what was the magnitude of the 1989 san francisco earthquake
1989 Loma Prieta earthquake The 1989 Loma Prieta earthquake occurred in Northern California on October 17 at 5:04 p.m. local time (1989-10-18 00:04 UTC). The shock was centered in The Forest of Nisene Marks State Park approximately 10 mi (16 km) northeast of Santa Cruz on a section of the San Andreas Fault System and was named for the nearby Loma Prieta Peak in the Santa Cruz Mountains. With a moment magnitude of 6.9 and a maximum Mercalli intensity of IX (Violent), the shock was responsible for 63 deaths and 3,757 injuries. The Loma Prieta segment of the San Andreas Fault System had been relatively inactive since the 1906 San Francisco earthquake (to the degree that it was designated a seismic gap) until two moderate foreshocks occurred in June 1988 and again in August 1989.
San Andreas Fault The San Andreas Fault is a continental transform fault that extends roughly 1,200 kilometers (750 mi) through California.[1] It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal). The fault divides into three segments, each with different characteristics and a different degree of earthquake risk, the most significant being the southern segment, which passes within about 35 miles (56 km) of Los Angeles. The slip rate along the fault ranges from 20 to 35 mm (0.79 to 1.38 in)/yr.[1]