EarthquakesThe Hayward Fault -- is it due for a repeat of the powerful 1868 earthquake?
On October 21, 1868, a magnitude 6.8 earthquake struck the San Francisco Bay area. Although the region was sparsely populated, the quake on the Hayward Fault was one of the most destructive in California’s history. The 150th anniversary of the 1868 earthquake, and all historical earthquake anniversaries, are opportunities to remind people that we live in earthquake country and we should all be prepared for the next big quake.
On October 21, 1868, a magnitude 6.8 earthquake struck the San Francisco Bay area. Although the region was sparsely populated, the quake on the Hayward Fault was one of the most destructive in California’s history. The 150th anniversary of the 1868 earthquake, and all historical earthquake anniversaries, are opportunities to remind people that we live in earthquake country and we should all be prepared for the next big quake. U.S. Geological Survey (USGS) studies show that similar Hayward Fault quakes have repeatedly jolted the region in the past and that the fault may be ready to produce another magnitude 6.8 to 7.0 earthquake. Such an earthquake could unexpectedly change people’s lives and impact the Bay Area’s infrastructure and economy, but updated building codes and retrofits, as well as planning, community training, and preparedness, will help reduce the effects of a future Hayward Fault earthquake.
In the early morning of October 21, 1868, seismic waves from a powerful earthquake raced through the fog-shrouded San Francisco Bay area. Frightened people ran out of their homes, and cattle and even fire-engine horses panicked and bolted. Strong shaking lasted more than 40 seconds, devastating several East Bay towns. Brick buildings, walls, and chimneys were also shaken down in Oakland, San Francisco, Santa Rosa, and San Jose, and there was serious damage in Napa and Hollister. Numerous witnesses reported seeing the ground move in waves. Shaking was felt as far away as Nevada, and aftershocks rattled the Bay Area for weeks. Even though the region was only sparsely populated at the time, the 1868 quake killed about 30 people and caused great property damage. It still ranks as one of the most destructive earthquakes in California’s history, but this is not the end of the story. The Hayward Fault will rupture violently again, and perhaps soon.
The earthquake of 1868
USGS researchers say that the 1868 earthquake on the Hayward Fault capped a decade-long sequence of seven increasingly strong quakes in the Bay Area. Ground cracking caused by this earthquake was traced for 20 miles along the Hayward Fault, from Warm Springs in Fremont north to San Leandro. Historical land-survey data suggest that the fault broke as far north as Berkeley, with an average horizontal offset of about 6 feet (2 meters).
