Science
5:14 pm
Tue February 22, 2011

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 and roughly follows Interstate-90.

"In fact, there’s sort of one per town," says John Vidale, a professor 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. It was bigger in magnitude than the one in New Zealand, but ten times as deep in the ground. 

Here's a comparison:

Christchurch quake, February 22 2011:

  • Magnitude - 6.3
  • Depth - 3.1 miles
  • Time of day - 12:51 pm

Nisqually quake, February 28 of 2001:

  • Magnitude - 6.8
  • Depth - 32 miles
  • Time of day - 10:54 am

On the ground, the forces you would have felt in New Zealand were three to four times as strong as the worst shaking from the Nisqually quake, based on preliminary data, Vidale said via e-mail.

The University of Washington's Vince Stricherz has written a nice look-back at the Nisqually quake and a few lessons that have been learned since then. For example, we have better maps of which neighborhoods have the highest risks, and more older buildings have been strengthened. 

Still, the devastation in a city with modern building codes (as opposed to a city like Port-au-Prince, Haiti) should be sobering in Seattle, Portland, and anywhere in between.

"I think [the damage] would probably be worse here than New Zealand, in that we are much more built up, and we have a lot of old structures built before we knew we have big earthquakes here," says Vidale.

Disaster planners like to remind us that some simple preparations can help – such as tying down your water heater, reinforcing your chimney, and making sure you have an emergency kit and a plan.

More KPLU stories about earthquakes and lessons for the Puget Sound area can be found here:

Lessons from Chilean earthquake for Seattle area

 

 

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