California sees uptick in sizable earthquakes since the Mexicali temblor

If you’ve been feeling more shaking this year, it’s not your imagination. The number of quakes greater than magnitude 4.0 in Southern California and Baja California has increased significantly in 2010. There have been 70 such quakes so far this year, the most of any year in the last decade. And it’s only April.

There were 30 in 2009 and 29 in 2008. Seismologists said they are studying the uptick but cannot fully explain it.

Major earthquakes tend to occur in cycles, and experts have said the region in recent years has been in a quiet cycle when it comes to sizable temblors. The string of quakes this year raises the possibility that Southern California might once again be entering a more active seismic period.

Scientists said the uptick does not mean that the Big One is any more imminent, but it could mean that more significant quakes are on the way.

Egill Hauksson, a geophysicist at Caltech, said the rate of quakes in the region is “probably ... picking up again” after a relative lull that lasted more than a decade.

“What it means is that we are going to have more earthquakes than in the average year,” said Hauksson. “With more earthquakes, we’re bound to have more bigger ones. But there are always fewer of those than the smaller ones.”

Scientists, however, have not been able to fully explain the increase. “We would like to be able to explain it,” said Kate Hutton, a seismologist at Caltech. “But there’s no real correlation with any cause.”

Many of the quakes this year have been aftershocks to the magnitude 7.2 temblor that rattled the Mexicali area earlier this month. The border area had experienced a swarm of smaller quakes before that one.

And there have been more than 1,000 aftershocks, including more than a dozen that registered more than magnitude 5.0. The Mexicali quake was the region’s largest in nearly two decades -- since the 7.3 Landers quake in the Mojave Desert in 1992.

Despite their size, neither quake did catastrophic damage because they occurred in relatively remote areas far from major population centers.

The Landers quake occurred during a particularly active seismic period in the L.A. area. Between 1987 and 1994, the region experienced five major quakes. In addition to Landers, there were the Whittier Narrows quake, which killed eight people, quakes in Big Bear and Joshua Tree, and the Northridge quake, which killed 57 people, injured 4,500 and caused about $40 billion in damage.

Beginning in the late 1990s, however, the number of these big, memorable quakes subsided. Experts are not sure of the reason for the cycles.

Experts said one possibility is that the ups and downs are random. Another possibility is a “cascade effect” in which a quake on one fault changes the stresses on another. “If that fault is ready to produce an earthquake anyway, it might do something. But it would have to be pretty close” for that to happen, Hutton said.

Earthquakes have been in the forefront of public consciousness this year after January’s devastating temblor in Haiti, which killed tens of thousands. It was followed weeks later by a destructive temblor in Chile.

And then came the Mexicali quake, which was stronger than Haiti's although much less destructive.

Hauksson said it’s easy to read too much into this year's quake uptick.

Although it comes after several relatively quiet years, he noted that it’s not uncommon for one large quake to produce months if not years of increased seismic activity. So in that sense, the quake pattern this year is fairly typical.

-- Cara Mia DiMassa

Map: Intensity shaking map for Mexicali quake. USGS

Comments

[My opinon means nothing]

I find it very interesting that with all the research that these scientests have over decades of data and earthquakes and they still say "they can't explain an uptick in activity." Odd.

[M Hurley]

I wonder how many tax dollars this operation cost to get two Mexican nationals in custody. I guess the agency involved needy a timely bust to happen to do damage to much needed legalization. When are we as a people going to say enough and turn this into the cash crop it should be...?

[Richard Guy]

Earthquakes are manifestations of Earth Expansion. As our Planet expands earthquakes occur anywhere and everywhere to release tension. At this time we are expereincing multiple shocks in southern California and The Baha area. The Baha Peninsular is splitting away from the Mexican mainland. Perhaps expansion is taking place in that area at this time. There have been several earthquakes recently in Indonesia and the Pacific Island Chains. We keep missing the the point with speculation upon speculation about earthquakes. After the recent earthquake in Chili the sea receded exposing a great stretch of Coastline. After the 2004 earthquake in Sumatra that caused the Tsunami the sea receded two hundred feet from the previous shoreline. After another quake recently in the Solomons the sea retreated and exposed the sea floor. This phenomenon has been occuring far back into prehistory and we still dont get it. Our Planet is expanding and our seas are receding: not rising. The National Science Foundation is funding research into "Rising Sea Levels" a non event. What they should be funding is research into "Receding Seas"

[Manny Tios]

PEOPLE GET READY.. EVEN IF WONT HAPPEN WE ALL STILL NEED TO BE PREPARED FOR THIS!!! SOME ONE CLOSE TO PEOPLE THAT WORK FOR A SEISMOLOGIST INSTITUTION IN CA HAD MENTIONED TO ME THAT SOME UNUSUAL MOVEMENTS ARE HAPPING IN THE EARTH NOW!! AND SOMETHING IS GONA HAPPEN SOON!!!

[JeB]

A reminder to finally get your earthquake / disaster kits in order. Always seems like they're too much trouble until you need one and then its a bit late.

[electronic cigarette]

Wow could you imagine what this means?

[angus]

****After another quake recently in the Solomons the sea retreated and exposed the sea floor. This phenomenon has been occuring far back into prehistory and we still dont get it. Our Planet is expanding and our seas are receding: not rising. ****

I'm not sure how you work out the seas are receding,even with the movement of the earths crust - with islands in the pacific having problems with wave action and the like - perhaps the islands really are sinking not as most people seem to think - the seas rising?

[cheapportabledvd]

Sure, but that's kind of like fortune telling. Be sufficiently vague or talk about things that are common occurrences and your foretelling will usually come true. Mankind has had wars for thousands of years and I'm pretty sure famines and earthquakes have also occurred in the past and will continue in the future.

[blender]

Yeah, I could see how releasing some of the built up energy in small bits could possibly function like a hot water tank's pressure valve, keeping the situation from getting supercritical.

Then again, it could also be more like an avalanche, where one small event can create a chain reaction causing it to increasingly lose its hold until the whole thing just snaps.

This is exciting, somebody should start taking bets. Actually, I'm guessing there's probably at least one bookie that is...