Dozens Of Tremors Hit San Andreas Fault - Newsweek

Dozens of small earthquakes rattled Northern California early this week, with a cluster of tremors striking near the infamous San Andreas Fault, one of the world's best-known seismic zones.

The tremors ranged in magnitude from 0.5 to 2.8 between Sunday and Monday, according to U.S. Geological Survey (USGS) data.

The San Andreas Fault is a narrow, continuous fracture in the Earth's crust that stretches from Northern California south to Cajon Pass near San Bernardino. The fault system extends for more than 800 miles and reaches depths of at least 10 miles beneath the surface.

USGS mapping showed a large cluster of the minor seismic events taking place near The Geysers, a geothermal field in the Mayacamas Mountains that regularly sees small earthquakes.

Among them was a 2.7-magnitude quake that hit shortly after 3 p.m. UTC on Monday at a depth of 2.8 kilometers (1.7 miles). More than two dozen less powerful earthquakes were also recorded nearby, according to the USGS data.

Another wave of low-magnitude earthquakes struck east of Lower Lake, Lake County, with USGS’ map showing events of magnitude 1.5, 2.1, 2.2, 2.5, and 2.8 within roughly an hour of each other on Monday.

Farther south, two small events jolted Concord, in Contra Costa County. A 2.1-magnitude quake on Sunday was followed Monday by a slightly larger, 2.5-magnitude event. Both struck at a depth of around 15 kilometers (9 miles), according to USGS.

Two more small tremors hit east of Berkeley, and another was detected along the fault line off the coast of San Francisco.

More than half a dozen additional tremors were recorded farther south along the fault line, according to USGS data.

As of publication, no major damage or injuries have been reported as a result of the events.

While the quakes that struck this week were small, fears of the "big one"—a term for a future great earthquake on the San Andreas Fault—have long loomed large.

This week’s burst of seismic activity comes after researchers recently found that stress along parts of the San Andreas and San Jacinto fault systems had climbed to the highest level seen in the past millennium.

The study, published in the Journal of Geophysical Research: Solid Earth, used geological records and a physics-based model to simulate roughly 1,000 years of stress buildup and release along the southern San Andreas and San Jacinto fault systems. Lead author Liliane Burkhard said stress on multiple fault segments was at or above the highest levels seen during that period, suggesting the region may be capable of a large rupture involving both systems.

"The most important thing to understand is that this is not a distant, theoretical risk," Burkhard told Newsweek. "The stress that drives large earthquakes has been building continuously since 1857, and our model shows it has now exceeded anything we have seen in a thousand years of earthquake history.

"That does not mean an earthquake will happen tomorrow, but it does mean the system is as loaded as it has ever been in our record, and that the question is not really if but when. For anyone living in Southern California, that is a reason to take preparedness seriously, to know evacuation routes, to have a communication plan with friends and family, to have an emergency kit with water, food, and medication ready."