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首页> 外文期刊>Pure and Applied Geophysics >Focal Mechanisms of Intermediate-depth Earthquakes Beneath Southeastern Hokkaido, Japan Implications of the Double Seismic Zone
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Focal Mechanisms of Intermediate-depth Earthquakes Beneath Southeastern Hokkaido, Japan Implications of the Double Seismic Zone

机译：日本北海道东南部中深度地震的震源机制双地震带的意义

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摘要

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 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 of 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 downdip extensional-type events are dominant, seven events that are located on the lower plane are constrained as down-dip compression mechanism. The T axes 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.
机译：本文研究并讨论了100次中深度地震的震源机制解和空间分布。这些地震发生在1985年至1993年之间，主要发生在北海道东南部以下的双重地震带的上，下平面。震源机制解及其震中的空间分布随深度，最小和最大压缩应力方向的变化确定了以下基本特征;在该区域清楚地揭示了在60至120 km深度之间的双重计划的深地震带，位于上平面的地震次数少于下部的地震次数。低角度逆冲断层机制占该区域深度约55-60 km。在深于约60 km的深度处，震源机制解的主要特征是在该区域的上下两面都具有下倾扩展型下倾压缩型。大多数深度超过60 km的地震都具有倾滑分量，某些解决方案也具有明显的走滑分量。尽管下倾扩展型事件占主导地位，但位于下平面的七个事件被限制为下倾压缩机制。下平面地震震源机制的T轴在大约N40°E和N35°W处延伸，倾角在25°和70°之间，几乎与俯冲太平洋板块在该区域的倾角重合。我们还将所有事件转换为与该地区俯冲岩石圈具有相同的走向和倾角的平面后，研究了上下平面上发生的地震应力方向的统计特征。最小压应力方向的72％主要位于下平面的平板表面上的NS或NNE-SSW方向（倾角的45°范围内），并且几乎平行于局部平板的倾角。这个地区。上层地震的数量少于下层地震的数量。发生在上平面的那些显示了各种类型的机制解决方案。在上平面应力的方向分布中发现了较弱的系统取向。

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