Seismicity in Utah, 1850 through June 1965

Abstract

abstractDuring 1850 through June 1965, at least 609 earthquakes occurred in Utah, of which at least 38 were damaging. Pertinent data of these earthquakes are listed, and an earthquake epicenter map of Utah is presented. The epicenter determinations of about 344 earthquakes (all felt) in Utah during 1850 through 1949 (Williams and Tapper, 1953) were non-instrumental. The epicenters and magnitudes and depths of focus (when determined) of the earthquakes during 1950 through June 1962 (77) were generally instrumental determinations taken from the Coast and Geodetic Survey, U. S. Department of Commerce (CGS). The epicenters of the earthquakes during July 1962 through June 1965 (188) were all instrumental and were obtained as follows: 23 were obtained from already-published CGS data; 165 were obtained by the University of Utah, of which 68 epicentral determinations were also made by the CGS. The comparisons of epicenter locations were generally good. Our epicenters were determined using a slightly modified Geiger's method programmed on an IBM 7044 digital computer at the University of Utah. The computer program used unpublished travel-time curves (B. H. Atwell, 1967) computed from the earth crustal model of Berg and others (1960) for the Utah region and included depths-of-focus data at 10-km-depth intervals from 0 to 60 km. The data show recent earthquake activity in the Ephraim (1961), Cache Valley (1962), and Levan (1963) areas, and swarm activity in the lehman Caves (1963) area. During 1962-1964 Utah averaged about 60 earthquakes per year for which instrumental epicenter determinations were made.