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

我们研究了基于微地震的远程触发机制，对地理区域捕获的地震数据进行了分析。我们于1998年5月在日本岩手地区开始进行高分辨率的地震观测，使用一个钻孔测量仪。However， 1998年9月3日M6.1地震严重受损，我们无法继续地震后的观测。因此，在这项研究中，我们分析了： （1）在Kakkonda东部5公里处安装了宽带同步计的连续记录;（2）在Kakkonda 1986-1990年、1993年7月和1994年12月记录的Bore-hole同步计的过去记录;（3）在世界各地远程触发现象报告。我们进一步计算了与较大地震相关的理论动力学应变、静态应变和最大加速。根据这些观察和理论研究，我们获得了以下结果：1。从远程触发的微地震的地震距离的观察范围和外延关系中，我们发现了与大型地震有关的动态神经元，作为触发微地震的主要作用，而10-D1-7中更多的动态神经元D1-D1需要远程触发的微型地震。地震群远程触发了0.1-1小时后的最大动态应变导致了大地震。远距离触发现象经常在地理区域和火山区域观察到。以下建议是，增加了磁性流体和热水的极压力，可能会在遥控触发机制中发挥重要的作用。

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.