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目前世界第三大水库溪洛渡的库首区遍布碳酸盐岩、灰岩,存在溶洞,蓄水后水位升高140m左右,随之发生6 000多次地震,但绝大多数是1级以下微震,最大震级仅仅ML3;集中在库岸两侧10km、深度5km、从大坝向上游沿库盆40km长度的范围内。微小地震对于水库、大坝的安全没有产生影响。使用较为密集的水库数字地震台网资料反演得到蓄水前后700多次地震的震源机制,并进一步反演了全区和分区的应力场,发现:震源机制空间取向复杂、破裂类型多样,应力状态不均匀、不稳定。与他人使用大量天然地震资料反演的区域应力场不一致,表明水库诱发地震没有受到区域应力场的严格控制。分析认为库水涌入溶洞、渗透到裂隙、节理,原来存在的小断层面或者间断面的孔隙压力增加,摩擦强度、岩石破裂强度降低以及库水载荷加大造成弹性变形等共同作用是地震的成因。并且首先主要释放的是已经积累的区域应力、局部应力,然后才表现出以库水载荷产生的附加应力为主。库首区没有较大的活动断层,2014年库水位将再度升高数十m,伴随裂隙的贯通,应力场的调整,回流的库水淹没库盆上游,还会发生中小地震乃至中等强度地震。溪洛渡水库大坝抗震设防水准较高,不会造成安全问题。建议在诱发地震继续活动期间,尽早实施详细的水文地质、地球物理探测,提供精细的科学资料,为确定诱发地震的成因、寻找控制诱发地震的技术条件,以减轻突发事件的影响,为其他类似水库发挥示范作用。
At present, the first reservoir of the Xiluodu, the third largest reservoir in the world, is allotted carbonate rocks and limestone and has caves. After the impoundment, the water level has risen about 140m and more than 6000 earthquakes have occurred, but the vast majority are microseisms less than level 1 , The maximum magnitude is only ML3; concentrated in 10km both sides of the bank, depth 5km, from the dam to the upper reaches of the basin within the range of 40km. Micro earthquakes have no effect on the safety of reservoirs and dams. Using the more intensive reservoir digital seismograph data, the focal mechanism of more than 700 earthquakes before and after the impoundment was obtained, and the stress fields in the whole area and the subarea were further inverted. The results show that: the focal mechanism has complex spatial orientation, various types of fractures, Uneven state, unstable. It is inconsistent with the regional stress fields retrieved by others using a large amount of natural seismic data, indicating that the reservoir-induced earthquakes are not strictly controlled by the regional stress field. The analysis shows that the combined action of reservoir water influx into caves, infiltration into fissures and joints, increase of pore pressure of small existing faults or discontinuities, decrease of frictional strength, decrease of rock burst strength, Cause. And the first release is the accumulation of regional stress, local stress, and then only to show the additional load generated by the reservoir water-based. There is no large active fault in the reservoir head area. In 2014, the reservoir water level will rise by several tens of meters again. With the breakthrough of fracture and adjustment of stress field, the returned reservoir will submerge the upper reaches of the basin and small to medium earthquakes and even moderate earthquakes will occur . Xiluodu reservoir dam seismic fortification level is higher, will not cause safety problems. It is suggested that detailed hydrogeology and geophysical exploration should be carried out as early as possible during the continuation of activities to induce earthquakes and provide detailed scientific information. In order to determine the causes of induced earthquakes and find out the technical conditions for controlling induced earthquakes so as to mitigate the impact of emergencies, Similar reservoir to play a demonstration role.