西藏崩错8级地震地表破裂的变形特征及其破裂机制   总被引：7，自引：2，他引：5       下载免费PDF全文

吴章明  邓起东 《地震地质》1989,11(1):15-25

1951年11月18日,西藏那曲崩错附近发生了一次8级地震,地表产生了长达约91公里的破裂带。本文总结了该破裂的几何、位移分布特征,讨论了破裂的形成机制和崩错地震的发震构造条件  相似文献   

Increasing critical sensitivity of the Load/Unload Response Ratio before large earthquakes with identified stress accumulation pattern   总被引：2，自引：0，他引：2  

Huai-zhong Yu  Zheng-kang Shen  Yong-ge Wan  Qing-yong Zhu  Xiang-chu Yin   《Tectonophysics》2006,428(1-4):87-94

The Load/Unload Response Ratio (LURR) method is proposed for short-to-intermediate-term earthquake prediction [Yin, X.C., Chen, X.Z., Song, Z.P., Yin, C., 1995. A New Approach to Earthquake Prediction — The Load/Unload Response Ratio (LURR) Theory, Pure Appl. Geophys., 145, 701–715]. This method is based on measuring the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. In this study, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. The Coulomb stress change before a hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. This new algorithm, by combining the LURR method with our choice of identified area with increased Coulomb stress, is devised to improve the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. Retrospective tests of this algorithm on four large earthquakes occurred in California over the last two decades show remarkable enhancement of the LURR precursory anomalies. For some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods, significant anomalies are found if circular areas are used, and are not found if increased Coulomb stress areas are used for LURR data selection. The unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events.  相似文献   

Effects of dynamic shear strength and time-histories stress analysis on newmark sliding block analyses     

LI Hong-jun  CHI Shi-chun  LIN Gao 《岩土力学》2006,27(Z1):1063-1068

A simplified procedure for evaluating aseismic stability of slope subjected to earthquake shaking, in which the effect of dynamic shear strength and time-history stress on the yielding angular acceleration of sliding block is taken into account, is presented. The fundamental feature of this procedure is the dynamic shear strength. The numerical computations are performed by using the proposed method. It is shown that the computed sliding displacement for a given core dam, with either method of dynamic shear strength properly considered, is more rational compared with the conventional computational results based on static shear strength.  相似文献   

The seismic hazard assessment of the Dead Sea rift, Jordan   总被引：1，自引：0，他引：1  

Abdallah S. Al-Zoubi  Z.S.H. Abu-Hamatteh  Amrat Abdealkaderer 《Journal of African Earth Sciences》2006,45(4-5):489-501

The Dead Sea fault system and its branching faults represent one of the most tectonically active regions in the Middle East. The aim of this study is to highlight the degree of hazards related to the earthquake activities associated with the Dead Sea rift, in terms of speculating the possible future earthquakes. The present investigation mainly is based on available data and vertical crustal modeling of Jordan and the Dead Sea model for the Dead Sea basin with particular emphasis of the recent earthquake activities, which occurred on December 31st, 2003 (Mc = 3.7), February 11th, 2004 (strongest Mc = 4.9 R), and March 15th, 2004 (Mc = 4). The present research examines the location of the strong events and correlates them with the various tectonic elements in the area. The source mechanism of the main shock and the aftershock events is also examined. The analyses were based on the available short period seismogram data, which was recorded at the Natural Resources Authority of Jordan, Seismological Observatory. The seismic energy appears to have migrated from the south to the north during the period from December 31st up to March 12th, where the released seismic energy showed a migration character to the southern block of the eastern side of the Dead Sea, which led the seismic event to occur on March 15th.  相似文献   

西南天山布隆金矿床成矿作用同位素地质年代学     

杨建国  杨林海  吕昌国  李智佩  于浦生 《地球学报》2006,27(1):51-55

位于新疆西南天山阿合奇县的布隆金矿是一个国内较少见的低温热液石英重晶石脉型金矿床,它赋存于上泥盆统细碎屑岩中,金矿体受层间缓倾斜破碎带控制。根据矿脉矿物组合及相互穿插关系,原生成矿期成矿作用可分为:①黄铁矿-石英阶段;②石英-黄铁矿-菱铁矿-重晶石阶段;③方解石-石英-重晶石阶段和④重晶石阶段。年代学研究表明,主成矿阶段(②阶段)含金石英脉RB-SR等时线年龄为258±15MA,表明成矿作用发生在晚二叠世末,与中亚南天山大规模的金成矿作用发生时期相一致。  相似文献   

Non-volcanic deep low-frequency tremors accompanying slow slips in the southwest Japan subduction zone   总被引：5，自引：1，他引：5  

Kazushige Obara  Hitoshi Hirose 《Tectonophysics》2006,417(1-2):33

Non-volcanic deep low-frequency tremors in southwest Japan exhibit a strong temporal and spatial correlation with slow slip detected by the dense seismic network. The tremor signal is characterized by a low-frequency vibration with a predominant frequency of 0.5–5 Hz without distinct P- or S-wave onset. The tremors are located using the coherent pattern of envelopes over many stations, and are estimated to occur near the transition zone on the plate boundary on the forearc side along the strike of the descending Philippine Sea plate. The belt-like distribution of tremors consists of many clusters. In western Shikoku, the major tremor activity has a recurrence interval of approximately six months, with each episode lasting over a week. The tremor source area migrates during each episode along the strike of the subducting plate with a migration velocity of about 10 km/day. Slow slip events occur contemporaneously with this tremor activity, with a coincident estimated source area that also migrates during each episode. The coupling of tremor and slow slip in western Shikoku is very similar to the episodic tremor and slip phenomenon reported for the Cascadia margin in northwest North America. The duration and recurrence interval of these episodes varies between tremor clusters even on the same subduction zone, attributable to regional difference in the frictional properties of the plate interface.  相似文献   

3-D seismic structure of the source area of the 1993 Latur, India, earthquake and its implications for rupture nucleations   总被引：1，自引：0，他引：1  

S. Mukhopadhyay  O.P. Mishra  D. Zhao  J.R. Kayal 《Tectonophysics》2006,415(1-4):1-16

The Latur earthquake (M_w 6.1) of 29 September 1993 is a rare stable continental region (SCR) earthquake that occurred on a previously unknown blind fault. In this study, we determined detailed three-dimensional (3-D) P- and S-wave velocity (V_p, V_s) and Poisson's ratio (σ) structures by inverting the first P- and S-wave high-quality arrival time data from 142 aftershocks that were recorded by a network of temporary seismic stations. The source zone of the Latur earthquake shows strong lateral heterogeneities in V_p, V_s and σ structures, extending in a volume of about 90 × 90 × 15 km³. The mainshock occurred within, but near the boundary, of a low-V_p, high-V_s and low-σ zone. This suggests that the structural asperities at the mainshock hypocenter are associated with a partially fluid-saturated fractured rock in a previously unknown source zone with intersecting fault surfaces. This might have triggered the 1993 Latur mainshock and its aftershock sequence. Our results are in good agreement with other geophysical studies that suggest high conductivity and high concentration of radiogenic helium gas beneath the source zone of the Latur earthquake. Our study provides an additional evidence for the presence of fluid related anomaly at the hidden source zone of the Latur earthquake in the SCR and helps us understand the genesis of damaging earthquakes in the SCR of the world.  相似文献   

A way to synchronize models with seismic faults for earthquake forecasting: Insights from a simple stochastic model     

lvaro Gonzlez  Miguel Vzquez-Prada  Javier B. Gmez  Amalio F. Pacheco 《Tectonophysics》2006,424(3-4):319

Numerical models are starting to be used for determining the future behaviour of seismic faults and fault networks. Their final goal would be to forecast future large earthquakes. In order to use them for this task, it is necessary to synchronize each model with the current status of the actual fault or fault network it simulates (just as, for example, meteorologists synchronize their models with the atmosphere by incorporating current atmospheric data in them). However, lithospheric dynamics is largely unobservable: important parameters cannot (or can rarely) be measured in Nature. Earthquakes, though, provide indirect but measurable clues of the stress and strain status in the lithosphere, which should be helpful for the synchronization of the models.The rupture area is one of the measurable parameters of earthquakes. Here we explore how it can be used to at least synchronize fault models between themselves and forecast synthetic earthquakes. Our purpose here is to forecast synthetic earthquakes in a simple but stochastic (random) fault model. By imposing the rupture area of the synthetic earthquakes of this model on other models, the latter become partially synchronized with the first one. We use these partially synchronized models to successfully forecast most of the largest earthquakes generated by the first model. This forecasting strategy outperforms others that only take into account the earthquake series. Our results suggest that probably a good way to synchronize more detailed models with real faults is to force them to reproduce the sequence of previous earthquake ruptures on the faults. This hypothesis could be tested in the future with more detailed models and actual seismic data.  相似文献   

The Gibraltar Arc seismogenic zone (part 2): Constraints on a shallow east dipping fault plane source for the 1755 Lisbon earthquake provided by tsunami modeling and seismic intensity     

M.-A. Gutscher  M.A. Baptista  J.M. Miranda 《Tectonophysics》2006,426(1-2):153

The Great Lisbon earthquake has the largest documented felt area of any shallow earthquake and an estimated magnitude of 8.5–9.0. The associated tsunami ravaged the coast of SW Portugal and the Gulf of Cadiz, with run-up heights reported to have reached 5–15 m. While several source regions offshore SW Portugal have been proposed (e.g.— Gorringe Bank, Marquis de Pombal fault), no single source appears to be able to account for the great seismic moment as well as all the historical tsunami amplitude and travel time observations. A shallow east dipping fault plane beneath the Gulf of Cadiz associated with active subduction beneath Gibraltar, represents a candidate source for the Lisbon earthquake of 1755.Here we consider the fault parameters implied by this hypothesis, with respect to total slip, seismic moment, and recurrence interval to test the viability of this source. The geometry of the seismogenic zone is obtained from deep crustal studies and can be represented by an east dipping fault plane with mean dimensions of 180 km (N–S) × 210 km (E–W). For 10 m of co-seismic slip an Mw 8.64 event results and for 20 m of slip an Mw 8.8 earthquake is generated. Thus, for convergence rates of about 1 cm/yr, an event of this magnitude could occur every 1000–2000 years. Available kinematic and sedimentological data are in general agreement with such a recurrence interval. Tsunami wave form modeling indicates a subduction source in the Gulf of Cadiz can partly satisfy the historical observations with respect to wave amplitudes and arrival times, though discrepancies remain for some stations. A macroseismic analysis is performed using site effect functions calculated from isoseismals observed during instrumentally recorded strong earthquakes in the region (M7.9 1969 and M6.8 1964). The resulting synthetic isoseismals for the 1755 event suggest a subduction source, possibly in combination with an additional source at the NW corner of the Gulf of Cadiz can satisfactorily explain the historically observed seismic intensities. Further studies are needed to sample the turbidites in the adjacent abyssal plains to better document the source region and more precisely calibrate the chronology of great earthquakes in this region.  相似文献   

Site Effects Study in the Serravalle Village (NE Italy) by Means of Spectral Ratios Analyses Relatively to Multiple Reference Sites     

Andrea Restivo  Carla Barnaba  Alberto Michelini 《Natural Hazards》2006,39(1):31-49

The area of Serravalle, sited in the northern part of the town of Vittorio Veneto (TV), NE Italy, has been the target of a seismic microzonation campaign. 10 seismic stations have been deployed for a 7 months period to record in continuous mode. Three stations were installed on bedrock outcrops and seven on sedimentary sites with variable cover thickness. Spectral analyses have been performed on the collected data-set using the Generalized Inversion Technique (GIT, e.g. Andrews, 1986). In particular, spectral ratios have been calculated for each station relatively to the average of the three reference, bedrock sites. The spectral ratios provide quantitative estimates of the seismic motion amplifications which occur in each of the monitored sites. Two sites show high values of amplification, 5 times larger than signal amplitude at the reference sites, in correspondence of well discernible peak frequencies of 5 Hz. Results for the other stations show smaller amounts of site amplification spreading over a broad range of frequencies. Sites where the highest amplifications were recorded all lie on the left bank of the Meschio River and in areas farther away from its outlet into the plain correlating with the presence of thick layers of Quaternary deposits.  相似文献