Catalog of Oroville, California, earthquakes; June 7, 1975 to July 31, 1976

Abstract

On August 1, 1975, at 2020 GMT a magnitude 5.7 (ML) earthquake occurred 15 km south of Oroville, California, in the western foothills of the Sierra Nevada. It was preceded by 61 foreshocks that began on June 7, 1975, and was followed by thousands of aftershocks. Several studies have reported locations or analyses of various subsets of the Oroville sequence, including Morrison and others (1975), Savage and others (1975), Lester and others (1975), Toppozada and others (1975), Ryall and others (1975), Bufe and others (1976), Morrison and others (1976), and Lahr and others (1976). In this report arrival time data have been compiled from the original records at several institutions to produce a single catalog of the Oroville sequence from June 7, 1975, through July 31, 1976. This study has four objectives: to compile a list of earthquakes in the Oroville sequence that is as complete as possible above the minimum magnitude threshold of approximately 1.0; to determine accurate and uniform hypocentral coordinates for the earthquakes; to determine reliable and consistent magnitude values for the sequence; and to provide a statistically uniform basis for further investigation of the physical processes involved in the Oroville sequence as revealed by the parameters of the foreshocks and aftershocks. The basis and procedures for the data analysis are described in this report.