汶川Ms8．0地震的短临地电波动（潮汐力谐振和共振波-HRT波）前兆   总被引：2，自引：0，他引：2  

钱复业  赵璧如  钱卫  赵健  何世根  李世愚  孙振凯  张东宁  张洪魁  卢军  李绍坤  郭纯生  夏坤寿  徐建明  鞠航  黎明  和泰名  唐宇雄  张平  赵玉林 《国际地震动态》2008,(7)

简要介绍了强震短临前兆的HRT波模型,和用HRT波模型分析强震前地电观测资料预测未来强震的时间、地点、震级三要素方法。用HRT波模型分析了2008年汶川MS8.0地震前四川红格地电台的记录资料,提取出了汶川MS8.0地震前短临前兆信息。  相似文献   

Swarms of similar long-period earthquakes in the mantle beneath Mauna Loa Volcano     

Paul G. Okubo  Cecily J. Wolfe 《Journal of Volcanology and Geothermal Research》2008

We present analyses of two swarms of long-period (LP) earthquakes at > 30 km depth that accompanied the geodetically observed 2002–2005 Mauna Loa intrusion. The first LP earthquake swarm in 2002 consisted of 31 events that were precursory and preceded the start of Mauna Loa inflation; the second LP swarm of two thousand events occurred from 2004–2005. The rate of LP earthquakes slowed significantly coincident with the occurrence of the December 26, 2004 M_w 9.3 Sumatra earthquake, suggesting that the seismic waves from this great earthquake may have had a dynamic triggering effect on the behavior of Mauna Loa's deep magma system. Using waveform cross correlation and double difference relocation, we find that a large number of earthquakes in each swarm are weakly similar and can be classified into two families. The relocated hypocenters for each family collapse to compact point source regions almost directly beneath the Mauna Loa intrusion. We suggest that the observed waveform characteristics are compatible with each family being associated with the resonance of a single fluid filled vertical crack of fixed geometry, with differences in waveforms between events being produced by slight variations in the trigger mechanism. If these LP earthquakes are part of the primary magma system that fed the 2002–2005 intrusion, as indicated by the spatial and temporal associations between mantle seismicity and surface deformation, then our results raise the possibility that this magma system may be quite focused at these depths as opposed to being a diffuse network. It is likely that only a few locations of Mauna Loa's deep magma system met the geometric and fluid dynamic conditions for generating LP earthquakes that were large enough to be recorded at the surface, and that much of the deep magma transfer associated with the 2002–2005 intrusion occurred aseismically.  相似文献   

福州电磁波异常与闽台地震的相关性研究     

陈小云 《国际地震动态》2008,(1):9-13

利用福州电磁波观测资料,对给定时段内、范围内的闽台地区地震进行相关分析,找出福州电磁波异常与地震的相关系数,探讨福州电磁波异常信息的映震效能,为今后利用电磁波观测资料异常信息进行临震预报提供科学依据。  相似文献   

Volcanic tremor and local earthquakes at Copahue volcanic complex, Southern Andes, Argentina     

J.M. Ibez  E. Del Pezzo  C. Bengoa  A. Caselli  G. Badi  J. Almendros 《Journal of Volcanology and Geothermal Research》2008,174(4):284-294

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Precursory seismicity of the 1994 eruption of Popocatépetl Volcano,Central Mexico   总被引：1，自引：1，他引：0  

Servando De la Cruz-Reyna  Izumi Yokoyama  Alicia Martínez-Bringas  Esteban Ramos 《Bulletin of Volcanology》2008,70(6):753-767

Popocatépetl Volcano is located in the central Mexican Volcanic Belt, within a densely populated region inhabited by over 20 million people. The eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions, including Plinian events. After nearly 70 years of quiescence, Popocatépetl reawakened in December 21, 1994. The eruptive activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth-and-destruction episodes, similar to events that have apparently been typical for Popocatépetl since the fourteenth century. In this regime, the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence. In this paper we analyze five years of volcano-tectonic seismicity preceding the initial eruption of the current episode. The evolution of the V-T seismicity shows four distinct stages, which we interpret in terms of the internal processes which precede an eruption after a long period of quiescence. The thermal effects of a magma intrusion at depth, the fracturing related to the slow development of magma-related fluid pathways, the concentration of stress causing a protracted acceleration of this process, and a final relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of V-T seismic energy release. A hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically forecast the time of the eruption. The total seismic energy release needed to produce an eruption after a long period of quiescence is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes, limit that was reached by Popocatépetl before the eruption.  相似文献   

8级特大地震前地震活动平静特征——以中国大陆西部近期2次8级地震为例     

陈玉华  马震 《高原地震》2008,20(4):1-7

中强地震平静图像已被许多研究者认为是强震前的一个典型异常指标。近期中国大陆西部2次8级地震前地震活动图像的研究认为,8级特大地震前不仅中强震出现大面积平静,而且中小地震也会出现大规模平静现象,形成地震空区。震前依据震级由大而小逐级形成配套出现的地震空区,可作为中国大陆西部8级特大地震的中短期预测与8级地震发生地区的判定的一项有实际意义的指标。  相似文献   

汶川8.0级地震前BSQ型数字垂直摆倾斜仪观测到的地形变异常现象     

荆燕  张鸿旭  孙毅  李宏  范良龙  熊玉珍 《高校地质学报》2009,15(3):358

地倾斜连续观测是地壳形变观测研究中重要内容。汶川8.0级地震前,布设在四川德阳金河测点的新型BSQ型数字垂直摆倾斜仪观测到了明显的地形变异常现象。分析其观测结果可知,汶川8.0级地震前约半月时间内德阳金河测点的地倾斜运动速度较过去的平均运动水平提高了数十倍,且震前地表快速倾斜的方向在N25°W左右。除此之外,德阳金河BSQ型数字垂直摆倾斜仪测点还观测到较为完整的,对应于可以反映地表应力集中、释放过程的震前地表破裂过程。上述现象为今后研究强震孕育机理提供了重要的信息。介绍与分析了布设在龙门山断裂带附近的其它类型地倾斜仪在震前的观测结果。事实证明,BSQ型数字垂直摆倾斜仪在强震前的浅表过程监测中具有重要意义,值得在今后的地震前兆台网工作中进行推广。  相似文献   

Crustal shear-wave splitting in the epicentral zone of the 2001 Mw 7.7 Bhuj earthquake, Gujarat, India     

Prantik Mandal   《Journal of Geodynamics》2009,47(5):246-258

We report here crustal shear-wave anisotropy, ranging from 1% to 10.76% with an average of 2.4% in the aftershock zone of the 2001 Bhuj earthquake, Gujarat, India, from a study of leading shear-wave polarization directions (LPSDs), which vary on average from NNW–SSE to E–W with a delay of 0.07–0.14 s. The delays in the NNW–SSE to NE–SW directions observed at seven stations, near the seismogenic fault, suggest cracks parallel to the direction of the maximum horizontal regional compressional stress prevailing in the region, suggesting a dilatancy-induced anisotropy resulting from approximately stress-aligned parallel vertical micro-cracks. In contrast, the LPSDs at Ramvav, Rapar and Vondh stations, away from the seismogenic fault, are fault parallel, approximately E–W and almost orthogonal to the stress-aligned polarizations inferred elsewhere. The maximum average time delay of 0.14 s is observed at Lodai, where the fast polarization direction is found to be N338°W. This has been observed from anisotropic poro-elastic (APE) modelling and observations that these are 90° flips in shear-wave polarization, resulting from propagation through micro-cracks containing fluids at critically high pore-fluid pressure surrounding the hypocenter of the 2001 mainshock. The presence of high pore-fluid pressure in the seismogenic fault zone could also explain the observed scatter in shear-wave time delays. Further, the coincidence of the N–S trending intrusive bodies (as inferred from tomographic studies in the area) with the N–S direction of regional maximum horizontal compressional stress supports the interpretation of stress-aligned vertical extensive-dilatant anisotropic (EDA) cracks. The depth distribution of the estimated anisotropy (1–10.76%), b-values and stress drop values suggests an increase at 18–30 km depths, which could be attributed to high pore-fluid pressures resulting from a fluid-filled fractured rock matrix or open micro-cracks (characterized by high crack density and high porosity) coinciding with a low velocity zone (at 18–30 km depths) as delineated from tomographic studies in the area.  相似文献   

2003年大姚6.2级、6.1级地震序列震源位置及震源区速度结构的联合反演   总被引：5，自引：0，他引：5  

周龙泉  刘杰  马宏生  周俊杰 《地震》2009,29(2)

采用震源位置和速度结构的联合反演方法确定2003年大姚6.2级、6.1级地震序列的分布和震源区的速度结构.该方法首先确定研究区的速度结构,然后在该速度结构的基础上对地震重新定位.结果表明:① 大姚6.2级地震序列明显分为地震较密集的东南段和地震较稀疏的北西段,而且这两段存在一定的错动,速度结构也显示出高、低速交界带在错动处具有转折特点;② 大姚6.2级地震序列在深度上呈"V"字形分布,这与该地区呈倒三角形分布的低速体相对应,即余震主要分布在高、低速交界带附近;③ 大姚6.2级、6.1级地震的破裂区都位于倒三角形低速体的东南侧,6.2级地震沿高、低速交界带往下破裂,而6.1级地震沿高、低速交界带往上破裂;④ 6 km深度的速度分布显示震源区具有高、低速度体交替呈四象限分布特征,而且余震主要沿北西向的高低速交界带分布;⑤ 大姚6.2级主震的东南侧的高、低速交界带处的低速体速度值较北西侧低速值高,其对6.2级地震往东南方向破裂具有阻碍作用,即东南侧处于能量积累状态,有利于6.1级地震的发生.  相似文献   

江苏及邻区中小地震能量场的时空变化分析     

王俊  孙业君  詹小艳  郑江蓉  江昊琳  霍祝青 《中国地震》2009,25(4)

采用随机能量场的概念,将地震活动能量场看作时间和空间的随机函数场,用自然正交函数展开的分析方法,研究江苏及邻区自1970年1月至2007年12月的中小地震(2.1≤M_L≤4.5)能量场变化特征,以及主要典型能量场的时间"权重"系数的变化特征.结果显示:前7个典型场的展开精度为0.9244.研究区内不同构造块体的地震活动能量场强度存在明显差异,其中下扬子块体的苏中、苏南地区及南黄海海域的地震背景能量值高于其他地区;从典型场的分布来看,该区域对研究区能量场的影响也最为显著.前6个主要典型场的时间"权重"系数随时间的变化幅度与研究区大部分中强震之间在时间上存在很强的相关性.  相似文献