Slow earthquakes are shifts in the earth's surface that take place so slowly that they cannot be felt. The shifts can be recorded with scientific instruments, however.

Earthquakes occur when two masses of rock within the earth move against one another along a fault. Usually this happens in a matter of seconds, producing the kind of shaking Hawai'i residents experienced last Oct. 15. A "slow earthquake" occurs when the same motion along the fault plays out over days.

For reasons scientists cannot yet explain, many slow earthquakes detected around the world seem to happen at regular intervals. At Kilauea, the pattern so far suggests slow earthquakes occur there about every 774 days, with the last one recorded over two days beginning on Jan. 26, 2005. The slow earthquake scientists are poised to record, therefore, was scheduled to occur last Saturday, March 17.

Scientists have no way to predict when the more destructive shaking from fast-moving earthquakes will happen, such as the mid-October temblors that tallied an estimated $200 million in damages. But they hope study of the slow moving variety of earthquakes will offer clues to help experts predict when destructive quakes will strike.

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 a statement from the USGS.

The data scientists expect to gather "will result from the focused deployment of new and existing equipment 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 Volcanoes Observatory.