Vladimir Sokolov - Academia.edu (original) (raw)
Papers by Vladimir Sokolov
The ground-motion database collected recently in Taiwan was used for evaluation of strong ground ... more The ground-motion database collected recently in Taiwan was used for evaluation of strong ground motion models. The database contains more then 2800 acceleration records from M > 3.0 -3.5 earthquakes occurred in 1993-2004. The records were obtained at rock (class B) sites located in the northern and eastern parts of Taiwan. Parameters of attenuation models (geometrical spreading and anelastic attenuation) were evaluated using acceleration spectra corrected for the site effect. The horizontal-to-vertical Fourier spectral ratio of the S-wave phase was used for the correction. The analysis was performed for three characteristic zones, namely: shallow (hypocentral depth < 30-35 km) earthquakes occurred beneath central Taiwan, shallow offshore earthquakes occurred to the east of island, and deep earthquakes (depth > 35 km). Analysis of spectra corrected for site effect, attenuation, and the influence of upper crust (kappa-factor) showed that the source spectra in Taiwan region may be described by the ω-square spectral model . The value of seismic moment is estimated from regional relationships between seismic moment and local magnitude. The stress parameter should be considered as a magnitude-dependent quantity (120-150 bars for M 5.0 and 250-300 bars for M 6.8) for shallow earthquakes beneath central Taiwan. The offshore and deep earthquakes are characterized by relatively constant values of the stress parameter.
Shakemaps are generated within a few minutes on a routine basis for Southern California (Wald et ... more Shakemaps are generated within a few minutes on a routine basis for Southern California (Wald et al., 1999) by extrapolation ground motion parameters such as PGA, PGV, response spectra (RS), and computed intensity (CI) from observational sites equipped with accelerometers with distances in the range of kilometers to tens of kilometers between them. Extrapolation is based on empirical hard-rock attenuation relations, geological classification of the sites, and on empirical relations of ground motion amplification for a given geological class. The Californian approach cannot be copied for many cases due to a lacking empirical strong motion data base and due to missing understanding of the relations between geological near-surface structure and ground motion amplification for PGA, PGV or CI. We suggest the following approach based on Fourier amplitude spectrum (FAS) that can be used in most cases and that allows obtaining site-dependent assessment in terms of various ground motion para...
Determination of earthquake magnitude and the strength of shaking at a site from the initial P-wa... more Determination of earthquake magnitude and the strength of shaking at a site from the initial P-wave portion of ground notion is the key problems for earthquake Early Warning (EEW). In this study we selected two parameters of ground motion, namely - characteristic period, which is used for magnitude estimation, and instrumental JMA intensity, which characterizes the level of shaking. We analyzed performance of the parameters scaling relations using datasets collected in various seismic regions in respect of (a) characteristics of datasets accumulated in the regions; (b) variation of initial conditions applying when determining the parameters (length of P-wave windows, number of stations used); (c) possible combinations of the parameters. The used datasets include more than 5350 records that were obtained from more than 130 earthquakes (moment magnitude range 4.1 - 7.6) occurred in Japan, Taiwan and California. We give a particular attention to the problem of proper consideration of e...
NATO Science for Peace and Security Series C: Environmental Security, 2009
... The macroseismic map of Demetrescu (1941) was made available by Traian Moldoveanu, GEOTEC Con... more ... The macroseismic map of Demetrescu (1941) was made available by Traian Moldoveanu, GEOTEC Consultant Bucharest, and was digitized and geo-referenced by W. Weisbrich, Institute of Photogrammetry and Remote Sensing, Karlsruhe University. ...
Natural Hazards, 2014
ABSTRACT Consideration of within-earthquake ground-motion correlation is essential for the estima... more ABSTRACT Consideration of within-earthquake ground-motion correlation is essential for the estimation of seismic hazards, damage, and loss for spatially distributed systems. In many seismically active regions, the strong motion data of real engineering significance are completely unavailable or very scarce. The absence of necessary data does not allow developing regional empirical correlation models, and the models obtained for other regions should be used with correspondent sensitivity analysis. The level of within-earthquake correlation may vary in broad range; therefore, development of correspondent criteria for selection from available models is important. In this paper, we analyzed the performance of a system of critical elements of electric power network (substations) depending on variations in within-earthquake correlation. The performance is described as probability of different levels of non-functionality, i.e., percentage of area suffering power outage, and probability of expected number of customers without power. We have shown that the proper choice of the within-earthquake correlation model is critical in comprehensive estimations of functionality of substations in electrical power system. Skipping the ground-motion variability and within-earthquake correlation may lead to unreliable results. Relevance of geology-based within-earthquake correlation models has been demonstrated, and a scheme, which allows reducing uncertainty in the choice of realistic correlation, has been proposed.
Soil Dynamics and Earthquake Engineering, 2004
The paper presents recent achievements in evaluations of site-dependent seismic hazard in Romania... more 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. q
Earthquake Microzoning, 2002
... It is assumed that earthquake occurrence is a stationary random process and the time ... are ... more ... It is assumed that earthquake occurrence is a stationary random process and the time ... are used for generation of ground-motion time series (``hazard-compatible accelerograms''). ... used in engineering practice: seismic intensity, peak ground acceleration and response spectra. ...
Earth, Planets and Space, 2009
Determination of earthquake magnitude from the initial P-wave portion of ground motion is the key... more Determination of earthquake magnitude from the initial P-wave portion of ground motion is the key problems for Earthquake Early Warning (EEW). We analyzed performance of scaling relations between one of the frequently used early warning parameters, so-called characteristic period τ C and moment magnitude M W in respect of (a) characteristics of datasets accumulated in various regions (earthquake depth, characteristics of network) and (b) variation of initial conditions applying for determination of the parameter τ C (length of Pwave window, number of used stations). The used data contain strong-motion records from 110 earthquakes (moment magnitude range 4.4-7.6) occurred in Japan and Taiwan. We show that, although the standard error of regression τ C = f (M W ) in general becomes smaller with the increase of the length of P-wave window (PL) and the number (N ) of averaged observations (stations), the uncertainty in estimation of M W given observed τ C does not decrease further for PL > 3-4 seconds and N > 3-4 stations. The information about earthquake depth also plays an important role in reducing the uncertainty of magnitude estimations. The table of confidence limits for estimations of the moment magnitudeM W based on observations of the characteristic period τ C is provided.
Bulletin of Earthquake Engineering, 2014
ABSTRACT The results of classical probabilistic seismic hazard analysis (PSHA) contain no informa... more ABSTRACT The results of classical probabilistic seismic hazard analysis (PSHA) contain no information about simultaneous ground motions at different sites during a particular earthquake. Seismic risk analysis for distributed critical structures requires estimates of the level of earthquake shaking that are likely to occur concurrently at multiple locations: whether the vulnerable elements of a lifeline system are likely to be simultaneously affected by shaking of sufficient strength to disable them and whether the shaking at any one of critical points may be sufficient to cause failure of the whole system. While the analysis of lifeline performance requires multiple-location estimations, the sparsely located elements of a network or critical facilities are designed on the basis of point-wise PSHA. In this paper we study specific features of multiple-location PSHA, as compared with the classical point-wise PSHA, using Monte Carlo simulations. We analyze the level of ground motion (PGA) that will be exceeded at any site inside a particular area or at several sites simultaneously with reference annual probability. The analysis has been performed for regions of Western and South-Western Germany, Northern and Eastern Taiwan, which represent different levels of seismicity (low, moderate and high, respectively). The relationship between the multiple-location and point-wise estimations are analyzed and quantified. Results of the study may be used to decide whether it may be possible to utilize the procedure of point-wise PSHA in particular cases of multiple-location PSHA, i.e. for assessment of maximum level of ground motion among several sites, or for estimation a reasonable lower safety level when considering simultaneous exceedances.
The ground-motion database collected recently in Taiwan was used for evaluation of strong ground ... more The ground-motion database collected recently in Taiwan was used for evaluation of strong ground motion models. The database contains more then 2800 acceleration records from M > 3.0 - 3.5 earthquakes occurred in 1993-2004. The records were obtained at rock (class B) sites located in the northern and eastern parts of Taiwan. Parameters of attenuation models (geometrical spreading and anelastic
Soil Dynamics and Earthquake Engineering, 2007
The frequency-dependent amplification for rock (NEHRP-class B) sites was studied using earthquake... more The frequency-dependent amplification for rock (NEHRP-class B) sites was studied using earthquake ground-motion database collected in Taiwan during implementation of the Taiwan Strong Motion Instrumentation Program. The database used includes several hundred records from earthquakes of M L 4.0-7.3 occurred between 1993 and 2004. The characteristics of amplification were evaluated using the well-known technique of horizontal-to-vertical Fourier spectral ratio (H/V) of the S-wave phase [Lermo J, Chavez-Garcia FJ. Site effect evaluation using spectral ratios with only one station. Bull Seism Soc Am 1993;83:1574-94]. The study allows us to analyze peculiarities of rock sites amplification in Northern and Eastern Taiwan. It was suggested to divide the NEHRP-class B site amplification into four types based on frequency of maximum amplification and the shape of amplification function. The applicability of the technique was also checked for a few stiff and soft soil sites (NEHRP-classes D and E). r
Soil Dynamics and Earthquake Engineering, 2000
... hypocentral distances (10, 50 and 100 km) using ω-squared spectral models and stochasticappro... more ... hypocentral distances (10, 50 and 100 km) using ω-squared spectral models and stochasticapproach for the ... Building Code design spectrum (4) represents rock and stiff soil sites and is used for design ... may differ in the various parts of the world and even within a seismic region. ...
Soil Dynamics and Earthquake Engineering, 2000
... In the second approach, the empirical attenuation relations developed for different site cond... more ... In the second approach, the empirical attenuation relations developed for different site conditions are ... A stochastic model, site response computations, and Monte Carlo statistics may be used [11] to ... 2) the variety of local soil conditions may be considered using soil/reference site ...
Pure and Applied Geophysics, 2005
The August 17, 1999 Kocaeli earthquake ruptured the earth's surface along 145 km and produced a m... more The August 17, 1999 Kocaeli earthquake ruptured the earth's surface along 145 km and produced a magnitude of M w ¼ 7.4. As expected for such an event Modified Mercalli intensities of typically IX and X in the vicinity of the fault were determined. Yet the observed accelerations at the five near-fault sites remained amazingly small with horizontal PGA values of 0.14 g to 0.4 g. We attempt to resolve the enigma by modeling surface ground motion with a finite-difference algorithm, utilizing two different rupture and slip histories derived from the strong-motion observations and 'translate' the computed horizontal motion in intensity values. We can show that (a) in a given simple crustal velocity model different slip distributions result in significantly different ground motion distributions in the vicinity of the fault even though both slip distributions fit the observed accelerometer data quite well. (b) Both slip distributions 'project' high ground motion into areas adjacent to the fault where no accelerometer was located. (c) Both slip distributions are not fully compatible with observed intensity observations around the fault, although this could be partly attributed to the lack of knowledge regarding to the crustal structure. In the light of our results it would thus be misleading if the few strong-motion observations around the Kocaeli earthquake fault were taken as typical or representative for the entire area and for potential future events.
Natural Hazards, 2007
Intermediate-depth earthquakes in the Vrancea region occur in response to stress generation due t... more Intermediate-depth earthquakes in the Vrancea region occur in response to stress generation due to descending lithosphere beneath the southeastern Carpathians. In this article, tectonic stress and seismicity are analyzed in the region on the basis of a vast body of observations. We show a correlation between the location of intermediate-depth earthquakes and the predicted localization of maximum shear stress in the lithosphere. A probabilistic seismic hazard assessment (PSHA) for the region is presented in terms of various ground motion parameters on the utilization of Fourier amplitude spectra used in engineering practice and risk assessment (peak ground acceleration, response spectra amplitude, and seismic intensity). We review the PSHA carried out in the region, and present new PSHA results for the eastern and southern parts of Romania. Our seismic hazard assessment is based on the information about the features of earthquake ground motion excitation, seismic wave propagation (attenuation), and site effect in the region. Spectral models and characteristics of site-response on earthquake ground motions are obtained from the regional ground motion data including several hundred records of small and large earthquakes. Results of the probabilistic seismic hazard assessment are consistent with the features of observed earthquake effects in the southeastern Carpathians and show that geological factors play an important part in the distribution of the earthquake ground motion parameters.
Earthquake Spectra, 2009
We establish and test a shake map methodology for intermediate-depth Vrancea earthquakes, based o... more We establish and test a shake map methodology for intermediate-depth Vrancea earthquakes, based on seismological information gathered in Romania during recent years. We use region-(azimuth-) dependent attenuation relations derived from stochastic simulations of ground motions using spectral models of Vrancea earthquakes. Both region boundaries and Fourier amplification spectra for the characterization of seismic site effects are based on several hundred weak, moderate and strong-motion records and macroseismic intensity maps. We determine region-specific, magnitude-and distance-dependent amplification factors of peak values and instrumental intensity relative to rock. We interpolate recorded ground motions and ground motion estimates from the obtained amplification factors and attenuation relations for rock conditions. The resulting shake maps show a good agreement with macroseismic descriptions of moderate-sized and large Vrancea earthquakes, demonstrating the feasibility of a seismological approach to shake map generation. Unlike previous methodologies, this approach requires neither expensive assessments of geology-dependent site amplification factors, nor large numbers of strong-motion records. Our results are in good agreement with empirical topographic slope-site amplification relations, but give a better reflection of the abnormal attenuation of seismic waves in the Transylvanian region and the strong amplification in the Focsani basin.
The ground-motion database collected recently in Taiwan was used for evaluation of strong ground ... more The ground-motion database collected recently in Taiwan was used for evaluation of strong ground motion models. The database contains more then 2800 acceleration records from M > 3.0 -3.5 earthquakes occurred in 1993-2004. The records were obtained at rock (class B) sites located in the northern and eastern parts of Taiwan. Parameters of attenuation models (geometrical spreading and anelastic attenuation) were evaluated using acceleration spectra corrected for the site effect. The horizontal-to-vertical Fourier spectral ratio of the S-wave phase was used for the correction. The analysis was performed for three characteristic zones, namely: shallow (hypocentral depth < 30-35 km) earthquakes occurred beneath central Taiwan, shallow offshore earthquakes occurred to the east of island, and deep earthquakes (depth > 35 km). Analysis of spectra corrected for site effect, attenuation, and the influence of upper crust (kappa-factor) showed that the source spectra in Taiwan region may be described by the ω-square spectral model . The value of seismic moment is estimated from regional relationships between seismic moment and local magnitude. The stress parameter should be considered as a magnitude-dependent quantity (120-150 bars for M 5.0 and 250-300 bars for M 6.8) for shallow earthquakes beneath central Taiwan. The offshore and deep earthquakes are characterized by relatively constant values of the stress parameter.
Shakemaps are generated within a few minutes on a routine basis for Southern California (Wald et ... more Shakemaps are generated within a few minutes on a routine basis for Southern California (Wald et al., 1999) by extrapolation ground motion parameters such as PGA, PGV, response spectra (RS), and computed intensity (CI) from observational sites equipped with accelerometers with distances in the range of kilometers to tens of kilometers between them. Extrapolation is based on empirical hard-rock attenuation relations, geological classification of the sites, and on empirical relations of ground motion amplification for a given geological class. The Californian approach cannot be copied for many cases due to a lacking empirical strong motion data base and due to missing understanding of the relations between geological near-surface structure and ground motion amplification for PGA, PGV or CI. We suggest the following approach based on Fourier amplitude spectrum (FAS) that can be used in most cases and that allows obtaining site-dependent assessment in terms of various ground motion para...
Determination of earthquake magnitude and the strength of shaking at a site from the initial P-wa... more Determination of earthquake magnitude and the strength of shaking at a site from the initial P-wave portion of ground notion is the key problems for earthquake Early Warning (EEW). In this study we selected two parameters of ground motion, namely - characteristic period, which is used for magnitude estimation, and instrumental JMA intensity, which characterizes the level of shaking. We analyzed performance of the parameters scaling relations using datasets collected in various seismic regions in respect of (a) characteristics of datasets accumulated in the regions; (b) variation of initial conditions applying when determining the parameters (length of P-wave windows, number of stations used); (c) possible combinations of the parameters. The used datasets include more than 5350 records that were obtained from more than 130 earthquakes (moment magnitude range 4.1 - 7.6) occurred in Japan, Taiwan and California. We give a particular attention to the problem of proper consideration of e...
NATO Science for Peace and Security Series C: Environmental Security, 2009
... The macroseismic map of Demetrescu (1941) was made available by Traian Moldoveanu, GEOTEC Con... more ... The macroseismic map of Demetrescu (1941) was made available by Traian Moldoveanu, GEOTEC Consultant Bucharest, and was digitized and geo-referenced by W. Weisbrich, Institute of Photogrammetry and Remote Sensing, Karlsruhe University. ...
Natural Hazards, 2014
ABSTRACT Consideration of within-earthquake ground-motion correlation is essential for the estima... more ABSTRACT Consideration of within-earthquake ground-motion correlation is essential for the estimation of seismic hazards, damage, and loss for spatially distributed systems. In many seismically active regions, the strong motion data of real engineering significance are completely unavailable or very scarce. The absence of necessary data does not allow developing regional empirical correlation models, and the models obtained for other regions should be used with correspondent sensitivity analysis. The level of within-earthquake correlation may vary in broad range; therefore, development of correspondent criteria for selection from available models is important. In this paper, we analyzed the performance of a system of critical elements of electric power network (substations) depending on variations in within-earthquake correlation. The performance is described as probability of different levels of non-functionality, i.e., percentage of area suffering power outage, and probability of expected number of customers without power. We have shown that the proper choice of the within-earthquake correlation model is critical in comprehensive estimations of functionality of substations in electrical power system. Skipping the ground-motion variability and within-earthquake correlation may lead to unreliable results. Relevance of geology-based within-earthquake correlation models has been demonstrated, and a scheme, which allows reducing uncertainty in the choice of realistic correlation, has been proposed.
Soil Dynamics and Earthquake Engineering, 2004
The paper presents recent achievements in evaluations of site-dependent seismic hazard in Romania... more 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. q
Earthquake Microzoning, 2002
... It is assumed that earthquake occurrence is a stationary random process and the time ... are ... more ... It is assumed that earthquake occurrence is a stationary random process and the time ... are used for generation of ground-motion time series (``hazard-compatible accelerograms''). ... used in engineering practice: seismic intensity, peak ground acceleration and response spectra. ...
Earth, Planets and Space, 2009
Determination of earthquake magnitude from the initial P-wave portion of ground motion is the key... more Determination of earthquake magnitude from the initial P-wave portion of ground motion is the key problems for Earthquake Early Warning (EEW). We analyzed performance of scaling relations between one of the frequently used early warning parameters, so-called characteristic period τ C and moment magnitude M W in respect of (a) characteristics of datasets accumulated in various regions (earthquake depth, characteristics of network) and (b) variation of initial conditions applying for determination of the parameter τ C (length of Pwave window, number of used stations). The used data contain strong-motion records from 110 earthquakes (moment magnitude range 4.4-7.6) occurred in Japan and Taiwan. We show that, although the standard error of regression τ C = f (M W ) in general becomes smaller with the increase of the length of P-wave window (PL) and the number (N ) of averaged observations (stations), the uncertainty in estimation of M W given observed τ C does not decrease further for PL > 3-4 seconds and N > 3-4 stations. The information about earthquake depth also plays an important role in reducing the uncertainty of magnitude estimations. The table of confidence limits for estimations of the moment magnitudeM W based on observations of the characteristic period τ C is provided.
Bulletin of Earthquake Engineering, 2014
ABSTRACT The results of classical probabilistic seismic hazard analysis (PSHA) contain no informa... more ABSTRACT The results of classical probabilistic seismic hazard analysis (PSHA) contain no information about simultaneous ground motions at different sites during a particular earthquake. Seismic risk analysis for distributed critical structures requires estimates of the level of earthquake shaking that are likely to occur concurrently at multiple locations: whether the vulnerable elements of a lifeline system are likely to be simultaneously affected by shaking of sufficient strength to disable them and whether the shaking at any one of critical points may be sufficient to cause failure of the whole system. While the analysis of lifeline performance requires multiple-location estimations, the sparsely located elements of a network or critical facilities are designed on the basis of point-wise PSHA. In this paper we study specific features of multiple-location PSHA, as compared with the classical point-wise PSHA, using Monte Carlo simulations. We analyze the level of ground motion (PGA) that will be exceeded at any site inside a particular area or at several sites simultaneously with reference annual probability. The analysis has been performed for regions of Western and South-Western Germany, Northern and Eastern Taiwan, which represent different levels of seismicity (low, moderate and high, respectively). The relationship between the multiple-location and point-wise estimations are analyzed and quantified. Results of the study may be used to decide whether it may be possible to utilize the procedure of point-wise PSHA in particular cases of multiple-location PSHA, i.e. for assessment of maximum level of ground motion among several sites, or for estimation a reasonable lower safety level when considering simultaneous exceedances.
The ground-motion database collected recently in Taiwan was used for evaluation of strong ground ... more The ground-motion database collected recently in Taiwan was used for evaluation of strong ground motion models. The database contains more then 2800 acceleration records from M > 3.0 - 3.5 earthquakes occurred in 1993-2004. The records were obtained at rock (class B) sites located in the northern and eastern parts of Taiwan. Parameters of attenuation models (geometrical spreading and anelastic
Soil Dynamics and Earthquake Engineering, 2007
The frequency-dependent amplification for rock (NEHRP-class B) sites was studied using earthquake... more The frequency-dependent amplification for rock (NEHRP-class B) sites was studied using earthquake ground-motion database collected in Taiwan during implementation of the Taiwan Strong Motion Instrumentation Program. The database used includes several hundred records from earthquakes of M L 4.0-7.3 occurred between 1993 and 2004. The characteristics of amplification were evaluated using the well-known technique of horizontal-to-vertical Fourier spectral ratio (H/V) of the S-wave phase [Lermo J, Chavez-Garcia FJ. Site effect evaluation using spectral ratios with only one station. Bull Seism Soc Am 1993;83:1574-94]. The study allows us to analyze peculiarities of rock sites amplification in Northern and Eastern Taiwan. It was suggested to divide the NEHRP-class B site amplification into four types based on frequency of maximum amplification and the shape of amplification function. The applicability of the technique was also checked for a few stiff and soft soil sites (NEHRP-classes D and E). r
Soil Dynamics and Earthquake Engineering, 2000
... hypocentral distances (10, 50 and 100 km) using ω-squared spectral models and stochasticappro... more ... hypocentral distances (10, 50 and 100 km) using ω-squared spectral models and stochasticapproach for the ... Building Code design spectrum (4) represents rock and stiff soil sites and is used for design ... may differ in the various parts of the world and even within a seismic region. ...
Soil Dynamics and Earthquake Engineering, 2000
... In the second approach, the empirical attenuation relations developed for different site cond... more ... In the second approach, the empirical attenuation relations developed for different site conditions are ... A stochastic model, site response computations, and Monte Carlo statistics may be used [11] to ... 2) the variety of local soil conditions may be considered using soil/reference site ...
Pure and Applied Geophysics, 2005
The August 17, 1999 Kocaeli earthquake ruptured the earth's surface along 145 km and produced a m... more The August 17, 1999 Kocaeli earthquake ruptured the earth's surface along 145 km and produced a magnitude of M w ¼ 7.4. As expected for such an event Modified Mercalli intensities of typically IX and X in the vicinity of the fault were determined. Yet the observed accelerations at the five near-fault sites remained amazingly small with horizontal PGA values of 0.14 g to 0.4 g. We attempt to resolve the enigma by modeling surface ground motion with a finite-difference algorithm, utilizing two different rupture and slip histories derived from the strong-motion observations and 'translate' the computed horizontal motion in intensity values. We can show that (a) in a given simple crustal velocity model different slip distributions result in significantly different ground motion distributions in the vicinity of the fault even though both slip distributions fit the observed accelerometer data quite well. (b) Both slip distributions 'project' high ground motion into areas adjacent to the fault where no accelerometer was located. (c) Both slip distributions are not fully compatible with observed intensity observations around the fault, although this could be partly attributed to the lack of knowledge regarding to the crustal structure. In the light of our results it would thus be misleading if the few strong-motion observations around the Kocaeli earthquake fault were taken as typical or representative for the entire area and for potential future events.
Natural Hazards, 2007
Intermediate-depth earthquakes in the Vrancea region occur in response to stress generation due t... more Intermediate-depth earthquakes in the Vrancea region occur in response to stress generation due to descending lithosphere beneath the southeastern Carpathians. In this article, tectonic stress and seismicity are analyzed in the region on the basis of a vast body of observations. We show a correlation between the location of intermediate-depth earthquakes and the predicted localization of maximum shear stress in the lithosphere. A probabilistic seismic hazard assessment (PSHA) for the region is presented in terms of various ground motion parameters on the utilization of Fourier amplitude spectra used in engineering practice and risk assessment (peak ground acceleration, response spectra amplitude, and seismic intensity). We review the PSHA carried out in the region, and present new PSHA results for the eastern and southern parts of Romania. Our seismic hazard assessment is based on the information about the features of earthquake ground motion excitation, seismic wave propagation (attenuation), and site effect in the region. Spectral models and characteristics of site-response on earthquake ground motions are obtained from the regional ground motion data including several hundred records of small and large earthquakes. Results of the probabilistic seismic hazard assessment are consistent with the features of observed earthquake effects in the southeastern Carpathians and show that geological factors play an important part in the distribution of the earthquake ground motion parameters.
Earthquake Spectra, 2009
We establish and test a shake map methodology for intermediate-depth Vrancea earthquakes, based o... more We establish and test a shake map methodology for intermediate-depth Vrancea earthquakes, based on seismological information gathered in Romania during recent years. We use region-(azimuth-) dependent attenuation relations derived from stochastic simulations of ground motions using spectral models of Vrancea earthquakes. Both region boundaries and Fourier amplification spectra for the characterization of seismic site effects are based on several hundred weak, moderate and strong-motion records and macroseismic intensity maps. We determine region-specific, magnitude-and distance-dependent amplification factors of peak values and instrumental intensity relative to rock. We interpolate recorded ground motions and ground motion estimates from the obtained amplification factors and attenuation relations for rock conditions. The resulting shake maps show a good agreement with macroseismic descriptions of moderate-sized and large Vrancea earthquakes, demonstrating the feasibility of a seismological approach to shake map generation. Unlike previous methodologies, this approach requires neither expensive assessments of geology-dependent site amplification factors, nor large numbers of strong-motion records. Our results are in good agreement with empirical topographic slope-site amplification relations, but give a better reflection of the abnormal attenuation of seismic waves in the Transylvanian region and the strong amplification in the Focsani basin.