摘要
集成活动构造与震源机制解、重新定位小震分布、历史与现今地震、GPS速度场等资料,综合分析了六盘山断裂带的构造动力学条件与变形方式、横剖面构造、历史强震破裂背景、GPS形变以及现代地震活动性,进而探讨了该断裂带的强震危险背景.结果表明:NNW向六盘山断裂带的运动与变形主要缘于青藏地块东北缘的向东水平挤出受到相对稳定的华北地块西缘(鄂尔多斯地块)阻挡而聚集的水平挤压作用;此外,海原和陇县—宝鸡两条NW向走滑断裂带的左旋运动在右阶区的局部会聚作用,也由六盘山断裂带的变形与运动来承受与转换.横剖面上,六盘山断裂带表现为向东推覆的大型逆冲构造带,主滑脱带位于~25km深处,之下很可能存在分隔青藏与华北地块的超壳-岩石圈型深断裂带.沿六盘山断裂带中-南段以及更靠南东的陇县—宝鸡断裂带存在总长为120~140km、至少最近~1400年未发生M≥61/2强震破裂的地震空区.地震空区内的断裂,GPS形变显示已有显著应变积累,地震活动上出现为小震稀疏或空缺的部位,以及低b值区,反映那里的断面业已闭锁,并已有高应力积累.因此,六盘山断裂带中-南段和陇县—宝鸡断裂带应是未来可能发生强震/大地震的两个危险地段,潜在地震的最大矩震级估值分别为M_W=7.3±和7.2±.
This work was based on integrated multidisciplinary data, including active tectonics, focal mechanism solutions, relocated small earthquakes, historical and modern seismicity, as well as GPS velocity fields. The authors have studied the Liupanshan fault zone （LPSFZ） in China, analyzing its tectonic-dynamic conditions and deformation style, cross-section structure, historical ruptures, GPS deformation, as well as modern micro-seismicity. Furthermore the authors discussed major earthquake hazard associated with the LPSFZ and one of its adjacent fault zones. The study suggests that the NNW-trending LPSFZ has been moving and deforming under the horizontal compression due to strike-slip fault zones. On the cross sections, the LPSFZ shows its characteristic as a large-scale reverse fault thrusting to the east, with a deep detachment zone at depth of -25 km. A seismic gap with a total length of 120-140 km exists along the middle-southern segment of the LPSFZ and the farther southeastern Longxian-Baoji fault zone （LXBJFZ）, in which no M≥61/2 events have occurred during the last -1400 years at least. GPS deformation suggests that the two fault zones along the seismic gap have accumulated significant amount of elastic strain. Furthermore, that modern small earthquakes along several parts of the two fault zones are either sparsely distributed or absent also suggests that some fault patches are locked. In addition, an area with long-term low b-values is present along the middle-southern segment of the LPSFZ and the northernmost segment of the LXBJFZ, probably indicating high stress built up there. Therefore, the middle-southern segment of the LPSFZ and the LXBJFZ should be two fault sections that have high potential of major earthquakes in the future. The estimated maximum moment magnitudes for the potential events are Mw7.3± and Mw7.2±, respectively.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2018年第2期545-559,共15页
Chinese Journal of Geophysics
基金
地震行业科研专项经费项目(20140823)资助.
关键词
地震构造
地震空区
GPS形变
断层闭锁
强震危险背景
Seismo-tectonics
Seismic gap
GPS deformation
Fault locking
Risk of major earthquakes
