Earthquakes

The 1906 San Francisco earthquake is one of the hardest earthquakes to hit the San Francisco area to date. Before the full force of the earthquake occured, a foreshock hit at about 5:12 am. The earthquake hit at about 20-25 seconds later, the magnitude reaching about 7.9 on the Richter scale!

Areas situated in sediment filled valleys sustained stronger than nearby bedrock sites, and the strongest shaking occured in areas where ground reclamied from San Francisco Bay failed in the earthquake. Modern seismic-zonation practice accounts for the difference in the seismic hazard posed by varying geologic conditions

The 1989 Voma Prieta was also a very destructive earthquake. It was frequently called, "a wake-up call", because it gave citizens fear and caution to prepare for another upcoming earthquake. Ever since this 1989 earthquake, many citizens and organizations have proceeded to take action. They promoted awareness of earthquake hazards, improved the understanding of the seismic threat in the Bay Area, and contributed to more effective strategies to reduce earthquake losses. The magnitude of the earthquake was 6.9.