HR: 0800h
AN: S51A-0988    [Abstracts]
TI: Crustal Structure Beneath the Kanto-Koshinetsu Region, Central Japan Inferred from Receiver Functions
AU: * Igarashi, T
EM: igarashi@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Hirata, N
S51A-0988 AF: Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: We applied the receiver function technique using multiple-taper method to estimate crust, uppermost mantle, and the subducting plate structure in the Kanto-Koshinetsu region, central Japan. This region is characterized by many faults and tectonic lines, and moreover the Philippine Sea plate subducts northward and the Pacific plate subducts westward. We analyzed P-wave seismograms recorded by regional seismographic networks from August 2002, a dense seismographic array which consists of 30 stations in the Boso Peninsula from February 2004, and temporary seismographic stations which installed in the source region of the 2004 Mid Niigata prefecture earthquake (M6.8) for a month. This study mainly used teleseismic events in the range of epicenter distances between 30 to 90 degrees. Moreover, we used local intermediate and deep events. They have almost the same characteristics as teleseismic traces and we can apply in the higher frequency, although they can be analyzed only in the short time width. A thick sediment layer with low velocity near surface may be preventing to resolve deep structure. To investigate the effect of sediment layer beneath stations, we make the synthetic receiver function traces assumed four layers structures with a sediment layer and compared them with observed trace. Estimated average S-wave velocities from surface to 5 km depth indicate very low velocity structures in the Mid-Niigata area and the Boso-peninsula and in some stations locally. Next, we estimated the structure beneath each station by forward modeling and investigated the depth of the Moho discontinuity. The Moho depth is the range of about 25 to 40 km, and increases in the mountain district. This result is consistent to the other previous studies. They also show a tendency to change around the tectonic lines. On the other hand, depth change of the southern part in this analysis region may be corresponding to the oceanic Moho discontinuity of the northward subducting Philippine Sea plate. However, receiver function traces in many stations have variety azimuthally and estimated structure in some stations was unstable for high noise level, the effect of a thick sediment layer or heterogeneous structure. We will have to investigate these in detail in consideration of the tangential component.
DE: 7218 Lithosphere (1236)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8150 Plate boundary: general (3040)
SC: Seismology [S]
MN: Fall Meeting 2005