thumbnail

Prediction of maximum earthquake intensities for the San Francisco Bay region

Open-File Report 75-180
By:  and 
https://doi.org/10.3133/ofr75180

Links

Abstract

The intensity data for the California earthquake of April 18, 1906, are strongly dependent on distance from the zone of surface faulting and the geological character of the ground. Considering only those sites (approximately one square city block in size) for which there is good evidence for the degree of ascribed intensity, the empirical relation derived between 1906 intensities and distance perpendicular to the fault for 917 sites underlain by rocks of the Franciscan Formation is: Intensity = 2.69 - 1.90 log (Distance) (km). For sites on other geologic units intensity increments, derived with respect to this empirical relation, correlate strongly with the Average Horizontal Spectral Amplifications (AHSA) determined from 99 three-component recordings of ground motion generated by nuclear explosions in Nevada. The resulting empirical relation is: Intensity Increment = 0.27 +2.70 log (AHSA), and average intensity increments for the various geologic units are -0.29 for granite, 0.19 for Franciscan Formation, 0.64 for the Great Valley Sequence, 0.82 for Santa Clara Formation, 1.34 for alluvium, 2.43 for bay mud. The maximum intensity map predicted from these empirical relations delineates areas in the San Francisco Bay region of potentially high intensity from future earthquakes on either the San Andreas fault or the Hazard fault.
Publication type Report
Publication Subtype USGS Numbered Series
Title Prediction of maximum earthquake intensities for the San Francisco Bay region
Series title Open-File Report
Series number 75-180
DOI 10.3133/ofr75180
Edition -
Year Published 1975
Language ENGLISH
Publisher U.S. Dept. of the Interior, Geological Survey, National Center for Earthquake Research,
Description 25 leaves, 2 sheets, :ill., maps (2 fold. in pocket) ;27 cm.
Google Analytic Metrics Metrics page
Additional publication details