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Search for the source fault of the Genroku Earthquake by the integrated seismic exploration along the on- and off-shore zone of the southern Boso peninsula, Japan

通过日本房总半岛南部陆上和近海的综合地震勘探寻找元禄地震的震源断层

基本信息

批准号：
16204038
负责人：
ITO Tanio
金额：
$ 32.36万
依托单位：
Chiba University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

The integrated seismic exploration was carried out in 2005 along the on- and off-shore zone of the southern Boso peninsula, Japan, in order to estimate the source fault of the Genroku Earthquake of 1703. 804 receiver points were set up onshore, and 1005 air-gun shots were done offshore. The seismic line reached more than 50 km long from Shirahama to Katsuura. As the line might not run perpendicular to the estimated trend of the upper surface of the Philippine Sea plate (PHS), we developed a new technique for processing instead of the conventional reflection method. The principle of the technique, called OAS (Optimum Azimuth Search) method, is to search the optimum azimuth for stacking by trial and error. By this technique, the prominent image of a big knoll emerges beneath the southern part of the Boso Peninsula. The combination of this result with reprocessed seismic profiles of the previous explorations (SK-78, Daidaitoku-Boso2002, NIED96 etc.) on and off the southern part of the Boso peninsula provides the 3 D image of a knoll with its base of about 30 km in diameter and its height of about 2 km relative to its surroundings. The knoll was probably formed originally as a volcanic sea mount, considering that volcanic sea mounts occur in common on the PHS between the Izu-Mariana trench and the Izu-Bonin arc. It is estimated that the knoll has been playing a role of an asperity on the subducting PHS. This provides a reasonable hypothesis that the northern slope of the knoll corresponds to the source fault of the Genroku Earthquake.

2005年在日本房总半岛南部的陆上和海上地带进行了沿着的综合地震勘探，以估计1703年元禄地震的震源断层。陆上设置了804个接收点，海上进行了1005次气枪射击。地震线从白滨到胜浦长达50多公里。由于测线可能不垂直于菲律宾海板块（PHS）上表面的估计趋势，我们开发了一种新的处理技术，而不是传统的反射方法。该技术的原理是通过试凑法寻找最佳叠加方位角，称为OAS（Optimum Azimuth Search）法。通过这种技术，在房总半岛南部的下面出现了一个大山丘的突出形象。将此结果与以往勘探（SK-78、Daidaitoku-Boso 2002、NIED 96等）的再处理地震剖面相结合，可获得较好的结果。在房总半岛南部和附近提供了一个圆丘的3D图像，圆丘的底部直径约为30公里，相对于周围环境的高度约为2公里。考虑到伊豆-马里亚纳海沟和伊豆-小笠原岛弧之间的PHS上常见的火山海山，该山丘最初可能是作为火山海山形成的。据估计，该小丘一直在俯冲的PHS上起着粗糙的作用。这提供了一个合理的假设，即圆丘的北方斜坡对应于元禄地震的震源断层。