Hayward Fault: Seismicity & Earthquake Potential

Seismicity & Earthquake Potential

In 1868, the Hayward fault ruptured along 52 km of its length, with an average offset of 1.9 m of right-lateral strike-slip motion. This earthquake caused considerable damage in the East Bay and San Francisco, and was known as the "Great San Francisco Earthquake" until that title was assumed by the 1906 San Francisco earthquake.

For many years, it was generally assumed that the northern Hayward fault had ruptured in a magnitude 7 earthquake in 1836. Evidence for this event was based on an account published in local newspapers after the 1868 earthquake. Recent research suggests that this earthquake did not occur on the northern Hayward fault - and instead was located toward the Monterey area (Toppozada and Borchard, 1998). New trenching studies confirm these results and suggest that the northern Hayward fault has not ruptured since the mid-1700s.

What does this mean for the future of the Hayward fault? Today, the seismicity of the Hayward fault is quite striking as earthquake epicenters along the fault, from the south Bay to Pt. Pinole where the Hayward enters San Pablo Bay, occur in clusters, or patches, that are spaced, on average, 10 km apart. These patches are from 2 to 8 km in length and are separated by quiet regions, or gaps, in which there is very little seismicity by comparison. The largest events on the Hayward fault in the last few years include an Mw 4.1 earthquake near Richmond in 1998 and Mw 4.2 earthquake in 1994.

The latest probability study for the San Francisco Bay Area assesses the probability of a M6.7 or larger earthquake on the Hayward-Rodgers Creek system as 27% in 2003-2032.

Hayward Fault
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