Thread: California's chances of having a magnitude-7 or greater earthquake in the next couple

California's chances of having a magnitude-7 or greater earthquake in the next couple days just skyrocketed

Sept 30, 2016 1:18 p.m. ET

A cluster of more than 200 small earthquakes beneath the Salton Sea in Southern California earlier this week has scientists waiting to see if the slumbering San Andreas fault nearby could be the next to move. The U.S. Geological Survey estimates that following the quake swarm at the Salton Sea on Monday and Tuesday, the likelihood of a magnitude-7 or greater earthquake being triggered is as high as 1 in 100 over the next seven days, though the odds will lower as time goes on.

But for now, local seismologists might feel their hearts racing. "When there's significant seismicity in this area of the fault, we kind of wonder if [the San Andreas] is somehow going to go active," Caltech seismologist Egill Hauksson told the Los Angeles Times. "So maybe one of those small earthquakes that's happening in the neighborhood of the fault is going to trigger it, and set off the big event."

And by big event, they mean big

A San Andreas earthquake starting at the Salton Sea has long been a major concern for scientists. In 2008, USGS researchers simulated what would happen if a magnitude-7.8 earthquake started at the Salton Sea and then barreled up the San Andreas fault, sending shaking waves out in all directions.

By the time the San Andreas fault becomes unhinged in San Bernardino County's Cajon Pass, Interstate 15 and rail lines could be severed. Historic downtowns in the Inland Empire could be awash in fallen brick, crushing people under the weight of collapsed buildings that had never been retrofitted.

Los Angeles could feel shaking for a minute — a lifetime compared with the seven seconds felt during the 1994 Northridge earthquake. Shaking waves reach as far as Bakersfield, Oxnard, and Santa Barbara. About 1,600 fires spread across Southern California. And powerful aftershocks larger than magnitude-7 pulverize the region, sending shaking into San Diego County and into the San Gabriel Valley. [Los Angeles Times]

Scientists say major earthquakes happen in Southern California about once every 150 or 200 years; the last big quake at the Salton Sea-tip of the San Andreas fault was 330 years ago. Read the full chilling report at the Los Angeles Times. Jeva Lange

http://theweek.com/speedreads/652311...st-skyrocketed

. . .
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."


An aerial view of the Salton Sea. Image via Shutterstock.

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."

http://patch.com/california/palmdese...sed-risk-large

https://earthquake.usgs.gov/misc/2016-09-27.php

Earthquakes in the Brawley Seismic Zone: Updated 09/30/2016


Earthquakes in the Brawley seismic zone as of the evening of 09/27/2016.

An earthquake swarm near Bombay Beach, California, started on Sept. 26, 2016, in the Brawley Seismic Zone, which lies near the southern terminus of the San Andreas Fault.

The swarm includes 96 earthquakes above magnitude 2 so far (as of 12:00 pm PDT on Sept. 30, 2016). Relocations of these events show that they are occurring in the depth range 4 to 9 km. The largest of these events were two M4.3 earthquakes and a M4.1 earthquake on Sept. 26.

The earthquakes are occurring near a set of north-northeast trending cross-faults beneath the Salton Sea. The cross-faults are part of a fault network that connect the southernmost end of the San Andreas Fault with the Imperial Fault. Some of the cross-faults are oriented such that they add stress to the San Andreas Fault and the San Jacinto Fault system when they rupture in small earthquakes like those in the ongoing swarm.

Swarm-like activity in this region has occurred in the past, so this week’s activity, in and of itself, is not necessarily cause for alarm.

Preliminary calculations indicate that, as of 12:00 pm (PDT) on Sept. 30, 2016, there is 0.006% to 0.2% chance (less than 1 in 10,000 to 1 in 500) of a magnitude 7 or greater earthquake being triggered on the Southern San Andreas Fault within the next seven days through October 7, with the likelihood decreasing over time. This range is estimated using several models developed in California to assess foreshock/aftershock probabilities, and the lower bound is about equal to the average chance of a magnitude 7 earthquake occurring on the Southern San Andreas Fault in any given week.

These revised probabilities are lower than those made earlier this week, due to decreasing swarm activity.

The probabilities may change if the swarm activity increases or decreases.

https://earthquake.usgs.gov/misc/2016-09-27.php

I live on the ocean in Cali and haven't felt any earthquakes.

Then again, I might be so used to them that I just don't feel them anymore.

USGS: Threat of imminent earthquake in Southern California diminished
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10News‎ - 2 hours ago

An alert issued last week warning Southern California residents of the increased possibility for a major earthquake is now being lifted, according to the United States ...