Peak ground accelerations from large (M≥7.2) shallow crustal earthquakes : a comparison with predictions from eight recent ground-motion models

Strong-motion data from large (M≥7.2) shallow crustal earthquakes invariably make up a small proportion of the records used to develop empirical ground motion prediction equations (GMPEs). Consequently GMPEs are more poorly constrained for large earthquakes than for small events. In this article peak ground accelerations (PGAs) observed in 38 earthquakes worldwide with M≥7.2 are compared with those predicted by eight recent GMPEs. Well over half of the 38 earthquakes were not considered when deriving these GMPEs but the data were identified by a thorough literature review of strong-motion reports from the past sixty years. These data are provided in an electronic supplement for future investigations on ground motions from large earthquakes. The addition of these data provides better constraint of the between-event ground-motion variability in large earthquakes. It is found that the eight models generally provide good predictions for PGAs from these earthquakes, although there is evidence for slight under- or over-prediction of motions by some models (particularly for M>7.5). The between-event variabilities predicted by most models match the observed variability, if data from two events (2001 Bhuj and 2005 Crescent City) that are likely atypical of earthquakes in active regions are excluded. For some GMPEs there is evidence that they are over-predicting PGAs in the near-source region of large earthquakes as well as over-predicting motions on hard rock. Overall, however, all the considered models, despite having been derived using limited data, provide reliable predictions of PGAs in the largest crustal earthquakes

Finite difference solutions to the equations of elastic wave-propagation, with application to Love waves over dipping interfaces.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1970.Vita.Bibliography: leaves 234-249.Ph.D

Average body-wave radiation coefficients

ABSTRACT Averages of P-and S-wave radiation patterns over all azimuths and various ranges of takeoff angles (corresponding to observations at teleseismic, regional, and near distances) have been computed for use in seismological applications requiring average radiation coefficients. Various fault orientations and averages of the squared, absolute, and logarithmic radiation patterns have been considered. Effective radiation patterns combining high-frequency direct and surfacereflected waves from shallow faults have also been derived and used in the computation of average radiation coefficients at teleseismic distances. In most cases, the radiation coefficients are within a factor of 1.6 of the commonly used values of 0.52 and 0.63 for the rms of P-and S-wave radiation patterns, respectively, averaged over the whole focal sphere. The main exceptions to this conclusion are the coefficients for P waves at teleseismic distances from vertical strike-slip faults, which are at least a factor of 2.8 smaller than the commonly used value

A SIMPLIFICATION IN THE CALCULATION OF MOTIONS NEAR A PROPAGATING DISLOCATION

ABSTRACT From Haskell's (1969) integral representations for the near-field displacements due to a propagating strike-slip and dip-slip dislocation, a solution is obtained for a dislocation "line source" by an analytic integration in the direction of the fault propagation. This reduces the numerical integration from a surface integral required for the usual evaluation of the near-field motion, to a one-dimensional integration over the fault width. Since the dislocation function modeled here is a Heaviside step function, these results may be extended to any arbitrary source time-function by convolving these displacements with the time derivative of the desired source function

Analysis of the ground accelerations radiated by the 1980 Livermore valley earthquakes for directivity and dynamic source characteristics

ABSTRACT The strong motion accelerograph recordings of the 24 January 1980 main shock and the 27 January 1980 aftershock of the Livermore Valley earthquake sequence are analyzed for systematic variations with azimuth or station location. The variation of the peak accelerations with epicentral azimuth is apparently reversed for the two events: the main shock accelerations are larger to the south, and the aftershock accelerations are larger to the northwest. We eliminate the site effects by forming the ratio of the peak accelerations recorded at the same station, after correcting for the epicentral distance. This analysis indicates that source direcUvity caused a total variation of a factor of 10 in the peak accelerations. Comparison of this variation with the spatia ! extent of the aftershock sequences suggests that the strong directivity in the radiated accelerations is the result of unilateral ruptures in both events. The accelerograms recorded at 10 stations within 35 km of the events were digitized to analyze the azimuthal variation of the rms acceleration, the peak velocity, and the radiated energy flux. The variation of rms acceleration correlates almost exactly with the variation of the peak accelerations. This correlation is analyzed using both deterministic and stochastic models for the acceleration waveforms. The peak velocities, corrected for epicentral distance, vary with azimuth by a factor of 5 for both events, while the radiated energy flux varies by a factor of 30 for the main shock and 15 for the aftershock. The peak velocities are strongly correlated with the radiated energy flux. The radiated seismic energies are estimated to be 2.6 ± 0.9 x 102° dyne-cm for the main shock and 1.5 ± 0.3 x 1020 dyne-cm for the aftershock

Compilation and critical review of GMPEs for the GEM-PEER Global GMPEs Project

International audienceGround-motion prediction equations (GMPEs) relate a ground-motion parameter (e.g. peak ground acceleration, PGA) to a set of explanatory variables describing the source, wave propagation path and site conditions. In the past five decades many hundreds of GMPEs for the prediction of PGA and linear elastic response spectral ordinates have been published. We discuss the pre-selection of GMPEs undertaken within the framework of the GEM-PEER Global GMPEs Project. The pre-selection criteria adopted were consistent with the current state-of-the-art in ground-motion characterization and sought to retain only the most robust GMPEs. Consideration of broad tectonic regionalization (e.g. shallow crustal seismicity in tectonically-active areas, stable continental regions and subduction zones) was made but it was assumed (based on previous studies) that strong regional differences were not present within these tectonic classes. In total about thirty GMPEs were pre-selected for closer inspection and testing to obtain a final set of ground-motion models

A Study of Possible Ground-Motion Amplification at the Coyote Lake Dam, California

Abstract The abutment site at the Coyote Lake Dam recorded an unusually large peak acceleration of 1.29g during the 1984 Morgan Hill earthquake. Following this earthquake another strong-motion station was installed about 700 m downstream from the abutment station. We study all events (seven) recorded on these stations, using ratios of peak accelerations, spectral ratios, and particle motion polarization (using holograms) to investigate the relative ground motion at the two sites. We find that in all but one case the motion at the abutment site is larger than the downstream site over a broad frequency band. The polarizations are similar for the two sites for a given event, but can vary from one event to another. This suggests that the dam itself is not strongly influencing the records. Although we can be sure that the relative motion is usually larger at the abutment site, we cannot conclude that there is anomalous site amplification at the abutment site. The downstream site could have lowerthan-usual near-surface amplifications. On the other hand, the geology near the abutment site is extremely complex and includes fault slivers, with rapid lateral changes in materials and presumably seismic velocities. For this reason alone, the abutment site should not be considered a normal free-field site

Predominant-Period Site Classification for Response Spectra Prediction Equations in Italy

Abstract We propose a site classification scheme based on the predominant period of the site, as determined from the average horizontal-to-vertical (H/V) spectral ratios of ground motion. Our scheme extends Zhao et al. (2006) classifications by adding two classes, the most important of which is defined by flat H/V ratios with amplitudes less than 2. The proposed classification is investigated by using 5%-damped response spectra from Italian earthquake records. We select a dataset of 602 three-component analog and digital recordings from 120 earthquakes recorded at 214 seismic stations within an hypocentral distance of 200 km. Selected events are in the moment-magnitude range 4.0 ≤ Mw ≤ 6.8 and focal depths from a few kilometers to 46 km. We computed H/V ratios for these data and used these to classify each site into one of six classes. We then investigate the impact of this classification scheme on empirical ground-motion prediction equations by comparing its performance with that of the conventional rock/soil classification. Although the adopted approach results in a only a small reduction of overall standard deviation, the use of H/V spectral ratios in site classification does capture the signature of sites with flat frequency-response, well as deep and shallow soil profiles, characterized 2 C:\di_alessandro\site_classification_italy\final_version_of_paper\bssa-d-11-00084_di_alessandro_etal_final_revisions.doc by long-and short-period resonance, respectively; in addition, the classification scheme is relatively quick and inexpensive, which is an advantage over schemes based on measurements of shear-wave velocity

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