Earth Planets Space, Vol. 57 (No. 10), pp. 961-972, 2005

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

Hitoshi Hirose and Kazushige Obara

National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenno-dai, Tsukuba, Ibaraki, Japan

(Received August 31, 2004; Revised February 19, 2005; Accepted March 27, 2005)

Abstract: We 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 highsensitivity 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 �eslow slip patches�f 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.
Key words: Subduction zone, Philippine Sea plate, plate interface, Hi-net, borehole tiltmeter, GPS, slow slip patch.