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1.
Seismic Ground Motion in Napoli for the 1980 Irpinia Earthquake 总被引：3，自引：0，他引：3
C. Nunziata 《Pure and Applied Geophysics》2004,161(5-6):1239-1264
— The seismic ground motion in the urban area of Napoli has been computed for the 1980 earthquake (Ms = 6.9) with a hybrid technique based on the mode summation and the finite difference methods. The detailed geological setting of each quarter has been reconstructed from several stratigraphies and six geological zones have been recognized. Shear-wave velocity profiles have been assigned, based on hole tests and inversion of Rayleigh group velocities artificially generated. Realistic SH and P-SV wave seismograms have been computed along the representative cross sections of each zone, by assuming selected velocity profiles. Spectral amplifications of 2–4 have been computed at frequencies roughly corresponding to the eigenfrequencies of the most damaged buildings. Moreover, following the intensity-PGA correlations found for the Italian territory, the predicted peak ground accelerations, 0.04–0.10 g correspond to the intensity range VII-VIII on the MCS scale, in agreement with the observed data. 相似文献
2.
Leonardo Alvarez Franco Vaccari Giuliano F. Panza Ramn Pico 《Soil Dynamics and Earthquake Engineering》2005,25(5):383-401
Synthetic seismograms (P-SV and SH waves) have been calculated along six profiles in Santiago de Cuba basin, with a cutoff frequency of 5 Hz, by using a hybrid approach (modal summation for a regional 1D structure plus finite differences for a local 2D structure embedded in the first). They correspond to a scenario earthquake of MS=7 that may occur in Oriente fault zone, directly south of the city. As initial data for a seismic microzoning, the characterisation of earthquake effects has been made considering several relative (2D/1D) quantities (PGDR, PGVR, PGAR, DGAR, IAR—ratios of peak ground values of displacement, velocity and acceleration, and of design ground acceleration and Arias intensity-, etc.) and functions representative of the ground motion characteristics in soil (2D) with respect to bedrock (1D). The functions are the response spectra ratio RSR(f), already routinely used in this kind of work, and the elastic energy input ratio EIR(f), defined, for the first time, in this paper. These data, sampled at 115 sites within all the profiles have been classified in two steps, using logical combinatory algorithms: connected components and compact sets. In the first step, from the original ground motion parameters or functions extracted from the synthetic seismograms, nine sets have been classified and the partial results show the spatial distribution of the soil behaviour as a function of the component of motion. In the second step, the results of the classification of the nine sets have been used as input for a further classification that shows a spatial distribution of sites with a quasi-homogeneous integral ground motion behaviour. By adding the available geological surface data, a microzoning scheme of Santiago de Cuba basin has been obtained. 相似文献
3.
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4.
To understand the ground-motion contribution by multiple-mode surface-wave arrivals, the surface-wave theory required for predicting ground-motion time histories is discussed. The adequacy of the theory in accounting for observed earthquake ground motion is tested by comparing theoretically predicted long-period seismograms with real seismograms for two earthquakes in the central United States. The agreement between the predicted and observed maximum vertical component Lg ground velocities and accelerations in the 2- to 3-sec period range is excellent over a distance range of 100 to 2,000 km. 相似文献
5.
Global epicentre maps show that the majority of earthquakes are inter-plate, although moderate to large earthquakes do occur intra-plate, i.e. within the plates. The seismicity of the Australian continent is typical of intra-plate environments and a magnitude ML 6 earthquake has an average return period of about 5 years. Recordings of Australian intra-plate earthquakes are investigated here to characterise their frequency content, peak acceleration and duration.Due to lack of quality strong motion records of large intra-plate earthquakes at short distances, synthetic seismograms are commonly used for testing structural behaviour. An empirical Green's Function method (Geophys. Res. Lett., 5 (1978), 1–4; Proceedings of the Third International Microzonation Conference, Seattle, USA, vol. 1, (1982), pp. 447–458.) is chosen to simulate a large earthquake by summation in time of a number of smaller earthquakes or sub-events, each given a slightly different origin time to represent more realistically the propagation of a rupture along an assumed fault plane. In the first instance, recordings on rock of the magnitude ML 2.3 aftershock of the 29 December 1989 Newcastle earthquake were used as sub-events to simulate the main shock of magnitude ML 5.6. Validation studies for events recorded elsewhere in Australia are also considered.The response spectra of such synthetic events will be compared with the recommended spectra developed empirically from a statistical analysis of strong motion data for magnitude 5.4–6.5 intra-plate earthquakes recorded in other parts of the world and normalised to a peak ground velocity of 50 mm/s which is typical for a return period of 500 years in Australia (Australasian Structural Engineering Conference, Auckland, New Zealand, (1998), pp. 439–444.). Preliminary results from this comparison with the response spectra recommended for the Building Code of Australia show that the synthetic waveforms produced by this method are realistic and can be used to represent ground motion during typical Australian intra-plate earthquakes. 相似文献
6.
Most of the present earthquake early warning systems are based on broadband or strong motion recordings. How-ever, the short-period instruments are still deployed. It is well-known that short-period recordings have saturation problems for large earthquakes when estimating the size of an earthquake. Thus, it is necessary to make clear the magnitude at which saturation starts to occur for the commonly used τc and Pd measurements, respectively. To investigate the possibility of using short-period seismic recordings for earthquake early warning, we conducted a simulated experiment using the strong motion data of the 1999 Chi-Chi earthquake sequence including its main shock and 31 aftershocks, with magnitude span from 4 to 7.6. The strong motion acceleration recordings were convolved with the instrument response of short-period seismographs in northern China to simulate short-period seismograms. Parameters τc and Pd from the first-three-second seismograms were calculated for the simulated short-period recordings and compared with that obtained by the original strong ground motion recordings. The result showed that to some extent, short-period recordings can be used for threshold earthquake early warning, while the magnitude saturation of Pd estimation can be up to 6.5, better than τc estimation. 相似文献
7.
The ShakeMap software automatically generates maps of the peak ground motion parameters (shakemaps) and of instrumental intensity
soon after an earthquake. Recorded data are fundamental to obtaining accurate results. In case observations are not available,
ShakeMap relies on ground motion predictive equations, but due to unmodelled site conditions or finite fault effects, large
uncertainties may appear, mainly in the near-source area where damage is relevant. In this paper, we aim to account for source
effects in ShakeMap by computing synthetics to be used for integrating observations and ground motion predictive equations
when near-source data are not available. To be effective, the computation of synthetics, as well as of the finite fault, should
be done in near real time. Therefore, we computed rapid synthetic seismograms, by a stochastic approach, including the main
fault features that were obtained through inversion of regional and teleseismic data. The rapidity of calculation is linked
to a number of assumptions, and simplifications that need testing before the procedure can run in automatic mode. To assess
the performance of our procedure, we performed a retrospective validation analysis considered as case study of the M
w = 6.3 earthquake, which occurred in central Italy on April 6, 2009. In that case, the first shakemaps, generated a few minutes
after the earthquake, suffered large uncertainties on ground motion estimates in an area closer to the epicenter due to the
lack of near-field data. To verify our approach, we recomputed shakemaps for the L’Aquila earthquake, integrating data available
soon after the earthquake at different elapse times with synthetics, and we compared our shaking map with the final shakemap,
obtained when all the data were available. Our analysis evidences that (1) when near-source data are missing, the integration
of real data with synthetics reduces discrepancies between computed and actual ground shaking maps, mainly in the near-field
zone where the damage is relevant and (2) the approach that we adopted is promising in trying to reduce such discrepancies
and could be easily implemented in ShakeMap, but some a priori calibration is necessary before running in an automatic mode. 相似文献
8.
Franco Vaccari M. Yanger Walling William K. Mohanty Sankar K. Nath Akhilesh K. Verma A. Sengupta Giuliano F. Panza 《Pure and Applied Geophysics》2011,168(3-4):479-493
Kolkata, one of the oldest cities of India, is situated over the thick alluvium of the Bengal Basin, where it lies at the boundary of the zone III and zone IV of the seismic zonation map of India. An example of the study of site effects of the metropolitan Kolkata is presented based on theoretical modeling. Full synthetic strong motion waveforms have been computed using a hybrid method that combines the modal summation and finite difference techniques. The 1964 Calcutta earthquake, which was located at the southern part of Kolkata, is taken as the source region, with the focal mechanism parameters of dip?=?32°, strike?=?232° and rake?=?56°. Four profiles are considered for the computation of the synthetic seismograms from which the maximum ground acceleration (A MAX) is obtained. Response spectra ratios (RSR) are then computed using a bedrock reference model to estimate local amplifications effects. The A MAX varies from 0.05 to 0.17?g and the comparison of the A MAX with the different intensity scales (MM, MSK, RF and MCS) shows that the expected intensity is in the range from VII to X (MCS) for an earthquake of magnitude 6.5 at an epicentral distance of about 100?km. This theoretical result matches with the empirical (historical and recent) intensity observations in Kolkata. The RSR, as a function of frequency, reaches the largest values (largest amplification) in the frequency range from 1.0 to 2.0?Hz. The largest site amplification is observed at the top of loose soil. 相似文献
9.
Leonardo Alvarez Julio García Franco Vaccari Giuliano F. Panza Bertha González Carmen Reyes Bárbara Fernández Ramón Pico José A. Zapata Enrique Arango 《Pure and Applied Geophysics》2004,161(5-6):1041-1059
— The expected ground motion in Santiago de Cuba basin from earthquakes which occurred in the Oriente fault zone is studied. Synthetic SH-waves seismograms have been calculated along four profiles in the basin by the hybrid approach (modal summation for the path source-profile and finite differences for the profile) for a maximum frequency of 1 Hz. The response spectra ratio (RSR) has been determined in 49 sites, distributed along all considered profiles with a spacing of 900 m. The corresponding RSR versus frequency curves have been classified using a logical-combinatorial algorithm. The results of the classification, in combination with the uppermost geological setting (geotechnical information and geological geometry of the subsoil) are used for the seismic zoning of the city. Three different main zones are identified, and a small sector characterized by major resonance effects, due to the particular structural conditions. Each zone is characterized in terms of its expected ground motion parameters for the most probable strong earthquake (MS=7), and for the maximum possible (MS=8). 相似文献
10.
Neo-deterministic seismic hazard assessment in North Africa 总被引：2，自引：2，他引：0
T. Mourabit K. M. Abou Elenean A. Ayadi D. Benouar A. Ben Suleman M. Bezzeghoud A. Cheddadi M. Chourak M. N. ElGabry A. Harbi M. Hfaiedh H. M. Hussein J. Kacem A. Ksentini N. Jabour A. Magrin S. Maouche M. Meghraoui F. Ousadou G. F. Panza A. Peresan N. Romdhane F. Vaccari E. Zuccolo 《Journal of Seismology》2014,18(2):301-318
North Africa is one of the most earthquake-prone areas of the Mediterranean. Many devastating earthquakes, some of them tsunami-triggering, inflicted heavy loss of life and considerable economic damage to the region. In order to mitigate the destructive impact of the earthquakes, the regional seismic hazard in North Africa is assessed using the neo-deterministic, multi-scenario methodology (NDSHA) based on the computation of synthetic seismograms, using the modal summation technique, at a regular grid of 0.2?×?0.2°. This is the first study aimed at producing NDSHA maps of North Africa including five countries: Morocco, Algeria, Tunisia, Libya, and Egypt. The key input data for the NDSHA algorithm are earthquake sources, seismotectonic zonation, and structural models. In the preparation of the input data, it has been really important to go beyond the national borders and to adopt a coherent strategy all over the area. Thanks to the collaborative efforts of the teams involved, it has been possible to properly merge the earthquake catalogues available for each country to define with homogeneous criteria the seismogenic zones, the characteristic focal mechanism associated with each of them, and the structural models used to model wave propagation from the sources to the sites. As a result, reliable seismic hazard maps are produced in terms of maximum displacement (D max), maximum velocity (V max), and design ground acceleration. 相似文献
11.
The authors proposed a method for obtaining high-quality acceleration seismograms from velocity type seismograms of digital Seismographic network, and took as an example the analysis and processing of the seismograms of a same earthquake that was simultaneously recorded by velocity seismograph CTS1-EDAS24 and strong motion seismograph EST-Q4128 installed in Jixian Station, Tianjin. The calculation steps and the processing method have been discussed in detail. From the analysis and the comparison of the obtained results, it is concluded that the proposed method is simple and effective, and it broadens the application of digital seismographic network. 相似文献
12.
正演模拟是叠前弹性波反演的基础.采用慢度法计算层状介质的叠前地震记录,分别对频率和慢度进行积分变换得到时-空域的地震道集,并对在慢度积分过程中产生的计算噪音提出了解决方案.为得到高精度合成地震记录,需将地层细分,但地层层数很多时,计算量较大;而对地层粗分虽然会大大加快运算速度,但合成记录会丢失很多信息,文中给出了地层的划分原则.该方法能够计算出包括转换波和多次反射在内的全地震响应.但在提高合成记录精度的同时,也导致计算量增大、计算效率降低,因此,本文对基于慢度法全波场模拟进行了并行算法设计,采用计算域分割、工作池并行技术,建立了慢度法全波场正演模拟的并行算法,使得弹性波正演问题求解更加高效,为充分利用叠前地震资料进行叠前反演提供了研究基础. 相似文献
13.
On 22 September 2002, the largest UK earthquake (mb4.3) of the last 10 years occurred near the town of Dudley in the West Midlands. Here we determine the earthquake focal mechanism and depth using data from stations at regional and teleseismic distances. Short-period teleseismic seismograms are interpreted in terms of P and surface reflections pP and sP. This analysis suggests that the source depth is deeper than the 9.7 km initially determined by the British Geological Survey (BGS). The relative amplitude method is applied to four teleseismic seismograms to support our interpretation of the surface reflections, and constrain the focal mechanism. Our preferred focal mechanism, a near vertical strike-slip with s = 94°, = 88° and = –179°, is in reasonable agreement with a moment tensor determined by the Swiss Seismological Service. Synthetic regional surface wave seismograms match the observed seismograms for a model focal depth of 19.5 (±3.0) km and scalar moment, M0, of 3.2 × 1015 N m. Our results emphasize that due to the well-known trade-off between depth and M0 from inversions of long period (0.02–0.1 Hz) surface waves, it is preferable to combine long- and short-period data to constrain reliably the depth and hence estimate M0. Our focal mechanism and depth are further validated by generating short-period synthetic seismograms that match the observations. 相似文献
14.
Haruko Sekiguchi Masayuki Yoshimi Haruo Horikawa Kunikazu Yoshida Sunao Kunimatsu Kenji Satake 《Journal of Seismology》2008,12(2):185-195
We studied the long-period ground motions in the Osaka sedimentary basin, Japan, which contains a 1- to 3-km thickness of
sediments and is the site of many buildings or construction structures with long-natural period. We simulated the broadband
ground motions likely to be produced by the hypothetical Nankai earthquake: the earthquake expected to give rise to the most
severe long-period ground motion within the basin. For the simulation, we constructed multiscale heterogeneous source models
based on the Central Disaster Management Council of Japan (CDMC) source model and adopted a hybrid computation method in which
long-period motion and short-period motion are computed using a 3-D finite difference method and the stochastic Green’s function
method, respectively. In computing long-period motions, we used a 3-D structure model of the crust and the Osaka sedimentary
basin. The ground motions are estimated to have peak velocities of 50–90 cm/s, prolonged durations exceeding 300 s, and long
predominant periods of 5–10 s in the area with great thickness of sediments. The predominant periods are in agreement with
an approximate evaluation by 4 H/V
s where H and V
s are the thickness of the sediment and the average S wave velocity, respectively. 相似文献
15.
16.
土体剪切波速是进行土层地震反应分析的动力学参数，对场地地震动参数确定具有重要意义。基于地质地貌分析，将大同盆地划分为5类典型地质单元。对盆地1429个钻孔剪切波速资料进行分析，探讨VS30与VS20的相关性，研究土体埋深、岩性、地质单元、标贯击数及密实度等地质特征对VS的影响，并基于地质单元、剪切波速比、密实度系数及第四系上部覆盖层厚度相关性分析给出土体VS30预测模型。研究结果表明，基于典型地质特征的VS30预测模型拟合优度R2>0.90，预测精度很高，对于离散性较大、直接拟合估算较差及无剪切波速场地来说，以区分地质单元及土体类型的方式进行VS30分解预测是良好的研究思路。首次在区分地质单元及土体类型的前提下提出剪切波速比及密实度系数，并将其与第四系上部覆盖层厚度综合应用于VS30预测研究。研究结果可为大同盆地城市防震减灾规划、震害预测、区域性地震安全评价提供重要技术支撑。 相似文献
17.
Data from a superconducting gravimeter were obtained from the Geodetic Observatory Pecny (GOPE), Czech Republic, and compared with acceleration data from a broadband seismometer at the same location. We calculated synthetic seismograms for several point- and finite-source fast solutions of the 2011 Tohoku earthquake obtained from surface waves and tested them only against the observed gravity data because of high-noise levels in the low-frequency seismic data. We have obtained a good fit of the synthetic amplitude spectrum with the data up to 1.7 mHz without an additional increase of the moment magnitude Mw. In this aspect, the 2011 Tohoku earthquake was similar to the 2010 Maule earthquake and different from the 2004 Sumatra-Andaman earthquake, where the free-oscillations studies resulted in an increase of the early Mw values. The degree-one mode 3S{ia1} dominates the 3S1?C2S2?C1S3 triplet at the GOPE station. 相似文献
18.
The Sannio seismogenic area turns out to be responsible for the highest peak ground accelerations (PGA) and seismic response spectra (SRS) at Napoli. The 1688 earthquake is considered representative of the area, and realistic synthetic seismograms have been computed for this scenario earthquake at the historical center and the eastern sector of Napoli. The use of a hybrid technique based on mode summation and finite-difference methods is fully justified by the available detailed knowledge about the geological and geophysical properties of the Neapolitan subsoil. This modeling makes it possible to recognize that amplifications of ~2 for PGA and >3 for SRS are to be expected because of the pyroclastic soil cover. Based on the information contained in the available catalogs, different magnitudes have been considered. Taking into account the correlation, valid for the Italian territory, between synthetic PGA and observed intensities, it turns out that the most probable magnitude (M) of the 1688 earthquake is 6.7, while M?=?7.3 should be assigned to a conservative scenario earthquake. Comparison of the computed response spectra for the 1688 scenario earthquake with the Italian seismic building code shows that the code is adequate with respect to the expected effects at the historical center of Napoli, but that it underestimates the possible ground motion at the eastern sector, in particular at the newly developed area built after the 1980 earthquake. 相似文献
19.
Deterministic Seismic Zoning of Eastern Cuba 总被引：1，自引：0，他引：1
—A deterministic seismic zoning of Cuba is performed by modelling, with modal summation, the complete P-SV and SH waves fields generated by point-source earthquakes buried in flat-layered anelastic media. The results of the computation, performed for periods greater than 1 second, are presented in two sets of maps of maximum displacement (d max), maximum velocity (v max) and design ground acceleration (DGA), obtained by using two different criteria in the definition of the input magnitude: (1) values reported in the earthquake catalogue (M obs) and (2) values determined from seismotectonic considerations (M max). A comparison with the results of a previous probabilistic seismic zoning is made to test the possibility of making intensity — ground motion conversion with the aid of log-linear regressions. 相似文献