290 Earthquakes in 104 Hours: Salton Sea 'Swarm' Prompts (Slight) Increased Risk of Large Quake

SALTON SEA, CA – The first one hit around 4 a.m. Then came another, and another... and then, many more.

Between Monday morning and noon Friday, some 290 earthquakes had shaken the Salton Sea, seismologists tell Patch. The "swarm," as it's being called, is one of only three in recorded history at the area, lasting much of the week. Previous occurrences happened in 2001 and 2009.

Of the quakes to strike the region-- a seismic zone near the southernmost tip of the infamous San Andreas Fault-- officials say 17 were greater than a magnitude-3 and 97 were greater than a magnitude-2. The three largest included:

• M4.3, Monday at 7:31 a.m. PST
• M4.3, Monday at 8:23 p.m. PST
• M4.1, Monday at 8:36 p.m. PST

But though the swarm appears to be tapering off Friday, that doesn't mean that we're in the clear quake-wise, officials warn. The California Office of Emergency Services even issued an "earthquake advisory" to remind Southern California residents to always be prepared for temblors.

This comes after the U.S. Geological Survey found the Salton Sea swarm may add stress to the San Andreas Fault, by the slightest amount, potentially increasing the likelihood of an earthquake of magnitude-7 between now and Oct. 4.

"Preliminary calculations indicate that, as of 10:00 am (PDT) Sept. 27, 2016, there is a 0.03%-1% chance (1 in 3000 to 1 in 100) of a magnitude 7 or greater earthquake being triggered on the Southern San Andreas fault within the next seven days through October 4, with the likelihood decreasing over time," the USGS said. "This probability range is estimated using several models developed in California to assess foreshock/aftershock probabilities."

But does this mean that we're due for The Big One this week? You don't need to pack up your bags to move back East just yet, seismologists caution.

"The [percentage increase numbers] are so small that really, I would say there isn't any more of a chance than normal," Jennifer Andrews of the Caltech Seismological Laboratory told Patch on Friday. "[The swarm] very very slightly increases the risk."

Famed Seismologist Dr. Lucy Jones added on Twitter on Friday that the "...Swarm is over" and the increased risk for a large quake was "mostly" gone.

Andrews says response from the general public to the swarm has been relatively low, as not many people reported feeling any of the quakes.

"It's pretty much back to background levels now," she added of seismic activity in the Brawley Seismic Zone come Friday. "Just always be prepared."

See Also:

• Are You Really Ready for the Next Big California Earthquake?

(Images courtesy of Caltech)