M 6.8 - The 1868 Hayward Fault, California Earthquake

Because of its location in the heart of the San Francisco Bay area [which at that time had a population of about 260,000 people], this was one of the most destructive earthquakes in the history of California. Property loss was extensive at towns in the Bay area, and 30 people were killed. The total property loss was about $350,000 [equivalent to approximately $6.324 million in 2019 dollars¹]. This earthquake was known as the "great San Francisco earthquake" until the shock on April 18, 1906.

Damage was most severe in Hayward and nearby towns along the Hayward fault. Slip was observed on the Hayward fault from San Leandro to Warm Springs, a distance of about 32 km; in places, the fault trace opened 25-30 cm. At Hayward, almost every building was wrecked or damaged extensively. San Jose, in the Santa Clara Valley several kilometers west of the fault trace, had many wrecked buildings and demolished chimneys. At San Leandro, the second floor of the courthouse collapsed, and other buildings were wrecked. At San Francisco, the Custom House sustained severe damage, and many cornices, awnings, and walls fell, but, as occurred later in the shock of 1906, well-constructed buildings on firm ground sustained little damage.

Damage occurred from Gilroy and Santa Cruz north to Santa Rosa. The maximum observed Modified Mercalli Intensity (MMI) was IX. The area shaken at MMI VIII or higher included about 2,300 km². Strong aftershocks continued into November 1868. (Ref. 38, 56, 368, 517, 521, 530, 533.)

Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.

¹Based on US Bureau of Labor Statistics Consumer Price Index and calculated in "Inflation Calculator", U.S. Official Inflation Data, Alioth Finance (https://www.officialdata.org/), retrieved 03 Sept 2019.

In addition, walls and plaster cracked in the Sacramento-Stockton area of the Central Valley and a landslide occurred in Santa Cruz County. The felt area extended from Monterey and Mariposa north to Clear Lake and Chico and into western Nevada at Carson City and Virginia City. It was also felt by a few people at Visalia, more than 280 km southeast of Hayward, and on-board a ship near the Farallon Islands, about 40 km off the California coast.

Abridged from Preparation of isoseismal maps and summaries of reported effects for pre-1900 California earthquakes, by T.R. Toppozada, C.R. Real and D.L. Parke, California Division of Mines and Geology Open-File Report 81-11 SAC, Sacramento: 1981; updated and presented by interactive map on California Geological Survey website (http://maps.conservation.ca.gov/cgs/historicearthquakes/).

Note that some sources, including the California Geological Survey (formerly the California Division of Mines and Geology), assign magnitude 7.0 to this earthquake.

CGS reference: Downloadable list of magnitude 4 and greater earthquakes, compiled from various sources (1769-2000)
online at https://www.conservation.ca.gov/cgs/Pages/Earthquakes/earthquake-catalog.aspx