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Algiers city is located in a seismogenic zone. To reduce the impact of seismic risk in this Capital city, a realistic modelling of the seismic ground motion (SGM) is conducted by using the hybrid method that combines the finite differences method and the modal summation. For this purpose, a complete database of geological, geophysical and earthquake data is constructed. A critical re-appraisal of the seismicity of the zone [2.25°E–3.50°E, 36.50°N–37.00°N] is performed and an earthquake list, for the period 1359–2002, is compiled. The analysis of existing and newly retrieved macroseismic information allowed the definition of earthquake parameters of macroseismic events for which a degree of reliability is assigned. Geological cross sections have been built up to model the SGM in the city, caused by the 1989 Mont-Chenoua and the 1924 Douera earthquakes. Synthetic seismograms and response spectral ratio is produced for Algiers, and they show that the soft sediments in Algiers centre are responsible of the noticed amplification of the SGM.

The seismic ground motion along a geological cross- section from Tilak Bridge to Punjabi Bagh in Delhi city has been simulated at every 130 m with a hybrid technique (modal summation and finite differences). We use two earthquake source scenarios: (1) 27 August 1960, M = 6.0 at a distance of about 45 km (near source) and (2) a large (M = 8.0) earthquake due in the central seismic gap in the Himalayan region, at a distance of about 225 km (far source). We focus on the influence of the seismic source location and focal mechanism on site-response, which, in general, is neglected in tradi- tional site-effect studies. We compare the Response Spectra Ratio (RSR) for frequency up to 3 Hz compu- ted due to far and near sources. We observe 6–7 times higher amplification in the radial component at around 2–2.5 Hz due to the far source as-compared to the near source. However, there is some amplification, of the order 2–3, at lower frequencies (less than 1 Hz) due to the near source, which is missing when the far source is considered. To validate our results, we compare the RSR, obtained from the signals at soft sites, namely CPCB, IHC and CSIR, normalized to the bedrock Ridge site, recorded during Chamoli earthquake of 1999, with that at similar sites theoretically computed along our 2D geological cross-sections.

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.

Frequently long-span bridges provide deep valley crossings, which require special consideration due to the possibility of local amplification of the ground motion as a consequence of topographical irregularities and local soil conditions. This does in fact cause locally enhanced seismic input with the possibility for the bridge piers to respond asynchronously. This introduces special design requirements so that possible out-of-phase ground displacements and the associated large relative displacements of adjacent piers can be accommodated without excessive damage. Assessment of the local variability of the ground motion due to local lateral heterogeneities and to attenuation properties is thus crucial toward the realistic definition of the asynchronous motion at the base of the bridge piers. We illustrate the work done in the framework of a large international cooperation to assess the importance of non-synchronous seismic excitation of long structures. To accomplish this task we compute complete synthetic accelerograms using as input a set of parameters that describes, to the best of our knowledge, the geological structure and seismotectonic setting of the investigated area.

The linear amplification of the larger horizontal component of strong ground motion along a selected profile in the city of Zagreb is estimated by examining the synthetic waveforms corresponding to a suite of 16 realistically chosen scaled point sources. The accelerograms, computed for the average bedrock model by modal summation, are propagated through local laterally heterogeneous anelastic models by the finite-difference algorithm. The ratio of peak ground acceleration (PGA) and of the response spectra (RS), obtained by using local and bedrock models, define the PGA and RS amplification AMP(PGA) and AMP(RS), respectively. Even variations of the order of commonly observed uncertainties of only dip and rake angles of the causative fault show that both AMP(PGA) and AMP(RS) vary at some sites by more than a factor of two. It follows that, especially for strongly laterally heterogeneous structures, local effects must be determined for each of the relevant sources considering all associated uncertainties as completely as possible. Such a conclusion certainly holds for the case of the microzonation of Zagreb, where the local geology is quite complex, and the seismicity is not confined to a single seismic source zone.

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.

— 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.

La ricerca illustrata ha come obiettivo fondamentale la stima dei Terremoti di Scenario ad Augusta, Siracusa e Noto mediante l’applicazione di approcci di tipo ingegneristico con criteri deterministici.

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.

The seismic ground motion of a test area in the eastern district of Naples is computed with a hybrid technique based on the mode summation and the finite difference methods. This technique allows us the realistic modelling of source and propagation effects, including local soil conditions. In the modelling, we consider the 1980 Irpinia earthquake, a good example of strong shaking for the area of Naples, which is located about 90 km from the epicenter. The detailed geological setting is reconstructed from a large number of drillings. The sub-soil is mainly formed by alluvial (ash, stratified sand and peat) and pyroclastic materials overlying a pyroclastic rock (yellow neapolitan tuff). representing the neapolitan bedrock. The detailed information available on mechanical properties of the sub-soil and its geometry warrants the application of the sophisticated hybrid technique. As expected, the sedimentary cover causes an increase of the signal's amplitudes and duration. If thin peat layers are present, the amplification effects are reduced, and the peak ground accelerations are similar to those observed for the bedrock model. This can be explained by the backscattering of wave energy at such layers, that tend to seismically decouple the upper from the lower part of the structure. For SH-waves, the influence of the variations of the S-wave velocities on the spectral amplification is studied, by considering locally measured velocities and values determined from near-by-down-hole measurements. The comparison between the computed spectral amplifications confirms the key role of an accurate determination of the seismic velocities of the different layers. The comparison performed between a realistic 2-D seismic response and a standard 1-D response, based on the vertical propagation of waves in a plane layered structure, shows considerable difference, from which it is evident that serious caution must be taken in the modelling of expected ground motion at a specific site.

We propose correlation relations between the macrosesimic intensity felt in Italy and displacement, velocity, acceleration, design ground acceleration obtained from synthetic seismograms modelling the ground motion generated by past seismicity. The results are in good agreement with empirical relations given by other authors and compare quite well with the few observations available in the Italian territory.

A detailed investigation, based on accelerometric and macroseismic data of the Irpinia 1980 event, is presented. The study is based on the use of synthetic seismograms, computed by the modal summation technique, and its purpose is to retrieve information concerning the rupturing process. Initially, for a first rough analysis, the 40 s sub-event has been neglected. The recorded accelerograms at the stations of Auletta, Bagnoli Irpino, Bisaccia, Brienza, Calitri and Sturno have been low-pass filtered with a cut-off frequency of 10 Hz, and the rupturing process has been modeled, by a trial-and- error technique, with twelve point sources properly distributed in space and time. An automatic inversion procedure has been successively applied to the whole observed waveforms, for frequencies not higher than 1 Hz. A very good fit has been achieved between observations and synthetics, and the obtained rupturing model is in gross accord with what retrieved by the first rough analysis. Finally, the information about the rupturing process has been used in order to compute synthetic isoseismals, which have been compared with the observed macroseismic field. Since the source radiation pattern has been also included in the computation, its influence on the shape of the isoseismals is discussed.

The 3–D model of the Earth, as obtained with a brand new investigative technique, is discussed. However an international collaborative project, involving researchers from the whole world, has uncovered a severe systematic error in the new data acquisition system making the results of this new model highly questionable.

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.

Summary In the computation of synthetic seismograms by modal summation, when a medium with a sharp lateral discontinuity is considered, a fundamental role is played by a coupling coefficient Γjj,. The coefficient Γjj, is defined via an integral relation involving products between displacements and stresses and can be evaluated both numerically and analytically. The calculation of Γjj can be reduced to the analytical computation of a sum of integrals of elementary functions. The analytical method proved to be particularly convenient for its speed and precision of the results obtained. The energy redistribution within the different modes is illustrated, both in the frequency and in the time domain. Mode conversion cannot be neglected when dealing with higher modes.

he Vrancea region seismicity, characterized by focal depths larger than 60 km and major events with magnitudes Mw ] 6.9, is responsible for the most destructive effects experienced in the Romanian territory, and may seriously affect high risk construction located on a wide area, from Central to Eastern Europe. This seismogenic volume must be taken into account both for seismic hazard analysis at the regional level (southeastern Europe) and national level (Romania and Bulgaria) as well as for microzonation studies of the highly populated cities located in the range of influence of this source. Since about four destructive earthquakes occur every century in Vrancea, the microzonation of Bucharest, the main city exposed to the potential damages due to these strong intermediate-depth shocks, represents an essential step towards the mitigation of the local seismic risk. Two main approaches can be considered for the evaluation of the local seismic hazard: (a) collection and extended use, for engineering purposes, of the recorded strong motion data, and (b) advanced modelling techniques that allow us the computation of a realistic seismic input, which can compensate for the lack of strong motion records, actually available only for a few events that occurred in the last 20–30 years. Using a ground motion simulation technique that combines modal summation and finite differences, we analyze, along a geologic profile representative of the Bucharest area, the differences in the expected ground motion when two source mechanisms corresponding to the May 30–31, 1990, intermediate-depth Vrancea earthquakes, typical events for the Vrancea seismogenic zone, are considered. All three components of motion are influenced by the presence of the deep alluvial sediments, the strongest local effect being visible in the transversal (T) one, both observed and computed. The details of the local effects vary with varying the earthquake scenario, R and V components being very sensitive. Therefore, for a reliable determination of the seismic input all three components of motion (R, V and T) should be used.

Seismic hazard assessment can be performed following a neo-deterministic approach (NDSHA), which allows to give a realistic description of the seismic ground motion due to an earthquake of given distance and magnitude. The approach is based on modelling techniques that have been developed from a detailed knowledge of both the seismic source process and the propagation of seismic waves. This permits us to define a set of earthquake scenarios and to simulate the associated synthetic signals without having to wait for a strong event to occur. NDSHA can be applied at the regional scale, computing seismograms at the nodes of a grid with the desired spacing, or at the local scale, taking into account the source characteristics, the path and local geological and geotechnical conditions. Synthetic signals can be used as seismic input in subsequent engineering analyses aimed at the computation of the full non-linear seismic response of the structure or simply the earthquake damaging potential. The same approach can be applied to tsunami hazard assesment: for a specific coastal area one has to characterize the seismic sources and select the earthquake scenarios that can drive the hazard; afterward the associated synthetic tsunamigrams are computed using the modal method. Massive parametric tests, to explore the influence not only of deterministic source parameters and structural models but also of random properties of the same source model, enable realistic estimate of seismic hazard and their uncertainty. The use of the EU-India Grid infrastructure allows to conduct massive parametric tests for evaluating the uncertainties in the computed hazard maps. In the framework of cooperation project between three Italian partners (DMG, University of Trieste; ICTP SAND Group; CNR/IOM uos Democritos) and two Indian partners (ISR, Gujarat; CSIR C-MMACS, Bangalore) a system will be set up for the scenario-based characterization of the seismic and tsunami hazard, integrated with the e-infrastructures of the project EU-India Grid. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial- ShareAlike License.

The CHAIN project, in collaboration with the GISELA project, has organised a workshop during the EGI Community Forum 2012 event. The workshop focused mainly on two topics: 1. The current Virtual Research Communities (VRC) vision of the CHAIN, EGI- InSPIRE, EUMEDGRID-Support, INDICATE and GISELA projects and an update of the Digital Cultural Heritage (DCH) and Seismic VRCs status and requirements and 2. The expected structure and content of the CHAIN roadmap. Two presentations in the workshop were introducing the CHAIN Project and the current status of its activities, while other three presentations were dedicated to the activities performed by the EGI-InSPIRE, EUMEDGRID-Support, INDICATE and GISELA projects to support VRCs. The workshop has also involved new VRCs (DCH and Seismic) to investigate their requirements, in terms of resources, their actual and potential geographical coverage and understand the possibility for them to exploit the existing regional e-Infrastructures. Virtual Research Communities (VRCs) could span a large organisational spectrum: from a group of researchers working together, sharing means to carry out common investigations, such as distributed resources: instruments, computing, storage and software tools, up to large international well-structured collaborations with or without large dedicated resources. The Grid infrastructures have been promoted, as it is well known, largely by the High Energy Physics community and their success in the analysis of the data coming from the Large Hadron Collider (LHC) at CERN is undisputable. However these infrastructures have demonstrated to be suited as well for several other scientific domains: from Biomedical to Weather Forecast research. Expanding the support to other VRCs is thus strategic not only towards sustainability, but also to evaluate new requirements and possibly evolve the services to fulfil them. CHAIN, EGI-InSPIRE, EUMEDGRID-Support and GISELA present here a status report on their main activities to support the VRCs. The contributions show many similarities, as expected, but also some significant differences due to the different constraints in the various regions of the World. Digital Cultural Heritage and Seismic communities presented their peculiar requirements which are different both in terms of resources and level of maturity. A true intercontinental infrastructure, based on the existing regional deployments, should provide services and organisational structures that allow VRCs to work seamlessly across the continents. The following chapters describe the contributions presented at the workshop and in the final chapter conclusions, coming out from the discussion, are drawn.

The seismic hazard of Romania is estimated in terms of peak-ground motion values— displacement, velocity, design ground acceleration (DGA)—computing complete synthetic seismograms, which are considered to be representative of the different seismogenic and structural zones of the country. The deterministic method addresses issues largely neglected in probabilistic hazard analysis, e.g., how crustal properties affect attenuation, since the ground motion parameters are not derived from overly simplified attenuation ‘‘functions,’’ but rather from synthetic time histories. The synthesis of the hazard is divided into two parts, one that of shallow-focus earthquakes, and the other, that of intermediate-focus events of the Vrancea region. The previous hazard maps of Romania completely ignore the seismic activity in the southeastern part of the country (due to the seismic source of Shabla zone). For the Vrancea intermediate-depth earthquakes, which control the seismic hazard level over most of the territory, the comparison of the numerical results with the historically-based intensity map show significant differences. They could be due to possible structural or source properties not captured by our modeling, or to differences in the distribution of damageable buildings over the territory (meaning that future earthquakes can be more spectacularly damaging in regions other than those regions experiencing damage in the past). Since the deterministic modeling is highly sensitive to the source and path effects, it can be used to improve the seismological parameters of the historical events.

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.

The influence of source and epicentral distance on the local seismic response in the Kolkata city is investigated by computing the seismic ground motion along 2-D geological cross-sections in the Kolkata city for the earthquake that occurred on 12 June 1897 (Mw = 8.1; focal mechanism: dip = 57◦, strike = 110◦ and rake = 76◦; focal depth = 9 km) in Shillong plateau. For the estimation of ground motion parameters, a hybrid technique is used, which is the combination of modal summation and finite difference method. This technique allows the estimation of site specific ground motion for various events located at different distances from Kolkata city, taking into account simultaneously the position and geometry of the seismic source, the mechanical properties of the propagation medium and the geotechnical properties of the site. The epicenter of the Shillong earthquake is about 460 km away from Kolkata. The estimated peak ground acceleration (PGA) varies in the range of 0.11–0.18 g and this range corresponds to the intensity of IX to X on the Mercalli-Cancani-Sieberg (MCS) scale and VIII on the Modified Mercalli (MM) scale. The maximum amplification in terms of response spectral ratio (RSR) varies from 10 to 12 in the frequency range 1.0–1.5 Hz. These amplifications occur in correspondence to low-velocity shallow, loose soil deposit. The comparison of these results with earlier ones obtained considering the Calcutta earthquake that occurred on 15 April 1964 (Mw = 6.5; focal mechanism: dip = 32◦, strike = 232◦ and rake = 56◦; focal depth = 36 km) shows that the source parameters (magnitude and focal mechanism) and epicentral distance play an important role on site response but the variation in the frequency of the peak values (RSR) is negligible. The obtained results match with observed reported intensities in Kolkata region.

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.

The Nile valley and the Nile delta are part of the active rift that is probably connected with the Red Sea tectonism. This zone is characterized by small-to-moderate size earthquakes that have caused extremely severe damage to recent and historical constructions. The most vulnerable area along the Nile valley is the one of Cairo-Faiyoum. Small local and large distant earthquakes could be a source of huge socio-economic damage in this area. The loose soft alluvial sediments of the Nile Canyon are the main factor behind this potential damage because they may greatly amplify the ground motion, as demonstrated by strong ground motion modelling. The largest amplification is generally concentrated along the edges of the graben and occurs at frequencies between 1 Hz and 2 Hz. This may explain the huge damage caused by distant earthquakes during recent and historical times. The distribution of intensity values during the events of 1926 and 1992 is well correlated with the modelled spatial distribution of the spectral amplification.

A neo-deterministic approach to seismic hazard assessment is proposed that, based on the available knowledge of the physical properties of the Earth structure and of the seismic sources allows for a time dependent definition of the seismic input, through the routine updating of earthquake predictions. In this way a set of deterministic scenarios of ground motion, which refers to the time interval when a strong event is likely to occur within a given region, can be defined at regional and local scale, thus providing informa- tion that can be useful in prioritizing the mitigation actions in North-Eastern Italy. A basic step in the integrated approach will consist in the realis- tic description of the seismic input, including space and time indica- tions, and of wave propagation in laterally heterogeneous media. Constraints about the space and time of occurrence of the impend- ing strong earthquakes are provided by the intermediate-term mid- dle-range earthquake predictions (performed by means of the algo- rithms CN and M8S) and by the pattern-recognition of the areas prone to large events. The scenarios of expected ground motion, associated with the alarmed areas are then defined by means of full waveforms modelling at bedrock, based on the possibility to com- pute synthetic seismograms by the modal summation technique. The practical example of regional ground motion scenarios at bedrock, which can be obtained by the proposed procedure, is pro- vided considering CN and M8S alarmed areas, as well as the earth- quake prone nodes (M ≥ 6.5) that determine the maximum ground motion in the cities of Milan, Trieste and Brescia. A detailed evalua- tion of the expected ground motion, considering site effects, is then proposed for the city of Trieste.