Spatial distribution and focal mechanisms of aftershocks of the 2011 off the Pacific coast of Tohoku Earthquake
Spatial distribution and focal mechanisms of aftershocks of the 2011 off the Pacific coast of Tohoku Earthquake
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DOI：
10.5047/eps.2011.06.016
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发表时间：
2011-01-01
影响因子：
3
通讯作者：
Sekiguchi, Shoji
中科院分区：
文献类型：
--
作者：
Asano, Youichi;Saito, Tatsuhiko;Sekiguchi, Shoji
我们估算了2011年日本东部M(w) 9.0特大逆冲地震震源区内和周边2003 - 2011年发生的地震的质心矩张量。结果表明，发生在主震前的地震，包括宫城外的前震，基本上是具有逆冲型震源机制的板块间地震。另一方面，余震表现出多种震源机制。具有推力震源机制的板块间余震并未发生在GPS数据估计的大同震滑动区内，而是发生在周边地区。这意味着，由于主震破裂过程中大量的应力释放，同震滑动区不再发生滑动，而周边地区的余震是由于主震剧烈的同震大滑动导致这些区域的应力集中而引起的。正断层型余震广泛分布于上覆板块和太平洋板块外隆。这些余震可能是由于同震滑动引起的张应力变化。俯冲太平洋板块的逆冲断层型余震也被解释为同震滑动造成的挤压应力变化。
We estimated centroid moment tensors of earthquakes that occurred from 2003 to 2011 in and around the focal area of the 2011 M(w) 9.0 megathrust earthquake in eastern Japan. The result indicates that earthquakes occurring before the mainshock, which included foreshocks off Miyagi, were basically interplate earthquakes with thrust-type focal mechanisms. On the other hand, the aftershocks exhibited a variety of focal mechanisms. Interplate aftershocks with thrust focal mechanisms did not occur within the large coseismic slip area estimated from GPS data but instead occurred in the surrounding regions. This implies that slip could no longer occur in the coseismic slip area due to the large amount of stress release during the mainshock rupture, whereas the aftershocks in the surrounding regions were caused by a stress concentration in these regions due to the large co-seismic slip associated with the mainshock asperity. Normal-fault-type aftershocks were widely distributed in the overriding plate and the outer-rise of the Pacific Plate. These aftershocks may have been due to a tensional stress change caused by the coseismic slip. Thrust-fault-type aftershocks in the subducting Pacific Plate were also interpreted as being due to compressional stress change as a result of the coseismic slip.