Seismicity of Morocco for the Period 1987–1994     

S. O. El Alami  B. Tadili  L. Aït Brahim  I. Mouayn 《Pure and Applied Geophysics》2004,161(5-6):969-982

— A seismic data file of 3,740 earthquakes from January 1987 to December 1994 has been elaborated for Morocco and the border regions, with 10 main events registering magnitudes from 5 to 5.6. Such seismicity is particularly important for Morocco as the released seismic energy constitutes a considerable part of the total energy radiated during the 20th century. Relative seismicity maps confirm the persistence of the major features of the seismicity of Morocco. An important seismic activity is observed in the Alboran region continental crust, which absorbs the maximum deformation resulting from the convergence of the African and Iberian plates. However, in the longitude window 3.5°– 6° W at depths of 25 to 50 km, a seismic gap zone seems to take place. An explanation of this phenomenon may be provided by the slab breakoff model. Even if the seismicity of Morocco remains moderate, heavy damage is observed when the magnitude of earthquakes exceeds 4.5, especially in the case of traditional buildings.  相似文献   

Coseismic slip resolution and post-seismic relaxation time of the 1999 Chi-Chi, Taiwan, earthquake as constrained by geological observations, geodetic measurements and seismicity   总被引：2，自引：0，他引：2  

Anne Loevenbruck  Rodolphe Cattin  Xavier Le Pichon  Stéphane Dominguez  Rémi Michel 《Geophysical Journal International》2004,158(1):310-326

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The design of optimum networks for aftershock recordings     

Matthias Hardt  Frank Scherbaum 《Geophysical Journal International》1994,117(3):716-726

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The Macquarie Ridge earthquake of 1989     

Shamita Das 《Geophysical Journal International》1993,115(3):778-798

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汶川地震余震震源参数及地震动衰减与场地影响参数反演分析   总被引：5，自引：2，他引：3       下载免费PDF全文

喻畑  李小军 《地震学报》2012,34(5):621-632

基于强震动观测台钻孔数据, 统计得到了四川、 甘肃地区20 m深的浅硬土层场地平均剪切波速模型． 通过与美国加州地区的波速模型对比, 结合四川、 甘肃地区地震预报的地壳模型, 延拓剪切波速模型至40 km． 应用四分之一波长法计算了浅硬土层场地的平均场地放大系数． 利用场地放大系数, 消除13次余震中浅硬场地的台站场地响应, 反演了龙门山断层上、 下盘的介质品质因子以及13次余震的有效应力降． 通过与普通土层场地的强震动记录对比, 对浅硬土层场地的放大系数进行调整, 得到了深厚土层场地的平均放大系数．   相似文献   

汶川地震余震区波速比与强余震的关系     

王志铄  李源 《山西地震》2012,(1):5-7

利用2008年5月12日汶川地震余震的P波和S波到时数据,对龙门山地区波速比进行了计算。结果表明,该地区的强余震全部发生在波速比相对较高的地区,这应该是地下介质的破碎原因造成的。  相似文献   

Aftershock collapse vulnerability assessment of reinforced concrete frame structures          下载免费PDF全文

Meera Raghunandan  Abbie B. Liel  Nicolas Luco 《地震工程与结构动力学》2015,44(3):419-439

In a seismically active region, structures may be subjected to multiple earthquakes, due to mainshock–aftershock phenomena or other sequences, leaving no time for repair or retrofit between the events. This study quantifies the aftershock vulnerability of four modern ductile reinforced concrete (RC) framed buildings in California by conducting incremental dynamic analysis of nonlinear MDOF analytical models. Based on the nonlinear dynamic analysis results, collapse and damage fragility curves are generated for intact and damaged buildings. If the building is not severely damaged in the mainshock, its collapse capacity is unaffected in the aftershock. However, if the building is extensively damaged in the mainshock, there is a significant reduction in its collapse capacity in the aftershock. For example, if an RC frame experiences 4% or more interstory drift in the mainshock, the median capacity to resist aftershock shaking is reduced by about 40%. The study also evaluates the effectiveness of different measures of physical damage observed in the mainshock‐damaged buildings for predicting the reduction in collapse capacity of the damaged building in subsequent aftershocks. These physical damage indicators for the building are chosen such that they quantify the qualitative red tagging (unsafe for occupation) criteria employed in post‐earthquake evaluation of RC frames. The results indicated that damage indicators related to the drift experienced by the damaged building best predicted the reduced aftershock collapse capacities for these ductile structures. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

2013年前郭M5.8级强震群序列特征分析   总被引：1，自引：0，他引：1  

陈作全  武成智  张淑洁  肖玉明  王迪 《防灾减灾学报》2015,(3):11-15

基于2013年吉林前郭M5.8级强震群序列资料,分析其余震序列空间分布、演化特征、测震学指标b值及震源机制特征等。结果发现,前郭强震群序列空间位置高度集中在长9 km,宽5 km的范围内,余震沿北西向分布。序列中M4.0以上地震呈连发特征,M2.0~3.0地震缺乏,余震主要集中在M1.0级以下,余震序列b值较低且介于0.3~0.4之间,M5.0以上地震震源机制以逆冲为主,兼具少量走滑分量。  相似文献   

Source Parameters for 1999 North Anatolian Fault Zone Aftershocks     

Rengin Gök  Lawrence Hutchings  Kevin Mayeda  Doğan Kalafat 《Pure and Applied Geophysics》2009,166(4):547-566

We develop a data set of aftershock recordings of the 1999, M = 7.4 Izmit and M = 7.2 Duzce (Turkey) earthquakes to study their source parameters. We combined seismograms from 44 stations maintained by several sources (organizations) to obtain a unified data set of events (2.1 ≤ M_w ≤ 5.5). We calculate source parameters of these small earthquakes by two methods that use different techniques to address the difficulty in obtaining source spectra for small earthquakes subject to interference from site response. One method (program NetMoment (NM), Hutchings, 2004) uses spectra of direct S waves in a simultaneous inversion of local high-frequency network data to estimate seismic moment, source corner frequency (f_c), site attenuation (k) and whole-path Q. This approach takes advantage of the source commonality in all recordings for a particular earthquake by fitting a common Brune source spectrum to the data with a and individual k. The second approach (Mayeda et al., 2003) uses the coda method (CM) to obtain “nonmodel-based” source spectra and moment estimates from selected broadband recording sites. We found that both methods do well for events that allow the comparison with seismic moment estimates derived from waveform modeling. Also, source spectra obtained from the two methods are very closely matched for most of the events they have in common. We use an F test to examine the trade-off between k and f_c picks identified by the direct S-wave method. About half of the events could be constrained to have less than a 50% average uncertainty in f_c and k. We used these source spectra solutions to calculate energy and apparent stress and compare these to estimates from the selected “good quality” source spectra from CM. Both studies have values mutually consistent and show a similar increase in apparent stress with increasing moment. This result has added merit due to the independent approaches to calculate apparent stress. We conclude that both methods are at least partially validated by our study, and they both have usefulness for different circumstances of recording local small earthquakes. CM would work well in studies for which there is a broad magnitude range of events and NM works well for local events recorded by band-limited recorders.  相似文献   

区域优势构造面和余震节面库仑应力变化相关性与地震预测意义.     

陈兵  崔笃信  张晓亮  王庆良 《地震学报》2009,31(4):357-366

根据2001年昆仑山口西8.1级地震震源机制,计算了主震破裂在区域优势直立走滑构造面上引起的库仑应力变化,发现3级以上余震大部分分布在库仑应力变化为正的区段,与应力的正相关性为56%——71%;5级余震与应力的正相关性达到60%——80%．5级余震节面上库仑应力变化的正相关性为60%——80%,其效果与优势构造面具有等价性．表明应用库仑应力函数方法分析区域优势构造面应力变化,可能是判断未来地震活动发生地点的一条有效途径．其物理机制可能源于地壳应变主体单元中区域应变能与单元中包含的不同尺度断层面上应力分布的正相关性．亦即主破裂造成沿区域优势构造产生应力的不均匀分布,应力的非均匀性引起区域应变能的非均匀分布,在应变能升高的区段,某些次生断裂面应力随之升高,从而引发余震活动．   相似文献