Interaction Between ETS (Episodic Tremor and Slip) and Long-Term Slow Slip Event in Nankai Subduction Zone

Date: 4/24/2019

Time: 10:45 AM

Room: Cascade II

ETS (Episodic tremor and slip), composed of low frequency tremor, very low frequency earthquake and short-term slow slip event (SSE), is one of slow earthquake phenomena occurring at the downdip side of the locked zone typically observed in Cascadia and Nankai subduction zones. ETS activity style is characterized commonly in both subduction zones by along-strike segmentation and along-dip gradual shortening of recurrence interval with increasing the depth. A big difference of ETS activity in both regions is existence of interaction with the long-term SSE at the gap between locked and ETS zones. The long-term SSE was originally detected in Tokai and Bungo channel at eastern and western edges of ETS zone; however, recently has been detected ubiquitously along the gap. The long-term SSE clearly interacts with surrounding ETS and other slow earthquakes. During the Bungo channel long-term SSE in 2003 and 2010, the tremor was activated for a few months at a narrow width of 10 km in the updip edge of ETS zone which is the adjacent region of the SSE source fault. On the other hand, the deeper tremor activity was stable irrespective of the SSE. Similar pattern of interaction between the long-term SSE and ETS tremor is also observed in Tokai and Mexico.

In the east side of the tremor region clearly triggered by the Bungo channel SSE, tremor activity seems to slightly increase after 2003 and 2010 SSEs. Such 7-year period variation in tremor activity is observed in only shallower part of the ETS zone and seems to migrate eastward at a speed of a few 10 km per year. This long-term variation of tremor activity is well coincident with a sequence of long-term SSEs with eastward migration detected between locked and ETS zones after Bungo channel SSEs. It also indicates interaction between ETS tremor and long-term SSE. Therefore, tremor activity is considered as a sensitive indicator for slipping at surrounding area.

Presenting Author: Kazushige Obara

Authors