Receiver function imaging around source region of slow earthquakes in western Shikoku, Japan by using a dense array
Abstract
Various types of slow earthquakes with different characteristic time scales occur along subducting plate interfaces of many subduction zones in the world. Mechanisms of these slow earthquakes can be controlled by the surrounding subsurface structure. Kato et al. (2010) applied seismic tomography and receiver function analyses to data of a dense seismic array in the Tokai region, central Japan. They revealed that episodic tremor and slip (ETS) events occurred at the boundary between the subducting Philippine Sea (PHS) plate and the mantle wedge, and that the long-term slow slip event occurred at the boundary between the continental crust and the PHS plate. In this study, we used a dense seismic array in western Shikoku in order to investigate the relationship between slow earthquakes and the surrounding seismic velocity structure.
We used records of 74 stations, including 69 temporary stations, and five permanent stations operated by NIED, JMA, and AIST. The receiver functions were calculated for 119 distant events from October 2011 to March 2013 with magnitudes larger than 5.5, and epicentral distance between 30and 90 degrees. The water level method (Langston, 1979) was applied to 80-s long records from 40 s before P wave arrival time, whose signal-to-noise ratio of the vertical components are greater than 3. We obtained receiver function image of the subducting structure by performing CCP stacking. As a result, we detected coherent negative and positive peaks descending northwestward at a depth of 20-45 km, which we interpret as the top of the subducting PHS plate and the oceanic Moho, respectively. Comparison with distribution of seismic events suggests that tremor occurs on the top boundary of the subducting PHS plate, and that intraplate earthquakes occur in the vicinity of the oceanic Moho. Since continental Moho within the overriding plate can be identified at a depth of 25-30 km just above the tremor region, we concluded that ETS occurs at the boundary between the subducting plate and the mantle wedge as observed in Tokai.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T33E0444H
- Keywords:
-
- 1242 Seismic cycle related deformations;
- GEODESY AND GRAVITYDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICSDE: 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS