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San Andreas Fault: USGS Advisory Sparks Fear Of A Big Earthquake Of Magnitude 7 Or More

By Rahul Srinivas
Published on: 11:10 PST, Sep 30, 2016

Is California about to be hit by a large earthquake next week? This is the question on everyone’s mind after the U.S. Geological Survey and the California Office of Emergency Services both issued separate statements asking citizens to be prepared for a large earthquake earthquake in the next few days. Both the statements made it clear that there is a possibility of a large earthquake (magnitude 7 or more) striking the state within the next 7 days. The advisory was issued just a few days after unusual seismic activity was recorded under the shallow waters of the Salton Sea, an endorheic rift lake located directly on the San Andreas Fault.

According to the USGS statement, the seismic activity started on Monday. The statement described the activity as a rapid succession of small earthquakes — two of which were above magnitude 4. The epicenter of these quakes were near the Bombay Beach. This unusual seismic activity continued for more than 24 hours. By the end of it, seismologists had recorded more than 200 small quakes. These quakes were also highly centralized and were not spread across a large area which has also piqued the interest of seismologists as well as raising concerns. This is because such seismic activity has taken place only thrice since 1932.

The official statement issued by the USGS read,

“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 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. This probability range is estimated using several models developed in California to assess foreshock/aftershock probabilities.”

At around the same time, another statement was issued by the California Office of Emergency Services which read,

“Following a swarm of recent small magnitude earthquakes that began on Monday near the Salton Sea in Southern California, the Director of the Governor’s Office of Emergency Services reminded local emergency managers and the public to be prepared for the potential of similar or larger earthquakes over the next week.”

An additional footnote was added on September 30 which indicated the possibility of a magnitude 7.0 plus earthquake. It read,

“This advisory was updated to clarify that CEPEC specifically evaluated the potential for the earthquake swarms to trigger a larger earthquake (M7.0+) on the San Andreas Fault. Scientists estimated values between 0.03 percent and 1.0 percent possibility of that happening.”

Mark Ghilarducci, the director of CalOES, has asked people to not let their guard down.

“California is earthquake country. We must always be prepared and not let our guard down. The threat of an earthquake on the San Andreas Fault hasn’t gone away, so this is another important opportunity for us to revisit our emergency plans and learn what steps you need to take if a significant earthquake hits.”

According to scientists, these activities are being taken very seriously because it happened in one of the most seismically complex areas in the state of California. The quakes were recorded a few miles south of where the San Andreas fault ends. Seismologists are worried that these temblors could be powerful enough to wake the San Andreas fault from a 330-year slumber. This area, located south of the fault, has not seen major seismic activity since 1680. With a major earthquake likely to happen once every 150-200 years, the area is long overdue for a major temblor.

USGS research geologist Kate Scharer explains why her fraternity is now a worried lot.

“The southern San Andreas is actually seismically fairly quiet. It doesn’t really make noise. So to have something right next to the main strand making a little noise — you have to pay attention to how it might be transferring stress onto the main strand of the fault.”

So, what could possibly happen if the much-feared magnitude 7 plus earthquake hit the area? According to a simulation created by USGS researchers, a magnitude 7.8 earthquake would result in major destruction across a large area as the shock waves move across. The quake will cause Los Angeles to shake for over a minute. It could also lead to massive fires. There would be several aftershocks which could be even larger in magnitude than the initial quake. The possible death toll would be in the 1000s with more than 50,000 people injured. The massive earthquake could also cause $200 billion worth of damage.

In case you are living in California, do let us know if your local agencies have issued advisories pertaining to this possible earthquake. Stay safe.

[Featured Image by Doc Searls/Flickr/CC BY-SA 2.0]

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