Estimated Peak Ground Acceleration Research Articles

New Ground-Motion Prediction Equations Using Multi Expression Programing

High-precision attenuation models were derived to estimate peak ground acceleration (PGA), velocity (PGV), and displacement (PGD) using a new variant of genetic programming, namely multi expression programming (MEP). The models were established based on an extensive database of ground-motion recordings released by Pacific Earthquake Engineering Research Center (PEER). For more validity verification, the models were employed to predict the ground-motion parameters of the Iranian plateau earthquakes. The results indicate that the MEP attenuation models are capable of effectively estimating the peak ground-motion parameters. The proposed models are able to reach a prediction performance comparable with the attenuation relationships found in the literature.

Estimation of Peak Ground Acceleration and Its Uncertainty for Northern Indian Region

In the present study the authors evaluate uncertainties in the seismic hazard assessment for the Northern Indian region, based on the probabilistic seismic hazard analysis (PSHA). The newly compiled earthquake data has been treated for the quality, consistency, and homogeneity in a systematic manner to find out the uncertainties in every step of calculations. Based on the geological and tectonic setup, seismicity and other geophysical anomalies, a seismotectonic model of the region has been developed. The seismic hazard parameters are calculated based on giving proper weight to specific region. The peak ground acceleration (PGA) is estimated for various return periods for the Northern Indian region using a logic tree approach. The variation at the input level in terms of the source models and different Ground Motion Prediction Equations (GMPEs) is used. To examine into the effect of source modelling and GMPEs, the Coefficient of Variation (COV) maps have been generated. To encompass the region and for better resolution, the peak ground acceleration (PGA) is estimated at 15 minute intervals. The COV values due to all branch points in the logic tree decrease with distance from the source and conspicuous increase toward fault boundaries are observed.

Neural Network Approach for Analyzing Seismic Data to Identify Potentially Hazardous Bridges

Examining the effect of strong ground motions on civil engineering structures is important as it concerns public safety. The present study initially selects twenty‐one bridges with lengths over 500 m in the Formosa freeway of Taiwan and collects a series of recorded seismic data from checking stations near these bridges. Then, three seismic parameters including focal depth, epicenter distance, and local magnitude are used as the input data sets, and a model for estimating the key seismic parameter—peak ground acceleration—for each of bridge site is developed by using the neural network approach. This model is finally combined with a simple distribution method and a new weight‐based method to estimate peak ground acceleration at each of the bridges along the freeway. Based on the seismic design value in the current building code as the evaluation criteria, the model identifies five bridges, out of all the bridges investigated, as having the potential to be subjected to significantly higher horizontal peak ground accelerations than that recommended for design in the building code. The method presented in this study hence provides a valuable reference for dealing with nonlinear seismic data by developing neural network model, and the approach presented is also applicable to other areas of interest around the world.

Peak Ground Acceleration Estimation by Linear and Nonlinear Models with Reduced Order Monte Carlo Simulation

Abstract: Estimation of the peak ground acceleration (PGA) is one of the main tasks in civil and earthquake engineering practice since it is an important factor for the design spectrum. The Boore–Joyner–Fumal (BJF) and the Crouse–McGuire formula are well-known empirical models by estimating the PGA with the magnitude of earthquake, the fault-to-site distance, and the site foundation properties. It is obvious that a predictive model class with more effective free parameters often fit the data better. However, this does not imply that the complicated formula is more realistic since overfitting may happen when the formula has too many free parameters. In this article, 32 linear and 16 nonlinear predictive model classes are constructed and investigated. The Bayesian model class selection approach is utilized to obtain the most suitable predictive model class for the seismic attenuation formula. In this approach, each predictive model class is evaluated by the plausibility conditional on the data and it is proportional to the evidence which involves a high-dimensional integral. This integral has closed-form solution for the linear model classes. Analytic work was done to improve the original asymptotic expansion in this study. For the nonlinear model classes, the evidence integral can be reduced to two-dimensional and then Monte Carlo simulation is utilized to evaluate the double integral. The most plausible model class is robust in the sense that it balances between the data-fitting capability and the sensitivity to noise. A database of 266 strong-motion records, obtained from the China Earthquake Data Center, is utilized for the analysis. The most plausible predictive model class and its updated model parameters are determined. It turns out that the most plausible model class is generally simpler than the full BJF empirical formula. In the case where no single model class has dominant plausibility, one can utilize the multi-model predictive formula that is a plausibility-weighted average of the prediction of different predictive models.

The Friuli Venezia Giulia Accelerometric Network: RAF

The first stations of the Friuli Venezia Giulia (NE Italy) Accelerometric Network (Rete Accelerometrica del Friuli Venezia Giulia—RAF) were installed by the Department of Earth Sciences, University of Trieste, in the early nineties in the framework of international scientific projects. Today RAF is configured, taking in to account also other network stations operating in Italy as well as in Austria and Slovenia, to record accelerations at several important sites in the seismic area of Friuli Venezia Giulia and near its borders with Slovenia and Austria. This allows an immediate estimate of peak ground acceleration as well as a first evaluation of possible damages. In the year 2000, DST and the Friuli Venezia Giulia Direction of the Civil Defence signed an agreement for the RAF management and its use for civil defence purposes, like the prompt estimate of the damage level after an earthquake occurrence, the emergency management, the reconstruction planning, and the validation and updating of seismic hazard maps. Moreover, RAF recordings are used also for prevention purposes by the civil defence. This is performed with the computation of real time shake maps, possible ground-shaking scenarios, studies of the physics of the seismic source, site effects estimates and microzonation analyses.

Constraining paleo PGA values by numerical analysis of overturned columns

AbstractThe estimated peak ground acceleration (PGA) for a specific region cannot always be determined reliably from compilation and statistical analyses of instrumental data acquired because of the relatively short time window available for such an approach, typically up to 100 years of instrumentation. We propose a complimentary approach for estimating PGA in a specific region, through back analysis of seismically driven column collapse in historic monuments, using the numerical discrete element discontinuous deformation analysis (DDA) method. Preliminary threshold ‘paleo PGA’ values thus obtained constrain the lower bound of PGA estimates using information from a much broader time window, in the case study presented here of approximately 1200 years. Copyright © 2009 John Wiley & Sons, Ltd.

Neural computing with genetic algorithm in evaluating potentially hazardous metropolitan areas result from earthquake

In this study, neural network models improved by genetic algorithm were employed to estimate peak ground acceleration (PGA) at seven metropolitan areas in the island of Taiwan, which is frequently subject to earthquakes. By considering a series of historical seismic records, and using the seismic design value in the current building code as the evaluation criteria, two metropolitan areas, Taichung and Chiayi, were identified by computational results as having higher estimated horizontal PGAs than the recommended design values. The approach implemented in this study provides a new and good basis for solving this type of seismic problems in the region studied.

Estimation of peak ground acceleration and spectral acceleration for South India with local site effects: probabilistic approach

Abstract. In this work an attempt has been made to evaluate the seismic hazard of South India (8.0° N–20° N; 72° E–88° E) based on the probabilistic seismic hazard analysis (PSHA). The earthquake data obtained from different sources were declustered to remove the dependent events. A total of 598 earthquakes of moment magnitude 4 and above were obtained from the study area after declustering, and were considered for further hazard analysis. The seismotectonic map of the study area was prepared by considering the faults, lineaments and the shear zones in the study area which are associated with earthquakes of magnitude 4 and above. For assessing the seismic hazard, the study area was divided into small grids of size 0.1°×0.1°, and the hazard parameters were calculated at the centre of each of these grid cells by considering all the seismic sources with in a radius of 300 km. Rock level peak horizontal acceleration (PHA) and spectral acceleration (SA) values at 1 s corresponding to 10% and 2% probability of exceedance in 50 years have been calculated for all the grid points. The contour maps showing the spatial variation of these values are presented here. Uniform hazard response spectrum (UHRS) at rock level for 5% damping and 10% and 2% probability of exceedance in 50 years were also developed for all the grid points. The peak ground acceleration (PGA) at surface level was calculated for the entire South India for four different site classes. These values can be used to find the PGA values at any site in South India based on site class at that location. Thus, this method can be viewed as a simplified method to evaluate the PGA values at any site in the study area.

An Atlas of ShakeMaps and population exposure catalog for earthquake loss modeling

We present an Atlas of ShakeMaps and a catalog of human population expo- sures to moderate-to-strong ground shaking (EXPO-CAT) for recent historical earthquakes (1973-2007). The common purpose of the Atlas and exposure catalog is to calibrate earth- quake loss models to be used in the US Geological Survey's Prompt Assessment of Global EarthquakesforResponse(PAGER).ThefullShakeMapAtlascurrentlycomprisesover5,600 earthquakes from January 1973 through December 2007, with almost 500 of these maps con- strained—tovaryingdegrees—byinstrumentalgroundmotions,macroseismicintensitydata, community internet intensity observations, and published earthquake rupture models. The catalog of human exposures is derived using current PAGER methodologies. Exposure to discrete levels of shaking intensity is obtained by correlating Atlas ShakeMaps with a global population database. Combining this population exposure dataset with historical earthquake lossdata,suchasPAGER-CAT,providesausefulresourceforcalibratinglossmethodologies against a systematically-derived set of ShakeMap hazard outputs. We illustrate two example uses for EXPO-CAT; (1) simple objective ranking of country vulnerability to earthquakes, and; (2) the influence of time-of-day on earthquake mortality. In general, we observe that countriesinsimilargeographicregionswithsimilarconstructionpracticestendtoclusterspa- tiallyintermsofrelativevulnerability.Wealsofindlittlequantitativeevidencetosuggestthat time-of-day is a significant factor in earthquake mortality. Moreover, earthquake mortality appears to be more systematically linked to the population exposed to severe ground shaking (Modified Mercalli Intensity VIII+). Finally, equipped with the full Atlas of ShakeMaps, we merge each of these maps and find the maximum estimated peak ground acceleration at any grid point in the world for the past 35years. We subsequently compare this "composite

Ground Motion Synthesis and Seismic Scenario in Guwahati City--A Stochastic Approach

Guwahati is fast emerging as a multi-ethnic cosmopolitan city with a burgeoning population and rapid unplanned urbanization. It is a commercial hub, catering to eight states in northeast India. The city is located in the lower Brahmaputra Valley and underlain by thick alluvial deposits ranging from 25 to 600 m with granitic exposure at places. The regional seismotectonics of northeast India exhibit a rather large potential for high-magnitude earthquakes, as reported by Thingbaijam et al. (2008). Large earthquakes in the past caused widespread damage to life and property in this terrain. Presently, the urban agglomeration in this area is quite vulnerable to possible future great earthquakes. Given the devastation caused recently by the Sichuan earthquake of 12 May 2008 ( MW 7.9), with a death toll of nearly 70,000 and loss of property worth billions of dollars, it is imperative that we have a realistic hazard scenario for this extremely vulnerable seismic province. Seismic hazard quantification at a site is based, essentially, on understanding the site response and the propagation path of seismic waves, as well as the source characterization of a damaging earthquake. A typical deterministic seismic hazard model takes these physical attributes into account while estimating peak ground acceleration (PGA). Figure 1. ▴ Seismotectonic map of northeast India adapted from Thingbaijam et al. (2008) wherein the fault rupture zones of four scenario earthquakes have been depicted with rectangular polygons. The results of the simulations of four scenario earthquakes based on four large historical earthquakes in the region have been reported here. An extended finite-fault stochastic modeling approach has been adapted for strong ground-motion synthesis for the predicted maximum earthquakes in the terrain as reported by Thingbaijam and Nath (2008). An attempt also has been made to establish regional as well as site-specific attenuation relations for Guwahati city through successive ground-motion …

Ground motion estimation during the Kashmir earthquake of 8th October 2005

In this article, analytical methods have been used to estimate ground motion during the 8 October 2005, Kashmir earthquake. Peak ground acceleration (PGA) values at several stations in the epicentral region have been estimated by empirical analytical source mechanism models. As an alternate analysis, PGA estimates have also been obtained using the stochastic finite fault seismological model. The estimated PGAs are compared with that obtained from damage values. A PGA contour map in the near-source region is provided. It is found that very near to the epicenter, PGA would have reached more than 1 g. It is demonstrated that empirical analytical models can be effectively used to estimate ground motion due to rupture of active faults.

An Overview of the Damaging and Low Magnitude Mw 4.8 La Paca Earthquake on 29 January 2005: Context, Seismotectonics, and Seismic Risk Implications for Southeast Spain

This article presents an overview of the La Paca earthquake of magnitude mbLg 4.7, which occurred on 29 January 2005, with its epicenter located near the town of Avile´s in the Murcia region in southeast Spain. Despite its low magnitude, the earthquake caused important damage in two towns of the epicentral area, La Paca and Zarcilla de Ramos. These areas recorded intensities of VI–VII (European Macroseismic Scale, 1998) and sustained estimated economic losses amounting to 10 million €. Aftershocks continued for more than 2 weeks, producing considerable alarm in the population and mobilizing emergency services from the whole region. The La Paca seismic series is the third registered in the region in the past 8 years, being preceded by the Mula (1999) and southwest Bullas (2002) seismic series. These main events had also low magnitudes (mbLg 4.8) and caused damage levels similar to the 2005 earthquake. The case is an example of a moderate seismic zone where low-magnitude and frequent earthquakes have important implications on the seismic hazard and risk of the region. Although these are not the largest expected earthquakes, they have yielded important information for improving the knowledge of the seismic activity of the area. With this aim in mind, different topics have been analyzed from a multidisciplinary perspective, including seismicity, local tectonics and surface geology, focal mechanisms, macroseismic effects, and ground motion. Results indicate a local tectonic interpretation, consistent with a strike-slip focal mechanism, the confirmation of a triggering process between the 2002 and 2005 earthquakes, a geotechnical and ground-motion characterization for the damaged sites (supporting local amplification effects and estimated peak ground acceleration values of �0.1g), and an understanding of damage patterns in relation to local building trends. The results may be used as guidelines for future revisions of the Spanish Building Code (Norma de la Construccio´n Sismorresistente Espan˜ola [NCSE-02], 2002). The study results should contribute to risk mitigation in a region where strong-motion records from the maximum expected earthquakes are not available. This approach can be extended to other regions with similar seismic backgrounds and a lack of strong-motion records.

Probabilistic Seismic Hazard Assessment of the Kermanshah-Sanandaj Region of Western Iran

Seismic hazard assessment and zoning of the Kermanshah-Sanandaj region in western Iran is conducted using probabilistic approach. Two maps have been prepared to indicate the earthquake hazard of the region in the form of iso-acceleration contour lines. They display a probabilistic estimate of peak ground acceleration (PGA) over bedrock for the return periods of 475 and 50 years. A uniform catalog of earthquakes containing historical and instrumental events covering the period from the eleventh century A.D. to 2003 is used. Twelve potential seismic sources are modeled as area sources in the region. Seismicity parameters are evaluated using the method in which magnitude uncertainty and incompleteness of earthquake data are considered. Seismic hazard assessment is carried out for a grid of 357 points with 0.1° intervals using the SEISRISKIII computer program for the study area encompassed by the 46–48° E longitudes and 34–36° N latitudes. This region includes the most active segments of the Zagros Main Recent Fault; among them, the Sahneh and Nahavand faults have a well-known history of intense seismic activity. PGA values for this region are estimated to be 0.35 g and 0.20 g for 475- and 50-years return periods, respectively.

Constraints on Probabilistic Seismic-Hazard Models from Unstable Landform Features in New Zealand

We undertake the first New Zealand-based pilot study to investigate the use of ancient precariously balanced rocks (rocks that are unstably balanced on top of a pedestal) as a criteria for testing estimates of earthquake shaking from probabilistic seismic hazard models for long-return periods. To date, research to test seismic-hazard models in New Zealand has been restricted to the short historical record of earthquakes. Our survey of five sites in the South Island of New Zealand has yielded a total of 28 precariously balanced rocks which, on the basis of established methodology, are used to provide estimates of the maximum ground motions that could have occurred at the sites since the rocks became precarious. Age estimates for the precariously balanced rocks (40,400 to 55,300 years for central Otago schist rocks, and 77,300 years for northwest Nelson granitic rocks) are made from a limited number of cosmogenic dates obtained from bedrock removed from the pedestals of the rocks. Comparisons of the maximum peak ground accelerations and ages of the precariously balanced rocks with seismic-hazard curves derived from the New Zealand national seismic-hazard model show that the rocks indicate considerably lower hazard than the seismic-hazard model at sites located within 5 km of active faults, whereas the agreement is favorable for sites located away from active faults. The variability about the median estimates of peak ground acceleration for the fault sources and/or the median accelerations for the fault sources assumed in the seismic- hazard model may therefore be overestimated for the sites near active faults.

Effect of Soil Aging on Assessing Magnitudes and Accelerations of Prehistoric Earthquakes

Increase in strength due to aging of sands is reflected in higher blow counts and tip resistance values in penetration resistance measurements. This affects the magnitudes and peak ground acceleration estimates of prehistoric earthquakes obtained from an analysis of geotechnical observations at paleoliquefaction sites in the South Carolina Coastal Plain. In this study, corrections were made to account for the effects of soil aging, which were neglected in earlier estimates. The results show that when the effects of aging of soils on their geotechnical properties are incorporated, the resulting back-calculations reduced earlier magnitude estimates of prehistoric earthquakes by about 0.9 units. The peak ground acceleration estimates were reduced by about 15% for those earthquakes originally estimated at approximately 0.15 g. For those earthquakes whose original estimates were greater than 0.2 g, there was no noticeable change when a correction was made for the aging of soils.

Neural network estimation of ground peak acceleration at stations along Taiwan high-speed rail system

It is essential to understand the characteristics of strong motion for reducing the negative impacts in a high-risk area. In this work, a combination of seismic parameters including epicentral distance, focal depth, and magnitude from historical records at 30 checking stations were used in back-propagation neural network model, to estimate peak ground acceleration at ten train stations along the high-speed rail system in Taiwan. The estimation was verified with available microtremor measurement at a specified station, and the calculated horizontal acceleration was checked with the existing building code requirements. A potential hazardous station was identified from the neural network estimation, which exhibited a significantly higher acceleration than that of the design value. The obtained results might be useful for revising the currently applied building code at this region to further fit in the actual earthquake response.

SEISMIC HAZARD ASSESSMENT OF METROPOLITAN TEHRAN, IRAN

This paper presents a probabilistic seismic hazard assessment of Tehran, the capital of Iran. Two maps have been prepared to indicate the earthquake hazard of Tehran and its vicinity in the form of iso-acceleration contour lines. They display the probabilistic estimate of Peak Ground Acceleration (PGA) over bedrock for the return periods of 475 and 950 years. Tehran is a densely populated metropolitan in which more than 10 million people live. Many destructive earthquakes happened in Iran in the last centuries. It comes from historical references that at least 6 times, Tehran has been destroyed by catastrophic earthquakes. The oldest one happened in the 4th century BC. A collected catalogue, containing both historical and instrumental events and covering the period from the 4th century BC to 1999 is then used. Seismic sources are modelled and recurrence relationship is established. For this purpose the method proposed by Kijko [2000] was employed considering uncertainty in magnitude and incomplete earthquake catalogue. The calculations were performed using the logic tree method and three weighted attenuation relationships; Ramazi [1999], 0.4, Ambraseys and Bommer [1991], 0.35, and Sarma and Srbulov [1996], 0.25. Seismic hazard assessment is then carried out for 12×11 grid points using SEISRISK III. Finally, two seismic hazard maps of the studied area based on Peak Ground Acceleration (PGA) over bedrock for 10% probability of exceedance in two life cycles of 50 and 100 years are presented. The results showed that the PGA ranges from 0.27(g) to 0.46(g) for a return period of 475 years and from 0.33(g) to 0.55(g) for a return period of 950 years. Since population is very dense in Tehran and vulnerability of buildings is high, the risk of future earthquakes will be very significant.

Earthquake ground motion estimation using strong-motion records: a review of equations for the estimation of peak ground acceleration and response spectral ordinates

Engineering seismology is the link between earth sciences and engineering. The main input of engineering seismology in engineering design are loading conditions which must satisfy certain conditions regarding their level and frequency of occurrence during the lifetime of a structure. One method for estimating these loading conditions is through equations based on strong ground motion recorded during previous earthquakes. These equations have a handful of independent parameters, such as magnitude and source-to-site distance, and a dependent parameter, such as peak ground acceleration (PGA) or spectral acceleration, and the coefficients in the equation are usually found by regression analysis. This review examines such equations in terms of data selection, accelerogram processing techniques of the strong-motion records used to construct the equations, the characterisation of earthquake source, travel path and local site used and regression techniques employed to find the final equations. It is found that little agreement has been reached in the past 30 years of ground motion estimation relation studies. Workers have chosen their techniques based on the available data, which varies greatly with geographical region. Also it is noted that there is a need to include more independent parameters into ground motion estimation equations if the large uncertainties associated with such equations are to be significantly reduced. The data required to do this is, unfortunately, scarce.

Neural networks approach and microtremor measurements in estimating peak ground acceleration due to strong motion

Peak ground acceleration is a very important factor that must be considered in construction site for examining the potential damage resulting from earthquake. The actual records by seismometer at stations related to the site may be taken as a basis, but a reliable estimating method may be useful for providing more detailed information of the strong motion characteristics. Therefore, the purpose of this study was by using back-propagation neural networks to develop a model for estimating peak ground acceleration at two main line sections of Kaohsiung Mass Rapid Transit in Taiwan. Additionally, the microtremor measurements with Nakamura transformation technique were taken to further validate the estimations. Three neural networks models with different inputs including epicentral distance, focal depth and magnitude of the earthquake records were trained and the output results were compared with available nonlinear regression analysis. The comparisons exhibited that the present neural networks model did have a better performance than that of the other methods, as the calculation results were more reasonable and closer to the actual seismic records. Besides, the distributions of estimating peak ground acceleration from both of computations and measurements might provide valuable information from theoretical and practical standpoints.

Seismic hazard model for loss estimation and risk management in Taiwan

We developed a seismic hazard model for Taiwan that integrates all available tectonic, seismicity, and seismic hazard information in the region to provide risk managers and engineers with a model they can use to estimate earthquake losses and manage seismic risk in Taiwan. The seismic hazard model is composed of two major components: a seismotectonic model and a ground-shaking model. The seismotectonic model incorporates earthquakes that are expected to occur on the Ryukyu and Manila subduction zones, on the intermediate-depth Wadati-Benioff seismicity zones, on the active crustal faults, and within seismotectonic provinces. The active crustal faults include the Chelungpu fault zone, the source of the damaging M W 7.6 Chi-Chi earthquake, and the Huangchi-Hsiaoyukeng fault zone that forms the western boundary of the Taipei Basin. The ground-shaking model uses both US, worldwide, and Taiwanese attenuation relations to provide robust estimates of peak ground acceleration and response spectral acceleration on a reference site condition for shallow crustal and subduction zone earthquakes. The ground shaking for other site conditions is obtained by applying a nonlinear soil-amplification factor defined in terms of the average shear-wave velocity in the top 30 m of the soil profile, consistent with the methodology used in the current US and proposed Taiwan building codes.