Monday, August 12, 2002

Fred Duennebier, front, Rhett Butler, left, and James Jolly got a reading Friday from the ocean bottom seismometer.

UH goes deep undersea
to find seismic discovery

New wave patterns reveal details
about the earth's structure

By Helen Altonn

A deep-sea observatory developed at the University of Hawaii is telling scientists things about the planet they did not expect or even imagine, says the manager of the Global Seismic Network.

"It's kind of like seeing stars or a galaxy you didn't expect," Rhett Butler, an adjunct UH geophysicist, said in an interview. But they can be visualized, using your eyes, he said. With seismic work, "It's like using your ears."

Butler, based in Washington, D.C., runs the seismic network for the Incorporated Research Institutes for Seismology, a consortium of 99 universities. He was a full-time UH geophysicist from 1982 to 1986 and former chairman of the Hawaii Institute of Geophysics seismology division.

He spends summers here on projects and research, and works with the Pacific Tsunami Warning Center at Ewa Beach to expand data links with seismic stations.

The global network of 128 stations is spread across the planet from the South Pole to the Amazon jungle and includes the Hawaii 2 Observatory on the ocean floor between Hawaii and California.

UH geology and geophysics professor Fred Duennebier and his team built the first sea floor seismic station, installed on an old AT&T telephone cable with instruments operating from a junction box.

The data pour into Duennebier's office in the School of Ocean & Earth Sciences & Technology. He sends it to the University of Washington, which operates a data center for the international seismic program.

"We have found what I call nano-earthquakes, incredibly tiny, that we never saw before," Butler said, describing some of the major findings with the deep-sea seismometer.

"We see whale migrations. We see energy propagating at the sea floor which was never expected before, seismic energy. We see a very interesting pattern of wave propagation that says something very interesting about land under the North Pacific, the structure of the top 100 kilometers of Earth."

Certain types of seismic waves, called sheer waves, are seen from the Big Island that are not seen anywhere else in the Pacific, he said.

"It means the volcanism creates a lot of heat, but it doesn't spread widely from the Big Island. It's much more localized than would be expected."

The data also reveal that waves are propagating at the bottom of the ocean, he said.

Butler and Cinna Lomnitz of the Institute of Geophysics, National Autonomous University of Mexico, co-authored a paper on the unique waves, "Coupled seismoacoustic modes on the sea floor."

They determined that a wave generated by an underwater earthquake off California in 2000 was "an unusually strong Rayleigh wave," a rolling wave with side-to-side motion rather than the usual acoustic wave.

The data showed the waves moved three miles below the ocean's surface with greater energy than traditional waves.

"It's entirely unexpected to see these things propagating from such a great distance," Butler said. "The only good explanation is, we're seeing a new kind of seismic migration" which represents an interfacing between water and sediments, he said.

The Hawaii 2 Observatory is not intended only for study of earthquakes and the structure of the earth, Butler said, noting plans in the next year or so to add equipment to study magnetism and some marine biology.

"It's more general purpose than just earthquakes, which makes it even more exciting. It's something out in the middle of nowhere, literally, and we can start measuring things over a long period of time."

The seismic network began in 1986 with a goal to have 140 stations.

"The hard ones are at the end," Butler said. "We're trying to get one in Pakistan. That's a challenge."

He said he is working with the tsunami warning center to get data delivered directly from stations via satellite. "If the Internet goes down, we want to make sure the guys here get the data."

Midway Island was just linked by satellite to the tsunami station; Easter Island will be hooked into it next month, and then Pitcairn Island, which will also use the satellite for an Internet connection, he said.

University of Hawaii

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