HR: 1340h
AN: T43A-1362    [Abstracts]
TI: Crustal Structure in and Around the Miura Peninsula, Japan, Using an Off-Line Seismographic Array
AU: * Kawamura, T
EM: tkawa@eri.u-tokyo.ac.jp
AF: ERI, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Okaya, D
T43A-1362 AF: University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089 United States
AU: Hirata, N
T43A-1362 AF: ERI, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: A deep seismic profiling around the Metropolitan Tokyo region, the Kanto district, started in 2002 under the project titled as the Regional Characterization of the Crust in Metropolitan Areas for Prediction of Strong Ground Motion. The deep seismic profiling, Tokyo Bay 2003, was performed along the major axis of the Tokyo Bay. During 90 days, we had continuous records including many shot signals produced by vibrators on land and air-guns at the bay area. These data provided far-offset first arrival signals and wide angle reflections. We focus on the common receiver gather records of the Tokyo Bay 2003 off-line stations data to identify first arrival and wide angle phases. We applied the first arrival tomography method using a finite difference travel time solver (Hole, 1992) to those data to obtain a 3-D P-wave velocity structure of the uppermost crust along the profile. Then, its tomography profile was assumed an initial model, and P wave velocity structure which satisfied an observed travel time for a trial and error was made. We obtained results of inversion tomography and forward modeling in and around the Miura peninsula as follows: Across the Tokyo Bay, near surface is a layer with velocities of 1.6-2.5 km/s. This low velocity area corresponds to the fore-arc basin sediment (post Early Miocene) which extends to a depth of approximately 4 km. Beneath a low velocity area, higher velocity (5.0-5.6 km/s) and low velocity-gradient basement rocks exist, which was estimated to Pre-Neogene rocks (Shimanto or Chichibu belt). At the Miura peninsula, higher velocity (3.0-4.0 km/s), in comparison with the Tokyo bay side, patches are located at a depth of approximately 6 km, which we interpreted as Pre-Neogene basement rocks. Finally, the velocity structure obtained by the forward and inversion analysis are used to improve the processing of the reflection profiling data to clarify the deeper structure in the peninsula, including a good velocity constraint for a pre-stack migration of the reflection profiling data.
DE: 0935 Seismic methods (3025, 7294)
DE: 7270 Tomography (6982, 8180)
DE: 8038 Regional crustal structure
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005