Focal Mechanisms of Intermediate-depth Earthquakes Beneath Southeastern Hokkaido, Japan Implications of the Double Seismic Zone
Focal Mechanisms of Intermediate-depth Earthquakes Beneath Southeastern Hokkaido, Japan Implications of the Double Seismic Zone
复制标题
日本北海道东南部中深度地震的震源机制 双地震带的影响
DOI：
10.1007/s00024-003-2396-y
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发表时间：
2003
影响因子：
2
通讯作者：
T. Moriya
中科院分区：
文献类型：
--
作者：
N. Ozel;T. Moriya
本文对100次中深源地震的震源机制解和空间分布进行了研究和讨论。这些地震发生于1985年至1993年，主要发生在北海道东南部双地震带的上下平面。震源机制解及其震中随深度和最小和最大压应力方向的空间分布证实了以下基本特征：该地区在60-120公里深度之间存在一个双平面深震带，且上平面的地震次数比下平面的地震少。在55~60 km深度内，以小角度逆冲断裂机制为主。在深度大于60公里的区域，震源机制解在上、下两个平面均以下倾伸展型或下倾压缩型为主。大多数60公里以下的地震都有倾滑成分，一些溶液也有明显的走滑成分。虽然下倾伸展型事件占主导地位，但位于下平面上的7个事件被约束为下倾挤压机制。下平面震源机制轴在N40°E和N35°W附近伸展，倾角在25°~70°之间，与该地区俯冲太平洋板块的倾角基本一致。我们还研究了将所有地震转换到与该地区俯冲岩石圈具有相同走向和倾角的平面上后，在上下平面上发生的地震的应力方向的统计特征。72%的最小压应力方向主要位于下平面板面的NS或NNE-SSW方向(与倾角方向成45°以内)，且几乎平行于该区域局部板片的倾角。位于上平面的地震次数比位于下平面的少。发生在上平面上的那些显示了各种类型的机制解。在上平面应力分布方向上，存在弱的系统性取向。
In this study, the focal mechanism solutions and spatial distributions of 100 intermediate-depth earthquakes are examined and discussed. These earthquakes occurred from 1985 to 1993 mostly in the upper and lower planes of the double seismic zone beneath the southeastern part of Hokkaido. The focal-mechanism solutions along with the spatial distribution of their epicenters as a function of depth and the minimum- and maximum-compressive stress directions confirm the following essential features; A double-planed deep seismic zone between the depths from 60 to 120 km has been clearly revealed in this region and the number of earthquakes located in the upper plane are less than those for the lower one. Low-angle thrust fault mechanism is dominant to a depth of about 55–60 km in the zone. At depths deeper than about 60 km focal mechanism solutions are mostly characterized by down-dip extension type or down-dip compression type in both lower and upper planes of the zone. Most of the earthquakes deeper than 60 km have dip-slip components and some of the solutions have significant strike-slip components, as well. Although the down-dip extensional-type events are dominant, seven events that are located on the lower plane are constrained as down-dip compression mechanism. TheTaxes of earthquake focal mechanisms on the lower plane show extension at about N40°E and N35°W, and the dip-angle between 25° and 70°, almost coincide with the dip of the subducting Pacific Plate in this region. We also investigate the statistical features of the stress directions of the earthquakes occurring both on the lower and upper plane after converting all the events onto the plane having the same strike and dip angle as the subducting lithosphere in the region. Seventy-two percent of the minimum compressive stress directions are oriented mainly in the NS or NNE- SSW directions (within 45° of the dip direction) at the plate surface of the lower plane and are almost parallel to the dip of the local slab in this region. The number of earthquakes located in the upper plane is less than that for the lower one. Those which occurred on the upper plane show various types of mechanism solutions. Weak systematic orientation is found in the direction distribution of stress in the upper plane.