While in LA Watch Out for Tsunamis

A team of geologists from the US and Haiti, that have been studying the January 12 Haiti earthquake, say that other cities like Los Angeles, Istanbul or Kingston also risk being struck by a tsunamis, and the actual catastrophe risk is much higher than expected.

The explanation for this statement is pretty logical: all these cities lie near the coast and near a strike-slip fault, an active geologic area where two tectonic plates slide past each other (just like rubbing two hands against one another).

We all remember the Haitian catastrophe: several minutes after the magnitude 7 earthquake, tsunami waves as high as 9 feet (3 meters) crashed into the shoreline.

The team of scientists carried out geological field surveys of sites, on and off shore near the epicenter of the earthquake, several weeks later.

They gathered data on faults beneath the seafloor and land, bathymetry (underwater topography) of the seafloor, vertical movement of the land and evidence of tsunami waves.

They found that the tsunamis were caused by weak sediments at the shore, which collapsed and slid along the ocean floor, thus displacing the overlying water.

Then, they made a survey of historic tsunamis and concluded that a third of the world's tsunamis began in this way.

This highly contradicts what was previously believed, that only 3% of overall tsunamis were caused by submarine landslides.

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, said that they “found that tsunamis around Haiti are about 10 times more likely to be generated in this way than we would have expected.”

Until this new research, the tsunami risk in LA, Kingston or Istanbul was not considered to be very high, because during earthquakes, the faults did not displace the seafloor vertically so much.

The last study concluded that even a small earthquake on a strike-slip fault could cause tsunamis through submarine landslides.

Hornbach said that “the scary part about that is you do not need a large earthquake to trigger a large tsunami.

“Organizations that issue tsunami warnings usually look for large earthquakes on thrust faults.

“Now we see you don't necessarily need those things; a moderate earthquake on a strike-slip fault can still be cause for alarm.”

From The University of Texas at Austin also took part at the research: Paul Mann, Cliff Frohlich, Fred Taylor, Sean Gulick and Marcy Davis.

Besides researchers from UT, there were scientists from Queens College – City University of New York, Lamont-Doherty Earth Observatory of Columbia University, US Geological Survey – University of Missouri, University of California – Santa Barbara, the Bureau of Mines and Energy in Haiti and Universite d'Etat de Haiti.

The survey was funded by a Rapid Response grant from the National Science Foundation and The University of Texas at Austin's Jackson School of Geosciences.

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