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Magnitude 5.3 earthquake rattles, but too weak to cause tsunami

Magnitude 5.3 earthquake rattles, but too weak to cause tsunami
Epicenter of the quake (Los Angeles Times)

The magnitude 5.3 earthquake that rattled Southern California was the strongest in the region in several years, but it did not produce any tsunami warnings.

Why?

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The quake was far too weak to generate a tsunami, said Chris Popham, lead oceanographer for the National Tsunami Warning Center in Palmer, Alaska. Generally, earthquakes of magnitude 7 or above are those that cause concern, he said.

"You need to be moving hundreds of miles of water to get a significant tsunami," said seismologist Lucy Jones. But Thursday's earthquake, by virtue of its modest magnitude, only ruptured a length of the fault of just two miles, Jones said.

Additionally, the earthquake occurred on a strike-slip fault, in which the faults are generally moving in a horizontal direction.

The worst tsunamis tend to occur on a different type of system, known as a subduction zone earthquake, in which faults produce a great deal of vertical motion. Subduction zone earthquakes are the kind that produced massive, deadly flooding in Japan in 2011 and happened off the coast of Oregon and Washington state in 1700.

There are, however, scenarios in which earthquakes in Southern California do cause significant tsunamis.

A study published in 2015 by U.S. Geological Survey and UC Riverside scientists found that tsunami wave heights could approach 20 feet in the Ventura Harbor and Channel Islands Beach area near Oxnard. That study focused on on a hypothetical scenario in which a magnitude 7.7 earthquake begins nine miles under the Earth's surface, under the mountains northeast of Santa Barbara.

Caltech seismologist Egill Hauksson said an offshore earthquake in 1812 caused a tsunami of perhaps 3 feet in the Ventura area. But because recorded history in California is so short, scientists don't have too much documented information of how big tsunamis have been.

UPDATES:

3:40 p.m.: This article was updated with a quote from seismologist Lucy Jones.

This article was originally published at 2:10 p.m.

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