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The Honolulu Advertiser
Posted on: Monday, June 25, 2001

Whole lotta shakin' in the Islands

By Jan TenBruggencate
Advertiser Staff Writer

Several St. Louis Heights residents were awakened on a recent Friday morning by what felt like an earthquake.

The St. Louis Heights 3 a.m. event lasted about 10 seconds, said area resident Doug Hazelwood, who woke up to what he called a "mild earthquake."

It caused no damage. He said a neighbor was also awakened.

Officials at the Tsunami Warning Center at 'Ewa Beach said they could find no sign of the shake on the recording devices either at Diamond Head or Waimanalo Ridge.

"It could have been a small earthquake, too small to register," said geophysicist Bob Cessaro.

Fellow Tsunami Warning Center geophysicist Stuart Weinstein said a small, shallow quake can easily be felt in a neighborhood without registering on the center's equipment.

"We're geared up for the big events," he said.

But he does not doubt that a real earthquake could have been what awakened the residents in St. Louis Heights June 15.

"It can be a small one and people can still feel it," Weinstein said.

There are all kinds of shaking events around the Islands, not all of them quakes.

Cessaro said he was awakened at 2:15 a.m. at 'Ewa Beach by a series of very loud noises.

"It was at the same pace as someone knocking at your door. Boom! Boom! Boom!" he said. "It sounded like explosions. I don't know what it was. It registered really small on the sensors here."

But actual earthquakes are regular events around the Islands. They are common around the geologically more active islands of Hawai'i and Maui, and less frequent as you move west up the chain.

A seismic hazard evaluation of the islands was updated in 1997 by the U.S. Geological Survey for the Uniform Building Code. It used a six-category code, ranging from 0, which means virtually no chance of a quake, to 4, which is a 10 percent chance of a severe quake within a 50-year period.

It established the Big Island with a seismic zone factor 4. The islands of Maui County are substantially lower at a factor of 2B, while O'ahu is a 2A. Kaua'i, the least active, is a 1.

Check on what's happening in ground tremors in Hawai'i at this Web site.

The Hawaiian Volcano Observatory on Kilauea has a great deal of information, primarily about Big Island earthquake activity, at its earthquake Web site.

Jan TenBruggencate is The Advertiser's Kaua'i bureau chief and its science and environment writer. Call him at (808) 245-3074 or e-mail jant@honoluluadvertiser.com.