断裂两盘井水位同震响应特征对比分析——以北京八宝山断裂带中段大灰厂两观测井为例

Comparison Analysis of Co-Seismic Response Characteristics of Groundwater Level at Two Sides of Fault:A Case Study of Dahuichang Observation Wells in the Middle of Babaoshan Fault in Beijing

地震常引起分布于断层两盘观测井的水位同震响应动态变化特征不同。而研究断裂两盘观测井同震响应能力、水位变化特征的差异性及其控制因素,有助于揭示断裂带的渗透性演化过程、可深化地下水位对地震响应机理的认识,对于指导地震观测井网布局具有重要意义。本文尝试从北京八宝山断裂带中段(大灰厂)上下两盘井的水位同震响应次数、形态、幅度、记震能力等方面进行对比分析,通过去除趋势项,采用数字滤波求取井孔气压系数,采用Baytap-G程序求取潮汐参数,并反演出7次大地震对大灰厂区两口井所在含水层产生的体应变量,进而判别两盘震前震后渗透性的变化。结果显示,两口井同震响应特征具有明显差异,上盘井对大震的同震响应次数较多、能力较强;这不仅与断裂带起屏蔽作用有关,而且与井所处含水层渗透性呈不同规律变化密切相关。

Earthquake often causes different co-seismic response of groundwater level in observation wells at two sides of the fault. The research on the difference of co-seismic response ability, groundwater level variation at different sides of the fault and its governing factors is helpful to reveal evolution process of fault zone permeability, to deepen understanding the response mechanism of groundwater level to earthquake, and to guide the layout of earthquake observation networks. This paper has made a try to analyze the times, form, amplitude and shock ability of co-seismic response of groundwater level to earthquake in the observation wells in upper and lower side of the middle section of Babaoshan fault zone in Beijing. The borehole pressure coefficient has been calculated with digital filter by trend removing and the tidal parameters have been calculated using Baytap-G program. The volumetric strain of the two aquifers where the observation well is located has also been inverted for the last 7 earthquakes and the permeability variation before and after the earthquake can thereby be discriminate＆ The results show that the co-seismic response of groundwater level to earthquake in these two observation wells is different and the co-seismic response times of groundwater level in upper side of the fault zone in Beijing has more times and stronger ability than that in lower side, which is in relation to fault belt shielding effect and the different variation of aquifer permeability where the observation well is located.