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1.
A simplified seismotectonic model is proposed for Bulgaria by introducing generalized seismogenic areas containing systems of complex geometry faults. A tectonic scheme, which considers the main faults only, is then derived from this. The assessment of the regional seismic hazard is done using different approaches: the Gumbel, the Cornell, and the fault rupture model methods. A series of relations among seismological parameters are derived from the available data. The results obtained by the different approaches are similar: the most dangerous area is the Struma zone, located in southwestern Bulgaria.  相似文献   

2.
可靠地划分地震区可奠定地震预测与地震危险性评价的地质基础,具有十分重要的意义。笔者等通过研究分析指出板内孕震构造块体侧向边界可由区域性大断层或由区域性大断层与板块边界界定,底边界为康拉德面或低速高导层;板间孕震构造块体为俯冲板块,可由区域性大断层和(或)板块边界约束;在同一个孕震构造块体和同一轮地震周期的地震具有内在联系。因此,地震区可定义为代表相应孕震构造块体地震活动的区域,其可表征该块体内源自锁固段破裂的地震活动。基于笔者等提出的孕震构造块体和相应地震区边界确定原则,把全球两大地震带(环太平洋地震带和欧亚地震带)划分为62个地震区;每个地震区的分区方案均通过了多锁固段脆性破裂理论的检验,这说明方案可靠。进而,笔者等归纳总结了地震区划分方法。  相似文献   

3.
The Neogene stratigraphic series is characterized by predominant clayey facies alternated by other sand layers. The outcrop and subsurface studies show varied and complex styles of deformations and lead to relate the structures to paleoseismic events. The seismicity of eastern onshore and offshore Tunisian margin follows the master fault corridors oriented globally N–S, E–W, and NW–SE that correspond to the bordering faults of grabens and syncline corridors and associated faulted drag fold structures oriented NE–SW. Epicenters of magnitudes between 3 and 5 are located along these border fault corridors. The Neogene strata record brittle structures, including numerous and deep faults and fractures with straight and high-angle dipping planes. The structuring of NE–SW en echelon folds and synclines inside and outside NW–SE and E–W right lateral and N–S and NE–SW left lateral tectonic corridors indicates the strike-slip type of bordering faults and their seismogenic nature. Wrench fault movements that induce mud and salt diapirs, mud volcanoes, and intrusive ascensions are related to seismic shocks. Seismic waves caused by activity along one, or most likely, several tectonic structures would have propagated throughout the Quaternary cover producing seismites. The similarity of deposits, structuring, and seismites between the Tunis-Bizerte to the North and Hammamet-Mahdia to the South accredits the hypothesis that the seismic episodes might have affected sedimentation patterns along the Sahalian large geographic area. The paleoseismic events in northeastern Tunisia might be related to tectonic fault reactivations through time. This hypothesis is consistent with the geomorphologic context of the study area, characterized by several morphostructural lineaments with strong control on the sediment distribution, as well as uplifted and subsiding terrains. The estimated magnitude of the seismic events and the great regional tectonically affected areas demonstrate that the northeastern Tunisia experienced stress through the last geological episodes of its evolution. This Neogene kinematic reconstruction highlights the neotectonic system inducing the actual seismicity on this margin. Therefore, there is a straight relationship between deepseated faults and seismicity.  相似文献   

4.
A systematization of active faults has been developed based on the progress of scientists from the leading countries in the world in the study of seismotectonics and seismic hazard problems. It is underlain by the concept of the fault-block structure of the geological-geophysical environment governed by the interaction of differently oriented active faults, which are divided into two groups—seismogenic and nonseismogenic faults. In seismogenic fault zones, the tectonic stress accumulated is relieved by means of strong earthquakes. Nonseismogenic fault zones are characterized by creep displacement or short-term, oscillatory, and reciprocal movements, which are referred to local superintense deformations of the Earth’s crust (according to the terminology used by Yu.O. Kuz’min). For a situation when a strong earthquake happens, a subgroup of seismodistributing faults has been identified that surround the seismic source and affect the distribution of the seismic waves and, as a consequence, the pattern of the propagation of the coseismic deformations in the fault-block environment. Seismodistributing faults are divided into transit and sealing faults. Along transit faults, secondary coseismic effects (landfalls, landslides, ground fractures, liquefaction, etc) are intensified during earthquakes. In the case of sealing faults, enhancement of the coseismic effects can be observed on the disjunctive limb nearest to the epicenter, whereas, on the opposite limb, the intensity of such effects appreciably decreases. Seismogenic faults or their systems are associated with zones of earthquake source origination (ESO), which include concentrated seismicity regions. In such zones, each earthquake source is related to the evolution of a fault system. ESO zones also contain individual seismogenic sources being focuses of strong earthquakes with M of ≥5.5 in the form of ruptures, which can be graphically represented in 2D or 3D as a surface projection of the source. Depending on the type of data based on which they are identified, individual seismogenic sources are divided into geological-geophysical and macroseismic sources. The systematization presented is the theoretical basis for and the concept of the relational database that is being developed by the authors as an information system for the generation of seismotectonic GIS projects required for the subsequent analysis of the seismic hazard and the assessment of the probability of the origination of macroseismic earthquake effects in a predetermined location.  相似文献   

5.
The use of recent ground motion prediction equations in probabilistic seismic hazard analysis (PSHA) with area type of seismic sources requires defining the probability distributions of various source-to-site distance metrics with finite fault rupture taken into account. This task is rendered very difficult due to large epistemic uncertainties involved in specifying the details of the causative faults for area sources of diffused seismicity. However, it may generally be possible to constrain the strike and dip angles for fault ruptures in area sources from regional seismotectonic and geological information. This paper proposes to estimate the various finite fault distance measures from a site to a location in an area source by averaging the distances for several fault rupture scenarios with randomly distributed strike and dip over specified ranges. To consider the spatial distribution of the seismicity, the paper then provides the guidelines for defining the distance distributions by assigning suitable weight factors to the distance estimates for a grid of locations in the source area. The PSHA computation based on the distance distributions thus defined is shown to provide quite realistic and objective estimate of the hazard.  相似文献   

6.
Strong seismic events once again confirm the view that great destructive earthquakes are produced by the reactivation of pre-existing faults although they have usually remained inactive for many, perhaps thousands of years. It is evident that such active seismogenic zones, with little or no seismicity, have presumably been ignored in the determination of the region's seismic hazard. At south Peloponnesus, Greece, is situated at Taygetos mountain. At its eastern front lies a large normal fault system, the southern segment being the Sparta fault. This area has been characterized by low seismicity for the last 25 centuries. However, during the 6th and 5th centuries B.C. several destructive earthquakes have been reported. That of 464 B.C., was the most destructive and devastated the city of Sparta. Detailed morphotectonic observations of this area, suggest that the earthquake of 464 B.C. could be related to the most recent reactivation of this fault. The ground accelerations that would be produced by a future activation of the Sparta fault, were calculated, by applying a method which takes into account information mainly from the seismotectonic parameters of the Sparta fault, the rupture pattern, the properties of the propagation medium and the local ground conditions. Moreover, these results were compared with those of other independent studies based mainly on the seismic data of the area. This method estimated greater expected values of ground acceleration than those computed by the conventional seismic hazard methods. The highest values correspond to the activation of the Sparta fault either in a unilateral rupture, which would start from the southernmost point of the fault, or in a circular one. Furthermore, an increase is observed of the order of 50% in the ground acceleration values in unconsolidated soft ground in relation to the corresponding values of hard ground. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

7.
建筑物的地震安全性是城市规划和建设过程首先要回答的问题。我国城市地震安全性评价的方法理论多针对地上建筑物,而对地下空间的地震安全性研究较为薄弱,严重滞后于城市发展对地下空间的需求。活断层是诱发地震、导致建筑物破坏的的直接因素。考虑到空间关系上,地下空间与断层之间的交互关系为相交或相离。因此,本文将地下空间分为两类:与断层相交的地下空间称为跨断层地下空间,远离断层的地下空间称为远离断层地下空间。本文尝试将断裂带同震地表破裂、地震峰值加速度、地震烈度等地表地震安全性评价考量的要素与地下空间埋藏深度建立联系,并在此基础上总结基于震害统计的地下空间地震安全性评价方法。最后,本文选取地下空间利用需求较高的深圳和北京地区为实例进行介绍。  相似文献   

8.
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9.
2014年10—12月期间,云南景谷接连发生了Ms6.6、Ms5.8、Ms5.9三次中-强地震。为确定地震的地质构造成因,在地表调查的基础上,综合该区的地质构造情况、烈度与余震分布、震源机制解等资料,确定此次震群活动的宏观震中位于永平盆地东南侧山地,发震断层为地质与地貌表现不显著的NW向右旋走滑断层。此次震群活动及余震迁移过程指示,由于断层斜接部位岩桥的临时阻碍,Ms6.6地震破裂在向南东扩展过程中发生短暂停滞,突破障碍后进一步引发了Ms5.8和Ms5.9地震,这符合震源破裂沿NW向发震断裂分段破裂的行为。区域活动断裂的遥感解译结果发现,发震断层位置恰好处于NW向右旋走滑的茶房断裂与普文断裂之间,区域上属于该断裂带的不连贯部位,指示此次中-强震群活动应该是茶房-普文断裂带贯通过程的构造活动表现。结合思茅地块的历史地震资料发现,思茅地块地震活动多以小于等于6.8级为主,发震构造多为NW向断裂。指示在现今构造应力场作用下,该区NW向断裂的活动性相对NE向断裂更加显著,属于该区主要控震构造,应在今后的地震地质工作中给予更多关注。  相似文献   

10.
The evolution of the seismogenic process associated with the Ms 5.8 Sangro Valley earthquake of May 1984 (Abruzzo, central Italy) is closely controlled by the Quaternary extensional tectonic pattern of the area. This pattern is characterised by normal faults mainly NNW striking, whose length is controlled by pre-existing Mio–Pliocene N100±10° left-lateral strike-slip fault zones. These are partly re-activated as right-lateral normal-oblique faults under the Quaternary extensional regime and behave as transfer faults.Integration of re-located aftershocks, focal mechanisms and structural features are used to explain the divergence between the alignment of aftershocks (WSW–ENE) and the direction of seismogenic fault planes defined by the focal mechanisms (NNW–SSE) of the main shock and of the largest aftershock (Ms=5.3).The faults that appear to be involved in the seismogenic process are the NNW–SSE Barrea fault and the E–W M. Greco fault. There is field evidence of finite Quaternary deformation indicating that the normal Barrea fault re-activates the M. Greco fault as right-lateral transfer fault. No surface faulting was observed during the seismic sequence. The apparently incongruent divergence between aftershocks and nodal planes may be explained by interpreting the M. Greco fault as a barrier to the propagation of earthquake rupturing. The rupture would have nucleated on the Barrea fault, migrating along-strike towards NNW. The sharp variation in direction from the Barrea to the M. Greco fault segments would have represented a structural complexity sufficient to halt the rupture and subsequent concentration of post-seismic deformation as aftershocks around the line of intersection between the two fault planes.Fault complexities, similar to those observed in the Sangro Valley, are common features of the seismic zone of the Apennines. We suggest that the zones of interaction between NW–SE and NNW–SSE Plio-Quaternary faults and nearly E–W transfer faults, extending for several kilometres in the same way as M. Greco does, might act as barriers to the along-strike propagation of rupture processes during normal faulting earthquakes. This might have strong implications on seismic hazard, especially for the extent of the maximum magnitude expected on active faults during single rupture episodes.  相似文献   

11.

The state of Chiapas (SE México) conforms a territory of complex tectonics and high seismic activity. The interaction among the Cocos, North American and Caribbean tectonic plates, as well as the active crustal deformation inside Chiapas, determines a variety of seismogenic sources of distinct characteristics and particular strong ground motion attenuation. This situation makes the assessment of seismic hazard in the region a challenging task. In this work, we follow the methodology of probabilistic seismic hazard analysis, starting from the compilation of an earthquake catalogue, and the definition of seismogenic source-zones based on the particular seismotectonics of the region: plate-subduction-related sources (interface and intraslab zones), active crustal deformation zones and the shear zone between the North American and Caribbean plates formed by the Motagua, Polochic and Ixcán faults. The latter source is modelled in two different configurations: one single source-zone and three distinct ones. We select three ground motion prediction equations (GMPEs) recommended for South and Central America, plus two Mexican ones. We combine the GMPEs with the source-zone models in a logic tree scheme and produce hazard maps in terms of peak ground acceleration and spectral acceleration for the 500-, 1000- and 2500-year return periods, as well as uniform hazard spectra for the towns of Tuxtla Gutiérrez, Tapachula and San Cristóbal. We obtain higher values in comparison with previous seismic hazard studies and particularly much higher than the output of the Prodisis v.2.3 software for seismic design in México. Our results are consistent with those of neighbouring Guatemala obtained in a recent study for Central America.

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12.
We present an overview of the seismogenic sources of northeastern Italy and western Slovenia, included in the last version of the Database of Individual Seismogenic Sources (DISS 3.0.2) and a new definition of the geometry of the Montello Source that will be included in the next release of the database. The seismogenic sources included in DISS are active faults capable of generating Mw > 5.5 earthquakes. We describe the method and the data used for their identification and characterization, discuss some implications for the seismic hazard and underline controversial points and open issues.In the Veneto–Friuli area (NE Italy), destructive earthquakes up to Mw 6.6 are generated by thrust faulting along N-dipping structures of the Eastern Southalpine Chain. Thrusting along the mountain front responds to about 2 mm/a of regional convergence, and it is associated with growing anticlines, tilted and uplifted Quaternary palaeolandsurfaces and forced drainage anomalies. In western Slovenia, dextral strike–slip faulting along the NW–SE trending structures of the Idrija Fault System dominates the seismic release. Activity and style of faulting are defined by recent earthquakes (e.g. the Ms 5.7, 1998 Bovec–Krn Mt. and the Mw 5.2, 2004 Kobarid earthquakes), while the related recent morphotectonic imprint is still a debated matter.We reinterpreted a large set of tectonic data and developed a segmentation model for the outermost Eastern Southalpine Chain thrust front. We also proposed the association of the four major shocks of the 1976 Friuli earthquake sequence with individual segments of three major thrust fronts. Although several sub-parallel active strike–slip strands exist in western Slovenia, we were able to positively identify only two segments of the Idrija Fault System. A comparison of the regional GPS velocity with long-term geological slip-rates of the seismogenic sources included in DISS shows that from a quarter to half of the deformation is absorbed along the external alignment of thrust faults in Veneto and western Friuli. The partitioning of the deformation in western Slovenia among the different strike–slip strands could not be quantified.  相似文献   

13.
This study presents the future seismic hazard map of Coimbatore city, India, by considering rupture phenomenon. Seismotectonic map for Coimbatore has been generated using past earthquakes and seismic sources within 300 km radius around the city. The region experienced a largest earthquake of moment magnitude 6.3 in 1900. Available earthquakes are divided into two categories: one includes events having moment magnitude of 5.0 and above, i.e., damaging earthquakes in the region and the other includes the remaining, i.e., minor earthquakes. Subsurface rupture character of the region has been established by considering the damaging earthquakes and total length of seismic source. Magnitudes of each source are estimated by assuming the subsurface rupture length in terms of percentage of total length of sources and matched with reported earthquake. Estimated magnitudes match well with the reported earthquakes for a RLD of 5.2% of the total length of source. Zone of influence circles is also marked in the seismotectonic map by considering subsurface rupture length of fault associated with these earthquakes. As earthquakes relive strain energy that builds up on faults, it is assumed that all the earthquakes close to damaging earthquake have released the entire strain energy and it would take some time for the rebuilding of strain energy to cause a similar earthquake in the same location/fault. Area free from influence circles has potential for future earthquake, if there is seismogenic source and minor earthquake in the last 20 years. Based on this rupture phenomenon, eight probable locations have been identified and these locations might have the potential for the future earthquakes. Characteristic earthquake moment magnitude (M w ) of 6.4 is estimated for the seismic study area considering seismic sources close to probable zones and 15% increased regional rupture character. The city is divided into several grid points at spacing of 0.01° and the peak ground acceleration (PGA) due to each probable earthquake is calculated at every grid point in city by using the regional attenuation model. The maximum of all these eight PGAs is taken for each grid point and the final PGA map is arrived. This map is compared to the PGA map developed based on the conventional deterministic seismic hazard analysis (DSHA) approach. The probable future rupture earthquakes gave less PGA than that of DSHA approach. The occurrence of any earthquake may be expected in near future in these eight zones, as these eight places have been experiencing minor earthquakes and are located in well-defined seismogenic sources.  相似文献   

14.
We tested a new hybrid method for the evaluation of seismic hazard. A recently proposed fault segmentation and earthquake recurrence model of peninsular Italy suggests that the interval for which the local historical catalogue is complete is shorter than the mean recurrence time of individual large faults (1000 years), or at the most comparable. These new findings violate the fundamental assumption of historical probabilistic seismic hazard methods that the historical record is representative of the activity of all the seismogenic sources. The hybrid method we propose uses time-dependent modelling of the major earthquakes and catalogue-based historical probabilistic estimates for all minor events. We assume that the largest earthquakes are characteristic for individual discrete fault segments, model their probability of occurrence by a renewal process and compute the shaking associated with each of them with a simplified procedure. Then we calculate the probability of exceeding a given threshold of peak ground acceleration for specific sites as the aggregate probability of occurrence of large characteristic earthquakes and minor shocks. We apply the method to the Calabrian Arc (Southern Italy) performing the calculations for five major towns. The exposure to seismic hazard of Reggio Calabria, Catanzaro and Vibo Valentia, which locate close to recently activated large faults, decreases with respect to traditional time-independent estimates. On the contrary, an increase of seismic hazard is obtained for Castrovillari, which locates in an area where large faults displaying Holocene activity have been recently recognized but no significant earthquake is reported in the historical catalogue. Cosenza has the highest probability to experience a significant peak ground acceleration with both the new hybrid and the traditional approaches. We wish to stress that the present results should be interpreted only in terms of the differences between the new hybrid and the traditional approaches, not for their absolute values, and that they are not intended to be used for updating or modifying the current national seismic zonation.  相似文献   

15.
Rondoyanni  Th.  Sakellariou  M.  Baskoutas  J.  Christodoulou  N. 《Natural Hazards》2012,61(2):843-860
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16.
This article focuses on the Montello thrust system in the Eastern Southern Alps as a potential seismogenic source. This system is of particular interest because of its lack of historical seismicity. Nevertheless, the system is undergoing active deformation. We developed a finite‐element model using visco‐elasto‐plastic rheology. The free parameters of the model (essentially, the locking status of the three thrusts included in the study), were constrained by matching the observed horizontal GPS and vertical levelling data. We show that the amount of interseismic fault locking, and thus the seismic potential, is not necessarily associated with the fastest‐slipping faults. More specifically, the locked Bassano thrust has a greater seismic potential than the freely slipping Montello thrust. The findings suggest that faults with subtle evidence of Quaternary activity should be carefully considered when creating seismic hazard maps.  相似文献   

17.
白龙江引水工程是我国拟建的一项重大战略工程,而代古寺水库是该工程的水源枢纽。代古寺水库及其周围地区(本文研究区)活动断层发育、大地震频发,故亟需开展可靠的地震危险性评估,为该研究区内的工程建设和运营保驾护航。由于传统评估方法物理依据不足,难以正确评估研究区的地震危险性,故本文采用了基于地震物理预测的地震危险性评估新方法。研究结果表明,该研究区位于海原地震区,未来100年内该研究区的地震危险性主要源于海原地震区的下一次MS8.5标志性地震。根据断层地震活动、发震潜力与展布特征,我们预判了该标志性地震的可能发震断层和震中位置;应用地震烈度衰减关系,考虑不同震中位置,分别计算了其产生的地震烈度。为确保“百年大计”的白龙江引水工程代古寺水库水资源枢纽安全,我们建议该研究区的抗震设防烈度不宜低于8度。  相似文献   

18.
Although the U.K. is in an area of only low to moderate seismicity, the seismic hazard is sufficient to pose a threat to sensitive structures such as chemical plants and nuclear facilities. In quantifying the level of hazard by conventional probabilistic methodology, however, some problems arise in attempting to interpret earthquake data in terms of geological structure and faults. In the U.K., not only is it impossible to identify any demonstrably active faults, but also it is extremely difficult to discern any relationship between the pattern of seismicity and local or regional geological structure.This study discusses the use of two zonation approaches which complement each other in such a way that the general character and trend of seismicity is preserved. In one approach, the zonation is informed by the structural geology, where possible; geological zonation is avoided if it produces sources with heterogeneous seismicity. In the other approach, the record of past earthquakes is divided up into very small zones around individual epicentres or groups of epicentres, the size of each zone usually being proportional to the uncertainty in the epicentral determination of the appropriate event. This zonation preserves an observed tendency of some British earthquakes to repeat themselves. It is suggested that, in intraplate areas such as the U.K., it is often inappropriate to attempt to model individual fault sources. No faults in the U.K. are provably active. Because an earthquake of moderate size can occur on a very short fault segment, it is impractical to restrict fault modelling to major features. Even the two largest U.K. faults, suspected to be active, pose problems in attributing historical seismicity to them as distinct features.  相似文献   

19.
A probabilistic seismic hazard analysis for the states of Tripura and Mizoram in North East India is presented in this paper to evaluate the ground motion at bedrock level. Analyses were performed considering the available earthquake catalogs collected from different sources since 1731–2010 within a distance of 500 km from the political boundaries of the states. Earthquake data were declustered to remove the foreshocks and aftershocks in time and space window and then statistical analysis was carried out for data completeness. Based on seismicity, tectonic features and fault rupture mechanism, this region was divided into six major seismogenic zones and subsequently seismicity parameters (a and b) were calculated using Gutenberg–Richter (G–R) relationship. Faults data were extracted from SEISAT (Seismotectonic atlas of India, Geological Survey of India, New Delhi, 2000) published by Geological Survey of India and also from satellite images. The study area was divided into small grids of size 0.05° × 0.05° (approximately 5 km × 5 km), and the hazard parameters (rock level peak horizontal acceleration and spectral accelerations) were calculated at the center of each of these grid cells considering all the seismic sources within a radius of 500 km. Probabilistic seismic hazard analyses were carried out for Tripura and Mizoram states using the predictive ground motion equations given by Atkinson and Boore (Bull Seismol Soc Am 93:1703–1729, 2003) and Gupta (Soil Dyn Earthq Eng 30:368–377, 2010) for subduction belt. Attenuation relations were validated with the observed PGA values. Results are presented in the form of hazard curve, peak ground acceleration (PGA) and uniform hazard spectra for Agartala and Aizawl city (respective capital cities of Tripura and Mizoram states). Spatial variation of PGA at bedrock level with 2 and 10 % probability of exceedance in 50 years has been presented in the paper.  相似文献   

20.
The aim of this paper was to provide a significant case‐history concerning the evolution of a segmented system of extensional faults and related basins, investigated by a set of seismic reflection profiles. We investigated two kinematically linked semi‐grabens, developed at the hangingwall of two opposite‐dipping normal faults: the Vallo di Diano and Auletta basins, located in the southern Apennines, one of the most seismically active regions of the Italian peninsula. Our interpretation suggests that the Pliocene–Quaternary tectonic history consists of a single extensional phase, where the major NW–SE trending normal faults, generating the basins, and the strike‐slip and transtensional faults connecting adjacent normal fault segments, simultaneously act, being part of the same extensional system. We also conclude that major normal faults, bordering the basins, should be considered as potential seismogenic sources in the seismic hazard evaluation.  相似文献   

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