Aftershocks expected for years, seismologists say
April 7, 2010 @ 11:34 am
More than 422 aftershocks measuring 3.0 or higher have been recorded in the Southern California desert by the U.S. Geological Survey since the 7.2 earthquake on Easter Sunday, according to USGS seismologist Morgan Page, PhD. That
The 7.2 Sierra El Mayor earthquake on Easter Sunday caused 2.5 meters of lateral slip in the ground. The rupture pictured here in the Pescadores fault 30 miles south of Calexico is estimated to be eight to 16 inches. --Photo Courtesy of U.S. Geological Survey
does not include the hundreds of lesser-magnitude tremors recorded.
Aftershocks from an earthquake the size of Sunday’s can last for years, Page said. “In Indonesia last night, the magnitude 7.7 is very likely an aftershock of the earthquake that caused the tsunami in that region in 2004,” she said. The magnitude 9.1 earthquake struck the north coast of Sumatra in December 2004, causing a tsunami that killed nearly 228,000 people.
For valley residents it might feel like the larger tremors following Sunday’s quake keep coming every 10 minutes, and looking at the complete list of quakes confirms constant movement of the ground in the Imperial and Mexicali valleys.
“Every day that passes, the aftershock activity decreases on average. Therefore, we are safer with each passing day, provided that a particularly large aftershock does not occur,” Page said. “Eventually, the activity decreases where you might feel a big aftershock once a week, then maybe once a month.”
A team of seismologists from USGS, CalTech University, San Diego State University and Mexico’s Centro de Investigacion Cientifica y de Educacion Superior went into Baja on Monday, Page said, to determine exactly where Sunday’s 7.2 Sierra El Mayor earthquake originated. “We were kind of surprised because it started on the small Pescadores fault and then propagated, or mostly ruptured on the Borrego fault,” she said.
The seismology team on Monday measured 2.5 meters of “slip,” which, in this case, was the earth getting torn in a lateral motion by about eight feet.
Several roads were closed throughout Imperial County following the earthquake. Imperial County Fire Chief/Emergency Services Coordinator Tony Rouhotas announced at a news conference on Monday that ground shifts caused the closures. The county is still reporting closures of the following:
- Drew Rd. from Evan Hewes Hwy. to Sunbeam Lake; from Kramar Rd. to Diehl Rd, including the New River bridge
- Lyons Rd. from Austin Rd. to Brockman Rd., including the New River bridge
- Brockman Rd. from McCabe Rd. to Schaniel Rd, including the New River bridge
- Austin Rd. from McCabe Rd. to Ross Rd.
- Worthington Rd. from Forrester Rd. to Huff Rd., including the New River bridge
- Boley Road from Huff Rd. to Hetzel Rd.
- Jeffery Rd. from Hardy Rd. to Evan Hewes Hwy
- Hetzel Rd. from Westmorland Rd. to Huff Rd., including the Salt Creek Canal bridge
View a gallery of Mexicali earthquake photos here.
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Ok, this could just be an (lack of) updating thing, but if you look at the state of the Easter quakes here:
http://earthquake.usgs.gov/earthquak….-125.-115.php
That map alone says we’re at 2,422 quakes, which doesn’t include Alaska quakes or elsewhere in the US. Plus I don’t think these are cumulative maps for the whole year, I think that once quake is over a week old it falls off these maps. Please correct me if I’m wrong.
Then look at the bottom graph on this page:
http://earthquake.usgs.gov/earthquak…ar/eqstats.php
So that map says we’ve had only 991 quakes up to April 8,2010. It could easily be a lack of updating as I said, but the math in these maps doesn’t add up for me.
The bottom chart of the second link I gave shows 4,500 quakes for the entire year of 2009? And it looks like it’s comprehensive and shows quakes of all magnitudes.
To the point: Have we just had about 3,000 quakes in the last week? And lord knows how many more throughout the year, compared to a rough average of 4,000 quakes a year since 2001?
I must be reading these charts wrong.
Can’t see what you’re talking about because the URLs you provided are broken. But, I think the story was pointing out only the locally originating earthquakes of 3.0 or higher between Sunday at 3:40 p.m. and Wednesday morning, about 60 hours later. Yeah, I would imagine there are thousands of earthquakes all over the globe in just one week, but USGS is the best source to get a good answer to your question.
Seems like most of the road closures were in southwest area of outskirts of El Centro. What’s with that? Older bridges and roads there? Or where stress was in quake?
Which all reminds me: Is there some investigating you can do on how post-quake integrity of Interstate 8 bridges from Yuma on thru to San Diego? That’s what worries me most.