Ground Motion Simulation Research Articles

Regional‐scale seismic fragility, loss, and resilience assessment using physics‐based simulated ground motions: An application to Istanbul

AbstractUsing results from 57 large‐scale physics‐based fault‐rupture and wave propagation simulations, this research aims to evaluate the seismic risk, loss, and resilience of more than 16,000 reinforced concrete buildings in the Zeytinburnu district of Istanbul, Turkey. For each building and under each earthquake scenario, the spatially varying site‐specific simulated ground motions were used for performing three‐dimensional nonlinear time‐history analyses. The resulting structural responses—such as peak story drift ratios (PSDR) and peak floor accelerations (PFAs)—were utilized to conduct three region‐scale tasks: (i) building‐ and site‐specific seismic fragility analysis for both structural and nonstructural components of each building; (ii) intensity‐based seismic loss assessment using the FEMA P58 methodology and Monte Carlo simulations; and (iii) resilience evaluation based on the expected time of recovery predicted through FEMA P58. Moreover, both inertial and kinematic soil–structure interaction (SSI) effects were considered using a substructuring method for all three tasks. Site‐specific soil properties were utilized to compute the coefficients of soil springs and dashpots, as well as the foundation input motions. The SSI effects were investigated by comparing the fragility, loss, and resilience indices obtained with and without considering SSI.

Internal Structure of the Central Garlock Fault Zone From Ridgecrest Aftershocks Recorded by Dense Linear Seismic Arrays

AbstractWe provide high‐resolution seismic imaging of the central Garlock fault using data recorded by two dense seismic arrays that cross the Ridgecrest rupture zone (B4) and the Garlock fault (A5). Analyses of fault zone head waves and P‐wave delay times at array A5 show that the Garlock fault is a sharp bimaterial interface with P waves traveling ∼5% faster in the northern crustal block. The across‐fault velocity contrast agrees with regional tomography models and generates clear P‐wave reflections in waveforms recorded by array B4. Kirchhoff migration of the reflected waves indicates a near‐vertical fault between 2 and 6 km depth. The P‐wave delay times imply a ∼300‐m‐wide transition zone near the Garlock fault surface trace beneath array A5, offset to the side with faster velocities. The results provide important constraints for derivations of earthquake properties, simulations of ruptures and ground motion, and future imaging studies associated with the Garlock fault.

A suite of broadband physics‐based ground motion simulations for the Istanbul region

AbstractPhysics‐based earthquake ground motion simulations (GMS) have acquired significant growth over the last two decades, mainly due to the explosive developments of high‐performance computing techniques and resources. These techniques benefit high/medium seismicity regions such as the city of Istanbul, which presents insufficient historical ground motion data to properly estimate seismic hazard and risk. We circumvent this reality with the aid of the Texas Advanced Computing Center (TACC) facilities to perform a suite of 57 high‐fidelity broadband (8–12 Hz) large‐scale physics‐based GMS for a region in Istanbul, Turkey. This paper focuses on the details of simulated GMS: (i) validation of the GMS approach against recorded ground motions produced by the 2019 Silivri earthquake; (ii) characteristics of 57 different source models, which aim to consider the uncertainties of many fault rupture features, including the length and width, dip, strike, and rake angles of considered fault planes, as well as hypocenter locations and earthquake magnitudes ranging between 6.5 and 7.2; (iii) high‐resolution topography and bathymetry and seismic data that are incorporated into all GMS; (iv) simulation results, such as PGAs and PGVs versus and distances to fault ruptures (), of 2912 surface stations for all 57 GMS. More importantly, this research provides a massive database of displacement, velocity and acceleration time histories in all three directions over more than 20,000 stations at both surface and bedrock levels. Such site‐specific high‐density and ‐frequency simulated ground motions can notably contribute to the seismic risk assessment of this region and many other applications.

A numerical study of 3D topographic site effects considering wavefield incident direction and geomorphometric parameters

The topographic site effect plays a vital role in controlling the characteristics of earthquake ground motions. Due to its complexity, the factors affecting topographic amplification have not been fully identified. In this study, 100 ground motion simulations generated by double-couple point sources in the homogeneous linear elastic half-space are performed based on the 3D (three-dimensional) Spectral Element Method, taking the Menyuan area of Qinghai Province, China as a local testbed site. A relationship between incident direction and the strength of topographic amplification has been observed. The horizontal ground motion is affected by the back-azimuth, which is typically chosen to be the direction from seismic station to seismic source measured clockwise from north. Specifically, the east-west PGA (Peak Ground-motion Acceleration) is significantly amplified when back-azimuth is about 90° or 270°, and the north-south PGA is significantly amplified when back-azimuth is around 0° or 180°. The vertical ground motion is affected by the dipping angle, which is the angle from vertical at which an incoming seismic wave arrives. The vertical PGA is strongly amplified when the seismic wave is almost horizontally incident (e.g., dipping angle = 78°). A correlation study between geomorphometric parameters and frequency-dependent topographic amplification indicates that relative elevation and smoothed curvature contain similar information, both of which are closely related to the topographic amplification of horizontal components, but not the vertical component. Our study reveals the influence of source and propagation path on topographic amplification and provides a reference for considering the topographic site effect in real engineering sites.

Preliminary Evaluation of Crustal Medium Parameters in Western China

The establishment of attenuation relation of ground motion is always an important research content in engineering earthquake field. In seismology-based ground motion attenuation relationship and ground motion simulation using the stochastic method, regional parameters are necessary. These parameters involve stress drop Δσ, two segmentation points R1 and R2 of the geometric spreading item, Q0 and η of the inelastic attenuation item and the near-surface high-frequency decay parameter κ0, which reflect the regional crustal medium and site characteristics and have little relation with the earthquake size. In this paper, we take Sichuan, Yunnan and Xinjiang regions in western China as examples and we inverse the parameters for each region by micro-genetic algorithm. The inversion ranges of crustal media parameters in the three regions were determined respectively. Finally, we get the inversion results of every parameters and find that the parameters of the three regions have a great difference.

Stochastic finite fault modeling of Mw 6.4 earthquake along Indo-Burmese arc and site classification of its seismic recording station

This study simulates the strong ground motion of an earthquake having magnitude 6.4 occurred on 4 February 2011 in Indo-Burmese Arc (IBA). This earthquake recorded on seven seismic recording stations namely Jowai, Jorhat, Sibsagar, Nagaon, Guwahati, Cooch Bihar and Kokhrajhar. Also, estimation of site class performed to observe the site effects of recording stations in this study. The simulation performed on the basis of revised stochastic finite fault model with dynamic corner frequency and site class for the seismic recording station where the earthquake recorded has been estimated by using Horizontal to Vertical Spectral Ratio (HVSR) technique because modeling and simulation of ground motion majorly depend upon the recorded ground motion as well as site effects, where earthquake has been recorded. The revised well known finite source simulation program (EXSIM) used in this study becomes efficient in providing the results for small magnitude earthquake occurred at large distance. The average HVSR curves plotted for all the recording stations, providing peak frequency for all 7 sites. It is observed from the present work that simulated time histories as far as primary attributes, for example, Fourier spectra, Peak ground acceleration (PGA), Response spectra, Predominant frequency are in close concurrence with the recorded ones. The predominant frequency (fpeak) obtained from HVSR technique has been validated from existing literature for the estimation of site class for seismic recording stations. The fpeak determines the average shear wave velocity (Vs30) at depth of 30 ​m of overburden thickness which varies from 200 ​m/s to 1600 ​m/s according to Program for Excellence in Strong Motion Studies (PESMOS). Whereas, National Earthquake Hazard Reduction Program (NEHRP) provision consider the site class for Vs30 below 180 ​m/s. Due its wide range of site characterization, it has been adopted globally. Therefore, in this study, the site class obtained has been compared with the site classification scheme recommended by PESMOS, NEHRP provisions and previous literature. However, the ground motion parameters and the soil classification of the earthquake recording stations for the IBA region has not been explored yet even after seeing its severity in the past decades. Productive representation of present earthquake gives the confidence to understand and evaluate seismic danger at various parts of Indo- Burmese region from tremors of various sizes. In this study it is proposed that PESMOS site classification data should be revised because it covers wide range of soil types just into three (A, B and C type) class.

Regional physics-based simulation of ground motion within the Rhȏne Valley, France, during the MW 4.9 2019 Le Teil earthquake

In this paper we introduce the 3D physics-based numerical simulations (PBS) of ground motion during the Nov 11, 2019, MW 4.9 Le Teil earthquake, which occurred in a low-to-moderate seismicity area in the South-East of France, within the Rhône river valley, which hosts several operating nuclear installations. The numerical code SPEED, developed at Politecnico di Milano, Italy, was used to produce the PBS. After introducing the criteria to construct the numerical model, based on the relatively limited data available, a numerical convergence test was made to identify the frequency range for accurate simulations. Furthermore, the performance of the numerical results against the available strong motion records was assessed quantitatively using Goodness-of-fit (GoF) measures. According to the GoF scores, a good-to-excellent agreement was found on the horizontal components up to 8 Hz, showing that, even without a very detailed 3D numerical model of the medium, that would imply detailed knowledge of the basin shape, of the bedrock-to-basin impedance ratio, as well as of the damping ratio in the basin and its dependence on frequency, the PBS may provide realistic broadband predictions of earthquake ground motion. Nevertheless, as shown by the poorer performance on the vertical component, the high-frequency limitations of PBS, also in relation to the energy radiated by the kinematic source model, is still an issue to be carefully addressed. In spite of these limitations, the results obtained in this work demonstrate that PBS, if suitably calibrated and validated, can be either an alternative or a useful complement to empirical ground motion models, especially in those cases where the region- and site-specific features of ground shaking, including near-source conditions, are typically not accounted for by ergodic empirical models, such as for the seismic risk evaluation of large urban areas and/or of strategic structures, infrastructures and industrial plants.

Large‐scale ground motion simulation of the 2016 Kumamoto earthquake incorporating soil nonlinearity and topographic effects

AbstractA large‐scale physics‐based simulation is conducted to investigate ground motion distribution in the Mw 7.0 2016 Kumamoto earthquake, Japan. The model simulates the earthquake scenario from fault rupture to wave propagation, and localized site response with consideration of the combined effect of soil nonlinearity and topographic amplification. The simulation domain is 51 km × 43 km × 25 km, and the obtained ground motion time histories are compared satisfactorily with recordings from KiK‐net and K‐NET. Ground motion distribution considering nonlinear soil response and topographic amplification is presented. A 3D equivalent linear model is developed to mimic the soil nonlinearity, and it is demonstrated that neglecting soil nonlinearity could over‐predict peak ground acceleration (PGA) and underestimate peak ground velocity (PGV) near the fault. The topographic amplification factors (TAFs) of PGA and PGV are found between 0.5 and 2.0, with a correlation coefficient of 0.7 between them. Predictive equations are proposed to correlate TAFs of PGA and PGV with topographic features, which are represented by relative heights obtained at different length scales. Finally, major earthquake damages are summarized with reference to the obtained ground motion intensity map.

Using a grid-search approach to validate the Graves–Pitarka broadband simulation method

This work assesses the ability of the Graves–Pitarka simulation approach to reproduce observed ground motions for 12 California and Baja California earthquakes. A total of 240 realizations are computed for each earthquake and compared with recorded strong motions from near-fault sites. In addition to spatial variability in slip, each realization samples from discrete combinations of average rupture speed, rise time, and down-dip fault width. Ground motions for each realization of a given earthquake are compared to the observations using a pseudo-spectral acceleration goodness-of-fit (GoF) metric. Parameters for the lowest misfit cases are then tabulated to develop relations for estimating median values and ranges for future applications. The results are generally consistent with published scaling relations for estimating rupture dimensions as a function of magnitude. Additionally, I find the average rise time scales as {2.3times alpha }_{T}times {10}^{-9}{times M}_{o}^{1/3} (Mo is seismic moment in dyne-cm) and average rupture speed as (0.765 pm 0.075)times {alpha }_{T}^{-1}times {V}_{s} (Vs is local shear wave velocity), where aT is a mechanism adjustment ranging from a value of 1.0 for pure strike-slip to 0.9 for pure reverse-slip cases. There are cases where slightly different combinations of parameters produce equally good fits to the observations, demonstrating the non-uniqueness of using a single GoF metric in this approach. Nonetheless, the results reinforce the importance of adequately sampling ranges of rupture parameters when performing validations, as well as when simulating ground motions for future events.Graphical

New generalized ANN-based hybrid broadband response spectra generator using physics-based simulations

Estimation of the seismic risk associated with infrastructures requires site-specific seismic hazard studies. Further, for nonlinear time history analysis, one requires broadband ground motion. In modern times, physics-based simulations (PBS) for deriving the ground motion for future earthquakes have been considered. The PBS helps decrease the uncertainties related to hazard estimation compared to ground motion prediction equations. The PBS methods have a specific frequency threshold limit resulting from high computational demand. Hence, hybrid methods are required to attain broadband spectra for the simulated ground motion. This study uses a new artificial neural network (ANN)-based model to generate broadband ground motion spectra using the low-frequency spectral acceleration from PBS, source, path, and site parameters as input variables. A detailed parametric study and performance evaluation was made to identify the optimal input parameters in conjunction with the best-suited ANN architecture. The performance of the ANN model is demonstrated for Iwate (\(M_w\) 6.9, 2008) earthquake. We found that the predicted values from the developed ANN model agree with the recorded data. Furthermore, time histories are generated using the spectral ordinate matching technique from the estimated broadband spectra.

A new approach for the computation of design shear force in reinforced concrete walls subjected to seismic loads

SummaryThis paper investigates the dynamic shear amplification in reinforced concrete shear walls designed according to the seismic provisions of the current Turkish Building Earthquake Code (TBEC‐2018). Shear walls with a high ductility level and different aspect ratios are examined to evaluate the design shear force calculated by using the dynamic amplification factor (βv) and overstrength factor (D) defined in TBEC‐2018. For this purpose, response spectrum analyses (RSAs) are first carried out on two‐dimensional cantilever shear walls with heights of 30, 45, and 60 m and with lengths of 1.5, 3, and 4.5 m in the plan. Then, a total of 198 nonlinear time history analyses (NLTHAs) are performed with real and simulated ground motions matched to the elastic design spectrum defined in TBEC‐2018. The comparison of the design shear forces obtained from RSA and the shear demands obtained from NLTHA along the heights of the walls reveals that the design shear forces calculated according to TBEC‐2018 may underestimate the actual shear demands from studied ground motions. Moreover, the applicability of the updates proposed to TBEC‐2018 for the design shear force and shear force diagram along the wall height in reinforced concrete shear wall‐frame systems to cantilever shear walls is also examined.

TFCGAN: Nonstationary Ground-Motion Simulation in the Time–Frequency Domain Using Conditional Generative Adversarial Network (CGAN) and Phase Retrieval Methods

ABSTRACTDespite the exponential growth of the amount of ground-motion data, ground-motion records are not always available for all distances, magnitudes, and site conditions cases. Given the importance of using time histories for earthquake engineering (e.g., nonlinear dynamic analysis), simulations of time histories are therefore required. In this study, we present a model for simulating nonstationary ground-motion recordings, which combines a conditional generative adversarial network to predict the amplitude part of the time–frequency representation (TFR) of ground-motion recordings and a phase retrieval method. This model simulates the amplitude and frequency contents of ground-motion data in the TFR as a function of earthquake moment magnitude, source to site distance, site average shear-wave velocity, and a random vector called a latent space. After generating the phaseless amplitude of the TFR, the phase of the TFR is estimated by minimizing all differences between the observed and reconstructed spectrograms. The simulated accelerograms produced by the proposed method show similar characteristics to conventional ground-motion models in terms of their mean values and standard deviations for peak ground accelerations and Fourier amplitude spectral values.

Response of a high-speed train travelling over a long and high-pier viaduct during moderate earthquakes

This contribution presents the results of numerical simulations in which a high-pier viaduct under lateral and vertical non-stationary spatially variable seismic ground motions is crossed by an articulated high-speed train at several speeds. The spectral representation method is employed to generate the required number of acceleration time-history series at each support location of the railway viaduct studied. Wave passage, local soil conditions and loss of coherency effects have been accounted for in the simulated ground-motion time histories, with several peak ground accelerations. Train and bridge responses have been obtained by means of a non-linear dynamic interaction multibody and finite element model. An analysis of train running safety indices has been carried out. The properties of earthquakes and train speeds which may cause problems to traffic safety are detailed, as is the train derailment probability. The numerical simulation outcomes show that it is not safe for the train to travel over the studied viaduct in earthquakes with peak ground acceleration equal to 0.03 g and for train speeds above 280 km/h.

Uncertainty quantification of seismic response of nuclear reactor building using a three‐dimensional finite element model

AbstractAfter the 2011 Fukushima accident, seismic regulations for nuclear power plants (NPPs) in Japan have been strengthened to include countermeasures beyond design‐basis events. Therefore, the importance of seismic probabilistic risk assessments is a topic that deserves attention. Generally, uncertainty quantification has been a crucial undertaking to assess the fragility of NPP buildings. This study aims to quantify realistic uncertainties using a three‐dimensional (3D) finite element (FE) model to reflect the obtained results to the conventional simple sway‐rocking (SR) model, and to develop a seismic fragility assessment method that considers 3D effects. As a first step, a 3D FE model was developed, and a seismic response analysis was performed to evaluate the seismic response of the buildings. For comparison, a seismic response analysis using the conventional SR model was performed. For input ground motions, 200 types of simulated seismic ground motions, generated using fault‐rupture models were adopted. As a second step, two types of uncertainties are evaluated for uncertainty quantification: uncertainty for input seismic ground motion and that due to different locations of equipment installed on a floor. As a third step, to reflect the 3D effect on the uncertainty of the conventional SR model, were investigated the median and logarithm standard deviation of the response ratio (3D FE/SR) of the maximum acceleration of the two models. The results of epistemic uncertainty tended to increase with the increasing elevation level and the epistemic uncertainty result in the basement floor, where important equipment was installed, was relatively small. By reflecting this epistemic uncertainty into the conventional SR model, a more realistic fragility assessment that considers the 3D effect is expected by applying this result as epistemic uncertainty of the SR model of the fragility assessment.

Simulation of strong earthquake characteristics of a scenario earthquake (MS7.5) based on the enlightenment of 2022 MS6.9 earthquake in Menyuan

The Menyuan area is an important transportation hub in the Hexi Corridor. The Menyuan MS6.9 earthquake that occurred on January 8, 2022 had a major impact on the local infrastructure and transportation of this region. Due to the high possibility of similar strong earthquakes occurring in this area in the future, preliminary assessment of the seismic intensity characteristics of destructive earthquakes in this region is essential for effective disaster control. This paper uses the empirical Green′s function (EGF) method as a numerical simulation tool to predict the ground motion intensity of Datong Autonomous County under the action of the scenario earthquake (MS7.5). Seismic records of aftershocks of the 2016 Menyuan MS6.4 earthquake were used as Green’s functions for this simulation. The uncertainties associated with various source parameters were considered, and 36 possible earthquake scenarios were simulated to obtain 72 sets of horizontal ground motions in Datong County. The obtained peak ground acceleration (PGA) vs. time histories of the horizontal ground motion were screened using the attenuation relationships provided by the fifth-edition of China's Seismic Ground Motion Parameter Zoning Map and the NGA-West2 dataset. Ultimately, 32 possible acceleration-time histories were selected for further analysis. The screened PGA values ranged from 78.8 to 153 cm/s2. The uncertainty associated with the initial rupture point was found to greatly affect the results of the earthquake simulation. The average acceleration spectrum of the selected acceleration-time history exceeded the expected spectrum of a intermediate earthquake, which means that buildings in Datong County might sustain some damage should the scenario earthquake occur. This research can provide reliable ground motion input for urban earthquake damage simulation and seismic design in Datong County. Growing the dataset of small earthquakes recorded in this region will facilitate the large-scale simulation of ground motions under different earthquake scenarios.

Ground Motion Simulations for the 19 January 2020 Jiashi, China, Earthquake Using Stochastic Finite‐Fault Approach

AbstractA 6.0‐magnitude (Mw) earthquake was reported to have occurred in Jiashi County, Xinjiang at 21:27 on 19 January 2020, Beijing time (13:27 UTC). This study applied a stochastic finite‐fault approach based on the dynamic corner frequency (EXSIM) to simulate 23 near‐field stations within a distance of 120 km from the epicenter. The stochastic finite‐fault approach is the simplest and most effective method for simulating high‐frequency ground motions. According to studies and empirical relationships, we estimated a region‐specific parameter (κ0) for use in simulations. In this study, two different slip models, namely, random and inverted slip models, were used to explain their influence on the simulation results. For most stations, the simulated seismic characteristics, such as the peak ground acceleration (PGA), pseudo spectral acceleration ,and Fourier acceleration spectrum, are highly compatible with the observed values in the frequency range (f > 1 Hz), indicating that the stochastic finite‐fault approach is not highly sensitive to input slip distributions and fault dimensions. The simulation results indicated no significance between the two slip models under high‐frequency conditions. Finally, based on the predicted PGA values of 1891 field points selected near the fault, the acceleration field of the Jiashi earthquake is plotted. The results show that the use of the acceleration time history predicted by modified EXSIM is feasible and practical in the high‐frequency band above 1 Hz.

The neglected Istanbul earthquakes in the North Anatolian Shear Zone: tectonic implications and broad-band ground motion simulations for a future moderate event

SUMMARYİstanbul (Marmara Region, NW Turkey) is one of the megacities in the world and suffered from destructive earthquakes on the North Anatolian Fault, a member of the North Anatolian Shear Zone, throughout history. The 1999 Kocaeli and Düzce earthquakes emphasize the earthquake potential of the fault, crossing the Sea of Marmara, and the importance of seismic hazards in the region. The studies in the last 20 yr have concentrated on the main fault and its future destructive earthquake potential. In this study, unlike the previous ones, we focus on the two main topics about the earthquakes not interested previously in İstanbul: (1) Investigating recent earthquake activity masked by the blasts in the metropolitan area and its tectonic implications, (2) revealing their effects in İstanbul utilizing numerical ground motion simulations for a future moderate event (Mw 5). First, the 386 earthquakes from 2006 to 2016 are relocated with the double-difference method using the dense seismic network operated in the same period. The source mechanisms of the events (ML ≥ 3), including the most recent 2021 Kartal–İstanbul earthquake (ML 4.1), are determined. In addition to the analysis of the recent seismic activity, the location of the two moderate and pre-instrumental-period İstanbul earthquakes, which occurred in 1923 (Mw 5.5) and 1929 (Mw 5.1), are revised. Using the relocated epicentres outside of the principal deformation zone and the fault plane solutions, the roles of the earthquakes in the stress regime of the Marmara region are explained. The epicentres on the Cenozoic or Palaeozoic formation in the Istanbul–Zonguldak Zone are interpreted as the re-activation of the palaeo-structures under the recent tectonic stresses, and their fault plane solutions agree with the synthetic/antithetic shears of a transtensional regime corresponding to the right lateral strike-slip system with mainly N–S extension in the Marmara Region. In the second part, we investigate the effects of moderate scenario events (Mw 5) considering the current earthquake epicentres in the İstanbul metropolitan area, using characterized earthquake source model and 1-D velocity structure verified with the broad-band (0.1–10 Hz) numerical ground motion simulation of the 2021 Kartal–İstanbul earthquake. The simulated PGAs agree with the ground-motion prediction equations for short epicentral distances (<30 km). Furthermore, according to the empirical relation for Turkish earthquakes, the maximum PGA value of the synthetic models (∼0.3 g) corresponds to the felt intensity of MMI IX. The simulated spectral accelerations for the Mw 5 earthquake scenarios may exceed the design spectrum between 0.2 and 0.6 s given in the Turkish Building Earthquake Code (2018). In addition, certain models also generate spectral accelerations close to the design-level spectrum between 0.4 and 1 s, leading to resonance phenomena. The results indicate that a moderate event (Mw 5) in the İstanbul metropolitan area is capable of damage potential for the mid-rise buildings (4–10 stories) because of the site condition with resonance phenomena and poor construction quality.

Near-source ground motion estimation for assessing the seismic hazard of critical facilities in central Italy

We apply the Probabilistic Seismic Hazard Analysis (PSHA) and compute Physics-Based Simulations (PBS) of ground motion for three dams in the Campotosto area (Central Italy). The dams, which confine an artificial water reservoir feeding hydroelectric power plants, are located in an active seismic zone between the areas that experienced the 2009 L’Aquila and 2016–2017 Central Italy seismic sequences. The probabilistic disaggregation estimated for a return period of 2475 years, corresponding to the collapse limit state for critical facilities, indicates that the most dangerous fault is associated with a maximum magnitude of 6.75 ± 0.25 within a distance of 10 km. This fault is used in PBS to emulate the Maximum Credible Earthquake scenario. To capture the ground motion variability, we input a pseudo-dynamic source model to encompass spatial and temporal variations in the slip, rise time and rupture propagation, heavily affecting the near-source ground motion. Indeed, the ground motion above the rupture volume is mainly influenced by the epistemic uncertainties of rupture nucleation and slip distribution. The computed broadband seismograms are consistent with the near-source shaking recorded during the 2016 MW 6.6 Norcia earthquake and constrain the upper bound of the simulated ground motion at specific sites. Our modelling reinforces the importance of considering vertical ground motion near the source in seismic design. It could reach shaking values comparable to or larger than those of the horizontal components. This approach can be applied in other areas with high seismic hazard to evaluate the seismic safety of existing critical facilities.

Probabilistic and Scenario-Based Seismic Hazard Assessment on the Western Gulf of Corinth (Central Greece)

The Gulf of Corinth (Central Greece) is one of the most rapidly extending rifts worldwide, with its western part being the most seismically active, hosting numerous strong (M ≥ 6.0) earthquakes that have caused significant damage. The main objective of this study was the evaluation of seismic hazard through a probabilistic and stochastic methodology. The implementation of three seismotectonic models in the form of area source zones via a logic tree framework revealed the expected level of peak ground acceleration and velocity for return periods of 475 and 950 years. Moreover, PGA values were obtained through the stochastic simulation of strong ground motion by adopting worst-case seismic scenarios of potential earthquake occurrences for known active faults in the area. Site-specific analysis of the most populated urban areas (Patras, Aigion, Nafpaktos) was performed by constructing uniform hazard spectra in terms of spectral acceleration. The relative contribution of each selected fault segment to the seismic hazard characterizing each site was evaluated through response spectra obtained for the adopted scenarios. Almost all parts of the study area were found to exceed the reference value proposed by the current Greek National Building Code; however, the three urban areas are covered by the Eurocode 8 regulations.

New Empirical Equations for Determination of Fourier Amplitude Spectrum of Acceleration

ABSTRACT In this study, new empirical relations are proposed to determine the Fourier amplitude spectrum of acceleration. The FASAs form the white-noise spectrum in the stochastic ground motion simulation methods. So far, various analytical and experimental models have been proposed to determine the FASA. ω−2 is among the most well-known models are used in the computational programs of ground motion simulation such as SMSIM or EXSIM. In this study, the relationship between the FASA, and the important seismological parameters such as moment magnitude, closest distance from rupture plane, site conditions and faulting mechanism is determined, and appropriate relations are presented. There are limited experimental models of FASA, and present models are mainly analytical. Therefore, the results of this research can be beneficial. To present models, the Iran Plateau earthquake catalog is used, including 2228 acceleration records of 749 earthquakes with magnitudes of 4.5–7.6 and rupture distance up to 200 km.