Super deep earthquake

(1)破裂速度低、上升时间长的慢变形可以使地震的低频分量的弯矩比欧米格方模型的标度律大。这些地震被称为“慢地震”。仅在局域台网观测到的小慢震可能具有预报地震的可能性，本文提出了利用地壳运动资料的“多台法”来寻找发生在Kii半岛和日田地区的慢震。我们使用了1990-1991年位于奇伊半岛的小型台网和位于日本西南部的大型台网的应变仪和水倾斜仪记录。在4分钟至256分钟的时间序列内，在本研究中未检测到慢事件。但考虑到前人研究中存在局部慢震，且没有发生大地震，这一结果有可能是在没有大地震的情况下没有局部慢震发生。(2)在日本中部平田地区的地壳中发现了缺乏高频波的微震。在150×200公里范围内的12年时间里，探测到了11个主要辐射低频波的事件。这些地震中有8次位于无震区，震源深度10-30公里，大部分发生在日达山地区北部以下。这意味着这些低频地震是由固体岩石中的液态岩浆输送引起的。

(1) Slow deformation which has low rupture velocity and long rise-time can make a earthquake which has a large moment of the low frequency components comparing to the scaling law as omega-square model. These earthquakes are called "slow earthquakes" . The small slow earthquakes observed only in the local network may have a possibility of earthquake prediction.In this study, we present the "multi-station method" of the crustal movement data for finding the slow earthquakes which are occurred in the Kii peninsula and the Hida region. We use the strain-meter and water-tilt meter records located in the small network in the Kii peninsula and larger network located in the Southwest Japan, from 1990 to 1991. Within time series from 4 minutes to 256 minutes, no slow events was detected in this study. However, considering that there occurred the local slow earthquakes in the previous studies and that there occurred no large earthquakes, this result has possibility that there is no local slow earthquake when there is no large earthquake.(2) Micro-earthquakes which lack high frequency waves have been found in the crust in the Hida region, central Japan. During a period of 12 years within an area of 150 X 200 km, eleven events were detected which radiated low-frequency waves predominantly. Eight of these events are located in aseismic zone, with depth of 10-30 km.Most of these events occurred beneath the northern part of the Hida Mountain region. This means these low frequency earthquakes were caused by transportation of liquid-magma in solid rocks.