October 11, 2010
Smaller Earthquakes Can Cause Tsunamis

Geologists at UT Austin are doing research that lays the foundations for new disaster movie plot lines.

Geologists studying the Jan. 12 Haiti earthquake say the risk of destructive tsunamis is higher than expected in places such as Kingston, Istanbul, and Los Angeles.

Like Haiti's capital, these cities all lie near the coast and near an active geologic feature called a strike-slip fault where two tectonic plates slide past each other like two hands rubbing against each other.

Until now, geologists did not consider the tsunami risk to be very high in these places because when these faults rupture, they usually do not vertically displace the seafloor much, which is how most tsunamis are generated. This latest research suggests even a moderate earthquake on a strike-slip fault can generate tsunamis through submarine landslides, raising the overall tsunami risk in these places.

The plot: A series of moderate earthquakes off coasts around the globe suddenly flood many port cities. A pretty young scientist tries to warn governments but is met with scorn. A surfer cult believes her warnings because she has a sexy body. They decide to live offshore of the first city (LA naturally) predicted to get the tsunami so that at a moment's notice they can paddle surfboards off their houseboats to get ready to ride the wave in. The earthquake happens and they surf up into the Hollywood Hills. After that ride they pack it up and go to Kingston Jamaica and buy cheap houseboats there to do it again. Days later they ride waves up into the hills there too. Oh, and one of them films all this in order to make a great surf movie.

Meanwhile, she's trying to figure out how to save Istanbul. Since the surfers are also skilled scuba divers she appeals to them for help in saving Istanbul. They are naturally torn by this request since preventing the Istanbul tsunami means losing a great ride. But saving the city involves swimming into submerged ancient Greek ruins. That sounds like fun so they decide to help her.

Naturally there's a scary part: The earthquakes that cause the tsunamis can be small. That' makes it easier.

"The scary part about that is you do not need a large earthquake to trigger a large tsunami," said Matt Hornbach, research associate at The University of Texas at Austin's Institute for Geophysics and lead author on a paper describing the research in the Oct. 10 online edition of the journal Nature Geoscience.

"Organizations that issue tsunami warnings usually look for large earthquakes on thrust faults," said Hornbach. "Now we see you don't necessarily need those things. A moderate earthquake on a strike-slip fault can still be cause for alarm."

Share |      Randall Parker, 2010 October 11 11:39 PM  Dangers Natural Geological

JKB said at October 12, 2010 7:29 PM:

Sorry but this isn't new information. Well, maybe as it relates to the specific sites. The 1946 Alaska tsunami was caused by an avalanche of sediment at the head of the Aleutian trench, although quake that caused the avalanche was also large.

What is confusing is the report doesn't give any specifics on why these sites have sediment overhang that is at risk of avalanche when disrupted by a moderate earthquake. It is the build up of sediment in a precarious location that is a better predictor of tsunami potential. Of course, you don't need an earthquake to cause the sediment to suddenly subside. They also do not report that the tsunami actually was actually recordable at any distance away from Haiti. Any locally generated waves will be coming ashore long before any warning system could activate. Rule of thumb is if you are on the beach and experience and earthquake that makes standing difficult, move away from the ocean.

About 10 years ago, there were reports of a huge gas bubble forming just beneath the sea floor off Virginia/Delaware (I beilieve). Much better, disaster movie to have DC and other sites filled with "we must save the earth" types inundated by a huge belch by Gaia.

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