Cataclasis and processes of particle size reduction   总被引：6，自引：0，他引：6  

Tom G. Blenkinsop 《Pure and Applied Geophysics》1991,136(1):59-86

The particle size distribution (P.S.D.) of fragmented geological materials is affected by the fragmentation process, initial size distribution, number of fracturing events, energy input, strain, and confining pressure. A summary of literature shows that the fractal dimension (D) of the P.S.D. is increased by the number of fracturing events, energy input, strain, and confining pressure. Cenozoic cataclasis of granite, granodiorites, gneisses and arkose seen in cores from the Cajon Pass drillhole, southern California, produced P.S.D.s with values ofD that varied from 1.88 to 3.08. Each rock type has a characteristic and more limited range ofD. Areas of dilatant texture and modeI fracture-fillings have low average values (2.32 and 2.37) compared to an average value of 2.67 in shear fracture-fillingsD has a good inverse correlation with average particle size. Data from fault rocks in the San Gabriel fault zone, southern California (Anderson et al., 1983) have been reanalyzed to show that values ofD are higher (2.10–5.52) and average particle size is lower than the Cajon Pass samples, but the ranges of values overlap, and the inverse correlation betweenD and average particle size is extended. Microstructural observations combined with these results suggest that three processes contributed to particle size reduction during cataclasis. The first process of feldspar alteration, which leads to low values ofD, has not been previously recognized. The second process is probably constrained comminution (Sammis et al., 1987), since the averageD in shear fracture-fillings is close to the value of 2.58 predicted by this theory. A further stage of particle size reduction is demonstrated by an increase ofD with cataclasis. This third process is selective fracture of larger particles, which may also operate during localization and the cataclastic flow-to-faulting transition as observed in experiments. A transition from constrained comminution to selective fracture of large particles, and increasingD values with cataclastic evolution and grain size reduction, may be general features of experimental and natural cataclasis.  相似文献   

长安—临潼断裂的活动与西安地区地震危险性探讨   总被引：5，自引：0，他引：5  

张安良  雷姚琪 《内陆地震》1991,5(3):216-225

阐述了西安地区最大规模的长安-临潼断裂带的展布、构造形迹、运动特征。指出了它是西安地区地震活动的主要发震构造。根据其地震活动特征等分析,对断裂带未来危险性作了评估。  相似文献   

流变介质中亚临界扩展前地震孕育过程的能量积累   总被引：5，自引：0，他引：5       下载免费PDF全文

滕春凯  白武明  王新华 《地球物理学报》1991,(1)

本文用流变断裂力学研究了地震孕育过程.与弹性力学不同,它是一个不可逆的时空过程.由于介质的粘性,外力功的一部分花在粘性耗散上,只有弹性应变能是地震发生及震后过程可利用的能量.我们将弹性应变能从总能量中分离出来,并就标准线性体给出了简洁公式.以海城地震为例,计算了两个共线不等长断层在地震孕育过程中其周围区域的应力场和能量场的时空变化图象及应变能积累曲线.结果表明,应变能分布复杂,在时间和空间上都很不均匀,能量积累在孕震初期较快而在后期渐趋平缓.由此讨论了某些地震前兆,认为当能量增加速率较大时某些早期前兆可能出现,比如唐山地震10年前出现的某些异常可能就是这种早期前兆表现.  相似文献   

湘西汞矿床的地质特征与成因   总被引：2，自引：0，他引：2  

谢文安  谢玲琳 《矿产与地质》1991,5(5):338-343

湘西汞矿床是湘黔汞矿带的重要组成部分.湘西汞矿受层位和构造双重控制,与岩浆活动没有直接联系,具有层带式整合矿体,矿物成分简单,汞锌矿化分带及后生成矿等地质特征.矿石硫来源于古海水硫酸盐的沉积硫;而汞的来源.则以上地幔去气作用产生的汞为主,寒武系等富汞建造的汞次之.燕山期地台活化时,以硫络合物或硫氢络合物的形式,在碱性溶液中沿深大断裂向上运转,当其与富含膏盐的客矿层相遇时,便与还原硫结合沉淀成矿.形成湘西层控后生汞矿床.  相似文献   

岩石强度的一种新判据     

李桂青  方建桥 《地球科学》1991,16(6):705-709

  相似文献   

中国滇西兰坪—思茅地洼盆地内中轴断裂带的初步研究   总被引：15，自引：0，他引：15  

林舸  范蔚茗 《大地构造与成矿学》1991,15(1):15-21

通过对中、新生代兰坪—思茅地洼盆地东、西部沉积特征、岩浆活动、地球物理场和卫星影像资料的综合研究与对比分析,论证了盆地内中轴断裂带的地质特征;讨论了中轴断裂带对盆地演化和成矿作用的重要意义。它是该区深部动力作用的主导构造 ,又是该区超大型、大型矿床形成的主要控制因素。  相似文献   

脆性断层运动学研究新进展   总被引：1，自引：0，他引：1  

吴树仁 《地质科技情报》1992,11(1):21-28

本文概述了80年代以来脆性断层运动研究方面的某些成果。介绍了脆性断层带中的一些小构造和显微构造的几何特征以及它们的运动学意义。重点论述了从露头尺度到薄片尺度确定脆性断层运动方向的三种构造判据,既从属裂隙、岩桥构造和方解石e双晶判据。  相似文献   

多级判别在地震综合预报中的应用     

石绍先  范杨 《地震研究》1990,13(4):329-336

本文阐述了多级判别在地震综合预报中应用的必要性,给出该数学方法的推导过程,并且以云南多震区——滇西南地震区为例进行实际判别计算,在所计算的工6个震例中其拟合预报准确率在80％以上;对1987年11月25日讯沧外.2级地震实际预报取得较好的效果。  相似文献   

Seismicity induced by gas production: I. Correlation of focal mechanisms and dome structure     

Bruno Feignier  Jean-Robert Grasso 《Pure and Applied Geophysics》1990,134(3):405-426

From August 1976 to June 1979, more than 220 seismic events were recorded by a 7-station network operating over an active gas field in France. 120 earthquakes with magnitudes greater than 1.0 were selected for a detailed study in order to understand the seismic response to a decrease in the gas reservoir pressure of 50 MPa. Composite focal mechanisms were determined for these events. We found that where preexisting fractures were known from well-logs, faults with the most favorable orientation were reactivated. In the part of the gas field where no preexisting faults were known, orientation of the fracture planes was close to the orientations of stratigraphic interfaces.Our kinematic model, constrained by the distribution of the earthquakes and their focal mechanisms, consists of the downward dropping of a block located close to the top of the gas field. The main faults, as defined by the spatial density of the seismic activity, define the limits of this block. The displacements observed along these faults can be either normal or reverse mechanism, dependent on the preexisting orientation of each fault. Another important result is the evidence that the depletion of the gas reservoir exerts the major influence on local seismic displacements, obscuring the effect of regional setting.  相似文献   

Parameter identification in tidal models with uncertain boundary conditions     

P. G. J. ten Brummelhuis  A. W. Heemink 《Stochastic Hydrology and Hydraulics》1990,4(3):193-208

In this paper a parameter estimation algorithm is developed to estimate uncertain parameters in two dimensional shallow water flow models. Since in practice the open boundary conditions of these models are usually not known accurately, the uncertainty of these boundary conditions has to be taken into account to prevent that boundary errors are interpreted by the estimation procedure as parameter fluctuations. Therefore the open boundary conditions are embedded into a stochastic environment and a constant gain extended Kalman filter is employed to identify the state of the system. Defining a error functional that measures the differences between the filtered state of the system and the measurements, a quasi Newton method is employed to determine the minimum of this functional. To reduce the computational burden, the gradient of the criterium that is required using the quasi Newton method is determined by solving the adjoint system.  相似文献