November 11, 2012
by John Vidale
With the numerous big quakes around us in the last few weeks: the M7.7 up the coast; the M6.3 off Vancouver Island; and the M7.4 with loads of aftershocks near Guatemala, we've been struck by the quiet in Oregon and Washington since network manager Paul Bodin and I arrived in 2006.
I've been meaning to explain that Canadian M7.7 earthquake in the next blog, but I don't understand myself, yet. It was a thrust event right next to a strike-slip fault, and I'm waiting for the Canadians to explain that to me so I can explain it to you. The Canadians, in turn, have responded by installing numerous temporary instruments in the epicentral region, which will doubtless illuminate the fault system well, but will require a few weeks or months until we see the results.
Here's a timeline since 1993 - you can see that no quake over M4.5 has hit since 2004. In contrast, between 1993 and 2004, there was an average of one a year, including several close to M6 and the nearly M7 Nisqually earthquake.
The PNSN cannot be given credit for the peace and quiet. Furthermore, given the variety of locations that earthquakes struck, most of these 10 earthquakes are unrelated to each other. Our peaceful 6 years has been due to random chance.
Here is the map view of these M3+ earthquakes - they cover our region. These are the earthquakes large enough to reliably feel, if one is close enough to the epicenter.
The cross-section view is below, with west to the left and the surface at the top. The red circles are the events larger than M5.0. The line of earthquakes on the left mark deformation of the Juan de Fuca Plate subducting under the North American Plate. The rest of the earthquakes occur in the crust of the North American plate.
The real point is that, on average, we expect $500M a year in damage from earthquakes each year in Oregon and Washington. That's the average, but in most years, there is $0 damage, and a few years are horrific. The Nisqually quake was a relatively mild earthquake, yet in 2001 we had several $B in damage.
And so we stay vigilant and watch.
(You can make any of these plots yourself and see which earthquake is which with the Custom Search option under Earthquake on the left PNSN menu.)
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- Seismology will again watch/help the Seahawk's playoff run
- Canadian ETS morphing to Washington one?
- Great ShakeOut, Great success!
- The Great ShakeOut 2014 is Tomorrow!
- Three Cascadia ETS events in past month??
- Is Mount St. Helens seismicity increasing?
- Warm weather triggers snow avalanches at St. Helens
- 2015 (4)
- November (1)
- October (2)
- September (1)
- July (1)
- May (1)
- April (1)
- March (2)
- February (3)
- January (4)
- October (1)
- September (1)
- August (1)
- June (1)
- April (3)
- March (4)
- February (1)
- January (2)
- December (1)
- November (2)
- October (3)
- September (1)
- August (3)
- July (2)
- June (4)
- May (4)
- April (2)
- The wech-o-meter takes over all of Cascadia
- Keystone Cops: Italy prosecutes seismologists for failure to predict deadly quake
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- Mount Hood earthquake swarm of Feb 23, 2012
- Web glitches: duplicate (and even triplicate!) earthquakes
- How earthquake magnitude scales work
- Mine blast masquerades as volcanic tremor
- The Spokane Swarm about 10 years ago
- Another hum around Mount St. Helens
- Slow slip: A new kind of earthquake under our feet
- PNSN and social media
- 3am M3.4 earthquake in St. Helens Seismic Zone
- The wrong kind of volcano noise
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- Rainier Repeating Earthquakes Update and Comparison with Weather Patterns
- 22-minutes drumbeat icequakes(?)
- Mount Rainier popping away
- Repeating Earthquakes on Mount Rainier - are glaciers the culprit?
- Debunking another SEC football myth by the PAC-12
- One year ago, Seattle Seahawks 12th Man Earthquake
- The odds this year of a megaquake on the Pacific Northwest coast
- Is the plague of great earthquakes this decade a sign of increased danger?
- Nile Valley landslide talks to PNSN seismologists
- Good vs evil in central US earthquake hazard analysis
- Why does a volcano scream?
- Predicting big quakes from patterns of little ones
- 1-hour warning for Japanese M9 earthquake?
- Sound Transit train under Interlaken keeps a rollin'
- Invisible changes under the hood at the PNSN
- Sound Transit Tunneling Noise
- "Visionary" toads
- Earthquake early warning in the PNW
- November (1)
- December (13)