Abstract: The water level annual change in Daqiao reservoir is about 40m,which imposes a static pressure change on its basin about 4?10⁵Pa,100 times as the role of earth tide.Therefore,the water level's change becomes the largest force source of loading or unloading effect on its basin.In this paper,we apply Load-Unload Response Ratio(LURR)theory on studying LURR value's changes pre-and after the M_s 4.6 Daqiao reservoir earthquake using earthquake number and energy data.The results show that:in the vicinity of the reservoir,for small earthquakes occurring in the reservoir water loading process,the earthquake number LURR value Y_n and C_r appeared as high-value anomalies,indicating that the rock in the study area was in a state close to failure,and then the M_s 4.6 reservoir earthquake occurred;the average value of Y_n and C_r showed significant difference before and after the impounding, as was high-value anomalies before the reservoir impounding,and resumed to normal afterwards. This case shows that reservoir water level's LURR could be beneficial to reservoir earthquake's monitoring and forecast.

Key words: Daqiao reservoir, reservoir-induced earthquake, LURR, earthquake forecast

摘要： 多年的实测数据表明,大桥水库的坝前水位年变化约40m,库水对库盆的静压变化大约为4×10⁵Pa,比固体潮的作用大2个量级,水库的蓄水和放水是对库区影响最大的加卸载力源。根据加卸载响应比理论(LURR),用库区的地震频次和能量分别研究在大桥水库诱发M_S4.6地震前后加卸载响应比的变化。结果表明:在大桥水库及附近相对较大的范围和水体附近相对较小的范围内,当库水加载过程中发生小震群时,地震频次加卸载响应比Y_n和C_r值显示高值异常,表明研究区岩石处于临近破裂状态,其后发生4.6级水库诱发地震;蓄水前后地震频次库水加卸载响应比Y_n和C_r值的平均值有明显差异;在大桥水库诱发的4.6级地震前,库水加卸载作用导致的地震频次及能量的加卸载响应比在震前存在明显的高值异常,震后异常消失。大桥4.6级震例表明库水加卸载响应比可有效应用于水库诱发地震的监测预报。

关键词: 大桥水库, 水库诱发地震, 加卸载响应比, 地震预测