Triggered earthquakes and deep well activities

Earthquakes can be triggered by any significant perturbation of the hydrologic regime. In areas where potentially active faults are already close to failure, the increased pore pressure resulting from fluid injection, or, alternatively, the massive extraction of fluid or gas, can induce sufficient stress and/or strain changes that, with time, can lead to sudden catastrophic failure in a major earthquake. Injection-induced earthquakes typically result from the reduction in frictional strength along preexisting, nearby faults caused by the increased formation fluid pressure. Earthquakes associated with production appear to respond to more complex mechanisms of subsidence, crustal unloading, and poroelastic changes in response to applied strains induced by the massive withdrawal of subsurface material. As each of these different types of triggered events can occur up to several years after well activities have begun (or even several years after all well activities have stopped), this suggests that the actual triggering process may be a very complex combination of effects, particularly if both fluid extraction and injection have taken place locally. To date, more than thirty cases of earthquakes triggered by well activities can be documented throughout the United States and Canada. Based on these case histories, it is evident that, owing to preexisting stress conditions in the upper crust, certain areas tend to have higher probabilities of exhibiting such induced seismicity.     

WINDOW FACTOR ANALYSIS:THEORETICAL DERIVATION AND APPLICATION TO FLOW INJECTION ANALYSIS DATA

Window factor analysis(WFA)is a self-modeling method for extracting the concentration profiles ofindividual components from evolutionary processes such as flow injection,chromatography,titrationsand reaction kinetics.The method takes advantage of the fact that each component lies in a specificregion along the evolutionary axis,called the‘window’.Theoretical equations are derived.The methodis used to extract the concentration profiles and spectra of seven bismuth species from data obtained byGemperline and Hamilton,who injected bismuth perchlorate into a flowing stream of hydrochloric acid.     

矽卡岩浆型铜矿床特征——以安徽铜陵东狮子山铜矿床为例

东狮子山铜矿床具有下列独特的特征:(1)矽卡岩是高温、高密度、粘稠的岩浆熔融体;(2)矽卡岩体与辉石二长岩体具有同源性;(3)矿体与矽岩体具有同源性;(4)成矿物质来自岩浆源,硫同位素测定的绝对值小于5‰;(5)矽卡岩矿物开始结晶温度为920C,可见熔融包裹体,成矿温度为620C;(6)成矿压力相当于1～2km深度条件;(7)矿石、矽卡岩具有典型的岩浆矿床的结构构造。     

流动注射-光度法测定地质样品中痕量碘

利用I~-对4,4′-四甲基二氨基二苯甲烷(4,4′-TMB-DPM)与氯胺T反应的催化作用,建立了流动注射-分光光度测定地质样品中痕量碘的方法。采用不等流速合并带法,分析速度快、节省试剂、灵敏度高。与高温水解法释放I~-相结合,使样品处理简单、干扰离子少。对于含I~-10μg/L的水样,其RSD(n=19)为1.1％,检出限为0.3ng/ml。用于水系沉积物、土壤分析时,含碘1.6×10~(-6)的样品RSD(n=10)为6.1％,检出限为0.08×10~(-6)。测量速度50N/h。     

Orbit injection error analysis for the Lageos III mission

An analysis is presented of the orbital injection errors for the Lageos III satellite mission. Several methods are introduced for the solution of the Inverse Problem in the Theory of Errors. The novelty of the present approach consists in the use of the full geopotential covariance matrix in the error propagation equations. The GEM-T1 covariance matrix is used. It is found that by properly accounting for the correlation among the even zonal harmonic coefficients the acceptable error bounds increase by an order of magnitude with respect to the case when only the variances are used. The most stringent constraint, even when using the full covariance, is on inclination, whose nominal value must be realized within approximately 0.1° for the recovery of the Lense-Thirring precession to be successful at the 3% level (accounting only for injection errors). The associated tolerance in the semimajor axis is about 30 km while that in eccentricity is approximately 0.2. However, if the errors in semimajor axis and eccentricity can be kept to the routinely achievable levels respectively of 10 km and 0.004, then the tolerance in inclination can be relaxed to 0.2°.     

Seismic Activity Around and Under Krakatau Volcano,Sunda Arc: Constraints to the Source Region of Island Arc Volcanics

There is general agreement that calc-alkaline volcanic rocks at convergent plate margins are genetically related to the process of subduction (Ringwood, 1974; Maaloe and Petersen, 1981; Hawkesworth et al., 1997). However, opinions on the mode and site of generation of primary magma for island arc volcanism differ substantially. The site of generation of calc-alkaline magma is thought to be either in the mantle wedge (Plank and Langmuir, 1988; McCulloch and Gamble, 1991) or in the subducting slab (White and Dupré, 1986; Defant and Drummond, 1990; Edwards et al., 1993; Ryan and Langmuir, 1993). We present seismological evidence in favour of the latter concept. A distinctive seismicity pattern around and under the Krakatau volcano was identified during systematic studies of the SE Asian convergent plate margins by means of global seismological data. A column-like cluster of events, probably associated with the dynamics of the volcano, is clearly separated from the events in the Wadati-Benioff zone. The accuracy of hypocentral determinations of the events of the cluster does not differ from the accuracy of the events belonging to the subducting slab. The depths of the cluster events vary from very shallow to about 100 km without any apparent discontinuity. On the other hand, there is a pronounced aseismic gap in the Wadati-Benioff zone directly beneath the volcano at depths between 100-150 km. The Krakatau cluster connects this aseismic gap to the volcano at the surface. The pervasive occurrence of earthquakes in the continental wedge between the subducting slab and the Earth surface bears witness to the brittle character of the continental lithosphere and casts doubt on the existence of large-scale melting of mantle material. The aseismic gap (Hanu and Vank, 1985), interpreted by us as a partially melted domain occurring in subducted slabs in practically all active subduction zones that reach depths greater than 100 km, is here used as evidence for the location of the primary source region of island arc volcanics in the subducting plate.     

浙江沐尘岩体与西山头组火山岩的岩浆同源性分析

沐尘岩体与旁侧西山头组火山岩、潜火山岩在空间上密切共生,形成时间相近;岩石类型都属中酸性岩类;具有相近的岩石化学成分,均属弱碱质岩系;各种岩石的稀土配分曲线除Eu外具有基本一致的型式,微量元素配分曲线形态也基本一致,说明它们是同源岩浆演化的产物。其岩石类型、岩石化学和稀土元素、微量元素地球化学方面具有相似性和一致性,岩浆演化均有反序现象,说明它们属同熔型火山-侵入岩组合。根据2004年国际地层委员会公布的侏罗系与白垩系的分界年龄(145.5±4.0Ma),并结合沐尘岩体与旁侧西山头组火山岩的成因关系,沐尘岩体的形成时代确定为早白垩世早期似更合理。     

赣东北前寒武纪港边杂岩体的岩浆混合（和）作用及其地质意义

赣东北地区沿江绍断裂北缘和江南造山带南侧有大量的前寒武纪火山侵入杂岩呈带状分布,主要由大面积的陆相火山岩和若干长英质镁铁质火成杂岩体组成,后者中出露面积最大的港边杂岩体在填图尺度上可划分为长英质岩、镁铁质岩和过渡性岩3大组成部分,长英质岩颗粒锆石U_Pb谐和不一致曲线上交点年龄为822±4Ma,代表杂岩体中岩浆混合作用发生的时间。港边岩体中长英质岩石的Nd模式年龄为1·49~1·68Ga,镁铁质岩中玄武质岩石为1·51~2·21Ga,辉长岩的Nd模式年龄与玄武质岩石基本相同,为1·54~2·13Ga,经计算的过渡性岩石的Nd模式年龄为1·58~1·90Ga,因此认为镁铁质岩石从源区分离的时间要远早于长英质岩石,而过渡性岩石含有前两个端员岩浆相互混合(和)的信息。长英质岩石的εNd(t=822Ma)值为-0·8~-4·4,87Sr/86Sr(822)比值为0·70368~0·70549;玄武质岩石的εNd(822)值为-2·6~+2·3,87Sr/86Sr(822)比值为0·70387~0·70527,这反映了镁铁质岩浆的源区接近总地球,长英质岩浆则来自具壳幔混合性质的EMⅠ型地幔的源区。可以推测,赣东北前寒武纪也曾发生过岩浆底侵作用。底侵作用对港边火成杂岩体岩浆的形成起着重要的作用。底侵于壳幔边界的玄武质岩浆使地壳熔融形成长英质岩浆并聚集于浅部岩浆房。随着长英质岩浆房降温,长英质岩浆的结晶度和粘度增加,其物理状态发生液态→(固+液)混合态→固态的变化;当玄武质岩浆穿透下地壳并不断进入物理状态变化的长英质岩浆房时,持续地发生两种岩浆的化学混合作用或两岩浆的机械混合作用或玄武质岩浆的侵入,其混合作用的时间以长英质岩锆石的U_Pb谐和不一致曲线上交点年龄822±4Ma界定。根据Nd模式年龄(tDM)和Nd富集系数(fSm/Nd)分布特征,可以确定中元古代江南造山带为太古宙扬子古陆核的横向增生体,而新元古代陆相火山侵入杂岩带则横向增生于江南造山带南缘。至此,扬子古陆横向增生作用结束,开始与华夏古陆拼贴,包括港边火成杂岩体在内的新元古代火山侵入杂岩带则成为两古陆连结的纽带。     

北京市老城区雨洪控制与利用示范工程运行中的水质研究

以北京市老城区雨洪控制与利用示范工程为背景．对天然降雨、不同下垫面雨水径流、示范工程处理过程雨水径流以及地下水水质进行分析研究,通过示范工程对雨洪的处理利用效果,探讨雨水回灌至地下能否对地下水环境产生负面影响。     

河北西北部熔积岩特征及其地质意义

熔积岩是火山碎屑岩的一种特殊类型，由熔浆和未固结的湿沉积物两种组分掺杂混合而成。熔积岩的形成主要受炽热熔浆与未固结的湿沉积物接触时引起的淬碎或蒸汽爆炸作用以及寄主沉积物流体化作用控制，通常分布于熔岩流底部或前缘，也可分布于超浅成侵人体周围。据熔浆碎屑物的结构特征，冀西北熔积岩可分为流状和块状两种类型。流状熔积岩多是熔浆与细粒沉积物混合的结果，块状熔积岩大多与粗粒沉积物相关。正确鉴别熔积岩对确定沉积作用与岩浆作用的时序、研究盆地发展演化历史具有重要意义。