Location

St. Louis, Missouri

Session Start Date

3-11-1991

Session End Date

3-15-1991

Abstract

The amplitudes of strong ground motions from the Loma Prieta earthquake recorded in the San Francisco and Oakland areas exceeded the levels predicted by standard empirical attenuation relations. Preliminary analysis of accelerograms having known trigger times suggests that the elevation of ground motion amplitudes in the distance range of approximately 40 to 100 km was due to critical reflections from the base of the crust. These reflections were large and occurred at relatively close range because of the deep focal depth of the earthquake and the strong velocity gradient at the base of the crust, and were enhanced by rupture directivity. These motions were further amplified, presumably by impedance contrast effects, at soft soil sites in San Francisco and Oakland. The effect of the critical reflections in amplifying peak accelerations of the Loma Prieta earthquake in the San Francisco and Oakland regions was as large as the effect of soft soil site conditions.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics

Meeting Name

Second Conference

Publisher

University of Missouri--Rolla

Publication Date

3-11-1991

Document Version

Final Version

Rights

© 1991 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

Share

COinS
 
Mar 11th, 12:00 AM Mar 15th, 12:00 AM

Source, Path and Site Effects on Loma Prieta Strong Motions

St. Louis, Missouri

The amplitudes of strong ground motions from the Loma Prieta earthquake recorded in the San Francisco and Oakland areas exceeded the levels predicted by standard empirical attenuation relations. Preliminary analysis of accelerograms having known trigger times suggests that the elevation of ground motion amplitudes in the distance range of approximately 40 to 100 km was due to critical reflections from the base of the crust. These reflections were large and occurred at relatively close range because of the deep focal depth of the earthquake and the strong velocity gradient at the base of the crust, and were enhanced by rupture directivity. These motions were further amplified, presumably by impedance contrast effects, at soft soil sites in San Francisco and Oakland. The effect of the critical reflections in amplifying peak accelerations of the Loma Prieta earthquake in the San Francisco and Oakland regions was as large as the effect of soft soil site conditions.