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Matteo Picozzi - One of the best experts on this subject based on the ideXlab platform.
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evaluation of proxies for seismic site conditions in large urban areas the example of santiago de chile
Physics and Chemistry of The Earth, 2011Co-Authors: Marco Pilz, Matteo Picozzi, Stefano Parolai, Joachim ZschauAbstract:Abstract Characterizing the local site response in large cities is an important step towards seismic hazard assessment. To this regard, single station seismic noise measurements were carried out at 146 sites in the northern part of Santiago de Chile. This extensive survey allowed the fundamental resonance frequency of the sedimentary cover, derived from horizontal-to-vertical (H/V) spectral ratios, to be mapped. By inverting the spectral ratios under the constraint of the thickness of the sedimentary cover, known from previous gravimetric measurements, local S-Wave Velocity profiles have been retrieved. After interpolation between the individual profiles, the resulting high resolution 3D S-Wave Velocity model allows the entire area, as well as deeper parts of the basin, to be represented in great detail. Since one lithology shows a great scatter in the Velocity values only a very general correlation between S-Wave Velocity in the uppermost 30 m ( v s 30 ) and local geology is found. Local S-Wave Velocity profiles can serve as a key factor in seismic hazard assessment, since they allow an estimate of the amplification potential of the sedimentary cover. Mapping the intensity distribution of the 27 February 2010 Maule, Chile, event ( Mw = 8.8) the results indicate that local amplification of the ground motion might partially explain the damage distribution and encourage the use of the low cost seismic noise techniques for the study of seismic site effects.
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shear wave Velocity model of the santiago de chile basin derived from ambient noise measurements a comparison of proxies for seismic site conditions and amplification
Geophysical Journal International, 2010Co-Authors: Marco Pilz, Matteo Picozzi, Felipe Leyton, Stefano Parolai, Rongjiang Wang, Jaime Campos, Joachim ZschauAbstract:SUMMARY We determined a high-resolution 3-D S-Wave Velocity model for a 26 km × 12 km area in the northern part of the basin of Santiago de Chile. To reach this goal, we used microtremor recordings at 125 sites for deriving the horizontal-to-vertical (H/V) spectral ratios that we inverted to retrieve local S-Wave Velocity profiles. In the inversion procedure, we used additional geological and geophysical constraints and values of the thickness of the sedimentary cover already determined by gravimetric measurements, which were found to vary substantially over short distances in the investigated area. The resulting model was derived by interpolation with a kriging technique between the single S-Wave Velocity profiles and shows locally good agreement with the few existing Velocity profile data, but allows the entire area, as well as deeper parts of the basin, to be represented in greater detail. The wealth of available data allowed us to check if any correlation between the S-Wave Velocity in the uppermost 30 m (v30S) and the slope of topography, a new technique recently proposed by Wald and Allen, exists on a local scale. We observed that while one lithology might provide a greater scatter in the Velocity values for the investigated area, almost no correlation between topographic gradient and calculated v30S exists, whereas a better link is found between v30S and the local geology. Finally, we compared the v30S distribution with the MSK intensities for the 1985 Valparaiso event, pointing out that high intensities are found where the expected v30S values are low and over a thick sedimentary cover. Although this evidence cannot be generalized for all possible earthquakes, it indicates the influence of site effects modifying the ground motion when earthquakes occur well outside of the Santiago basin.
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combining genetic and linearized algorithms for a two step joint inversion of rayleigh wave dispersion and h v spectral ratio curves
Geophysical Journal International, 2007Co-Authors: Matteo Picozzi, Dario AlbarelloAbstract:SUMMARY The joint inversion of Rayleigh wave dispersion and H/V curves from environmental noise measurements allows the retrieval of S-Wave Velocity profiles for the shallow subsoil. For this purpose, genetic and linearized algorithm have been combined in a two-step inversion procedure, that allows the principal drawbacks typical of the application of each algorithm separately to be overcome. In the first step, a genetic algorithm procedure is used to constrain the subvolume of the parameter space where the absolute minimum of the misfit function is located. In the second step, a linearized inversion algorithm, having as an initial guess the minimum misfit model deduced from the first step, is applied to force the inversion towards the optimal solution. To evaluate the feasibility and effectiveness of this approach, seismic noise recordings at a test site in the Po river valley (North Italy) have been analysed. Here, detailed geophysical and geological information is available along with earthquake recordings, which allow a well constrained definition of both the local shear wave profile and transfer function. Comparisons between theoretical and experimental S-Wave Velocity profiles and, above all, between the theoretical and experimental site response functions shows that this combination of inversion procedures can very efficiently to manage the extreme non-linearity of the problem.
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joint inversion of h v ratios and dispersion curves from seismic noise estimating the s wave Velocity of bedrock
Geophysical Research Letters, 2005Co-Authors: Matteo Picozzi, Stefano Parolai, Sandra M RichwalskiAbstract:[1] A joint inversion of phase Velocity and H/V ratio curves, both obtained from seismic-noise recordings, permits the retrieval of the shear-wave Velocity structure of local sedimentary cover. Our inversion scheme uses a genetic algorithm and considers the influence of higher modes on the data sets. Encouraged by the results published previously on joint inversion (Parolai et al., 2005) we went one step further. We found, using a synthetic data set, that the impedance contrast at the sediment-bedrock interface has a strong influence on the shape of the H/V ratio curve, which therefore allows the bedrock S-Wave Velocity to be well constrained in the joint-inversion procedure. Our observations were further confirmed using a real data set.
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joint inversion of phase Velocity dispersion and h v ratio curves from seismic noise recordings using a genetic algorithm considering higher modes
Geophysical Research Letters, 2005Co-Authors: Stefano Parolai, Matteo Picozzi, Sandra M Richwalski, Claus MilkereitAbstract:[1] Seismic noise contains information on the local S-Wave Velocity structure, which can be obtained from the phase Velocity dispersion curve by means of array measurements. The H/V ratio from single stations also contains information on the average S-Wave Velocity and the total thickness of the sedimentary cover. A joint inversion of the two data sets therefore might allow constraining the final model well. We propose a scheme that does not require a starting model because of usage of a genetic algorithm. Furthermore, we tested two suitable cost functions for our data set, using a-priori and data driven weighting. The latter one was more appropriate in our case. In addition, we consider the influence of higher modes on the data sets and use a suitable forward modeling procedure. Using real data we show that the joint inversion indeed allows for better fitting the observed data than using the dispersion curve only.
Stefano Parolai - One of the best experts on this subject based on the ideXlab platform.
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evaluation of proxies for seismic site conditions in large urban areas the example of santiago de chile
Physics and Chemistry of The Earth, 2011Co-Authors: Marco Pilz, Matteo Picozzi, Stefano Parolai, Joachim ZschauAbstract:Abstract Characterizing the local site response in large cities is an important step towards seismic hazard assessment. To this regard, single station seismic noise measurements were carried out at 146 sites in the northern part of Santiago de Chile. This extensive survey allowed the fundamental resonance frequency of the sedimentary cover, derived from horizontal-to-vertical (H/V) spectral ratios, to be mapped. By inverting the spectral ratios under the constraint of the thickness of the sedimentary cover, known from previous gravimetric measurements, local S-Wave Velocity profiles have been retrieved. After interpolation between the individual profiles, the resulting high resolution 3D S-Wave Velocity model allows the entire area, as well as deeper parts of the basin, to be represented in great detail. Since one lithology shows a great scatter in the Velocity values only a very general correlation between S-Wave Velocity in the uppermost 30 m ( v s 30 ) and local geology is found. Local S-Wave Velocity profiles can serve as a key factor in seismic hazard assessment, since they allow an estimate of the amplification potential of the sedimentary cover. Mapping the intensity distribution of the 27 February 2010 Maule, Chile, event ( Mw = 8.8) the results indicate that local amplification of the ground motion might partially explain the damage distribution and encourage the use of the low cost seismic noise techniques for the study of seismic site effects.
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shear wave Velocity model of the santiago de chile basin derived from ambient noise measurements a comparison of proxies for seismic site conditions and amplification
Geophysical Journal International, 2010Co-Authors: Marco Pilz, Matteo Picozzi, Felipe Leyton, Stefano Parolai, Rongjiang Wang, Jaime Campos, Joachim ZschauAbstract:SUMMARY We determined a high-resolution 3-D S-Wave Velocity model for a 26 km × 12 km area in the northern part of the basin of Santiago de Chile. To reach this goal, we used microtremor recordings at 125 sites for deriving the horizontal-to-vertical (H/V) spectral ratios that we inverted to retrieve local S-Wave Velocity profiles. In the inversion procedure, we used additional geological and geophysical constraints and values of the thickness of the sedimentary cover already determined by gravimetric measurements, which were found to vary substantially over short distances in the investigated area. The resulting model was derived by interpolation with a kriging technique between the single S-Wave Velocity profiles and shows locally good agreement with the few existing Velocity profile data, but allows the entire area, as well as deeper parts of the basin, to be represented in greater detail. The wealth of available data allowed us to check if any correlation between the S-Wave Velocity in the uppermost 30 m (v30S) and the slope of topography, a new technique recently proposed by Wald and Allen, exists on a local scale. We observed that while one lithology might provide a greater scatter in the Velocity values for the investigated area, almost no correlation between topographic gradient and calculated v30S exists, whereas a better link is found between v30S and the local geology. Finally, we compared the v30S distribution with the MSK intensities for the 1985 Valparaiso event, pointing out that high intensities are found where the expected v30S values are low and over a thick sedimentary cover. Although this evidence cannot be generalized for all possible earthquakes, it indicates the influence of site effects modifying the ground motion when earthquakes occur well outside of the Santiago basin.
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s wave Velocity profiles for earthquake engineering purposes for the cologne area germany
Bulletin of Earthquake Engineering, 2006Co-Authors: Stefano Parolai, Sandra M Richwalski, Claus Milkereit, Donat FahAbstract:Local S-Wave Velocity-depth profiles are a key factor in seismic hazard assessment, as they allow the amplification potential of the sedimentary cover to be evaluated. Ambient seismic noise is mainly composed of surface waves, and therefore contains vital information about the S-Wave Velocity structure, allowing polarization or dispersion curves to be obtained from single station or array noise recordings. At two sites in the area of Cologne, Germany, the extended spatial correlation method was applied to such recordings and apparent phase Velocity curves in the frequency range of interest for earthquake engineering were obtained. Using this data, a linearized inversion, the simplex downhill method, and a genetic algorithm yielded similar S-Wave profiles. However, the latter method is recommended since it is less dependent upon a good starting model. Importantly, the presence of low-Velocity layers in the Cologne area made it necessary to consider in the frequency range of interest higher modes in the inversion procedures. Finally, independent information on the total thickness of the sedimentary cover permitted the estimation of a 2D S-Wave Velocity profile crossing the Cologne area. Here, the H/V ratio inversion using 20 single-station noise recordings was used, with the results in good agreement with a geological profile.
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joint inversion of h v ratios and dispersion curves from seismic noise estimating the s wave Velocity of bedrock
Geophysical Research Letters, 2005Co-Authors: Matteo Picozzi, Stefano Parolai, Sandra M RichwalskiAbstract:[1] A joint inversion of phase Velocity and H/V ratio curves, both obtained from seismic-noise recordings, permits the retrieval of the shear-wave Velocity structure of local sedimentary cover. Our inversion scheme uses a genetic algorithm and considers the influence of higher modes on the data sets. Encouraged by the results published previously on joint inversion (Parolai et al., 2005) we went one step further. We found, using a synthetic data set, that the impedance contrast at the sediment-bedrock interface has a strong influence on the shape of the H/V ratio curve, which therefore allows the bedrock S-Wave Velocity to be well constrained in the joint-inversion procedure. Our observations were further confirmed using a real data set.
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joint inversion of phase Velocity dispersion and h v ratio curves from seismic noise recordings using a genetic algorithm considering higher modes
Geophysical Research Letters, 2005Co-Authors: Stefano Parolai, Matteo Picozzi, Sandra M Richwalski, Claus MilkereitAbstract:[1] Seismic noise contains information on the local S-Wave Velocity structure, which can be obtained from the phase Velocity dispersion curve by means of array measurements. The H/V ratio from single stations also contains information on the average S-Wave Velocity and the total thickness of the sedimentary cover. A joint inversion of the two data sets therefore might allow constraining the final model well. We propose a scheme that does not require a starting model because of usage of a genetic algorithm. Furthermore, we tested two suitable cost functions for our data set, using a-priori and data driven weighting. The latter one was more appropriate in our case. In addition, we consider the influence of higher modes on the data sets and use a suitable forward modeling procedure. Using real data we show that the joint inversion indeed allows for better fitting the observed data than using the dispersion curve only.
Sandra M Richwalski - One of the best experts on this subject based on the ideXlab platform.
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s wave Velocity profiles for earthquake engineering purposes for the cologne area germany
Bulletin of Earthquake Engineering, 2006Co-Authors: Stefano Parolai, Sandra M Richwalski, Claus Milkereit, Donat FahAbstract:Local S-Wave Velocity-depth profiles are a key factor in seismic hazard assessment, as they allow the amplification potential of the sedimentary cover to be evaluated. Ambient seismic noise is mainly composed of surface waves, and therefore contains vital information about the S-Wave Velocity structure, allowing polarization or dispersion curves to be obtained from single station or array noise recordings. At two sites in the area of Cologne, Germany, the extended spatial correlation method was applied to such recordings and apparent phase Velocity curves in the frequency range of interest for earthquake engineering were obtained. Using this data, a linearized inversion, the simplex downhill method, and a genetic algorithm yielded similar S-Wave profiles. However, the latter method is recommended since it is less dependent upon a good starting model. Importantly, the presence of low-Velocity layers in the Cologne area made it necessary to consider in the frequency range of interest higher modes in the inversion procedures. Finally, independent information on the total thickness of the sedimentary cover permitted the estimation of a 2D S-Wave Velocity profile crossing the Cologne area. Here, the H/V ratio inversion using 20 single-station noise recordings was used, with the results in good agreement with a geological profile.
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joint inversion of h v ratios and dispersion curves from seismic noise estimating the s wave Velocity of bedrock
Geophysical Research Letters, 2005Co-Authors: Matteo Picozzi, Stefano Parolai, Sandra M RichwalskiAbstract:[1] A joint inversion of phase Velocity and H/V ratio curves, both obtained from seismic-noise recordings, permits the retrieval of the shear-wave Velocity structure of local sedimentary cover. Our inversion scheme uses a genetic algorithm and considers the influence of higher modes on the data sets. Encouraged by the results published previously on joint inversion (Parolai et al., 2005) we went one step further. We found, using a synthetic data set, that the impedance contrast at the sediment-bedrock interface has a strong influence on the shape of the H/V ratio curve, which therefore allows the bedrock S-Wave Velocity to be well constrained in the joint-inversion procedure. Our observations were further confirmed using a real data set.
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joint inversion of phase Velocity dispersion and h v ratio curves from seismic noise recordings using a genetic algorithm considering higher modes
Geophysical Research Letters, 2005Co-Authors: Stefano Parolai, Matteo Picozzi, Sandra M Richwalski, Claus MilkereitAbstract:[1] Seismic noise contains information on the local S-Wave Velocity structure, which can be obtained from the phase Velocity dispersion curve by means of array measurements. The H/V ratio from single stations also contains information on the average S-Wave Velocity and the total thickness of the sedimentary cover. A joint inversion of the two data sets therefore might allow constraining the final model well. We propose a scheme that does not require a starting model because of usage of a genetic algorithm. Furthermore, we tested two suitable cost functions for our data set, using a-priori and data driven weighting. The latter one was more appropriate in our case. In addition, we consider the influence of higher modes on the data sets and use a suitable forward modeling procedure. Using real data we show that the joint inversion indeed allows for better fitting the observed data than using the dispersion curve only.
Jiatie Pan - One of the best experts on this subject based on the ideXlab platform.
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an upper mantle s wave Velocity model for east asia from rayleigh wave tomography
Earth and Planetary Science Letters, 2013Co-Authors: Jiatie Pan, Fengxue ZhangAbstract:Abstract We present a new shear Velocity model of the upper mantle beneath the East Asia region derived by inverting Rayleigh wave group Velocity measurements between 10 and 145 s combined with previously published Rayleigh wave phase Velocity measurements between 150 and 250 s. Rayleigh wave group Velocity dispersion curves along more than 9500 paths were measured and combined to produce 2D dispersion maps for 10–145 s periods. The group Velocity maps benefit from the inclusion of new data recorded by the China National Seismic Network and surrounding global stations. The increase in available data has resulted in enhanced resolution compared with previously published group Velocity maps; the horizontal resolution across the region is about 3° for the periods used in this study. The new shear-wave Velocity models indicate varying Velocity structure beneath eastern China, which yields estimates of a lithosphere–asthenosphere boundary depth from around 160 km beneath the Yangtze block to approximately 140 km beneath the western part of the North China Craton (NCC), up to depths of 70–100 km beneath the eastern NCC, Northeast China, and the Cathaysia block. The models reveal the subduction of two opposite-facing continental plates under the southern and northern margin of Tibet. An obvious low-Velocity anomaly appears in the top 200 km of the upper mantle beneath northern Tibet, which is inconsistent with the presence of subducted Asian or Indian mantle lithosphere beneath northern Tibet. The Cenozoic volcanism fields in the Mongolian plateau are characterized by an obvious upper mantle negative anomaly, but no signature of deep-seated plume was observed.
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s wave Velocity structure of northeastern china from joint inversion of rayleigh wave phase and group velocities
Geophysical Journal International, 2012Co-Authors: Jiatie Pan, Lian SunAbstract:SUMMARY We imaged the crust and uppermost mantle structure beneath northeastern (NE) China with fundamental mode Rayleigh waves recorded by 125 broad-band stations deployed in the region. Rayleigh wave phase and group velocities along more than 700 interstation paths were estimated using the wavelet transformation method and then these data were utilized to construct 2-D phase and group Velocity maps in the period range of 15–60 s. Owing to the dense ray coverage and short ray path, our results provide better lateral resolution in the NE China region compared with previous phase and group Velocity studies. The regularized Rayleigh wave phase and group Velocity dispersions at each cell were jointly inverted to determine 1-D shear wave Velocity structure using the linear inversion method and then assembled into a 3-D model. Our results show that obvious low velocities exist in the uppermost mantle beneath the Changbaishan volcanic region, which may be due to asthenospheric upwelling. The thin lithosphere with fast S-Wave Velocity in the lower crust of the Songliao Basin implies that the lithospheric mantle beneath NE China is partly removed.
Ling Chen - One of the best experts on this subject based on the ideXlab platform.
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crustal structure in the middle southern segments of the tanlu fault zone and adjacent regions constrained by multifrequency receiver function and surface wave data
Physics of the Earth and Planetary Interiors, 2020Co-Authors: Zigen Wei, Risheng Chu, Ling ChenAbstract:Abstract We successively adopt H-k stacking of receiver functions (RFs) and joint inversion of RF and surface wave dispersion with Gaussian factors of 1.0, 2.0 and 3.0 to invert the crustal thickness (H), average Vp/Vs ratio (k) and S-Wave Velocity beneath 146 broadband seismic stations in the middle-southern segments of the Tanlu Fault Zone (TLFZ) and adjacent regions. These observations, together with previous geologic and geophysical studies, are further used to investigate Phanerozoic tectonic evolution in the study region and the seismogenic environment of the Tancheng Ms 8.5 earthquake. Our results show that the Moho depth and k generally range from 25 to 38 km and 1.65–1.95, respectively. The study region is roughly divided into three parts with different crustal structures from north to south, based on the Cretaceous Tiefogou fault and Triassic Lu'an fault and their extensional profiles, which may reflect different responses to the westward subduction of the Paleo-Pacific and Pacific Plates in the Mesozoic-Cenozoic. In addition to the observed uplifted Moho, high k and vertically alternating high-/low-Velocity layers, lateral variations in S-Wave Velocity and junctions of multiple faults are imaged beneath the Tancheng earthquake zone, which may also contribute to the occurrence of strong earthquakes.
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local modification of the lithosphere beneath the central and western north china craton 3 d constraints from rayleigh wave tomography
Gondwana Research, 2013Co-Authors: Mingming Jiang, Ling Chen, Yingjie YangAbstract:article i nfo We have imaged the lithospheric structure beneath the central and western North China Craton (NCC) with Rayleigh wave tomography. The Rayleigh waveforms of 100 teleseismic events recorded by 208 broadband stations are used to yield high-resolution phase Velocity maps at 13 periods from 20 s to 143 s. A 3-D S-Wave Velocity model is constructed based on the phase Velocity maps. Our S-Wave Velocity model is broadly consistent with the results of previous tomography studies, but shows more detailed variations within the lithosphere. The Trans-North China Orogen (TNCO) is generally characterized by low-Velocity anomalies but exhibits great heterogeneities. Two major low-Velocity zones (LVZs) are observed in the north and south, respectively. The northern LVZ laterally coincides with sites of Cenozoic magmatism and extends to depths greater than 200 km. We propose that a small-scale mantle upwelling is present, confined to the north of the TNCO. A high-Velocity patch in the uppermost mantle is also observed between the two LVZs adjacent to the narrow transtensional zone of the Cenozoic Shanxi-Shaanxi Rift (SSR). We interpret this as the remnant of a cratonic mantle root. The Ordos Block in the western NCC is associated with high-Velocity anomalies, similarly reflecting the existence of cratonic mantle root, but a discernible low-Velocity layer is ob- served at depths of 100-150 km in this location. We interpret that this mid-lithospheric structure was prob- ably formed by metasomatic processes during the early formation of the NCC. Based on the observations from our S-Wave Velocity model, we conclude that the current highly heterogeneous lithospheric structure beneath the TNCO is the result of multiphase reworking of pre-existing mechanically weak zones since the amalgamation of the craton. The latest Cenozoic lithospheric reworking is dominated by the far-field effects of both Pacific plate subduction and the India-Eurasia collision.
