张渤地震带现今形变特征研究

张家口—渤海地震构造带是华北地震构造区中具有相当规模的NW向活动构造带,通过对断层两侧基线—时间序列、区域速度场、应变场等进行分析,发现张渤带断层两侧速度场具有较大的差异,为典型的左旋走滑断层。区域应变场主应变自西向东依次为拉张—挤压—拉张—挤压,主应变由西向东逐步增大,在天津宝坻到河北唐山一带,主应变最大,为20nanostr/yr,天津蓟县—宝坻一带为拉张变形,在唐山一带为挤压变形。根据Zoback判断震源机制应力类型的方法对张渤地震带及邻区研究时段内19个ML4.0以上地震的震源机制进行分类,震源错动方式以正断和走滑为主;区域应变显示的应力状态与震源机制解的错动类型基本吻合,天津宝坻—河北唐山的主应变变化比较剧烈,同时震源机制的类型也发生变化,表明该地区的深部与浅部的变形一致。

Study on Deformation Characteristics of Zhangjiakou-Bohai Seismic Belt based on GNSS Data and Focal Mechanism Solution

The Zhangjiakou-Bohai Seismic Tectonic Belt is a large-scale NW-oriented active tectonic belt in the North China Seismic Tectonic Zone. Based on the analysis of the GNSS baseline-time sequence, regional velocity field and strain field on both sides of the fault, it is found that the velocity field has a large difference on both sides of the fault within the Zhang-Bo belt and is a typical left-lateral strike-slip fault. The principal strain of the regional strain field is tension-extrusion-tension-extrusion from west to east, and the principal strain gradually increases from west to east. In the area from Baodi, Tianjin to Tangshan, Hebei, the principal strain is the largest at 20 nanostr/yr. From Jixian to Baodi, Tianjin, the principal strain is tension deformation; and Tangshan area is compression deformation. According to Zoback"s method of determine the stress type of focal mechanism, the focal mechanism of 19 earthquakes above ML4.0 in the study period of the Zhangbo seismic belt and adjacent areas was classified. The main modes of focal dislocation are normal fault and strike-slip. The results show that the stress state of regional strain is basically consistent with the dislocation type of the focal mechanism solution. The principal strain changes drastically from Tianjin Baodi to Tangshan, Hebei, and the type of focal mechanism also changes, indicating that the deep and shallow deformations of the region is consistent.