通过计算2003—2021年吴忠—灵武地区M_L≥2.0地震的震源机制解,利用震源机制解结果和叠加应力场反演方法计算了吴忠—灵武地区的应力张量方差,得到应力张量方差的空间和时序分布特征,分析吴忠—灵武地区4次M_S≥4.0地震和该地区震源机制一致性参数的关系,提取了该地区震源机制一致性参数预测指标,并讨论了其预报效能。结果表明,2003—2021年吴忠—灵武地区的应力张量方差空间值范围主要介于0.13～0.22之间,以38.1°N为分界线,呈现南低北高的分区特征,4次M_S≥4.0地震均发生在应力张量方差高低值的过渡区域附近,应力张量方差的时序图存在两处显著的“异常”变化,其变化特征为应力张量时序方差持续低于0.1且维持1年左右,并呈现显著的“V”型变化,该两处“V”型变化之后各自对应了2012年永宁 M_S4.6 和2021年灵武 M_S4.0 地震,即震前其应力张量时序方差均经历了“下降—转折—回升—发震”的变化,回升到发震的时间间隔约为1年左右。该地区的预报效能分析结果认为,可以将震源机制一致性参数作为吴忠—灵武地区M_S≥4.0地震的中长期预测指标。

Using calculated focal mechanism solutions of M_L≥2.0 earthquakes from 2003 to 2021 in Wuzhong-Lingwu area,the stress tensor variances in Wuzhong-Lingwu area were inverted using superposition stress field inversion method,and its spatial and temporal distribution characteristics were also studied. The relationship between four M_S≥4.0 earthquakes in Wuzhong-Lingwu region and focal mechanism consistency parameters in the region was analyzed,and then the prediction index of focal mechanism consistency parameters in the region was extracted,and its prediction efficiency was discussed. The results show that the spatial range of stress tensor variance in Wuzhong-Lingwu region from 2003 to 2021 is mainly between 0.13 and 0.22,with the latitude of 38.1ås the dividing line,showing the zoning characteristics of low in the south and high in the north. The four M_S≥4.0 earthquakes generally occurred in the transition region between high and low values of the stress tensor variance. There are two significant “abnormal” changes in the temporal sequence diagram of the stress tensor variance,which is characterized by the temporal sequence stress tensor variance being lower than 0.1 for about one year and showing a significant “V-shaped” change. These two “V-shaped” changes correspond to the 2012 Yongning M_S4.6 earthquake and 2021 Lingwu M_S4.0 earthquake respectively. Before the earthquake happens,the temporal stress tensor variances all have experienced a change of descending,turning,rising and earthquake occurring,and the time interval between rising and an earthquake occurrence is about one year. By analyzing prediction efficiency in the area,it is shown that the consistency parameters of focal mechanism can be used as the medium and long term prediction index of M_S≥4.0 earthquakes in Wuzhong-Lingwu region.

P315

宁夏自然科学基金项目(2022AAC03687)、地震科技星火计划项目(XH21040)、中国地震局震情跟踪定向工作任务(2021010118、2022010104、2023010113)共同资助