Study on crustal earthquakes along cinvergent plate boundary

点击翻译按钮获取中文摘要

Sichuan Province in China is located at a plate convergent zone where two continental plates are converging, and hence seismic activity is very high. Northestern Japan is alsolocated at the plate convergent zone, having a very high seismic activity, but a continental plate and an oceanic plate are converging there. A comparative study has been made between these two types of plate convergent zones, Sichuan province of China and northeastern Japan, in order for deeper understanding of generation process of intraplate shallow crustal earthquakes typical to the plate convergent zone.An automatic event detection, location and recording system, developed by Tohoku University, has been installed in the telemetering seismic network of Seismological Burean of Sichuan Province, actually at the two recording centers : Chengdu and Xichang. A temporary seismic observation system is also constructed to improve the observation station density of the existing network. These two systems have worked well by the effort of operation and maintenance done by the Chinese group, and have accumulated many high quality seismic waveform data.By using accumulated data, we have obtained the seismic structure beneath Sichuan Province which was not clear so far. P and S wave velocity structure of the crust beneath this region has been estimated from travel time data of shallow earthquakes and explosions. The crustal structure estimated has a thick crust compared with that beneath northeastern Japan, as expected from the different types of the two plate convergent zones. Hypocenter distribution based on this crustal structure shows that earthquakes concentrate along the main fault of the Rongmenshang Fault Zone, and that the seismogenic zone is confined to the upper 20km depth which is similar to northeastern Japan. Coda Q and S wave splitting are also estimated from the accumulated data, and their relations to seismotectonics are discussed.