Calaveras Fault 6.5 that occurred in 1911 in the Morgan Hill area. The most recent of these was a magnitude 6.2 earthquake near Morgan Hill in 1984. A magnitude 5.6 earthquake occurred on the Calaveras Fault on October 30, 2007 at 20:04 PDT (October 31, at 03:04 UTC), near Alum Rock. Prior to the 2014 South Napa earthquake, it was the most powerful quake to hit the Bay Area since the Loma Prieta earthquake of 1989, and the largest on the Calaveras Fault since 1984. Although it has been known for some time that the Calaveras and Hayward faults merge in the
Earthquake prediction "resoundingly debunked". Probably the most celebrated seismo-electromagnetic event ever, and one of the most frequently cited examples of a possible earthquake precursor, is the 1989 Corralitos anomaly. In the month prior to the 1989 Loma Prieta earthquake measurements of the earth's magnetic field at ultra-low frequencies by a magnetometer in Corralitos, California, just 7 km from the epicenter of the impending earthquake, started showing anomalous increases in amplitude. Just three hours before the quake the measurements soared to about thirty times greater than normal, with amplitudes tapering off after the quake. Such amplitudes had not been seen in two years