Lateral variation of the cutoff depth of shallow earthquakes beneath the Japan Islands and its implications for seismogenesis
Lateral variation of the cutoff depth of shallow earthquakes beneath the Japan Islands and its implications for seismogenesis
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DOI：
10.1016/j.tecto.2011.11.013
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发表时间：
2012-01-20
期刊：
影响因子：
2.9
通讯作者：
Okada, Tomomi
中科院分区：
文献类型：
--
作者：
Omuralieva, Aiymjan M.;Hasegawa, Akira;Okada, Tomomi
我们估计的截止深度的空间分布的浅地震活动的日本群岛的基础上，最近建成的全国密集的地震网络的数据。为了避免不均匀地震速度结构的影响，我们确定了整个日本的三维地震速度结构，然后使用它来重新定位震源。截止深度是通过计算D90来确定的，90%的地震发生在D90以上的深度。D 90估计值的空间分布显示出相当大的横向变化，从大约5公里到大约40公里不等。D90深沿着日本东部的太平洋沿岸。局部较浅的D90沿沿着火山区延伸。日本东部太平洋沿岸的热流沿着低，火山地区的热流高。这表明D90的横向变化主要是由地热的横向变化形成的。古老的、非常寒冷的太平洋板块的俯冲冷却可能会导致日本东部太平洋沿岸沿着的深度D90。从地幔楔下部供给的岩浆加热被认为是火山区浅部D90的主要原因。岩浆和/或来自凝固岩浆的含水流体不仅有助于局部浅D90，而且还削弱了下地壳中的环境岩石，导致上地壳中的应力集中。内陆浅层大地震往往发生在这些地区，这表明适用于东北地区的浅层地震生成模型也可以用于日本其他地区。(C)2011 Elsevier B. V.保留所有权利。
We estimated the spatial distribution of the cut-off depth of shallow seismicity beneath the Japan Islands based on data from a recently constructed nationwide dense seismic network. In order to avoid the effect of heterogeneous seismic velocity structure, we determined the 3D seismic velocity structure for the whole of Japan, which was then used to relocate the hypocenters. The cut-off depth was determined by calculating D90, the depth above which 90% of the earthquakes occur. A spatial distribution of estimated D90 values shows a considerable lateral variation, ranging from about 5 km to about 40 km. The D90's are deep along the Pacific coast of eastern Japan. Locally shallow D90's extend along belt-like stretches of volcanic areas. Heat flow is low along the Pacific coast in eastern Japan and high in the volcanic areas. This indicates that the lateral variation of D90's is formed mainly by lateral geotherm variation. Cooling by the subducting old, very cold Pacific plate may cause the deep D90's along the Pacific coast in eastern Japan. Heating by magma supplied from the mantle wedge below is considered to be the main cause of the shallow D90's in the volcanic areas. Magma and/or aqueous fluids derived from solidified magma contribute not only to locally shallow D90's but also to the weakening of ambient rocks in the lower crust, resulting in stress concentrations in the upper crust just above them. Large shallow inland earthquakes tend to occur in such areas, suggesting that a model of shallow earthquake generation applied to Tohoku can be used in other areas in Japan as well. (C) 2011 Elsevier B.V. All rights reserved.