Sunday, August 28, 2005

1868 Hayward Earthquake

I had heard of the 1868 earthquake on the Southern Hayward Fault, but knew little about it until I was recently googling around.
Known as the "great San Francisco earthquake" until 1906, one of California's most destructive earthquakes occurred on October 21, 1868, resulting from slip on the Hayward Fault. Heavy damage occurred in communities situated along the fault and in San Fransico and San Jose. Sadly, many of the engineering lessons learned from this earthquake and openly discussed at the time, such as the hazards of building on "made ground" reclaimed from the San Francisco Bay or the admonition to "build no more cornices," were long forgotten by the time of the 1906 quake.
The land around the Hayward Fault is much more heavily populated today than it was in 1868, so the $300,000 damage (1868 dollars) would translate into many millions today (not to mention the potential injuries and fatalities). The greatest concern is that the Northern portion of the Hayward fault - running through San Pablo, El Cerrito, and Berkeley - has not had a significant earthquake since written records began in 1776. That's a lot of strain to be released if (when) there is a big quake; a probability of 27% over the next 30 years. However, some studies suggest that the "big one" is more likely on the Southern part of the fault. Southern or Northern portion, a quake on the Hayward fault has the potential to cause enormous damage all around the Bay.

The Hayward fault appears to be one of the best studied, leading to lots of links:

HISTORICAL INFORMATION
Predictive intensity map of the equivalent of the 1868 earthquake.
Damage from the 1868 earthquake in San Francisco and Alameda County
• October 22, 1868 articles from the San Francisco Call describing the aftermath of the quake in San Francisco and the East Bay. (note that Centreville is now part of Fremont)
Overview of the 1868 quake from the Berkeley Seismological Laboratory
Topographical map of Bay Area earthquake faults

THE FAULT TODAY
Tour the fault from Fremont to Point Pinole (see the impressive movement of a curb in "Residential Area North of Downtown Hayward").
Tour the North section of the Hayward fault through the UC Berkeley Campus
Take your own field trip along the fault (from the USGS)
Paleoseismology along the Hayward Fault
Bay Area earthquake hazard shaking maps by city (old, noninteractive version)

GENERAL EARTHQUAKE LINKS
Earthquake preparedness information
Real-time Forecast of Earthquake Hazard (showing how low the overall probability is)
Earthquake activity over the last week (usually updated within about 5 minutes of a quake)


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