In the first deep sea drilling expedition designed to gather seismic data, scientists have successfully drilled nearly a mile beneath the ocean floor into one of the world’s most active earthquake zones.

Researchers aboard the drilling vessel Chikyu — meaning “planet Earth” in Japanese — used a special technology called riser drilling to penetrate the upper portion of the Nankai Trough, an earthquake zone located about 36 miles southeast of Japan. By collecting rock samples and installing long-term monitoring devices, the geologists hope to understand how stress builds up in subduction zones like Nankai, where the Philippine Sea plate plate is sliding beneath the island of Japan.

Riser drilling involves encasing a deep sea drill in a giant metal tube, called a riser, that extends from the ship down to the drilling site, effectively bolting the ship to the sea floor. The researchers circulate lightly pressurized mud down through the drilling tube and back up through the riser.

“One of the key benefits is the pressurized mud keeps the wall rock from collapsing on the drilling pipe, which allows you to drill deeper and with better control,” geologist Timothy Byrne of the University of Connecticut wrote in an e-mail. “For example, nearly perfectly vertical holes or steeply inclined holes can be drilled,” wrote Byrne, who co-led the project.

Using a riser also makes it easier to send core samples and cuttings, or small chips of rock collected during drilling, back up to the surface.

The Nankai Trough last ruptured twice in 1944 and 1946, generating earthquakes greater than magnitude 8 that shook the region and caused deadly tsunamis. Since then, the two plates have continued to move, but the boundary between them has been locked, causing pressure to build.

“We know that a locked fault is not a quiet thing, but we don’t quite understand why,” said geologist Kelin Wang of the Geological Survey of Canada, who was not involved in the research. “When we understand what is meant by locking, we can understand how energy is building up for the next event.”

The Nankai project is part of an international effort called the Integrated Ocean Drilling Program, designed to investigate a variety of scientific questions through drilling. The IODP chose to drill for seismic data in Nankai because of the region’s history of recent earthquakes and the accessible location of the rupture zone. The drilling is not powerful enough to trigger an earthquake.

What is learned in Japan will help scientists understand other earthquake-prone plate boundaries, such as the Cascadia subduction zone, which extends along the Pacific coast from British Columbia to Northern California

“For us in North America, the good news is that the Nankai subduction zone is strikingly similar to ours,” Wang said. Both zones are hotter and accumulate more sediment than average. “By studying Nankai, we North Americans can actually benefit pretty directly from the project. It’s almost as if we are drilling our own subduction zone, because we’ll see a lot of the same things.”

The first drilling and sampling operations in Nankai began on May 12 and are expected to conclude on August 1. After the initial drilling stage, scientists lowered various gauges and logging instruments into the hole to measure temperature, stress, water pressure and rock permeability. Once they gather enough data, the scientists will prepare the hole for future installation of long-term monitoring equipment.

See Also:

• Video: Installing the World’s Deepest Drilling Oil Rig
• Wired 12.07: The Seismic Underground
• Top 5 Ways to Cause a Man-Made Earthquake
• Tsunami Risk for West Coast Higher Than Expected

Image 1: Riser aboard Chikyu vessel, JAMSTEC/IODP. Image 2: D. Sawyer, JOI/USSAC/IODP. Video: JAMSTEC/IODP.

A massive simulated earthquake will rock a six-story wooden condominium to the brink of collapse

Tuesday, during one of the largest shake-table experiments undertaken to date.

The simulation, which will be webcast live July 14 at 11 a.m. EDT on the National Science Foundation website, is designed to test how a mid-rise wood-frame building would stand up to shaking from an earthquake around magnitude 7.5.

“We’re taking it to an earthquake level that’s associated with being on the verge of collapse,” said civil engineer Michael Symans of Rensselaer Polytechnic Institute, who helped design the test building. “We don’t expect it to collapse, but we expect it to be very vulnerable to a strong aftershock that could cause it to collapse.”

The 23-unit condo building currently sits on the world’s largest shake table, a 50-by-60-foot structure in Miki, Japan. The table will simulate the motions of the 1994 earthquake in Northridge, California, amplified about 1.5 times. Sensors on each floor of the building will record motion and detect internal damage, generating valuable data about how wooden structures perform in a quake.

Although wooden buildings are cheaper and faster to construct than those made of steel, very few mid-rise structures in the United States are currently built of wood. “Even in seismically vulnerable parts of the West Coast, there just isn’t much of an understanding of how taller wood structures will behave under ground shaking,” Symans said. “It might be desirable to build in wood, but at this point that’s not an option from a building-code point of view, partially because we just don’t know what will happen in an earthquake.”

The test marks the final experiment in a four-year collaboration called the Network for Earthquake Engineering Simulation Wood project, funded by a $1.4 million grant from NSF and donated materials from the industrial manufacturer Simpson Strong-Tie.

The project’s first experiment subjected a two-story wooden house to a magnitude 6.7 earthquake, which severely damaged the structure. The engineers determined that homes built to current building standards might not topple during a large earthquake, but they’d likely never be livable again.

For the current test, they experimented with new design principles meant to help the condominium withstand shaking.

“Basically, what happens during an earthquake in multiple-story building is something called a ’soft story,’” said civil engineer John van de Lindt of Colorado State University, who led the condo design. “It’s not as stiff as the story above it, and the earthquake demands more stiffness from the lower story. This can develop into a pancake collapse, which damages the building and can kill people.”

The new design distributes the stiffness vertically throughout the height of the building, van de Lindt said, to reduce the chance of a soft-story collapse.

On June 30 and July 6, engineers subjected the condo to preliminary testing, seen in the video below.

In the two smaller earthquake simulations, the building sustained very little damage. “So far, it looks like it’s working like a charm,” he said. “If there were families living in this condo, they wouldn’t even have to move out.”

Tuesday’s quake may be a different story. Numerical models predict a 3 percent drift, which means that each story of the building will shift over about three inches — enough to cause significant damage, but not enough to cause collapse. The only way to validate the computer models is to do a full-scale simulation, and that’s something that’s never been done before on such a large building.

“The reality is that we really don’t know what will happen,” Symans said.

See Also:

• Mondo Quake in Pacific Northwest?
• Videos Simulate Earthquake in San Francisco Bay Area
• Video Podcast No. 8: Quake Tech Brings Down the House
• 5 Most Dangerous U.S. Earthquake Hot Spots Beyond California

Image: Simspon-Strong Tie.