考虑断裂破碎带的丹江口水库诱发地震成因数值模拟分析

Analysis of the causes of induced earthquakes in the Danjiangkou Reservoir area considering the fracture zones

根据丹江口库区的地质构造特征,考虑库区已有的断裂破碎带和岩石力学参数随深度的变化,运用ABAQUS软件建立丹江口库区三维有限元模型,模拟计算其构造应力场和水压应力场,分析两场的共同作用,在此基础上探讨丹江口水库提高水位后的诱发地震成因。结果表明：一期蓄水引起的水压应力场和位移场是诱发库岸外围一系列微震的主要因素;二期蓄水引起水压应力和位移的增加,会在库岸外围—厚坡、九重、彭桥、仓房、田川等地再次诱发一系列微震,在宋湾—关防滩—旧淅川、上寺—黑桃园、林茂山—丹江口—青山港和紫山凹—旧均县等地新诱发一系列小震,震源深度在5~11km范围内;蓄水后的构造应力场和蓄水前的基本相同,由水体静压力引起的应力变化很小,水体荷载产生的应力直接诱发较大震级的地震是不可能的。

According to the geological structure characteristics of the Danjiangkou reservoir,a 3-D finite element model is established using the software ABAQUS,with the main fracture zones within the reservoir area and the variations of the mechanical properties of the rock with depth taken into consideration.Tectonic stress field and hydraulic-pressure stress filed are simulated,and the coupling between these two stress fields is also analyzed to investigate the causes of reservoir induced earthquakes after raising the water level.Calculation results show that the hydraulic-pressure stress field and displacement field resulted from the phase-Ⅰ impoundment is the main cause of a series of microseisms around the periphery of the reservoir.The increases of the hydraulic pressure and displacement induced by the phase-Ⅱ impoundment can activate a series of microseisms again at Houpo,Jiuzhong,Pengqiao,Cangfang and Tianchuan around the periphery of the reservoir,as well as a series of minor earthquakes in Songwan-Guanfangtan-Jiuxichuan,Shangsi-Heitaoyuan,Linmaoshan-Danjiangkou-Qingshangang and Zishan＇ao-Jiujunxian,with the hypocenter depths ranging from 5 to 11km.The tectonic stress field remains almost the same after the impoundments,and hydrostatic pressure induces little variation in the stress field.Thus,high intensity earthquakes are not likely to be activated by the stress generated by the static water load.