Ground Motion Values Research Articles

Ground Motion Prediction Equations in the San Jacinto Fault Zone: Significant Effects of Rupture Directivity and Fault Zone Amplification

We present a new set of Ground Motion Prediction Equations (GMPEs) for horizontal Peak Ground Acceleration, Peak Ground Velocity, and 5 % damped pseudo-spectral acceleration (PSA), developed for the San Jacinto Fault Zone (SJFZ) area. Besides using these equations to quantify seismic shaking in the area, the results allow us to examine the physics and local properties controlling the observed ground motions. The analyzed dataset includes ~30,000 observations from ~800 events spanning a magnitude range of 1.5 < M < 6.0 and recorded by up to 140 stations at epicentral distances ranging from essentially zero to 150 km. The local GMPE is developed for the SJFZ by applying classical regression techniques with predictive variables that include first distance and magnitude, and then site characteristics, rupture directivity, and fault zone amplification. The significance of these effects is determined by measuring the uncertainty-reduction of the GMPE due to each factor. The results show that, in contrast to many regional studies, traditional site characteristic has a relatively minor effect on peak amplitudes in our study area. However, rupture directivity is a significant factor controlling the amplitudes of ground motion even for small events. The dense seismic network and newly developed directivity tool enable us to extract efficiently directivity effects with statistical significance, using the ground-motion dataset during the regression analysis process. The obtained rupture directivities are consistent with the main focal mechanism orientations and surface trace orientations, known from other studies, and predictions for bimaterial ruptures in the trifurcation area of the SJFZ. Fault zone amplification is a second important factor, showing strong impact on the peak ground motion values, with increasing role for the lower frequency range (<10 Hz) examined in the 5 % damped PSA values. We also observe signatures of large amplitude-variances, which indicate additional source-related control on the distribution of amplitudes (besides rupture directivity) for aftershocks close in time and location to the M L 5.1 earthquake of March 2013. Using the full set of records we present the most complete set of GMPEs for the SJFZ area, including a higher-amplitude prediction for regions in the direction of rupture.

Effects of surface topography on ground shaking prediction: implications for seismic hazard analysis and recommendations for seismic design

This study examines the role of topographic effects on the prediction of earthquake ground motion. Ground motion prediction equations (GMPEs) are mathematical models that estimate the shaking level induced by an earthquake as a function of several parameters, such as magnitude, source-to-site distance, style of faulting and ground type. However, little importance is given to the effects of topography, which, as known, may play a significant role on the level, duration and frequency content of ground motion. Ridges and crests are often lost inside the large number of sites considered in the definition of a GMPE. Hence, it is presumable that current GMPEs are unable to accurately predict the shaking level at the top of a relief. The present work, which follows the article of Massa et al. about topographic effects, aims at overcoming this limitation by amending an existing GMPE with an additional term to account for the effects of surface topography at a specific site. First, experimental ground motion values and ground motions predicted by the attenuation model of Bindi et al. for five case studies are compared and contrasted in order to quantify their discrepancy and to identify anomalous behaviours of the sites investigated. Secondly, for the site of Narni (Central Italy), amplification factors derived from experimental measurements and numerical analyses are compared and contrasted, pointing out their impact on probabilistic seismic hazard analysis and design norms. In particular, with reference to the Italian building code, our results have highlighted the inadequacy of the national provisions concerning the definition of the seismic load at top of ridges and crests, evidencing a significant underestimation of ground motion around the site resonance frequency.

Probabilistic seismic hazard analysis and spectral accelerations for United Arab Emirates

In recent years, the United Arab Emirates (UAE) has experienced an unprecedented growth which is coupled with the increase in seismic activity in the surroundings. Previous studies presents significant variations in their results whereas some recent studies although very detailed focus on only few cities. This study reviews the results of previous studies and presents new findings for the whole of UAE based on the improved source model and use of next generation attenuation (NGA) equations. The peak ground accelerations, spectral accelerations and deaggregation of hazard for major cities are presented. Moreover, the breakdown of the range of mapped spectral accelerations (S 0.2 and S 1) is proposed to form the basis for the development of site amplification factors in subsequent studies. The results of this study indicate almost similar values of ground motion compared to some recently published studies and smaller values compared to some earlier studies.

Comment on "Seismic Hazard Assessment (2003-2009) for the Italian Building Code" by Massimiliano Stucchi, Carlo Meletti, Valentina Montaldo, Helen Crowley, Gian Michele Calvi, and Enzo Boschi

A new reference probabilistic seismic hazard map of Italy was recently presented by Stucchi et al. (2011). The map represents the most recent development of the “Cornell‐McGuire” approach adopted in Italy in the last 20 years for hazard assessment and implements current models for epistemic uncertainty treatment. This comment does not address the possible limitations of the considered approach itself, but some important (and possibly misleading) consequences of the representation chosen for hazard outcomes, selection of alternative procedures to be included in the logic‐tree considered to manage the epistemic uncertainty, and some statements about the possibility of using recent seismicity to validate these outcomes. This last point is of major importance since any future development of hazard mapping in Italy strongly depends on a careful evaluation of possible drawbacks inherent in the present formulations that should be pointed out by comparing theoretical outcomes and observations. The first aspect is related to one main result provided in the new hazard map that made it possible to base the design spectra for a building on point hazard data instead of on four intervals of peak ground acceleration (PGA), as was the case for the previous code. The authors claim the advantage of the new map is that it provides unprecedented detail of reference ground motion values associated with a fixed return time. In particular, officially released values (INGV, 2008) provide a PGA with four significant digits at more than 16,000 points. This appears overwhelming when compared to the mere four values associated with the zones of the previous map, with PGA set at 0, 0.15, 0.25, and 0.35 g . However, a closer look at the starting data may cast some doubts …

Comparative study of codes for the seismic design of structures

A general evaluation of some points of the South American seismic codes is presented herein, comparing them among themselves and with the American Standard ASCE/SEI 7/10 and with the European Standard Eurocode 8. The study is focused in design criteria for buildings. The Western border of South America is one of the most seismically active regions of the World. It corresponds to the confluence of the South American and Nazca plates. This region corresponds roughly to the vicinity of the Andes Mountains. This seismicity diminishes in the direction of the comparatively seismically quieter Eastern South American areas. The South American countries located in its Western Border possess standards for seismic design since some decades ago, being the Brazilian Standard for seismic design only recently published. This study is focused in some critical topics: definition of the recurrence periods for establishing the seismic input; definition of the seismic zonation and design ground motion values; definition of the shape of the design response spectra; consideration of soil amplification, soil liquefaction and soil-structure interaction; classification of the structures in different importance levels; definition of the seismic force-resisting systems and respective response modification coefficients; consideration of structural irregularities and definition of the allowable procedures for the seismic analyses. A simple building structure is analyzed considering the criteria of the several standards and obtained results are compared.

Estimation of seismic ground motions using deterministic approach for major cities of Gujarat

Abstract. A deterministic seismic hazard analysis has been carried out for various sites of the major cities (Ahmedabad, Surat, Bhuj, Jamnagar and Junagadh) of the Gujarat region in India to compute the seismic hazard exceeding a certain level in terms of peak ground acceleration (PGA) and to estimate maximum possible PGA at each site at bed rock level. The seismic sources in Gujarat are very uncertain and recurrence intervals of regional large earthquakes are not well defined. Because the instrumental records of India specifically in the Gujarat region are far from being satisfactory for modeling the seismic hazard using the probabilistic approach, an attempt has been made in this study to accomplish it through the deterministic approach. In this regard, all small and large faults of the Gujarat region were evaluated to obtain major fault systems. The empirical relations suggested by earlier researchers for the estimation of maximum magnitude of earthquake motion with various properties of faults like length, surface area, slip rate, etc. have been applied to those faults to obtain the maximum earthquake magnitude. For the analysis, seven different ground motion attenuation relations (GMARs) of strong ground motion have been utilized to calculate the maximum horizontal ground accelerations for each major city of Gujarat. Epistemic uncertainties in the hazard computations are accounted for within a logic-tree framework by considering the controlling parameters like b-value, maximum magnitude and ground motion attenuation relations (GMARs). The corresponding deterministic spectra have been prepared for each major city for the 50th and 84th percentiles of ground motion occurrence. These deterministic spectra are further compared with the specified spectra of Indian design code IS:1893-Part I (2002) to validate them for further practical use. Close examination of the developed spectra reveals that the expected ground motion values become high for the Kachchh region i.e. Bhuj city and moderate in the Mainland Gujarat, i.e. cities of Surat and Ahmedabad. The seismic ground motion level in the Saurashtra is moderate but marginally differs from that as presently specified in IS:1893-Part I (2002). Based on the present study, the recommended PGA values for the cities studied are 0.13 g, 0.15 g, 0.64 g, 0.14 g and 0.2 g for Ahmedabad city, Surat City, Bhuj City, Jamnagar City and Junagadh city, respectively. The prepared spectra can be further used for seismic resistant design of structures within the above major city boundaries of Gujarat to quantify seismic loading on structures.

Risk-based damage potential and loss estimation of earthquake scenarios in the moderate endangered Austrian Federal Province of Tyrol

Although geophysical hazards like earthquakes can lead to tremendous losses, they are often neglected or not considered in risk analyses within an Alpine context. However, lately and especially in the framework of multi-risk analyses, earthquake risk studies are being increasingly implemented within an Alpine relation too. The presented study was conducted to quantitatively estimate potential consequences of earthquake events in the Austrian Province of Tyrol. The methodological study framework integrates the general risk components (i) hazard, (ii) elements at risk, and (iii) vulnerability. They are considered on a regional scale, accepting pragmatic approaches with simplified procedures and assumptions. Scenarios for different potential epicentres were calculated based on two different macroseismic hazard maps derived from punctual ground motion values of the building code and microzonation studies. The maps take into account the design event definitions of existing building code and a, thereupon based, simple and mono-causal Maximum Credible Earthquake assumption. Corresponding elements at risk and damage potentials were identified and potential losses were estimated under consideration of different vulnerability approaches. It can be shown that most scenarios based on the design event definition of the Austrian and European building codes, respectively have the potential of building and inventory losses solely of some hundred million up to approximately €4 billion. Additional, building and inventory losses of maximum credible events can lead to losses of more than €7 billion merely in connection with the primary earthquake event neglecting all other cascading effects.

Seismic site effects at near-fault strong-motion stations along the Aterno River Valley during the Mw=6.3 2009 L'Aquila earthquake

An Mw=6.3 earthquake originating at a normal fault in proximity of the city of L'Aquila produced a significant amount of near-fault strong-motion data recorded by an array deployed in the upper Aterno River Valley, NW of L'Aquila. This set of data deserves attention since it is the first well documented earthquake occurring in a near-fault area which was recorded from a moderate magnitude earthquake on a normal fault. For most of the stations geotechnical conditions are ascertained by means of drilling and geophysical investigation. To provide insights on the relevance of site conditions on measured near-source ground motions, peak and spectral values of acceleration and velocity recordings at stiff soil sites are compared with those at “rock” reference sites. Events of magnitude ranging between 3.0 and 6.3 (main event) were used. The results show that peak and response spectra values of ground motion, for the horizontal component and to a lesser extent for the vertical one, are affected by soil profile characteristics, especially for the station located on alluvium at the centre of the valley. For this station, observed amplification ratios were compared with numerical ones computed from 1D site response analyses. Evidence is presented that 1D numerical modelling is not able to completely explain the recorded motions.

Widespread landslides induced by the Mw 5.1 earthquake of 11 May 2011 in Lorca, SE Spain

On 11 May 2011, a moderate magnitude (Mw 5.1) earthquake struck the city of Lorca (SE Spain) and nearby areas, causing notable damage, injuries and fatalities. Field inspection of the area affected allowed the location and characterization of more than 250 induced landslides, mainly of disrupted type (rock/soil falls, disrupted soil slides and rock avalanches). This number was very high when compared with the inventories of previous events of similar magnitude (Mw 4.7 to 5.0) in the zone and with the results of previous models for predicting slope behavior during earthquakes. Several factors are proposed here to explain the observed differences: (i) the comparatively high magnitude (Mw 4.5) of a foreshock of the seismic series that may have weakened the slopes; (ii) the high peak ground motion values recorded for these events and (iii) the occurrence of topographic site effects. The results of this study point out the importance of including such effects as improvements in the models for studying the regional behavior of slopes.

Site-Response Study of Thessaloniki (Northern Greece) for the 4 July 1978 M 5.1 Aftershock of the June 1978 M 6.5 Sequence Using a 3D Finite-Difference Approach

The 3D wave-propagation characteristics of the 4 July 1978 aftershock (M 5.1) of the 20 June 1978 strong mainshock (M 6.5) that struck the city of Thessaloniki are studied using a 3D finite-difference approach. Synthetics are esti- mated for a dense grid of receivers and compared with available accelerograms from soft-soil sites in the city of Thessaloniki, exhibiting a good agreement both in time and frequency domain for the frequency band studied (0.7-3 Hz). Moreover, the spatial distribution of various measures of ground motion (peak values, spectral values) is used for the quantitative study of site effects in the broader city area. Comparisons show that the coastal zone, including the city harbor and large areas of the eastern parts of the city, exhibit high values of ground motion (and significant site amplifications), in good qualitative correlation with the observed damage distribution of the main- shock of the 1978 seismic sequence. Finally, the 3D synthetics are compared with available 2D simulations, as well as amplifications derived from macroseismic infor- mation for three typical cross sections spanning the urban area of the city. The com- parisons confirm the strong spatial variability of ground motion throughout the Thessaloniki area, as well as the superiority of 3D modeling of actual recordings against previous modeling attempts. These results verify the practical usefulness of 3D wave-propagation tools for hazard mitigation, especially of specific target events, in complex geometry sedimentary basins such as the Thessaloniki area.

Deterministic earthquake damage and loss assessment for the city of Bucharest, Romania

On March 4, 1977, an earthquake with a moment magnitude Mw 7.4 at a hypocentral depth of 94 km hit the Vrancea region (Romania). In Bucharest alone, the earthquake caused severe damage to 33,000 buildings while 1,424 people were killed. Under the umbrella of the SAFER project, the city of Bucharest, being one of the larger European cities at risk, was chosen as a test bed for the estimation of damage and connected losses in case of a future large magnitude earthquake in the Vrancea area. For the conduct of these purely deterministic damage and loss computations, the open-source software SELENA is applied. In order to represent a large event in the Vrancea region, a set of deterministic scenarios were defined by combining ranges of focal parameters, i.e., magnitude, focal depth, and epicentral location. Ground motion values are computed by consideration of different ground motion prediction equations that are believed to represent earthquake attenuation effects in the region. Variations in damage and loss estimates are investigated through considering different sets of building vulnerability curves (provided by HAZUS-MH and various European authors) to characterize the damaging behavior of prevalent building typologies in the city of Bucharest.

Discussion on the influence of truncation of ground motion residual distribution on probabilistic seismic hazard assessment

Recent studies on assessment of a very low annual probability of exceeding (APE) ground motions, 10−4 or less, have highlighted the importance of the upper bound of ground motions when very low probability results are acquired. The truncation level adopted in probabilistic seismic hazard analysis (PSHA) should be determined by an aleatory uncertainty model (i.e., distribution model) of ground motions and the possible maximum and minimum ground motion values of a specific earthquake. However, at the present time, it is impossible to establish the upper bound model for ground motions based on the source characteristics and/or ground motion propagation. McGuire suggested a truncation level be fixed at a number of ɛ = 6, or the distribution of residuals be truncated in such a manner that site intensity cannot be greater than the epicenter intensity. This study aims to find a reasonable and feasible truncation level to be used in PSHA when the physical mechanism is not available to find the extreme ground motion. A mathematical analysis of the influence of the truncation level on PSHA, case studies of sites in different seismotectonic settings, and a distribution analysis of ground motion residuals are conducted in this study. It is concluded that ɛ = 4 is the minimum acceptable value for engineering applications for APEs within 0.002 to 10−4, and for low APEs, such as 10−5 and 10−6, the value of e should be no less than 5 in most regions of China.

Felt Intensity versus Instrumental Ground Motion: A Difference between California and Eastern North America?

We examine the question of whether a single ground-motion intensity correlation equation (GMICE) is applicable to both eastern North America (ENA; intraplate) and California (interplate). We initially address this issue with the datasets from previous studies and separate them into central United States (CUS), California, and Canada datasets. We then add data from the 2008 M 5.2 Mt. Carmel, Illinois, and the 2005 M 4.7 Riviere du Loup earthquakes to the CUS and Canada datasets, respectively. For each dataset, the median of ground-motion values at each modified Mercalli intensity (MMI) level and their 95% confidence limits are calculated for peak ground velocity (PGV), peak ground acceleration (PGA), and spectral acceleration (SA) at 0.3, 1.0, and 2.0 s. The California median value is relatively higher than the CUS and Canada for PGV and SA at 1.0 and 2.0 s. Based on the median values and the associated uncertainty, we combine all datasets for PGA and 0.3-s SA in order to determine a GMICE. The CUS and Canada datasets are combined separately from California for PGV, 1.0-s SA, and 2.0-s SA. ENA earthquakes have a different spectral shape than those in California, particularly at intermediate periods (∼1.0 s) where ENA spectral amplitudes are reduced, which may explain the difference we see at longer periods. Finally, a log-linear-fit of MMI to the median values of ground motion is used to determine GMICE.

Response spectral attenuation relations for shallow crustal earthquakes in Taiwan

In this study, a local set of response spectral attenuation equations, developed for seismic hazard analysis in Taiwan, are introduced as an example for determining the local strong motion attenuation relationship for a region. Strong ground-motion data for shallow crustal earthquakes are obtained from the Taiwan Strong-motion Instrumentation Program (TSMIP). These data are used to establish peak ground acceleration (PGA) and response spectral acceleration (SA) attenuation equations taking into consideration both hanging-wall effects and site conditions. The obtained results show that the local set of attenuation equations gives significantly lower values of PGA and SA for structural periods shorter than 0.3 s as compared to a set of global relations obtained from international data. The SAs obtained for structural periods longer than 0.3 s are similar to those obtained for global sets. This indicates that developing a local set of ground-motion attenuation equations is necessary for more accurate prediction of ground motion values.

Selection of Empirical Green's Functions by Waveform Similarity Analysis: An Approach to Predict Ground Motion in Areas with Saturated Records

Abstract This work is focused on a procedure based on selecting suitable empirical Green’s functions (EGFs), able to predict ground motion for moderate earthquakes, in the case where no records are available due to saturation phenomena. The aim of the article is to generate synthetic seismograms for the 24 November 2004, M L 5.2, Salo earthquake (northern Italy), an event capable of saturating all velocimetric stations installed within the first 100 km from the epicenter. The proposed approach uses a waveform similarity analysis, based on the normalized cross-correlation technique, and it is able to identify EGFs that represent doublet events of a target. The ground motion was finally simulated using the method proposed by Irikura (1986). In this case, due to the saturation of near-source velocimetric instruments, the normalized cross-correlation matrix was calculated considering the first not saturated velocimetric station (ASO2, 108 km northeast to the epicenter), including the same selected portion of signals (on the base of signal-to-noise ratio) related both to the target and to 11 events, with M L ranging from 2.2 to 3.0, that occurred in the same area. The similarity analysis, performed through the bridging technique, allows us to detect an M L 2.9 aftershock characterized by a meaningful degree of similarity (70%) compared to the target. Given as a fact that if two events are similar for a far-field station they have to be similar also for a near-source one, it was in this way possible to use the selected aftershock (doublet), recorded in near source to reproduce the target for the saturated near-source stations. The results of the simulations were compared with ground-motion values predicted by empirical ground-motion prediction equations (GMPEs), calibrated using both Italian and European data.

Effects of Impedance Contrast and Soil Thickness on Basin-Transduced Rayleigh Waves and Associated Differential Ground Motion

This paper presents the effects of impedance contrast (IC) across the basin edge, velocity contrast between the basin and underlying bedrock, Poisson’s ratio and soil thickness on the characteristics of basin-transduced Rayleigh (BTR) waves and associated differential ground motion (DGM). Analysis of simulated results for a two-dimensional (2D) basin revealed complex mode transformation of Rayleigh waves after entering the basin. Excellent correlation of frequencies corresponding to different spectral ratio peaks in ellipticity curves of BTR waves and spectral amplification peaks was obtained. However, such correlation was not observed between values of peaks in ellipticity curves and spectral amplification at the corresponding frequencies. An increase of spectral amplification with IC was obtained. The largest spectral amplification was more than twice the IC in the horizontal component and more than the IC in the vertical component in the case of large and same impedance contrast for P- and S-waves. It was concluded that the frequency corresponding to the largest spectral amplification was greater than the fundamental frequency of soil by around 14% and 44% in the vertical and horizontal components, respectively. Spectral amplification of the vertical component was negligible when soil thickness was less than around 15–20 times the S-wave wavelength in the basin. The largest values of peak ground displacement (PGD) and peak differential ground motion (PDGM) were obtained very near the basin edge, and their values with offset from the edge were strongly dependent on the IC across the basin edge, Poisson’s ratio, velocity contrast between the basin and underlying bedrock (dispersion), damping and soil thickness. The obtained value of PDGM for a span of 50 m in the horizontal and vertical components due to the BTR wave was of the order of 0.75 × 10−3 and 1.32 × 10−3 for unit amplitude (1.0 cm) in the horizontal component of the Rayleigh wave at rock very near the basin edge.

RISe: Illustrating Georeferenced Data of Seismic Risk and Loss Assessment Studies Using Google Earth

Predicting the consequences of large earthquakes to the built environment is of high importance for disaster control, civil protection and emergency planning. A number of software tools are now available to estimate physical building damage and associated losses in terms of casualties and economic losses. In recent years, SELENA, a seismic risk and loss assessment software which makes use of the capacity spectrum method (CSM), has been developed into a widely applicable tool. Since SELENA functions independently from a Geographic Information System, we developed RISe ( Risk Illustrator for Selena), a stand-alone tool that illustrates SELENA files in Google™ Earth. RISe is customized to the SELENA file structure and allows easy conversion of all geographically referenced files such as building inventory data, soil conditions, ground motion values, as well as final risk and loss results. RISe is distributed as public domain open-source software that allows the user to take full advantage of Google™ Earth's features including high-resolution satellite images from nearly every built environment worldwide.

Application of Generalized Pareto Distribution to Constrain Uncertainty in Peak Ground Accelerations

Abstract Probabilistic seismic hazard analysis (PSHA) has become standard practice to characterize earthquake ground-motion hazard and to develop ground-motion inputs for seismic design and performance analyses. One emerging issue is the application of PSHA at low annual exceedance probabilities, particularly the characterization of scatter (aleatory variability) in the recorded ground-motion parameters, including peak ground acceleration (PGA). Lognormal distributions are commonly used to model ground-motion variability. However, a lognormal distribution, when unbounded, can yield a nonzero probability for unrealistically high ground-motion values. In this article, we evaluate the appropriateness of the lognormal assumption for low-probability ground motions by examining the tail behavior of the PGA recordings from the Pacific Earthquake Engineering Research–Next Generation Attenuation of Ground Motions (PEER NGA) database and the PGA residuals using Abrahamson–Silva NGA ground-motion relations. Our analyses show that the tail portion of the PGA and the residual data do not always follow a lognormal distribution and are instead often better characterized by the generalized Pareto distribution (GPD). We propose using a composite distribution model (CDM) that consists of a lognormal distribution (up to a threshold value of ground-motion residual) combined with GPD for the tail region. We demonstrate implications of the CDM in PSHA using a simple example and GPD parameters derived from the residual fit. Our results show that, at low annual exceedance probabilities, the CDM yields considerably lower PGA values than the unbounded lognormal distribution. It also produces smoother hazard curves than truncated lognormal distributions because the PGA increases asymptotically with a decreasing probability level. The presented approach is readily adapted to spectral accelerations and other ground-motion parameters.

Near-Fault Earthquake Ground-Motion Simulation in the Grenoble Valley by a High-Performance Spectral Element Code

Near-fault effects are known to produce specific features of earthquake ground motion (such as long-period velocity pulses and directivity) that cannot be predicted by numerical approaches involving vertical plane wave propagation in one-dimensional (1D) soil models that are used as a standard in engineering applica- tions. Coupling near-fault conditions with site effects induced by complex geological structures (such as deep alluvial basins or steep topographic irregularities) further con- tributes to the complexity of earthquake ground motion and to the difficulty to provide reliable predictions without making use of large-size 3D numerical simulations. In this article, we present a parametric study of the seismic response of the Grenoble Valley, France (due to an Mw 6 seismic source at some 10 km epicentral distance from the urban area) that was carried out in the framework of an international benchmark for earthquake ground-motion prediction. The spectral element code GeoELSE for seismic-wave propagation analyses in 3D heterogeneous media, in the linear and non- linear range, was used for this purpose; full advantage was taken of its implementation on parallel computer architectures. After introducing GeoELSE and its parallel per- formance, and after introducing some of its validation benchmarks, the spatial varia- bility of the seismic response of the Grenoble Valley is quantitatively investigated taking into account two effects: (i) the hypocenter location and (ii) the nonlinear soil behavior through a nonlinear viscoelastic soil model. Finally, numerical results are compared with available data and attenuation relationships of peak values of ground motion in the near-fault region. Based on the results of this work, the unfavorable interaction between fault rupture, radiation mechanism, and complex geological con- ditions may give rise to large values of peak ground velocity (exceeding 1 m=sec) even in low-to-moderate seismicity areas; it may therefore considerably increase the level of seismic risk, especially in highly populated and industrially active regions, such as the Alpine valleys.

Seismic Hazard Map for Cuba and Adjacent Areas Using the Spatially Smoothed Seismicity Approach

The seismic hazard assessment for Cuba and the surrounding regions has been performed according to the spatially smoothed seismicity approach. The major motivation for using this methodology is to avoid drawing seismic sources in a region where the seismogenic structures are not well known. We have defined two different seismicity models and three zonation models, based on the evidence of seismotectonic heterogeneity of the broader Cuban region, and two attenuation models for rock and three for soil. The resulting hazard estimates have been treated with a logic tree approach. The highest hazard was obtained around Santiago de Cuba with a PGA larger than 0.28 g on rock and 0.40 g on soil, for a 475-year return period. When the epistemic uncertainties of the different models considered are taken into account, these ground motion values exceed 0.40 g on rock and 0.60 g on soil. A comparison between these new hazard estimates and those computed according to the standard approach of the seismotectonic probabilism indicates the areas where the spatial distribution of the seismicity supports the seismogenic zonation and the areas where a disagreement exists.