中国大陆井水位观测网对甘肃岷县漳县6.6级地震同震响应特征分析

Coseismic Changes of Water Level Caused by the Mianxian-Zhangxian M_S6.6 Earthquake

基于全国地下流体前兆台网数据库的统计,本文了整理中国大陆井水位观测网中对甘肃岷县漳县6.6级地震水位同震响应的台站特征。分析结果是:(1)岷县漳县6.6级地震烈度Ⅵ度区的1.5倍的范围内主要由静态应变引起的水位同震变化仅有一个台站,水位同震阶升幅度仅1.5cm,静态应变触发地震的可能性不大;(2)震中距大于1 000km的远震响应均为水位阶升,但是其同震变化幅度小于0.3cm,为含水层被压缩引起;(3)该地震引起的水位同震变化的观测井较少,分布范围大,整体上以水位同震阶升占据主体,其分布主要在静态应力变化引起的范围之外,并且与构造带的对应关系无规律可循,此次地震静态应变范围内的应力应该已经得到释放。

On the basis of research reported during the past few decades and data from the national underground fluid precursory network, this study examines the coseismic changes of water level caused by the Minxian--Zhangxian Ms6. 6 earthquake. Coseismic change was observed in only one water well level in the static strain field with an epicentral distance of ~ 1.5 the fault rupture length, and its amplitude was only 1. 5 cm. Such static strain is not likely to trigger further earthquake activity. The total water level changes in observation wells indicated that the distance between the water level changes to the epicenter was distributed from 230 km to 1470 kin. In the far field, in which the epicentral distance was larger than 1 000 kin, coseismic changes were ob- served in two observation well, both of which showed abrupt water level changes. The mecha- nism and characteristics of this result could indicate the dominant factor between the elastic-plas- tic spread and shutting of the rock fracture shown by the influence of quaking around the wells. When the elastic-plastic spread was less than the shutting, the decreased rock porosity resulted in a jump in observation well water level. Moreover, eight observation wells showed coseismic changes of water level in the entire Chinese mainland, which is less than the number of the earth- quake coseismic changes. The distribution of the coseismic changes of water level in the wells waslarge and irregular with geologic structure. From the perspective of all the coseismic changes in observation wells, six observation wells showed abrupt changes in water level. Such increases were the main type of change and were attributed to 75~ of the total coseismic changes in water level. Regional tectonic stress should have been released by the Minxian--Zhangxian Ms6. 6 earthquake. In addition, the structure and hydrogeological conditions of the observation wells were key to the coseismic changes in the water level, and the lithology effect of the observation wells on the coseismic changes was far less than the distance effect.