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Size of isle volcanoes factors into severity of potential quake

For Tuesday, April 12, 2011

By June Watanabe

POSTED:



Question: Do scientists and seismologists think that what happened in Japan could happen in Hawaii, meaning a 9.0-magnitude earthquake and tsunami?

Answer: Thankfully, Hawaii cannot have an earthquake of that magnitude.

“The islands are just too small to sustain a shallow earthquake larger than magnitude 8,” said tsunami expert Gerard Fryer, a geophysicist with the Pacific Tsunami Warning Center.

And, while “big basal-slip earthquakes (locally) do pose a tsunami hazard, especially to the Big Island,” it would be “nothing like what happened in Japan,” he said.

“We are pretty confident that the existing evacuation maps are adequate for locally generated tsunamis as well as tsunamis from across the ocean.”

Fryer explained that the “greatest earthquakes in Hawaii are at or close to the base of volcanoes, where they sit on the old sea floor.”

During a big quake, the flank of the volcano essentially slides out over the sea floor, driven both by gravity and pressure from magma in the volcano rift zones.

“The largest possible earthquake is determined by how much volcano there is to move,” Fryer said.

In the largest known local earthquake — the Kau Earthquake of 1868 — scientists believe the whole southeast flank of Mauna Loa moved, taking the south flank of Kilauea with it.

“That was about a magnitude-7.8 earthquake,” Fryer said. “While a slightly larger earthquake is possible, you very quickly run out of real estate.”

Question: During the TV coverage of the tsunami alert last month, there was an interview with an official of the Pacific Tsunami Warning Center. The official mentioned a partnership between PTWC and a website, in which a text message and email of the center’s alerts can be sent. Given that some residents might not hear the warning sirens, could you provide information on the site and its operation?

Answer: You can sign up to receive the alerts on the Pacific Tsunami Warning Center’s own website. Go to ptwc.weather.gov and click on “subscribe” on the left side.

“It has all the information on how to subscribe via email or RSS (Real Simple Syndication feed),” said Brian Shiro, a geophysicist with the center.

Currently, there is no text message option available to the general public, which Shiro acknowledged is “our most requested thing.” However, it is being tested and might be available in the future.

Meanwhile, in the event of a large local earthquake that could generate a tsunami, “PTWC will get a warning out fast, probably in under three minutes,” said geophysicist Gerard Fryer.

But he advises not waiting for the warning.

“If ever you feel very severe ground shaking (so severe that you feel it might knock you off your feet) and you are close to the ocean, move inland or up without delay,” he said.

Fryer added that “in Hawaii you won’t have to go far to safety, typically just a block or two … or you can just go up a couple of floors in a high-rise.”

MAHALO

To a First Hawaiian Bank customer. It was one of those days. I dashed off to the bank, then left to go shopping. But as I stood in line to pay for my items, I could not find my wallet in my backpack. After frantically retracing my steps, I figured I must have lost it between the bank and my car. Imagine my relief when I was told that someone had turned it in to a teller. Mahalo to the customer, whose name I did not get. I am thankful for your honesty and integrity. God bless you.

Loretta

Write to “Kokua Line” at Honolulu Star-Advertiser, 7 Waterfront Plaza, Suite 210, 500 Ala Moana Blvd., Honolulu 96813; call 529-4773; fax 529-4750; or email kokualine@staradvertiser.com.






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