Tadahiro Kishida

NGA-West2 Database

The NGA-West2 project database expands on its predecessor to include worldwide ground motion data recorded from shallow crustal earthquakes in active tectonic regimes post-2000 and a set of small-to-moderate-magnitude earthquakes in California between 1998 and 2011. The database includes 21,336 (mostly) three-component records from 599 events. The parameter space covered by the database is M 3.0 to M 7.9, closest distance of 0.05 to 1,533 km, and site time-averaged shear-wave velocity in the top 30 m of VS30 = 94 m/s to 2,100 m/s (although data becomes sparse for distances >400 km and VS30 > 1,200 m/s or <150 m/s). The database includes uniformly processed time series and response spectral ordinates for 111 periods ranging from 0.01 s to 20 s at 11 damping ratios. Ground motions and metadata for source, path, and site conditions were subject to quality checks by ground motion prediction equation developers and topical working groups.

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.

Implications of the Mw9.0 Tohoku-Oki Earthquake for Ground Motion Scaling with Source, Path, and Site Parameters

The Mw9.0 Tohoku-oki Japan earthquake produced approximately 2,000 ground motion recordings. We consider 1,238 three-component accelerograms corrected with component-specific low-cut filters. The recordings have rupture distances between 44 km and 1,000 km, time-averaged shear wave velocities of VS30 = 90 m/s to 1,900 m/s, and usable response spectral periods of 0.01 sec to >10 sec. The data support the notion that the increase of ground motions with magnitude saturates at large magnitudes. High-frequency ground motions demonstrate faster attenuation with distance in backarc than in forearc regions, which is only captured by one of the four considered ground motion prediction equations for subduction earthquakes. Recordings within 100 km of the fault are used to estimate event terms, which are generally positive (indicating model underprediction) at short periods and zero or negative (overprediction) at long periods. We find site amplification to scale minimally with VS30 at high frequencies, in contrast with other active tectonic regions, but to scale strongly with VS30 at low frequencies.

Liquefaction at Strong Motion Stations and in Urayasu City during the 2011 Tohoku-Oki Earthquake

The 2011 MW = 9.0 Tohoku-oki earthquake generated a large number of unique soil liquefaction case histories, including cases with strong ground motion recordings on liquefiable or potentially liquefiable soils. We have compiled a list of 22 strong motion stations (SMS) where surface evidence of liquefaction was observed and 16 SMS underlain by geologically recent sediments or fills where surface evidence of liquefaction was not observed. Pre-earthquake standard penetration test data and borehole shear wave velocity (Vs) profiles are available for some stations, but critical information, such as grain size distribution and fines plasticity, are often lacking. In the heavily damaged city of Urayasu, we performed post-earthquake cone penetration testing at seven SMS and Vs profiles, using surface wave methods at 28 additional locations to supplement existing geotechnical data. We describe the liquefaction effects in Urayasu, the available site characterization data, and our initial data interpretations.

Seismic Demand of the Liquefaction Potential with Equivalent Number of Cycles for Probabilistic Seismic Hazard Analysis

AbstractEquivalent number of cycles (Ncyc) is a significant factor in assessing liquefaction potential during earthquakes. However, the effects of Ncyc are considered a deterministic value by using a magnitude scaling factor, and the uncertainties of these effects have not been included in the current design practice. This paper calculates Ncyc within the soil mass by deconvolution analysis as a function of the period of soil layer from the ground surface (Ts) and the soil property (b) using a wide range of acceleration time histories. The predictive model of Ncyc is developed as variable dependent on earthquake magnitude, peak ground acceleration (PGA), and ratio of spectral acceleration, Ts and b. Then, the Ncyc model is combined with the ground-motion prediction equation of PGA and the prediction equation of seismic shear-stress reduction coefficient (rd) to obtain the prediction equation of the seismic demand of the liquefaction potential (K1cyc). The standard deviation of K1cyc is also modeled on the...

Site Effects for the Sacramento-San Joaquin Delta

Seismic site response and site effects models are presented for levees in the Sacramento-San Joaquin Delta where the subsurface soils include thick deposits of highly organic soils. Sources of uncertainty that contribute to the variation of seismic wave amplification are investigated, including variations in the input ground motions, soil profiles, and dynamic soil properties through Monte Carlo simulations of equivalent-linear site response analyses. Regression models for seismic wave amplification for levees in the Delta are presented that range from a function of peak outcrop acceleration alone to a vector of response spectra ordinates and soil profile parameters. The site effects models were incorporated into a probabilistic seismic hazard analysis for a representative location, and the relative impacts of the various models on the computed hazard are evaluated.

Seismic Response of Levees in the Sacramento-San Joaquin Delta

The seismic response of levees in the Sacramento-San Joaquin Delta, where the subsurface soils include thick deposits of highly organic soils, is evaluated. One-dimensional (1-D) and two-dimensional (2-D) equivalent-linear analyses were performed that accounted for variability in ground motions, dynamic properties, and soil profiles. Regression models were developed for: (1) the ratio of spectral accelerations at levee crests computed by 2-D versus 1-D response analyses, (2) stress reduction factors from 1-D site response analyses and seismic coefficient reduction factors for various failure surface depths from the 2-D response analyses, and (3) Newmark sliding block displacements computed for the input NEHRP site D ground motions and the computed seismic coefficient time series. The results of these regression models are compared to those obtained in previous studies involving different soil conditions, geometries, and motions. Newmark sliding block displacement hazard curves were calculated for a representative site in the Sacramento-San Joaquin Delta, and the contributions of various uncertainties to the displacement hazard curves are described.

Comparison and Correction of Modulus Reduction Models for Clays and Silts

AbstractPrediction models of normalized modulus reduction curves (G/Gmax) for clays and silts have been proposed by several researchers in the past decades. However, model uncertainties have been recognized in these studies. This study compares five prediction models of G/Gmax from previous studies, which use common predictor variables of cyclic shear strain amplitude, effective confining stress, and plasticity index. The relative differences between these models are described against these predictor variables. Then the model biases are evaluated through residual analyses using the modulus reduction database. Modulus reductions of G are also discussed by combining the prediction models of G/Gmax and Gmax to illustrate the importance of these combinations. Correlations among the residuals of ln(G) are calculated, and the correction factors of the G/Gmax model are presented conditioned on the Gmax and shear strength measurements.

Conditional Mean Spectra Given a Vector of Spectral Accelerations at Multiple Periods

Conditional mean spectra (CMS) are generally defined as expected pseudo-spectral accelerations (PSA) conditioned on uniform hazard spectra (UHS) at a selected period. Many design practices prefer CMS because UHS conservatively envelop the large amplitudes of PSA within a single ground motion. However, in some situations, CMS are preferred given target spectra from UHS at multiple periods (CMSV) for satisfying design requirements. This study presents the mathematical formula of CMSV and describes the methodology to compute CMSV with application examples. The presented method for computing CMSV can provide the transitional design spectra between currently used CMS and UHS depending on the selected conditioning periods.

Response to Discussion by P. Malhotra on “NGA-West2 Research Project”

Manuscript Reference: Yousef Bozorgnia, Norman A. Abrahamson, Linda Al Atik, Timothy D. Ancheta, Gail M. Atkinson, Jack W. Baker, Annemarie Baltay, David M. Boore, Kenneth W. Campbell, Brian S.-J. Chiou, Robert Darragh, Steve Day, Jennifer Donahue, Robert W. Graves, Nick Gregor, Thomas Hanks, I. M. Idriss, Ronnie Kamai, Tadahiro Kishida, Albert Kottke, Stephen A. Mahin, Sanaz Rezaeian, Badie Rowshandel, Emel Seyhan, Shrey Shahi, Tom Shantz, Walter Silva, Paul Spudich, Jonathan P. Stewart, Jennie Watson-Lamprey, Kathryn Wooddell, and Robert Youngs, Earthquake Spectra, vol. 30, no. 3 (August 2014): 973–987.