Fault geometry of the 2004 off the Kii peninsula earthquake inferred from offshore pressure waveforms
Fault geometry of the 2004 off the Kii peninsula earthquake inferred from offshore pressure waveforms
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DOI：
10.1186/bf03351809
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发表时间：
2005-01-01
影响因子：
3
通讯作者：
Mikada, H
中科院分区：
文献类型：
--
作者：
Matsumoto, H;Mikada, H
在2004年9月5日发生在Kii半岛附近的一系列两次地震之后，我们使用部署在Muroto附近深海海底的两个压力计，成功地获得了水压波动。地震在日本西南部南部海岸引发了两次海啸，最大波高为0.9m，我们可以从采集的数据集中识别出海啸信号，大约在海啸到达距离传感器最近的海岸线之前20分钟。假设两次地震一次为前震，另一次为主震。虽然地震学研究表明，在没有余震分布的情况下，缺乏区分主震是由西南倾向断层还是由另一断层即东北倾向断层引起的约束，但我们发现，海啸压力波动的差异可能归因于断层模型中断层面的确定。在本文中，我们利用这些独特的仪器获得的海啸波形来评估主震的断层几何形状：(1)首先在压力计的位置模拟两种断层几何形状的地震引起的压力波形，其中一种为西南倾角，另一种为东北倾角，然后将模拟结果与观测波形进行比较。结果表明，主震应由一条走向为北西向东南的断层引起，断层走向为西南方向。
We could Successfully obtain water pressure fluctuations after a series of two off the Kii peninsula earthquakes that took place on September 5 in 2004, using two pressure gauges deployed at deep ocean-bottom off Muroto. The earthquakes caused two tsunamis in the southern coast of the southwestern Japan with maximum wave heights of 0.9 m, and we could identify the tsunami signals from the acquired dataset ca. 20 min before the arrivals of the tsunamis to the coastline nearest to the sensors. Two earthquakes are assumed as one for a fore-shock and the other for a main-shock. Although seismological studies, without aftershock distributions, showed a lack of constraints to distinguish if the main-shock was caused by either southwest dipping fault or by the other, i.e., northeast dipping fault, we found that the difference in the pressure fluctuations for the tsunamis could attribute to the determination of the fault plane in the fault models. In this paper, we evaluate the fault geometry of the main shock by using tsunami waveforms obtained by those unique instruments in following procedure: (1) We first simulate pressure waveforms caused by earthquakes of the two fault geometries, one for southwest dipping place and the other for the northeast, at the location of the pressure gauges, and (2) we then compare the simulated results with observed waveforms. Our results demonstrate that the main-shock should be caused by a fault whose strike lies in north west-to-southeast with a clip towards southwest direction.