Seismic Velocity Discontinuities beneath The Japan Islands Revealed by Receiver Function Analysis

Research Project

Project/Area Number	11440131
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Research Field	固体地球物理学
Research Institution	Nagoya University
Principal Investigator	HIRAHARA Kazuro Nagoya University, Environmental Studies, Professor, 大学院・環境学研究科, 教授 (40165197)
Co-Investigator(Kenkyū-buntansha)	TODOKORO Keiichi Nagoya University, Science, Assistant Prof., 大学院・理学研究科, 助手 (70324390) FURUMURA Takashi Univ. of Tokyo, Assosiate Prof., 地震研究所, 助教授 (80241404) SHIBUTANI Takuo Kyoto Univ. DR2, Assistant Prof., 防災研究所, 助手 (70187417) 熊谷博之名古屋大学, 防災科学技術研究所, 研究官 (00260589) 吉田康宏気象庁, 気象研究所, 研究官
Project Period (FY)	1999 – 2001
Project Status	Completed (Fiscal Year 2001)
Budget Amount *help	¥14,400,000 (Direct Cost: ¥14,400,000) Fiscal Year 2001: ¥4,100,000 (Direct Cost: ¥4,100,000) Fiscal Year 2000: ¥3,800,000 (Direct Cost: ¥3,800,000) Fiscal Year 1999: ¥6,500,000 (Direct Cost: ¥6,500,000)
Keywords	Receiver Function / Teleseismic Events / Seismic Discontinuity / Moho Discontinuity / Conrad Discontinuity / Slab Interface / 410 - 660 km / Tomography / レシーバ / 410km,660km不連続面 / 達地地震 / SVDフィルター / 日本列島 / 3次元構造 / 地震波不連続面 / 地震波形トモグラフィー / 地震観測網
Research Abstract	Seismic velocity structure including seismic discontinuities beneath the Japan Islands is investigated using receiver function array analysis method We use a large number of broad band (FREESIA. J-array) and short-period high density (J-array, Hi-net) stations installed all over the Japan Islands. First, we obtained receiver functions (RFs) in a traditional way which has been so fer employed. Then we applied SVD (Singular Value Decomposition) filtering to the original RFs for the short period ones, and to the depth transformed RFs for the broadband ones. Using short period data with high spatial resolutions, we clearly recognized lateral variation of the Conrad, and the Moho discontinuities in the crust Especially in southwest Japan where the station are closely distributed, we detected the inclined Conrad and the downwarping ofthe Moho around the Lake Biwa. For the upper mantle seismic discontinuities, we detected the inclined upper and lower boundaries of the descending Pacific slab in the Tohoku region. For the Philippine Sea slab, it seems to be rather difficult to see Hie boundaries. Also we detected 410 km and 660 km discontinuities. 410 km discontinuity is especially clear in comparison to 660 km one, and seems to be upwarping within the descending slab. 660 km discontinuity seems to be divided into three discontinuities. At last, we added the data of Hi-net, which has been only recently installed. They have a sampling rate of 100 Hz, which enables us to produce higher frequency RFs for imaging the far detailed structure. Though this is only preliminary, there is a possibility that we can image the reflective layering structure in the lower crust, which provides us an important information relating to the initiation of large inland earthquakes.