Specific Barrier Model Research Articles

Ground motion simulations of the 1887 Pinal de Amoles (MW = 5.53) and the 1989 Landa de Matamoros (MW = 4.94) earthquakes, Querétaro, Mexico

Ground motions characteristics of the 1887 Pinal de Amoles (MW = 5.53) and the 1989 Landa de Matamoros (MW = 4.94) Querétaro earthquakes were studied. For this purpose, the specific barrier model (SBM) was implemented in the context of the stochastic ground motion representation of earthquakes. The SBM was calibrated by modeling the peak ground acceleration (PGA) and the Fourier acceleration spectra (FAS) of the 11 May 2016 (MW = 4.80) Guadalajara earthquake. The calibration results showed that the SBM and selected source and path parameters were able to reproduce synthetic PGA and spectra in good agreement with observed waveforms; in particular, a stress drop of 160 bars fits the results better. Several rupture scenarios for the 1887 and 1989 events were performed by obtaining synthetic seismograms considering different values of stress drop (10, 30, 50, 100, 150, 200, 300, and 500 bars). For a typical stress-drop value of 100 bars, the PGA at distances of 10 and 200 km are in the following intervals: 2.57–295 cm/s2 and 1.72–186 cm/s2 for the Pinal de Amoles and Landa de Matamoros earthquakes, respectively. The results obtained in this study contribute toward a better understanding of strong ground motions in the region.

A modified specific barrier model based on new time functions and approach for cracks location on the fault plane: application to the 2008 Iwate–Miyagi earthquake

SUMMARYSpecific barrier method (SBM) is a method used for ground motion generation from a finite fault surface. It is based on a regular distribution of rupturing circular subevents located on the fault plane and random arrival times of the waves generated by those cracks. This approach does not consider the whole rupture kinematics, that is the rupture propagation from the hypocentre to the subevents, and leaves parts of the fault unbroken (barriers). In this paper, we propose a modified version of the SBM for generation of synthetic ground motions from a fault surface. In this version, we modify the probability density function (PDF) for the arrival time of the waves coming from different parts of the fault in order to better account for the fault kinematics and the distance between fault point and receiver. In this way, we can simulate the middle part of the acceleration spectrum (i.e. between 0.1 and 7 Hz) with more accuracy. Moreover, a new arrangement for locating cracks throughout the fault plane is proposed to add flexibility to the model and enable it to make the part of the spectrum with frequency larger than 7 Hz more like what happens in nature. In such an arrangement, called geometry packing in this paper, the size of circles varies within a chosen specific allowable range, while the circles cover all over the fault plane without any overlaps. To validate the proposed modified SBM technique, the synthetic Fourier spectra are compared with recordings of the 2008 Mw6.9 Iwate–Miyagi (Japan) earthquake. Finally, we present some parametric studies to show how different features of the proposed PDFs affect the results from the SBM approach.

Extended Slip-Weakening Model and Inference of Rupture Velocity

The slip-weakening model developed by Ohnaka and Yamashita is extended over the breakdown zone by equating the scaling relationships for the breakdown zone and the whole rupture area. For the extension, the study uses the relationship between rupture velocity and radiation efficiency, which was derived in the theory of linear elastic fracture mechanics, and the definition of fmax given in the specific barrier model proposed by Papageorgiou and Aki. The results clearly show that the extended scaling relationship is governed by the ratio of rupture velocity to S wave velocity, and the velocity ratio can be determined by the ratio of characteristic frequencies of a Fourier amplitude spectrum, which are corner frequency, fc, and source-controlled cut-off frequency, fmax, or vice versa. The derived relationship is tested by using the characteristic frequencies extracted from previous studies of more than 130 shallow crustal events (focal depth less than 25 km, MW 3.0~7.5) that occurred in Japan. Under the assumption of a dynamic similarity, the rupture velocity estimated from fmax/fc and the modified integral timescale give quite similar scale-dependence of the rupture area to that given by Kanamori and Anderson. Also, the results for large earthquakes show good agreement to the values from a kinematic inversion in previous studies. The test results also indicate the unavailability of the spectral self-similarity proposed by Aki because of the scale-dependent rupture velocity and the rupture velocity-dependent fmax/fc; however, the results do support the local similarity asserted by Ohnaka. It is also remarkable that the relationship between the rupture velocity and fmax/fc is quite similar to Kolmogorov’s hypothesis on a similarity in the theory of isotropic turbulence.

Bayesian inference of a physical seismological model for earthquake strong-motion in south Iceland

Earthquake ground motion prediction in Iceland where strong-motion data is scarce poses a challenge as empirical ground motion models (GMM) developed from data in other regions systematically fail to capture the consistently large near-fault peak amplitudes and their rapid attenuation with distance from the earthquake source. Therefore, regional GMMs must be constructed but due to the limited data, and none above Mw6.5, earthquake source scaling is unconstrained at larger magnitudes. Instead, physics-based GMMs should be applied based on realistic earthquake source modeling. For that purpose, a seismological model constructed around the specific barrier model (SBM) has been calibrated in the context of the stochastic method using random vibration theory, to earthquake high-frequency strong-motions in the South Iceland Seismic Zone. The SBM is used as it provides a physically consistent and efficient description of the heterogeneous faulting processes that are responsible for the generation of high-frequency waves. On the basis of the concise point-source representation of radiated spectra from N subevents of the SBM the pseudo-spectral accelerations were modeled and compared with that of data in the spectral domain. Backwards model selection was then carried out using Bayesian inference with Monte Carlo simulations and Markov Chains. The number of parameters in the model inference was reduced to obtain stable Markov chains and posterior probability density functions for each parameter, eliminating parametric cross-correlations to the extent possible. The seismological model has been shown to be unbiased with respect to strong-motions in the SISZ, with a total standard deviation of 0.216 (common logarithm), with only a minor contribution from inter-event variability, suggesting a relatively uniform character of SISZ earthquake strong-motions. We showcase the application of the SBM extended into a finite-fault and model the three Mw6.3-6.5 earthquakes in the dataset, allowing subevents of varying sizes to populate the fault plane and provide a more realistic earthquake source and acceleration ground motion time history modeling. The time domain results are shown to capture the essential characteristics of the ground motions of the three largest earthquakes in the dataset. We present therefore the SBM as a physically consistent source model of SISZ earthquakes for the generation of synthetic strong-motion time histories or peak parameters, with potential applications in scenario simulations and probabilistic or deterministic seismic hazard assessment.

Seismic fragility analysis of LNG sub-plant accounting for component dynamic interaction

Earthquakes can cause significant damage to liquefied gas terminals, a critical part of lifeline facilities of energy supply networks, failure of which may lead to loss of hazardous material, explosion, environmental contamination, loss of functionality and disruption of business. To date, seismic risk analysis of such facilities mainly focuses at component level, with the inherent dynamic interaction between the supporting structure and non-structural components not receiving the merited attention. In the present study, the seismic performance of an actual facility comprising of a piping system and a reinforced concrete (RC) supporting structure is analyzed through a finite element model in the nonlinear regime, both as coupled and decoupled case. Plastic strains are used as engineering demand parameters (EDP) to define leakage limit state for pipes. Since the RC pipe rack supporting structure is designed for low seismic loads, shear is recognized as the predominant failure mode. The same components are then analyzed in unison, considering coupling due to dynamic interaction. Fragility functions are estimated for both cases using multiple stripe analysis. A set of strong ground motions artificially generated using the specific barrier model, are employed for developing fragility curves. They are expressed with peak ground acceleration (PGA) as an intensity measure. Statistical estimation of the parameters of fragility functions are based on maximum likelihood method. It is inferred that in the decoupled case, pipes show higher vulnerability at lower PGA, at higher PGA pipe rack can fail suddenly resulting in total failure of the system. Moreover, in coupled case the fragility of the pipes and RC rack changes substantially because of the piping system boundary conditions. Thus, concluding that the risk estimation could be erroneous if dynamic interaction is neglected.

Simulation of strong ground motion from the 1995 Mw 6.5 Kozani-Grevena, Greece, earthquake using a hybrid deterministic-stochastic approach

The 1995 Mw 6.5 Kozani-Grevena earthquake struck an area in northwestern Greece characterized by relatively low seismicity based on historical information and instrumental data. The ground shaking in the near-fault region was recorded by a strong-motion accelerograph in the city of Kozani, at a distance of about 23 km from the epicenter. In this article, broadband ground motions are generated at selected locations and at a dense grid of observation points extending over the causative fault of the 1995 Kozani-Grevena earthquake using a hybrid deterministic-stochastic method. Based on a multi-segment fault model with curved geometry proposed in the literature, the low-frequency components of the synthetic ground motion are simulated using the discrete wavenumber representation method and the generalized transmission and reflection coefficient technique. The high-frequency components of the synthetic ground motion are generated using the stochastic modeling approach and the specific barrier model. The two independently derived ground-motion components are then combined using matched filtering at a crossover frequency of 1.2 Hz to generate broadband ground-motion time histories and response spectra. The simulation results are validated by comparing the synthetic ground motions with the recorded ones in the city of Kozani and with estimates of peak ground-motion quantities inferred from ground-motion prediction equations.

A Site-specific ground-motion simulation model: Application for Vrancea earthquakes

A large number of ground-motion time histories is required for a reliable probabilistic seismic-hazard analysis. However, insufficient ground-motion records has been a major issue in earthquake engineering even in high-seismicity areas. Stochastic and seismological ground-motion models are used to simulate time histories in order to overcome this issue. Many times these models require a large number of records for calibration, are available only for regions with a wealth of data, or fail to characterize well specific sites.The current paper introduces a novel stochastic ground-motion model that allows simulation of realistic non-stationary, non-Gaussian time histories that are statistically consistent with data even at sites with very low numbers of records. This goal is achieved by combining the prior knowledge from a seismological model, calibrated to global data, with the site-specific data within a Bayesian framework. The proposed model uses the specific barrier model as the seismological model and numerical results consistent with records from a nuclear powerplant site in Romania are presented.

Revisiting the 1995 MW 6.4 Aigion, Greece, earthquake: Simulation of broadband strong ground motion and site response analysis

The 1995 MW 6.4 Aigion earthquake is one of the largest and most destructive seismic events that have occurred in Greece over the past few decades. The ground shaking in the near-fault region was recorded by a strong-motion accelerograph in the city of Aigion, at a distance of about 16km from the epicenter. The recorded horizontal ground acceleration exceeded 0.5g, whereas the horizontal components of ground velocity exhibited pulse-like motions of large amplitude. These ground-motion characteristics have been attributed to forward rupture directivity combined with the effects of soil and topography. In this article, broadband synthetic ground motions are generated at selected locations and at a dense grid of observation points extending over the causative fault of the 1995 Aigion earthquake using a hybrid deterministic-stochastic method. The low-frequency components of the synthetic ground motion are simulated using the discrete wavenumber method and the generalized transmission and reflection coefficient technique, whereas the high-frequency components of the synthetic ground motion are generated using the stochastic modeling approach and the specific barrier model. The two independently derived ground-motion components are then combined using matched filtering at a crossover frequency of 2Hz to generate broadband ground-motion time histories and response spectra. The effects of soil and topography on the simulated ground motion in the city of Aigion are also investigated through site response analysis. In addition, the strong motion recorded at Aigion is corrected for crustal anisotropy using the cross-correlation technique, thus further enhancing the alignment of recorded and synthetic ground-motion time histories. Finally, the synthetic ground motions are compared with ground-motion estimates obtained from observed geotechnical damage, USGS ShakeMaps, and ground-motion prediction equations.

Seismic Analysis of Municipal Solid Waste Dumps: Site Specific Case Studies From Delhi, India

Abstract Site specific seismic analysis is necessary for reliable assessment of performance of municipal solid waste (MSW) dump sites/landfills due to the highly heterogeneous nature of waste mass. This paper presented the results of one-dimensional site specific seismic studies performed for two old and tall MSW dump sites in Delhi, India. Unit weight profile and dynamic properties of emplaced MSW at these two sites, evaluated from field and large scale laboratory tests, were utilized in seismic analysis. Synthetically generated strong ground motions using finite source model and specific barrier model, with appropriate seismological parameters for the Delhi region, were used. It is observed that the ground motion amplification potential of MSW for low intensity events in the present study compared well with that reported for Operating Industries Inc. landfill in California, which is instrumented with strong ground motion recording stations. Amplification observed in the present study can be useful for the design of a final cover system during the closure of the dump sites studied herein. In addition, results in terms of the maximum horizontal equivalent acceleration for base-sliding case were in agreement with those reported in the literature, and can be used for preliminary estimates for the design of liner system of new engineered MSW landfills in Delhi.

Effects of tectonic regime and soil conditions on the pulse period of near-fault ground motions

In this article, the effects of site conditions (rock vs. soil) and tectonic regime (interplate vs. intraplate) on the pulse period of near-fault forward-directivity ground motions are investigated through linear regression analyses, and appropriate scaling laws that relate the pulse period to the earthquake magnitude are derived. The analyses of rock and soil sites are performed using interplate records only. The results show that for earthquakes of smaller magnitude, the pulse period is longer at soil sites than at rock sites. As the earthquake magnitude increases, the pulse period values at rock and soil sites converge. This observation is in agreement with findings reported in previous studies. However, as shown in this article, the effect of soil conditions on the pulse period is not statistically significant at the 10% level based on the available near-fault ground motion datasets. Regression analyses for interplate and intraplate records are also performed, including regressions with and without self-similarity. The results show that the pulse periods of interplate records are significantly longer (factor of 2.45, on average) than the pulse periods of intraplate records with similar magnitude. It is demonstrated that this difference should also be reflected in the rise times of the events originating in the two different tectonic regimes. Using the specific barrier model as a “tool” of analysis, it is shown that the significant difference in the pulse periods also implies a significant difference (factor of 4) in the local stress drops for the events of the two tectonic regimes. This latter conclusion is supported by recent reports in the literature of the reanalysis of eastern North American earthquakes, accounting more carefully for attenuation.

Generating Stationary Gaussian Processes Using The Spectral Representation Theorem

Abstract The paper presents the Spectral Representation Theorem of a stationary process and two simulation methods derived from it. In order to test the accuracy of the two simulation methods two numerical applications are employed. First, using a theoretical power spectral density (PSD), two sets of sample functions, corresponding to each method, are generated and a comparison of the obtained numerical results with the analytical PSD is carried out. The second example is more complex and consists in using the stationary zone of the strong motion of the recorded NS acceleration registered at INCERC during the 1977 Vrancea earthquake. The corresponding Fourier Spectrum is calculated. In order to obtain a smoother PSD representation for the real Fourier spectrum, a specific barrier model spectrum (SBM) is fitted to it and the corresponding PSD calculated. This PSD is used to generate two sets of samples. The mean PSD obtained using both methods of simulation is compared with that characterizing the registered acceleration. The paper shows that the generated time series possess all the theoretical probabilistic characteristics discussed below, when the number of terms used in the simulation formulas is large. Three types of estimators are employed in the numerical evaluation of both simulation methods

A Site-Specific Seismological Model for Probabilistic Seismic-Hazard Assessment

Abstract Seismic site characterization requires large numbers of ground‐motion records, and such datasets are rarely available. Seismological models are generally used to enrich the existent sets of earthquake records with artificial ground acceleration time histories. The specific barrier model (SBM) is an earthquake source model that, as an integrating part of a seismological model, produces spectral densities of the ground‐motion process as a function of the moment magnitude m and source‐to‐site distance r . It is calibrated to regional records and, therefore, may only provide partial information on the site seismic characteristics. We propose a statistical update of the seismological model, constructed with the SBM such that it accounts for the site observations. A parametric probabilistic model is sought for the SBM spectral densities, and a Bayesian framework is used to statistically update it to local records. This new, enhanced version of the seismological model is used to simulate any number of ground‐motion samples and perform site‐specific probabilistic seismic‐hazard analyses (PSHAs). A numerical example of the PSHA calculations using the statistically updated seismological model is shown for a site in southern California. Online Material: MATLAB scripts to calculate basis functions, and parameter update.

Finite-Fault Simulation of Broadband Strong Ground Motion from the 2010 Mw 7.0 Haiti Earthquake

Abstract Because of the socioeconomic environment in the small island nation of Haiti, no seismic recording stations were operating in the source region at the time of the 2010 M w 7.0 earthquake. The lack of strong motion instruments has hindered the estimation of the amplitude, duration, and frequency content of the ground shaking caused by the seismic event. In this study, synthetic broadband strong ground motions are generated in the vicinity of the 2010 Haiti earthquake. The low‐frequency components of the synthetic motions are simulated using a slip model compatible with seismological observations, geologic field data, and space geodetic measurements. The computations are carried out using the discrete wavenumber representation method and the generalized transmission and reflection coefficient technique. The high‐frequency ground‐motion components are generated using the stochastic modeling approach and the specific barrier model. The two independently derived ground‐motion components are subsequently combined using matched filtering at a crossover frequency of 1 Hz to generate broadband ground‐motion time histories and response spectra for the city of Port‐au‐Prince and other sites in the vicinity of the earthquake. Finally, the synthetic strong ground motions are compared against peak ground‐motion estimates inferred from the U.S. Geologic Survey ShakeMap of peak ground accelerations, ground‐motion prediction equations, and observed structural damage. The synthetic time histories and response spectra generated in this study should be seen as plausible, but not necessarily unique, ground motions that capture the primary features of the 2010 Haiti earthquake.

Simulation of Ground Motion in the Zagros Region of Iran Using the Specific Barrier Model and the Stochastic Method

Abstract Physically based ground‐motion prediction equations for soil and rock sites in the Zagros region have been developed based on the specific barrier model (SBM) used within the context of the stochastic model. Instead of direct time‐domain simulation, random vibration theory was used to estimate measures of peak motion in terms of the pseudospectral velocity of anelastic harmonic oscillator with 5% viscous damping. To avoid the uncertainties, calibration of the source model uses a database of carefully selected strong motion data without ambiguity about the site condition. Therefore, only rock sites are selected for determining source parameters. Also, to avoid any inconsistencies caused by magnitude conversion formulas, we restricted the dataset only to events with available moment magnitudes. Regression analysis is performed using the random effects model that considers both interevent and intraevent variabilities to effectively deal with the problem of an unequal number of records from different earthquakes. No sign of self‐similarity breakdown is observed between the source radius and its seismic moment. The local and global stress drops derived for the Zagros region (39 and 116 bars, respectively) are more consistent with the values obtained by other authors for an interplate regime than the values for an intraplate region. However, from the viewpoint of source heterogeneity (as the ratio of the stress drops is an indicator of the complexity of the source and heterogeneity of slip on the fault) the Zagros events, which have a stress‐drop ratio of about three are more homogeneous than other interplate events. Stochastic simulations are then implemented to predict peak ground motion and response spectra parameters for rock and soil site conditions. Online Material: Catalog tables of earthquakes and attenuation tables.

Calibration of the Specific Barrier Model to the NGA Dataset

The seismic design of structures sometimes necessitates the use of synthetic strong ground motion time histories (European Committee for Standardization 2003; International Code Council 2000). Toward this end, the stochastic method with a point-source representation of the seismic source is a fast and efficient way to generate synthetic time histories ( e.g. , Boore 2003). While other modeling procedures may be more refined and physically realistic ( e.g. , full finite-fault simulations), they generally require a larger number of input parameters for which calibration relations do not exist (see Douglas and Aochi 2008, and references therein). Even for well-recorded earthquakes, these parameters are difficult to develop calibration relations for because of (1) the observed variability in the results from earthquake source process inversion and its dependence on available data ( e.g. , Custodio et al. 2005) and (2) the overall lack of confidence in even the best estimates of the parameters controlling fault rupture (Monelli and Mai 2008; e.g. , Monelli et al. 2009). The simple seismological models also have advantages over empirical ground motion predictive equations (GMPE) (Abrahamson and Shedlock 1997; Power et al. 2008), although the forms of the source, path, and site functions in the simple seismological models may be somewhat less flexible than empirical GMPEs when trying to fit existing data. Seismological models can provide information on the physical nature of the parameters controlling the strong motion while the GMPEs cannot ( e.g. , Boore 2003; Olafsson et al. 2001; R. Sigbjornsson and Ambraseys 2003). Moreover, despite the increase in strong motion recordings over the last couple of decades, and presumably the corresponding increase in knowledge, there are still considerable differences among the median ground motions estimated using the various GMPEs. These differences are a measure of epistemic uncertainty and have not been …

Variations of the specific barrier model—part I: effect of subevent size distributions

The specific barrier model (SBM), introduced and developed by Papageorgiou and Aki (1983a; 1983b; 1985) and recently re-calibrated by Halldorsson and Papageorgiou (2005) for earthquakes of different tectonic regions, is a particular case of a composite seismic source model according to which the seismic moment is distributed in a deterministic manner on the fault plane on the basis of moment and area constraints. Namely, it assumes that a rectangular fault surface is filled with an aggregate of non-overlapping subevents modeled as circular cracks of equal diameter, the ‘barrier interval’, on which a ‘local stress drop’ takes place. In the present work, we relax the basic assumption regarding subevent size of the SBM. Subevents, still modeled as circular cracks, are allowed to vary in size according to various prescribed probability density functions controlling the frequency of occurrence of subevent sizes. Closed form expressions of the ‘far-field’ spectra of the composite source are derived using an approach proposed by Joyner and Boore (1986). The seismic energy radiated by individual subevents arrives at a site in a time window the duration of which is related to the duration of rupture and the source-site geometry. The effect of the distribution of ‘arrival times’ on the spectral amplitudes of the composite source is investigated in a companion paper, referred to as Part II. The type of subevent size distribution and its allowed size range directly affects the number of subevents required to satisfy the moment constraint. A larger number of subevents leads to increased ‘complexity’ of the earthquake which generally results in relatively higher source acceleration spectral levels at high-frequencies. The level of the plateau of the high-frequency acceleration spectral amplitudes, corresponding to different size-distributions, does not differ significantly from that of the far-field spectrum of the SBM, for a constant local stress drop. Furthermore, the differences observed in the spectral amplitudes of the SBM and its variants are likely to be less than the expected uncertainty associated with local stress drop values determined from strong-motion data. Thus, despite its simplifying assumptions, the SBM appears to provide the most simple, yet effective, description that captures the essential characteristics of a composite seismic source. This is especially advantageous for consistent strong-motion modeling in the ‘near-fault’, as well as in the ‘far-field’ region for earthquake engineering applications.

Variations of the specific barrier model—part II: effect of isochron distributions

The specific barrier model (SBM) is a particular case of a composite earthquake source model where the seismic moment is distributed in a deterministic manner on a rectangular fault plane on the basis of moment and area constraints. It is assumed that the fault surface is composed of an aggregate of subevents of equal diameter, the ‘barrier interval’. Furthermore, the subevents are assumed to rupture randomly and statistically independent of one another as the rupture front sweeps the fault plane. In the formulation of the far-field source spectrum of the SBM the ‘arrival time’ of the seismic radiation emitted by each subevent is specified via a probability density function (PDF). In the SBM the subevents are assumed to be of equal sizes (an assumption relaxed in a companion paper, referred to as Part I) and the PDF of ‘arrival times’ is assumed to be uniform. In this study we investigate the effects of different PDFs of ‘arrival times’ on the far-field source spectrum of the SBM. Different PDFs of ‘arrival times’ affect the source spectra primarily at the intermediate frequency range (between the first and second corner frequencies). Such effects become more pronounced as the earthquake magnitude increases. The far-field spectrum of seismic energy observed/recorded at a site depends on the location of the site relative to the causative fault plane, the location of rupture initiation (hypocenter) and the onset times of the rupturing subevents. All the above factors are effectively taken into account by the ‘isochrons’, which vary with source-site geometry. We investigate the selection of the appropriate PDF of seismic energy arrival times at a given site by computing isochrons for a grid of stations surrounding the earthquake fault, represented by the SBM. We show that only for stations located in a direction normal to the fault plane is the assumption of uniform PDF of ‘arrival times’ valid. At other sites non-uniform PDFs of ‘arrival times’ are observed. We identify and categorize the prevalent types of PDFs by directivity (forward vs. backward vs. neutral) and source-site distance (near-fault vs. far-field), show examples in which we group the stations accordingly. We investigate the effects of the different PDF-groups on the SBM source spectrum. Selection of the appropriate PDF for a given source-site configuration when simulating strong ground motions using the SBM in the context of the stochastic method is expected to yield more self-consistent, and physically realistic simulations.

Simulation of strong ground motion in northern Iran using the specific barrier model

SUMMARY In this study, based upon the calibrated specific barrier model (SBM) against the latest available strong motion data, ground motion prediction equations for soil and rock sites in northern Iran are developed. The SBM may provide the most complete, simple and self-consistent description of the faulting process, which is applicable in both ‘near-fault’ and ‘far-field’ regions. Consequently, the SBM may provide consistent ground motion simulations over the entire necessary frequency range and for all distances of engineering interests. To determine source parameters in this study, we used 163 three-component records of 32 earthquakes with magnitude ranging from MW 4.9 to 7.4 in northern Iran. In the database, records with hypocentral distances less than 200 km are chosen and only earthquakes whose moment-magnitude estimates are available have been used. Furthermore, using the best available information, recording sites are classified into two main geologic categories: rock and soil. Because of the lack of site amplification information in the most regions of the world including Iran, we used the H/V ratio method for estimating the site amplification. Moreover, the Kappa factor that shows diminishing the high-frequency amplitude is determined. In this study, two data sets are considered for determining the source parameters (ΔσG and ΔσL) and the H/V ratio and the Kappa factor. Only S-wave part of signals is used in each analysis. Regression analysis is performed using ‘random effects’ method that considers both interseismic (event-to-event) and coseismic (within-event) variabilities to effectively deal with the problem of weighting observations from different earthquakes. The residuals are controlled against available northern Iranian strong ground motion data to verify that the model predictions are unbiased and that there are no significant residual trends with magnitude and distance. At first, it is assumed that no sign of self-similarity breakdown is observed between the source radius and its seismic moment. After controlling the results, the modified SBM should be used as some deviations have been observed. To verify the robustness of the results, the number of observations is changed by removing various randomly selected data sets from the original database, which results in unchanged results of the model. Stochastic simulations are then implemented to predict peak ground motion and response spectra parameters. The stochastic SBM predictions are in relatively good agreement with other available attenuation relationships proposed for Iran, Europe and Middle East. It has been shown that the proposed SBM of this study provides unbiased ground motion estimates over the entire frequency range of most engineering applications. It provides a reliable and physically realistic, yet computationally efficient, way to model strong ground motions.

An assessment of seismic hazard and risk in the islands of Cephalonia and Ithaca, Greece

The region of the islands of Cephalonia and Ithaca, Western Greece, is characterized by continuous seismic activity and frequent occurrence of large magnitude earthquakes, which have resulted many times in the past in severe structural destruction and large human and economic losses. This work represents an effort to assess seismic hazard and risk in these two islands. Due to the scarcity of seismic data in the region, artificial accelerograms are generated on the basis of the specific barrier model in order to provide estimates of strong ground motion. Peak ground accelerations of the artificial accelerograms are compared with those coming from an empirically derived ground motion prediction model. The response spectra of the artificial accelerograms are compared with the design spectrum of the Greek seismic code and the seismic damage potential of old and new building structures is assessed and found to be high. From the present study it is concluded that there is a need of monitoring continuously the seismic activity in the region. Thus, the establishment of a dense and time continuous strong ground motion recording network is proposed and briefly described.

Special Issue on Earthquake Ground-Motion Selection and Modification for Nonlinear Dynamic Analysis of Structures

Over the past decade, considerable progress has been made in developing tools to predict nonlinear response of structures to ground motions, an important consideration in the design and assessment of earthquake-resistant structures. With increase in computational power, nonlinear response-history analysis (RHA) is becoming a common tool in practice. This rigorous method of analysis requires a suite of records as direct input. These records should be selected and modified appropriately to make them compatible with the site-specific hazard level considered. Most of the procedures to modify ground-motion records fall into one of two categories: spectral matching and amplitude scaling. This special volume contains 17 technical papers. These papers evaluate current procedures and present new, practical procedures for ground-motion selection and modification. The first four papers of this issue focus on ground-motion modification procedures. The paper by Kunnath et al. compares and contrasts spectralmatching and amplitude-scaling methods considering realistic structural systems. How to characterize and spectrally match bidirectional ground motions to two separate target spectra is presented next by Grant. The following paper, by Kalkan and Chopra, proposes a modal-pushover-based scaling (MPS) procedure to scale ground motions. In the MPS method, the ground motions are scaled to match a target value of the inelastic deformation of the first-mode inelastic single degree-of-freedom system whose properties are determined by first-mode pushover analysis. Huang et al. compares displacement responses from amplitude scaling of ground motions based on three different methods with those from spectrally matched records. The next eight papers focus on ground-motion selection. The paper by Baker uses “conditional mean spectrum” as a new target for selecting spectrum-compatible records. Haselton et al. also considers spectral shape in selecting and scaling ground motions for use in nonlinear dynamic analysis for collapse assessment. The following paper, by Stafford et al., selects records providing the best match to the target spectrum and demonstrates a procedure to approximate the distributions of interstory or roof drifts. Without amplitude scaling, Hines et al. recommends a ground-motion selection process based on deaggregation of hazard into magnitude and distance bins. The paper by Masi et al. identifies the measure of seismic intensity that provides the best scaling of effect with respect to input and compares different approaches to selecting or generating synthetic records. Cimellaro et al. explores the influence of spectrum-matched and amplitude scaled ground motions on the development of fragility functions for structures and investigates the sensitivity of the number of accelerograms producing consistent results. The following paper by Honda and Ahmed presents a simple scheme for selecting few numbers of records representing the set of large numbers of possible ground motions generated considering the uncertainties of structural and seismic parameters. For ground-motion selection, a new intensity parameter considering the expected elongated period of the structure in the inelastic range has been proposed by Kadas et al. The next two companion papers by Dickinson and Gavin provide a quantitative measure of the variability among ground motions and develop response-spectrum-compatible models for biaxial synthetic ground motions. The next paper by Halldorsson et al. utilizes a “specific barrier model” to simulate ground motions that can be used with confidence in seismic design. In order to reduce the computational effort in the prediction of the incremental dynamic analysis (IDA) using a large set of records, Azarbakh and Dolsek introduces progressive IDA for the selection of representative ground-motion records. The last paper of this volume, by Moustafa, develops a new framework for modeling earthquake loads for seismic-resistant design of structures using the method of critical excitations. His method relies on the high uncertainty associated with the occurrence of earthquakes, their characteristics, and also on the structural safety requirements. The 17 papers presented here meet the goals of having the potential to inform and advance ground-motion selection and modification techniques for practice and pointing to new investigation avenues for future studies.