Crustal structure in and around the region of the 1995 Kobe Earthquake deduced from a wide-angle and refraction seismic exploration

Citation
T. Ohmura et al., Crustal structure in and around the region of the 1995 Kobe Earthquake deduced from a wide-angle and refraction seismic exploration, ISL ARC, 10(3-4), 2001, pp. 215-227
Citations number
39
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
ISLAND ARC
ISSN journal
1038-4871 → ACNP
Volume
10
Issue
3-4
Year of publication
2001
Pages
215 - 227
Database
ISI
SICI code
1038-4871(200109/12)10:3-4<215:CSIAAT>2.0.ZU;2-P
Abstract
The 1995 Kobe (Hyogo-ken Nanbu) earthquake (M-JMA 7.2, M-w 6.9) occurred on Jan. 17, 1995, at a depth of 17 km, beneath the areas of southern part of Hyogo prefecture and Awaji Island. To investigate P-wave velocity distribut ion and seismological characteristics in the aftershock area of this great earthquake, a wide-angle and refraction seismic exploration was carried out by the Research Group for Explosion Seismology (RGES). The profile includi ng 6 shot points and 205 observations was 135 km in length, extending from Keihoku, Northern Kyoto prefecture, through Kobe, to Seidan on Awaji Island . The charge of each shot was 350-700 kg. The P-wave velocity structure mod el showed a complicated sedimentary layer which is shallower than 2.5 km, a 2.5 km-thick basement layer whose velocity is 5.5 km/s, overlying the crys talline upper crust, and the boundary between the upper and lower crust. Almost all aftershock hypocenters were located in the upper crust. However, the structure model suggests that the hypocenters of the main shock and so me aftershock clusters were situated deeper than the boundary between the u pper and lower crust. We found that the P-velocity in the upper crust benea th the northern part of Awaji Island is 5.64 km/s which is 3% lower than th at of the surrounding area. The low-velocity zone coincides with the region where the high stress moment release was observed.