Empirical ground motion models for the average horizontal component from shallow crustal earthquakes in active tectonic regions are derived using the PEER NGA-West2 database. The model is applicable to magnitudes 3.0–8.5, distances 0–300 km, and spectral periods of 0–10 s. The model input parameters are the same as those used by Abrahamson and Silva (2008) , with the following exceptions: the loading level for nonlinear effects is based on the spectral acceleration at the period of interest rather than the PGA; and the distance scaling for hanging wall (HW) effects off the ends of the rupture includes a dependence on the source-to-site azimuth. Regional differences in large-distance attenuation and V S30 scaling between California, Japan, China, and Taiwan are included. The scaling for the HW effect is improved using constraints from numerical simulations. The standard deviation is magnitude-dependent, with smaller magnitudes leading to larger standard deviations at short periods, but smaller standard deviations at long periods. Directivity effects are not included through explicit parameters, but are captured through the variability of the empirical data.

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 nonlinear soil amplification models developed by Walling et al. (2008) are revisited for three main reasons: (a) the simulation database on which the models were developed has been updated and extended, (b) two alternatives for the input shaking parameter—(PGA and Sa( T))—are explored, and (c) a constraint on the nonlinearity at long periods is removed. The model is based on site amplification factors, relative to a V S30 = 1;180 m/s site. Simulations included a wide range of soil profiles, shaking amplitudes and soil properties, from which only a subset was used herein. Finally, four models for the nonlinear site amplification are developed using two nonlinear material property models (peninsular range and EPRI) and two input-shaking parameters ( PGA1180 and Sa1180( T)). These results are intended for use by the NGA-West2 developers to constrain the nonlinear scaling of the site response for the horizontal ground motion models.

A presentation of the model parameters and comparison of the median ground-motion values from the NGA-West2 GMPEs is presented for a suite of deterministic cases. In general, the median ground motions are similar, within a factor of about 1.5–2.0 for 5 < M < 7 and distances between 10–100 km. Differences increase (on the order of 2–3) for large-magnitude (M > 8) earthquakes at large distances ( R > 100–200 km) and for close distances ( R < 10 km). A similar increase is observed for hanging-wall sites, and slightly larger differences are observed for soil sites as opposed to rock sites. Regionalization of four of the GMPEs yields similar attenuation rate adjustments based on the different regional data sets. All five GMPE aleatory variability models are a function of magnitude with higher overall standard deviations values for the smaller magnitudes when compared to the large-magnitude events.

SUMMARYAn innovative approach is presented, in which the discontinuous deformation analysis (DDA) method is used to estimate historic ground motions by back analysis of unique structural failures in archaeological sites. Two archaeological sites in Israel are investigated using this new approach and results are presented in terms of displacement evolution of selected structural elements in the studied masonry structure. The response of the structure is studied up to the point of incipient failure, in a mechanism similar to the one observed in the field. Structural response is found to be very sensitive to dynamic parameters of the loading function such as amplitude and frequency.Prior to back analysis of case studies, two validations are presented. Both compare the performance of DDA with analytical solutions and present strong agreement between the two.Using comprehensive sensitivity analyses, the most likely peak ground acceleration (PGA) and frequency that must have driven the observed block displacements are found for the two case studies-the Nabatean city of Mamshit and the medieval fortress of Nimrod in southern and northern Israel, respectively. It is found that horizontal peak ground accelerations (HPGA) of 0.5g and 1g were required to generate the observed deformations in Mamshit and Nimrod, respectively. Although these might seem too high, considering structural and topographic amplifications it is concluded that the analyses suggest ground motions of 0.2g at a frequency of 1.5 Hz for Mamshit and up to 0.4g at a frequency of 1 Hz for Nimrod. These values provide constraints on the seismic risk associated with these regions as appears in the local building code using a completely independent approach.