Each of these studies worked with limited data, and the effects of the shock and various fault rupture details led to Mercalli intensities of VII (Very strong) to IX (Violent) being proposed.

The primary tectonic feature in California is the strike-slip San Andreas (SAF) system of faults that form part of the diffuse Pacific–North American plate boundary.

The San Jacinto Mountains and the Salton Sea lie between the two faults as they continue to the southeast towards the Mexico–United States border.

[7] In the 1980s several seismologists attributed the source of the event to the southern Newport–Inglewood Fault due to its proximity to the zone of greatest damage at Mission San Juan Capistrano.

The northern portion of the fault was excluded as a potential source due to a lack of damage at San Buenaventura.

Other more distant sources have also been proposed, including the Mojave segment of the SAF to the north of San Juan Capistrano, substantiated by tree distress evidence preserved in tree rings along the fault zone and paleoseismic evidence in an investigative trench at Pallet Creek.

[4][10] Influenced by the work of several dendrochronologists and a seismologist who examined trauma to trees near Wrightwood, Toppozada et al. 2002 came about in support of the SAF as the source.

Mission San Buenaventura lay outside the ring, but is annotated with possibly also having experienced intensity VII effects.