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Driving stress and seismotectonic implications of the 2013 Mw5.8 Awaji Island earthquake, southwestern Japan, based on earthquake focal mechanisms before and after the mainshock
Earth, Planets and Space ( IF 3.0 ) Pub Date : 2020-10-22 , DOI: 10.1186/s40623-020-01292-1
Kazutoshi Imanishi , Makiko Ohtani , Takahiko Uchide

A driving stress of the M w 5.8 reverse-faulting Awaji Island earthquake (2013), southwest Japan, was investigated using focal mechanism solutions of earthquakes before and after the mainshock. The seismic records from regional high-sensitivity seismic stations were used. Further, the stress tensor inversion method was applied to infer the stress fields in the source region. The results of the stress tensor inversion and the slip tendency analysis revealed that the stress field within the source region deviates from the surrounding area, in which the stress field locally contains a reverse-faulting component with ENE–WSW compression. This local fluctuation in the stress field is key to producing reverse-faulting earthquakes. The existing knowledge on regional-scale stress (tens to hundreds of km) cannot predict the occurrence of the Awaji Island earthquake, emphasizing the importance of estimating local-scale (< tens of km) stress information. It is possible that the local-scale stress heterogeneity has been formed by local tectonic movement, i.e., the formation of flexures in combination with recurring deep aseismic slips. The coseismic Coulomb stress change, induced by the disastrous 1995 M w 6.9 Kobe earthquake, increased along the fault plane of the Awaji Island earthquake; however, the postseismic stress change was negative. We concluded that the gradual stress build-up, due to the interseismic plate locking along the Nankai trough, overcame the postseismic stress reduction in a few years, pushing the Awaji Island earthquake fault over its failure threshold in 2013. The observation that the earthquake occurred in response to the interseismic plate locking has an important implication in terms of seismotectonics in southwest Japan, facilitating further research on the causal relationship between the inland earthquake activity and the Nankai trough earthquake. Furthermore, this study highlighted that the dataset before the mainshock may not have sufficient information to reflect the stress field in the source region due to the lack of earthquakes in that region. This is because the earthquake fault is generally locked prior to the mainshock. Further research is needed for estimating the stress field in the vicinity of an earthquake fault via seismicity before the mainshock alone.

中文翻译:

基于主震前后震源机制的2013年日本西南部淡路岛地震的驱动应力和地震构造意义

使用主震前后地震的震源机制解研究了日本西南部 M w 5.8 逆断层淡路岛地震(2013 年)的驱动应力。使用了区域高灵敏度地震台站的地震记录。此外,应用应力张量反演方法来推断源区中的应力场。应力张量反演和滑移趋势分析结果表明,源区内应力场偏离周围区域,其中应力场局部含有ENE-WSW压缩的逆断层成分。应力场的这种局部波动是产生逆断层地震的关键。现有的区域尺度应力(数十至数百公里)知识无法预测淡路岛地震的发生,强调估计局部尺度(<数十公里)应力信息的重要性。局部尺度应力非均质性可能是由局部构造运动形成的,即弯曲的形成与反复发生的深地震滑动相结合。由 1995 M w 6.9 神户灾难性地震引起的同震库仑应力变化沿淡路岛地震的断层面增加;然而,震后应力变化是负面的。我们得出的结论是,由于沿南开海槽的地震间板块锁定,逐渐增加的应力克服了几年内的震后应力降低,2013年淡路岛地震断层超过其破坏阈值。 观测到地震响应于震间板块锁定对日本西南部的地震构造具有重要意义,有助于进一步研究内陆地震活动之间的因果关系还有南海海槽地震。此外,这项研究强调,由于该地区缺乏地震,主震前的数据集可能没有足够的信息来反映该地区的应力场。这是因为地震断层通常在主震之前就被锁定了。仅通过主震前的地震活动来估计地震断层附近的应力场还需要进一步的研究。此次地震是响应于震间板块锁定而发生的观测,对于日本西南部的地震构造具有重要意义,有助于进一步研究内陆地震活动与南海海槽地震之间的因果关系。此外,这项研究强调,由于该地区缺乏地震,主震前的数据集可能没有足够的信息来反映该地区的应力场。这是因为地震断层通常在主震之前就被锁定了。仅通过主震前的地震活动来估计地震断层附近的应力场还需要进一步的研究。此次地震是响应于震间板块锁定而发生的观测,对于日本西南部的地震构造具有重要意义,有助于进一步研究内陆地震活动与南海海槽地震之间的因果关系。此外,这项研究强调,由于该地区缺乏地震,主震前的数据集可能没有足够的信息来反映该地区的应力场。这是因为地震断层通常在主震之前就被锁定了。仅通过主震前的地震活动来估计地震断层附近的应力场还需要进一步的研究。有助于进一步研究内陆地震活动与南海海槽地震的因果关系。此外,这项研究强调,由于该地区缺乏地震,主震前的数据集可能没有足够的信息来反映该地区的应力场。这是因为地震断层通常在主震之前就被锁定了。仅通过主震前的地震活动来估计地震断层附近的应力场还需要进一步的研究。有助于进一步研究内陆地震活动与南海海槽地震的因果关系。此外,这项研究强调,由于该地区缺乏地震,主震前的数据集可能没有足够的信息来反映该地区的应力场。这是因为地震断层通常在主震之前就被锁定了。仅通过主震前的地震活动来估计地震断层附近的应力场还需要进一步的研究。该研究强调,由于该地区缺乏地震,主震前的数据集可能没有足够的信息来反映该地区的应力场。这是因为地震断层通常在主震之前就被锁定了。仅通过主震前的地震活动来估计地震断层附近的应力场还需要进一步的研究。该研究强调,由于该地区缺乏地震,主震前的数据集可能没有足够的信息来反映该地区的应力场。这是因为地震断层通常在主震之前就被锁定了。仅通过主震前的地震活动来估计地震断层附近的应力场还需要进一步的研究。
更新日期:2020-10-22
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