2012年天津地区三次地震前水位对固体潮振幅响应计算分析

2012年在天津及其周边地区发生了唐山4.8级, 宝坻4.0级和宝坻3.5级三次地震。 本文收集整理了天津地区固体潮反映较好的宝坻井、 王3井、 高村井以及张道口井2012年的水位观测数据和气压数据。 采用卷积回归和多项式拟合方法, 对水位观测数据进行气压效应及趋势项的去除, 并对水位数据进行数字滤波处理, 增强水位固体潮信号。 在对数据进行以上有效预处理后, 采用类似于Nakai拟合模型, 以每两天数据为一组, 分别对不同窗口长度滤波处理后的水位数据进行体应变固体潮响应振幅因子比的计算。 计算结果表明, 三次地震前比值均出现明显高值变化。 经比较当窗长选取96 h和120 h进行滤波时计算效果最为明显, 其异常成组出现, 并且变化幅度较大。 由以上这四口井水位对固体潮响应振幅因子比在三次地震发生前后的变化分析, 地震前由于应力的积累, 比值会出现高值变化, 小震活动对应力的积累具有缓解释放作用, 并且结合地震活动以及震源机制解可以对应力的积累-释放过程有一定的了解与印证。

Responses of Groundwater Level to Earth Tides Amplitude before Three 2012 Earthquakes in Tianjin Area

In 2012, three earthquakes occurred in Tianjin and surrounding areas, which are Tangshan M_S4.8, Baodi M_S4.0 and Baodi M_S3.5 earthquakes. This article collected water level observation data and barometric pressure data of the Baodi well, the Wang3 well, the Gaocun well and the Zhangdaokou well in 2012, which have good responses to earth tides. We removed barometric pressure effects and trend component from water level observation data, then performed digital filtering in order to enhance tidal signal of water leve. After that, we adopted fitting model similar to the Nakai to calculate loading and unloading response ratio (LURR) of water level by taking data of two days into a group. The results show that, LURR increases anomalously before the three earthquakes, and it has a better result when digital filtering window length is 96 h or 120 h. We propose that LURR shows high value change before earthquake due to accumulation of stress, and small earthquakes have relieving effect to accumulation of stress. Combining seismicity and focal mechanism with LURR, we can have a better understanding of the stress accumulationrelease process.