Skip Links

USGS - science for a changing world

Open-File Report 96-532

National Seismic Hazard Maps: Documentation June 1996

By Arthur Frankel, Charles Mueller, Theodore Barnhard, David Perkins, E.V. Leyendecker, Nancy Dickman, Stanley Hanson, and Margaret Hopper

APPENDIX:GROUND MOTIONS FOR NEHRP B-C BOUNDARY SITES IN CEUS

Two ground-motion attenuation relations were used in constructing the interim hazard maps for CEUS, one due to Toro et al. (1993) with a modification for amplification by near-surface materials, and the other constructed especially for this application. The purpose of this note is to document the new attenuation relation and the amplification factors applied to the Toro et al (1993) curves. The reference site condition is the boundary between NEHRP classes B and C, i.e, a site with an average shear wave velocity (Vs) of 760 m/sec in the top 30m. We refer to this site as "firm rock," differentiating it from "hard rock" with shear-wave velocities near 3.0 km/sec at the surface.

The need for a new attenuation relation was apparent from discussion at our northeastern U.S. hazard workshop of August 1994 (see Frankel et al., 1995). Most workshop participants wanted an attenuation relation with a relatively high median stress drop of 150-200 bars, to accommodate the possibility of occasional Saguenay events with very high stress drops of about 500 bars. Atkinson and Boore (1995) used a stress drop of 180 bars (albeit with a high shear-wave velocity of 3.8 km/sec), higher than the 100 bars (with Vs= 3.5 km/sec) used in Boore and Atkinson (1987) and the median stress drop of 120 bars used in Toro et al. (1993). The workshop participants were not comfortable, however, with the two-corner frequency model advocated by Atkinson and Boore (1995) which dramatically decreases the intermediate-period (about 1.0 sec) spectral values compared to a single-corner frequency Brune model. Thus, we decided to construct a new set of attenuation relations based on a higher stress drop consistent with the high-frequency Fourier spectral levels specified in Atkinson and Boore (1995), but with a source model with a single corner frequency. These new attenuation relations also incorporate frequency-dependent amplification appropriate for a "firm-rock" CEUS site with a hypothetical shear-wave velocity profile at shallow depth (< 500 m) and an average Vs of 760 m/sec in the top 30m.

 

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubsdata.usgs.gov/pubs/of/1996/532/AppendixA.html
Page Contact Information: GS Pubs Web Contact
Page Last Modified: Wednesday, 07-Dec-2016 16:06:06 EST