HILO, Hawai'i — Scientists at the Hawaiian Volcano Observatory are geared up to record a "slow earthquake" expected under Kilauea volcano within the next few days.

Earthquakes occur when two masses of rock within the earth move against one another along a fault, usually with a sudden, powerful jolt. Scientists have no way to predict when ordinary earthquakes will happen, such as the Oct. 15 temblors that caused an estimated $200 million in damages.

With slow earthquakes, the motion along the fault plays out over days, with the earth moving so slowly that the earthquakes can't be felt. The shifts from a slow earthquake can be detected with scientific instruments.

Many slow earthquakes detected around the world occur at regular intervals, but scientists have yet to fully understand why.

"Things in nature as chaotic as earthquakes generally just aren't periodic," said Mike Poland, geophysicist at Hawaiian Volcano Observatory. "It's amazingly odd to have something like this."

At Kilauea, University of Hawai'i-Manoa scientists Benjamin Brooks and James Foster identified a series of slow earthquakes occurring almost due south of the caldera on an average of every 774 days, give or take seven days.

The latest in the series was recorded over two days beginning on Jan. 26, 2005, which means the next in the series was expected last Saturday.

As of last night, there was no sign of the next temblor in the slow earthquake series, but scientists are ready.

The U.S. Geological Survey, Stanford University, the University of Hawai'i and the University of Wisconsin have been working together in recent months to deploy a large temporary network of seismometers, global positioning system receivers and tiltmeters in addition to equipment already in place on the south flank of Kilauea volcano, according to the observatory.

The data scientists expect to gather "will result from the focused deployment of new and existing equipment and will aid in the understanding of how and why slow earthquakes occur, and will provide new insights into the subsurface structure of Kilauea volcano," according to the statement from Hawaiian Volcano Observatory.

"It would be like watching an earthquake in slow motion," Poland said. "That's why we have instant replay in the NFL, right? There's a hope that we might learn more about how faults slip."

In particular, scientists hope the study of the slow-moving variety of earthquakes will offer clues to help experts predict when destructive quakes will strike.

The last slow earthquake in January 2005 caused the south flank to shift by about an inch, a movement of mass that would have generated a magnitude-6 earthquake if it had happened in just a few seconds.

Foster said there have been some "tantalizing suggestions" that the regularly occurring slow earthquakes at Kilauea might be caused by some sort of volcanic activity.

"People have proposed different ideas, but we don't even really have an operating hypothesis for Kilauea," Foster said.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com.