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STUDY ON REMOTE TRIGGERING MECHANISMS OF MICRO-EARTHQUAKES AT GEOTHERMAL AREAS

地热区微地震远程触发机制研究

基本信息

批准号：
09640501
负责人：
OHTAKE Masakazu
金额：
$ 0.51万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

项目摘要

We studied the remote triggering mechanism of micro-earthquakes based on analyses of the seismic data obtained at geothermal areas. We started a high resolution seismic observation at the Kakkonda geothermal area, Iwate Prefecture, Japan, in May 1998 by using a bore-hole seismometer. However, the Kakkonda area were severely damaged by the M6.1 earthquake on September 3, 1998, and we could not continue the observation after the earthquake. In this study, therefore, we analyzed : (1) continuous records of a broad-band seismometer that was installed 5 km east of the Kakkonda area, and (2) past records of bore-hole seismometer at Kakkonda that were recorded in 1986-1990, July 1993 and December 1994, (3) remote triggering phenomena reported in the world. We further calculated theoretical dynamic strain, static strain and maximum acceleration associated with a large earthquake. Based on these observations and theoretical studies, we obtained the following results :1. From the observed relations between seismic magnitude and epicentral distance of the earthquakes that remotely triggered micro-earthquakes, we find that dynamic strain associated with a large earthquake plays a main role to trigger micro-earthquakes, and that dynamic strain of more than 10ィイD1-7ィエD1 is necessary to remotely trigger micro-earthquakes.2. The earthquake swarms are remotely triggered 0.1-1 hour after the maximum dynamic strain due to a large earthquake.3. Remote triggering phenomena are often observed at geothermal and volcanic areas. This suggests that an increase of pore pressure of magnetic fluid and hot water in the crust may play an important role in the remote triggering mechanism.

本文在分析地热区地震资料的基础上，研究了微地震的远发机制。我们于1998年5月开始在日本岩手县Kakkonda地热区使用钻孔地震仪进行高分辨率地震观测。然而，1998年9月3日的6.1级地震使卡孔达地区受到严重破坏，地震后我们无法继续进行观测。为此，本文分析了（1）卡孔达以东5 km处的宽频带地震计的连续记录，（2）卡孔达钻孔地震计1986-1990年、1993年7月和1994年12月的历史记录，（3）世界上报道的遥触发现象。进一步计算了理论动应变、静应变和大震最大加速度。基于这些观测和理论研究，我们得到了以下结果：1.从观测到的远程触发微震的地震震级与震中距的关系中发现，大震伴随的动应变是触发微震的主要因素，远距离触发微震的动应变必须大于10 ~ 70 kD_1。大地震最大动应变发生后0.1-1小时远程触发震群。3.在地热和火山地区经常观察到远距离触发现象。这表明磁流体和热水的孔隙压力的增加可能在远程触发机制中起重要作用。