Repeating short- and long-term slow slip events with deep tremor activity around the Bungo channel region, southwest Japan

Hitoshi Hirose,Kazushige Obara

doi:10.1186/bf03351875

Abstract

AbstractWe report the repeating occurrence of short- and long-term slow slip events (SSE) which are accompanied by deep tremor activity around the Bungo channel region, southwest Japan. Both of these activities are detected by NIED Hi-net, which is composed of densely distributed observatories equipped with a set of tiltmeter and a high-sensitivity seismograph. Since the short-term SSE is small in magnitude, GPS can detect only the long-term SSE. Some of these episodes have nearly the same surface deformation pattern. This shows the existence of ‘slow slip patches’ on a plate interface, where the episodic slow slip is the characteristic slip behavior. We observe a change in periodicity and size of the short-term episode after the onset of the long-term SSE. Moreover, the long-term slow slip accelerates when the short-term activity takes place. This suggests that there is an interaction between these two types of SSEs.

Highlights

At subduction zones, so called slow slip events (SSE)have been detected by geodetic measurements (e.g., Hirose, H. et al, 1999; Hirose, I. et al, 2000; Dragert et al, 2001; Lowry et al, 2001; Ozawa et al, 2002, 2003)
In 2003, crustal deformation caused by these SSEs was observed in both tiltmeter and Global Positioning System (GPS) networks around the Bungo channel region
We focus on the observational results of the crustal deformations due to the short- and long-term SSEs occurred in 2003 and early 2004

Summary

Introduction

Have been detected by geodetic measurements (e.g., Hirose, H. et al, 1999; Hirose, I. et al, 2000; Dragert et al, 2001; Lowry et al, 2001; Ozawa et al, 2002, 2003). In 2003, crustal deformation caused by these SSEs was observed in both tiltmeter and Global Positioning System (GPS) networks around the Bungo channel region These events are accompanied by the deep tremor activity. A borehole tiltmeter time series record generally shows a long-term relaxation pattern, just after the installation or the replacement of the sensor (e.g., Sato et al, 1980). This pattern can be modeled as an exponential time function (e.g., NIED, 2002), so that we fit this function to the original data and subtract this. See Obara (2002b) for detailed procedure of the tremor source determination

Crustal Deformations and Tremor Activity at West Shikoku in 2003 and 2004

Short-term episodes following the 2003 long-term event

Discussion

Conclusion