摘要
南北地震带作为中国大陆地应力场一级分区的边界,其构造应力场的研究对理解大陆强震机理、构造变形和地震应力的相互作用具有重要意义.本文收集南北地震带1970—2014年的震源机制解819条,按照全球应力图的分类标准对震源机制解进行分类,发现其空间分布特征与地质构造活动性质比较吻合.P轴水平投影指示了活动块体的运动方向,T轴水平投影在川滇块体及邻近地区空间差异特征最为突出,存在顺时针旋转的趋势.南北地震带的最大水平主应力方向具有明显的分区特征,北段为NE向走滑类型的应力状态,中段为NEE—EW—NWW向的逆冲类型,南段为SE—SSE—NS—NNE向走滑和正断类型,在川滇块体的北部和西边界应力状态为EW—SE—SSE的正断层类型,表明来自印度板块的NNE或NE向的水平挤压应力和青藏高原物质东向滑移沿大型走滑断裂带向SE向平移的复合作用控制了南北地震带的岩石圈应力场.川滇块体西边界正断层类型应力状态范围与高分辨率地震学观测得到的中下地壳低速带范围基本吻合,青藏高原向东扩张的塑性物质流与横向边界(丽江—小金河断裂带)的弱化易于应变能的释放,在局部地区使NS向拉张的正断层向EW向拉张正断层转变.反演得到的应力状态基本上与各种类型地震的破裂方式比较吻合,也进一步验证反演结果的可靠性,可为地球动力学过程的模拟和活动断层滑动性质的厘定提供参考.
The North-South Seismic Belt is the boundary between the first-order blocks of the tectonic stress field in China.The focal mechanisms of 819 events that occurred in this belt from1970 to 2014are used to study its tectonic stress field,which is important for understanding the mechanism of continental earthquakes,tectonic deformation and seismic stress interaction.According to the classification criteria of World Stress Map（WSM）,focal mechanism solutions are divided into six types,in which the horizontal projections of P axes mark the movement direction of the block.The stress tensors and the orientations of the maximum horizontal stress of the North-South Seismic Belt were determined by the MATLAB Package for Spatial And Temporal Stress Inversion（MSATSI）using 2°×2°grids with the damping parameter1.6at the 95% confidence level.The spatial distribution of different types of focal mechanisms is consistent with the nature of tectonic activity in the North-South Seismic Belt.It demonstrates that the regional tectonic stress field is controlled by tectonic movement.The horizontal projections of P axes show the segmentation patterns from north to south：NNE—NE—nearly EW—NW—nearly NS—NNE direction,the horizontal projections of Taxes exhibit the most prominent characteristic of spatial differences in the Sichuan-Yunnan block and neighboring regions,a clockwise rotational pattern.The spatial distribution of stress regime and the orientation of the maximum horizontal stress has obvious regional characteristics,i.e.NE direction strike-slip type stress state in the northern section,NEE—EW—NWW direction thrusting type in the middle section,SE—SSE—NS—NNE direction strike-slip and normal faulting type in the southern section,and the stress regime in the northern part and west boundary of the Sichuan-Yunnan block is EW—SE—SSE direction normal faulting.The normal fault stress regime in the western boundary of the Sichuan-Yunnan block is consistent with the scope of the low velocity zone in mid-lower crust observed by the high resolution seismic array,the ductile flow of eastern expansion of the Tibetan Plateau and the weakness of lateral boundaries（Lijiang-Xiaojinhe fault）facilitate energy release,limiting earthquake magnitude.It also localizes the transition from normal fault earthquakes with N—S extension to normal faulting with E—W extension.The results suggest that the lithospheric stress field of the North-South Seismic Belt is controlled jointly by the NE or NNE directed horizontal compressive stress from the Indian plate and eastward motion of the material of the Tibetan Plateau that slip towards SE along large strike-slip faults.Stress regime is almost consistent with the rupture mechanism of all types of earthquakes,verifying the reliability of the inversion.It can offer a reference for simulation of geodynamic processes and determination of the nature of fault slip.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第11期4149-4162,共14页
Chinese Journal of Geophysics
基金
中国地震局地震科技星火计划(XH12027)
大地测量与地球动力学国家重点实验室开放基金(SKLGED2013-5-4-E)
国家自然科学基金重大研究计划项目(91214201)资助
关键词
南北地震带
震源机制解
构造应力场
最大水平主应力方向
North-South Seismic Belt
Focal mechanism
Tectonic stress field
Orientation of the maximum horizontal stress
