宁强MS5.3地震前的LURR综合分析

A comprehensive analysis of LURR before the Ningqiang MS5.3 earthquake

摘要:

2018年9月12日在陕西省汉中市宁强县发生了M_S5.3地震,震源深度11 km。基于陕西区域2014—2018年地球物理观测资料,选取地下水位、洞体应变、体应变以及地电场等观测手段的20个观测站点,采用库仑应力触发模型的加卸载响应比计算方法,计算各个站点的加卸载响应比(LURR),对此次地震前的异常信息进行分析讨论。初步获知:(1)LURR异常出现时间集中在2017年底至2018年5月,其中地下水位LURR出现异常变化时间最早,出现极大值的时间也最早,而洞体应变、体应变、地电场LURR异常开始时间较晚,集中在2018年2—5月,极大值出现时间集中在2018年3—7月。(2)从各观测手段的异常变化幅度来看,地下水位的变化幅度最小,洞体应变和体应变的变化幅度最大,地电场的变化幅度居中；从空间分布看,不同测项的异常站点有分布较为集中的现象。(3)周至地电场LURR与优势方位角异常变化在时域上较为同步。(4)总体上,地下水位、洞体应变、体应变以及地电场这几种地球物理观测资料反映的LURR异常演化具有准同步性。这为尝试多种观测资料计算LURR,进行多重物理量相互验证,提高异常信息的可信度等提供参考。

Abstract:

On September 12, 2018, an M_S5.3 earthquake occurred in Ningqiang County, Hanzhong City, Shaanxi Province, with a focal depth of 11 km. Based on the geophysical data obtained during the period from 2014 to 2018 in the Shaanxi region, 20 observation stations monitoring the groundwater level, cave strain, volumetric strain, and geoelectric field are selected, and the load/unload response ratio (LURR) of each station is calculated using the Coulomb stress triggered model. The abnormal information obtained before the M_S5.3 earthquake is analyzed, and the following preliminary conclusions are extracted: (1) LURR anomalies appeared in the period from the end of 2017 to May 2018, during which the LURR of the groundwater level exhibited the earliest abnormal variation and the earliest maximum value. The LURR anomalies in the cave strain, volumetric strain, and geoelectric field appeared relatively late, from February to May 2018, and their maximum values were observed from March to July 2018. (2) The abnormal variation range of various observation elements shows that the variation range of the groundwater level is the smallest, the variation range of the geoelectric field is larger than that of the groundwater level, and those of the cave and volumetric strains are the largest. The abnormal stations with different measurement elements exhibit a relatively spatial concentration. (3) The abnormal variations of LURR and the dominant azimuth of the Zhouzhi geoelectric field are relatively synchronous in the time domain. (4) Generally, the abnormal evolutions of LURR obtained from the geophysical data of the groundwater level, cave strain, volumetric strain, and geoelectric field are quasi-synchronous. These findings provide a reference for calculating LURR from various observation data, are mutually verified by multiple physical quantities, and improve the reliability of abnormal information.