GNSS速度场的小江断裂带动态闭锁特征研究及地震危险性评估

Dynamic locking characteristics and seismic risk assessment of Xiaojiang fault zone based on GNSS velocity field

针对小江断裂带地壳形变、应变特征分析,及其地震危险性评估问题,该文利用1998—2007、2009—2014、2015—2021年3个时段的GNSS水平运动速度场资料,结合断层地表应变率、2008年汶川地震和1970—2021年小江断裂带主要地震资料,基于块体负位错模型,顾及莲峰-昭通断裂、安宁河-则木河断裂的影响,计算了小江断裂带断层闭锁程度和断层滑动亏损速率。分析研究结果表明:(1)小江断裂带北段巧家附近闭锁程度减弱并保持不变,深度10~25 km处为蠕滑状态,东川附近一直处于强闭锁状态,中段、南段的闭锁程度逐渐增强;整体滑动亏损速率先减小,后增大;小江断裂带表现为左旋走滑运动特征,其中第1、3时段由北到南断裂滑动速率呈减小的趋势,第2时段无此变化趋势;整体的地表应变率由“强-弱-强”变化;汶川地震对小江断裂带的应变积累起到一定的减缓作用,随着震后影响的减弱,滑动亏损速率恢复震至间水平,滑动速率恢复震前的运动趋势。(2)以上结果显示小江断裂带不同段的动态活动特征存在明显的差异;综合1970—2021年的小震分布与断层地震空区、第3时段的断层闭锁程度和地表应变分析,地震危险段为小江断裂带北段东川附近、中段。

In response to the analysis of crustal deformation and strain characteristics,as well as the assessment of seismic risk in the Xiaojiang Fault Zone,this article uses GNSS horizontal motion velocity field data from three periods of 1998—2007,2009—2014,2015—2021,combined with fault surface strain rate,2008 Wenchuan earthquake,and 1970—2021 main seismic data of the Xiaojiang Fault Zone.Based on a block negative dislocation model,taking into account the influence of the Lianfeng Zhaotong Fault and Anninghe Zemuhe Fault,the degree of fault locking and the rate of fault sliding loss in the Xiaojiang Fault Zone are calculated.The analysis and research results show that:(1)The degree of locking near Qiaojia in the northern section of the Xiaojiang Fault Zone has weakened and remained unchanged,with a creep slip state at a depth of 10~25 km.The area near Dongchuan has been in a strong locking state,and the locking degree in the middle and southern sections has gradually increased;The overall sliding loss rate first decreases and then increases;The Xiaojiang Fault Zone exhibits characteristics of sinistral strike slip movement,with a decreasing trend in the sliding rate of the fault from north to south in the first and third periods,and no such trend observed in the second period;The overall surface strain rate varies from strong weak strong;The Wenchuan earthquake has played a certain role in slowing down the strain accumulation of the Xiaojiang fault zone.As the post earthquake impact weakens,the sliding loss rate returns to the inter seismic level,and the sliding rate returns to the pre earthquake motion trend.(2)The above results show that there are significant differences in the dynamic activity characteristics of different segments of the Xiaojiang Fault Zone;Based on the analysis of the distribution of small earthquakes from 1970 to 2021,the fault seismic gap,the degree of fault locking in the third period,and surface strain,the seismic risk zone is located near Dongchuan in the northern and middle sections of the Xiaojiang Fault Zone.