Integration of transient strain events with models of plate coupling and areas of great earthquakes in southwest Japan

Zhen Liu,Danan Dong,Mark Simons,Eric Hetland,Susan Owen,Frank Webb,Paul Lundgren

doi:10.1111/j.1365-246x.2010.04599.x

Zhen Liu, Danan Dong + Show 5 more

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https://doi.org/10.1111/j.1365-246x.2010.04599.x

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Abstract

We model the crustal deformation caused by two long-term subduction slip transients in southwest Japan, which we refer to as the 2000–2004 Tokai and the 2002–2004 Bungo Channel slow slip events (SSEs). We use re-analysed GEONET position time-series, and a Kalman filter based network inversion method to image the spatiotemporal slip variation of the two events on the plate interface during the period of 1998–2004.67 and 2000–2005. Both events are found to have complex slip histories with multiple subevents. In addition to a newly identified slip subevent in 2002–2003, we find that the major event in the Bungo Channel SSE initiated in early 2003 beneath the northeastern corner of the region and expanded southwestward, in contrast to the slip characteristics suggested by other studies. The re-analysed GPS data in the Tokai region shows a renewed slip activity for the Tokai SSE in early 2003–2004 at a similar location as in the period of 2001–2002. The equivalent M_w for both the Tokai and Bungo Channel SSEs are about 7.0. Our results show that the Tokai SSE appears to start before the Miyaki-Kozu seismovolcanic event. Integrating plate coupling and SSEs shows that the transient slip zones are located in a region between the locked zones and the epicentres of the low frequency earthquakes (LFEs). At least part of the interseismic slip deficit is released by episodic SSEs beneath the Bungo Channel region. We find excellent temporal correspondence between transient slip and adjacent LFEs for both SSE, suggesting that they are closely related and possibly reflect that long-term slow slip may modulate the occurrence of LFEs.

Highlights

Japan is one of the prime places to study ongoing crustal deformation and subduction zone dynamics
But do not present, the static Coulomb failure stress change ( CFS) on the plate interface due to the transient slip in the Bungo Channel and Tokai L-slow slip events (SSEs), assuming that the low frequency earthquakes (LFEs) occurred on the plate interface
We reprocessed and analysed 10 yr of GEONET GPS data using a consistent processing and time-series analysis strategy for the entire network. We inverted these cleaned GPS time-series for the fault slip variations of two long-term transient slip events, one in the Bungo Channel and one in the Tokai region, assuming both slip events occurred on the plate interface

Summary

Introduction

Japan is one of the prime places to study ongoing crustal deformation and subduction zone dynamics. In southwest Japan (Fig. 1) the Philippine Sea Plate is subducting beneath the Amurian Plate at an annual rate of ∼60–70 mm yr–1, causing M ∼ 8 earthquakes every 100–200 yr over the past 1000 yr Thanks to the deployment of a dense continuous GPS network (GEONET) and a high-sensitivity seismograph network (Hi-net), a wide range of slow earthquake phenomena including long- and short-term slow slip events (L-SSE and S-SSE), non-volcanic episodic tremors, and low/very-low frequency earthquakes (LFE and VLF) have been discovered in southwest Japan LFEs, and VLFs occur over shorter time periods than S-SSEs, with VLFs having durations of hours to days. We collectively refer to seismic tremor, LFE, VLF and S-SSE as ‘short-term slow earthquakes’, which are in contrast to the much longer phenomena of L-SSE. We use both ‘transient slip’ or ‘slow slip’ to refer to the slip that appears in a SSE

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