小江断裂带强震危险性分析

Analysis on Strong Earthquake Risk of Xiaojiang Fault Zone

利用1985年7月至2015年6月云南测震台网记录的地震资料,分段计算小江断裂带的b值、a/b值、单位面积的年频度和年应变能,并结合历史地震空区的识别结果,综合分析了小江断裂带各段的强震危险性。研究结果表明:巧家北至东川南b值较低,处于较高应力状态,小震频发,且强震平静时间达到了极限,具备发生强震的条件;东川至宜良段应力水平高,但小震不活跃,处于积累应变阶段,不具备发生强震的条件;宜良至华宁段具有小江断裂带最高的b值,应力水平低,小震不活跃,不具备发生强震的条件;华宁以南至小江断裂南端处于高应力状态,小震频发,且强震平静时间间隔达到了极限,具备发生强震的可能,但由于该段断裂交错,较为复杂,强震可能发生在小江断裂与石屏—建水断裂的交叉部位。

Selecting the data recorded by the Yunnan Seismic Network from Jul.,1985 to Jun.,2015,we calculated b value,a / b value,annual frequency and annual strain energy on unit area. Then,referring to the seismic gaps which had been determined by the previous seismologists,we analyzed the strong earthquake risk on the four segments of the Xiaojiang Fault Zone. We found that the segment from north part of Qiaojia County to the south part of Dongchuan City with lowb value and frequent small earthquakes was in the state of high stress. And the quiescent period of strong earthquakes on this segment had reached the limit,which indicated that this segment had the conditions for strong-earthquake occurrence. The segment from Dongchuan City to Yiliang County was in the state of relative high stress,and small earthquakes were inactive. This segment was in the stage of stress accumulation and the possibility of strong earthquakes was low. The segment from Yiliang County to Huaning County with the highest b value of the whole fault zone was in the state of lowstress. Small earthquakes were inactive and the possibility of strong earthquakes was lowon this segment. The segment from the south part of Huaning Country to the end of the fault zone with frequent small earthquakes was in the state of high stress,and the quiescent period of strong earthquakes on this segment had reached the limit,which indicated that this segment had the conditions for strong-earthquake occurrence. However,since several other faults cross on this segment,strong earthquakes may occur on the crossing site of the Xiaojiang Fault and the Shiping-Jianshui Fault.