Observations of mine seismicity in the eastern Wasatch Plateau,Utah, U.S.A.: A possible case of implosional failure     

Ivan G. Wong  James R. Humphrey  Janet A. Adams  Walter J. Silva 《Pure and Applied Geophysics》1989,129(3-4):369-405

In the summer of 1984, a three-dimensional, high-resolution microearthquake network was operated in the vicinity of two coal mines beneath Gentry Mountain in the eastern Wasatch Plateau, Utah. During a six-week period, approximately 3,000 seismic events were observed of which the majority were impulsive, higher frequency (>10 Hz), short duration (<2–3 sec) events probably associated with the caving of the roof from a longwall operation. In contrast, 234 of the largest located events appeared to occur predominantlybeneath the mines to a depth of 2 to 3 km consistent with previous studies. The magnitudes of these events ranged from less thanM _c 0 to 1.6. In addition to the unusual depths of these latter events, an anomalous aspect displayed by the events was an apparent dilatational focal mechanism suggesting a non-double-couple, possibly implosional source. Implosional events have been observed in other studies of mine seismicity; however, the generally inadequate instrumental coverage of the focal sphere has cast some doubt on the validity of such mechanisms. Previously suggested source mechanisms for such implosional events have included tensional failure through strata collapse, and a shear-implosional displacement mechanism. Shear failure must be involved in the failure process of the Gentry Mountain implosional events as evidenced by well-defined shear waves in the observed seismograms. Simultaneous monitoring in the East Mountain coal mining area to the south by the University of Utah revealed typical shear failure events mixed with implosional events. The observed double-couple, reverse focal mechanisms at East Mountain were similar to mechanisms determined in previous studies and a composite focal mechanism determined in this study for a sequence outside the mining areas. This suggested that the shear events within the mining areas are being influenced by the regional tectonic stress field. Thus in addition to the seismic events associated with caving of the roof from the longwall operation, there appear to be at least two other types of mining-induced seismic events occurring in the eastern Wasatch Plateau, both submine in origin: (1) events characterized by apparent non-double-couple possibly implosional focal mechanisms and well-defined shear waves; and (2) shear events, which are indistinguishable from tectonic earthquakes and may be considered mining triggered earthquakes. The small mining-induced stress changes that occur beyond a few hundred meters from the mine workings suggest both types of seismic events are occurring on critically stressed, pre-existing zones of weakness. Topography, overburden, method of mining, and mine configuration also appear to be significant factors influencing the occurrence of the implosional submine events.  相似文献   

Earth pillar formation on the Mountain Pine Ridge,Belize     

Mark Francek 《地球表面变化过程与地形》1988,13(2):183-186

The roadcuts of Belize's Mountain Pine Ridge feature numerous coarsely textured earth pillars less than 10 cm in height. Preferential impregnation of iron occurs over a buried pebble resulting in a dripline. The higher concentration of iron along the buried pebble's dripline is later oxidized and exposed to the surface by rainsplash erosion. For slopes greater than five degrees, the intensity of sheetwash erosion is great enough to remove pillars. Earth pillar genesis thus seems a function of laterization, slope angle, and sheetwash intensity.  相似文献   

广东山区工业发展刍议     

李禄增 《热带地理》1994,14(1):27-33

本文分析了广东山区工业发展的有利条件与存在问题，提出山区工业发展要采取超常规，跳跃式发展战略，立足本地优势资源，发展资源型工业，重点发展以生物资源为原料的工业，把资源优势转变为经济优势，同时根据市场需求发展市场型工业，尤其高新技术工业；既要立足理现有工业，加速改造挖潜，促其上水平、上规模、出效益、又要选准项目，大胆投入，发展有造血功能的骨干企业并调整和优化工业结构。  相似文献   

祁连山东段山地土壤性质及垂直分布规律   总被引：5，自引：0，他引：5  

胡双熙 《地理科学》1994,14(1):38-48

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天山高山冰缘环境的融冻泥流作用   总被引：2，自引：0，他引：2  

刘耕年  熊黑钢 《地理学报》1994,49(4):363-370

根据实地观测结果分析，本文得出：天山冰缘环境发育的融冻泥流分布在海拔２５００─３６００ｍ间的阴坡。融冻泥流发育要求地下含水丰富，粒度以细粉砂为主，地表坡度１０─３１°。融冻泥流的形态多数为长宽比小于１的叶状，少量为舌状。融冻泥流表面平均运动速度为１１．１４ｃｍ／ａ，舌前缘前进的平均速度的１．８６ｃｍ／ａ，中轴部位的运动速度比两侧大。  相似文献   

太行山中段的焚风   总被引：7，自引：2，他引：7  

赵世林  王荣科  郭彦波  谭建龙  石志增 《气象》1993,19(2):3-6

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南太行——中条山植物区系地理研究   总被引：8，自引：0，他引：8  

张镱锂  陈家治 《地理研究》1993,12(4):1-9

南太行—中条山地区是中国种子植物区系研究薄弱地区之一。本区约有种子植物1627种,隶属618属142科。通过该区种子植物各类地理成分分析及与相关地区的比较,得出:本地区植物区系具有温带区系特点,又具有温带向亚热带区系过渡性质,是华北植物区系分区南部亚区的一条重要界线。该地区存在许多古老及残遗植物,表明该区系起源古老,同时也是产生新分化的中心之一。  相似文献   

地形影响地面运动的观测研究     

吴富春  许俊奇 《地球物理学报》1990,33(2):186-195

本文利用矿山爆破,进行了地形对地面运动影响的观测研究.9次爆破的结果表明,山顶处位移和速度的谱曲线的峰区较山前和其它测点的集中,振幅的量值也大,其放大倍率约为3,其中与山体走向平行的水平分量放大得最大,与之垂直的次之,而垂直于地面的最小;山顶测点不同分量上最大位移所对应的周期接近,其对山前的放大量值近于2,也是水平分量大于垂直分量;山顶处地面运动的延续时间取决于爆破的药量和方式,山前等测点延时的放大为3-4倍,也是水平分量大于垂直分量.山顶上地面运动的这种特殊性,是由于入射波所激发的山体共振所引起的.  相似文献   

新疆阿拉套山花岗岩类的岩石化学   总被引：6，自引：0，他引：6  

周泰禧  陈江峰 《地球科学》1994,19(2):149-156

新疆阿拉套山南坡东西向展布的花岗岩石的岩石化学研究表明，本区同时存在Ｉ型和Ｓ型两种类型的花岗岩，其分布受构造环境控制，靠近古板块缝合线为Ｉ型花岗岩分布区、远离古板块缝合线为Ｓ型花岗岩分布区。源岩性质和作用强弱等因素可能是造成岩石化学成分差异的原因。  相似文献   

太行山区龙华河群的建立与否定     

徐朝雷  徐有华  张平 《地球科学》1985,(4)

太行山北段早前寒武系龙华河群为六十年代所建,后来发现五台山区的五台群底界已延入龙华河群之中。近年来,许多新资料表明,它实际上包括了龙泉关群、五台群及滹沱群的一部分。因而,应废除龙华河群,并对它进行重新划分。  相似文献