Development of a seismic network in the Western Pacific

点击翻译按钮获取中文摘要

The main purpose of this project is to install a broad-band seismic station in the Palau Islands and we have completed it successfully. The station lies at the middle part of Koror Island. We repaired an old air-raid shelter whose length is longer than 40 m, and made a seismometer table in a back room of the shelter. The seismometer room is divided from the other part of the shelter by three doors, and lies about 1 m deep from the land surface. Therefore, the temperature change is quite small in the seismometer room The recording system can be accessed using telephone line and has magnetic tape drives for data backup. We also setup a computer in PCC for retrieving the data by telephone line and storing on MO disk drive.We analyzed source processes of large earthquakes occurred in the Western Pacific region. The details of rupture history of the 1994 Sanriku-Haruka-Oki earthquake and the 1995 Kobe earthquake are revealed by waveform inversion analyzes. The rupture process of the 1994 Sanriku-Haruka-Oki earthquake shows that the heterogeneity of the plate interface between the oceanic and the continental lithospheres affect rupture velocity, slip distribution, and the characteristics of earthquake sequences. We review our study for the P-wave velocity structure of the whole mantle, that are obtained by inverting first arrival times with better resolution under the Western Pacific. It reveals the fate of subducting slabs of lithosphere. The P-wave and PcP-wave arrival time data are also analyzed to get a velocity structure of the core-mantle boundary. These results are already published or will be published soon in the international journals.The data obtained in this research project are supplied by the Data Center of the Ocean Hemisphere Center, Earthquake Research Institute, University of Tokyo.