Swarms or aftershocks?



Brawley Seismic Zone
The Brawley Seismic Zone connects the San Andreas and the Imperial Fault

(August 28, 2012, BRAWLEY) – Kate Hutton a seismologist at the California Institute of Technology in Pasadena, California said Brawley’s swarm of earthquakes is “common” for what she termed the Brawley Seismic Zone.  The area doesn’t experience quakes like Northridge where they had a 6.7 magnitude earthquake and aftershocks for weeks afterwards.

Each earth movement here is an earthquake and not an aftershock. “They are called swarms because they are like swarms of bees. Each one comes by and stings and then leaves. No aftershock from the bite, each one new and unique,” Hutton explained.

Also, another trait of swarms is that they usually build to a crescendo and then begin to decrease, making the strongest shakes in the middle of the swarm. On Sunday, that is how it appeared with experiencing the 5.3 and 5.5 minutes from each other in the middle of the day.

“We cannot predict earthquakes with any certainty,” Hutton went on to say. “These could last for days, weeks, or as it looks now, begin to end.”

The Brawley Seismic Zone connects the San Andreas Fault which peters out around Bombay Beach and the Imperial Fault. The Imperial Fault is responsible for the Easter Sunday quake in 2010 and the other large quake of 6.7 the valley experienced in 1979. Hutton said the 1979 quake re-awakened the Brawley Seismic Zone as it had been quiet for decades.

Old timers will remember the previous swarms Brawley experienced in 1981, and the 1950’s and 1960’s.

Swarms are also prevalent where there is geothermic activity.

Hutton said that the very early discoverers of this area, the De Anza Party, wrote about the earthquakes they experienced as they traveled across the Imperial and Coachella Valleys.

Hutton ended by reminding the public that their best defense is to have a plan, get an emergency kit together, plan where the family is to meet in case of separation during a major quake, and remain calm.