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61.
62.
汶川强余震流动观测与典型余震记录分析 总被引:1,自引:0,他引:1
2008年5月12日汶川大地震发生后,我国大陆的固定强震动台网获得了大批的主震加速度记录,中国地震局同时迅速组织开展了余震强震动流动观测任务.通过结合汶川地震余震趋势及其空间分布特征,此次流动观测沿龙门山断裂附近布设了59台强震动仪器,观测期间发生了超过万余次的余震,并获得了3000多组3分量的强余震记录.本文选取了4次震级为6.0左右的较强余震中获取的强震动记录进行简要谱分析及衰减关系对比,旨在为进一步结合主震记录,研究近场地震动特性、地震动衰减规律等地震工程相关的科研工作提供宝贵的基础资料.最后本文针对此次流动观测部分记录出现的异常现象进行初步探讨,给出了两种解释原因.汶川地震的流动观测充分表明,在大地震发生后,及时有效地开展强震动流动观测是十分必要的. 相似文献
63.
We use the slowness-azimuth station correction (SASC) method to improve the location accuracy of the Wenchuan aftershocks recorded by the Nagqu and Hotan seismic arrays. The results show that the standard deviations of back-azimuth and slowness errors of Wenchuan aftershocks recorded by the Nagqu array decreased by 32% and 58% respectively after correction. The decrease is 38 % and 71% for the Hotan array. After the correction, the location accuracy of all Wenchuan aftershocks recorded by the Nagqu array is improved. For the Hotan array, the accuracy is improved in the slowness estimation for 78 % of aftershocks and in back-azimuth estimation for all aftershocks. 相似文献
64.
Aftershocks of the 2011 Tohoku-Oki great earthquake have a wide range of focal depths and fault plane mechanisms. We constrain the focal depths and focal mechanisms of 69 aftershocks with M w > 5.4 by modeling the waveforms of teleseismic P and its trailing near-surface reflections pP and sP. We find that the “thrust events” are within 10 km from the plate interface. The dip angles of these thrust events increase with depth from ~5° to ~25°. The “non-thrust events” vary from 60 km above to 40 km below the plate interface. Normal and strike-slip events within the overriding plate point to redistribution of stress following the primary great earthquake; however, due to the spatially variable stress change in the Tohoku-Oki earthquake, an understanding of how the mainshock affected the stresses that led to the aftershocks requires accurate knowledge of the aftershock location. 相似文献
65.
We analysed aftershocks recorded by a temporary digital seismic network following the moderate M w = 5.5 1993, Scotts Mills, Oregon, earthquake. A technique to retrieve source moment tensors from local waveforms was developed, tested, and applied to 41 small earthquakes ( M w ranging from 1.6 to 3.2). The derived focal mechanisms, although well resolved, are highly variable and do not share a common nodal plane. In contrast, the majority of the events, relocated with a joint hypocentre determination algorithm, collapse to a well-focused plane. The incompatibility of the nodal planes of most events with the plane defined by their locations suggests that the aftershocks did not occur on the fault plane, but tightly around it, outlining the rupture area rather than defining it. Furthermore, the moment tensors reveal stable P -axes, whereas T -axes plunges are highly dispersed. We detect a rotation of average T -axis plunge with depth, indicating a change from shallower, predominantly dip-slip mechanisms to deeper strike-slip mechanisms. These characteristics are difficult to explain by remnant stress concentrations on the main-shock rupture plane or asperity- and barrier-type models. We suggest that the aftershocks occurred under the ambient regional stress, triggered by a sudden weakening of the region surrounding the main-shock slip, rather than from a shear stress increase due to the main shock. 相似文献
66.
We consider a general stochastic branching process,which is relevant to earthquakes as well as to many other systems, and we study the distributions of the total number of offsprings (direct and indirect aftershocks in seismicity) and of the total number of generations before extinction. We apply our results to a branching model of triggered seismicity, the ETAS (epidemic-type aftershock sequence) model. The ETAS model assumes that each earthquake can trigger other earthquakes (aftershocks). An aftershock sequence results in this model from the cascade of aftershocks of each past earthquake. Due to the large fluctuations of the number of aftershocks triggered directly by any earthquake (fertility), there is a large variability of the total number of aftershocks from one sequence to another, for the same mainshock magnitude. We study the regime in which the distribution of fertilities is characterized by a power law ~1/1+. For earthquakes we expect such a power-distribution of fertilities with =b/ based on the Gutenberg-Richter magnitude distribution ~ 10–bm and on the increase ~ 10–m of the number of aftershocks with the mainshock magnitude m. We derive the asymptotic distributions pr(r) and pg(g) of the total number r of offsprings and of the total number g of generations until extinction following a mainshock. In the regime < 2 for which the distribution of fertilities has an infinite variance, we find
This should be compared with the distributions
obtained for standard branching processes with finite variance. These predictions are checked by numerical simulations. Our results apply directly to the ETAS model whose preferred values =0.8–1 and b=1 puts it in the regime where the distribution of fertilities has an infinite variance. More generally, our results apply to any stochastic branching process with a power-law distribution of offsprings per mother 相似文献
67.
Earthquakes occurring during the night or early morning hours cause a heavy loss of life. Also, an earthquake occurring in the late evening hours poses serious handicap for disaster mitigation efforts due to failure of electricity and blocking of roads due to fall of debris. The larger aftershocks may cause further damage depending upon the magnitude of the main earthquakes of magnitude 5.5 and more in the Indian region. Out of 7 great earthquakes (M >7.8) in the Indian region during the last 200 years, five (1819, 1897, 1905, 1941 and 1950) have occurred during the evening or early morning hours. About 67% of all the earthquakes of magnitude >7.0 show similar result. It is found that in general, the percentage of earthquakes occurring during evening/early morning is larger than that during the daytime. However, the difference in time of occurrence is not significant at 95% level of confidence using 2 test. Keeping in view that most of the earthquakes in India of magnitude more than 6 have caused significant damage in the last decade (Uttarkashi, 1991; Latur, 1993; Jabalpur, 1997; Chamoli, 1999) and have occurred in the night/ early morning, disaster management plans need to be designed for awareness and education separately for the night and day times.The limitations of the seismic zoning map with reference to the earthquakes in Koyna (1967) and Latur (1993) have suggested to safeguard the life and property of the Indian population from the effects of future damaging earthquakes which should be failsafe instead of following the code and then introduce further changes in the code. It is suggested that residential houses (including tall structures) should be built for a design earthquake of magnitude 6.0 in all the three seismic zones namely I, II and III demarcated by the Bureau of Indian Standards giving proper weight age to site response. However, for Zones IV and V usual code recommendations may be followed through micro zoning of important, densely populated or most vulnerable areas. 相似文献
68.
By calculating the azimuth,phase angle and change rate of tidal force,and contrasting their rupture types,we find that in 6 of 11 reverse faulting earthquakes,the angles between the direction of the horizontal tidal force and compressive principal stress are within 33°,the vertical phase angles of all 8 strike-slip earthquakes are in the upward peak section and the vertical phase angles of two extensional normal faulting earthquakes are in the downward peak section.According to the above statistics,the mechanism of tidal force triggering of the Wenchuan MS8.0 Earthquake and its strong aftershocks is discussed. 相似文献
69.
??????????λ????2010-04-14??12-31?????????????????????????????λ??????????????????????????????????????????仯?й?????????????????????????????????????????????????????????????????????????????????????????????????????????????????-??????????????????????????????????????????-????????й?????????????????????????????????????????桱?й?? 相似文献
70.
2010年4月14日青海省玉树县发生Ms7.1级地震。利用地震前后2期ALOS雷达数据进行了地表同震形变场InSAR解译研究,获取了高质量的干涉图像,并解算出定量变形场。进而根据干涉计算的变形方向、变形范围、变形量和变形梯度,参考该区的构造背景和走滑断裂的力学机理对本次地震构造活动进行了分析并得出如下结论:1)玉树地震引发了地表NWW走向、由5段构成的“S”形走滑断裂,总体为左阶排列,走滑量从10.2 cm到133.2 cm不等,走滑极值可达195 cm,其中在结古镇和隆宝镇附近的两段出现较明显的地表破裂;2)断裂两侧的雷达视线向运动方向和运动量的差异预示发震断裂以左旋走滑运动为主,SW盘为主动盘;3)宏观震中可以定位于玉树县城西北约16 km的地表陡变带附近;4)发震断裂地表行迹、变形量和地表破裂幅度预示余震将主要沿发震断裂向NW迁移;5)根据青藏高原东部地块的分区,本次地震属于羌塘地块活动的结果,与巴颜喀拉地块活动引发的汶川地震不存在直接的关联。 相似文献