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Analysis of the Pacoima dam accelerogram—San Fernando, California, earthquake of 1971

Trifunac, M. D. and Hudson, D. E. (1971) Analysis of the Pacoima dam accelerogram—San Fernando, California, earthquake of 1971. Bulletin of the Seismological Society of America, 61 (5). pp. 1393-1411. ISSN 0037-1106.

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Integrated ground velocities and displacements calculated from the accelerogram recorded at the Pacoima dam site indicate that the strong ground motion was predominately in the vertical and NS direction, in general agreement with the mechanism of faulting as inferred from aftershock studies, and with fault displacements observed in the field. High-frequency peak accelerations of 1.25 g were recorded in two horizontal directions, these being the highest ground accelerations so far recorded for earthquakes. Response spectrum curves calculated from the accelerograms do not show unusual features, and the numerical values are consistent with past experience. The high-frequency, high-amplitude impulsive ground motion associated with the highest peak accelerations did not contribute significantly to the over-all response spectrum values. The presence of the high-frequency motions in the recorded accelerograms is presumably the consequence of the proximity of the recording site to the fault dislocation.

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Additional Information:© 1971 Seismological Society of America. Manuscript received May 3, 1971. The existence of the Pacoima accelerogram is a tribute to the success of the long-range program establishing the Southern California strong-motion accelerograph network under the supervision of W. K. Cloud, Chief of the Seismological Field Survey, and R. P. Maley, in charge of the Los Angeles office, of the NOAA National Ocean Survey. We much appreciate the numerous contributions of Richard J. Dielman of the Earthquake Engineering Research Laboratory of the California Institute of Technology to all aspects of the program of instrument installation, servicing, record collection and development, and laboratory instrument evaluation. V. Perez of the NOAA Seismological Field Survey assisted with the digitization of the Pacoima accelerogram; and Dr. A. G. Brady of the Caltech group carried out details of the data processing. We are indebted to the Los Angeles County Flood Control District for their forward-looking program of instrumentation and in particular to Mr. E. J. Zielbauer of that organization for cooperation with instrument siting, site visits after the earthquake, and for providing maps and information on the site and the dam. We wish to thank Professors C. Allen and B. Kamb of the California Institute of Technology for permission to reproduce their data in Figures I and 2. Special thanks are due to Engineering Mechanics Division of the National Science Foundation for their very prompt action after the earthquake in making support available to carry out data processing of the unprecedented body of strong-motion accelerograms. This research was also supported in part by the National Science Foundation Grant GA 22709 to the Lamont-Doherty Geological Observatory of Columbia University.
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NSFGA 22709
Issue or Number:5
Record Number:CaltechAUTHORS:20140915-125446485
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49714
Deposited By: Tony Diaz
Deposited On:15 Sep 2014 19:59
Last Modified:03 Oct 2019 07:16

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