Existence of a seismic belt in the upper plane of the double seismic zone extending in the along-arc direction at depths of 70-100 km beneath NE Japan
Existence of a seismic belt in the upper plane of the double seismic zone extending in the along-arc direction at depths of 70-100 km beneath NE Japan
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DOI：
10.1029/2006gl028239
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发表时间：
2006-12-23
影响因子：
5.2
通讯作者：
Hasegawa, Akira
中科院分区：
文献类型：
--
作者：
Kita, Saeko;Okada, Tomomi;Hasegawa, Akira
我们利用密集地震台网获得的数据重新定位了微地震，并系统地检测了日本东北部下方太平洋板片内上部地震平面地震活动的特征分布。我们在弧前区下方70~100 km深度处发现了一条平行于板块界面等深线的地震“带”，表明上平面地震分布不均匀。该带较深界限的位置和上部地震面的地震活动似乎分别对应于板片地壳中H2O含量变化的两个相边界。上部地震面的事件主要具有下倾压缩型震源机制，但一些事件具有正断层型（NF型）版本，其空间分布似乎与这些边界相对应。这些 NF 事件可能是由脱水反应引起的体积减少引起的张力应力场引起的。
We relocated microearthquakes using data obtained via a dense seismic network and systematically detected the characteristic distribution of the upper seismic plane seismicity within the Pacific slab beneath NE Japan. We found a seismic "belt" parallel to the iso-depth contour of the plate interface that is beneath the forearc area at depths of 70-100 km, indicating that the distribution of the upper plane earthquakes is non-uniform. The location of the deeper limits of this belt and seismicity of the upper seismic plane appear to correspond respectively to two facies boundaries where H2O contents change in the slab crust. Events in the upper seismic plane have mainly down-dip compression-type focal mechanisms but several events have normal fault-type (NF-type) versions, whose spatial distribution appears to correspond to these boundaries. These NF events might be induced by the tensional stress field that is caused by volume reduction due to dehydration reactions.