Geophysicist Tobin on Research Cruise

by George Zamora

SOCORRO, N.M., August 30, 2000 -- New Mexico Tech research geophysicist Harold Tobin had to book his "research cruise" seven years in advance, but the unparalleled opportunity to participate in an intensive, eight-week-long, interdisciplinary study conducted aboard a specially fitted ship floating above one of Earth's most seismically active areas was well worth the long wait.

Tobin was one of only 28 scientists from around the world chosen to participate in the most recent leg of the international Ocean Drilling Program (ODP), which was conducted this summer 100 miles off the east coast of Japan aboard the JOIDES Resolution, a one-of-a-kind research ship outfitted with state-of-the-art laboratory, drilling, and navigation equipment.

Tobin's particular area of the study focused on the processes associated with faulting which occurs where two tectonic plates collide with each other.

The Nankai Trough, the offshore area where the bulk of the ocean floor study was conducted, is a deep-sea trench where the Philippine plate subducts, or is pushed under, the much larger Eurasian plate.

"The area is in a subduction zone which makes up a portion of the Pacific Ocean's famous 'Ring of Fire,'" Tobin explains. "This is one of the most, if not the most, seismically active areas in the world. A magnitude 8 earthquake occurs here every 100 years or so. . . . It's definitely a great place to go to study the processes associated with faulting and earthquakes."

In order to conduct studies on subsurface processes occurring below the seafloor, the 480-foot-long research vessel carries over five-and-a-half miles of drilling pipe onboard, enough to permit researchers to drill down nearly three-quarters of a mile into subsurface sediments and rocks virtually anywhere in the world's oceans.

"We periodically moved to various locations along a transect across the main fault line throughout the eight weeks to do the actual drilling," Tobin says. "The core samples brought back up and measurements made down the hole give us clues to the state of the subsurface rocks, including damage due to faulting, pressures, temperature, and chemistry to which they were subjected. This, in turn, lets us know what physical processes take place in the fault.

"If we can better understand the physical environment inside faults, we can better understand how and when faults slip and therefore how and when earthquakes take place," he adds.

The core samples taken of the Earth's crust were first sectioned off into 30-foot-long segments, which were then cut in half and laid open, so as to be more manageable for testing purposes.

Most of the larger sections of samples eventually ended up catalogued in a core repository -- essentially, a refrigerated warehouse -- run by Texas A & M University.

Tobin, however, was allowed to bring back 150 sub-samples of the cores he collected during the sea-going research program and will continue to conduct specific analyses of the samples at New Mexico Tech.

"My grad students and I will continue studying characteristics of those samples, such as their geology, porosity, and seismic velocity, in a high-pressure laboratory and with SEM (scanning electron microscopy) to give us some basic fundamental data on faulting," Tobin says.

Although this marks Tobin's fourth time "out at sea" doing research with the ODP, each time has been just as exciting as that first time he set sail off the coast of Oregon in his graduate student days, Tobin says.

"It's quite stimulating to work with some of the top researchers from around the world--scientists from Spain, England, Germany, France, Japan, and the United States, all onboard together, each with their own expertise in their respective specialties," Tobin relates. "It's like participating in a floating interdisciplinary seminar in plate tectonics."

To save costs associated with such a massive international and interdisciplinary research project, the JOIDES Resolution operates "24/7" during its research cruises.

"We were divided up into 12-hour shifts around the clock," Tobin recounts. "You worked either noon to midnight or midnight to noon. It was just as busy at 3 a.m. as it was at 3 p.m."

The research ship floated directly above the selected drill sites for a week or two at a time, being able to maintain its steadiness, even in rough waters, through a computer-controlled system which regulates 12 powerful thrusters, in addition to the main propulsion system.

An international effort spearheaded by the Japanese government currently is being mounted to build an even bigger and better "floating laboratory" than the JOIDES Resolution -- a drilling ship which will have the capacity to bring up core samples from as deep as four miles into the Earth's crust.

"In a few years, because of the new ship's expanded capabilities, drilling one location will take one or two years instead of just a few weeks," Tobin speculates. "No one wants to go out to sea for that long, so researchers will have to shuttle back and forth to the offshore drilling site."

Tobin further points out that even though over 70 percent of the Earth's surface is covered by oceans, only a small percentage of current scientific research is being conducted on what lies beneath.

"We know less about the bottom of the oceans than we do about the surface of the Moon," he says. "So, we need to continue this type of drilling and other marine research if we hope to better understand the Earth as a whole."

The ODP is an international partnership of scientists and research institutions organized to explore the evolution and structure of Earth. ODP provides researchers around the world access to a vast repository of geological and environmental information recorded far below the ocean surface in seafloor sediments and rocks.

-NMT-

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Last updated: 2000/08/30 22:20:51,