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Research on the Quaternary Tectonics in the surrounding area of the Epicenter of 2000 Tottoriken-seibu Earthquake

2000年鸟取县西武地震震中周边地区第四纪构造研究

基本信息

批准号：
13640461
负责人：
YAMAUCHI Seiki
金额：
$ 1.15万
依托单位：
Shimane University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640461/
关键词：
2000 Tottoriken-seibu earthquke epicenter after shock zone fracture system alkali basalt active fault middle Pleistocene reactivation 中期更新世アルカリ玄武岩岩体余地域

项目摘要

A surrounding area of the epicenter of the 2000 Tottoriken-seibu Earthquake is widely occupied by granitic rocks, which is unconformably covered by the late Pliocene to the early Pleistocene basalt lavas in places. Analysis of fracture systems in granitic rocks are carried out by using large joints, joint zones and shear zones, and a sequence of activity of each system is estimated on the basis of cross-cutting relationships. The results show that 13 fracture systems (A〜L) develop in this area and 3 systems (A〜C) reactivated at the last stage.Deep fractures which are recognized by linear arrangements of eruption centers of basalt lavas and faults cutting the lavas belong to A to D systems, which are estimated to have acted already in the early Pleistocene. An active fault which newly was found in the Koshikibara Basalt about 10km northeast of the epicenter belongs to B system and is parallel with and shows the same style of displacement with an earthquake source fault of the earthquake. Between both faults a deep fracture indicated by a linear arrangement of eruption centers of basalt is developed parallel with them. These similalities imply that three fractures may be formed under the same stress fields, probably in the early Pleistocene.Recently seismicity in this area have been active and their after shock zones coincide with B system. An after shck zone of the 2000 Tottoriken-seibu Earthquake appeared parallel with B system at the earliest stage, immediately it changed its direction to be parallel with C system. It may be concluded that the change was resulted from continuous reactivation of B and C systems at an epicenter of the earthquake, and instantly triggered to reactivate a nearby larger fracture of C system.

2000年鸟取县西武地震震中周围地区广泛分布着花岗质岩石，局部被上新世晚期至更新世早期玄武岩熔岩不整合覆盖。本文利用大节理、节理带和剪切带对花岗岩类岩石中的断裂系统进行了分析，并根据横切关系估计了各断裂系统的活动顺序。结果表明，本区发育13个断裂系统（A-L）和3个断裂系统（A-C），其中深断裂（由玄武岩喷发中心的线状排列和切割熔岩的断层所识别）属于A-D系统，估计早更新世就已活动。在距震中东北约10 km的越木原玄武岩中新发现的一条活动断层，属B系，与本次地震的震源断层平行，并表现出相同的位移方式。在这两条断裂之间，平行于它们发育一条深断裂，其特征是玄武岩喷发中心呈线性排列。这些相似性表明，这三条断裂可能是在同一应力场作用下形成的，时间可能是早更新世，近期本区地震活动活跃，其余震带与B系统一致。2000年鸟取县西武地震的余震带最早出现与B系统平行的方向，但随即改变方向与C系统平行。这一变化是由于震中附近的B、C系统连续激活，并在瞬间触发附近较大的C系统断裂激活所致。