An outbreak yesterday of small earthquakes in Southern California is being closely monitored as to whether it might raise the chance of a much larger event on the San Andreas fault. The largest earthquake was a magnitude 4.6, reported at 8:56 a.m. under the southeastern part of the Salton Sea, according to the U.S. Geological Survey (USGS). It was among a series that began at 6:33 a.m. with a magnitude 3.2 earthquake. Magnitude 4 quakes struck at 9:03 a.m. and 12:29 p.m. It’s only the fourth time in the 88 years of modern records that such a swarm has occurred in this part of California. The San Andreas fault’s southernmost stretch has not ruptured since 1680 to 1690. Big earthquakes on this section of the southern San Andreas fault rupture on average every 250 years – although there can be wide variations as to how often they actually do occur. In general, there’s a 20 percent chance of a magnitude 7 or larger quake on this part of the San Andreas fault over the next 30 years. The last time a similar swarm happened was nearly four years ago. That series of moderate quakes – the worst of which were two at magnitude 4.3 and one at magnitude 4.1 – prompted a rare warning by the USGS. Monday’s outbreak “does increase the chance of a big earthquake on the San Andreas somewhat,” said USGS research geophysicist Morgan Page. Still, “it’s not necessarily doom and gloom,” she observed, given that the last three similar swarms – in 2001, 2009, and 2016 – did not result in larger, catastrophic quakes. “But every time it happens, we do worry that this could be the time that it triggers something,” she added. Read the article at the Los Angeles Times.