Wednesday, March 28, 2012

The Science of Tsunamis and Earthquakes

Japan earthquake, other tectonic surprises left science in a mess
What happened last March 11 wasn't supposed to be possible. The seismic hazard maps didn't entertain the idea of a 9.0 magnitude earthquake off the Tohoku coast of Japan. But the Earth paid no heed to scientific orthodoxy. A massive slab of the planet's crust lurched 180 feet to the east.

It rose about 15 feet, lifted the ocean and tipped the Pacific's waters onto the Japanese coast.

The quake and the resulting tsunami killed about 20,000 people, wiped out entire towns and triggered power outages and then meltdowns at the Fukushima nuclear power plant.

It also humbled the scientific community.

Since 2004, earthquake scientists have been caught off guard, or to some extent consternated, by huge killer earthquakes in the Indian Ocean, Haiti, China, Japan and New Zealand.

Now the geologists are in a state of soul-searching. They want to do better, get smarter and help save lives on a shaky planet. But they feel chastened by what happened in Japan and are reexamining their basic assumptions about earthquakes.


Seismic hazard maps typically show where earthquakes are most likely to occur over a certain period of time, and the expected maximum intensity. But critics say these maps merely describe what has happened before and have virtually no predictive value. They call it "Texas sharpshooting" - shooting the side of a barn and then drawing a bull's-eye around the bullet hole.

Defenders of the maps argue that they are better than nothing. Policymakers have to decide where to put resources. Which locations have older buildings that are most in need of seismic retrofitting? How high should a tsunami wall be?

Public officials may say, in effect, we know this map is probably wrong, but we still need it for planning purposes.

If there's one obvious change in attitude among geophysicists since Japan's 3/11 disaster, it's a recognition that huge earthquakes can potentially happen on any subduction zone - any of the places where one tectonic plate is diving beneath another.

As Thorne Lay, a seismologist at the University of California, noted in a commentary in the journal Nature: "We must allow for the possibility of larger quakes in regions where we thought that potential did not exist." [...]

Thus, Tsunami inundation and evacuation maps the state of Oregon have been putting out, are positing a worst-case scenario, in order to avoid under-estimating the potential for an event, as happened in Japan.

But I wanted to know more, to find out what science was used in creating these maps. So I attended one of the "Tsunami Roadshow" meetings, where the state geologists explain their findings and answer questions. Much of the information at their presentation can be found in this PDF file: The 2011 Japan earthquake and tsunami: Lessons for the Oregon Coast.

More information for Oregon can be found at the link below:

Oregon Tsunami Clearinghouse/Resource Library

Also see:

On NW coast, potential for tsunami waves up to 100 feet now seems possible

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