Showing papers by "David M. Boore published in 1998"

Evaluation of models for earthquake source spectra in eastern North America

Abstract: There have been several relations proposed in the last few years to describe the amplitudes of ground motion in eastern North America (ENA). These relations differ significantly in their assumptions concerning the amplitude and shape of the spectrum of energy radiated from the earthquake source. In this article, we compare ground motions predicted for these source models against the sparse ENA ground-motion database. The source models evaluated include the two-comer models of Boatwright and Choy (1992), Atkinson (1993a), Haddon (1996), and Joyner (1997a,b), and the one-comer model of Brune (as independently implemented by Frankel et al. (1996) and by Toro et al. (1997)). The database includes data from ENA mainshocks of M > 4 and historical ENA earthquakes of M > 5.5, for a total of 110 records from 11 events of 4 _-__ M _-__ 7.3, all recorded on rock. We also include 24 available rock records from 4 large earthquakes in other intraplate regions; con- clusions are checked to determine whether they are sensitive to the addition of these non-ENA data. The Atkinson source model, as implemented in the ground-motion relations of Atkinson and Boore (1995), is the only model that provides unbiased ground-motion predictions over the entire period band of interest, from 0.1 to 10 sec. The source models of Frankel et al. (1996), Toro et aL (1997), and Joyner (1997a,b) all provide unbiased ground-motion estimates in the period range from 0.1 to 0.5 sec but over- estimate motions at periods of 1 to 10 sec. The Haddon (1996) source model over- predicts motions at all periods, by factors of 2 to 10. These conclusions do not change significantly if data from non-ENA intraplate regions are excluded, although the ten- dency of all models toward overprediction of long-period amplitudes becomes more pronounced. The tendency of most proposed ENA source models to overestimate long-period motions is further confirmed by an evaluation of the relationship between Ms, a measure of the spectrum at 20-sec period, and moment magnitude. A worldwide catalog of shallow continental earthquakes (Triep and Sykes, 1996) is compared to the Ms-M relations implied by each of the source models. The Atldnson source model is consistent with these data, while other proposed ENA models overpredict the average Ms for a given M. The implications of MMI data from historical earthquakes are also addressed, by exploiting the correlation between felt area and high-frequency source spectral level. High-frequency spectral amplitudes, as specified by the Atkinson and Boore (1995), Frankel et al. (1996), Toro et aL (1997), and Joyner (1997a,b) source models, equal or exceed the levels inferred from the felt areas of most of the large ENA events, with the noteable exception of the Saguenay earthquake. By contrast, high-frequency spectral amplitudes specified by the Haddon (1996) source model agree with the felt area of the Saguenay earthquake but overpredict the felt areas of nearly all other large events. In general, models that fit the Saguenay data--be it intensity data, strong-ground-motion data, regional seismographic data, or teleseismic data--will not fit the data from the remaining earthquakes. A source model derived from the California database, suitably modified for re- gional differences in crustal properties, is also evaluated. This model is not signifi-

Use of Technical Expert Panels: Applications to Probabilistic Seismic Hazard Analysis*

Abstract: Probabilistic Seismic Hazard Analysis (PSHA) is a methodology that estimates the likelihood that various levels of earthquake-caused ground motions will be exceeded at a given location in a given future time period. Due to large uncertainties in all of the geosciences data and in their modeling, multiple model interpretations are often possible. This leads to disagreements among the experts, which in the past has led to disagreement on the selection of a ground motion for design at a given site. This paper reports on a project, co-sponsored by the U.S. Nuclear Regulatory Commission, the U.S. Department of Energy, and the Electric Power Research Institute, that was undertaken to review the state-of-the-art and improve on the overall stability of the PSHA process, by providing methodological guidance on how to perform a PSHA. The project reviewed past studies and examined ways to improve on the present state-of-the-art. In analyzing past PSHA studies, the most important conclusion is that differences in PSHA results are commonly due to process rather than technical differences. Thus, the project concentrated heavily on developing process recommendations, especially on the use of multiple experts, and this paper reports on those process recommendations. The problem of facilitating and integrating the judgments of a diverse group of experts is analyzed in detail. The authors believe that the concepts and process principles apply just as well to non-earthquake fields such as volcanic hazard, flood risk, nuclear-plant safety, and climate change.

Determination of Δσ and κ0 from response spectra of large earthquakes in Greece

Abstract: We fit an 09 -2 model to response spectra from eight recent Greek earth- quakes ranging in size from M = 5.8 to M = 6.9. The diminution parameter K o was determined for each site, with a value near 0.06 for a typical soil site. The stress parameter (Aa) showed little variation from earthquake to earthquake and had a mean value of 56 bars over all earthquakes. Predictions of peak velocity, peak acceleration, rupture duration, and fault length using the derived stress parameters are consistent with observations. Frequency-dependent site amplifications were included in all es- timates; the combined effect of amplification and attenuation had a maximum value close to a factor of 2.5 for a typical soil site, relative to the motions at the surface of a perfectly elastic uniform half-space composed of materials near the source. The results form the foundation for predictions of strong motions in Greece for distances and magnitudes other than those for which data are available.

Comparing Shear-Wave Velocity Profiles From Inversion of Surface-Wave Phase Velocities with Downhole Measurements: Systematic Differences Between the CXW Method and Downhole Measurements at Six USC Strong-Motion Sites

Abstract: INTRODUCTION Shear-wave velocity profiles are used in a variety of engineering and seismological applications, and several methods are available to determine the velocities, including borehole and surface-wave methods (Woods and Stokoe, 1985; Stokoe et al. , 1988; Stokoe etal. , 1994; Poran et al. , 1994; Poran et al. , 1996). Surface-wave methods offer the advantage of being non-invasive and less costly than boreholes, but their reliability needs to be established by comparison with more direct methods. The best way to do this is a “blind” test in which the velocities determined independently from surface-wave and borehole measurements at the same site are compared. By “blind” we mean that the determination of the shear-wave velocity profile by the two methods were done independently of one another. It is surprisingly difficult to find situations in which the velocity determinations are truly independent of one another. We report on one such case in this paper. In...