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2006, Advances in Structural Engineering
The earthquake attenuation behaviour is a critical part of seismic hazard modelling for regions of low and moderate seismicity. This paper presents a new approach for attenuation modelling, which does not involve the use of strong motion data, and is based on taking measurements of the shear wave velocity (SWV) in bedrock by a noninvasive technique to characterize the transmission of seismic waves. The developed filters are then applied to the generic source model for intraplate earthquakes for calculating the frequency content of seismic waves at the bedrock surface and was used as input to soil response analyses for the determination of site seismic hazard. Ground motion parameters and response spectra are then obtained from the stochastically simulated accelerograms to develop representative attenuation models for rock conditions. The described approach of obtaining a seismic attenuation relationship based on modelling the rock and soil crustal properties is not constrained to an...
Response spectral attenuation law is a useful tool used in the seismic hazard assessment. The principle purpose of the study was to develop the attenuation laws based on the acceleration response spectra at the time periods of 0.3 and 1 sec for 2011 Sikkim and 2009 Bhutan earthquakes, having magnitudes of greater than 6.0. The study was conducted on the basis of the earthquake ground motion data recorded at 22 different stations with strong ground motion accelerographs and the acceleration response spectra were generated for different time periods and soil profiles. The results of the study supported the fact of attenuation relations that the response spectral amplitude of the ground motion increases with earthquake magnitude and decrease as propagation distance increases. The acceleration response at 0.3 sec was significantly stronger at short distance than the response at 1 sec for the both events in all directions. The results also observed that the soil values remain stronger than the rock values at shorter time periods. The developed acceleration response spectra based attenuation equations may be used in better ground motion estimation and in probabilistic seismic hazard analysis for Bangladesh and its surrounding areas.
Earthquake refers to the sudden release of energy in the earth's crust that creates seismic waves. Earthquakes are unpredictable and their intensity attenuates over long distances. In an idealized situation earth is considered to be elastic and the seismic waves can propagate indefinitely once they are excited. But it is known that the real earth is not perfectly elastic. This causes the waves that are propagating to attenuate with time as they travel. Uncertainties persist in the attenuation equations as they depend on many factors such as epicentral distance, focal depth, geology, fault characteristics, magnitude, topography etc. Many attenuation equations have been developed over the years considering various factors. The present work focuses on validating and critically comparing popular attenuation equations such as etc. for earthquake data of recent times (2005 onwards). An attempt is made to collect as much information as possible from different stations during different earthquakes. The accuracy and effectiveness of different attenuation equations are verified. Also attempt is made to study the sensitiveness of different factors influencing the seismicity. Further it has been inferred that each formula has its own merits and demerits and an attempt is made to identify the most effective attenuation formula for wide range of earthquake data.
Earthquake Spectra, 2007
Spatial distribution of ground motion data of recent earthquakes unveiled some features of peak ground acceleration (PGA) attenuation with respect to closest distance to the fault ͑R͒ that current predictive models may not effectively capture. As such, PGA: (1) remains constant in the near-fault area, (2) may show an increase in amplitudes at a certain distance of about 3-10 km from the fault rupture, (3) attenuates with slope of R −1 and faster at farther distances, and (4) intensifies at certain distances due to basin effect (if basin is present). A new ground motion attenuation model is developed using a comprehensive set of ground motion data compiled from shallow crustal earthquakes. A novel feature of the predictive model is its new functional form structured on the transfer function of a single-degree-of-freedom oscillator whereby frequency square term is replaced with closest distance to the fault. We are proposing to fit ground motion amplitudes to a shape of a response function of a series (cascade) of filters, stacked separately one after another, instead of fitting an attenuation curve to a prescribed empirical expression. In this mathematical model each filter represents a separate physical effect.
2006
The "Next Generation of Ground Motion Attenuation Models" (NGA) project is a partnered research program conducted by Pacific Earthquake Engineering Research Center-Lifelines Program (PEER-LL), U.S. Geological Survey (USGS), and Southern California Earthquake Center (SCEC). The project has the objective of developing updated ground motion attenuation relationships through a comprehensive and highly interactive research program. Five sets of updated attenuation relationships are developed by teams working independently but interacting throughout the development process. The main technical issues being addressed by the NGA teams include magnitude scaling at close-in distances, directivity effects, polarization of near-field motion (faultstrike-normal component vs. fault-strike-parallel component), nonlinear amplification by shallow soil, and sedimentary basin amplification. The attenuation relationships development is also facilitated by the development of an updated and expanded database of recorded ground motions; conduct of supporting research projects to provide constraints on the selected functional forms of the attenuation relationships; and a program of interactions throughout the development process to provide input and reviews from both the scientific research community and the engineering user community. An overview of the NGA project components, process, and products developed by the project is presented in this paper.
Earthquake Engineering & Structural Dynamics, 2000
Seismic hazard modelling for regions of low and moderate seismicity is often hampered by the lack of indigenous strong motion data. Thus, empirical attenuation models developed for analogous &data rich' seismic regions have typically been used as the basis for de"ning the ground motion attenuation properties of the subject region. Alternatively, limited data recorded from small tremors, or aftershocks, have been used to extrapolate the attenuation relationships of potentially destructive but infrequent, large magnitude events. However, as explained and demonstrated in this paper, both approaches are prone to error in the absence of a rational and viable analytical framework to support their application. Addressing this, the methodology introduced herein combines the component attenuation model (CAM) (developed in the companion paper (Earthquake Engng Struct. Dyn. 2000; 29:1457}1489) with observations on local isolated earthquake events, to determine representative design response spectra for both force-and displacementbased seismic applications.
Bulletin of the Seismological Society of America, 2004
This study presents effective probabilistic procedures for evaluating ground-motion hazard at the free-field surface of a nonlinear soil deposit located at a specific site. Ground motion at the surface, or at any depth of interest within the soil formation (e.g., at the structure foundation level), is defined here in terms either of a suite of oscillator-frequency-dependent hazard curves for spectral acceleration, , or of one or more spectral acceleration uniform-hazard spectra, each associated s S (f) a with a given mean return period. It is presumed that similar information is available for the rock-outcrop input. The effects of uncertainty in soil properties are directly included. This methodology incorporates the amplification of the local soil deposit into the framework of probabilistic seismic hazard analysis (PSHA). The soil amplification is characterized by a frequency-dependent amplification function, AF(f), where f is a generic oscillator frequency. AF(f) is defined as the ratio of to the spectral s S (f) a acceleration at the bedrock level,. The estimates of the statistics of the ampli-s S (f) a fication function are obtained by a limited number of nonlinear dynamic analyses of the soil column with uncertain properties, as discussed in a companion article in this issue (Bazzurro and Cornell, 2004). The hazard at the soil surface (or at any desired depth) is computed by convolving the site-specific hazard curve at the bedrock level with the probability distribution of the amplification function. The approach presented here provides more precise surface ground-motion-hazard estimates than those found by means of standard attenuation laws for generic soil conditions. The use of generic ground-motion predictive equations may in fact lead to inaccurate results especially for soft-clay-soil sites, where considerable amplification is expected at long periods, and for saturated sandy sites, where high-intensity ground shaking may cause loss of shear strength owing to liquefaction or to cyclic mobility. Both such cases are considered in this article. In addition to the proposed procedure, two alternative, easier-to-implement but approximate techniques for obtaining hazard estimates at the soil surface are also briefly discussed. One is based on running a conventional PSHA with a rockattenuation relationship modified to include the soil response, whereas the other consists of using a simple, analytical, closed-form solution that appropriately modifies the hazard results at the rock level.
2012
Attenuation relationships are commonly used for engineering studies to estimate the peak ground acceleration values. This paper presents the role of attenuation relationship in defining the seismic hazard in an area. It is seen that the seismic hazard in an area, which is calculated using attenuation relationships, is mostly controlled by the type of attenuation relationship used in the study. The present work aims to study the effect of attenuation relationship on seismic hazard study. In the present work, seismic hazard maps have been prepared in the seismically very active northeast Himalaya using the approach given by
This study presents a framework to perform Probabilistic Seismic Hazard Analysis (PSHA) for soil sites, which yields accurate soil UHS and associated seismic hazard curves. The variabilities of soil parameters, the nonlinear responses of soils, and the vector-valued site responses analysis comprehensively integrate into the PSHA for soil sites. In this framework, site amplification is used to modify the Ground Motion Prediction Equations (GMPEs) to make them suitable for a soil site. Based on the modified GMPEs with updated uncertainties, PSHA for soil sites are performed accurately; thus, acceptable soil UHS and associated seismic hazard curves considering site-specific uncertainties could be achieved. Using an example soil site, influences of soil parameter variabilities and soil nonlinearity on UHS and associated seismic hazard curves are discussed in this study.
Journal of Earthquake Engineering, 2007
The aim of this article is to investigate the ground motion attenuation of the most industrialized and populated regions of Italy, evaluating the capability of different approaches to estimate site dependent models. The 5.2 magnitude earthquake on November 24, 2004 shocked the areas of Northern Italy producing damage of about 215 million euros. The data set, including 243 earthquakes of local magnitude up to 5.2, has been collected in the period December 2002-October 2005 by 30 threecomponent seismic stations managed by Istituto Nazionale di Geofisica e Vulcanologia, Sezione of Milano (INGV-MI). Empirical attenuation relationships have been estimated for horizontal peak ground velocity (PGHV), acceleration (PGHA), displacement (PGHD), and for response spectral acceleration (SA) for periods between 0.1 and 1.5 s. To estimate suitable attenuation models, in particular for sites characterized by thick sedimentary geological formations, a soil discrimination based on EU8 code can lead to wrong evaluations. On the contrary, a classification based on H/V spectral ratios of seismic ambient noise (NHV) allows the models to fit better real and predicted data and to reduce the uncertainties of the process. For each receiver, NHV have been strengthened by additional H/V spectral ratio of earthquake data (EHV), calculated considering different portions of the analysed signals. In order to validate the PGHA attenuation relationship for greater magnitudes, accelerometric records, relative to Central-Northern Italy strong motions occurring in the last 30 years, have been collected and superimposed to our attenuation curves. 5 5 10 15 20 25 30 35 2 M. Massa et al.
Stochastic Control, 2010
Earthquake Engineering & Structural Dynamics
Seismic hazard modelling for regions of low and moderate seismicity is often hampered by the lack of indigenous strong motion data. Thus, empirical attenuation models developed for analogous &data rich' seismic regions have typically been used as the basis for de"ning the ground motion attenuation properties of the subject region. Alternatively, limited data recorded from small tremors, or aftershocks, have been used to extrapolate the attenuation relationships of potentially destructive but infrequent, large magnitude events. However, as explained and demonstrated in this paper, both approaches are prone to error in the absence of a rational and viable analytical framework to support their application. Addressing this, the methodology introduced herein combines the component attenuation model (CAM) (developed in the companion paper (Earthquake Engng Struct. Dyn. 2000; 29:1457}1489) with observations on local isolated earthquake events, to determine representative design response spectra for both force-and displacementbased seismic applications.
IASME/WSEAS International Conference …, 2007
A site-dependent response spectral attenuation model is an important element in a site-dependent seismic hazard assessment. Seismic attenuation behaviour is controlled by a large number of wave modification mechanisms, some of which have characteristics specific to a local area or a particular site, whilst others can be generalised to the entire seismic region. Factors representing these mechanisms are often not resolved. An attenuation modelling approach is demonstrated in this paper, to evaluate individual regional and local wave modification factors. The upper-crust amplification factor computed from the modelled rock shear wave velocity profile was then combined with predicted attenuation parameters to determine the upper-crust modification filter function associated with Singaporean geological formations. Stochastic simulations of the seismological model for the magnitude 9.3 Aceh earthquake (Indonesia) on the 26 th of December in 2004, were performed and compared with the response spectra recorded on a rock site in Singapore.
2004
A pilot study conducted in Melbourne involving shear wave velocity (SWV) profiling in the bedrock formation is used to illustrate a new approach for predicting the potential seismic attenuation characteristics for the region. A complete SWV profile for the entire seismogenic depth of the earth's crust is first developed by combining the SWV profiles measured by the Spatial Auto-Correlation (SPAC) method with regional information provided by a global crustal database. Secondly, the crustal amplification function calculated from the representative SWV profile is combined with predicted attenuation parameter values (kappa k and Q 0 ) to form a complete filter function representing the potential wave modification characteristics of the earth's crust in the area. Thirdly, a seismic attenuation model is developed by combining this filter function with the source function of the earthquake, using a stochastic procedure and the framework of the Component Attenuation Model (CAM). Lastly, the developed attenuation relationship is compared with seismic Intensity information obtained from three historical earthquakes that affected Melbourne and its surrounding region. The modelling described in this paper only deals with seismic wave modifications within the bedrock formation whilst modifications within the soil sedimentary layers are to be addressed in separate analyses.
The significance of near-surface attenuation in bedrock, as distinct from attenuation in unconsolidated soft soil sediments, has been identified. The k parameter, which characterizes the extent of this attenuation mechanism, is generally difficult to measure, particularly in regions of low and moderate seismicity. Empirical correlation of k with the near-surface shear wave velocity parameter in rock has been developed using global information obtained from limited independent studies. The influence of shaking intensity on the value of k has been found to be negligible in conditions that are consistent with the average seismicity of Australia (as also for other intraplate regions). Thus, adjustment in the value of k to account for variations in earthquake magnitude, or the intensity of ground shaking, has not been recommended for intraplate conditions. In parallel with the empirical correlations, values of k have also been obtained from calibration analyses employing stochastic simul...
The Component Attenuation Model (CAM) has been developed over the past five years to model the seismic demand for low and moderate seismic regions. The key objective of this paper is to explain the underlying concept of CAM which is primarily to address problems arising from the paucity of strong motion records. Emphasis is on how to incorporate regional geological and seismological parameters into the modelling. Important features to highlight include the modelling for source effects, long distance attenuation, regional upper crustal effects, and soil resonance with particular reference to velocity and displacement response spectra. CAM is currently used in the assessment of seismic hazard for Australia, Southern and Eastern China, Singapore and Indo-China.
This paper presents a probabilistic framework to accurately estimate ground motions at the soil surface. In this framework, the variability of soil parameters, the nonlinear property of soils, and the vector-valued seismic site responses analysis comprehensively integrate into Probabilistic Seismic Hazard Analysis (PSHA) for soil sites. Local soil conditions greatly affect ground motions propagating from bedrock to soil surface; the evaluation of ground motions at the soil surface needs to consider effects of the local soil conditions. Ground Motion Prediction Equations (GMPEs) using the generic soil to characterize local soil conditions are possible to estimate ground motions at the soil surface, but the estimation is not acceptable for critical structures because of lacking accuracy. Site amplification is used to modify the bedrock GMPEs to make them suitable for soil site. Based on the modified GMPEs, PSHA for soil sites are performed accurately and a method to construct acceptable soil UHS are proposed. Finally, this paper constructs the soil UHS for an example soil site by GMPEs and by the modified GMPEs, respectively, compares the soil UHS by the different methods, studies influences of variability of soil parameters and nonlinear property of soils on spectral shapes and spectral amplitudes of UHS.
Earthquake Spectra, 2010
This paper presents the process and fundamental results of a comprehensive ground motion prediction equation (GMPE, or “attenuation” relationship) developed for inelastic response spectra. We used over 3,100 horizontal ground motions recorded in 64 earthquakes with moment magnitudes ranging from 4.3–7.9 and rupture distances ranging from 0.1–199 km. For each record, we computed inelastic spectra for ductility ranging from one (elastic response) to eight. Our GMPE correlates inelastic spectral ordinates to earthquake magnitude, site-to-source distance, fault mechanism, local soil properties, and basin effects. The developed GMPE is used in both deterministic and probabilistic hazard analyses to directly generate inelastic spectra. This is in contrast to developing “attenuation” relationships for elastic response spectra, carrying out a hazard analysis, and subsequently adopting approximate rules to derive inelastic response from elastic spectra.
Bulletin of the Seismological Society of …, 1996
Italian strong-motion data were used to study the attenuation of response spectra and to simulate artificial accelerograms as a function of magnitude, distance, and site geology. The database has already been utilized for the study of the attenuation of peak ground acceleration (PGA) and velocity and consists of 95 accelerograms from 17 earthquakes of magnitudes ranging from 4.6 to 6.8. Using multiple regressions, we developed empirical predictive equations for the vertical and horizontal components of response spectra corresponding to 14 frequencies ranging from 0.25 to 25 Hz. Predictive equations, aimed at the ground-motion simulation, were also estimated for time-dependent frequency parameters, strong ground motion duration, and Arias intensity.
2005
Ground-motion attenuation models have been derived for the Australian crust. These models employ both empirical and stochastic methods and are the first spectral groundmotion models to be based entirely on Australian ground-motion data. Two key datasets have been employed to derive empirical ground-motion attenuation models for Australia; one from data recorded in the Palaeozoic crust of southeastern Australia (SEA) and the other from the Archean shield region of southwestern Western Australia (WA). Empirical ground-motion models are derived for each of these datasets. In general, low-frequency (e.g. 1 Hz) ground-motion energy appears to attenuate less in WA than in SEA. These empirical models suggest that SEA has similar near-source attenuation with eastern North America. Stochastic methods are employed to simulate ground-motions for larger earthquakes in regions where recordings from real events are not available. These models are largely based upon source and attenuation paramete...
European Online Journal of Natural and Social Sciences, 2013
Considering the situation of Iran on the seismic belt and its permanent exposure to earthquakes with different magnitudes, in design of structures, special attention should be paid to seismic parameters. To this effect, and in order to reduce the structures exposures to the expectable earthquakes short-term, mid-term and longterm planning is required. Numerous methods have been so far applied to assessment of earthquake magnitude some of which were built up on a single parameter such as PGA and PGV and some others were multi-parameters such as spectral displacement and spectral acceleration (SA). At any rate, today scientists using new parameters such as earthquake energy, earthquake intensity have introduced different methods for design purposes. One of the most widely applied design methods is the single parameter measure Peak Ground Acceleration (PGA) which has its own limitations and shortcomings such as error input into the calculations and ignoring earthquake content. Therefore, researchers decided by applying spectrum-based attenuation relation to use direct relationships for determining input data of structure design. In line with these efforts, profiting from SA-based power attenuation relation, this research as a case study attempts to retry the seismic hazard analysis calculations on the Qazvin region.
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