九寨沟Ms7.0地震前地应变LURR异常演化特征

Evolutionary Characteristics of Ground Strain LURR Anomaly before Jiuzhaigou MS7.0 Earthquake

从岩石应力-应变的本构关系出发,以能够反映岩石应变变化的地应变观测数据作为"响应量",通过库伦应力触发模型的加卸载响应比计算方法,计算2017年8月8日九寨沟MS7.0地震前震中及周边500km范围内应变观测的加卸载响应比结果。结果显示,基于应变观测的加卸载响应比方法能够较好地从潮汐频段提取地震前LURR异常,九寨沟地震前,300km范围内的多个应变观测台站出现LURR异常,其中相距96km的两水台EW分量Y值最大达到3.27;LURR空间演化特征显示,在震前约9个月内震中及周边地区陆续出现异常"集中-增强-减弱"过程,证明该地区在长期应力累积的背景下,应力的不断累积增强导致震中及附近区域的岩石出现不断损伤或弱化,最终位于树正断裂上的应变能积累超过了介质强度而引发了此次地震。

Based on the stress-strain constitutive relationship of rock,we use the ground strain observation data that can reflect the change of rock strain as the"response amount",and apply the loading and unloading response ratio(LURR) calculation method include coulomb stress-triggered model to calculate the LURR results of the ground strain observation within 500 km of the epicenter before the Jiuzhaigou M_S7.0 earthquake.Our results suggest that the method based on the strain observation is of better extracting the LURR anomaly from the tidal frequency band before the earthquake.We find that the LURR anomaly appeared in several strain observation stations within 300 km before the Jiuzhaigou earthquake,and the maximum Y value of Liangshui station EW component at a distance of 96 km reached 3.27.The spatial evolution characteristics of LURR indicate that the epicenter and surrounding areas have experienced an abnormal concentration-enhancement-weakening process within about 9 months before the earthquake.It is proved that under the background of long-term stress accumulation in this area,with the continuous accumulation of stress,the rocks are constantly damaged or weakened.Eventually,the accumulation of strain energy on the Shuzheng fault exceeds the strength of the medium and triggers this earthquake.