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Reliable assessments of ground shaking scenarios with the aid of computers before the occurrence of an earthquake can be of extreme value in planning the design of new structures, or in retrofitting of existing ones in the areas of interest. Obtaining realistic estimates of the ground motion expected in case of an earthquake is a task that seismologists tackle using dedicated and powerful computational software. The time series generated, and the corre- sponding response spectra, can be used by civil engineers in designing seismo- resistant structures capable of surviving future earthquakes with limited dam- age. The complexity of the earthquake phenomenon usually translates into powerful but unfriendly software that can intimidate those who might be inter- ested but not familiar with the matter. A web application has been developed that isolates the user from the intricacies of the underlying computational en- gine, and a friendly graphical user interface allows for the modelling of ground shaking scenarios based on the knowledge of the physical properties of the earthquake source and of the medium through which travel the seismic waves. Some predetermined source and soil models can be selected, or new, ad-hoc models can be generated or uploaded by the user. The underlying computation- al engine allows the generation of the time series (displacement, velocity, ac- celeration) in a matter of seconds for the simplest configurations. With an ac- ceptable computational time, more detailed modelling of the source rupturing process and of the layering underneath the sites of interest can be taken into ac- count, depending on the characteristics of the model.

The purpose of this work is to evaluate the regional seismic hazard for Morocco, following the deterministic approach proposed by Costa et al [1], based on the computation of complete P-SV and SH synthetic seismograms. The input for the computations is represented by source and structural models. Seismic sources are parameterized using the knowledge about past seismicity and the tectonic regime. The regional structural model we adopted is the one proposed by Cherkaoui [2], modified in its shallower part to account for the effects of the uppermost sedimentary layers. Maps of peak acceleration, velocity, and displace- ments are used for the general representation of the hazard. Accelerations are in good agreement with the values determined by Jimenez et al [3] with the standard probabilistic approach.

The project addresses the problem of pre-disaster orientation: hazard prediction, risk assessment, and hazard mapping, in connection with seismic activity and man-induced vibrations. The definition of realistic seismic input can be obtained from the computation of a wide set of time histories and spectral information, corresponding to possible seismotectonic scenarios for different source and structural models. The availability of realistic numerical simulations enables us to estimate the amplification effects in complex structures exploiting the available geotechnical, lithological, geophysical parameters, topography of the medium, tectonic, historical, palaeoseismological data, and seismotectonic models. The realistic modeling of the ground motion is a very important base of knowledge for the preparation of groundshaking scenarios that represent a valid and economic tool for seismic microzonation. This knowledge can be very fruitfully used by civil engineers in the design of new sesimo-resistant constructions and in the reinforcement of the existing built environment, and, therefore, supplies as particularly powerful tool for the prevention aspects of Civil Defense. At present, the project is active in Antananarivo, Bangalore, Beijing, Bucharest, Budapest, Cairo, Catania, Damascus, Delhi, Kathmandu, Ljubljana, Mexicali, Mexico City, Naples, Rome, Santiago de Chile, Santiago de Cuba, Silistra, Sofia, Thessaloniki, Tijuana and Zagreb.

The special geological conditions in the Xiji-Langfu area are the main reason for the anomalous high macroseismic intensity caused by the Tangshan, 1976 earthquake. The area is formed by deep deposits - mainly alluvium sands and clays poorly consolidated and with high water content - that have been trapped by the Xiadian fault. From simulated ground motion we have computed quantities commonly used for engineering purposes like the acceleration maximum amplitude (AMAX) and the total energy of ground motion (W), which is related to the Arias Intensity. Th thick low velocity deposits are responsible for the large increment of the values of AMAX and W inside the basin. On the two sides of the Xidian fault AMAX and W can vary by 200% and 700% respectively, and these variations are quite stable with varying thickness and sedimentary deposit used in the models. With the existing relationships between acceleration (AMAX) and macroseismic intensity (I) our results can explain the large values of I observed in the Xiji-Langfu area, in connection with the Tangshan earthquake.

The aim of this work is two-fold: 1) to compare the results of national scale NDSHA modelling for the Italian region at 10 Hz cut-off, based on the relevant available knowledge, with observations (e.g., peak ground motion values) and existing empirical attenuation relations; 2) to update the scaling law for source spectra (SLSS) to be used for the selected area. The new set of source spectra, defined along the lines suggested by the comparison with empirical attenuation relations, produces acceptable results in terms of PGV and spectral acceleration at long periods. Synthetic PGA and SA at short periods show a faster attenuation with respect to the observed ones and, therefore, the effect of complex attenuation factors should be explored in future ad hoc studies.

A web application prototype is described, aimed at the generation of synthetic seismograms for user-defined earthquake models. The web application graphical user interface hides the complexity of the underlying computational engine, which is the outcome of the continuous evolution of sophisticated computer codes, some of which saw the light back in the middle 1980s. With the web application, even the non-experts can produce ground shaking scenarios at the local or regional scale in very short times, depending on the complexity of the adopted source and medium models, without the need of a deep knowledge of the physics of the earthquake phenomenon. Actually, it may even allow neophytes to get some basic education in the field of seismology and seismic engineering, due to the simplified intuitive experimental approach to the matter. One of the most powerful features made available to the users is indeed the capability of executing quick parametric tests in near real-time, to explore the relations between each model’s parameter and the resulting ground motion scenario. The synthetic seismograms generated through the web application can be used by civil engineers for the design of new seismo-resistant structures, or to analyse the performance of the existing ones under seismic load.

The P-SV- and SH-wave field in the Talchir Basin is simulated along eight profiles: four profiles strike across the basin and the other four along the basin. The hybrid method, which combines two computational techniques, modal summation and finite differences, is used to produce multiphase synthetic seismograms. An M = 6 earthquake is considered, with hypocenter along the North Orissa Boundary Fault (NOBF) at a depth of 5 km and with the focal mechanism parameters: dip = 90°, strike = 160° and rake = 180°. The peak acceleration (A MAX ) along each profile is determined considering the maximum acceleration obtained at the horizontal components. The response spectra ratio (RSR) as a function of frequency is computed for the eight profiles and the higher amplification is seen to increase in correspondence with the thicker sedimentary cover, especially for the radial component. Higher site amplification for all the profiles is observed in the frequency range from 0.5 to 1.4 Hz. To validate the obtained site-effects, the sources, for the profiles across the basin, are placed near to the southern end of the profile and the site amplifications are recomputed. Even if the spatial distribution of A MAX is mainly controlled by the epicentral distance, i.e. the geometrical spreading prevails on local soil effects, the RSR shows a pattern that can be easily correlated with the local site conditions. The RSR at the intersection of the profiles is dependent not only upon the local lithology and sediment thickness but also upon the epicentral distance. The Talchir Basin is classified into three zones based on the RSR values: low RSR zone (1.6–1.9), intermediate RSR zone (2.0–2.8) and high RSR zone (2.9–5.2). The PGA estimated for the bedrock model by Bhatia et al. (1999) for the study region is around 0.05 to 0.10 g while the Indian seismic zonation map estimated it to be in the range from 0.1 to 0.2 g. In the present study, that considers the effects of lateral variations in the structure, the PGA is estimated to be as high as 0.55 g along the BA profile.

The aim of our study is to determine the design ground acceleration values at different parts of Debrecen along two profiles crossing the city. Synthetic seismograms are computed by the so called “hybrid technique”. This technique consists of the modal summation method, followed by finite difference modelling. Two independent computations have been performed using two different seismic sources and profiles. In both computations the seismic sources have been located in the so called “Mobile Zone”. The Mobile Zone is a seismically active fault system between the villages of Hosszupalyi and Galospetri. The focal mechanism and the homogeneous and heterogeneous parts of the profile are known from geophysical and geological data of the investigated area. The maximum response spectra ratio values of the horizontal component are found below 1 Hz all along the profile and the frequencies below 1 Hz are in good agreement with the natural frequencies of the multi-storeyed buildings. Computed effective peak acceleration (EPA) values are found to be in good agreement also with the higher than 6° MSK macroseismic intensity values estimated from the assessment records of damages wrought by the 1834 Ermellek earthquake.

SUMMARY The regional seismic hazard in Egypt is assessed using a deterministic approach based on the computation of synthetic seismograms at a set of gridpoints located at distances of 0.2u from each other. The main input for this computation are earthquake sources and structural models. The earthquake sources are parametrized using focal mechanisms, seismogenic areas and regional seismicity. A number of deep seismic profiles have been used to define the crustal structures. Similar sets of gravity profiles have been used to define the density of the layers. The peak displacement (DMAX), peak velocity (VMAX) and design ground acceleration (DGA) are chosen and plotted to construct the seismic hazard maps. There are similarities between computed and observed amplitudes of ground motion in terms of their values and spatial distributions. The results obtained from the deterministic and probabilistic approaches are comparable. The areas of high seismic hazard level are of great socio-economic importance.

—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.

The strong influence of lateral heterogeneities and of source properties on the spatial distribution of ground motion indicates that the traditional methods require an alternative when earthquake records are not available. The computation of broadband synthetic seismograms makes it possible, as required by a realistic modelling, to take source and propagation effects into account, fully utilizing the large amount of geological, geophysical and geotechnical data, already available. For recent earthquakes, where strong motion observations are available, it is possible to validate the modelling by comparing the synthetic seismograms with the experimental records. The realistic modelling of the seismic input has been applied to a first-order seismic zoning of the whole territory of several countries. Even though it falls in the domain of the deterministic approaches, the method is suitable to be used in new integrated procedures which combine probabilistic and deterministic approaches and allow us to minimize the present drawbacks which characterise them when they are considered separately. Detailed modelling of the ground motion for realistic heterogeneous media (up to 10 Hz) can be immediately used in the design of new seismo-resistant constructions and in the reinforcement of existing buildings, without having to wait for a strong earthquake to occur. The discrepancies between the ground responses computed with standard methods and the results of our detailed modelling cannot be ignored when formulating building codes and retrofitting the built environment.

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 (AMAX) is obtained. Response spectra ratios (RSR) are then computed using a bedrock reference model to estimate local amplifications effects. The AMAX varies from 0.05 to 0.17 g and the comparison of the AMAX 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.

The city of Sofia has the densest population of Bulgaria – around 1.27 million people. The capital is exposed to high seismic risk. According to the Bulgarian seis- mic code, Sofia has been included in a seismic category characterized by intensity IX (MSK), which corresponds to a horizontal acceleration of 0.27 g for the anchoring of the elastic response spectrum. Because of the lack of instrumental seismic data, real- istic synthetic strong motion waveforms for two opposite positions of seismic sources, have been generated for an expected earthquake scenarios (M = 7) along three ge- ological profiles. A hybrid modeling method has been used for the modeling, which is based on the modal summation technique and finite difference scheme. The calcu- lation has been done using an extended source model. The site effect is represented in terms of response spectra ratio (RSR), with respect to a bedrock model. The three components synthetic seismograms, computed in the domain of displacement, velocity and acceleration have been processed to extract some parameters very useful for engineering applications.

— We present the results of complete P-SV and SH waves modelling, up to a maximum frequency of 1 Hz, along two profiles in Santiago de Cuba city. The seismic sources are located in the depth range from 10 to 40 km on the Oriente fault zone at distances of several tens of kilometres from the city. The calculation has been made by a hybrid method: Modal summation in the regional anelastic model (one-dimensional) where the source is buried, and finite differences in the local sedimentary anelastic models (two-dimensional). The analysis of the influence of the depth and of the distance of the source on the site effects shows that standard traditional methods, based on the deconvolution analysis of the rock outcrop motion, can lead to erroneous results.

Deterministic seismic hazard computations have been done for the Hungarian part of the Pannonian basin within the framework of a cooperation of five countries. Synthetic seismograms have been computed by the modal summation method up to 1 Hz in order to determine the expected maximum displacement (D MAX), velocity (V MAX) and the design ground acceleration (DGA) on a 0.2° x 0.2° grid. DGA values have been estimated from the seismograms by using the Eurocode 8 (1993) standard.

Observations of short-period surface waves, Lg waves (Panza and Calcagnile, 1974), indicate that there are large differences between propagation properties in various geographic regions. One example of this is the North Sea, shown in Fig. 1. We have evaluated the possibility of explaining these observations by making computations of theoretical seismograms in various laterally homogeneous models. By summation of as many as 205 Rayleigh-wave modes we have generated synthetic seismograms for those S and P waves that arrive at times later than a specified phase velocity. The procedure, which has been thoroughly described by Panza (1985), works up to frequencies of 10 Hz Marson et al.

The project addressed the problem of pre-disaster orien- tation: hazard prediction, risk assessment, and hazard mapping, in connection with seismic activity and man- induced vibrations. The definition of realistic seismic input has been obtained from the computation of a wide set of time histories and spectral information, corre- sponding to possible seismotectonic scenarios for dif- ferent source and structural models. The innovative modeling technique, that constitutes the common tool to the entire project, takes into account source, propaga- tion and local site effects. This is done using first princi- ples of physics about wave generation and propagation in complex media, and does not require to resort to con- volutive approaches, that have been proven to be quite unreliable, mainly when dealing with complex geologi- cal structures, the most interesting from the practical point of view. In fact, several techniques that have been proposed to empirically estimate the site effects using observations convolved with theoretically computed signals corresponding to simplified models, supply reli- able information about the site response to non-interfer- ing seismic phases. They are not adequate in most of the real cases, when the seismic sequel is formed by several interfering waves. The availability of realistic numeri- cal simulations enables us to reliably estimate the amplification effects even in complex geological struc- tures, exploiting the available geotechnical, lithologi- cal, geophysical parameters, topography of the medium, tectonic, historical, palaeoseismological data, and seismotectonic models. The realistic modeling of the ground motion is a very important base of knowl- edge for the preparation of groundshaking scenarios that represent a valid and economic tool for the seismic microzonation. This knowledge can be very fruitfully used by civil engineers in the design of new seismo- resistant constructions and in the reinforcement of the existing built environment, and, therefore, supply a par- ticularly powerful tool for the prevention aspects of Civil Defense. We present a selection of the main results obtained for the cities of Algiers, Beijing, Bucharest, Cairo, Debrecen, Delhi, Naples, Rome, Russe, Santiago de Cuba, Sofia, Thessaloniki and Zagreb.

In this paper a hybrid method, based on mode summation and finite differences, is used to simulate the ground motion of SH wave in the Xiji-Langfu area of Beijing induced by the 1976 Tangshan earthquake. We estimate the maximum acceleration amplitude and total energy of ground motion for engineering purposes. On the two sides of the Xiadian fault the maximum acceleration amplitude and total energy can vary by afactor of 200% and 700% respectively. Our results can explain the observed anomalous intensity in the Xiji-Langfu area induced by the 1976 Tangshan earthquake.