Seismotectonics of the 2018 northern Osaka M6.1 earthquake and its aftershocks: joint movements on strike-slip and reverse faults in inland Japan
Seismotectonics of the 2018 northern Osaka M6.1 earthquake and its aftershocks: joint movements on strike-slip and reverse faults in inland Japan
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DOI：
10.1186/s40623-019-1016-8
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发表时间：
2019-03-27
影响因子：
3
通讯作者：
Gallovic, Frantisek
中科院分区：
文献类型：
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作者：
Hallo, Miroslav;Oprsal, Ivo;Gallovic, Frantisek
2018年6月18日，日本大阪盆地东北缘发生6.1级内陆地壳地震。这次地震对该地区的影响最大可达0.9g以上，随后发生了一系列较弱的余震。这些地震位于阿里玛-高崎构造线(ENE-WW向右行走滑断裂)和上马池断裂系统(N-S逆断层)附近，因此我们假定的地震构造解释相当复杂。在此，我们根据地震学资料和应力场考虑，提出了该序列的地震构造模型。特别地，我们利用贝叶斯全波反演法从强震记录中推断出主震的质心矩张量。M(W)5.6的解包含一个重要的CLVD分量，我们将其解释为复杂断层几何上的破裂过程。将非DC力矩张量分解为主要的和次要的纯剪切力矩张量，表明走滑和反转断裂机制的结合。我们还利用宽带台和短周期台站的记录，分析了M-JMA在2.0到4.1之间的108次最强余震。由P波幅反演余震矩张量主要表现为走滑和逆断层机制，具有明显的空间差异。从这些机制反演出的局部应力场在ESE-WNW方向上具有最大(压缩)主应力σ(1)，而在ESE-WNW方向上具有主导的最大(压缩)主应力sigma(2)sigma(3)。在主震所观察到的应力场中，ENE-WSW向右行走滑断裂和N-S逆断层均可活动(不需要任何应力空间不均一性)。总之，活动的走滑断裂平行于有马-高崎构造线。活动的N-S逆断层与上马池断裂系统相似，向东倾斜50度。这两条断层上的联合剪切运动对主震的总地震矩贡献很大。
On June 18, 2018, an M(JMA)6.1 inland crustal earthquake occurred on the northeast edge of the Osaka basin, Japan. This event impacted the region by the maximum PGA larger than 0.9g, and it was followed by a series of weaker aftershocks. The earthquakes were located near the Arima-Takatsuki Tectonic Line (ENE-WSW dextral strike-slip faults) and the Uemachi fault system (N-S reverse faults), hence the seismotectonic interpretations we assumed to be rather complex. Here we propose a seismotectonic model of this sequence based on seismological data and stress field considerations. In particular, we infer to a centroid moment tensor for the mainshock using Bayesian full-waveform inversion from strong motion records. The solution of M(w)5.6 involved a significant CLVD component, which we interpreted as being due to rupture process on a complex fault geometry. Decomposition of the non-DC moment tensor into major and minor pure-shear moment tensors suggests a combination of strike-slip and reverse faulting mechanisms. We also analyzed the 108 strongest aftershocks with M-JMA between 2.0 and 4.1 using records from broadband and short-period stations. Aftershocks' moment tensors inverted from P-wave amplitudes exhibit mainly strike-slip and reverse faulting mechanisms, having significant spatial variations. The local stress field inverted from these mechanisms had a dominant maximum (compressional) principal stress sigma(1) in ESE-WNW direction, while sigma(2)sigma(3). Both ENE-WSW dextral strike-slip and N-S reverse faults can be active in such stress field as observed in the mainshock (without any need for stress spatial inhomogeneity). To conclude, the activated strike-slip fault is parallel to the Arima-Takatsuki Tectonic Line. The activated N-S reverse fault is dipping to east by 50 degrees similarly as the Uemachi fault system. Joint shear movements on both of these faults contributed significantly to the total seismic moment of the mainshock.