August 27, 2012
Swarm Of Quakes Rock Southern California Sunday Morning, Afternoon
Lawrence LeBlond for redOrbit.com - Your Universe Online
UPDATE : 08-27-2012 10:00 a.m. (EST)
Most of the quakes were in the range of magnitude of 3.0, but some measured as high as 5.5. “Obviously, all this activity is related or interconnected, but it doesn't really follow the typical main shock, aftershock activity,” said Rob Graves, a seismologist with the USGS.
Brawley resident Alfonso Alvarez, who owns a party supply business, said he and his family had felt at least 15 shakes over a two-and-a-half-hour period Sunday afternoon, and ultimately moved his family into the yard after the biggest one hit.
“It´s been pretty bad. Some of them are slow and then they get intense,” he said. “We´re so anxious right now we can´t sit still.”
USGS Seismologist Lucy Jones said Sunday´s quakes accounted for the most shaking felt in the Imperial Valley of Southern California since the 1970s. “We are having a swarm,” she told CNN. “We expect thousands of events (like this) over several days.”
Graves said of the 300 quakes, more than 30 had magnitudes greater than 3.5, and the biggest were “a little bit larger than what we have seen in these types of processes in the past.” He noted, however, that the area is a “zone of transition” between the Imperial and San Andreas faults and tends to have more frequent activity that other parts of California.
He said that previous swarms were not precursors to a bigger quake, but “that´s not to say it won´t happen.”
“At the very least, use this is a reminder: We live in earthquake country. If we're going to have an earthquake, it's as likely today as it is tomorrow or next week. So the message here, if nothing else, is make sure you're prepared, you have your emergency kit, your emergency supplies and know what you're going to do.”
MAIN STORY FOLLOWS BELOW
A swarm of moderately-sized earthquakes struck Imperial County, north of El Centro, California late Sunday morning and early Sunday afternoon, according to the US Geological Survey. The series of temblors, some magnitude 5.0 and above, have been felt as far away as Orange County, and into Arizona and Baja California.
The USGS has so far recorded more than four dozen quakes in Imperial County, many near the city of Brawley. The first quake, a magnitude 3.9 event, struck at 10:02 a.m. (PST) northwest of Brawley and was followed by a series (swarm) of other quakes in the same general area, the USGS said in a statement.
As of 3 p.m. (PST), there have been no reports of serious damage or injuries, according to authorities in the region.
Some buildings in downtown Brawley did receive minor damage, however. Captain Jesse Zendejas of the Brawley Fire Department described the damage as “cosmetic” and said it occurred in at least three older buildings. Assessments were still ongoing as of press time.
Earthquake swarms are events where a local area experiences sequences of many earthquakes occurring over a relatively short period of time. The length of time used to define a swarm varies, but the USGS points out that an event may be on the order of days, weeks, or months, depending on circumstances.
Swarms are differentiated from aftershocks by the observation that no single earthquake can be attributed as the main shock. Earthquake swarms are generally grouped as events that precede volcanic eruptions in areas where volcanoes exist.
The quakes that have been rattling off have been in the magnitude range of 2.0 to 5.3. However, USGS geophysicist Bob Dollar said some of the larger quakes may be downgraded once scientists have a chance to analyze all the data. Most of the quakes have shook about 16 miles north of El Centro and about 92 miles north of Tijuana, Mexico. According to the USGS, there have been six earthquakes of magnitude 3.0 or greater centered near El Centro in the last 10 days.
The USGS is asking for anyone in the region who feels, or have felt any of the quakes to report it on their USGS “Did You Feel It?” page. These reports help the agency gauge the effects of the tremors.
Deanna Witte, an area resident in the affected region, told redOrbit.com that this “actually isn't anything that we are not used to down here. We just take breakables off of the shelves and wait the quakes out.” She said that an Easter quake in 2010 was similar to these. “My daughter is freaking out cuz she remembers the Easter one. She was only 4. She is 6 now.”
Dollar said it might be difficult to sort out just which fault system caused the quakes. “It´s one of the conjunctions that consists of multiple, small little faults, multiple blocks, all moving around,” he said. The area, however, has seen numerous quakes over decades, including 13 magnitude 5 quakes or greater and 84 magnitude 4 or higher quakes since 1932. “This is a very active area,” he said.
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