BRAWLEY, CA — New Year’s Eve seemed like a war zone to the residents and pets of Brawley as all night long, illegal celebratory fireworks were accompanied by earthquake swarms, unnerving this small Southern California town.
As a finale in the waning hours of 2016, the desert town experienced a rare, violent thunderstorm, drenching the town in rain and lightning that replaced the booming fireworks. The events had many Brawley residents commenting on social media about waiting for locusts to invade, while others sent out desperate missing pet reports due to animals being frightened by the chaotic noise.
National news organizations stated many quakes were too small to be felt ranging from the 1 to 2 in magnitude. But Brawley residents disputed the claim, saying the small ones were not only felt, but heard. Earthquake reporting agencies determined the quakes were centered directly under the city, with computer apps pinpointing the exact locations.
The USGA website listed a swarm of more than 250 small earthquakes since New Year’s Eve. Some residents said they hoped the swarms were relieving stress in the tectonic plates and perhaps saving the town from a stronger jolt.
The strongest earthquake in the sequence was reported as a magnitude 3.9, striking directly underneath of Brawley on December 31 at 3:06 p.m., followed within the minute with a 3.4 jolt.
The earthquakes struck in the southern end of the Brawley Seismic Zone, a seismically active region where tectonic plates are moving away from each other and the Earth’s crust is getting stretched out “and basically adding land,” said Pasadena’s Caltech seismologist Egill Hauksson.
The Brawley Seismic Zone is particularly important to watch because it is the region that connects the San Andreas and Imperial faults, both of which can produce damaging earthquakes, according to seismologists. Its north–south extent ranges from the northern section of the Imperial fault, starting approximately six miles north of the United States–Mexico international border and connecting to the southern end of the San Andreas fault, where it terminates near Bombay Beach.
Hauksson said he was closely monitoring the swarm that began Saturday, as there was a chance that an earthquake of magnitude 5 or larger could be triggered.
In late September, another swarm began in the northern Brawley Seismic Zone closer to the Salton Sea, with three measuring above magnitude 4. That event led the U.S. Geological Survey to warn that chances of a magnitude 7 or greater earthquake on the San Andreas fault could rise as a result of the swarm.
Before that was the 2012 Brawley earthquake swarm which also occurred in the lower Brawley Seismic Zone (BSZ). That Brawley swarm produced more than 600 events recorded by the United States Geological Survey (USGS)–California Institute of Technology (Caltech) Southern California Seismic Network (SCSN).
During the Valley’s seismically active period of the 1970s, the BSZ produced close to half of the earthquakes recorded in California. However, for two decades following the 1979 Imperial Valley main shock 6.4 and its aftershock sequence, the BSZ was much less active.
The last major earthquake felt in the region was the 2010 Easter Baja California tremor, which occurred on April 4, Easter Sunday, with a moment magnitude of 7.2. The shock originated at 3:40 p.m. local time south of Guadalupe Victoria, Baja California, Mexico.
It was the strongest to rock Southern California in at least 18 years, according to data. Most of the damage occurred in the cities of Mexicali and Calexico on the Mexico–United States border.
That quake is believed to have occurred on the Laguna Salada Fault, which is about 36 miles, long and straddles the California–Baja California border
In 1979, a magnitude 6.5 earthquake sent violent shaking into El Centro, injuring 91 and causing so much damage to the concrete Imperial County Services Building that it had to be demolished. There was also major damage to the irrigation system in the Imperial Valley.
The historic magnitude 7.1 earthquake that hit El Centro in 1940 claimed nine lives and swayed buildings as far away as Los Angeles. Irrigation systems were damaged, and railroad tracks were left warped where they crossed the fault.
Another swarm of small earthquakes, topping out at magnitude 3.5, struck the town of Niland near the eastern shore of the Salton Sea on Halloween.
The last major earthquake to hit Brawley was in 2012, registering at magnitude 5.4.