Variability Of Ground Motion Research Articles

2D Geotechnical site-response analysis including soil heterogeneity and wave scattering

This study describes an approach for modeling wave scattering and the spatial variability of ground motion in geotechnical site-response analysis by modeling soil heterogeneity through 2D correlated random fields. Importantly, the required site-specific inputs to apply the proposed approach in a practical setting are the same as those associated with conventional 1D site-response analysis. The results, which are affected by wave scattering attenuation, are compared to those from conventional laterally homogeneous 1D site-response analyses and 1D analyses with randomized velocity profiles extracted from heterogeneous 2D velocity model realizations. A sensitivity study, involving 5400 2D model realizations, investigates the influence of random field input parameters on wave scattering and site response. The computed ground surface acceleration waveforms and transfer functions show that this method is capable of scattering seismic waves. Multiple ground-motion intensity measures are analyzed to quantify this influence and distinguish between the effects of 1D vertical heterogeneities and averaging across many nodes and realizations, from the effects of wave scattering and 2D ground-motion phenomena. The redistribution of ground-motion energy across wider frequency bands and scattering attenuation of high-frequency waves in the 2D analyses resemble features observed in empirical transfer functions computed in other studies. While analyses with 1D randomized velocity profiles are able to replicate median results from 2D analyses for some low-frequency intensity measures (e.g. transfer functions at [Formula: see text] Hz, and spectral acceleration at the fundamental period), medians and standard deviations of high-frequency intensity measures (e.g. transfer function at [Formula: see text] Hz, [Formula: see text], and Arias intensity), which are influenced by wave scattering, are not appropriately captured. Given the equivalent input information requirements as conventional 1D analysis, and the availability of large computational resources, we advocate that the proposed 2D (and eventually 3D) approach is a fruitful path forward to improve the modeling of site-response physics and realize improved predictive capabilities.

Seismic analysis of high-speed railway irregular bridge\u2013track system considering V-shaped canyon effect

To explore the effect of canyon topography on the seismic response of railway irregular bridge–track system that crosses a V-shaped canyon, seismic ground motions of the horizontal site and V-shaped canyon site were simulated through theoretical analysis with 12 earthquake records selected from the Pacific Earthquake Engineering Research Center (PEER) Strong Ground Motion Database matching the site condition of the bridge. Nonlinear seismic response analyses of an existing 11-span irregular simply supported railway bridge–track system were performed under the simulated spatially varying ground motions. The effects of the V-shaped canyon topography on the peak ground acceleration at bridge foundations and seismic responses of the bridge–track system were analyzed. Comparisons between the results of horizontal and V-shaped canyon sites show that the top relative displacement between adjacent piers at the junction of the incident side and the back side of the V-shaped site is almost two times that of the horizontal site, which also determines the seismic response of the fastener. The maximum displacement of the fastener occurs in the V-shaped canyon site and is 1.4 times larger than that in the horizontal site. Neglecting the effect of V-shaped canyon leads to the inappropriate assessment of the maximum seismic response of the irregular high-speed railway bridge–track system. Moreover, engineers should focus on the girder end to the left or right of the two fasteners within the distance of track seismic damage.

Predictive performance of current ground motion models for recorded strong motions in 2020 Samos Earthquake

The 2020 M7.0 Samos earthquake had occurred on the north of Samos Island; however, structural damage was observed in İzmir-Bayraklı, which is located approximately 65 km away from the epicenter. Strong ground motions recorded in İzmir Bay showed unique site amplifications, mostly due to the interaction between the basin and deep alluvial deposit response. The objective of this study is to evaluate the predictive performance of current ground motion models (GMMs) for estimating the recorded strong motions, especially the recordings over or near the Bayraklı-Bornova basin. 66 strong motion stations from Turkey with rupture distance (RRUP) < 200 km are used in the residual analysis, considering the ambiguities in the magnitude and depth to the top of the rupture estimations. Event terms of the earthquake for tested GMMs are found to be small and lie within the expected scatter, except for T = 0.5–1.5 s spectral accelerations. Event-specific distance attenuation for RRUP<100 km is consistent with the median predictions of current GMMs; however, the distance scaling for 100 km<RRUP<200 km are significantly different at high frequencies, indicating faster attenuation for Southwestern Anatolia. Relatively long period (0.5–1.5 s) spectral energy is present in both soft sites on the Bayraklı-Bornova basin and rock/stiff-soil sites on the basin edge and these stations contribute significantly to the positive event terms at T = 0.5–1.5 s. For sites within the basin or close to the basin edge, factors such as the direction of the rupture front, basin width and depth, and the seismic structure of the basin contribute to the ground motion variability.

A regionally adaptable ground-motion model for fourier amplitude spectra of shallow crustal earthquakes in Europe

Typical seismic ground-motion models predict the response spectral ordinates (GMM-SA), which are the damped responses of a suite of single-degree-of-freedom oscillators. Response spectra represent the response of an idealized structure to input ground-motion, but not the physics of the actual ground-motion. To complement the regionally adaptable GMM-SA of Kotha et al. (2020), we introduce a model capable of predicting Fourier amplitudes (GMM-FA); developed from the Engineering Strong Motion (ESM) dataset for pan-Europe. This GMM-FA reveals the very high variability of high frequency ground-motions, which are completely masked in a GMM-SA. By maintaining the development strategies of GMM-FA identical to that of the GMM-SA, we are able to evaluate the physical meaning of the spatial variability of anelastic attenuation and source characteristics. We find that a fully data-driven geospatial index, Activity Index (AIx), correlates well with the spatial variability of these physical effects. AIx is a fuzzy combination of seismicity and crustal parameters, and can be used to adapt the attenuation and source non-ergodicity of the GMM-FA to regions and tectonic localities sparsely sampled in ESM. While AIx, and a few other parameters we touch upon, may help understand the spatial variability of high frequency attenuation and source effects, the high frequency site-response variability—dominating the overall aleatory variance—is yet unresolvable. With the rapid increase in quantity and quality of ground-motion datasets, our work demonstrates the need to upgrade regionalization techniques, site-characterisation, and a paradigm shift towards Fourier ground-motion models to complement the traditional response spectra prediction models.

Scenario-based earthquake risk assessment for central-southern Malawi: The case of the Bilila-Mtakataka Fault

A regional seismic risk analysis for central-southern Malawi is conducted by focusing on the Bilila-Mtakataka Fault within the East African Rift System and by incorporating local information on population exposure and building vulnerability. The scenario-based earthquake risk assessments account for uncertainty in geometry, position, and rupture pattern of the Bilila-Mtakataka Fault as well as ground-motion variability and are based on the latest 2018 national census data. In addition, Malawi-specific seismic fragility functions, which were developed based on building surveys and laboratory tests of local construction materials, are implemented to reflect realistic seismic vulnerability of unreinforced masonry constructions in Malawi. The results from the earthquake risk assessments and sensitivity analyses based on alternative data and models highlight the importance of incorporating local information on seismic hazard characterisation, population data, and seismic vulnerability of buildings, in comparison with global data and models. For the considered case study region, individual effects of the above-mentioned model components tend to result in 20–30 % or greater differences in regional seismic risk metrics, such as the affected population experiencing a certain ground shaking intensity level or the number of collapsed housing units. The improved seismic hazard-risk assessments are more effective in informing future seismic risk mitigation policies and actions.

The computation of strong ground motion for the near fault of the Kanding earthquake

In this study, the earthquake fault of the Kanding earthquake that occurred on November 22, 2014 is set as the target fault. Based on the Kanding earthquake fault geometry parameters and the technology of broadband simulation of ground motion, the near-fault strong ground motion of the Kangding earthquake is synthesized. Compared with the inversion achievements on the slip distribution of the Kangding earthquake fault, the slip distribution of the Kangding earthquake fault is first decided and selected. Using the representation theory of ground motion, the near-fault strong ground motion of the Kangding earthquake is then calculated. To validate the simulation method, the recordings at the strong motion stations and the simulation results on the location of the strong-motion stations are compared. Lastly, the spatial contour of the peak ground acceleration (PGA) and the peak ground velocity (PGV) in a region less than 100 km away from the epicenter of the Kangding earthquake are computed and analyzed. The results show some correlations between the amplitude of PGA, PGV, the spectral shapes of acceleration of the ground motion, and the slip distributions of the earthquake faults. For the ground motion stations with epicenter distances less than 50 km, the calculations of the ground motion velocity spectra shape is similar to those of the recordings except for the high-frequency components. For the ground motion stations with epicenter distances longer than 50 km, the calculations of the PGV amplitude at the strong ground motion station location are similar to the ground motion recordings. In general, the theoretical computation can ascertain the strong ground motion variation of the Kanding earthquake. Additionally, the correlations between the slip distributions of the Kanding fault and the ground PGA are analyzed, and the reasons why only minor damages were caused by the Kangding earthquake on the Kanding city are explained.

Phase-Structure in Conditional Simulation of Spatially Varying Ground Motion and Possible Influence on Structural Demand

Recorded ground motion is nonstationary in both intensity and frequency contents. Two methodologies were reported by the authors elsewhere for generating spatially varying ground motion (SVGM), namely, (i) auto-spectral density (ASD)-based framework, and (ii) evolutionary power-spectral density (EPSD)-based framework. While the former framework imparts nonstationarity through a uniform modulation (that accounts for nonstationarity only in intensities), the latter framework accounts for nonstationarity in both intensity and frequency contents. Reported EPSD-based framework was modeled through a decay function and a random component and was investigated only in the context of horizontal ground motion. Reported EPSD-based framework made two strong assumptions that need further investigation: (i) spatial variation of the random component was assumed to be frequency independent; and (ii) phase-structure of the ground excitation simulated around the reference station (with seed motion) was assumed to be same as that of the seed motion. This paper investigates the possible impact of these two assumptions on the simulated SVGM through appropriately revising the framework and introducing the phase-structure accordingly. Possible effects of the phase-structure on structural demand are investigated through an idealized long-span bridge. Revised EPSD-based framework is next assessed against the vertical recordings of SMART1 array along with the auto-spectral density (ASD) framework. Though spectral representation is nearly identical in both the frameworks, the acceleration time series simulated using the revised EPSD-based framework matches the recorded data better when compared with the ASD-based framework. Possible effect of spatially varying vertical ground motion on the seismic design is investigated through the same idealized bridge model. Significant increase in the demand of axial force in piers and mid-span moment in the deck are observed. Although these inferences are contingent on the idealized example considered for illustration, the spatially varying vertical ground motion is expected to contribute significantly to the seismic design of long-span bridges.

Simulation of Spatially Correlated Multipoint Ground Motions in a Saturated Alluvial Valley

Based on Biot’s theory, the boundary element method, and spectral representation method, an effective simulation method for multiple-station spatially correlated ground motions on both bedrock and surface is developed, incorporating the spectral density function, coherence function, and site transfer function that consider both the wave scattering effect and the medium saturation. The accuracy and feasibility of the present method are validated by a typical numerical example. Our results indicate that the local site conditions and the saturation property of the medium significantly affect the multipoint spatially correlated earthquake ground motions, especially in the long-period range. It is necessary to use spatially varying ground motions with the rational consideration of local site effects and medium saturation as input during the seismic analysis of large-span structures.

Seismic reliability evaluation of bridges under spatially varying ground motions using a four-parameter distribution

Large-span bridges are often subjected to spatially varying ground motion (SVGM) excitations. Meanwhile, bridge structures and ground motion excitations generally present a large degree of inherent uncertainties. Carrying out the seismic reliability analysis of bridges under SVGMs can provide a direct assessment for the safety probability of bridges during an earthquake event and is of paramount importance for the probabilistic performance analysis of bridges. To this end, this study proposes a new method for the seismic reliability evaluation of random nonlinear bridges subjected to SVGMs, which tackles the drawback of the current seismic reliability analysis method that can only be applied for uniform seismic excitations. To implement, the space correlated ground motions are first generated via a random function-based spectral representation method, based on which the uncertainty of ground motions is characterized by three elementary random variables. The first-passage probability of bridges under SVSGMs is then derived by the equivalent extreme value distribution (EVD), which is approximated by a flexible four-parameter distribution, i.e., shifted generalized lognormal distribution (SGLD). To estimate the parameters in the SGLD model with high efficiency and accuracy, a novel fractional moment-based method is proposed. A numerical example of a two-span continuous box-girder bridge subjected to space varying site conditions is investigated to verify and exemplify the proposed method. The results demonstrate that: 1) The proposed method is efficient and accurate for the seismic reliability of bridge under SVGM, even at low failure probability levels, and the computational burden of the proposed method is less than 2% of that of MCS; 2) The spatial variability is significantly influential on the seismic reliability of the bridge, ignoring the spatial variability of seismic excitation will significantly underestimate the failure probability of the bridge.

Reduction of Bias and Uncertainty in Regional Seismic Site Amplification Factors for Seismic Hazard and Risk Analysis

Site amplification factors in National Building Codes are typically specified as a function of the average shear wave velocity over the first 30 m (Vs30) or site class (A, B, C, D and E) for defined ranges of Vs30 and/or ranges of depth to bedrock. However, a single set of amplification factors may not be representative of site conditions across the country, introducing a bias in seismic hazard and seismic risk analyses. This is exemplified by significant differences in geological settings between East and West coast locations in North America. Western sites are typically characterized by lower impedance contrasts between recent surface deposits and bedrock in comparison to Eastern sites. In North America, site amplification factors have been derived from a combination of field data on ground motions recorded during West Coast earthquakes and numerical models of site responses that are meant to be representative of a wide variety of soil profiles and ground motions. The bias on amplifications and their impact on seismic hazards is investigated for the Montreal area, which ranks second for seismic risks in Canada in terms of population and hazard (PGA of 0.25 g for a 2475 years return period). Representative soil profiles at several locations in Montreal are analyzed with 1-D site response models for natural and synthetic ground motions scaled between 0.1 to 0.5 g. Since bedrock depths are typically shallow (&lt;30 m) across the island, bedrock shear wave velocities have a significant influence on the impedance contrast and amplifications. Bedrock shear wave velocity is usually very variable due to the differences in rock formations, level of weathering and fracturing. The level of this uncertainty is shown to be greatly decreased when rock quality designation (RQD) data, common information when bore hole data are logged, is available since it is highly correlated with both shear and compression wave velocities. The results are used to derive region-specific site amplification factors as a function of both Vs30 and site fundamental frequency and compared to those of the National Building Code of Canada (2015). The results of the study indicate that there are large uncertainties associated with these parameters due to variability in soil profiles, soil properties and input seismic ground motions. Average and confidence intervals for the mean and for predictions of amplification factors are calculated for each site class to quantify this uncertainty. Amplifications normalized relative to class C are obtained by accounting for the correlation between site class amplifications for given ground motions. Non-linearity in the analysis of equivalent linear 1-D site response is taken into account by introducing the non-linear G/Gmax and damping ratios curves. In this method, it is assumed that the shear strain compatible shear modulus and damping ratio values remains constant throughout the duration of the seismic excitation. This assumption is not fully applicable to a case when loose saturated soil profile undergo heavy shaking (PGA &gt; 0.3 g). In this study, all simulations with input motion PGA &gt;0.3 g have been performed by using the EL method instead of the NL method considering that cohesive soils (clay and silt) at Montreal sites are stiff and cohesionless soils (sand and gravel) are considerably dense. In addition, the field and laboratory data required to perform NL analyses are not currently available and may be investigated in future works.

Construction of the spatially varying ground motion field of a bedrock-overburden layer site and its influence on the seismic response of earth-rock dams

Construction of the spatially varying ground motion field of a bedrock-overburden layer site and its influence on the seismic response of earth-rock dams

Frequency-dependent site factors for the Icelandic strong-motion array from a Bayesian hierarchical model of the spatial distribution of spectral accelerations

The earthquake ground motions of over 1700 earthquakes recorded on a small-aperture strong-motion array in south Iceland (ICEARRAY I) that is situated on a relatively uniform site condition characterized as rock, exhibit a statistically significant spatial variation of ground-motion amplitudes across the array. Both earthquake and microseismic horizontal-to-vertical spectral ratios (HVSR) have been shown to exhibit distinct and in some cases, bimodal peaks in amplification, indicating site resonance at periods of 0.1–0.3 s, a phenomenon that has been attributed to a surface layer of lava rock lying above a sedimentary layer, a structure that is then repeated with depth under the array. In this study, we implement a Bayesian hierarchical model (BHM) of the seismic ground motions that partitions the model residuals into earthquake event term, station term, and event–station term. We analyzed and compared peak ground acceleration (PGA) with the 5% damped pseudo-acceleration response spectrum (PSA) at oscillator periods of T = 0.05–1.0 s. The results show that the event terms, dominate the total variability of the ground-motion amplitudes over the array. However, the station terms are shown to increase in the period range of 0.1–0.3 s on most stations and to different extents, leading to an increase in the overall variability of ground motions at those periods, captured by a larger inter-station standard deviation. As the station terms are a measure of how much the ground motions at those stations deviate from the array average, they act as proxies for localized site effects and amplification factors. These results, improve our understanding of the key factors that affect the variation of seismic ground motions across the relatively small area of ICEARRAY I. This approach can help to improve the accuracy of earthquake hazard assessments on local scales, which in turn could contribute to more refined seismic risk assessments and engineering decision-making.

ANALYSIS OF THE OBSERVED LAGGED COHERENCY OF CHLEF CITY (ALGERIA) DEPENDING ON Vs30

The assumption that the seismic ground motion imposed on the supports of extended structures is uniform is no longer valid. Especially those which are generally constructed at sites with different soil characteristics. Among the causes which contribute to the non-uniformity of the seismic ground motion is the site effect. However, several coherency models which estimate this spatial variability of seismic ground motion do not consider this effect. In addition, these models have concentrated only on the horizontal direction while neglecting the vertical direction. The work at hand is an analysis of the observed lagged coherency by taking into account the site effect, which is often estimated by the average shear wave velocity over the upper 30 m of depth . This analysis tackles the three directions of the seismic ground motion. In this context, this study relies on fifteen seismic events recorded by nine seismological stations located in different sites in Chlef city from December 2014 to October 2015. As expected, the observed lagged coherency decreases with the increase of the separation distance between two recording stations. The results prove that affects the observed lagged coherency. Thus, the tendency of the observed lagged coherency decreases with the decrease of defined for one or both recording stations. Therefore, the observed lagged coherency is influenced significantly by the site effect. Comparing three components of the observed lagged coherency indicates that the Vertical component is more significant than those of the East-West and North-South components.

Influence of strong spatially varying near fault ground motion on steel box arch bridge

In violent earthquakes, ground motion is considered to change dramatically in the process of spatial propagation. Strong spatially varying exists in ground motion near fault area, and it can cause the large-span and large stiffness structure to be damaged. In this paper, a typical long-span steel box arch bridge is selected as an engineering case. In order to simulate the spatial variation of near fault ground motion accurately, the records that sampled in former earthquake are used as ground motion input. The shaking table experiment and finite element analysis are used as analysis means. Through the analysis of the internal force and displacement response of the key position of the arch rib, it is found that the spatially varying in the near fault ground motion can bring severe seismic response. If the spatially varying is ignored, the damage of the bridge will be seriously underestimated.

Nonstationary spatial correlation in New Zealand strong ground‐motion data

AbstractThis paper presents new techniques for quantifying nonstationary spatial variations in strong ground motion, using data from recent well‐recorded earthquakes in New Zealand. The data set is unique in that many recording stations are relatively densely spaced, and multiple strong ground motions have been recorded at the same stations. This allows calculation of site‐specific and region‐specific correlations in ground‐motion amplitude for Wellington and Christchurch, and the results are compared to a model assuming stationary correlations at all locations. Strong nonstationarity in spatial correlation is observed in the Wellington and Christchurch regions. Heterogeneous geologic conditions appear to be associated with the nonstationary spatial correlation. Several factors influencing nonstationary spatial correlation were studied: (a) site‐specific residuals indicate deviation of correlation from a stationary model; (b) most earthquakes have no systematic effect on spatial correlations and there is no indication of a trend in correlations with magnitude; (c) rupture complexity is related to the variation of spatial correlations in ground‐motion residuals; (d) variation of site‐specific correlations cannot be resolved by using terms in Ground‐Motion Models. The nonstationary correlation approach provides an opportunity to incorporate the site‐specific effects in future correlation models.

Earthquake Early Warning System for Structural Drift Prediction Using Machine Learning and Linear Regressors

In this work, we explored the feasibility of predicting the structural drift from the first seconds of P-wave signals for On-site Earthquake Early Warning (EEW) applications. To this purpose, we investigated the performance of both linear least square regression (LSR) and four non-linear machine learning (ML) models: Random Forest, Gradient Boosting, Support Vector Machines and K-Nearest Neighbors. Furthermore, we also explore the applicability of the models calibrated for a region to another one. The LSR and ML models are calibrated and validated using a dataset of ∼6,000 waveforms recorded within 34 Japanese structures with three different type of construction (steel, reinforced concrete, and steel-reinforced concrete), and a smaller one of data recorded at US buildings (69 buildings, 240 waveforms). As EEW information, we considered three P-wave parameters (the peak displacement, Pd, the integral of squared velocity, IV2, and displacement, ID2) using three time-windows (i.e., 1, 2, and 3 s), for a total of nine features to predict the drift ratio as structural response. The Japanese dataset is used to calibrate the LSR and ML models and to study their capability to predict the structural drift. We explored different subsets of the Japanese dataset (i.e., one building, one single type of construction, the entire dataset. We found that the variability of both ground motion and buildings response can affect the drift predictions robustness. In particular, the predictions accuracy worsens with the complexity of the dataset in terms of building and event variability. Our results show that ML techniques perform always better than LSR models, likely due to the complex connections between features and the natural non-linearity of the data. Furthermore, we show that by implementing a residuals analysis, the main sources of drift variability can be identified. Finally, the models trained on the Japanese dataset are applied the US dataset. In our application, we found that the exporting EEW models worsen the prediction variability, but also that by including correction terms as function of the magnitude can strongly mitigate such problem. In other words, our results show that the drift for US buildings can be predicted by minor tweaks to models.

Future magnitude 7.5 earthquake offshore Martinique: spotlight on the main source features controlling ground motion prediction

SUMMARY The eastern offshore of Martinique is one of the active areas of the Lesser Antilles Subduction Zone (LASZ). Although its seismicity is moderate compared to other subduction zones, LASZ is capable of generating a M 7+ interplate earthquake and recent studies and historical events, such as the M 8 1839 and M 7–7.5 1946 earthquakes, confirm this possibility. Given the high risk that Martinique can face in case of unpreparedness for such a M 7+ earthquake, and the lack of a regional seismic hazard study, we investigated through numerical modelling how ground motion can vary for a hypothetical Mw 7.5 interplate earthquake. Our main objective is to highlight the major factors related to earthquake source that can cause the highest variation in ground motion at four broad-band seismic stations across Martinique. For this purpose, we generated 320 rupture scenarios through a fractal kinematic source model, by varying rupture directivity, source dimension, slip distribution. We computed the broad-band ground motion (0.5–25 Hz) by convolution of source–time functions with empirical Green’s functions (EGFs), that we selected from the analysis of moderate events (M 4–4.5) recorded in the area of interest since 2016 by the West Indies network. We found that the fault geometry and the spatial extension of the largest slip patch are the most influential factors on ground motion. The significance of the variation of the predicted ground motion with respect to ground motion prediction equations (GMPEs) depends on the evaluated frequency of ground motion and on the station. Moreover, we concluded that the EGF selection can be another significant factor controlling the modelled ground motion depending on station. Our results provide a new insight for the seismic source impact on ground motion across Martinique and can guide future blind seismic hazard assessment studies in different regions.

Investigation on low-cost friction-based isolation systems for masonry building structures: Experimental and numerical studies

Masonry structures do not exhibit adequate seismic performance but they are still the most commonly constructed buildings across the globe. To enhance their seismic capacity and to protect them from the damaging effects of earthquakes in seismic active regions, an innovative low-cost friction-based seismic isolation system is developed in this study. The proposed isolation system, installed between the foundation and superstructure is made up of a 50 mm thick isolation layer material having low lateral stiffness, which is sandwiched between two 4 mm thick Teflon sheets and is further reinforced by vertical rebars. To establish the mechanical properties of the isolation system, experimental trials were performed using weak mortar, asphalt cushion, steel balls enclosed in mortar, coarse sand mortar, and rubberized mortar as an isolation layer material, and the proposed isolation system is installed between two hollow concrete blocks for testing purpose. Cyclic load tests were performed on the specimens and force-deformation curves were achieved. Two numerical models, one with a fixed base and another with the proposed isolator were developed using finite element analysis approach and analyzed against five different ground motions input. The isolation layer material used in the numerical model was selected based on friction coefficient and cyclic loading tests. In case of low seismic excitation, the isolation system does not activate to ensure structural integrity, however, when the lateral forces exceed the permissible limit then the isolation system permit deformation in both horizontal directions to dissipate seismic energy through friction while the vertical reinforcement ensure the re-centering mechanism of the structure. It is observed that the proposed isolation system considerably reduces the transmission of earthquake energy to the superstructure over a variety of ground motions. Depending upon the type of ground motion, an overall 45% − 56% reduction was observed in the absolute acceleration response of the top roof level of the isolated structure.

Probabilistic assessment of seismic-induced slope displacements: an application in Italy

Earthquake-induced slope instability is one of the most important hazards related to ground shaking, causing damages to the environment and, often, casualties. Therefore, it is important to assess the seismic performance of slopes, especially in the near fault regions, evaluating the permanent displacements induced by seismic loading. This paper applies a probabilistic approach to evaluate the seismic performance of slopes using an updated database of ground motions recorded during the earthquakes occurred in Italy. The main advantage of this approach is that of accounting for the aleatory variability of both ground motions and prediction of seismic-induced displacements of slopes. The results are presented in terms of hazard curves, showing the annual rate of exceedance of permanent slope displacement evaluated using ground motion data provided by a standard probabilistic hazard analysis and a series of semi-empirical relationships linking the permanent displacements of slopes to one or more ground motion parameters. The procedure has been implemented on a regional scale to produce seismic landslide hazard maps for the Irpinia district, in Southern Italy, characterised by a severe seismic hazard. Seismic landslide hazard maps represent a useful tool for practitioners and government agencies for a regional planning to identify and monitor zones that are potentially susceptible to earthquake-induced slope instability, thus requiring further detailed, site-specific studies.

Application of generalized Pareto distribution for modeling aleatory variability of ground motion

The lognormal distribution is commonly used to characterize the aleatory variability of ground-motion prediction equations (GMPEs) in probabilistic seismic hazard analysis (PSHA). However, this approach often leads to results without actual physical meaning at low exceedance probabilities. In this paper, we discuss how to calculate PSHA with a low exceedance probability. Peak ground acceleration records from the NGA-West2 database and 15,493 residuals calculated by Campbell-Bozorgnia using the NGA-West2 GMPE were applied to analyze the tail shape of the residuals. The results showed that the generalized Pareto distribution (GPD) captured the characteristics of residuals in the tail better than the lognormal distribution. Further study showed that the shapes of the tails of the distributions of residuals with different magnitudes varied significantly due to the heteroscedasticity of the magnitude; the distribution of residuals with larger magnitudes had a smaller upper limit on the right side. Moreover, the residuals of the three magnitude ranges given in this study were more consistent with the GPD of different parameters at the tail than the lognormal distribution and the GPD fitted by all the residuals, leading to a bounded PSHA hazard curve. Therefore, the lognormal distribution is more representative up to a determined threshold, and the GPD fitted to the residuals of three ranges of magnitude better characterizes the tail for PSHA calculation.