A Validation Study of a Seismically Induced Ground Strain Model Using Strong Motion Array Data

This study concerns ground strains that result from spatially variable ground motions unrelated to ground failure. Prior empirical work shows a dependence of peak ground strain (PGS) on peak ground displacement (PGD) but is applicable only for weak motions (PGD \u3c 10 cm). Prior semi-empirical work, in which strains were evaluated from simulated ground motions that preserve the coherency, Fourier amplitude variability and wave passage observed in array recordings, found a similar dependence of PGS on PGD but also a significant dependence on separation distance of observation points. Here we describe a procedure to calculate PGS between pairs of stations in an array to test the separation dependence of PGS. The Lotung LSST array was selected due to its closely spaced stations (6 to 85 m) and large number of recordings. The PGS estimated from station pairs from 11 events illustrate that the distance dependence of PGS is statistically significant, with PGS increasing as separation distance decreases

Conditional simulation of spatially variable motions on 2D grid

Conditional simulation of spatially variable earthquake ground motion is required to incorporate kinematic interaction effects within response history analysis of structures. We present an approach that takes as input a seed motion and models for Fourier amplitude and phase variability that are functions of frequency and separation distance. The conditional simulation outputs are ground motions modified from the seed on a 2D grid having appropriate non-stationary characteristics while maintaining compatibility with the amplitude and phase variability models. The method applies the Fourier Integral Method to simulate random fields and extends short time Fourier transform analysis and synthesis to account for time and frequency nonstationary characteristics of earthquake time series.Non UBCUnreviewedThis collection contains the proceedings of ICASP12, the 12th International Conference on Applications of Statistics and Probability in Civil Engineering held in Vancouver, Canada on July 12-15, 2015. Abstracts were peer-reviewed and authors of accepted abstracts were invited to submit full papers. Also full papers were peer reviewed. The editor for this collection is Professor Terje Haukaas, Department of Civil Engineering, UBC Vancouver.FacultyOthe

Engineering Characterization of Earthquake Ground Motion Coherency and Amplitude Variability

Earthquake ground motions exhibit spatial variability manifest as random variations of Fourier amplitude and phase. These variations increase with frequency and distance between observations points (d), and introduce demands for lifeline systems and foundations. Spatially variable ground motions (SVGM) are quantified by: (1) apparent horizontal wave velocity (Vapp), which controls wave passage effects that shift Fourier phase; (2) lagged coherency, representing random phase variations; and (3) standard deviation terms representing Fourier amplitude variability. We examine empirical relations for the three SVGM sources through analysis of data from the Borrego Valley Differential Array (BVDA) in California and re-analysis of data from the LSST array in Taiwan, both having a number of stations at d < 120 m. We show that Vapp from the two arrays have medians of 2.1 and 2.6 km/s and natural log standard deviations of about 0.5. We show that previous models for lagged coherency and standard deviation from amplitude variability have bias, and propose revisions. We show that amplitude and coherency residuals from the baseline model are uncorrelated, although frequency-to-frequency residuals for both quantities are weakly correlated for small frequency offsets

Engineering Characterization of Earthquake Ground Motion Coherency and Amplitude Variability

Earthquake ground motions exhibit spatial variability manifest as random variations of Fourier amplitude and phase. These variations increase with frequency and distance between observations points (d), and introduce demands for lifeline systems and foundations. Spatially variable ground motions (SVGM) are quantified by: (1) apparent horizontal wave velocity (Vapp), which controls wave passage effects that shift Fourier phase; (2) lagged coherency, representing random phase variations; and (3) standard deviation terms representing Fourier amplitude variability. We examine empirical relations for the three SVGM sources through analysis of data from the Borrego Valley Differential Array (BVDA) in California and re-analysis of data from the LSST array in Taiwan, both having a number of stations at d < 120 m. We show that Vapp from the two arrays have medians of 2.1 and 2.6 km/s and natural log standard deviations of about 0.5. We show that previous models for lagged coherency and standard deviation from amplitude variability have bias, and propose revisions. We show that amplitude and coherency residuals from the baseline model are uncorrelated, although frequency-to-frequency residuals for both quantities are weakly correlated for small frequency offsets

Preliminary estimation of seismically induced ground strains from spatially variable ground motions

A model for horizontal peak ground strain (PGS) is developed in consideration of three fundamental contributions to spatially variable ground motion (SVGM): (1) spatial incoherence effects, which contribute to phase variability in a stochastic sense; (2) wave passage effects, which contribute to phase variability in a deterministic sense; and (3) amplitude variability. Previous models for each of these effects are reviewed and compared to array data from Borrego Valley, California. Published empirical models for coherency and amplitude variability are found to represent reasonably well the Borrego data. We extend previous work by considering correlations of amplitude and phase variability (generally found to be small) and characterizing the coherency-dependent probabilistic distribution of phase variability. Using the aforementioned amplitude and phase variability models, a procedure is developed to generate simulated acceleration records from a seed record. The procedure is applied to a suite of Northridge earthquake recordings to predict ground strains, which are found to be strongly dependent on the peak ground velocity (PGV) of the seed motion and the separation distance between the seed and simulated motions. The dependence of PGS on PGV saturates for large PGV (> 50 cm/sec)

PEER NGA-East database

This article documents the earthquake ground motion database developed for the NGA-East Project, initiated as part of the Next Generation Attenuation (NGA) research program and led by the Pacific Earthquake Engineering Research Center (PEER). The project was focused on developing a ground motion characterization model (GMC) model for horizontal ground motions for the large region referred to as Central and Eastern North America (CENA). The CENA region covers most of the U.S. and Canada, from the Rocky Mountains to the Atlantic Ocean and is characterized tectonically as a stable continental region (SCR). The ground-motion database includes the two- and three-component ground-motion recordings from numerous selected events relevant to CENA (M \u3e 2.5, with distances up to 3500 km) that have been recorded since 1976. The final database contains over 27,000 time series from 82 earthquakes and 1271 recording stations. The ground motion database includes uniformly processed time series, 5% damped pseudo-spectral acceleration (PSA) median-component ordinates for 429 periods ranging from 0.01 to 10 s, duration and Arias intensity in 5% increments, and Fourier amplitude spectra for different time windows. Ground motions and metadata for source, path, and site conditions were subjected to quality checks by topical working groups and the ground-motion model (GMM) developers. The NGA-East database constitutes the largest database of processed recorded ground motions in SRCs and is publicly available from the PEER ground-motion database website