利用小震和GPS资料分析冷龙岭地区现今变形过程与地震活动

Study on Current Deformation Process and Seismicity of Lenglongling Area Based on Small Earthquakes and GPS Data

利用小震资料对冷龙岭地区主要断裂的几何结构进行了研究,结合利用震源机制解反演的区域构造应力场和利用GPS资料计算的应变率场,分析探讨冷龙岭地区的地壳变形特征。结果表明:①冷龙岭地区的主压应力方向为NE向,与GPS主压应变率方向一致。应变率场峰值位于冷龙岭断裂以北的民乐—大马营断裂附近,然而该区域小震活动弱。②皇城—双塔断裂西段和东段地震基本上发生在15 km深度以内,倾向SW,浅部倾角较大,随着深度增加倾角逐渐变缓;皇城—双塔断裂中段存在一个近乎垂直的地震条带,震源深度明显大于其西段和东段。③冷龙岭断裂以左旋走滑运动为主,断裂南侧存在明显的挤压缩短变形。平行于冷龙岭断裂的GPS速度分量减小,呈现出明显的震间“S”型变形特征。利用反正切法计算得到该断裂的滑动速率和闭锁深度分别为3.9 mm/a和7.9 km,估算得到该断裂存在M_(0)=7.21×10^(19)N·m的地震矩亏损,表明冷龙岭断裂未来存在发生M_(W)7.2地震的危险性。

In this paper,the geometric structures of major faults in Lenglongling area are studied by using the data of small earthquakes,and the crustal deformation characteristics of Lenglongling area are analyzed by combining the regional tectonic stress field inverted by using focal mechanism solution with the strain rate field calculated by GPS data.The results show that the main compressive stress in Lenglongling area is in NE direction,which is consistent with the direction of GPS main compressive strain rate.The peak value of strain rate field appears near the Minle-Damaying Fault to the north of the Lenglongling Fault.However,the activity of small earthquakes in this area is weak.The earthquakes in the western and eastern sections of the Huangcheng-Shuangta Fault occurred in the range of 15 km deep,with a tendency of SW and a large dip angle in the shallow part of the Crust,which getting gentler and gentler with the increase of depth.There is a seismic band in the middle section of the Huangcheng-Shuangta Fault,which is nearly perpendicular to this section,and the focal depth in this section is obviously larger than the ones in the western and eastern sections.The Lenglongling Fault is dominated by sinistral strike-slip movement and there is obvious compressional deformation on the south side of the fault.The GPS velocity component parallel to the Lenglongling Fault decreases and displays an obvious S-shaped deformation among the earthquakes.The slip rate 3.9 mm/yr and the latching depth 7.9 km of the Fault are respectively calculated by using the arctangent method.The Fault is estimated to have a seismic moment deficit of M_(0)=7.21×10^(19)N·m.This indicates that there is a risk of M_(W)7.2 earthquake in the future.