Scientists focus on earthquakes that literally break the ground along the main plate boundary because they’re the ones that actually do the job of relieving centuries of tectonic strain. A famous example of the ground breaking was during the great 1906 earthquake that destroyed much of San Francisco; at Point Reyes in Marin County, a fence that intersected the fault was suddenly cut in two, separated on each side of the San Andreas by 18 feet.

Source: Los Angeles Times April 03, 2019 12:13 UTC