On October 17, 1989, at 5:04 pm, a 6.9 magnitude earthquake centered at the Forest of Nisene Marks State Park in Santa Cruz County, California, shook the area for upward of 15 seconds. This earthquake is known at the Loma Prieta earthquake, named for the area of the San Andreas Fault system where the earthquake was centered. The earthquake was preceded by two foreshocks. The first took place in June of 1988 with a magnitude of 5.2, and the second took place in August of 1989 and had a magnitude of 5.3. These foreshocks took place within three miles of the Loma Prieta’s center and, although they took place on different sections of the fault, they are believed to have aided in the rupture sequence within the Loma Prieta quake. There were also as many as 51 aftershocks the day after the earthquake that reached 3.0 or greater in magnitude, and 16 the following day.

The Loma Prieta earthquake resulted in 63 deaths caused directly or indirectly by the earthquake and more than 3700 injuries. The highest number of deaths took place in Oakland, California, due to the collapse of the Cyprus Street Viaduct on the Nimitz Freeway. This collapse resulted in the crushing of multiple cars and caused the deaths of 43 people.