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The Honolulu Advertiser

Posted on: Sunday, January 16, 2005

Quakes common, but usually not felt

By Christie Wilson
Advertiser Neighbor Island Editor

Earthquakes are a constant occurrence in Hawai'i, but most people hardly notice.

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Visit hvo.wr.usgs.gov for daily volcano updates and nearly real-time Hawai'i earthquake information.

Of the more than 13,000 earthquakes recorded last year by the U.S. Geological Survey's Hawaiian Volcano Observatory, only three were greater than magnitude 4. By comparison, the earthquake off Sumatra that triggered a killer tsunami registered magnitude 9.

Observatory seismologist Paul Okubo said a rough average for Hawai'i would be 10,000 earthquakes per year. He said although the overall number for 2004 may be greater, there have been fewer moderate to large quakes in the past year.

An observatory summary of earthquakes in 2004 shows 4,228 quakes were magnitude 1.5 or greater, and only 79 were big enough to have been felt by Big Island residents. But those were small enough to be considered microearthquakes, Okubo said.

None caused any damage.

The three largest quakes of 2004 — none greater than 4.5 — occurred beneath Kilauea on Feb. 5, Oct. 11 and Oct. 12.

The principal source of earthquakes are Kilauea, Mauna Loa and Lo'ihi, all active volcanoes. Lo'ihi, about 6 miles south of the Big Island and 2,000 feet deep, is the youngest. It is expected to rise above sea level sometime in the next few thousand years. Recent history shows that these are the areas that also have produced large earthquakes, and Okubo said some of the research taking place at the Hawaiian Volcano Observatory is exploring how the microseismicity patterns might relate to larger earthquakes.

The most recent big earthquake in Hawai'i occurred in 1975 when a magnitude 7.2 temblor shook the Big Island, causing a tsunami that killed two campers in Halape, Puna.

"The smaller earthquakes are a constant reminder that we are in an area where we could get larger earthquakes and volcanic eruptions, and we have to always be mindful of the hazards we face and what each of us should do to mitigate" the potential impact of these types of events, Okubo said.

During the week ending Jan. 13, four earthquakes were felt by Big Island residents who called in to report the jolts. The largest was a magnitude 3.6 quake Wednesday between Waiki'i and the Mauna Kea summit at a depth of 13 miles.

Okubo said the observatory last year recorded significant numbers of deep earthquakes beneath the summit caldera regions of both Kilauea and Mauna Loa.

Reach Christie Wilson at cwilson@honoluluadvertiser.com or (808) 244-4880.