共查询到20条相似文献，搜索用时 31 毫秒
1.
本文研究了溧阳两次地震的前震活动现象,发现溧阳两次地震的前震活动图象具有某些共性特征:(1)前震活动的时间尺度雷同;(2)前震活动频度和强度同具有时强时弱的分期活动特点;(3)震前孕震空区形态相似;(4)临震前地震活动同具有条带分布图象;(5)前震活动在时—空图形上分别形成“时—空”弯形平静区。溧阳两次同源地震前震活动图象具有共性特征这一客观事实,可能反映两次地震在同一区域应力场作用下具有类似的孕震破裂过程。追溯这些过程,它们可能同受震源区及其附近的同一介质和构造条件的制约。 相似文献
2.
3.
4.
例举了杭州地震台投入超低频数字地震电磁辐射仪（EMAOS-L）以来的两组临震前电磁辐射观测异常资料现象,并对观测资料进行了分析和探讨。 相似文献
5.
Vishal Chauhan O.P. Singh Vinod Kushwah Vikram Singh Birbal Singh 《Journal of Geodynamics》2009,48(2):68-74
Employing a three-component search coil magnetometer (f = 0.01–30 Hz) the ultra-low-frequency (ULF) magnetic field observations have been taken in a noise free rural site at Bichpuri, Agra, India since 20 April 2007. We have analysed 7 months of night time data from 01 May to 30 November 2007. The data show seven occurrences of ULF bursts with periods ranging from a few minutes to an hour in a wide frequency range up to 15 Hz. The occurrence of such ULF bursts has been statistically analysed. The polarization parameter analysis shows that two of these bursts occurred from sources in the ionosphere and magnetosphere (Z/X < 1). It is further seen that four bursts correlated very well with some regional earthquakes (M > 4.5), which occurred at distances less than 628 km from the observation site at Agra. In some cases the bursts occurred 1–3 days prior to the main shocks.Since earthquakes are also known to perturb the ionosphere, we have analysed total electron content (TEC) data obtained from a GPS receiver stationed at Agra since June 2006. Analysis of the data for the same period as the magnetic field observations shows that there existed TEC anomalies on all the days when ULF bursts occurred. The TEC anomalies show enhancement and depletion in the data in all cases. While the mechanisms of the ULF and TEC anomalies are not well known, it is expected that the ULF bursts occurred due to microfracturing of the earth's crust during stress accumulation and that the TEC anomalies occurred as a result of the electric field induced in the ionosphere during such processes. 相似文献
6.
Katsumi Hattori Peng Han Chie Yoshino Febty Febriani Hiroki Yamaguchi Chieh-Hung Chen 《Surveys in Geophysics》2013,34(3):293-316
In order to clarify the ultra low frequency (ULF) seismo-magnetic phenomena, a sensitive geomagnetic network has been installed in Kanto, Japan. In this study, we have analyzed geomagnetic data observed during the past decade in Izu and Boso Peninsulas. Energy of ULF geomagnetic signals at the frequency around 0.01 Hz has been investigated by wavelet transform analysis. To identify anomalous changes in ionospheric disturbances, the station Memabutsu has been chosen as a reference station. Case studies of magnitude 6 class earthquakes have demonstrated that there are unusual geomagnetic energy enhancements in the vertical component before the main shocks. Statistical studies by superposed epoch analysis have indicated that, before a sizeable earthquake, there are clearly higher probabilities of ULF anomalies than after the earthquake: statistical results of daily counts were found significant at about 3–4 weeks before, 1 week before, few days before, and 1 day after the event for Seikoshi station in Izu and around 2 weeks before, few days before, and 1 day after the event for Kiyosumi station in Boso, respectively. 相似文献
7.
通过吴忠—灵武地区现有的地震活动性资料,并结合该区域过去的几次中强震震例和已有的研究结果,本文梳理与总结了中强震前该区域地震活动乃至中国大陆大震活动的时空特征,而且基于最小完整性震级分析了1970—2019年该区域中小地震的地震活动性特点。综合认为,吴忠—灵武地区中强震的广义前震和中小地震的活动性具有较为鲜明的特征,中强震发生前1—2年内该区域及邻区形成ML2.0以上地震集中区或其西北方向的阿左旗腰坝区域大都出现ML3.0以上信号震,而且一年前其主震的广义前震的确比较发育,存在一定程度的地震增强;地震序列统计分析表明,该区域的多重共轭构造可能是其主要原因,其多震型、双震型和震群型占有相对较高的比例。另外,从大形势角度来看,过去大部分5级以上中强震发生的主导因素很可能由华北地块主导的强震活跃幕引起,该区域的强震危险性不仅仅和局部特殊构造特征、区域前震活动变化有关,更重要的是,华北—东北亚地块大震活动对其也起到了较大的影响作用,相比而言,青藏高原、龙门山断裂带及祁连山构造带等区域的大震活动对吴忠—灵武地区中强地震触发影响不显著,而且吴忠—灵武地区的中强地震活动和华北—东北亚地块的大震活动可能存在一定的构造响应。 相似文献
8.
依据地震破裂、地震形变带、前震和余震分布,对中国大陆共轭破裂强震进行了初步研究。结果表明,强震共轭破裂现象较普遍,据资料至少有12个单强震、7个双主震和2个主震——强余震为共轭破裂强震。其共轭破裂特征在地震形变带展布、烈度等震线形态、前震和余震分布等方面表现明显。另外,共轭破裂强震具有共轭破裂面方位之一多为北北西向、双主震之间和主——强余震之间相隔时间为“7”和“9”的节律这2个主要的共同点。 相似文献
9.
The seismic regime taking place before the Tohoku mega-earthquake was studied using the catalog of the Japan Meteorological Agency (JMA). We show that the Tohoku earthquake was preceded by a 6–7-year period of regional reduction in the b-value and in the rate of main shocks. The space-time regions that involved precursory activation were nearly identical with the predictive phenomena that were previously detected by A.A. Lyubushin from an analysis of seismic noise based on data from the Japanese F-net. We discovered a previously unknown effect of correlation between the number of main shocks and the b-value. Both the ordinary foreshock activation and the longer weaker tendency, which consist in a precursory increase in the seismicity rate, were identified in the vicinities of M ≈ 7 Japanese earthquakes (similarly to the seismicity in the Generalized Vicinities of large earthquakes based on worldwide data). 相似文献
10.
Ultra low frequency electromagnetic wave anomaly and its spectrum characteristics before earthquakes 总被引：1，自引：0，他引：1
Jian-Guo Hao Yun-Fu Zhang Huai-Wen Pan De-Rui Li Tian-Ming Tang Xiao-Qin Liu 《地震学报(英文版)》1995,8(1):101-109
Many observations and researches show that abundant and intense ultra low frequency (ULF) electromagnetic anomalies appeare
before local earthquakes. In order to understand this phenomenon systematically, the transmission property and the formation
of the seismic-electric dipole are discussed in this paper. The results show that the vertical component of the ULF electric
anomaly before earthquake has the properties of better penetration, less disturbance and high signal-to-noise ratio. The signal
can be easily extracted and received. The anomaly should be an important way to seek for reliable short-term and imminent
earthquake precursors. After the spectrum analysis of the (ULF) electric field anomalies, we found that the periods of the
anomaly related to local earthquakes are from a few minutes to a dozens minutes. There is a relation between the spectrum
of the anomaly and the epicentral distance. The ULF electric field anomalies strongly rely on the orientation of the seismogenic
zone. The percolation electric field anomaly and its spectrum amplitude do not have obvious relation with the size of local
earthquakes.
Contribution No. 94A0097, Institute of Geophysics, SSB, China.
The English version is improved by Prof. Guo-Hua FAN, Institute of Geophysics, State Seismological Bureau. 相似文献
11.
Pattern Characteristics of Foreshock Sequences 总被引：1，自引：0，他引：1
—Earthquake clusterings in both space and time have various forms, in particular, two typical examples are the foreshock sequences and earthquake swarms. Based on the analysis of 8 foreshock sequences in mainland China during 1966–1996, this study concentrates on the pattern characteristics of foreshock sequences. The following pattern characteristics of foreshock sequences have been found (1) the epicenters of foreshock sequences were densely concentrated in space; (2) the focal mechanisms of foreshocks were similar to that of the main shock. Such consistency of focal mechanisms with main shocks did not exist in aftershock series as well as in several earthquake swarms; (3) we found no case in mainland China during the past thirty years that a main shock is preceded by an earthquake clustering with inconsistent focal mechanisms. Finally, we found 5% of the main shocks in mainland China are preceded by foreshock sequences. 相似文献
12.
13.
介绍了当前国内外前震研究领域的一些进展。 对比了不同前震定义条件下前震序列的共性特征, 对几种主要的前震机理及主要的前震识别方法进行了简要综述, 对其特点及存在的问题进行了评述和讨论。 前震指主震之前在主震断层面上、 紧邻主震破裂起始点发生的小地震。 主震发生之前的一系列前震活动构成前震序列。 在不同的前震定义条件下, 具有“直接前震”的震例比例从10%至40%不等。 理论上前震可用级联应力触发或预滑动模型进行解释。 前震空间上主要集中分布在距离主震10~75 km范围内, 但其时间分布形式复杂, 大多发生在主震前1~2天, 部分前震序列的地震活动率显示明显的加速特征, 但许多前震序列单独来看却往往显示主-余型序列的衰减特征。 序列地震震源机制一致、 序列b值偏低是前震序列最突出的特征。 前震的发生与主震破裂形式和构造环境似有一定关系, 在有限的前震震例中, 逆冲型主震似乎具有相对较多的前震。 部分震例的研究结果显示, 随主震的临近, 前震震源深度有逐渐下迁的特点。 到目前为止, 震前很难判定一次地震或一个地震序列是否为前震或前震序列, 所使用的前震识别主要有基于统计类比的方法、 基于震源机制一致及衍生的相关方法以及基于对地震成核过程精细检测的方法。 从现有不多的震例研究结果来看, 尽管地震时空丛集和震源机制高度一致是前震序列的最显著特征, 但却不是判定前震序列的充分条件。 由于成核的破裂扩展速度和滑动位移有随时间较快增大的趋势, 因而基于对地震成核过程精细检测的方法有望在前震识别中发挥更为重要的作用, 但需更多震例进行验证。 相似文献
14.
15.
16.
强震发生前震源及其周围地区可能会出现前震活动, 这种前震活动可以分为二种: 一种为连续型, 即前震的频度或震级随时间渐渐增大, 直至主震发生; 另一种为不连续型, 前震的频度和震级先增大后减小, 然后发震。 这种现象不但在破裂声发射试验中观测到, 也在中国大陆地区多次强震前被观测到。 文中基于细胞自动机模型, 引入时间-状态依从摩擦本构关系, 即把自组织非线性系统的普适特征与真实断层摩擦的具体特征结合起来, 研究了强震前短期前兆地震活动的时间演化过程的机理。 文中研究了模型中各参数对模拟事件时间过程的影响, 结果表明, 静摩擦强度在断层上的分布, 或是说静摩擦系数的离散程度直接影响强震前地震活动时间演化过程。 相似文献
17.
2008年5月12日T14:28汶川发生8.0级大地震,2008年5月13日T5:00江苏省发生滨海ML3.8地震。滨海地震是否是由汶川地震触发的、可指示滨海附近中短期内将发生中强地震的"诱发前震"?基于此,本文进行了如下研究:①统计南北地震带及中国台湾7.3级以上、日本7.5级以上大地震;②统计①中大震发生后3天时间(72 h)内,华北中南部地区发生的M_L 3以上地震;③统计大震发生后1年内在M_L 3地震附近地区(距震中350 km以内)发生的5级以上地震;④对上述3组地震是否存在链式关系进行统计研究,即研究特定条件下的A—F—B链式地震现象在华北中南部的预报效果。研究结果表明:根据目前所拥有的统计资料,无法确定2008年5月13日滨海M_L 3.8地震是由汶川8级地震诱发的"前兆地震"。 相似文献
18.
1989年到1999年,大同—阳高地区发生了一系列MS≥5的中强地震.本文基于前人对1989年三次MS≥5地震的震源机制反演的结果,通过建立不同断层模型,利用库仑应力方法,计算前震对于主震,以及前震和主震对于余震的库仑应力触发关系,提出了一种可能的破裂模型,即1989年前震沿北西西方向发生左旋破裂,之后主震和余震沿北北东方向发生右旋破裂.根据这种破裂模式计算得出,前震发生后,主震震源处的库仑应力增加了约2×105 Pa,余震震源处的库仑应力出现下降;主震发生后,余震处的库仑应力出现回升,最后余震处的库仑应力几乎没有变化.基于大同地震台网的近场观测数据,用JHD(Joint Hypocentral determination)定位方法,对1999年11月1日MS=5.6地震后一个月的余震进行重定位,得到一条走向118°,倾角85°的左旋走滑断层,余震的深度分布在5km至20km范围内,显示该断层是隐伏断层.另外提出对主震震中位置约10km的修正.本文对1989年三次MS≥5地震序列和1999年MS=5.6地震余震空间分布的研究揭示该地区存在两条活跃的共轭隐伏走滑断层(1989年主震的北北东方向和1999年地震的北西西方向),并且推断已知的大王村断裂和团堡断裂是地下这两条共轭的隐伏走滑断层构造/地震活动在地表的响应. 相似文献
19.
20.
On September 3rd (22:07 UTC), 1997 a small earthquake with Mw=4.54 started the foreshocks sequence (1500 events with ML <3.1) of the September 26th seismic sequence. Two days after, three seismic stations of the University of Camerino were installed around the macroseismic epicenter of the foreshock. We present in this paper the location of foreshocks (with 2.1L<3.3) which occurred between September 3rd and 26th. Foreshocks location, with horizontal (ERH) and vertical (ERZ) error less than 1.5 km, define an area 4 km large. Foreshocks have been localized between the epicenters of the two major events of September 26th, which occurred at 00:33 UTC with Mw=5.6 and at 09:40 UTC with Mw=6.0 (Amato et al., 1998; Ekström et al., 1998). In a vertical cross-section, hypocenters show a low angle (30°) structure with SW dip-direction. Focal mechanisms for three of the major events show dip-slip fault solutions with strike direction of about N130, in agreement with the CMT solutions of September 3rd and September 26th earthquakes (Ekström et al., 1998). Data recorded at two stations Popola (POP) e Capodacqua (CPQ) located on the rupture area of the September 26th faults, allowed us to calculate a mean Vp/Vs ratio of 1.84±0.03 for the foreshock. This value is lower than the Vp/Vs ratio of 1.89±0.02 calculated for the aftershock sequence occurred in the same area. Besides, the Vp/Vs ratio during the foreshocks sequence is not stable in time but it seems to increase approaching September 26th. After September 26th mainshocks, this value tends to stabilize around a higher value of 1.89. Following the dilatancy model, we suggest that the relative low Vp/Vs ratio before the main shocks could indicate the presence of fluid in the focal volume. The presence of fluids could have increased the effective stress on the fault plane and could be responsible for the long foreshock activity before the two main earthquakes of September 26th. Therefore, we suggest that this foreshock activity could have also contributed to reduce the friction along the September 26th fault plane, breaking the active structure in two smaller segments. In this hypothesis, foreshock activity could have drastically contributed to mitigate the seismic potential of the Colfiorito's active structure. 相似文献