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Thursday, December 30, 2010

Quakes shake No. 2 year-end spot


Editor's note:

The Yuma Sun will be taking a look back at the top 10 stories of the year in Yuma County in the coming days, as chosen by the Yuma Sun newsroom staff. We are continuing with story No. 2 today and will work our way up each day to this year's top story of the year on Dec. 31.

Yuma has been a hot spot for seismic activity this year. The region has experienced thousands of aftershocks from the massive El Mayor-Cucapah earthquake on Easter Sunday.

While there were no injuries or severe damage to local structures as a result of the quakes, due to their epic scale, Yuma Sun newsroom staff voted the story the second-most important of 2010.

The 7.2-magnitude Easter Day earthquake struck at 3:40 p.m. on April 4, 16 miles south of Guadalupe Victoria, Baja Calif.

“This was a pretty big quake,” Jill McCarthy, director of geological hazards for the U.S. Geological Survey (USGS) told the Yuma Sun in April.

The earthquake, centered about 42 miles south/southeast of Calexico, was the largest in the region since 1973, McCarthy added.

The quake caused a power outage for about 4,900 Arizona Public Service customers and shook food off of grocery store shelves at many local stores.

The city of Yuma even set up an emergency operations center as a precaution.

The quake hit during the Yuma County Fair but did not cause any rides to be shut down.

While Yuma escaped many of the ravages associated with a large earthquake, neighbors in El Centro and Calexico, as well as San Luis Rio Colorado, Son., did not fare so well.

The California cities west of the Imperial Sand Dunes suffered millions of dollars in damages to buildings, as well as to water and wastewater facilities.

Just days after the first major quake, the Imperial County cities experienced 2,000 aftershocks, Brad Jennings, editor of the Imperial Valley Press, told the Yuma Sun. There were 560 aftershocks in the first 24 hours alone.

In San Luis Rio Colorado, Son., nearly 150 homes were destroyed. The damage caused an estimated cost of more than $900,000, the Mexican border city's mayor, Manuel Baldenebro, reported at the time.

The city also suffered severe damage to its education system, when 126 classrooms were damaged.

In June, a team of scientists working for NASA's Jet Propulsion Laboratory (JPL) reported the quake had physically moved the city of Calexico, Calif., 2-1/2 feet in a southern direction. They also discovered a previously unknown fault line in northern Baja California.

Andrea Donnellan, a geophysicist with NASA's JPL, said it is normal for massive quakes to move cities. “The amount was very typical for that size earthquake.”

The NASA science team used an Uninhabited Aerial Vehicle Synthetic Aperture Radar to measure surface changes from the quake.

The NASA data showed the quake moved the Calexico region in a downward and southerly direction up to 31 inches.

On June 14, a 5.7-magnitude earthquake shook Yuma County. According to USGS, that earthquake was just another hiccup caused by the Easter Sunday earthquake. It occurred at 9:27 p.m. and was located 35 miles southwest of San Luis Rio Colorado.

Two more large aftershocks hit the area on Sept. 14.

The first, a 5.0, struck at 3:52 a.m., with an epicenter 35 miles southwest of San Luis Rio Colorado, Son. The second, a 4.8 with an epicenter 30 miles southwest of San Luis Rio Colorado, struck at about 11:10 p.m. There were no reports of serious damage or injuries as a result of those quakes.

With thousands of aftershocks in the area, USGS wanted to reassure those living here such events are completely normal and not necessarily an indicator of a larger quake in the future.

“There is always the normal background noise,” said Don Blakeman, USGS geophysicist.

“There are always a few quakes in the Baja just like there are quakes in Southern California and Northern California. That is kind of the normal seismic level.

“Then we have these large earthquakes and the activity in general is elevated as that aftershock series continues. At some point down the road, it kind of blends back into that background level of earthquakes.”

All of the earthquakes have been part of the same series, Blakeman reported.

“They are in the same aftershock zone. There have definitely been a significant amount (of quakes), and it's because of that 7.2. It is just a series of aftershocks. It is not strange at all. This is just business as usual for that part of California and Mexico.”

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