The 8.6 temblor and its 8.2 aftershock rattled inhabitants of the countries bordering the East Indian Ocean, but did little damage. Image courtesy of USGS.

Large 2012 earthquake triggered temblors worldwide for nearly a week

 

By Robert Sanders, Media Relations | September 26, 2012

BERKELEY —

This year’s largest earthquake, a magnitude 8.6 temblor on April 11 centered in the East Indian Ocean off Sumatra, did little damage, but it triggered quakes around the world for at least a week, according to a new analysis by seismologists from UC Berkeley and the U.S. Geological Survey (USGS).

The April 11 quake was unusually large — the tenth largest in the last 100 years and, similar to a few other recent large quakes, triggered small quakes during the three hours it took for seismic waves to travel through Earth’s crust.

The new study shows, however, that some faults weren’t rattled enough by the seismic waves to fail immediately, but were primed to break up to six days later.

The findings are a warning to those living in seismically active regions worldwide that the risk from a large earthquake could persist — even on the opposite side of the globe — for more than a few hours, the experts said.

“Until now, we seismologists have always said, ‘Don’t worry about distant earthquakes triggering local quakes,’” said Roland Burgmann, professor of earth and planetary science at Berkeley and coauthor of the study. “This study now says that, while it is very rare – it may only happen every few decades – it is a real possibility if the right kind of earthquake happens.”

“We found a lot of big events around the world, including a 7.0 quake in Baja California and quakes in Indonesia and Japan, that created significant local shaking,” Burgmann added. “If those quakes had been in an urban area, it could potentially have been disastrous.”

Burgmann and Fred F. Pollitz, Ross S. Stein and Volkan Sevilgen of the USGS will report their results online on Sept. 26 in advance of publication in the journal Nature.

The 8.6 temblor and its 8.2 aftershock rattled inhabitants of the countries bordering the East Indian Ocean, but did little damage. Image courtesy of USGS.

Burgmann, Pollitz, a research seismologist, and their colleagues also analyzed earthquake occurrences after five other recent temblors larger than 8.5 — including the deadly 9.2 Sumatra-Andaman quake in 2004 and the 9.0 Tohoku quake that killed thousands in Japan in 2011 — but saw only a very modest increase in global earthquake activity after these quakes. They said this could be because the East Indian Ocean quake was a “strike-slip” quake that more effectively generates waves, called Love waves, that travel just under the surface and are energetic enough to affect distant fault zones.

Burgmann explained that most large quakes take place at subduction zones, where the ocean bottom sinks below another tectonic plate. This was the origin of the Sumatra-Andaman quake, which produced a record tsunami that took more than 200,000 lives. The 2012 East Indian Ocean quake involved lateral movement — referred to as strike-slip, the same type of movement that occurs along California’s San Andreas Fault — and was the largest strike-slip quake ever recorded.

“This was one of the weirdest earthquakes we have ever seen,” Burgmann said. “It was like the 1906 San Francisco earthquake, a strike-slip event, but it was huge – 15 times more energetic. This earthquake and an 8.3 that followed were in a very diffuse zone in an oceanic plate close to the Sumatra subduction zone, but it wasn’t a single fault that produced the quake, it was a crisscrossing of three or four faults that all ruptured in sequence to make such a big earthquake, and they ruptured deep.”

The seismologists analysis found five times the expected number of quakes during the six days following the April 11 quake and aftershock. An unusually low occurrence of quakes during the 6-12 days before that 8.6 quake may have accentuated the impact, possibly because there were many very-close-to-failure faults sensitive to a triggering shock wave, Pollitz said.

One possible mechanism for the delayed action, Burgmann said, is that the East Indian Ocean quake triggered a cascade of smaller, undetectable quakes on these faults that led to larger ruptures later on.

Alternatively, large quakes could trigger nearly undetectable tremors or microquakes that are a sign of slow slip underground.

“One possibility is that the earthquake immediately triggers slow slip in some places, maybe accompanied by detectable tremor, and then that runs away into a bigger earthquake,” Burgmann speculated. “Some slow slip events take days to a week or more to evolve.”

The work was supported by the USGS.

A February map from the U.S Geological Survey shows the estimated range of the great Cascadia earthquake of 1700.

Quake catastrophe like Japan's could hit Pacific Northwest, new data show

 

A February map from the U.S Geological Survey shows the estimated range of the great Cascadia earthquake of 1700.

By M. Alex Johnson, msnbc.com

A massive earthquake like the one that unleashed a giant tsunami and killed nearly 16,000 people in Japan a year ago not only could happen here in the U.S., but probably will — and relatively soon in terms of seismological history.

The Tohoku earthquake was the most closely monitored in history, yielding an unprecedented breadth of data, geophysicists and seismologists say. And for residents of the Pacific Northwest, the new data should be worrisome.

"It's just like Japan, only a mirror image," said Gerard Fryer, a geophysicist at the University of Hawaii and the Pacific Tsunami Warning Center.

The disaster in Japan occurred because of stress from the Pacific tectonic plate sliding below Japan, according to new research discussed last month at the annual conference of the American Association for the Advancement of Science in Vancouver, British Columbia.

The lead researcher, John Anderson, a geophysicist at the University of Nevada-Reno, said the plates locked together, slowly pushing Japan westward.
The plates released catastrophically on March 11, 2011, creating a magnitude-9.0 earthquake and tsunami waves that topped 100 feet, said Anderson, who spent most of the past year in Japan as a visiting research professor in Tokyo.

While most Americans probably think the San Andreas fault running through California poses the greatest threat of unleashing a killer mega-quake, data from the Japanese quake indicate that the distinction actually belongs to the Cascadia fault line, which runs through southern Canada, Washington and Oregon to Northern California, Anderson said at the conference.

USGS earthquake information by state


Like Fryer, he called the Pacific Northwest trench a "mirror image" of the Japanese trench — except potentially even more dangerous.

"In this mirror image, one can see that if the same earthquake occurred in Cascadia, the fault would rupture to a significant distance inland, since the Cascadia trench sits much closer to the coastline than the trench off the coast of Japan," Anderson said.

While some probability models predict that a Cascadia earthquake wouldn't rupture so far under the land, "if it does, the data from the Tohoku earthquake predict stronger ground motions along our West Coast than those seen in Japan," he said.

In layman's terms, what's happening is that the region "is being deformed because the plates are locked together, and the shoreline is sinking and the rest of the thing is being bent," Fryer said in an interview with NBC station KHNL of Honolulu.

Fryer said the big question is not whether a Japan-like quake will happen, but when.

A coastal Oregon town considers building a tsunami- and earthquake-proof city hall. Experts and residents debate whether the plan will work.

"Where are we here? Are we close or are we not close?" he asked. "I think the suspicion is that it could be sooner rather than later."

Anderson's research supports that conclusion.

Experts generally agree that last great Cascadia earthquake happened on Jan. 26, 1700. It generated tsunami waves that indicated that its magnitude was also about 9.0.

"Earthquakes of this size in the past may have recurred with intervals of as small as about 300 years," Anderson said at the AAAS conference last month. "So it would not be a scientific surprise if such an event were to occur in the near future. If you live in the Pacific Northwest, look at the videos of Tohoku as a reminder to be prepared."

In January, experts discussed lessons from the Japanese earthquake at a conference of the Cascadia Region Earthquake Workgroup.

The warnings come as the White House is proposing a 2013 budget that would cut $4.6 million from National Oceanic and Atmospheric Administration's tsunami programs. Much of that would come from the National Tsunami Hazard Mitigation Program, which funds evacuation maps, training and education efforts — important services given how deeply the Japanese quake and tsunami transformed the science of seismology.

"The Japan earthquake told us that a lot of what we understand about how earthquakes work is wrong," Fryer said. "Do we now have to go back and look at all of our evacuation maps and make sure that they're right? That's a question that's still unanswered, and that question would be answered with tsunami hazard mitigation program funds."

The Unthinkable

I started reading a fascinating book on the human response to disaster. 

Think you are good in a crisis?  You should read this book and find out why. 

Or maybe you will find out that you might not respond as well as you expect.

Since Seattle is in the heart of earthquake country, this applies to most of us. 

Since our clients are interested in a seismic retrofit because they understand our earthquake risk, this book could be of interest to them.

Check it out:  The Unthinkable.

Happy reading!

Kudos

I was shopping for a service the other day.  Like most people, I started my search online.  I found a few Seattle businesses that did what I was looking for, and visited a few web sites. 

One of them caught my attention in a way that resonated with me - but not necessarily in a good way.

One of the tabs on this site was for "customer testimonials".  I clicked on it, wanting to read all the rave reviews that this company's satisfied clients had written.

There was ONE testimonial on that page.  One.

Even a company that had only been in business a couple of years would have more than one nice letter from a client.  Wouldn't they?

Sound Seismic has more testimonials than we know what to do with.  Not everybody writes to tell us how awesome we are, but we strive to impress every single client.

I'd toot Sound Seismic's horn and list off all the things we do in our quest for raving fans, but it's a lot more effective to hear it from a third party. 

Now THIS is what a testimonial page should look like!  http://soundseismic.com/about-sound-seismic/testimonials

USGS Earthquake Notification

For those of us interested in earthquake news, the USGS has an email notification system that might be worth a look.

You can adjust some parameters, like where in the world an earthquake must occur for you to receive an email.  Mine is set for anywhere in the world, as long as it is a magnitude 6.0 or greater.

Pretty fascinating how many earthquakes occur somewhere on the planet.  The other day, I received 5 separate notifications!  Three were off Honshu, Japan; one was in Cuba, and one in Indonesia.

The link is:  https://sslearthquake.usgs.gov/ens/

Enjoy!