A 4.7 magnitude earthquake struck the Hill just before 10 a.m. Monday, March 11. Initially reported as a 5.2 quake by the United States Geological Survey, the temblor was preceded by 6 foreshocks, the largest of which was a 2.7 magnitude at 10:36 a.m.
The quake was centered 12.4 miles east southeast of Anza, at a depth of 7.5 miles.
The series of quakes was likely part of San Jacinto fault activity although USGS research geophysicist Morgan Page said her agency is not ready yet to make that call. “There are a lot of minor faults that cross the San Jacinto,” said Page, “and it could have been on one of those.”
Page reported there have been 29 aftershocks greater than 2 magnitude, with the largest, a 2.8 at 11:25 a.m.
She noted there was only a 5 percent possibility that today’s quake is a foreshock of a larger quake.
The San Jacinto is historically the most active fault zone in southern California. The largest quake on the fault, in modern history, occurred in 1918 and measured 6.6.
Each quake reminds Hill residents to be prepared to be cut off from outside help for prolonged periods and to stock up on water and other disaster supplies.