Intermediate-Depth Earthquakes and Seismotectonics beneath southern Kyushu, Japan

日本九州南部的中深度地震和地震构造

• 批准号: 11640418
• 负责人: GOTO Kazuhiko
• 金额: $ 0.83万
• 依托单位: Kagoshima University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11640418/
• 关键词: Wadati-Benioff zone; southern Kyushu; intermediate-depth earthquake; Philippine-Sea plate; island arc; focal mechanism solution; discontinuity of seismic zone; サイスモテクトニクス; メカニズム解

Seismic activities and focal mechanism solutions of intermediate-depth earthquakes and the structure of Wadati-Benioff zone beneath southern Kyushu, Japan are investigated based on the high quality data observed by the micro-seismic network of Kagoshima University and Kyushu University. It is revealed that the Wadati-Benioff zone shows the complicated structure. The most characteristic feature is that the seismic zone slides horizontally, that is, the seismic zone in NNE region of Sakurajima volcano shifts to WNW by about 10km compared to that in SSW region. Sliding occurs gradually along about 50km extent at the depth of 130km and about 80km at the depth of 70km. It is interesting that the extreme high seismic activity at about 160km in depth beneath Kaimon volcano, which is one of the characteristic features in this region, occurs at the rim of the sliding region. The section of seismic zone shows to be continued to the depth of about 150-200km with changing its curvature. In detail, it has the wavelike feature, that is, it is convex upward at about 65km in depth and downward at the depths of about 50km and 100km. Focal mechanism solution indicates that the principal axes of tensional stresses are parallel to and those of compressional ones are perpendicular to the descending direction of slab in the vertical plane. However, in the horizontal plane, the axes of compressional stresses are aligned to the converging direction of oceanic plate. From these facts, it is considered that some force acts to the descending Philippine-Sea plate beneath southern Kyushu adding to the force produced by the descending process as seen in almost all island arc. And such force works the complicated structure of seismic zone and the generation of non-down-dip mechanism of intermediate-depth events.

基于Kagoshima University和Kyushu University的微观网络观察到的高质量数据，研究了日本南部南部南部丁寿岛的地震活性和焦点解决方案以及日本南部南部瓦达蒂 - 贝尼奥夫区的结构。据显示，瓦达蒂 - 贝尼奥夫区显示了复杂的结构。最有特征的特征是，地震带水平滑动，即樱花岛火山区域的地震带，与SSW地区相比，Sakurajima Volcano的地震区向WNW移动约10公里。滑动在130公里的深度逐渐沿约50公里的范围逐渐发生，在70公里的深度约为80公里处。有趣的是，在凯蒙火山（Kaimon Volcano）下方约160公里处的极端高地震活动（这是该地区的特征之一）出现在滑动区域的边缘。地震区的一部分显示，随着其曲率的改变，将继续至约150-200公里的深度。详细说明，它具有小波般的特征，即，它的深度约为65公里，深度约为50公里和100公里。焦点机理解决方案表明，紧张应力的主要轴平行于压缩应力，而压缩应力的主要轴垂直于垂直平面中平板的下降方向。但是，在水平面中，压缩应力的轴与海洋板的融合方向排列。从这些事实来看，人们认为，某些力量作用于九州南部下降的菲律宾海上板块，从而增加了几乎所有岛屿弧的下降过程产生的力量。这种力是地震带的复杂结构，以及中等深度事件的非下降机理的产生。