Numerical Modeling of ETS in the Cascadia Region - An Application of Nankai Model -

Abstract:

Episodic tremor and slip (ETS) is found in various subduction zones. We have modeled slip of subducting plate interface including the ETS region in Shikoku, and successfully reproduced the characteristics of the segments and recurrences of ETS (Matsuzawa et al., 2013). However, it is important to examine whether our model can explain the characteristics of ETS in the other region. We have tentatively applied our model to the ETS in Cascadia. In our numerical model, a rate- and state- dependent friction law (RS-law) with a cutoff velocity is adopted, as in our previous studies. Low effective normal stress and a low cutoff velocity are assumed at the depth where ETS occur. Negative and positive (a-b) value in the RS-law is assumed within and outside of the ETS region, respectively. In this study, the ETS region is based on the actual distribution of tremor which is located by the monitoring system of Wech (2010). We assume that frictional parameters have similar depth-dependence to our previous study (Matsuzawa et al., 2013). Subducting plate interface is modeled by 203,064 triangular elements, based on the configuration in McCrory et al. (2004). In our numerical result, SSEs recur at the intervals of about 1 year. In addition, SSEs are relatively active between the south of Vancouver Island and the Olympic Peninsula. These characteristics are similar to observations (e.g. Brudzinski and Allen, 2007). Minor ETS activities at the down-dip portion occur between the major ETS activities both in the up-dip and down-dip portion. This feature is similar to the actual ETS in Cascadia (Wech and Creager, 2011). In addition, long-term SSEs recur between the ETS region and shallow locked region where large earthquakes are expected. These long-term SSEs are frequently found around the region with curved plate interface, and may be characterized by the configuration of the plate as in Shikoku (Matsuzawa et al., 2013).