Scientists find new
fault zone under Kilauea

The discovery alters what scientists
had previously thought about the volcano

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By Helen Altonn
haltonn@starbulletin.com

A research team led by a University of Hawaii seismologist has discovered an active fault zone more than 18 miles beneath the Big Island's Kilauea volcano.

The finding significantly changes the picture of the volcano's deep structure, said Cecily Wolfe, of the Institute of Geophysics and Planetology, lead researcher.

Deep earthquakes are known to happen under Kilauea, but the fault zone is a surprise, she said.

The classic interpretation, presented in many textbooks, was that the mantle earthquakes outlined a magma conduit to the volcano's surface, she said.

"Imagine the magma has to come up to get to the volcano. People hypothesized that it comes up through the conduit, and around the conduit are all these cracks they believed were (caused by) earthquakes."

Wolfe's research colleagues were Paul Okubo, of the U.S. Geological Survey's Hawaiian Volcano Observatory, and Peter Shearer, seismologist at Scripps Institute of Oceanography, University of California-San Diego.

Their study appears in today's publication of the journal Science.

"One reviewer said the results are really quite amazing," Wolfe said. "For years, scientists had a classic view of what Kilauea is. Yes, there are deep earthquakes but the pattern is completely different."

The researchers applied sophisticated new techniques to analyze 14,604 seismic events around Hawaii recorded by the Volcano Observatory from 1988 to 1998.

Wolfe said the techniques sharpened the picture, like looking through a focused lens instead of an unfocused one. "You could see the leaves on the bush."

What the team saw was evidence of earthquakes on a deep fault zone, more than 6 miles long, she said.

"In fact, we found several fault zones in the mantle around Hawaii."

Although these deep fault zones cause earthquakes, she does not believe they pose a hazard.

"They don't cause big earthquakes -- not big enough for us to worry about."

She said they are "little bitty faults" compared, for example, to the San Andreas Fault.

A magnitude-5.3 earthquake occurred on the Kilauea fault zone in 1994 but was not big enough to do any damage, nor was it known then to be a fault zone, she said.

However, that earthquake was key to helping identify the deep fault zone, she said.

Wolfe believes the Kilauea fault zone is the most active of all those around Hawaii because it is near an erupting volcano. Kilauea's Puu Oo-Kupaianaha eruption has continued since 1983.

"Magma does generate stresses that help keep the fault zone as active as it is."

Both the weight of the erupting volcano above and the magma moving up from below are contributing factors, she said.

"The area under Hawaii is experiencing a lot of force."

Wolfe said she is continuing her research on a broader scale, looking at fault zones found in many places in the earth's mantle around Hawaii.

"I saw this as an opportunity to work on these very interesting earthquakes studied many years before," she said. "People hadn't applied these new techniques."