Dec. 15, 1999
Dec. 15, 1999
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Study: Tsunami Could Hit L.A.
A deadly surprise tsunami like the one that slammed Papua New
Guinea last year could occur off the coast of Los Angeles, say scientists
who are now revising their maps of tsunami danger zones.
Until surprise tsunamis killed hundreds in Papua New Guinea, Nicaragua and
Mexico earlier this decade, emergency planners had thought the only tsunamis
likely to threaten California would come from large earthquakes in Alaska.
But near-shore tsunamis generated by earthquakes and undersea landslides
can -- and have -- caused sudden "tidal waves" that have inundated the land
of Baywatch.
"Tsunamis got a rebirth of interest in 1992 when an unexpected wave hit
Nicaragua," says Jose Borrero, a University of Southern
California geologist who presented the ongoing work on a new so-called Inundation Map for California at the American Geophysical Union meeting in San Francisco on
Monday.
There is historical evidence of near-shore tsunamis in Santa Barbara
and Santa Monica, says Borrero, but it has gone mostly unnoticed.
"If the 1812 Santa Barbara earthquake happened tomorrow, I guarantee there
would be heavy damage," says Jose Borrero. An upward-thrusting fault underlying Santa Cruz Island probably caused that tsunami, he says.
Preliminary work on the near-shore tsunami map has revealed that emergency
planners should probably raise the flood zones to about two meters in Santa
Barbara and one meter in Ventura, says Borrero. Areas further south, like
Santa Monica, could also get some flooding from such a tsunami, he says.
"There is evidence of past landslides offshore that may have been
tsunamigenic (tsunami-making)," says Borrero. "The real kicker is that there
was undeniably a tsunami in Santa Barbara after the earthquake of 1812.
"Records are sketchy in terms of how high the water actually rose, but the
missionaries felt it was high enough to relocate some settlers and Indians
further inland in the weeks after."
Similar landslide slumps appear in bathymetric maps of areas off the coast
of Long Beach. The steep undersea slopes just off Palos Verde, between L.A.
and Long Beach, look particularly ripe for landslides, says USGS geologist
Brian Edwards, who studies the offshore geology of Southern California for a
different purpose, but has noticed the dangerous slopes.
The tsunami danger mapping project is underwritten by the National Oceanic
and Atmospheric Administration, the Federal Emergency Management Agency and
the California Office of Emergency Management.
By Larry O'Hanlon, Discovery Online News
Copyright © 1999 Discovery Communications Inc.
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