1970年以来鲜水河断裂带地震活动特征与2014年康定M_S6.3地震

The characteristics of seismic activity on Xianshuihe fault since 1970 and the preliminary study on seismogenesis of the Kangding M_S6.3 earthquake

本文基于1970年以来的地震目录及四川地区4.0级以上地震的震源机制解资料,分析鲜水河断裂带分段(炉霍段、道符段、康定段、石棉段)的地震活动特征及研究区现代构造应力场,结合深部速度结构,探讨鲜水河断裂带上地震活动频度与龙门山断裂带地震活动的关系及康定地段6.3级地震的孕震环境。结果发现:(1)鲜水河断裂带北段和南段地震活动性存在差异,炉霍段和道孚段的地震活动频度1981年前要高于2000年后,康定段和石棉段的地震活动频度2000年以后高于1981年前;(2)分析地壳P波速度结构发现康定震区西侧川滇块体表现出低速异常,东侧表现出高速异常;(3)对构造应力场的分析结果表明龙门山断裂带主要以NW-SE向挤压为主,鲜水河断裂带构造应力场以NWW-SEE向为主。综合鲜水河断裂带应力场特征、深部速度结构、断层间的相互作用等信息推断,康定M6.3地震的发生与该地区应力积累及深部孕震环境相关,同时由于龙门山断裂带地震活动性影响,导致鲜水河断裂带康定段的能量释放。

Seismicity feature of different scaled rectangles （ Luhuo, Dawu, Kangding, Shimian） of Xianshuihe Fault and the principal compress axes of the recent stress filed are analyzed by investigating seismic activity data since 1970 and the data of focal mechanism of Sichuan region. Moreover, we preliminarily discuss the relationship between the earthquake frequency on Xianshuihe Fault and the seismic activity on Longmenshan Fault. We analyze seismogenic conditions of the Kangding Ms6.3 earthquake. The results show that： （ 1 ） seismic activity along Xianshuihe fault exhibits different features at northern and southern segments：the seismic activity frequency before 1981 is higher than the activity after 2000 on Luhuo and Dawu zone （northern segment）. On the other hand, seismic activity frequency after 2000 beneath Kangding and Shimian zone（southern segment）is higher than the activity before 1981. （2）From the picture of P wave velocity structure, we can find that western side of the Kangding earthquake zone （ Sichuan-Yunnan tectonic block）appears to have low velocity abnormal, which is different from the eastern part. （3） The principal compressional stresses of the Longmenshan fault and Xianshuihe Fault are mainly NW-SE and NWW-SEE under the recent structural stress field. Combined with the information of ground surface deformation, the deep structure, and the fault interaction, we infer that the seismogenesis of Kangding Ms6.3 is attributed to two factors--the accumulation of stress and induced earthquake of high-frequency seismic activity of Longmenshan Fault.