共查询到18条相似文献,搜索用时 156 毫秒
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选取1970年至1999年晋冀蒙三省交界4次中强地震事件,进行地震视应变演化分析。得出,地震视应变异常与晋冀蒙三省交界区中强以上地震具有较好的对应关系。震前,晋冀蒙三省交界区地震视应变演化模式有:增强-减弱-发震、增强-减弱-迁移-发震、增强-减弱-消失-增强-发震、增强-减弱-维持-发震。"大同窗"必是异常区,其震前地震视应变演化模式有:增强-维持-消失-发震、增强-减弱-发震、增强-维持-减弱-发震。异常区多形成于震前3年,随着时间的推移,有扩散或向特定方向(震源方向)迁移的特征。中强地震多发生在视应变高值异常区、视应变高值异常迁移区、视应变高值异常区迁移的方向。 相似文献
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利用湖南省地震台网记录到的资料,研究了1970年以来湖南地区五次ML≥4.0级地震的地震视应变场的分布和时空演化特征.ML≥4.0以下的地震视应变与震级相关性较小,ML≥4.0以上地震的视应变值随震级增加呈非线形快速增大,说明:湖南地区地震视应变的时空演变与地震具有较好的对应关系. 相似文献
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本利用山东,江苏省地震台网的资料,对苍山5.2级地震前沂沭带南段地震活动性参 的变化特征进行了分析研究。发现苍山5.2级地震前沂沭带南段3、4级地震活动增强,应变能释放速率加速,地震波速比的时空变化,震前出现明显的低值异常时段和低值异常区。据比异常变化曾在震前提出过预报意见。 相似文献
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1994年9月16日台湾海峡7.3级地震前的地震活动异常 总被引:1,自引:0,他引:1
应用“八五”地震攻关成果及相关软件,对1994年9月16日台湾海峡7.3级地震前震中周围中小地震活动性能量的计算分析表明,震前震中及邻区地震活动明显增强,累计频度和应变释放产生突变,从1991年起出现孕震空区,多项地震活动参量在时空方面中短期异常显著。 相似文献
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通过对广西及邻区(以下简称研究区)地震活动的背景,包括研究区地震活动特征、断裂带的分布、主压应力轴方向与强震发生的主体地区、地震活动时空扫描异常特点、强震发生的时间特点进行了分析,说明该地区存在发生中强震的可能。并对2004年广东阳江4.9级2、005年云南文山5.3级、2005年广西平果4.4级地震前的异常进行了分析,说明研究区地震活动特征显著。同时获得了区域中强以上地震前的主要异常指标,对今后地震预测有一定指导意义。 相似文献
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许多学者认为2008年汶川8级地震可能对龙门山断裂带及其周围不同断裂带上后续发生的6级以上地震有一定的影响.本文以地震应变场作为地震活动的变量,通过自然正交函数展开方法,研究2008年以来龙门山断裂带周围5次6级以上地震前的地震应变场,提取出震前应变场时空异常的变化.结果表明:(1)2008年汶川8.0级地震前和2013年芦山7.0级地震前地震应变场时间因子分别出现明显的中短期异常和短临异常;而2013年岷县漳县6.6级地震前、2014年康定6.3级地震前和2017年九寨沟7.0级地震前地震应变场时间因子中短期异常不明显,分析其原因主要是受到2008年汶川8.0级地震应变场时间因子最大幅度异常的影响.(2)研究应变场时间因子对应的区域空间等值线变化,发现2009年以后地震应变场空间等值线高值异常区以及异常区周围发生的强震,均可能受到2008年汶川8.0级地震应变场的影响.(3)最后分析1970年以来龙门山断裂带周围地震应变的空间演化过程,总结强震应变变化特征的发震模式,从地震应变演变角度探讨强震之间的相互影响,以及断裂带所在块体间的相互牵制和调整作用. 相似文献
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应用广东数字遥测地震台网的数字化的地震形资料,研究阳江地震前,地震波波形时间线性度、平均半周期和地震波波形空间线性度等地震波参数变化特征。结果表明,震前半年时间内,上述地震波参数不同程度地出现下降异常。利用线性偏振度自动检测的P、S波初至具有可靠的精度,为广泛利用地震波参数预报地震提供了方便。 相似文献
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华北地震活动中短期异常图像研究 总被引:2,自引:0,他引:2
系统研究了多种地震活动性方法后认为, 1970年以来华北地区发生的MS≥5.8中强震前, 约83%具有3级或4级地震异常条带、 孕震空区及信号震出现。 震前有信号震的比例占92%, 83%的信号震距主震150 km以内, 距主震发生时间小于1年的占67%。 条带时间形成进程在2年内的约占90%, 震前条带形成后到主震发生83%在5个月内。 空区形成进程在1年半内的占83%, 空区形成后到主震发生91%在50天内, 为有意义的地震活动图像短期异常特征。 文中还探讨了异常条带图像的定量判别指标及其与未来强震的关联。 相似文献
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On the basis of our predecessors' research,we study the distribution and the space-time evolution characteristics of the seismic apparent strain field in Yunnan since the 1970's using the seismic data of Yunnan and its surrounding areas.The result shows that there is a rather strong corresponding relationship between the anomaly region of seismic apparent strain and strong earthquakes.In the nine earthquakes studied,anomaly areas of seismic apparent strain had appeared before eight earthquakes,including five occurring in the anomaly region and three on the edge.Finally,the investigative result is demonstrated primarily. 相似文献
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1987年8月2日,江西省寻邬发生MS5.5地震。本文研究了这次地震和震前的各种异常现象,研究发现,震前该区地壳形变和震活动出现了中、长期同步变化,短临阶段,出现了异常地震活动和宏观现象。根据岩石破裂实验结果和地震前兆理论,对这次地震的孕育过程作了阶段性的划分。 相似文献
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本文基于自然正交函数展开方法, 以地震应变为变量, 计算1980年以来中国大陆7级以上大震前的地震应变, 提取出大震前区域地震活动应变场的时空异常。 结果表明大震前时间因子在平稳背景上会出现突跳上升或突跳下降异常变化。 一般情况下, 前4个应变场中至少有3个出现异常变化, 异常分布具有多分量特点, 出现的最早时间大约在震前3年, 少数出现在震前1~6个月。 对比应变场时间因子异常与研究区域每个网格单元(0.5°×0.5°)内的地震能量时间因子异常形态的相似性、 时间的一致性, 找出地震应变场空间异常位置。 结果表明, 多数大震前的空间异常分布在主震震中周围; 少数大震的空间异常远离主震震中。 产生这种现象的原因是大震前与主震不同距离的单元网格内发生中短期或者临震的震群、 显著地震等地震活动性异常。 相似文献
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S. R. Steele 《Pure and Applied Geophysics》1984,122(2-4):353-368
Anomalous soil-radon activity, including several spike-like surges over periods of 5, 2, and 2 1/2 months, and a year-long declining trend, preceded the most significant earthquakes of the central mid-continental region of North America during 1981 and early 1984. The 5-month period of erratic weekly radon activity, February–June 1981, was followed by a tremor of magnitudeM=4.0, 40 km from the monitoring site in the New Madrid seismic zone. An unusual earthquake swarm in central Arkansas, 160 km from the New Madrid seismic zone and 230 km from the monitoring site in the seismic zone, began in January 1982, shortly after a year-long declining trend in anomalous radon emanation. Earthquakes of magnitudes 4.5, 4.1, and 4.0 occurred at the swarm's outset in early 1982, fitting a pattern anticipated for the New Madrid seismic zone on the basis of the radon activity. Two periods of coincident peak radon emanation have since been observed in the Arkansas and New Madrid seismic regions, as have synchronous seismic pulses for the two separate areas.Two more recent periods of highly erratic soil-radon emanation, March–May 1983 and November–January 1984, were followed by a 4.3 earthquake in southwestern Illinois on 15 may 1983, and 3.5–3.6 tremors and swarm activity in the New Madrid seismic zone in late January and mid-February 1984. Prior to the 4.3 event, radon peaked at three widely separated monitoring sites 1–3 weeks before the tremor at distances of 120, 225, and 320 km from the epicentral region, the station at 225 km, in the New Madrid seismic zone, recording the longest period of anomalous radon activity. As for the recent 3.5–3.6 tremors of 1984, seismic activity of this magnitude had been anticipated for January or February on the basis of the amplitude of the November radon anomaly.These observations provide further evidence of (a) the existence of soil-radon anomalies precursory to the large earthquakes in this intraplate region, (b) the utility of such anomalies in anticipating events of small to moderate magnitudes for the region, and (c) the occurrence of regional-scale strain events prior to some of the larger mid-continental earthquakes.A very recent radon anomaly, the strongest yet to be detected in the seven years of monitoring in the mid-continental region, occurred in the New Madrid seismic zone from mid-February through mid-June 1984. A 4.0 earthquake occurred one month after a peak in the radon activity. The amplitude and duration of the anomaly suggest that a significant change in the state of stress or strain may have occurred in the mid-continental region during 1984. 相似文献
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Geodetic deformation vs. seismic strain deduced by historical earthquakes across the Alborz Mountains 总被引:1,自引:0,他引:1
Mohammad Reza Zolfaghari 《Journal of Seismology》2009,13(4):647-663
Historical seismicity is used in order to map spatial distribution of seismic moment released by past earthquakes and to compare
strain rate deduced from seismicity to those measured by geodetic GPS survey. Spatial analyses are performed on the seismicity
of northern boundary of Central Iranian Block which coincides with the Alborz Mountains. This belt has been responsible for
several catastrophic earthquakes in the past. In this study, the records of historical and instrumental earthquakes in the
Alborz Mountains are used to calculate and plot geographical distribution of seismic moment released in time. A two-dimensional
distribution function is proposed and used here to spread seismic moment along causative tectonic features. Using accumulated
seismic moment, average slip rates across active faults are estimated for 32 sub-zones along the Alborz Mountains and western
Kopet Dag. Seismic moment released by historical and recent earthquakes on this belt accounts for slip rate of 3–5 mm/year
which is in good agreement with the geodetic vectors recently deduced from GPS survey in this region. The study also reveals
geographical variations of slip rates along some 900 km length of this zone based on seismic history. The results are compared
against finding from similar study in this region. Portions of Central and Eastern Alborz show lower seismic strain rate which
could imply aseismic motion or overdue earthquakes. Completeness of historical earthquake catalogue and its reliability with
regard to earthquake magnitudes, locations, and rupturing systems are among many plausible factors controlling the credibility
of such results. Therefore, any conclusions derived from these results remain as reliable as the data and assumptions used
for the analyses. 相似文献