Earthquake Rattles Half Moon Bay
A M2.9 earthquake jolted Half Moon Bay at 9:22 last night.
A M2.9 earthquake struck just south of Half Moon Bay shortly before 9:30 last night.
Residents of San Mateo and Redwood City also reported feeling the jolt. It happened at a depth of 10.4 kilometers, or 6.4 miles, beneath the rugged coastline within the San Gregorio Fault Zone.
The San Gregorio Fault is the longest-running fault west of the San Andreas. It is also the Bay Area’s most quiet. The United States Geological Survey says the last “large, surface-rupturing earthquake” occurred “between 1270 and 1776 AD.” They call intervals between major quakes on the San Gregorio “poorly constrained,” ranging anywhere from “300 and 690 years.” In 2003, they assigned the San Gregorio Fault a 10% probability of producing a M6.7 or larger earthquake within the next thirty years.
Most earthquakes carry a five percent chance that a stronger one will follow. That risk dies down over time, peaking within the first twenty-four hours.
The USGS later downgraded Tuesday night’s earthquake to M2.8. Last Saturday, another M2.8 struck near Alamo. On October 25th, a M5.1 hit San Jose, the Bay Area’s largest quake in eight years.
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