Showing papers by "David M. Boore published in 2013"

The Uses and Limitations of the Square‐Root‐Impedance Method for Computing Site Amplification

Abstract: The square-root-impedance (SRI) method is a fast way of computing approximate site amplification that does not depend on the details from velocity mod- els. The SRI method underestimates the peak response of models with large imped- ance contrasts near their base, but the amplifications for those models is often close to or equal to the root mean square of the theoretical full resonant (FR) response of the higher modes. On the other hand, for velocity models made up of gradients, with no significant impedance changes across small ranges of depth, the SRI method system- atically underestimates the theoretical FR response over a wide frequency range. For commonly used gradient models for generic rock sites, the SRI method underestimates the FR response by about 20%-30%. Notwithstanding the persistent underestimation of amplifications from theoretical FR calculations, however, amplifications from the SRI method may often provide more useful estimates of amplifications than the FR method, because the SRI amplifications are not sensitive to details of the models and will not exhibit the many peaks and valleys characteristic of theoretical full resonant amplifications (jaggedness sometimes not seen in amplifications based on averages of site response from multiple recordings at a given site). The lack of sensitivity to details of the velocity models also makes the SRI method useful in comparing the response of various velocity models, in spite of any systematic underestimation of the response. The quarter-wavelength average velocity, which is fundamental to the SRI method, is useful by itself in site characterization, and as such, is the fundamental parameter used to characterize the site response in a number of recent ground-motion prediction equations.

GEM-PEER Task 3 Project : Selection of a Global Set of Ground Motion Prediction Equations

Abstract: Ground-motion prediction equations (GMPEs) relate a ground-motion parameter (e.g., peak ground acceleration, PGA) to a set of explanatory variables describing the earthquake source, wave propagation path and local site conditions. In the past five decades many hundreds of GMPEs for the prediction of PGA and linear elastic response spectral ordinates (e.g., pseudospectral acceleration, PSA) have been published. The Global Earthquake Model (GEM) Global GMPEs project, coordinated by the Pacific Earthquake Engineering Research Center (PEER), brought together ground-motion experts from various institutions around the world to develop recommendations on what GMPEs should be used by GEM when conducting global seismic hazard assessments. The GEM-PEER Project has seven tasks, as listed below: Task 1a Defining a Consistent Strategy for Modeling Ground Motions Task 1b Estimating Site Effects in Parametric Ground Motion Models Task 2 Compile and Critically Review GMPEs Task 3 Selection of a Global Set of GMPEs Task 4 Include Near-Fault Effects Task 5 Build an Inventory of Recorded Waveform Databases Task 6 Design the Specifications to Compile a Global Database of Soil Classification This report presents the methodology used in, and results of, Task 3, Selection of a Global Set of GMPEs. The reports of the other tasks of the GEM-PEER project are published by the GEM foundation and posted at: http://www.globalquakemodel.org.

Ground Motions Recorded in Rome during the April 2009 L’Aquila Seismic Sequence: Site Response and Comparison with Ground‐Motion Predictions Based on a Global Dataset

Abstract: The mainshock and moderate-magnitude aftershocks of the 6 April 2009 M 63 L'Aquila seismic sequence, about 90 km northeast of Rome, provided the first earthquake ground-motion recordings in the urban area of Rome Before those record- ings were obtained, the assessments of the seismic hazard in Rome were based on intensity observations and theoretical considerations The L'Aquila recordings offer an unprecedented opportunity to calibrate the city response to central Apennine earthquakes—earthquakes that have been responsible for the largest damage to Rome in historical times Using the data recorded in Rome in April 2009, we show that (1) published theoretical predictions of a 1 s resonance in the Tiber valley are con- firmed by observations showing a significant amplitude increase in response spectra at that period, (2) the empirical soil-transfer functions inferred from spectral ratios are satisfactorily fit through 1D models using the available geological, geophysical, and laboratory data, but local variability can be large for individual events, (3) response spectra for the motions recorded in Rome from the L'Aquila earthquakes are signifi- cantly amplified in the radial component at periods near 1 s, even at a firm site on volcanic rocks, and (4) short-period response spectra are smaller than expected when compared to ground-motion predictions from equations based on a global dataset, whereas the observed response spectra are higher than expected for periods near 1 s Online Material: Velocity models used in computing theoretical site response