Ibaraki, Japan, Kazushige Obara, Earthquake Research Institute, University of Tokyo, Tokyo, Japan and Hitoshi Hirose, Kobe University, Research Center for Urban Safety and Security, Kobe, Japan
Abstract:
In recent years, slow slip events (SSEs) are studied intensively in several plate boundaries, for example, the Nankai and Cascadia subuduction zones. In both zones, SSEs are found with active tremor. Thus, they are sometimes called as episodic tremor and slip (ETS). In the Shikoku and Tokai region in Nankai, SSEs are also found between the ETS region and the locked region where megathrust earthquakes are expected. These SSEs are called as long-term SSEs, as they have a long characteristic duration (typically more than several months). In our previous study (Matsuzawa et al., 2013), we reproduced ETS and long-term SSEs in the Shikoku region in Nankai. However, the modeled region is too narrow to evaluate the behavior in seismic cycles. In this study, we applied our model to the whole Nankai and Cascadia regions, and discuss the behavior in seismic cycles.

In our numerical model, a rate- and state- dependent friction law (RS-law) with a cutoff velocity is adopted. Low effective normal stress and a low cutoff velocity are assumed at the depth where the ETS is found. Negative and positive (a-b) values in the RS-law are assumed within and outside of the ETS region, respectively. In this study, the ETS region is based on the actual distribution of tremor. Plate interfaces are modeled by small triangular elements, considering actual plate configurations. Combining the friction law and elastic response in a half space, we calculated temporal evolution of slip velocity and state variable on each element.

Our numerical model reproduces recurring ETS both in Nankai and Cascadia, and long-term SSEs in the Shikoku and Bungo channel region in Nankai. ETS are relatively active, for example, in the western Shikoku region in Nankai, and the region between the south of Vancouver Island and the Olympic Peninsula in Cascadia, as found in observations. In addition, our model predicts that long-term SSEs occur at the late stage in the seismic cycles in the Kii region in Nankai, and Cascadia, while they have not been confirmed by actual observations yet. Our result suggests that long-term SSEs may be also common in subduction zones, and the behavior in seismic cycles may be characterized by the configuration of the subducting plate.

Previous Abstract | Next Abstract >>