Revisiting the 1872 Owens Valley , California , Earthquake by Susan E . Hough and Kate Hutton

The 26 March 1872 Owens Valley earthquake is among the largest historical earthquakes in California. The felt area and maximum fault displacements have long been regarded as comparable to, if not greater than, those of the great San Andreas fault earthquakes of 1857 and 1906, but mapped surface ruptures of the latter two events were 2–3 times longer than that inferred for the 1872 rupture. The preferred magnitude estimate of the Owens Valley earthquake has thus been 7.4, based largely on the geological evidence. Reinterpreting macroseismic accounts of the Owens Valley earthquake, we infer generally lower intensity values than those estimated in earlier studies. Nonetheless, as recognized in the early twentieth century, the effects of this earthquake were still generally more dramatic at regional distances than the macroseismic effects from the 1906 earthquake, with light damage to masonry buildings at (nearest-fault) distances as large as 400 km. Macroseismic observations thus suggest a magnitude greater than that of the 1906 San Francisco earthquake, which appears to be at odds with geological observations. However, while the mapped rupture length of the Owens Valley earthquake is relatively low, the average slip was high. The surface rupture was also complex and extended over multiple fault segments. It was first mapped in detail over a century after the earthquake occurred, and recent evidence suggests it might have been longer than earlier studies indicated. Our preferred magnitude estimate is Mw 7.8–7.9, values that we show are consistent with the geological observations. The results of our study suggest that either the Owens Valley earthquake was larger than the 1906 San Francisco earthquake or that, by virtue of source properties and/or propagation effects, it produced systematically higher ground motions at regional distances. The latter possibility implies that some large earthquakes in California will generate significantly larger ground motions than San Andreas fault events of comparable magnitude. Online Material: Summary of macroseismic effects including assigned MMI for the 1872 event. Introduction: Historical Context The 26 March 1872 Owens Valley earthquake is one of three historical events that generated perceptible shaking over the full, or nearly full, extent of the state of California. The felt extent of the earthquake is especially noteworthy given that the event occurred at approximately 2:30 in the morning, local time, a time when most people were soundly asleep. (The modern tungsten filament light bulb, which is inferred to have had a significant impact on sleep patterns [Coren, 1996] was not introduced until 1913.) According to census figures, the population of California grew from under 100,000 at the start of the gold rush to 560,000 by 1870. By 1860, silver had been discovered in and around Owens Valley, and gold had been discovered farther north in and around Bodie, California (Piatt, 2003). Mining communities were quickly established in the region. The 1872 earthquake occurred within Inyo County, which had been established in 1866 (Chalfant, 1933). The population was sparse; in 1867, there were an estimated 500 voters (i.e., male citizens of any race, 21 years old and older) scattered between a half-dozen principle settlements (Chalfant, 1933). The total population of Lone Pine was estimated at 250–300 at the time of the earthquake (Whitney, 1872a). There were, however, scattered small settlements throughout the county, including mining settlements along the Sierra and Inyo ranges, and the town of Swansea, established in the late 1860s as a hub for smelting operations (Fig. 1). By 1880, the total population of the county was 2937 (U. S. Census Office, 1883). To the west of the Sierra Nevada, agricultural communities sprang up in the central valley soon after the gold rush began. 931 Bulletin of the Seismological Society of America, Vol. 98, No. 2, pp. 931–949, April 2008, doi: 10.1785/0120070186