Abstract
Abstract On March 20, 2005 the West off Fukuoka Prefecture earthquake (magnitude of 7.0 on the JMA scale) occurred in southeastern Japan. The earthquake fault was a left-lateral strike-slip having a nearly vertical fault plane and a strike in the WNW-ESE direction. The largest aftershock with a magnitude of 5.8 (JMA) followed 1 month later. To gain more detailed aftershock data, several teams from different Japanese universities jointly installed a number of temporary seismic stations and positioned Ocean Bottom Seismometers (OBSs) immediately above the focal area. Double-difference tomography was used to estimate the three-dimensional (3D) (Zhang and Thurber, 2003) velocity structures in and around the focal area based on the travel time data collected during seismic observations. The high-velocity regions estimated by the inversion are located on the edge of the aftershock area and on the shallow part of asperity, as inferred from the slip distribution. Conversely, the V p/V s ratio is not always as high as that found at the location of the asperity. This finding suggests that the construction of the medium is not uniformly elastic but complex, with different relations between elastic constants and strength.
Highlights
The West off Fukuoka earthquake occurred on March 20, 2005 in the northern part of Kyushu, Japan
On the basis of the aftershock distribution and the mechanism inferred from the P wave first motion, the earthquake fault was determined to be a left-lateral strike-slip type with a strike in WNW-ESE direction (Shimizu et al, 2006)
We report here the acquisition of detailed threedimensional (3D) seismic velocity structure data in and around the focal area of the 2005 West-off Fukuoka Prefecture earthquake by means of DD tomography
Summary
The West off Fukuoka earthquake (magnitude of 7.0 on the JMA scale) occurred on March 20, 2005 in the northern part of Kyushu, Japan. The maximum seismic intensity of 6-lower (JMA scale) was recorded in the Fukuoka and Saga Prefectures. This earthquake killed one person and injured more than 1000 as well as destroying many homes and buildings. On the basis of the aftershock distribution and the mechanism inferred from the P wave first motion, the earthquake fault was determined to be a left-lateral strike-slip type with a strike in WNW-ESE direction (Shimizu et al, 2006). The principal stress has the same direction as that inferred from the mechanisms of occurrence of microearthquakes in this region (Shimizu et al, 2006)
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