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Lessons learnt from the destructive earthquakes occurred during the new millennium provide new opportunities to take action, revise, and improve the procedure for seismic hazard assessment (SHA). A single hazard map cannot meet the requirements from different end-users; the mapping of the expected earthquake ground motion that accounts for events’ recurrence may be suitable for insurances. When dealing with cultural heritage and critical structures (e.g., nuclear power plants), where it is necessary to consider extremely long time intervals, the standard hazard estimates are by far unsuitable, due to their basic heuristic limitations. While time-dependent SHA may be suitable to increase earthquake preparedness, by planning adequate mitigation actions, for critical structures (i.e., those for which the consequences of failure are intolerable) the maximum possible seismic input is relevant. Therefore the need for an appropriate estimate of the seismic hazard, aimed not only at the seismic classification of the national territory, but also at the capability of properly accounting for the local ampli␣cations of ground shaking, as well as for the fault properties, is a pressing concern for seismic engineers. A viable alternative to traditional SHA is represented by the use of the scenario earthquakes, characterized at least in terms of magnitude, distance, and faulting style, and by the treatment of complex source processes. The relevance of the realistic modeling, which permits the generalization of empirical observations by means of physically sound theoretical considerations, is evident, as it allows the optimization of the structural design with respect to the site of interest. The time information associated with the scenarios of ground motion, given by the intermediate-term middle-range earthquake predictions, can be useful to public authorities in assigning priorities for timely mitigation actions. Therefore, the approach we have developed naturally supplies realistic time series of ground motion useful to preserve urban settings, historical monuments, and relevant man-made structures.

A hybrid technique consisting of modal summation and subsequent ®nite differences modelling is applied for the computation of synthetic accelerograms along a pro®le crossing the city of Zagreb, the capital of Croatia. Assuming the source geometry is known, the ampli®cation properties of the underlying soil may be determined by comparison of synthetics and their response spectra computed for a bedrock model with the ones obtained under the assumption of a realistic laterally varying local model. The peak ground acceleration is larger by a factor of up to 3.5 than the value obtained for the bedrock model. The ampli®cation of the response spectra is most prominent for frequencies below 2 Hz, and increases sharply to the SW from the mapped fault running through the centre of the city. q 2002 Published by Elsevier Science Ltd.

Seismic wave propagation in laterally heterogeneous anelastic media: Theory and applications to seismic zonation

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 earthquake record and the Code for design and construction in seismic regions in Bulgaria have shown that the territory of the Republic of Bulgaria is exposed to a high seismic risk due to local shallow and regional strong intermediate‐depth seismic sources. The available strong motion database is quite limited, and therefore not representative at all of the real hazard. The application of the neo‐deterministic seismic hazard assessment procedure for two main Bulgarian cities has been capable to supply a significant database of synthetic strong motions for the target sites, applicable for earthquake engineering purposes. The main advantage of the applied deterministic procedure is the possibility to take simultaneously and correctly into consideration the contribution to the earthquake ground motion at the target sites of the seismic source and of the seismic wave propagation in the crossed media. We discuss in this study the result of some recent applications of the neo‐deterministic seismic microzonation procedure to the cities of Sofia and Russe. The validation of the theoretically modeled seismic input against Eurocode 8 and the few available records at these sites is discussed.

Current computational resources and physical knowledge of the seismic wave generation and propagation processes allow for reliable numerical and analytical models of waveform generation and propagation. From the simulation of ground motion, it is easy to extract the desired earthquake hazard parameters. Accordingly, a scenario-based approach to seismic hazard assessment has been developed, namely the neo-deterministic seismic hazard assessment (NDSHA), which allows for a wide range of possible seismic sources to be used in the definition of reliable scenarios by means of realistic waveforms modelling. Such reli- able and comprehensive characterization of expected earthquake ground motion is essential to improve building codes, particularly for the protection of critical infrastructures and for land use planning. Parvez et al. (Geophys J Int 155:489–508, 2003) published the first ever neo-deterministic seismic hazard map of India by computing synthetic seismograms with input data set consisting of structural models, seismogenic zones, focal mechanisms and earthquake catalogues. As described in Panza et al. (Adv Geophys 53:93–165, 2012), the NDSHA methodology evolved with respect to the original formulation used by Parvez et al. (Geophys J Int 155:489–508, 2003): the computer codes were improved to better fit the need of producing real- istic ground shaking maps and ground shaking scenar- ios, at different scale levels, exploiting the most significant pertinent progresses in data acquisition and modelling. Accordingly, the present study supplies a revised NDSHA map for India. The seismic hazard, expressed in terms of maximum displacement (Dmax), maximum velocity (Vmax) and design ground acceleration (DGA), has been extracted from the synthetic signals and mapped on a regular grid over the studied territory.

Seismic hazard maps for Alborz region (north of Iran) and adjacent areas are prepared using the neo-deterministic seismic hazard assessment (NDSHA) based on the computation of synthetic seismograms at the regional scale. The study area is zoned according to different geophysical structural models delimited at the surface by polygons, used to define the mechanical properties of the source-site paths. We have refined the velocity structures of Iran, as obtained from surface waves tomography, to obtain the velocity structure of Alborz region by applying the joint inversion of the P-wave receiver functions (PRF) and surface wave's dispersion. The input data set consists of attenuation-velocity structural models (representing bedrock conditions), seismogenic zones, focal mechanisms and the catalog of past seismicity. The seismic hazard, expressed in terms of maximum displacement (PGD), maximum velocity (PGV) and design ground acceleration (DGA), is extracted from the synthetic seismograms and mapped on a regular grid of 0.2° × 0.2° over the entire region. The results of this first order NDSHA zoning indicate a high seismic hazard in the Alborz region and may represent an important knowledge basis towards detailed and comprehensive seismic microzonation studies.

This paper describes the outcome of the advanced seismic hazard and seismic risk estimates recently performed for the city of Sofia, based on the state-of-the-art of knowledge for this site. Some major results of the neo-deterministic, scenario-based, seismic hazard assessment approach (NDSHA) to the earthquake hazard assessment for the city of Sofia are considered. Further validations of the recently constructed synthetic strong motion database, containing site and seismic source-specific ground motion time histories are performed and discussed. Displacement and acceleration response spectra are considered. The elastic displacement response spectra and displacement demand are discussed with regard to earthquake magnitude, seismic source-to-site distance, seismic source mechanism, and local geological site conditions. The elastic response design spectrum from the standard pseudo-acceleration, versus natural period, T n, format, converted to a capacity diagram in S a − S d format is discussed in the perspective of the Eurocode 8 provisions. A brief overview of the engineering applications of the seismic demand obtained making use of the NDSHA is supplied. Some applications of the outcome of NDSHA procedure for engineering purposes are shown. The obtained database of ground shaking waveforms and time-histories, computed for city of Sofia is used to: (1) extract maximum particle velocities; (2) calculate the space distribution of the horizontal strain factor Log10 e; (3) estimate liquefaction susceptibility in terms of standard penetration test, N values, and initial over burden stress; (4) estimate damage index distribution; and (5) map the distribution of the expected pipe breaks and red-tagged buildings for given scenario earthquakes, etc. The theoretically obtained database, based on the simultaneous treatment of the data from many disciplines, contains data fully suitable for practical use. The proper use of this database can lead to a significant seismic vulnerability reduction and thus contributes to earthquake preparedness.

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.

A hybrid method for the calculation of realistic synthetic seismograms in laterally heterogeneous, anelastic media has been used to model the ground motion in Tehran city. The synthetic records compare reasonably well with the observed ground motion due to the 2004 Firozabad Kojor earthquake located 60 km north of Tehran. The ratio between the response spectrum for the signals calculated along a laterally varying structure, Sa(2D), and that for the signals at the bedrock regional reference structure, Sa(1D), shows a high amplification of seismic waves in Tehran. The procedure can be readily implemented for the entire Tehran city, which experienced large historical earthquakes in the past, simply by extending the analysis, made so far, in space and to different scenario earthquakes, consistent with the local and regional tectonics.

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.

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.

A review of the recent achievements of the innovative neo-deterministic approach for seismic hazard assessment through realistic earthquake scenarios has been performed. The procedure provides strong ground motion parameters for the purpose of earthquake engineering, based on the deterministic seismic wave propagation modelling at different scales— regional, national and metropolitan. The main advantage of this neo-deterministic procedure is the simultaneous treatment of the contribution of the earthquake source and seismic wave propagation media to the strong motion at the target site/region, as required by basic physical principles. The neo-deterministic seismic microzonation procedure has been successfully applied to numerous metropolitan areas all over the world in the framework of several international projects. In this study some examples focused on CEI region concerning both regional seismic hazard assessment and seismic microzonation of the selected metropolitan areas are shown.

The capital of Bulgaria, Sofia is a growing city with population around 1.22 million. The city is exposed to a high seismic risk since it is placed in the centre of Sofia seismic area. Over the centuries in the town of Sofia the macroseismic intensities have been larger than IX (MSK). A study of the site effects and the microzonation of a part of metropolitan Sofia, based on a modelling of seismic ground motion along three cross sections are presented. Realistic synthetic strong motion waveforms have been computed for an expected scenario earthquake (M=7) applying a hybrid modelling method, based on the modal summation technique and finite differences scheme. The site amplification is determined in terms of response spectra ratio (RSR). A set of time histories and quantities of earthquake engineering interest are supplied, that allow the definition of six zones characterized by specific response spectra. The results from this study constitute a “database” that describes the ground shaking of the urban area. The synthetic velocigrams are employed to calculate the distribution of the horizontal strain factor Log10e using a simplified relation between particle velocity and velocity of shear waves in the surface layer. It is shown that it is possible to estimate liquefaction susceptibility in terms of standard penetration tests (SPT), Nvalues and initial over burden stress. Using the data for maximum particle velocity and empirical relationships developed from the Northridge earthquake, 1994 the distributions of the expected pipe breaks and red-tagged buildings for Sofia city are shown.

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.

— The city of Sofia is exposed to a high seismic risk. Macroseismic intensities in the range of VIII – X (MSK) can be expected in the city. The earthquakes that can influence the hazard in Sofia originate either beneath the city or are caused by seismic sources located within a radius of 40 km. The city of Sofia is also prone to the remote Vrancea seismic zone in Romania, and particularly vulnerable are the long-period elements of the built environment. The high seismic risk and the lack of instrumental recordings of the regional seismicity make the use of appropriate credible earthquake scenarios and ground-motion modelling approaches for defining the seismic input for the city of Sofia necessary. Complete synthetic seismic signals, due to several earthquake scenarios, were computed along chosen geological profiles crossing the city, applying a hybrid technique, which combines the modal summation technique and finite differences. The modelling takes into account simultaneously the geotechnical properties of the site, the position and geometry of the seismic source and the mechanical properties of the propagation medium. Acceleration, velocity and displacement time histories and related quantities of earthquake engineering interest (e.g., response spectra, ground-motion amplification along the profiles) have been supplied. The approach applied in this study allows us to obtain the definition of the seismic input at low cost, exploiting large quantities of existing data (e.g. geotechnical, geological, seismological). It may be efficiently used to estimate the ground motion for the purposes of microzonation, urban planning, retrofitting or insurance of the built environment, etc.

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.

Delhi – the capital of India lies on a severe earthquake hazard threat not only from local earthquakes but also from Himalayan events just 200–250 km apart. The seismic ground motion in a part of Delhi City is computed with a hybrid technique based on the modal summation and the finite-difference scheme for site-specific strong ground motion modelling. Complete realistic SH and P-SV wave seismograms are computed along two geological cross sections, (1) north-south, from Inter State Bus Terminal (ISBT) to Sewanagar and (2) east-west, from Tilak Bridge to Punjabi Bagh. Two real earthquake sources of July 15, 1720 (MMI 1⁄4 IX, M 1⁄4 7:4) and August 27, 1960 (M 1⁄4 6:0) have been used in modelling. The response spectra ratio (RSR), i.e. the response spectra computed from the signals synthesized along the laterally varying section and normalized by the response spectra computed from the corresponding signals, synthesized for the bedrock reference regional model, have been determined. As expected, the sedimentary cover causes an increase of the signal amplitude, particularly in the radial and transverse components. To further check the site-effects, we reversed the source location to the other side of the cross section and recomputed the site amplifications. There are only a few sites where a large amplification is invariant with respect to the two source locations considered. The RSR ranges between 5 to 10 in the frequency range from 2.8 to 3.7 Hz for the radial and transverse components of motion along the NS cross section. Along the EW cross section RSR varies between 3.5 to 7.5 in the frequency range from 3.5 to 4.1 Hz. The amplification of the vertical component is considerable at high frequency (>4 Hz.) whereas it is negligible in lower frequency range.