Tidal triggering of earthquakes in the subducting Philippine Sea plate beneath the locked zone of the plate interface in the Tokai region, Japan
Tidal triggering of earthquakes in the subducting Philippine Sea plate beneath the locked zone of the plate interface in the Tokai region, Japan
复制标题
DOI：
10.1016/j.tecto.2005.09.013
复制
发表时间：
2006-04
期刊：
影响因子：
2.9
通讯作者：
Sachiko Tanaka;H. Sato;S. Matsumura;M. Ohtake
中科院分区：
文献类型：
--
作者：
Sachiko Tanaka;H. Sato;S. Matsumura;M. Ohtake
在日本中部东海地区板块界面锁定带之下的俯冲菲律宾海板块中，我们发现了一种潮汐触发地震发生效应的特征时空模式，那里可能即将发生一次大的板间地震。我们使用菲律宾海板块大约二十年来发生的微地震来测量地球潮汐与地震发生之间的相关性。对于每一个事件，我们指定的潮汐相位角在起源时间的理论计算的潮汐剪切应力的断层面。根据潮汐相位角的分布，利用Schuster检验，对潮汐相位角是否集中在某个特定角度附近进行了统计检验。在该检验中，结果由p值评估，p值表示拒绝地震随机发生而不考虑潮汐相位角的零假设的显著性水平。作为分析的结果，没有发现包括所有地震的数据集的相关性。然而，我们发现潮汐效应的时间变化有一个系统的模式，P值在M ≥ 4.5地震发生之前显著降低，之后恢复到一个较高的水平。我们注意到，这些M ≥ 4.5地震比研究区的正常背景地震活动大得多。震前潮汐相位角的频率分布在潮汐剪应力最大的相位角处有一个峰值，加速了断层的滑动。这表明观测到的小p值是潮汐效应的物理后果。我们还发现了p值空间分布的一个显著特征。根据过去几年的地震活动率变化，小的p值出现在板块界面强耦合部分的正下方。
We found a characteristic space–time pattern of the tidal triggering effect on earthquake occurrence in the subducting Philippine Sea plate beneath the locked zone of the plate interface in the Tokai region, central Japan, where a large interplate earthquake may be impending. We measured the correlation between the Earth tide and earthquake occurrence using microearthquakes that took place in the Philippine Sea plate for about two decades. For each event, we assigned the tidal phase angle at the origin time by theoretically calculating the tidal shear stress on the fault plane. Based on the distribution of the tidal phase angles, we statistically tested whether they concentrate near some particular angle or not by using Schuster's test. In this test, the result is evaluated by p-value, which represents the significance level to reject the null hypothesis that earthquakes occur randomly irrespective of the tidal phase angle. As a result of analysis, no correlation was found for the data set including all the earthquakes. However, we found a systematic pattern in the temporal variation of the tidal effect; the p-value significantly decreased preceding the occurrence of M≥4.5 earthquakes, and it recovered a high level afterwards. We note that those M≥4.5 earthquakes were considerably larger than the normal background seismicity in the study area. The frequency distribution of tidal phase angles in the pre-event period exhibited a peak at the phase angle where the tidal shear stress is at its maximum to accelerate the fault slip. This indicates that the observed small p-value is a physical consequence of the tidal effect. We also found a distinctive feature in the spatial distribution of p-values. The small p-values appeared just beneath the strongly coupled portion of the plate interface, as inferred from the seismicity rate change in the past few years.