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1.
The numerical block-model of the lithosphere dynamics is used to simulate seismicity in Italy and its surroundings, based
on the available structural and geodynamics information. The purpose of the study is to understand which are the tectonic
processes that control the main features of the observed seismicity and the kinematics of the region. The influence of the
rheology of the fault systems is studied as well. The model we use differs from other modeling approaches in that it simulates
earthquakes and hence it possibly relates to seismicity and geodynamics. The model provides an effective capability to include
the set of documented constraints supplied by widely available earthquake catalogs. This is done by means of the comparison
of the GR relation, of the focal mechanisms and of the space distribution for observed and computed seismicity. The region
is modeled as a system of perfectly rigid blocks, separated by infinitely thin fault planes, in viscoelastic interaction between
themselves and with the underlying medium. The movement of the boundary blocks and of the underlying medium determines the
motion of the blocks. The synthetic seismicity obtained with the defined block-model is similar to the observed one for the
most seismically active areas. A linear frequency-magnitude (FM) relation (Gutenberg-Richter law) is obtained for synthetic
earthquakes; the slope (b-value) of the FM plot appears larger for the synthetic seismicity than for the observed one. Nevertheless, the b-value is essentially larger in northern and central Italy than that in southern Italy, both in the model and in the observations.
The analysis of the source mechanisms of the synthetic earthquakes shows a good agreement with the observations. In the model
normal faulting is typical for the Apennines, the eastern edge of Sicily and the Calabrian arc, while reverse faulting takes
place at the northwestern boundary of the Adriatic Sea, in the southern Alps and along the eastern edge of the Adria, along
the Dinarides. The model correctly reproduces the extension zone along the Apennines and the contraction zone along the northwestern
boundary of the Adriatic Sea; the counter-clockwise rotation of the Adria is mimed. The resulting movements of the blocks
are in overall agreement with GPS (Global Positioning System) observations. The results of the modeling experiments suggest
that the main features of dynamics and seismicity in the central Mediterranean region cannot be satisfactorily explained as
a consequence of Africa and Eurasia convergence only; the passive subduction in the Calabrian arc and the different rheology
of faults are essential as well. 相似文献
2.
试论安宁河断裂带新活动的分段性与地震活动 总被引：4，自引：0，他引：4
本文根据近几年来对安宁河断裂带的野外调查资料,结合地震活动性、地壳形变、断层带中断层泥SEM特征分析,着重讨论了安宁河断裂带活动性的分段特征及其与地震活动的关系。资料表明,断裂带在晚更新世以来活动的强弱与地震活动在时间上和空间上分布的不均匀性有较好的一致性,即地震活动的强度、频度,严格受断裂带在晚更新世以来的活动强度、活动方式的制约。研究活动断层的活动分段性,对判定地震危险区及工程稳定性评价具有重要的科学意义和应用价值。 相似文献
3.
The best estimate method (BEM), which shifts an object event towards the centroid of the events within its location uncertainty, was originally proposed to clarify the pattern of seismicity distribution. It was later widely applied to constrain the location and geometry of seismogenic structures. The goal of this study is to improve the efficiency, robustness and effectiveness of the BEM. We perform a series of synthetic experiments by generating a three-dimensional (3D) event dataset representing complex tectonic features and perturbing the presumed hypocenter locations. The synthetic experiments show that appropriate expression for the location uncertainty of the object event and restrictive thresholds of the event selection can significantly improve the collapsing seismicity image. We also demonstrate that the performance of our revised BEM (RBEM) is better than that of the original BEM. We then apply our RBEM to the seismicity catalog for the Taiwan region, collapsing the diffusive catalog hypocenters into sharp images of seismicity. Our RBEM result delineates a clearer low-seismicity zone in central Taiwan and a wider separation between the Wadati–Benioff double seismic layers in northeastern Taiwan than the corresponding features in either the catalog seismicity or the 3D relocation seismicity. Because of the simplicity and efficiency of the RBEM, it is perfectly suited to delineate the location and geometry of active faults in routine operations. 相似文献
4.
长乐—诏安断裂带活动特征与继承性活动 总被引：8，自引：0，他引：8
对长乐－诏安断裂带的新、老断裂构造不同时期的活动规律及地震活动特征进行了分析,结果表明,该断裂在晚第四纪时期以继承性活动为特征,并表现出南强北弱的特点。 相似文献
5.
The analysis of seismic hazards relies on the statistical analysis of historical seismic data and the instrumental seismic catalog to obtain the regional earthquake recurrence interval and earthquake probability. The accuracy of analysis thus depends strongly on the completeness of the seismic data used. However, available seismic catalogs are too short or incomplete for the reliable analysis of the statistical characteristics of earthquakes. If a long-term synthetic seismic catalog can be generated using a physics-based numerical simulation, and the simulation results match the crustal deformation, seismicity, and other observations,then such a synthetic catalog helps us to further understand the characteristics of seismic activity and analyze the regional seismic hazard. In this paper, taking the northeastern Tibetan Plateau as a case study, we establish a three-dimensional visco-elastoplastic finite-element model to simulate earthquake cycles and the spatiotemporal evolution of earthquakes on the model fault system and obtain a seismic catalog on a time scale of tens of thousands of years. On the basis that the model satisfies the regional geodynamics of the northeastern Tibetan Plateau, we analyze seismicity on the northeastern Tibetan Plateau using the simulated synthetic earthquake catalog. The characteristics of earthquake recurrence at different locations and different magnitudes, and the long-term average probability of earthquake occurrence within the fault system on the northeastern Tibetan plateau are studied. The results are a reference for regional seismic hazard assessment and provide a basis for the physics-based numerical prediction of earthquakes. 相似文献
6.
Wavelet-based multifractal analysis of earthquakes temporal distribution in Mammoth Mountain volcano,Mono County,Eastern California 总被引：1，自引：1，他引：0
This paper presents a wavelet-based multifractal approach to characterize the statistical properties of temporal distribution of the 1982–2012 seismic activity in Mammoth Mountain volcano. The fractal analysis of time-occurrence series of seismicity has been carried out in relation to seismic swarm in association with magmatic intrusion happening beneath the volcano on 4 May 1989. We used the wavelet transform modulus maxima based multifractal formalism to get the multifractal characteristics of seismicity before, during, and after the unrest. The results revealed that the earthquake sequences across the study area show time-scaling features. It is clearly perceived that the multifractal characteristics are not constant in different periods and there are differences among the seismicity sequences. The attributes of singularity spectrum have been utilized to determine the complexity of seismicity for each period. Findings show that the temporal distribution of earthquakes for swarm period was simpler with respect to pre- and post-swarm periods. 相似文献
7.
Existing loading protocols for quasi-static cyclic testing of structures are based on recordings from regions of high seismicity. For regions of low to moderate seismicity they overestimate imposed cumulative damage demands. Since structural capacities are a function of demand, existing loading protocols applied to specimens representative of structures in low to moderate seismicity regions might underestimate structural strength and deformation capacity. To overcome this problem, this paper deals with the development of cyclic loading protocols for European regions of low to moderate seismicity. Cumulative damage demands imposed by a set of 60 ground motion records are evaluated for a wide variety of SDOF systems that reflect the fundamental properties of a large portion of the existing building stock. The ground motions are representative of the seismic hazard level corresponding to a 2 % probability of exceedance in 50 years in a European moderate seismicity region. To meet the calculated cumulative damage demands, loading protocols for different structural types and vibration periods are developed. For comparison, cumulative seismic demands are also calculated for existing protocols and a set of records that was used in a previous study on loading protocols for regions of high seismicity. The median cumulative demands for regions of low to moderate seismicity are significantly less than those of existing protocols and records of high seismicity regions. For regions of low to moderate seismicity the new protocols might therefore result in larger strength and deformation capacities and hence in more cost-effective structural configurations or less expensive retrofit measures. 相似文献
8.
In the paper, we have discovered the abnormal area distribution features of maximum variation values of ground motion parameter uncertainty with different probabilities of exceedance in 50 years within the range of 100°～120°E,29°～42°N for the purpose to solve the problem that abnormal areas of maximum variation values of ground motion parameter uncertainties emerge in a certain cities and towns caused by seismicity parameter uncertainty in a seismic statistical region in an inhomogeneous distribution model that considers tempo-spatial nonuniformity of seismic activity. And we have also approached the interrelation between the risk estimation uncertainty of a site caused by seismicity parameter uncertainty in a seismic statistical region and the delimitation of potential sources, as well as the reasons for forming abnormal areas. The results from the research indicate that the seismicity parameter uncertainty has unequal influence on the uncertainty of risk estimation at each site in a statistical region in the inhomogeneous distribution model, which relates to the scheme for delimiting potential sources. Abnormal areas of maximum variation values of ground motion parameter uncertainty often emerge in the potential sources of Mu≥8 (Mu is upper limit of a potential source) and their vicinity. However, this kind of influence is equal in the homogeneous distribution model. The uncertainty of risk estimation of each site depends on its seat. Generally speaking, the sites located in the middle part of a statistical region are only related to the seismicity parameter uncertainty of the region, while the sites situated in or near the juncture of two or three statistical regions might be subject to the synthetic influences of seismicity parameter uncertainties of several statistical regions. 相似文献
9.
ＰａｔｅｒｎｓａｎｄｒｅｇｕｌａｒｉｔｙｏｆｒｉｎｇｄｉｓｔｒｉｂｕｔｉｏｎｏｆｓｅｉｓｍｉｃａｃｔｉｖｉｔｙｂｅｆｏｒｅｇｒｅａｔｅａｒｔｈｑｕａｋｅｓｉｎＣｈｉｎａＳＨＩ－ＲＯＮＧＭＥＩ（梅世蓉），ＺＨＩ－ＰＩＮＧＳＯＮＧ（宋治平）ａｎｄＹＡＮ... 相似文献
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11.
A systematic study on “ring phenomena” frequently occurring before great earthquakes has made in this paper, which has analyzed the features of ring distributions before 16 great earthquakes and part of large earthquakes in China and its boundary areas, and discussed their features of generality, regularity and predictive meaning. The results have showed that moderate earthquakes or larger earthquakes distribute around the epicenter like a ring from decades to hundred years before the great earthquakes of magnitude more than 7, which is a general phenomenon of great earthquakes without an exception. The active ring generally occurs in the areas from hundreds to thousands of kilometers from the epicenter (according to the magnitude). The seismicity in the ring has three basic stages with different features. in the first stage, seismicity remains at low level and the earthquakes distribute scatteredly, while the source area of the future great earthquake remains quiet; in the second stage, the seismicity strengthens, whose frequency, intensity, concentrated degree, released rate of strain and ratio of distributed area etc. increase, while the quiet area decreases or disappears; in the third stage, the seismicity is weaker than in the former stage, and the quiet area appears again. The source area surrounded by the active ring might have three periods of activity (called as early-term, medium-term and late-term foreshocks activity). The length of the quiet area undergoes the process from large to small, then to large. Therefore, we can estimate the occurring place, magnitude and seismogenic stage of great earthquake according to the area, length and the seismicity in the active ring, which is valuable to make a long-term prediction of great earthquakes. At last, we had a preliminary discussion on the mechanism of active ring formation. 相似文献
12.
本文改进了地震活动性模拟方法,使模型可以使用GPS反演得到的断层滑动速率的结果作为应力加载,进行区域的地震活动性模拟.选取太原地区作为研究区域,模拟并分析太原地区地震活动性.计算太原地区长达20000年的理论地震目录,通过对理论地震目录进行分析发现模拟结果的震级频度关系与实际观测资料具有相似性.太原地区的震级大于6级的模拟地震在时间上表现出很强的随机性,与年平均发生率为0.0129a~(-1)的Poisson过程对比,当采用卡方检验进行检验时,置信水平达到99.0%;然而,单一断层的强震的时间分布与相应年平均发生率的Poisson分布并不完全相近,部分断层拟合置信水平为90%左右,部分断层置信水平接近为0.这一结果表明,用Poisson过程估计太原地区长期地震发生率是比较合理的,估计单一断层上的地震危险性不是十分合理.地震危险性模拟结果显示,太原盆地地区7级以上地震的复现周期为4000年. 相似文献
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14.
西藏中部及其与青海邻近地区强震活动特征与玛尼7.5级地震预测研究 总被引：2，自引：0，他引：2
依据西藏中部强震活动特征及１９８５年以来中国大陆强震活动新格局,于１９９６年将藏北玛尼一唐古拉山口一带列为未来几年７１／４级地震危险区。这旬刚发生的１９９７．１１．８玛尼７．５级地震有较好的对应。再次表明采用活构造与强震研究相结合、震源区个性和地震带（区）共性相结合,追踪大震发展过程及研究不同必质的强震活动图象等分析方法是有研究前景的。 相似文献
15.
Based on the morphostructural zoning scheme of the Caucasus, the block structure reflecting the real fault geometry and the block formation of the region is constructed. Several dozens of numerical experiments are conducted for simulating the dynamics of the block structure and the arising seismicity. The modeling relies on the following principles. It is assumed that the structure is composed of perfectly rigid blocks separated by infinitely thin fault planes. On the fault planes and on the blocks' bottoms, the blocks viscoelastically interact with each other and with the underlying medium. At each time instant, the translational displacements and rotations of the blocks are calculated from the condition of the quasi-static equilibrium of the entire block structure. The earthquakes occur in accordance with the dry friction model at the time instants when within a certain segment of the fault the stress-to-pressure ratio exceeds the given threshold. The modeling yields the synthetic catalog of the Caucasian earthquakes the spatial distribution of which reflects a set of characteristic features of the real seismicity. The similarity is observed in the magnitude–frequency diagrams of the synthetic and real seismicity. The comparison of the positions of the epicenters of the strong synthetic earthquakes with the results of recognizing the highly seismically active areas in the Caucasus demonstrates the presence of such epicenters in a few highly active areas where, according to the observations, strong earthquakes have not occurred to date. 相似文献
16.
We investigate spatio-temporal properties of earthquake patterns in the San Jacinto fault zone (SJFZ), California, between Cajon Pass and the Superstition Hill Fault, using a long record of simulated seismicity constrained by available seismological and geological data. The model provides an effective realization of a large segmented strike-slip fault zone in a 3D elastic half-space, with heterogeneous distribution of static friction chosen to represent several clear step-overs at the surface. The simulated synthetic catalog reproduces well the basic statistical features of the instrumental seismicity recorded at the SJFZ area since 1981. The model also produces events larger than those included in the short instrumental record, consistent with paleo-earthquakes documented at sites along the SJFZ for the last 1,400 years. The general agreement between the synthetic and observed data allows us to address with the long-simulated seismicity questions related to large earthquakes and expected seismic hazard. The interaction between m ≥ 7 events on different sections of the SJFZ is found to be close to random. The hazard associated with m ≥ 7 events on the SJFZ increases significantly if the long record of simulated seismicity is taken into account. The model simulations indicate that the recent increased number of observed intermediate SJFZ earthquakes is a robust statistical feature heralding the occurrence of m ≥ 7 earthquakes. The hypocenters of the m ≥ 5 events in the simulation results move progressively towards the hypocenter of the upcoming m ≥ 7 earthquake. 相似文献
17.
魏富胜 《地震地磁观测与研究》1993,14(2):42-48
简要回顾了地震活动性定量化研究的进程,概述了各综合定量指标参量的特点,介绍了地震活动度 S 及其在定量描述地震活动性中的某些应用成果,展望了 S 应用于地震监测预报中的可能性。 相似文献
18.
使用2005年11月26日江西九江5.7级地震前震中附近地区的地震资料, 选择反映地震活动时、 空、 强特征的地震频次N(ML≥3.0)、 b值、 η值、 A(b)值、 Mf值、 Ac值、 C值和D值参量进行因子分析。 这些参量之间具有一定的相关性, 各参量在不同时段的变化各有所异, 预报效果并不理想。 但是根据因子分析可以得到反映地震活动时、 空、 强特征的综合指标Wfa值, 该指标在九江5.7级地震前出现明显的异常变化。 表明综合指标Wfa值可以较好地反映地震活动的异常特征。 文中还对与因子分析结果的有关问题进行了讨论。 相似文献
19.
影响地震活动性因素的非均匀细胞自动机模拟研究 总被引：1，自引：0，他引：1
基于细胞自动机模型,构建了由81×81个细胞单元组成非均匀二维单断层介质样本,研究了断层结构细观非均匀性以及相关模型参数变化对模拟输出结果和强度分布特征的影响。研究结果表明:结构非均匀性是影响地震活动性的控制性参量,随着非均匀程度的增强,地震事件数量增多,震级分布变得越来越均匀,破裂演化模式由相对"脆性"向"塑性"变化;介质结构的初始条件和应力加载的随机性对地震活动演化过程基本不产生影响,此外,应力降分配系数减小使b值主体线性段向大震级延伸;随着局部摩擦损耗系数增大,模拟地震事件的数量有所增加,大震级事件数量和震级衰减增强b,值主体线性区间变窄,使断层的变形破坏方式由相对"脆性"向"塑性"变化。这些对理解孕震过程的复杂性是有帮助的。 相似文献
20.
Rodolfo Console Massimo Chiappini Liliana Minelli Fabio Speranza Roberto Carluccio Michele Greco 《Acta Geophysica》2018,66(5):931-943
The application of a newly developed physics-based earthquake simulator to the active faults inferred by aeromagnetism in southern Calabria has produced a synthetic catalog lasting 100 ky including more than 18,000 earthquakes of magnitude ≥?4.0. This catalog exhibits temporal, spatial and magnitude features, which resemble those of the observed seismicity. As an example of the potential use of synthetic catalogs, a map of the peak ground acceleration (PGA) for a given exceedance probability on the territory under investigation has been produced by means of a simple attenuation law applied to all the events reported in the synthetic catalog. This map was compared with the existing hazard map that is presently used in the national seismic building regulations. The comparison supports a strong similarity of our results with the values given in the present Italian seismic building code, despite the latter being based on a different methodology. The same similarity cannot be recognized for the comparison of our present study with the results obtained from a previous study based on our same methodology but with a different geological model. 相似文献