岷江较场台地地震裂缝形成机制及其边坡稳定影响
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摘要
岷江上游的大、小海子是两个相连的地震滑坡、崩塌堰塞湖。几十年来对湖泊东岸较场镇台地的认识不一,其岸坡稳定问题是利用该天然湖泊建设水电站的关键。通过现场调查与钻探、测试,发现岷江上游的较场台地是一个向岷江凸出的、1万a前形成的湖相沉积台地。1933年,在强烈地震作用下,较场台地发生了强烈裂陷,未发生大规模的滑移,在台地上形成了两组近于垂直的地裂缝。进一步研究表明,这两组地裂缝虽然是在同一诱发因素下,在同一时间、同一地点形成的,但它们的形成机制却不同。一组走向近SN,是在强烈地震作用下,追踪岩体中原有的两组构造节理进一步裂开的产物,可称为地震构造追踪型地裂缝;另一组走向近EW,是顺向边坡中的层状岩体,在地震作用下沿软弱层发生层间滑动,地面被拉开、沉陷而形成的,可称为地震层间滑动型地裂缝。两种类型的地裂缝与层面的空间组合,控制着台地的稳定与演化。特别是当遇到类似1933年那样的地震,甚至由于两种地震地裂缝与层间错动面的存在,不需要那么高强度的地震,就可能诱发大规模的边坡稳定问题。这应该引起天龙湖水电站与213国道等管理部门的重视。
Dahaizi Lake and Xiaohaizai Lake are conjoint lakes which locate in the upriver of Minjiang River.They formed by the rock landslide induced by earthquake in 1933.There are a few different viewpoints for decades on the stability of Jiaochang platform that is situated on the east bank of the Xiaohaizi Lake,which has become a key to the construction of hydropower station.According to the investigation,drilling and testing of the fieldwork,it is found that Jiaochang platform was a lake deposition mesa that formed ten thousand years ago,protruding to the river.In 1933,the platform cracked and subsided during a strong motion earthquake.Two ground fissure groups which are perpendicular to each other are formed.The further study shows that the forming mechanisms of the two ground fissure groups are different,although they are all formed on the platform,causing by the same earthquake at the same time.One fissure group formed by the vibration of earthquake in the basis of tectonic trailing tension joints,stretches in N-S,called earthquake-tectonic trailing tension fissures;another formed by the interlayer sliding caused by earthquake,stretches in E-W,called earthquake-interlayer sliding fissures.The spatial combination between the two ground fissure groups and the terrane layers controlled the stability of the Jiaochang platform and its development.Especially,when an intensity earthquake as 1933′s occurred,even without so strong earthquake because of the two fissures and interlayer-sliding plane,the slopes will lose its stability.Therefore,the administrative organs of the hydropower station and 213 road should pay attention to the problem.
Dahaizi Lake and Xiaohaizai Lake are conjoint lakes which locate in the upriver of Minjiang River.They formed by the rock landslide induced by earthquake in 1933.There are a few different viewpoints for decades on the stability of Jiaochang platform that is situated on the east bank of the Xiaohaizi Lake,which has become a key to the construction of hydropower station.According to the investigation,drilling and testing of the fieldwork,it is found that Jiaochang platform was a lake deposition mesa that formed ten thousand years ago,protruding to the river.In 1933,the platform cracked and subsided during a strong motion earthquake.Two ground fissure groups which are perpendicular to each other are formed.The further study shows that the forming mechanisms of the two ground fissure groups are different,although they are all formed on the platform,causing by the same earthquake at the same time.One fissure group formed by the vibration of earthquake in the basis of tectonic trailing tension joints,stretches in N-S,called earthquake-tectonic trailing tension fissures;another formed by the interlayer sliding caused by earthquake,stretches in E-W,called earthquake-interlayer sliding fissures.The spatial combination between the two ground fissure groups and the terrane layers controlled the stability of the Jiaochang platform and its development.Especially,when an intensity earthquake as 1933′s occurred,even without so strong earthquake because of the two fissures and interlayer-sliding plane,the slopes will lose its stability.Therefore,the administrative organs of the hydropower station and 213 road should pay attention to the problem.
引文
[1] 四川省地震局.一九三三年叠溪地震[R].1985.
[2] 李天池.地震与滑坡的关系及地震滑坡预测的探讨[A].滑坡文集(第二集)[C].北京:人民铁道出版社,1979.
[3] 孙崇绍,等.我国历史地震时滑坡崩塌的发育及分布特征[J].自然灾害学报,1997,16(62).
[2] 李天池.地震与滑坡的关系及地震滑坡预测的探讨[A].滑坡文集(第二集)[C].北京:人民铁道出版社,1979.
[3] 孙崇绍,等.我国历史地震时滑坡崩塌的发育及分布特征[J].自然灾害学报,1997,16(62).
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