Stability of earthquake moment tensor inversions: effect of the double-couple constraint   总被引：1，自引：0，他引：1  

C. Henry  J. H. Woodhouse  S. Das   《Tectonophysics》2002,356(1-3)

We show that spurious large non-double-couple components can be obtained in inversions for the full deviatoric moment tensor for shallow crustal earthquakes due to inaccurate Earth models. The traditional “best double-couple” solution does not in general provide an optimal estimate of a double-couple mechanism, and is only reliable when the non-double-couple component of the full deviatoric solution is small. The inverse problem for the moment tensors of the 1998 Antarctic Plate and 2000 Wharton Basin strike-slip earthquakes is shown in each case to have two well-fitting minima in the misfit function of pure double-couple solutions. Such pairs of solutions are most likely to exist for earthquakes which are close either to vertical strike-slip or to dip-slip on a fault plane dipping at 45°. It is shown theoretically that these pairs of solutions arise from the combination of the pure double-couple constraint and the instability of two elements of the moment tensor. No significant non-double-couple component is found for the shallow thrusting 1996 Biak, Indonesia earthquake.  相似文献   

Documentary and Geological Records of Tsunamis in the Aegean Sea Region of Greece and their Potential Value to Risk Assessment and Disaster Management     

Dominey-Howes  Dale 《Natural Hazards》2002,25(3):195-224

Understanding the nature and impacts of tsunamis within the Aegean Sea region ofGreece is of importance to both the academic community and those organisationsconcerned with tsunami disaster management. In order to determine hazard and riskand consequently pre-plan mitigative strategies, it is necessary to analyse historical(documentary) and geological records of former tsunami events. Therefore, firstlythis paper provides a summary of the written sources of information on Aegeantsunamis paying particular attention to published catalogues. From the availabledata, it is noted that a large number of events have been reported during the last3500 years. Secondly, the paper provides a review of the published on-shore(terrestrial) geological records of tsunamis within the region. From this analysisit is seen that little geological evidence has been identified for the large numberof tsunamis reported in the catalogues. Thirdly, the paper considers the reliabilityof the written and geological records and how problems of accuracy, coverage,extent and reliability, may have potential implications for the estimation of hazardand risk. The paper concludes by making recommendations for disaster managers,geologists and historians to work closely together.  相似文献   

Large-scale mass wasting in ancient volcanic materials     

Vicki Moon  Christine J Simpson 《Engineering Geology》2002,64(1):41-64

Giant landslides are significant hazards associated with many active volcanic edifices. We describe a similar feature on ancient (>4 Ma) volcanic deposits subject to active tectonism. The landslide is approximately 3 km long by 1 km wide, with an estimated depth of 400 m. Side margins are straight and parallel, mimicking regional structure; narrow valleys incised down these margins provide low-strength side-release surfaces. Between these is a giant slump consisting of at least four, largely intact, discrete blocks that have moved down-dip a distance of >500 m. A series of flows with areal extents ranging from 0.01 to 0.5 km² extends from the front of the failure. The materials represent an eroded sequence of andesite flows on the flanks of a stratovolcano. These have undergone two phases of hydrothermal alteration, and are deeply weathered to low-density (1040±80 kg m⁻³) silt (59%) and clay (35%) materials with strength properties typical of weathered silts (c=26±3 kN m⁻²; φ=42±8°). The size and location of this landslide preclude detailed geotechnical investigation of the failure. The worth of numerical stability analysis as an alternative technique in assessing the nature of the failure and hence the risk it poses to nearby communities is investigated. Sensitivity analysis identified likely conditions under which initial failure may have occurred: analyses for sensitivity to strength and earthquake acceleration needed conversion to critical combinations (F=1.0) of water table and strength/acceleration to remove the overriding influence of water table fluctuations. Failure was likely initiated either by a high water table level (83-84%), or some combination of intensity VII-IX earthquake waves together with water table heights of 40-80%. A general hazard assessment indicates that the risk associated with creep and catastrophic failure of the main mass is small, whereas the risk from flow failures near the toe of the landslide may be high. Important parameters (hydrological regime, flow failure morphology, age of initiation, and rates of movement) requiring closer investigation are identified. Development of a model is crucial to assessing the hazard associated with a feature such as that described here. With limited resources, a detailed stability analysis is a powerful tool as an initial stage in hazard analysis.  相似文献   

Method of Data Reduction and Uncertainty Estimation for Platinum-Group Element Data Using Inductively Coupled Plasma-Mass Spectrometry   总被引：1，自引：0，他引：1  

James C. Ely  Clive R. Neal 《Geostandards and Geoanalytical Research》2002,26(1):31-39

A data reduction method is described for determining platinum-group element (PGE) abundances by inductively coupled plasma-mass spectrometry (ICP-MS) using external calibration or the method of standard addition. Gravimetric measurement of volumes, the analysis of reference materials and the use of procedural blanks were all used to minimise systematic errors. Internal standards were used to correct for instrument drift. A linear least squares regression model was used to calculate concentrations from drift-corrected counts per second (cps). Furthermore, mathematical manipulations also contribute to the uncertainty estimates of a procedure. Typical uncertainty estimate calculations for ICP-MS data manipulations involve: (1) Carrying standard deviations from the raw cps through the data reduction or (2) calculating a standard deviation from multiple final concentration calculations. It is demonstrated that method 2 may underestimate the uncertainty estimate of the calculated data. Methods 1 and 2 do not typically include an uncertainty estimate component from a regression model. As such models contribute to the uncertainty estimates affecting the calculated data, an uncertainty estimate component from the regression must be included in any final error calculations. Confidence intervals are used to account for uncertainty estimates from the regression model. These confidence intervals are simpler to calculate than uncertainty estimates from method 1, for example. The data reduction and uncertainty estimation method described here addresses problems of reporting PGE data from an article in the literature and addresses both precision and accuracy. The method can be applied to any analytical technique where drift corrections or regression models are used.  相似文献   

有限元分析方法在黄土地基震陷预测中的应用   总被引：1，自引：0，他引：1       下载免费PDF全文

张冬丽  王兰民  王玉华 《地震工程学报》2002,24(3):208-214

将有限元方法应用于黄土地基的震陷量预测，定量地研究了黄土地基地震沉陷特性与场地条件、基础形式、土动力特性等因素的相关关系，为黄土地基基础的抗震增稳设计与处理提供了科学依据。  相似文献   

天祝-古浪5.4级地震震源机制和发震断层以及海原西断裂大震危险性讨论          下载免费PDF全文

李亚荣  朱新运 《地震工程学报》2002,24(3):236-240

研究了发生在海西断裂天祝拉分盆地1996年6月1日5.4级地震的震源机制，利用位于天祝－古浪地区的数字式微震监测台网纪录的余震的精确定位确定了本次地震的发震断层，研究表明这次地震是天祝拉分盆地中垂直于主断裂的近南北向断裂所形成，根据破裂模型和海原西断裂的应力积累状况，讨论了海原西断裂近期的大震危险性。  相似文献   

山西水2井和岳42井水位记震能力分析   总被引：2，自引：1，他引：2       下载免费PDF全文

张子广  张素欣  郑云贞  王贺生 《地震工程学报》2002,24(3):262-266

对比分析了唐山地区同一地质单元内、同一观测含水层、水位动态相同的山西水2井和岳42井记录的水震波曲线，显示两井记震能力相差很大，从井孔结构、地震面波特性等方面分析了两井记震能力差异性的成因机理，结果表明，井孔的固有周期是影响水位记震能力大小的首要条件。  相似文献   

山西夏县台热水井水氡异常特征与地震的关系初探     

范玉俊  黄春玲 《山西地震》2002,(4):24-27

为弄清山西夏县中心地震台水氡震前异常的原因 ,对山西夏县中心地震台热水井水氡 1984年以来的观测资料用概率论的数据处理方法进行了处理 ,以负异常的发震原理进行了分析 ,结果表明震前负异常的发震概率为 70 %。  相似文献   

昆仑山口西8.1级地震前青海省形变及地温前兆特征分析   总被引：6，自引：0，他引：6  

张晓清  顾永康 《高原地震》2002,14(1):70-75

通过对青海省地倾斜、地应力、深井地温3种前兆手段在昆仑山口西8．1级地震前异常的分析与研究，得出了强地震远场前兆的一些初步特征，并与近场前兆异常特征做了比较，这对该省今后强震短期预报将是有益的。  相似文献   

以2000年4月29日河南内乡地震为例谈谈关于计算震级误差的有关问题     

谢智  刘尧兴  谢健健  许孝法  王世昌 《华南地震》2002,22(3):52-57

2000年4月29日河南内乡发生地震，地这次地震，河南地震局台网和中国地震局台网震级量度之间有一定差异。采用不同量规函数和尾波持续时间震级公式计算发现，它们之间所产生的最大差异可达0.5-0.7级。综合分析后认为，2000年4月29日河南内乡地震震级定为ML5.0级较为适宜。  相似文献