Strong-Motion Instrumental data on the San Fernando Earthquake of Feb. 9, 1971

Abstract

The San Fernando Earthquake of February 9, 1971 occurred virtually at the center of the Southern California strong-motion earthquake instrumentation network, and provided an unprecedented amount of valuable data on strong earthquake -generated ground motions, This data will be of key significance in interpreting the severe damage to many modern engineering structures which occurred, and marks a major development in the field of earthquake engineering. It was evident immediately after the event that the problems of recovering field records, of processing the information, and of disseminating the results as quickly and as widely as possible would severely tax the available resources. Fortunately, the close cooperation which had been built up over the years between the Seismological Field Survey of the U. S. Department of Commerce and the Earthquake Engineering Research Laboratory of the California Institute of Technology provided an operating group which could be quickly expanded to meet the challenge. In the days and weeks following the earthquake, each of these organizations issued numerous preliminary reports aimed at the quickest possible distribution of information. The present report up-dates and brings together a number of these initial releases, along with much new material. It is hoped that in this way a more complete picture of the overall instrumentation results can be presented in one convenient place. The report also makes available for the first time a complete description of the Southern California networks, and a detailed account of the performance of these networks during the earthquake, A notable feature of the present report is the reproduction in accurate scale form of the complete set of seismoscope records obtained during the earthquake. These seismoscope records offer an unparalleled picture of the complexity of the pattern of ground shaking throughout the Southern California region. The primary purpose of the present compilation is to make available the basic data itself, and no attempt has been made to add interpretive material. Many interpretive studies have, of course, already been made, and the full exploitation of this basic data to increase our knowledge of earthquake engineering will no doubt go on for a number of years. In reporting the accelerograph measurements, numerous examples of accelerograms have been given, and samples of standard data processing procedures leading to digitized print-outs and calculated velocity and displacement curves, and response spectrum curves, have been included. The complete set of accelerograms in computer -plotted form, along with the digital print-outs, are being issued by the Earthquake Engineering Research Laboratory of the California Institute of Technology as a part of the series "Strong-Motion Earthquake Accelerograms - Digitized and Plotted Data." The first volume devoted to the San Fernando earthquake has already been issued as Vol. 1, part C, Report No. EERL 71-20. These volumes of digitized accelerograms will be followed during the next year by additional volumes containing integrated ground velocity and displacement curves, and response spectrum curves, which will be prepared for all of the records obtained during the San Fernando earthquake. The existence of this unusually complete ground motion data is a tribute to the cooperative efforts of a large number of people over a period of many years. Many of the individuals involved have been named in the acknowledgements included in the separate sections. Hundreds of individual accelerograph and seismoscope owners have pooled their resources to make the Southern California region the best instrumented area in the world for strong earthquake ground motion investigations. A complete list of organizations, building owners, and others who deserve thanks for making possible the acquisition and the operation of the instruments would be an imposing indication of the extent of the cooperative effort involved. Special mention should be -made of the very important contributions of the late John C. Monning, former general manager and superintendent of the Department of Building and Safety of the City of Los Angeles. It was Mr, Monning's vision and foresight, implemented with great energy and patience, which resulted in the code requirements for accelerographs in tall buildings which made this earthquake the most extensive structural dynamic test of full-scale buildings ever carried out. His colleagues and successors in the Department of Building and Safety have carried this work forward in a very effective manner, and have thus played a key role in the development of the accelerograph network.

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