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Double-difference relocations of the 2004 off the Kii peninsula earthquakes

机译:2004年基伊半岛地震后的双差重定位

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Two large earthquakes (Mw7.3 and Mw7.5) occurred off-shore of the Kii peninsula (Japan) on 5th September 2004. The insufficient station coverage in the area where the large events and their aftershocks occurred led to significant uncertainty regarding their depth location. By using a double-difference approach, we were able to determine more accurate hypocenter locations and better define the main characteristics of the aftershock distribution. The data we used in this study comprise of about 700 earthquakes recorded by the Japanese Meteorological Agency ( JMA ) from 5 to 12 September 2004. We assume several depth ranges for the initial double difference earthquake locations and select the solution with the smallest rms residual. The resulting hypocenter distribution has two distinctive features: 1) on average the depths are about 20 km shallower than the initial JMA location and 2) the hypocenters are divided into two groups: one shallow (around 12 km depth) and another deep (around 27 km depth). The epicenters of the relocated events define a finer, more clustered structure compared with the epicentral distribution of JMA . The splitting of the earthquake locations into two depth groups is still obs erved when using a significantly different velocity structure. Our results of the two depth groups for the hypocenters resemble the independently determined hypocentral distribution from the OBS survey.
机译:2004年9月5日,日本纪伊半岛近海发生了两次大地震(Mw7.3和Mw7.5)。在发生大地震及其余震的地区,地震台的覆盖不足,导致其深度存在很大的不确定性。位置。通过使用双差方法,我们能够确定更准确的震源位置,并更好地定义余震分布的主要特征。我们在这项研究中使用的数据包括2004年9月5日至12日由日本气象厅(JMA)记录的大约700次地震。我们为初始双差地震位置假定了多个深度范围,并选择了具有最小均方根值的解。产生的震源分布具有两个鲜明的特征:1)平均深度比初始JMA位置浅约20 km; 2)震源分为两类:一组浅(约12 km深度),另一组深(约27 km)公里深度)。与JMA的震中分布相比,重定位事件的震中定义了更精细,更聚集的结构。当使用明显不同的速度结构时,仍然可以将地震位置分为两个深度组。我们对震源的两个深度组的结果类似于从OBS调查中独立确定的震中分布。

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