Ground-motion prediction equations for the intermediate depth Vrancea (Romania) earthquakes

We present the regional ground-motion prediction equations for peak ground acceleration (PGA), peak ground velocity (PGV), pseudo-spectral acceleration (PSA), and seismic intensity (MSK scale) for the Vrancea intermediate depth earthquakes (SE-Carpathians) and territory of Romania. The prediction equations were constructed using the stochastic technique on the basis of the regional Fourier amplitude spectrum (FAS) source scaling and attenuation models and the generalised site amplification functions. Values of considered ground motion parameters are given as the functions of earthquake magnitude, depth and epicentral distance. The developed ground-motion models were tested and calibrated using the available data from the large Vrancea earthquakes. We suggest to use the presented equations for the rapid estimation of seismic effect after strong earthquakes (Shakemap generation) and seismic hazard assessment, both deterministic and probabilistic approaches.     

Prediction of strong earthquakes in Vrancea,Romania, using the CN algorithm

The application of the CN algorithm to a new earthquake catalogue, for the period from 1932 to 1993, obtained by merging Romanian and U.S.S.R. data, allows us to monitor, on the intermediate time scale. the preparation of strong, intermediate-depth earthquakes in the Vrancea region. Four of the five strong earthquakes with magnitudes above 6.4 are predicted. The total duration of the Time of Increased Probability (TIP) of the occurrence of an earthquake (TIP) occupies 21.7% of the time interval under consideration, i.e., about 2.5 years for each strong earthquake.     

Prediction of the strong earthquakes in Vrancea,Romania, using the CN algorithm

The application of the CN algorithm to a new earthquake catalogue, for the period from 1932 to 1993, obtained by merging Romanian and U.S.S.R. data, allows us to monitor, on the intermediate time scale, the preparation of strong, intermediate-depth earthquakes in the Vrancea region. Four of the five strong earthquakes with a magnitude above 6.4 are predicted, the total duration of the Time of Increased Probability of the occurrence of an earthquake (TIP) occupies 21.7% of the time interval under consideration, i.e., about 2.5 years for each strong earthquake.     

Multifractal and Chaotic Analysis of Vrancea (Romania) Intermediate-depth Earthquakes: Investigation of the Temporal Distribution of Events

The Vrancea seismic region contains an isolated cluster of events beneath the Carpathian Arc Bend in Romania, dipping to about 200 km depth. Seismic activity mainly occurs at intermediate depths (h > 60 km). The main goal of the paper is to perform an in-depth, complex analysis of the occurrence times of these intermediate-depth events. We also try to show the versatility of the methods used to characterize different aspects of the seismicity evolution and to offer a user-friendly software toolbox to do most of the related computations. The earthquake catalog used in this study spans from 1974 to 2002 and includes only the intermediate-depth events. In the first part of the paper, we analyze the multifractal characteristics of the temporal distribution of earthquakes. The study reveals two distinct scaling regimes. At small scales we found a clear nonhomogeneous, multifractal pattern, while at large scales the temporal distribution of events shows a monofractal, and close to Poissonian (random), behavior. The multifractal behavior at small scales (minutes-hours) is shown to be clearly an effect of the short aftershock sequences that occurred after some major Vrancea earthquakes. In the second part of the paper we analyze whether our temporal series shows a persistent (or anti-persistent) long-term behavior, by using the Detrended Fluctuation Analysis (DFA) method. The results suggest that the analyzed temporal series of Vrancea earthquakes is a non-correlated process. In part three of the paper we seek to determine whether the dynamics of our earthquake system (described by the occurrence time of Vrancea earthquakes) is deterministically chaotic, deriving from a rather simple evolution law, or whether it is stochastic and is generated by a system that possesses many degrees of freedom. The results suggest that our signal is stochastic (probably does not possess an attractor). The limited time-span of the catalog and the analysis performed in this paper cannot rule out the emergence of an interesting, quasi-deterministic and low-dimensional structure in the case of major Vrancea earthquakes.Acknowledgement One of the authors (BE) is grateful to the Japanese Ministry of Education for providing him a Monbusho scholarship for studying in DPRI, Kyoto University. We thank Z.R. Struzik, M Holschneider, J. Mori and D. Kaplan for their useful comments, and acknowledge the support of the staff of DPRI, Kyoto University and the National Inst. for Earth Physics, Bucharest. We thank the two reviewers, M.B. Geilikman and M. Anghel, for their useful suggestions which improved the quality of this work.     

Test of the Empirical Green's Function Deconvolution on Vrancea (Romania) Subcrustal Earthquakes

Vrancea is one of the few singular seismic regions of the world where intermediate-depth earthquakes are permanently generated (around 10 events/month with M _L > 3) within an extremely confined focal volume. This particularity and the relatively large number of short-period waveforms recorded by the Romanian local network provides us the opportunity to test the performance of the empirical Green's function technique in retrieving the source time function and source directivity of the Vrancea earthquakes. Three earthquakes that occurred on March 11, 1983 (M _L = 5.4), April 12, 1983 (M _L = 5.1) and August 7, 1984 (M _L = 5.1) in the lower part of the subducting lithosphere (h 150 km) were analyzed. A set of 28 adjacent events (3.0 < M _L < 4.4) which occurred between 1981 and 1997 were selected as corresponding empirical Green's functions. To test the confidence of the retrieved source time function, we compare the deconvolved pulses using Green's functions of different sizes and recorded simultaneously by short-period and broad-band instruments. Our tests show that the durations of the source time function is well-constrained and is not affected by the limited frequency range of the short-period instruments, or by the relative difference in the focal mechanism between the main event and Green's event. The apparent duration of the source time function outlines source directivity effects, and when these effects are sufficiently strong, they can identify the real fault plane. Relatively short source duration and correspondingly high stress drop values are in agreement with other previous results emphasizing a specific seismic regime in the lower part of the Vrancea subducting lithosphere.     

Active deformation in the Vrancea region,Rumania

Recent and historical seismicity as well as reliable fault plane solutions are used to study the active deformation caused by the occurrence of intermediate depth (60–170 km) earthquakes of the Vrancea region, Rumania. In this area, located in the southeastern part of the Carpathian arc, the westward subduction of the Carpathian trench has terminated, leaving continental lithosphere, at present, at the arc. The principalT axis of the intermediate depth events trends N159°E and has a plunge of 74°, which is the same as the dip of the subducted plate. TheP axis has a trend of 314° and a shallow plunge of 15°. The analysis of the moment tensor of six focal mechanisms showed that the dominant mode of deformation of the subducted lithosphere is a down-dip extension at a rate of about 2 cm/yr, based on seismicity data.     

Waveform inversion of weak vrancea (Romania) earthquakes

Summary The inversion of high-frequency seismograms is performed to retrieve source mechanisms, hypocentral depths and source time functions of two weak Vrancea earthquakes (M_L=3.3), one that occurred in the crust, the other in the lithospheric part of the mantle. The digital waveforms recorded by the local Romanian network are used. Synthetic seismograms are computed by the modal summation method, using the point source approximation, for horizontally layered anelastic media. For each source-to-station path a different structural model is adopted which represents the best 1-D approximation of the medium in this azimuth. Thus, lateral inhomogeneities are taken into account in a simplified way. The source is described by the full moment tensor, allowing both deviatoric and volumetric components to be resolved.Although the structural models are simplified for the range of epicentral distances (15<<<170 km) considered, we find that the fit between the synthetic and observed seismograms is satisfactory for frequencies less than a few Hz. The few P-wave polarities available are not sufficient to determine a reliable source mechanism by standard methods, while the waveform inversion allows us to retrieve source mechanisms that are stable with respect to different boundary conditions and in good agreement with the observed polarities. The source time function is the less stable inverted parameter, being the most influenced by the simplification of the structural models.     

Probabilistic seismic hazard assessment for Romania and sensitivity analysis: A case of joint consideration of intermediate-depth (Vrancea) and shallow (crustal) seismicity

The earthquake risk on Romania is one of the highest in Europe, and seismic hazard for almost half of the territory of Romania is determined by the Vrancea seismic region, which is situated beneath the southern Carpathian Arc. The region is characterized by a high rate of occurrence of large earthquakes in a narrow focal volume at depth from 70 to 160 km. Besides the Vrancea area, several zones of shallow seismicity located within and outside the Romanian territory are considered as seismically dangerous. We present the results of probabilistic seismic hazard analysis, which implemented the “logic tree” approach, and which considered both the intermediate-depth and the shallow seismicity. Various available models of seismicity and ground-motion attenuation were used as the alternative variants. Seismic hazard in terms of macroseismic intensities, peak ground acceleration, and response spectra was evaluated for various return periods. Sensitivity study was performed to analyze the impact of variation of input parameters on the hazard results. The uncertainty on hazard estimates may be reduced by better understanding of parameters of the Vrancea source zone and the zones of crustal seismicity. Reduction of uncertainty associated with the ground-motion models is also very important issue for Romania.     

Macroseismic field of the October 27, 2004 Vrancea (Romania) moderate subcrustal earthquake

On October 27, 2004, a moderate size earthquake occurred in the Vrancea seismogenic region (Romania). The Vrancea seismic zone is an area of concentrated seismicity at intermediate depths beneath the bending area of the southeastern Carpathians. The 2004 M _w?=?6 Vrancea subcrustal earthquake is the largest seismic event recorded in Romania since the 1990 earthquakes. With a maximum macroseismic intensity of VII Medvedev–Sponheuer–Kárník (MSK-64) scale, the seismic event was felt to a distance of 600 km from the epicentre. This earthquake caused no serious damage and human injuries. The main purpose of this paper is to present the macroseismic map of the earthquake based on the MSK-64 intensity scale. After the evaluation of the macroseismic effects of this earthquake, an intensity dataset has been obtained for 475 sites in the Romanian territory. Also, the maximum horizontal accelerations recorded in the area by the K2 network are compared to the intensity values.     

基于GIS的中国地震危险性模式研究

从与历史地震数据的时间衔接考虑,合理选择初始地震危险性模式。借鉴美国地震危险性图编制的思路,并基于GIS的思想和技术,使用历史地震数对初始模式进行多次叠加改造,获得当今中国地震危险性模式。与实际地震灾害的对照结果,验证了该方法的有效性。可见,基于GIS的中国地震危险性模式研究具有一定的现实意义。     

我国地震海啸危险性分析方法研究

美国、日本等国家已经建立了完善的海啸防灾减灾机制，对海啸危险性分析方法的研究也做了很多的工作，而我国目前在这方面尚属空白。本文首次对我国的海啸危险性分析方法进行了研究，提出了我国地震海啸危险性分析的基本原则，在此基础上，借鉴我国成熟的地震危险性分析方法，建立了我国地震海啸危险性分析方法的主要步骤。在根据我国一些历史地震海啸资料的基础上，通过统计的方法对我国珠江三角洲的海啸危险性进行了研究。     

Attenuation of P and pP waves in Vrancea area – Romania

The seismic attenuation in the Vrancea region (Romania) is investigated from teleseismic recordings of P and pP waves during the four major, intermediate-depth Romanian events that occurred since the onset of digital instrumentation. Most stations are located in Canada and in the United States, being equipped with a variety of sensors, especially short-period ones. The amplitude spectral ratio method is used, assuming no frequency dependence of the Q _P factor in the range 0.2–2 Hz. No apparent correlation between the derived attenuation value and the type of recording sensor is observed. Lateral variations of the attenuation are obtained, with a very low Q _P area (values down to 33) located in the northwestern part of the Vrancea seismogenic volume. For the stations with different azimuth angles in relation to the epicentral area, Q _P values routinely exceed 200. Most likely, the low attenuation values are related to an upwelling mantle material located immediately beneath the crust, but limited in depth to at least 100 km.     

华北地区震群活动的阶段性特征

通过对华北地区1970年以来震群活动的分析表明，唐山地震的震群活动显示出一定的迁移性和阶段性。应用流变介质包体孕震模型的理论进行了初步力学分析。张北地震的预测检验表明，震群活动的迁移性与阶段性对强震的中期预测具有一定指导意义。     

关于地震灾害快速评估系统的思考

基于地震快速评估经济损失结果与地震现场调查得到的经济损失结果有较大的差异现象, 为了进一步提高地震快速评估经济损失结果的精确性, 笔者通过对地震快速评估经济损失结果和实际现场调查得到的经济损失结果进行对比研究, 并从建筑物单价和建筑物损失比的角度对快速评估结果进行修正, 以发生在云南境内的10次典型地震为例, 初步得出了对地震经济损失快速评估结果粗略的修正系数。 在一定程度上较大提高了地震快速评估经济损失的精确性。 为地震救援指挥工作提供了更加可靠的依据。     

Accounting for site effect in probabilistic assessment of seismic hazard for Romania and Bucharest: a case of deep seismicity in Vrancea zone

The paper presents recent achievements in evaluations of site-dependent seismic hazard in Romania and the capital city of Bucharest caused by the Vrancea focal zone (SE-Carpathians). The zone is characterized by a high rate of occurrence of large earthquakes in a narrow focal volume at depths 60–170 km. The database that was used for the hazard evaluation includes parameters of seismicity, ground-motion source scaling and attenuation models (Fourier amplitude spectra), and site-dependent spectral amplification functions. Ground-motion characteristics were evaluated on the basis of several hundred records from more than 120 small magnitude (M 3.5–5) earthquakes occurred in 1996–2001 and a few tens of acceleration records obtained during four large (M 7.4, 7.2, 6.9 and 6.3) earthquakes. The data provide a basis for probabilistic seismic hazard assessment in terms of peak ground acceleration, peak spectral acceleration and MSK intensity using Fourier amplitude spectra for various exceedance probabilities or average return periods. It has been shown that the influence of geological factors plays very important role in distribution of earthquake ground-motion parameters along the territory of Romania.     

汶川大地震中德阳地区液化特点分析

汶川大地震中八个主要地区均有液化现象出现,其中德阳地区液化现象及其震害最为显著.通过现场调查和工程地质资料分析,德阳地区的液化特点为:液化带主要集中在绵竹市、什邡市和德阳市,绵竹市最为严重;液化在烈度Ⅶ、Ⅷ、Ⅸ度区均有出现,但Ⅷ度区最为集中;液化喷水高度多在几公分到2m之间,最高一处超过10 m;液化场地喷出物基本涵盖...     

Reconstruction of earthquake hazard in regions of sparse seismic monitoring

Studying strong motion records and the spatial distribution of ground shaking is of great importance in understanding the underlying causes of damage in earthquakes. Many regions in the world are either not instrumented or are sparsely instrumented. As such, significant opportunities for motion-damage correlations are lost. Two recent and damaging earthquakes belong to the class of lost opportunities, namely the Kashmir (Pakistan) earthquake of October 2005 and the Yogyakarta (Indonesia) earthquake of May 2006. In this paper, an overview of the importance of supply and demand studies in earthquake-stricken regions is given, followed by two examples of investigative engineering seismology aimed at reconstructing the hazard from sparse data. The paper closes with a plea for responsible authorities to invest in seismic monitoring networks in the very near future.     

云南地区地震序列的波速比(Vp/Vs)异常研究

针对2000年姚安6.5级、2001年施甸5级、2001年永胜6.0级和2003年大姚6.2、6.1级地震序列,分别采用多台法和固定台站方法计算了这些地震序列的波速比。由于采用的均是数字波形资料,到时读取精度达到0.02s。考虑台站因素,计算波速比的置信度最低达到95%。文中讨论强余震之前波速比的变化特征,发现强余震前出现波速比趋势性下降的特征,这对强余震的短临预测有实用价值;主震发生时和发生以后波速比的波动范围的对比,对震区的震情趋势判定有一定的指示和参考。     

Seismogenic mechanism of the Lancang and Gengma earthquakes

Ｓｅｉｓｍｏｇｅｎｉｃ　ｍｅｃｈａｎｉｓｍ　ｏｆ　ｔｈｅ　Ｌａｎｃａｎｇ　ａｎｄ　Ｇｅｎｇｍａ　ｅａｒｔｈｑｕａｋｅｓ（俞维贤）（周瑞琦）（候学英）（周光全）ＳｅｉｓｍｏｇｅｎｉｃｍｅｃｈａｎｉｓｍｏｆｔｈｅＬａｎｃａｎｇａｎｄＧｅｎｇｍａｅａｒｔｈ...     

西南地区前兆观测异常特征和地震短期预测方法研究

通过对西南地区1970～2001年39组52次6级以上地震及四川部分5级以上地震震例资料的剖析,进一步研究西南地区各类前兆中、短期异常判据和指标;研究西南地区强震孕育前兆异常由中期向短期(临震)过渡、演化的标志和判据并作物理解释;并进行了西南地区前兆短期预测方法及强震短期预测时、空、强指标和判据的研究和西南地区地下流体新观测方法及灵敏测项的研究。