Yousef Bozorgnia

NGA Ground Motion Model for the Geometric Mean Horizontal Component of PGA, PGV, PGD and 5% Damped Linear Elastic Response Spectra for Periods Ranging from 0.01 to 10 s

We present a new empirical ground motion model for PGA, PGV, PGD and 5% damped linear elastic response spectra for periods ranging from 0.01–10 s. The model was developed as part of the PEER Next Generation Attenuation (NGA) project. We used a subset of the PEER NGA database for which we excluded recordings and earthquakes that were believed to be inappropriate for estimating free-field ground motions from shallow earthquake mainshocks in active tectonic regimes. We developed relations for both the median and standard deviation of the geometric mean horizontal component of ground motion that we consider to be valid for magnitudes ranging from 4.0 up to 7.5–8.5 (depending on fault mechanism) and distances ranging from 0–200 km. The model explicitly includes the effects of magnitude saturation, magnitude-dependent attenuation, style of faulting, rupture depth, hanging-wall geometry, linear and nonlinear site response, 3-D basin response, and inter-event and intra-event variability. Soil nonlinearity causes the intra-event standard deviation to depend on the amplitude of PGA on reference rock rather than on magnitude, which leads to a decrease in aleatory uncertainty at high levels of ground shaking for sites located on soil.

Earthquake Engineering : From Engineering Seismology to Performance-Based Engineering

This multi-contributor book provides comprehensive coverage of earthquake engineering problems, an overview of traditional methods, and the scientific background on recent developments. It discusses computer methods on structural analysis, provides access to the recent design methodologies, and serves as a reference for both professionals and researchers involved in earthquake engineering. With an entire chapter dedicated to seismic resistant design through supplemental damping and structural control, this volume includes important advances in the characteristics of earthquake ground motions, behavior and design of structures, seismic design of non-structural systems, and more.

An Overview of the NGA Project

The “Next Generation of Ground-Motion Attenuation Models” (NGA) project is a multidisciplinary research program coordinated by the Lifelines Program of the Pacific Earthquake Engineering Research Center (PEER), in partnership with the U.S. Geological Survey and the Southern California Earthquake Center. The objective of the project is to develop new ground-motion prediction relations through a comprehensive and highly interactive research program. Five sets of ground-motion models were developed by teams working independently but interacting with one another throughout the development process. The development of ground-motion models was supported by other project components, which included (1) developing an updated and expanded PEER database of recorded ground motions, including supporting information on the strong-motion record processing, earthquake sources, travel path, and recording station site conditions; (2) conducting supporting research projects to provide guidance on the selected functional forms of the ground-motion models; and (3) conducting a program of interactions throughout the development process to provide input and reviews from both the scientific research and engineering user communities. An overview of the NGA project components, process, and products is presented in this paper.

Updated Near-Source Ground-Motion (Attenuation) Relations for the Horizontal and Vertical Components of Peak Ground Acceleration and Acceleration Response Spectra

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Comparisons of the NGA ground-motion relations

The data sets, model parameterizations, and results from the five NGA models for shallow crustal earthquakes in active tectonic regions are compared. A key difference in the data sets is the inclusion or exclusion of aftershocks. A comparison of the median spectral values for strike-slip earthquakes shows that they are within a factor of 1.5 for magnitudes between 6.0 and 7.0 for distances less than 100 km. The differences increase to a factor of 2 for M5 and M8 earthquakes, for buried ruptures, and for distances greater than 100 km. For soil sites, the differences in the modeling of soil/sediment depth effects increase the range in the median long-period spectral values for M7 strike-slip earthquakes to a factor of 3. The five models have similar standard deviations for M6.5-M7.5 earthquakes for rock sites and for soil sites at distances greater than 50 km. Differences in the standard deviations of up to 0.2 natural log units for moderate magnitudes at all distances and for large magnitudes at short distances result from the treatment of the magnitude dependence and the effects of nonlinear site response on the standard deviation.

NGA-West2 Ground Motion Model for the Average Horizontal Components of PGA, PGV, and 5% Damped Linear Acceleration Response Spectra

We used an expanded PEER NGA-West2 database to develop a new ground motion prediction equation (GMPE) for the average horizontal components of PGA, PGV, and 5% damped linear pseudo-absolute acceleration response spectra at 21 periods ranging from 0.01 s to 10 s. In addition to those terms included in our now superseded 2008 GMPE, we include a more-detailed hanging wall model, scaling with hypocentral depth and fault dip, regionally independent geometric attenuation, regionally dependent anelastic attenuation and site conditions, and magnitude-dependent aleatory variability. The NGA-West2 database provides better constraints on magnitude scaling and attenuation of small-magnitude earthquakes, where our 2008 GMPE was known to be biased. We consider our new GMPE to be valid for estimating horizontal ground motion from shallow crustal continental earthquakes in an active tectonic domain for rupture distances ranging from 0 km to 300 km and magnitudes ranging from 3.3 to 7.5–8.5, depending on source mechanism.

NGA-West2 Research Project

The NGA-West2 project is a large multidisciplinary, multi-year research program on the Next Generation Attenuation (NGA) models for shallow crustal earthquakes in active tectonic regions. The research project has been coordinated by the Pacific Earthquake Engineering Research Center (PEER), with extensive technical interactions among many individuals and organizations. NGA-West2 addresses several key issues in ground-motion seismic hazard, including updating the NGA database for a magnitude range of 3.0–7.9; updating NGA ground-motion prediction equations (GMPEs) for the “average” horizontal component; scaling response spectra for damping values other than 5%; quantifying the effects of directivity and directionality for horizontal ground motion; resolving discrepancies between the NGA and the National Earthquake Hazards Reduction Program (NEHRP) site amplification factors; analysis of epistemic uncertainty for NGA GMPEs; and developing GMPEs for vertical ground motion. This paper presents an overview of the NGA-West2 research program and its subprojects.

THE VERTICAL-TO-HORIZONTAL RESPONSE SPECTRAL RATIO AND TENTATIVE PROCEDURES FOR DEVELOPING SIMPLIFIED V/H AND VERTICAL DESIGN SPECTRA

This paper presents the results of a study on the engineering characteristics of vertical ground motion. A ground-motion model for the vertical-to-horizontal ratio (V/H) of peak ground acceleration and 5%-damped acceleration response spectra was derived by using a database of 443 near-source accelerograms recorded from 36 worldwide earthquakes of M w 4.7-7.7. The recordings were all located within 60 km of the seismogenic rupture zone of worldwide shallow crustal earthquakes in active tectonic regions. We found no bias in the V/H estimates from independent analyses of vertical and horizontal response spectra. We also found V/H to be a strong function of natural period, local site conditions, and source-to-site distance; and a relatively weaker function of magnitude, faulting mechanism, and sediment depth. V/H exhibits its greatest differences at long periods on firm rock (NEHRP site category BC), where it has relatively low amplitudes, and at short periods on firm soil (NEHRP site category D), where it has amplitudes that approach 1.8 at large magnitudes and short distances. We propose a tentative simplified model for estimating V/H spectra and two relatively simple procedures for developing a preliminary vertical design spectrum that could be used for practical engineering appli-cations where site-specific spectra (e.g. from a seismic hazard analysis) are not available. Extensive vetting from the seismological and engineering communities will be needed be-fore such simplified spectra are officially accepted and adopted in codified procedures in the United States.

A Ground Motion Prediction Equation for the Horizontal Component of Cumulative Absolute Velocity (CAV) Based on the PEER-NGA Strong Motion Database

Cumulative absolute velocity (CAV), defined as the integral of the absolute acceleration time series, has been used as an index to indicate the possible onset of structural damage to nuclear power plant facilities and liquefaction of saturated soils. However, there are very few available ground motion prediction equations for this intensity measure. In this study, we developed a new empirical prediction equation for the horizontal component of CAV using the strong motion database and functional forms that were used to develop similar prediction equations for peak response parameters as part of the PEER Next Generation Attenuation (NGA) Project. We consider this relationship to be valid for magnitudes ranging from 5.0 up to 7.5–8.5 (depending on fault mechanism) and distances ranging from 0–200 km. We found the interevent, intra-event, and intracomponent standard deviations from this relationship to be smaller than any intensity measure we have investigated thus far.

Selection of Ground Motion Prediction Equations for the Global Earthquake Model

Ground motion prediction equations (GMPEs) relate ground motion intensity measures to variables describing earthquake source, path, and site effects. From many available GMPEs, we select those models recommended for use in seismic hazard assessments in the Global Earthquake Model. We present a GMPE selection procedure that evaluates multidimensional ground motion trends (e.g., with respect to magnitude, distance, and structural period), examines functional forms, and evaluates published quantitative tests of GMPE performance against independent data. Our recommendations include: four models, based principally on simulations, for stable continental regions; three empirical models for interface and in-slab subduction zone events; and three empirical models for active shallow crustal regions. To approximately incorporate epistemic uncertainties, the selection process accounts for alternate representations of key GMPE attributes, such as the rate of distance attenuation, which are defensible from available data. Recommended models for each domain will change over time as additional GMPEs are developed.