The Tectonic Conditions of Shanxi Reservoir Induced Earthquake in Wenzhou
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摘要: 自2002年7月温州珊溪水库首次发生地震后,其地震活动持续至今,但目前人们对水库地震成因了解较少.基于对库区所处的区域地震地质背景、库区地形地貌、岩性及新构造运动特征的分析,采用野外地质调查的方法,获得了库区主要断层的地质特征,并评价了其渗透性.在此基础上,结合地震活动特征及震源机制解的研究成果,探讨了水库地震时间序列及发震机理.结果表明珊溪水库地震活动与库区岩性、断层(尤其是库区内的双溪-焦溪垟断层)及库水特征关系密切.水库地震主要发生在侏罗系凝灰岩夹砂岩、泥岩等隔水性好的层状岩层中,而渗透性较好的双溪-焦溪垟断层结构面则更利于库水下渗,这种岩体结构面组合方式一方面使库水容易沿断层结构面向深部渗透,另一方面断层结构面上的孔隙压力容易升高,因此降低了断层结构面上的正应力,应力平衡被打破,进而诱发地震.在水的渗透和地震活动的相互作用下,水库地震沿双溪-焦溪垟断层(尤其是第三分支断层)从SE向NW持续发生.Abstract: The Wenzhou Shanxi reservoir-induced earthquake has been active since its first occured in July 2002. However, less is known about the genesis of Shanxi reservoir-induced earthquake. Based on the analysis of regional seismic geological background, reservoir topography, geomorphology, lithology and new tectonic movement characteristics, the reservoir area's geological characteristics of the main faults were obtained and its permeability was evaluated by using field geological survey method. On this basis, time series and mechanism of the earthquake were discussed in combination with the study of seismicity and focal mechanism solutions. Finally we concluded that the earthquakes activities in Shanxi reservoir were closely related to the lithology, fault (especially the Shuangxi-Jiaoxiyang fault) and water in the reservoir. The earthquakes occurred mainly in Jurassic sandstone, mudstone rock tuff, etc. which belong to aquifuge tuff, while the structure plane in Shuangxi-Jiaoxiyang fault is beneficial to the infiltration of the reservoir water. This combination of rock mass structural plane induced, on the one hand, easy infiltration of the reservoir water to the deep underground through the fault, on the other hand, the increase of pore pressure on the fault structure plane. Therefore, the normal stress was reduced on the fault structure plane, and the stress balance was broken, which induced the occurrence of the earthquake activities finnally. Under the double influence of water infiltration and earthquake activity, the earthquakes contiuously occured from southeast to northwest along the Shuangxi-Jiaoxiyang fault (especially the third branch fault).
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Key words:
- Shanxi reservoir /
- earthquake /
- tectonic condition /
- fault
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表 1 珊溪水库库区主要断层特征
Table 1. Features of the main faults in the Shanxi reservoir
断层名称 产状 性质 破碎带宽度 长度 最新活动时代 走向 倾向 倾角 江口-汇溪断层F1 40°~50° NW 陡 正断 2~3 m 13 km AnQ 岩上-程坑断层F2 NEE NW 陡 正断兼走滑 小于2 m 8 km AnQ 双溪-焦溪垟断层F3-1分支 310° SW 78°以上 逆冲 0.25~1.00 m 10 km AnQ 双溪-焦溪垟断层F3-2分支 310° SW 60°~70° 逆冲 小于0.2 m 10 km Q1-2 双溪-焦溪垟断层F3-3分支 310° SW 70°以上 右旋走滑兼逆冲 小于5 m 大于20 km AnQ~Q1-2 表 2 珊溪水库地震震源机制(部分ML≥3.0)
Table 2. Shanxi reservoir earthquake focal mechanism (part of ML≥3.0)
事件 节面Ⅰ 节面Ⅱ P轴 T轴 年-月-日 时间 震级 走向(°) 倾角(°) 滑动角(°) 走向(°) 倾角(°) 滑动角(°) 方位(°) 仰角(°) 方位(°) 仰角(°) 2002-07-28 19:39 3.5 310 71 26 211 66 159 80 4 122 32 2002-09-05 12:18 3.9 352 89 -132 261 42 -1 352 42 115 31 2006-02-04 11:13 4.0 27 53 176 294 87 38 347 23 244 28 2006-02-04 16:52 4.1 24 88 175 294 85 2 159 2 249 5 2006-02-08 01:29 4.4 40 87 136 307 46 4 165 27 273 31 2006-02-09 03:24 4.6 53 84 171 322 81 6 187 2 278 11 2006-02-09 18:51 4.2 206 90 -168 296 78 0 160 9 251 8 2006-02-10 07:59 4.2 206 77 -142 305 53 -16 159 36 260 16 2006-02-10 14:37 4.1 217 85 -158 309 68 -6 171 19 265 11 2006-02-11 04:36 4.2 50 89 143 319 53 2 178 24 281 26 2006-08-01 13:28 4.0 56 81 178 326 88 9 11 5 281 8 2006-08-01 14:07 4.5 235 81 -177 325 87 -9 190 9 99 4 2014-9-15 13:23 3.5 224 82 11 133 79 172 358 2 89 13 2014-9-15 15:01 3.1 36 73 -5 128 84 -162 353 17 261 8 2014-9-16 11:42 3.3 36 78 -4 127 85 -167 352 12 261 5 2014-9-17 20:47 3.5 38 81 0 128 89 -170 353 7 262 5 2014-9-21 12:07 3.1 36 82 -1 127 88 -171 352 7 261 4 2014-9-22 06:37 3.8 223 85 -178 313 89 -4 178 4 88 3 2014-9-23 13:20 4.2 220 86 7 129 83 176 354 2 85 8 2014-9-23 14:12 3.6 219 83 3 128 87 173 174 2 83 7 2014-9-23 15:02 3.0 224 87 9 133 81 177 358 4 89 9 2014-9-23 17:40 3.7 37 83 -2 127 87 -172 352 7 262 3 2014-9-23 17:57 3.3 33 83 -2 123 87 -172 348 7 258 3 2014-9-24 00:20 3.4 220 89 2 130 88 179 355 1 85 2 2014-9-25 12:38 3.0 232 77 13 139 77 167 186 0 96 18 2014-9-27 08:30 4.1 215 86 4 125 86 176 350 0 80 6 2014-9-27 08:41 3.5 35 87 180 305 90 3 350 2 260 2 2014-9-29 02:58 3.0 36 86 178 305 88 4 351 2 260 4 2014-10-03 11:59 3.1 229 84 1 139 89 174 184 4 94 5 2014-10-05 06:27 3.4 38 85 180 308 90 5 353 3 263 4 2014-10-08 21:58 3.2 45 89 -6 135 83 -178 359 5 90 4 2014-10-09 01:14 3.2 43 89 -5 133 84 -178 358 5 89 3 2014-10-09 01:17 3.0 43 87 -3 133 86 -176 358 5 88 1 2014-10-09 02:30 3.3 215 84 -164 307 76 -6 170 15 262 6 2014-10-11 11:00 4.1 220 84 8 130 82 173 355 1 85 10 2014-10-12 00:00 3.8 219 90 1 129 89 180 354 0 84 1 2014-10-14 01:14 4.2 38 82 0 128 89 -171 353 6 263 4 2014-10-15 15:45 3.9 37 83 -6 128 83 -172 352 10 262 0 2014-10-15 15:49 4.0 38 67 174 306 85 24 354 12 259 20 2014-10-15 16:37 4.0 222 85 11 131 79 175 356 4 87 12 2014-10-23 08:35 3.7 44 74 -28 144 63 -161 2 32 96 7 2014-10-24 10:09 3.1 42 78 -11 136 78 -167 360 17 90 0 2014-10-25 18:42 4.4 220 86 8 130 82 176 355 3 85 8 2014-10-25 19:29 3.7 38 87 0 128 89 -176 353 3 263 2 2014-10-26 07:03 3.2 37 80 174 306 84 10 352 3 261 11 2014-10-28 01:50 3.3 42 78 -4 133 85 -167 358 12 267 5 2014-10-28 03:28 3.6 39 79 0 129 89 -168 354 9 263 7 -
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