Search

We propose an interdisciplinary approach to time-dependent neo-deterministic seismic hazard assessment (T-NDSHA) for the China Seismic Experimental Site (CSES) at a 1-year time scale. The approach is based on the neo-deterministic seismic hazard assessment (NDSHA), with the “controlling” earthquakes (or “scenario” earthquakes) as defined by the Annual Consultation on the Likelihood of Earthquakes. The Annual Consultation, organized by the China Earthquake Administration (CEA), has been an interdisciplinary practice since 1972, with the output of “alert regions” with increased probabilities of strong earthquakes, featured by real forward forecasting characteristics. We take the year 2014, in which there were four strong earthquakes in the CSES region, as a showcase example to illustrate how the T-NDSHA may be conducted and evaluated. Considering the alert regions provided by the Annual Consultation, the expected strong ground motion parameters and the macroseismic intensities are mapped by the NDSHA algorithms considering the regional Earth structures and the focal mechanisms of historical earthquakes. The estimated intensities are then subjected to comparison with the intensities produced by the actual earthquakes. Evaluation of the performance of such annual seismic hazard assessment is performed using a confusion matrix and Molchan error diagram, respectively, indicating that the combination of the NDSHA and the annual forecasting provides the emergency preparation with a ready-to-use mapping of expected intensities which outperforms random forecasting. The proposed approach provides a substantial improvement to the Annual Consultation, and it can naturally be applied to other regions where intermediate-term middle-range earthquake forecasts are available and where the need for emergency preparation are duly considered.

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.

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.

We conducted a tomographic inversion of Rayleigh-wave dispersion to obtain 2D phase and group velocity tomographic images in the 10-100 s period range and shear-wave velocity structures for the Iranian plateau. For this purpose, the fun- damental mode of Rayleigh waves, recorded along 1586 paths by 29 broadband sta- tions, was identified by applying the frequency time analysis (FTAN) to each epicenter-station path which simultaneously satisfies the two-station method condi- tions. The fundamental modes identified by FTAN have been used to determine the path-average interstation phase and group velocities at selected periods. With this pro- cedure, 243 group and phase velocity dispersion curves were processed to obtain to- mographic maps by applying the Yanovskaya-Ditmar formulation for periods in the 10-100 s range. Averaged dispersion curves of phase and group velocities, which represent six rather homogeneous regions, are computed. Finally, we used a fully non- linear inversion procedure to derive tomographic images of the elastic structure of the lithosphere and asthenosphere of the six main structural and seismotectonic features of the Iranian plateau. The dense path coverage in the Iranian plateau permits us to pro- duce images that have substantially higher lateral resolution compared to images cur- rently available from global and regional group velocity studies. Tomographic maps at high frequencies are well correlated with the upper crust structure, especially with sediment layers thickness. Estimated shear-wave velocity structures are well corre- lated with the shield-like lithosphere structure in Zagros. A low-velocity zone (LVZ) is not detected in Alborz or the south Caspian basin, which can imply thrusting of the oceanic crust of the southern Caspian Sea under the Alborz to the south. LVZs are derived for the region east of Iran, central Iran, and Kopeh Dagh.

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.

Some of the elements of regional seismic hazard in Croatia are assessed by computing synthetic accelerograms at a predetermined set of sites. The input dataset consists of structural models, parameters of seismic sources, and an updated earthquake catalog. Synthetic strong-motion time series for frequencies below 1 Hz are computed on a grid of sites using the modal summation technique. The long-period hazard is described by the distribution of estimated peak values of ground displacement, velocity and acceleration, while the short-period hazard is represented by the map of design ground acceleration values (DGA). The highest values of DGA exceeding 0.35 g on the base-rock level are found in the southeastern coastal part of the country, in the greater Dubrovnik area.

—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.

North Africa is one of the most earthquake-prone areas of the Mediterranean. Many devastating earthquakes, some of them tsunami-triggering, inflicted heavy loss of life and considerable economic damage to the region. In order to mitigate the destructive impact of the earthquakes, the regional seismic hazard in North Africa is assessed using the neo-deterministic, multi-scenario methodology (NDSHA) based on the computation of synthetic seismograms, using the modal summation technique, at a regular grid of 0.2 × 0.2°. This is the first study aimed at producing NDSHA maps of North Africa including five countries: Morocco, Algeria, Tunisia, Libya, and Egypt. The key input data for the NDSHA algorithm are earthquake sources, seismotectonic zonation, and structural models. In the preparation of the input data, it has been really important to go beyond the national borders and to adopt a coherent strategy all over the area. Thanks to the collaborative efforts of the teams involved, it has been possible to properly merge the earthquake catalogues available for each country to define with homogeneous criteria the seismogenic zones, the characteristic focal mechanism associated with each of them, and the structural models used to model wave propagation from the sources to the sites. As a result, reliable seismic hazard maps are produced in terms of maximum displacement (D max), maximum velocity (V max), and design ground acceleration.

Estimates of seismic hazard obtained using the neo-deterministic approach (NDSHA) and the probabilistic approach (PSHA) are compared for the Italian territory. The NDSHA provides values larger than those given by the PSHA in areas where large earthquakes are observed and in areas identified as prone to large earthquakes, but lower values in low-seismicity areas. These differences suggest the adoption of the flexible, robust and physically sound NDSHA approach to overcome the proven shortcomings of PSHA, thus allowing for a reliable seismic hazard estimation, especially for those areas characterized by a prolonged quiescence, i.e. in tectonically active sites where events of only moderate size have occurred in historical times.

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.

An integrated neo-deterministic approach to seismic hazard assessment has been developed that combines different pattern recognition techniques, designed for the space–time iden- tification of impending strong earthquakes, with algorithms for the realistic modeling of seismic ground motion. The integrated approach allows for a time-dependent definition of the seismic input, through the routine updating of earthquake predictions. The scenarios of expected ground motion, associated with the alarmed areas, are defined by means of full waveform modeling. A set of neo-deterministic scenarios of ground motion is defined at regional and local scales, thus providing a prioritization tool for timely preparedness and mitigation actions. Constraints about the space and time of occurrence of the impending strong earthquakes are provided by three formally defined and globally tested algorithms, which have been developed according to a pattern recognition scheme. Two algorithms, namely CN and M8, are routinely used for intermediate-term middle-range earthquake predictions, while a third algorithm allows for the identification of the areas prone to large events. These independent procedures have been combined to better constrain the alarmed area. The pattern recognition of earthquake-prone areas does not belong to the family of earthquake prediction algorithms since it does not provide any information about the time of occurrence of the expected earthquakes. Never- theless, it can be considered as the termless zero-approximation, which restrains the alerted areas (e.g. defined by CN or M8) to the more precise potential location of large events. Italy is the only region of moderate seismic activity where the two different pre- diction algorithms, CN and M8S (i.e. a spatially stabilized variant of M8), are applied simultaneously and a real-time test of predic- tions, for earthquakes with magnitude larger than a given threshold (namely 5.4 and 5.6 for CN algorithm, and 5.5 for M8S algorithm) has been ongoing since 2003. The application of the CN to the Adriatic region, which is relevant for seismic hazard assessment in the northeastern part of the Italian territory, is also discussed. Examples of neo-deterministic scenarios are provided, at regional and local scale and for the cities of Trieste and Nimis (Friuli Venezia Giulia region), where the knowledge of the local geological conditions permitted a detailed evaluation of the expected ground motion.

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 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.

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.

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.

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 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.