Slim chance of tsunami event along Newport Beach

Jeff Benson

The death toll from Sunday’s tsunami in the Indian Ocean races toward

100,000 almost as rapidly as the wave that overcame villages in

Indonesia, Sri Lanka and India.

But it’s anyone’s guess what kind of damage the tsunami, caused by

a magnitude 9.0 earthquake, could have done had it occurred in

Southern California.

Could a tsunami hit Newport Beach and surrounding communities near

the coast? Geologists say yes, but probably not one of that

magnitude.

Thomas Heaton, a professor of engineering seismology at Caltech,

said tsunamis can occur along any coast, but the probability of one

hitting a coast increases if the area has several subduction zones --

points where the Earth’s tectonic plates meet -- and active volcanic

activity.

A subduction zone exists along the West Coast, from Eureka in

Northern California to Vancouver Island in Canada. Southern

California has several fracture zones, the most notable being the San

Andreas Fault.

The Newport-Inglewood Fault runs parallel to the coastline until

just south of Newport Bay, where it heads offshore.

A tsunami could physically hit Newport Beach, but there’s a slim

chance of one originating anywhere off the Southern California coast,

Heaton said.

“In a sense, since the coast curves inward, Southern California is

a little sheltered from tsunamis coming from the north,” Heaton said.

“They don’t hit with much force.

“If you were to rank places around the world and say which ones

were high-risk tsunami areas, Southern California would not be in

that ranking.”

Since magnitude-9.0 earthquakes typically occur only twice per

century worldwide, the recent disaster shouldn’t send anyone in

Orange County scrambling to reach higher ground just yet.

But if a quake of that size hit anywhere along the Pacific Coast,

people living along the coasts of Washington, Oregon, Hawaii and

Japan should be more concerned, he said. Those areas have more active

volcanic activity and little shelter from tsunamis.

“There’s evidence that there have been numerous times in the past

where the island of Hawaii has been hit by tsunamis hundreds of feet

high, caused by large submarine run-out landslides on the ocean

floor,” Heaton said.

“The most common source is large earthquakes, which uplift the

ocean floor.”

The large subduction zone between Vancouver Island and Eureka is

capable of having similar tsunamis to the one Sunday off the Sumatran

coast, he said.

Lori Dengler, a geology professor at Humboldt State University

said it’s very possible that a tsunami could hit Newport Beach.

Plenty of faults exist off the California coast that could trigger

a magnitude-6.0 or 7.0 quake, she said, but tsunamis are caused when

the sea floor’s topography is deformed.

Wave size depends on earthquake magnitude and other sea floor

movement.

“The sea floor is very complex,” she said.

“The reason for the complex offshore symmetry is because there are

lots of strike-slip faults that kind of step over each other, and the

ground is either compressed and popped up or dropped down.

There is evidence of submarine landslides, and it may be that

these submarine slumps could produce small tsunamis locally.”

Few researchers dispute that California’s crinkling underwater

topography is rising and falling rapidly, which is the breeding

ground for tsunamis.

In 2000, Monterey Bay Aquarium researchers obtained evidence of a

giant underwater landslide roughly 9 by 6 1/2 miles off the coast

of Santa Barbara.

“This slide evidently moved in three different events,” said

Monterey Bay Aquarium researcher Gary Greene on https://www.mbari.com.

“Each event displaced enough sediment to be capable of generating

a tsunami, if the displacements occurred rapidly.”

Most experts once believed that distant events, such as a 1960

Chilean tsunami that damaged San Diego, were the greatest hazards,

Dengler said.

Now, she said, they look at large underwater slump landslides and

stepping faults, overlapping faults that cause a chain reaction

during an earthquake.

She added that most California tsunami experts have changed their

thinking since a 7.2 earthquake in 1998 in Papua, New Guinea,

produced a 40-foot-high wave that crashed onto the coastline.

“The prevailing mythology was that Southern California’s tsunami

hazard was not great due to big earthquakes far away,” Dengler said.

“In the New Guinea tsunami, 25 miles of coastline got waves, and over

2,200 died. It’s very tragic and an example of, hey, it’s not just

big earthquakes we need to be worried about.”

If there has recently been an earthquake or if coastal waters

begin receding suspiciously, those are good signs a tsunami could be

approaching, both experts agreed.

“The bottom line is that if anyone experiences sizable shaking

near the ocean, they should think about evacuating to higher ground,”

Heaton said.

“It’s not time to wonder. It’s time to move.”

One local surfer, whose surf exploits include a ride on a 12-foot

wave in Hawaii, agreed with the possibility that a tsunami could

reach Newport Beach.

“I guess it could,” said Marty Bounds, 25, a manager at Jack’s

Surfboards in Newport Beach.

“We’re on a big sandbar here, and it would probably have to break

between Catalina and here.

“Every west swell blocks it.”