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Abstract: This paper deals with the neo-deterministic definition of the seismic input in the municipality of Nimis (Italy), aimed at the design of residential seismically isolated buildings. The seismic input is defined by the computation of realistic synthetic seismograms considering different levels of detail for the earthquake source, both for a bedrock model and taking into account the specific site conditions. The horizontal response spectrum, calculated in the centre of the municipality by modelling the most dangerous source, advises against the construction of a building with a fixed base, but it is compatible with the seismic isolation, and it has been, therefore, used for the design of a residential seismically isolated building. The maximum displacement for the isolation system has been estimated about 17 cm, a value much lower than that provided by the code design response spectrum (28 cm). The importance of the realistic modelling, which permits the generalization of empirical observations by means of, physically sound, theoretical considerations, is evident, as it allows for the optimisation of the structural design with respect to the site of interest. [Copyright &y& Elsevier]

Abstract: Synthetic seismograms (P-SV and SH waves) have been calculated along six profiles in Santiago de Cuba basin, with a cutoff frequency of 5Hz, 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 M S=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, I A R—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 E I R(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. [Copyright &y& Elsevier]

A seismic hazard map of the territory of India and adjacent areas has been prepared using a deterministic approach based on the computation of synthetic seismograms complete with all main phases. The input data set consists of structural models, seismogenic zones, focal mechanisms and earthquake catalogues. There are few probabilistic hazard maps available for the Indian subcontinent, however, this is the first study aimed at producing a deterministic seismic hazard map for the Indian region using realistic strong ground motion modelling with the knowledge of the physical process of earthquake generation, the level of seismicity and wave propagation in anelastic media. Synthetic seismograms at a frequency of 1 Hz have been generated at a regular grid of by the modal summation technique. The seismic hazard, expressed in terms of maximum displacement , maximum velocity , and design ground acceleration (DGA), has been extracted from the synthetic signals and mapped on a regular grid over the studied territory. The estimated values of the peak ground acceleration are compared with the observed data available for the Himalayan region and are found to be in agreement. Many parts of the Himalayan region have DGA values exceeding 0.6 g. The epicentral areas of the great Assam earthquakes of 1897 and 1950 in northeast India represent the maximum hazard with DGA values reaching 1.2–1.3 g. The peak velocity and displacement in the same region is estimated as 120–177 cm s−1 and 60–90 cm, respectively. [ABSTRACT FROM AUTHOR]

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 reliable 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 realistic ground shaking maps and ground shaking scenarios, 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. [ABSTRACT FROM AUTHOR]

In the network‐based on‐site earthquake early warning system (EEWS), the 'blind zone', namely the zone where the issued warning arrives later than the destructive S and surface waves, is one of the challenges affecting its effectiveness. The 'blind zone' is determined by the interstation distance, or equivalently the density of seismic stations, of the network. In this paper, we suggest a practical approach according to which, when in a region a temporary increase of seismic hazard is declared, additional stations are deployed in such a way that the blind zone is temporarily reduced. In the procedure, the time‐dependent neo‐deterministic seismic hazard assessment (TD‐NDSHA) plays a vital role in the identification of the regions potentially exposed to high macroseismic intensities. As a showcase example, we consider the scenario of year 2014 at the Sichuan‐Yunnan border of southwest China. The TD‐NDSHA is based on the standard NDSHA procedure at regional scale (bedrock conditions), with the 'controlling earthquakes' defined on the basis of the Annual Consultation. We show that the 'blind zone' can be reduced in the identified areas of interest (e.g., MMI ≥ VI), by deploying a limited number of additional seismic stations. In the case where false alarms can be tolerated, significant reduction of the 'blind zone' can be implemented by moving from a network‐based EEWS to a single‐sensor‐based EEWS and skipping the process of location and magnitude‐determination/prediction procedures. [ABSTRACT FROM AUTHOR]

In the neo-deterministic seismic hazard assessment (NDSHA) evaluation, great-earthquake-prone areas (GEPAs) play an important role in defining the 'controlling earthquakes' or 'scenario earthquakes'. When considering great earthquakes, their finite rupture attributes, which contribute to determine the strong ground motions and intensities, have to be taken into account. For continental earthquakes in China, the great earthquakes are located mainly within the boundary zones of the 'tectonic blocks'. The 'tectonic block' model indicates the focal mechanisms and some finite rupture attributes of the great earthquakes within the boundary zones. Accordingly, in the NDSHA for China, it is both necessary and feasible for the GEPAs to consider the finite rupture attributes of great earthquakes. The Sichuan-Yunnan border in southwest China has been taken as an example to naturally develop the originally used circular shape of GEPAs into one with more degrees-of-freedom, better reflecting the possible rupture processes of the considered earthquakes. [ABSTRACT FROM AUTHOR]

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 ( M = 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 ( M = 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. [ABSTRACT FROM AUTHOR]

Abstract: 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 (AMAX) 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 AMAX 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. [Copyright &y& Elsevier]

Examines the numerical modelling of waveforms in heterogeneous anelastic media. Seismic microzonation of urban areas; Factors contributing to seismic signal; Use of synthetic computations in determining the properties of seismic input.

Many devastating earthquakes inflicted heavy casualties and property losses in the seismically active China Seismic Experimental Site area (CSES: 97.5° ~ 105.5°E, 21° ~ 32°N). We performed a first-order seismic zoning based on Neo-deterministic Seismic Hazard Assessment (NDSHA) in the study area delimited by 94° ~ 108°E and 19° ~ 35°N, containing the South-East margin of the Tibetan Plateau and the Sichuan-Yunnan region. The seismic hazard is expressed by maps of peak ground displacement (PGD), peak ground velocity (PGV) and design ground acceleration (DGA) values, extracted from synthetic seismograms computed at a regional scale and mapped on a regular grid of 0.2° × 0.2° over the study area. For the computation of synthetic seismograms, we considered and updated all the available geophysical-geological-tectonic information, including historical and instrumental earthquake catalogues, seismogenic zones, seismogenic nodes, focal mechanisms, and geophysical structural models. We tested the performance of our assessments with available data (i.e., after the Great Wenchuan (2008, May 12th, M s = 8.0) and Lushan (2013, April 20th, M s = 7.0) earthquakes) and verified the negligible influence of large events located "far" from the study area. The results indicate the high seismic hazard of the region, with a particular attention (i.e., where DGA > 0.6 g) to the areas located around the main fault zones, e.g., the Longmenshan, Anninghe and Zemuhe Fault Zones. These first-order NDSHA zoning findings may serve as a knowledge basis to support both large- to mid-range preparedness actions and (multi-scenario) site-specific studies. • Neo-Deterministic Seismic Hazard Assessment maps for China Seismic Experimental Site. • The "predictive" power of NDSHA before and after the 2008 M 8.0 Wenchuan earthquake. • Validation of NDSHA against instrumental records of the 2008 M 8.0 Wenchuan earthquake. • Formulation of seismic hazard maps derived from M design for efficient practical applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A hybrid technique consisting of modal summation and subsequent finite differences modelling is applied for the computation of synthetic accelerograms along a profile crossing the city of Zagreb, the capital of Croatia. Assuming the source geometry is known, the amplification 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 amplification 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. [Copyright &y& Elsevier]

Throughout time, the area of historical Cairo has been affected by several earthquakes from near and distant seismogenic zones. The maximum earthquake intensity reported in Cairo is VII, on the Modified Mercalli Intensity scale, due to the 1992 Cairo earthquake (Mw=5.9). About 212 Coptic and Islamic monuments were damaged. The spatial distribution of damage, suggests the occurrence of strong local site effects in combination with high vulnerability of the cultural heritage buildings. This study presents the application of a novel seismic hazard analysis approach at a local scale based on physics-based ground motion simulations. A site-specific multi-scenario seismic input (ground motion time histories and response spectra) is computed at a heritage building in Cairo, considering the local site effect. The seismic input is calculated in three steps: a regional scale analysis followed by a site-specific analysis and the combinations of the computed scenarios ground motion. In the regional scale analysis synthetic accelerograms are computed at the site bedrock. Then, the site-specific analysis is performed to calculate the site surface ground motions or response spectra considering the local site effect. Three earthquake scenarios have been considered, characterized by different locations, magnitudes, and fault configurations. The last step consists in the combination of the computed scenario ground motion into one single multi-scenario seismic input specific for the site of interest. This input is represented by spectral ordinates and their variability. For the engineering purpose of time history analysis, the method allows also to extract the computed site specific physics-based accelerograms, requiring no amplitude scaling nor filtering by magnitudes, distances, or site classifications, as usually done with real ground motion records. • Site-Specific seismic hazard assessment for the historical Cairo has been accomplished. • Seismic hazard is evaluated through a detailed ground motion modeling using a hybrid approach. • A multi-scenario site-specific seismic input at a cultural heritage site has been provided. • A database for seismic input has developed at any desired site in historical Cairo. • Computed seismic input can be used to evaluate the dynamic behavior of the historical buildings. [ABSTRACT FROM AUTHOR]

Ischia island, in the province of Naples, is a densely populated volcanic island, in which small to moderate magnitude earthquakes occur. Due to the very shallow depth of such events (<2 km), they can generate serious damage and casualties, up to the complete destruction of urban centers located within short epicentral distance. Almost all of the earthquakes at Ischia island occur at shallow depth, beneath the Northern slopes of the Mt. Epomeo horst, which is located very close to the town of Casamicciola. In fact, Casamicciola was completely destroyed by the 1883 earthquake (2313 victims) and experienced intensities up to XI degree on the Mercalli scale. Historical records show that the background seismicity here is almost absent, but larger earthquakes tend to occur in clusters, lasting some decades and with intervals between consecutive events on the order of years to decades. The clustering in time and the very shallow hypocentres, which cause, with respect to tectonic earthquakes of similar magnitude, larger effects though limited to a relatively small area, make the seismicity in this island very peculiar. Despite such destructive record, till now official hazard maps strongly underestimated the seismic hazard in this area. On August 21st 2017, a very shallow earthquake with rather small magnitude struck the area of Casamicciola, killing two people, injuring many more and causing huge damage and partial to total collapse of edifices located just above the earthquake fault. The maximum acceleration recorded for this earthquake exceeded by more than a factor of two the reference acceleration that should be sustained by edifices, according to official hazard maps. We propose here a complete procedure to assess and mitigate the risk, which can be rapid and economically affordable and, at the same time, can avoid further grief due to possible occurrence of other destructive earthquakes within a short time interval. We describe the most likely building collapse and casualty scenarios, in case that low-to-moderate magnitude earthquakes would occur before the edifices would be appropriately reinforced and secured. Our scenarios demonstrate the urgent need for securing operations. The proposed procedures for assessing seismic hazard and for securing urban areas provide an example that is potentially applicable to the whole Italian peninsula. They may allow in fact the mitigation of the destructive impact of a large number of earthquakes, which in Italy are often characterized by low or moderate magnitudes. • Low magnitude, very shallow earthquakes can be locally destructive • Ischia island is prone to shallow, destructive earthquakes, clustered in time • The 2017, M = 4.0 earthquake caused victims, injured people, and might indicate the beginning of a new earthquake cluster • Innovative methods to reliably assess seismic hazard, based on NDSHA, are presented • A fast, comprehensive procedure to secure urban areas from shallow earthquakes is presented [ABSTRACT FROM AUTHOR]

Ischia island, Naples province, is a densely populated volcanic island, in which small to moderate magnitude earthquakes occur that, due to their very shallow depth (less than 2 km), are able to generate serious damage and casualties, up to the complete destruction of urban centers within a small distance (2-3 km) from the epicentre. Earthquake at Ischia island almost all take place at shallow depth below the Northern slopes of the Mt. Epomeo horst, very close to the town of Casamicciola, which was in fact completely destroyed by the 1883 earthquake, experiencing intensities up to XI degree on the Mercalli scale. The 1883 earthquake, killing about 2300 people, was forerun in 1881 by a smaller earthquake, killing about 130 people; the whole sequence of moderate magnitude, destructive earthquakes, started in 1828, with an earthquake killing about 30 people. Similar sequences of destructive earthquakes, clustered in some tens of years, occurred in the former centuries. Seismicity in this island is hence peculiar, both because of the very shallow depth (which amplifies the effect with respect to normal tectonic earthquakes, though involving a small damaged area) and of the clustering in time. Despite such destructive character, seismic hazard in this area has been strongly underestimated till now by official hazard maps, which take into account only the effects of continental earthquakes, hence neglecting the most effective source of hazard, which is the local seismicity. On August 21st 2017, a moderate magnitude earthquake struck the area of Casamicciola, killing two people, injuring many more and causing huge damage and partial to total collapse of edifices locate just above the earthquake fault.The maximum acceleration recorded for this earthquake exceeded the reference acceleration imposed to be sustained by edifices, according to official hazard maps, of a factor more than double. The observation of seismic accelerations overcoming the reference ones prescribed by hazard maps, and the difficulty to manage the vulnerability of ancient edifices, is common for many recent earthquakes in Italy, generally causing grief and destruction also for moderate magnitude earthquakes. A further problem of Ischia earthquakes, which make them very different from tectonic earthquakes occurring in the Apennine and Alpine chains, is that the stress accumulation times and mechanisms are absolutely unpredictable, because linked to complex volcano-tectonic phenomena. Clusters of destructive earthquakes can then occur in few years or decades, making urgent the securing of buildings in the most hazardous areas. We propose here a complete procedure to assess and mitigating the risk, which can be fast and cheap, avoiding further grief due to possible occurrence of other destructive earthquakes in short time. We further evidence the most likely building collapse and casualty scenarios, if new significant magnitude earthquakes should occur before securing the areas; just to show the imperative needing to act very fast. The proposed procedures for hazard assessment and for urban areas securing can be then generalized to the whole Italian peninsula, then mitigating the catastrophic character of most earthquakes in Italy, even of moderate magnitudes. [ABSTRACT FROM AUTHOR]