共查询到20条相似文献，搜索用时 15 毫秒
1.
J. Carvalho E. Ramalho R. Dias C. Pinto R. Ressurrei??o 《Pure and Applied Geophysics》2012,169(1-2):183-200
The Algarve province is located a few hundred kilometres north of the crossing of the E–W Eurasia–Africa plate boundary in an area of diffuse seismicity and broad deformation. It is characterised by a moderate seismicity, with some important historical and instrumental earthquakes causing loss of lives and significant material damages. The area is affected not only by plate boundary earthquakes but also by moderate to large events generated by local sources. The assessment of onshore local sources is, therefore, of vital importance for an evaluation of the regional seismic hazard. This paper discusses the application of geophysical data to the study of the Carcavai fault zone, an outcropping structure more than 20?km long which is seen to deform sediments of the Plio-Quaternary age. The location of some sectors of the fault zone, as well as the vertical offsets of the structure, are still to be confirmed. In order to estimate these and to study the geometry of the fault zone at depth, geophysical data were acquired together with new geological data. Where the location of the fault was less certain, EM and seismic reflection profiles with coarse spatial sampling were carried out. After the detailed location of the fault zone, seismic reflection profiles with a more dense spatial resolution were acquired. The integrated interpretation of the geological and geophysical data confirmed the presence of a large fault zone. The total fault length is still unknown as its extension offshore is still being studied. Together with estimated values of the throw obtained, this data set has improved understanding the seismic hazard in the area by providing more refined estimates of co-seismic rupture, maximum expected earthquake and return periods. 相似文献
2.
3.
S. Gentili 《Pure and Applied Geophysics》2010,167(8-9):933-958
The Region–Time–Length (RTL) algorithm has been applied to different instrumental catalogues to detect seismic quiescence before medium-to-large earthquakes in Italy in the last two decades. RTL performances are sensitive to the choice of spatial and temporal parameters. The method for automatic parameters selection developed by Chen and Wu has been applied to twelve Italian earthquakes with magnitude greater than 5. The limits of the method in constructing maps of seismic quiescence before the earthquake are demonstrated, and a simple improvement is proposed. Then a new technique, namely RTLsurv, is proposed for routine surveys of the Italian seismicity. RTLsurv has been applied to all the earthquakes with magnitude greater than 4 in the Italian area in the time interval 1994–2004; four different sub-areas have been identified, with different characteristics in the level of recorded seismicity. One subarea—Tyrrhenian Sea—was characterized by a too low level of recorded seismicity for the application of the method. In the other three subareas a seismic quiescence was detected before at least the 66% of the earthquakes with magnitude greater or equal to 4 and all the earthquakes with magnitude greater than 5. 相似文献
4.
7级以上的强震并不是在一片空白上突然发生的,而是在一种间歇性的地震活动背景下发生的,研究这种背景地震活动的规律,为判定一个活动期的强震的潜在震源区提供信息。本文通过对华北历史上记录到的18次7级以上强震的震前史和震后史的研究,提出了华北地区强震背景地震活动的四条规律:①强震前多有6级以上的背景地震发生;②并且多有信息地震发生;③短时间近距离的两个强震之间可能出现缓震现象;④强震具有一定的减震作用。文中根据这四条规律,对华北地区1501——1730年的强震潜在震源区做了判别分析。 相似文献
5.
Thierry Camelbeeck Pierre Alexandre Kris Vanneste Mustapha Meghraoui 《Soil Dynamics and Earthquake Engineering》2000,20(5-8):405-414
In western Europe, the knowledge of long-term seismicity is based on reliable historical seismicity and covers a time period of less than 700 years. Despite the fact that the seismic activity is considered as low in the region extending from the Lower Rhine Embayment to England, historical information collected recently suggests the occurrence of three earthquakes with magnitude around 6.0 or greater. These events are a source of information for the engineer or the scientist involved in mitigation against large earthquakes. We provide information relevant to this aspect for the Belgian earthquake of September 18, 1692. The severity of the damage described in original sources indicates that its epicentral intensity could be IX (EMS-98 scale) and that the area with intensity VII and greater than VII has at least a mean radius of 45 km. Following relationships between average macroseismic radii and magnitude for earthquakes in stable continental regions, its magnitude Ms is estimated as between 6.0 and 6.5. To extend in time our knowledge of the seismic activity, we conducted paleoseismic investigations in the Roer Graben to address the question of the possible occurrence of large earthquakes with coseismic surface ruptures. Our study along the Feldbiss fault (the western border of the graben) demonstrates its recent activity and provides numerous lines of evidence of Holocene and Late Pleistocene large earthquakes. It suggests that along the 10 km long Bree fault scarp, the return period for earthquakes with magnitude from 6.2 to 6.7 ranges from 10,000 to 20,000 years during the last 50,000 years. Considering as possible the occurrence of similar earthquakes along all the Quaternary faults in the Lower Rhine Embayment, a large earthquake could occur there each 500–1000 years. These results are important in two ways. (i) The evidence that large earthquakes occur in western Europe in the very recent past which is not only attested by historical sources, but also suggested by paleoseismic investigations in the Roer Graben. (ii) The existence of a scientific basis to better evaluate the long-term seismicity in this part of Europe (maximal magnitude and return period) in the framework of seismic hazard assessment. 相似文献
6.
Laurentiu Danciu Karin Şeşetyan Mine Demircioglu Levent Gülen Mehdi Zare Roberto Basili Ata Elias Shota Adamia Nino Tsereteli Hilal Yalçın Murat Utkucu Muhammad Asif Khan Mohammad Sayab Khaled Hessami Andrea N. Rovida Massimiliano Stucchi Jean-Pierre Burg Arkady Karakhanian Hektor Babayan Mher Avanesyan Tahir Mammadli Mahmood Al-Qaryouti Doğan Kalafat Otar Varazanashvili Mustafa Erdik Domenico Giardini 《Bulletin of Earthquake Engineering》2018,16(8):3465-3496
7.
川滇地区是我国地震危险性较高的地区之一.本文基于对特大强震的风险性考虑,使用全球地震模型OpenQuake软件,建立了川滇地区地震危险性预测新模型.首先根据构造特征划分多个震源分区,并整理出这些震源分区内断层活动特征与滑动速率;基于震源分区和断层模型,使用GPS应变率转换成的锥形古登堡-里克特关系作为整个区域的地震积累率,并允许超过历史最大震级的特大地震的出现,结合活动断层滑动速率所积累的地震发生率,给出震源分区内断层地震源和背景地震源的地震发生率的比率分配关系;在活动断层分段上,保留了大型断裂或其主要部分,没有根据小的阶区来对断层进行详细分段,以便分配特大地震发生率;并使用地震率平滑方法分配背景地震发生率.最后在OpenQuake中加入地震动预测方程,计算出了川滇地区的PGA分布图,为区域地震危险性提供科学依据. 相似文献
8.
H.K. Acharya 《Physics of the Earth and Planetary Interiors》1981,24(1):53-65
The distribution of large shallow earthquakes (magnitude ?5.5) in central Luzon, Philippines, related to the underthrusting of the Eurasian plate, is examined by the technique of pattern recognition. The objective of the study is (1) to forecast restricted zones of seismic activity, (2) to determine geological features which, in combination, are associated with the earthquakes in the environment of subduction, and (3) to determine whether more insight into regional seismicity can be gained by pattern recognition studies than by conventional seismicity studies. It appears from this analysis that large earthquakes occur (a) in a zone between the shallower portion of Manila Trench on its landward side and the belt of volcanoes and (b) on large strike-slip faults in the region such as Verde Island Passage fault and the Philippine fault. In these zones, large earthquakes occur at locations identified by large topographic relief in the vicinity and a high degree of fractured crust. In contrast to characteristics in California and central Asia, the intersection of faults nearby is not a major characteristic for large earthquakes in and near central Luzon. Topography and degree of fractured crust are important characteristics in all areas studied so far. Several earthquakes which are known to have occurred were considered unknown, and control experiments were carried out to determine whether the locations of these earthquakes would be identified as having potential for large earthquakes. The results of control experiments indicate that the pattern recognition technique is fairly successful in spatial forecasting if the known historical record is assumed almost complete for various major zones (85% in this case). It fails to forecast if information is totally lacking about earthquake activity on a tectonic feature. In the present study, a control experiment was able to correctly identify the locations of two of the largest earthquakes known to have occurred in the area. It was better able to identify locations of large earthquakes than a simple contouring of known earthquake locations would suggest. 相似文献
9.
Statistical estimates of earthquake magnitudes are unreliable when based onvery few historical data. Additional sources of information, such asgeological data, are then necessary to update estimates of seismicityparameters. The Bayesian probability theory is a tool to combine priorinformation of seismicity obtained from geological data with historicalobservations. This theory is tested in the case of the Inner Messiniakosfault zone, southern Greece, for the estimation of the probability ofoccurrence of strong earthquakes. Prior estimates of seismicity aredeveloped from slip rate measurements, obtained from offsets of geologicalformations, on the basis of both onshore and offshore neotectonic data.The analysis emphasizes the importance of the input seismicity parameters,particularly the significance of the upper bound magnitude in the estimationof the seismic potential of active faults. 相似文献
10.
发震构造特性是潜在震源区划分及其地震年发生率确定的重要依据。潜在震源区除了反映“未来具有发生破坏性地震的地区”的内涵外,还应反映高震级档地震具有相似复发特征的涵义。由于在地震活动性参数统计单元内,有一些具有不同本底地震的活动构造块体,为更好地反映地震活动的空间不均匀性,考虑潜在震源区的三级划分是有必要的。通过分析潜在震源区内高震级档地震的复发特征,计算预测时段内潜在震源区的高震级档地震的发震概率,采用预测时段内概率等效转换获得地震年平均发生率的方法,有助于在中国地震危险性分析框架内考虑潜在震源区的强震复发特性。另外,文中还对潜在震源区内特征地震次级震级档频度不足的特性和发震构造上强震非均匀性在地震危险性分析中的应用问题进行了探讨 相似文献
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川滇藏邻区巴塘——丽江地震块体强震活动特征的初步探讨 总被引：4，自引：0，他引：4
本根据１９８６￣１９９６年川滇藏三省（区）邻界区巴塘－丽江－带频繁的强震活动的资料,结合活动构造带分布及历史强震记录,分析了该邻界区强震活动若干特征,提出了“存在川滇藏邻界区巴塘－丽江地震块体”的认识,并就其与相邻地区强震活动关系及未来强震趋势作了讨论。 相似文献
12.
本文讨论了广西河池地区地震活动的时空分布、应力场“窗口”效应和小震级高烈度等特征,並利用岩石实验的某些结果对该区地震的发震机制作了一些定性解释。该区是一个两组断裂交汇的应力敏感区,地震是在低应力条件下在极不均匀介质宁原有裂隙发生粘滑的结果,其特殊的地体环境下可能构成蕴育大震的条件,其地震活动不会对邻近的龙滩库坝区造成威胁。 相似文献
13.
Andaman-Sumatra island arc: 1. Spatiotemporal manifestations and focal mechanisms of the earthquakes 总被引：1，自引：0，他引：1
The spatiotemporal manifestations of seismicity in the Andaman-Sumatra island arc are studied using the instrumental data
for 1900–2010. The data on the largest tsunamigenic earthquakes of the 18th–19th centuries were also taken into account. The
epicenters of the earthquakes are established to cluster in some areas; their possible relation to the structural features
of the island arc is considered. A distinctive feature of seismicity in the region of the Andaman Sea is the presence of compact
swarms of numerous earthquakes occurring during short intervals of time. The distribution of the earthquakes by the depth
of their hypocenters in different segments of the island arc is investigated. The focal mechanisms of the earthquakes are
analyzed using the centroid-moment-tensor (CMT) determinations over the period of 1980–2004, and the characteristic features
of their parameters in different segments of the Andaman-Sumatra island arc are formulated. The focal parameters of the earthquakes
determined by CMT and the moment-tensor-solution (MTS) are compared; the possible uncertainty in the estimates of the focal
mechanisms is assessed. The pattern of the spatiotemporal manifestations of the Andaman-Sumatra earthquakes and their focal
mechanisms are compared to the data on the Kuril-Kamchatka and the Aleutian island arcs previously studied by the authors.
The results of analyzing the long-term seismicity and focal mechanisms in the Andaman-Sumatra island arc provide a necessary
basis for the further thorough investigation of the geological conditions and source parameters of the major Sumatra earthquakes
of 2000–2010. 相似文献
14.
本文根据月球交点运动周期规律,发现全球主要地震区的浅源大地震(1897—1990,Ms≥7.0)都存在18.6年地震轮回:活跃期为12.4年,平静期为6.2年。根据最好的统计结果,13个研究区中有4个区这种轮回存在的置信水平为95%,有9个区为98%。本文给出了各研究区的范围、各活跃期的具体时间、x~2检验结果和时空分布图。本文还定义了标志震级Mm来反映各研究区不同的地震活动水平。本文的结果可以充分代表全球浅源大地震的活动图象,为认识地震轮回的机制和地震的混沌性提供了新的资料。 相似文献
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大连及其邻区存在金州、庄河、大洋河等多条区域活动构造带,历史上中强地震较活跃,并有破坏怀地震发生。本文依据区域地质构造,地震活动性,地壳应力场待方面资料,讨论了该地区地震地质背景及区域构造与华北统一应力场的一致性,并据此指出了本区未来可能发生地震及应重点加强监视的地区。 相似文献
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D. Shanker H. N. Singh H. Paudyal A. Kumar A. Panthi V. P. Singh 《Pure and Applied Geophysics》2010,167(6-7):655-666
A long-range correlation between earthquakes is indicated by some phenomena precursory to strong earthquakes. Most of the major earthquakes show prior seismic activity that in hindsight seems anomalous. The features include changes in regional activity rate and changes in the pattern of small earthquakes, including alignments on unmapped linear features near the (future) main shock. It has long been suggested that large earthquakes are preceded by observable variations in regional seismicity. Studies on seismic precursors preceding large to great earthquakes with M ≥ 7.5 were carried out in the northeast India region bounded by the area 20°–32°N and 88°–100°E using the earthquake database from 1853 to 1988. It is observed that all earthquakes of M ≥ 7.5, including the two great earthquakes of 1897 and 1950, were preceded by abnormally low anomalous seismicity phases some 11–27 years prior to their occurrence. On the other hand, precursory time periods ranged from 440 to 1,768 days for main shocks with M 5.6–6.5 for the period from 1963 to 1988. Furthermore, the 6 August, 1988 main shock of M 7.5 in the Arakan Yoma fold belt was preceded by well-defined patterns of anomalous seismicity that occurred during 1963–1964, about 25.2 years prior to its occurrence. The pattern of anomalous seismicity in the form of earthquake swarms preceding major earthquakes in the northeast India region can be regarded as one of the potential seismic precursors. Database constraints have been the main barrier to searching for this precursor preceding smaller earthquakes, which otherwise might have provided additional information on its existence. The entire exercise indicates that anomalous seismicity preceding major shocks is a common seismic pattern for the northeast India region, and can be employed for long-range earthquake prediction when better quality seismological data sets covering a wide range of magnitudes are available. Anomalous seismic activity is distinguished by a much higher annual frequency of earthquake occurrence than in the preceding normal and the following gap episodes. 相似文献
17.
本文根据我国境内及邻近地区地壳结构的分布特征,特别是近年来我国发生的几个大地震所处的深部地壳构造背景,讨论了地震孕育与发生的可能构造模式。结果表明,近代地震活动地带均为地壳厚度急剧变化的地带和地壳构造的转折交汇部位。在深部构造上又为上地幔顶部局部的隆起地区及邻近隆起地带的边缘或斜坡上。此外,地震发生的深部部位与重力场、磁力场的高梯度变化以及地壳中的低电阻层、低速层和高速层的分布密切相关。这种与地震有关的深部构造背景与地球物理场特征,是今后地震预报和地震成因研究必须十分重视的。 相似文献
18.
本文基于对我国华北地区地震活动在时间和空间不均匀分布的认识,吸收了近20年来地震预测方面的科研成果,采用目前国际通用的地震危险性概率分析方法,通过对华北区划的试验,对地震区划的原则和方法提出了如下改进: 1.以地震带作为地震活动性参数的统计单元.引入地震活动趋势估计因素,评定表征地震活动水平的年平均发生率,以使区划结果同预测未来时间段地震活动水平相适应; 2.采用按震级挡次分配各潜在震源区的年平均发生率,可以合理地评估高震级地震的危险程度; 3.采用以震级挡次为条件概率的空间分布函数,刻画地震带内各潜在震源区之间发生相应震级挡次地震的相对危险程度,使区划结果更好地反映地震活动在时间和空间上不均匀性分布的特点; 4.在地震危险性分析计算中,引入了方向性函数项,使得分析模型更接近我国地震震源的实际情况. 相似文献
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我国东北和华北地区中强地震潜在震源区的划分原则和方法 总被引：18，自引：5，他引：18
中强地震潜在震源区的不确定性，对弱地震活动区地震危险性分析结果的影响较大。因此，正确二划分中强地震潜在震源区，是地震区划加和工程场地地震安全性评价的基础。本文以东北和华北地区为例，较为系统地整理了大量基础资料，从众多典型震例分析结果中提出了该地区中强地震潜在震源区的划分原则和方法，对长春，吉林等地区进行了实验划分结果表明，本文所提出了划分原则和方法具有较好的适应性。与此同时，还对本文取得的进展和有 相似文献