But what does that faraway (e.g. Japanese) earthquake mean for me, in the Pacific Northwest?

Every time an earthquake, somewhere, is big enough to dominate headlines, everyone here in this northwestern corner of the United States starts wondering what it means for us.

Travel times map for Honshu quake

Warning map from NOAA National Tsunami Warning Ctr, for a tsunami generated by the March 11, 2011, Honshu earthquake (yellow star is the epicenter, with the Americas to the right).

This has happened frequently enough (e.g. Haiti, Chile, New Zealand) that I’m thinking it would be useful to create a basic FAQ for earthquakes. Lots of FAQ’s exist, written by scientists, or emergency preparedness teams. But I haven’t come across one that’s written with the fears and fascinations of the public in mind. I guess I’d start with a basic fact:

Not all earthquakes are of the same kind.

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Shallow New Zealand quake a warning to Pacific Northwest

Experts in the northwest warn the deadly earthquake in New Zealand was similar to what might happen here.

The quake hit Christchurch, New Zealand, a city comparable in size to Spokane, along a fault-line that was unknown until last September. That’s when an even larger quake hit New Zealand — but with limited damage, since it was centered farther from any city. Authorities in Christchurch were predicting the death-toll would rise to 300.

In recent years, scientists have found evidence of shallow faults across the northwest, such as the Seattle fault that runs beneath Qwest Field (the Seahawks stadium) and roughly follows Interstate-90. <--break->

In fact, there’s sort of one per town,” says John Vidale, a professor of earth sciences at the University of Washington and director of the Pacific Northwest Seismic Network. “There’s the Tacoma fault, there’s the Olympia fault, there’s the Portland hills fault, there’s the south Whidbey fault, which runs up the east side of the Puget Sound.”

Just like in New Zealand, these shallow faults shake only rarely – perhaps once every 1,000 years, or even once in 10,000 years. Rare, but extremely deadly.

Comparing to Nisqually, ten years ago — smaller but stronger

In contrast, the most recent major earthquake in western Washington was the Nisqually earthquake. The tenth anniversary happens to be on Monday.

Fenix Underground club after Nisqually quake

Seattle's Pioneer Square shortly after the 2001 quake.

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Seattle area’s evolving earthquake threat

Several recent studies from the world of geology have relevance in this damp corner of the country.  They point to the possibility that “the big one” might be bigger than we thought.

Lesson from Indonesia. They’ve had 5 major earthquakes in the past 5 years, including the famous tsunami of 2004.  A more recent quake and tsunami off the coast of Sumatra was eerily like the one that’s predicted to hit the coast of Washington and Oregon some day.  Major lessons?  As I reported for KPLU, it showed that these deep quakes could be more powerful than previously thought.   There was no tsunami this time, but the public knew enough to head for high ground anyway, just in case.

Slow quakes and Mega-quakes. You may have heard of “slow earthquakes” (also known as “deep tremors”). They happen pretty regularly in the land of Cascadia, as the power of a big earthquake is released slowly over a period of weeks.  We don’t feel anything, because the energy is spread out over time.  The leading theory is these release energy in one area as two plates on Earth’s crust slide past each other–but add to the pent-up energy at a deeper spot.  Now, scientists (led by Ken Creager at the U. of Washington) find a second type of unfelt tremor may be adding even more tension to the fault zone that runs beneath the Interstate-5 zone.  If so, that means “the big one,” whenever it happens, could be bigger than previously thought.  Geologists and engineers have to go back and re-do some calculations to see if we need to change our building codes.

Could this seismograph fit in your basement?

Volunteer to be a basement seismologist. The U.S. Geological Survey and U.W. are looking for modest size homes throughout the Seattle area, to create a network of sensors.  A similar project is underway in the San Francisco area.  They’ll get data on how different soils and different types of structures respond to shaking.  They need a spot on a concrete floor about 2 ft. x 2 ft. with electrical power and potential internet connection.  To sign up, check out the NetQuakes program.

More about that “slow earthquake”

I wrote about “deep tremors” (also nicknamed “slow earthquakes”) last January, both in this blog and for KPLU.  You didn’t feel it, no matter where you live, but the quake happened under western Washington during April and May.  That was a couple months earlier than scientists expected.  So, they didn’t get their instruments in the ground in time to record it.  No matter — the deep tremors come back approximately every 15 months.

There’s a nice write-up by Sandy Doughton in The Seattle Times today.  She went on the scene, in Sequim, as the researchers lay down their seismometers in the Olympic forest (great photos, too), and she gives a lengthier explanation of the science behind (or beneath) these episodic tremors.

Redoubt redux … (kaboom!)

It was a bit late (or the scientists were premature) but the Redoubt Volcano has finally begun erupting.  (See my previous post for context.) You’ve probably heard the top news on this by now.  Here are tidbits that might have been lost in the headlines.

  • As of noon today (Tues, 3/24), there had been six eruptions.  Tuesday has been calm, but the official alert level remains at “High.”
  • Besides the ash plume, and steam plume, there have been lahar flows — mud and water.  Some have reached all the way to Cook Inlet, 21 miles away. (But no damage so far at the Cook Inlet oil terminal, although workers were evacuated.)
  • Some of these watery lahars have been 20-25 feet deep.
  • A glacier has melted (causing the flooding).
  • 24 hours before the first eruption, seismologists at the Alaska Volcano Observatory raised the alert level around the volcano, after swarms of earth tremors in the area. (So, yes there was some warning immediately before the explosion.)

Here’s a photo of one of the eruptions, on Monday March 23rd, 2009.

Mt. Redoubt erupting on March 23rd (AVO)

Mt. Redoubt erupting on March 23rd (AVO)

Volcano rumbling near Anchorage

We think of Mt. St. Helens as America’s star volcano.  But, outside the continental U.S. there’s a lot of action.  Not only Hawaii’s dramatic Mauna Loa and Kilauea, but along Alaska’s Cook Inlet there are several “restless” volcanos.

Lately, it’s Redoubt Volcano, about 100 miles from Anchorage. It’s a striking peak, at 10,197 feet (just a little shorter than Mt. Baker in the Washington Cascades).  The U.S. Geological Survey says it expects “an eruption to begin within the next few days or weeks.”  Well, they started saying that more than a week ago.  So, hold onto your hats.

Areas of current activity on Redoubt Volcano, Alaska

Areas of current activity on Redoubt Volcano, Alaska

Last time, in 1989 and 1990, it erupted more than 20 times over a period of several months.  It shot a huge ash plume into the air that almost caused a commercial jetliner to crash.  And melting glaciers turned a nearby river into roaring torrent — which nearly wiped out an oil terminal.  No oil leaked, but buried pipelines were scoured to the surface and thousands of gallons of crude were hastily transferred away.

What will happen this time?  The USGS says the most likely scenario is something similar to 1990.  But, volcano prediction is not the most precise of sciences.  (And for those wondering if there’s any seismic connection between Redoubt and Mt. St. Helens, the answer is no.)

Earthquakes, today’s and tomorrow’s

I slept through it.  Did you feel it?  At 5:25 am today (Friday) there was a moderate earthquake in the Puget Sound area, centered near Poulsbo, WA on the Kitsap peninsula.  The USGS says it was a magnitude 4.5.

In my personal, Keith Seinfeld metrics, having lived for nine years in California, that qualifies as big enough to feel, and maybe enough to unnerve you.  But, otherwise, pretty minor.  Officially, it’s a “light” but “notable earthquake,” and the biggest we’ve had since a similar one on October 7th, 2006 (which was centered near Buckley, WA).

If you felt it, you can share your report here with the USGS (and see where the shaking was felt most strongly).

Coincidentally, the seismology team at the U.W. reported new details this week on “slow earthquakes” and “deep tremors.”

Burying a seismometer on Washingtons Olympic Peninsula

Seismologist Mario La Rocca and U.W. grad student Wendy McCausland placing a seismometer near Sequim in 2004. (La Rocca is an Italian geologist who works closely with the U.W.)

As I explained in my radio story, these are imperceptible quakes which recur on a fairly predictable cycle — every 15 months.  The next one is due this summer, under the Olympic Peninsula.

The deep tremors and slow quakes are explained in this week’s journal Science.  It appears they’re related to the Juan de Fuca plate subducting under the North American plate.  Each slow quake adds a little more stress and strain to the major fault along the Washington coast.  Every 500 years, roughly, that fault releases in a mega-thrust earthquake.  Ken Creager at the U.W. says it seems possible or even likely that the next mega-quake will happen during one of the slow earthquakes.

Unfortunately, he can only test the theory after the Big One happens.