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U.S. Geological Survey Open-File Report 76–296

In cooperation with the Division of Reactor Research and Development, U.S. Atomic Energy Commission

Analysis of Seismograms from a Downhole Array in Sediments Near San Francisco Bay

By William B. Joyner, Richard E. Warrick, and Adolph A. Oliver III

Thumbnail of and link to report PDF (50.9 MB)Abstract

A four-level downhole array of three-component instruments was established on the southwest shore of San Francisco Bay to monitor the effect of the sediments on low-amplitude seismic ground motion. The deepest instrument is at a depth of 186 meters, two meters below the top of the Franciscan bedrock. Earthquake data from regional distances (29 km ≤ Δ ≤ 485 km) over a wide range of azimuths are compared with the predictions of a simple plane-layered model with material properties independently determined. Spectral ratios between the surface and bedrock computed for the one horizontal component of motion that was analyzed agree rather well with the model predictions; the model predicts the frequencies of the first three peaks within 10 percent in most cases and the height of the peaks within 50 percent in most cases. Surface time histories computed from the theoretical model predict the time variations of amplitude and frequency content reasonably well, but correlations of individual cycles cannot be made between observed and predicted traces.

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For additional information:
Contact Information, Earthquake Science Center, Menlo Park Science Center
U.S. Geological Survey
345 Middlefield Road, MS 977
Menlo Park, California 94025
http://earthquake.usgs.gov/

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Suggested citation:

Joyner, W.B., Warrick, R.E., and Oliver, III, A.A., 1976, Analysis of seismograms from a downhole array in sediments near San Francisco Bay: U.S. Geological Survey Open-File Report 76–296, 61 p., available at http://pubs.usgs.gov/of/1976/0296/.



Contents

Abstract

Introduction

The Site

Instrumentation and Data Analysis

Theoretical Model

Determination of Material Properties

Comparison Between Observations and Model Predictions

Discussion

Acknowledgments

References

List of Illustrations

1 appendix


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