When a magnitude 7.1 earthquake rocked the Mojave Desert in Southern California on October 16, seismic waves rippled through the ground under Los Angeles and continued westward under the Pacific Ocean.

The GOES-WEST satellite knew about it in seconds.

Less than a minute after the earthquake, the satellite had transmitted data to a computer in Seattle, where researchers spend their days worrying that such a quake might cause a deadly tsunami if it were centered offshore.

Think of the Pacific Ocean as a giant, full-to-capacity bathtub, with California sitting on one side and Japan on the other. Then imagine a child's hand splashing down near California. The energy creates a wave that moves across the tub without much fanfare -- until it runs into Japan and is forced up and over the edge of the tub and onto the floor.

In the real ocean, plenty of natural disasters can trigger a similar event.

Caused by a paddle-effect from an earthquake, an underwater volcano, or even an asteroid, tsunamis are enormously dangerous stealth waves that travel vast distances across the ocean. You wouldn't notice one if it passed beneath your boat in deep water -- it would be gentle and rolling, not more than 3 feet high, and indiscernible from the general roll of the ocean.

But tsunamis are long-period waves, meaning their wave crests are far apart -- sometimes hundreds of miles on the open ocean. They can move as fast as 400 mph, and have enough energy to carry them great distances.

It's when they reach shallow water, where all this energy is forced upward, that the true nature of the wave becomes frighteningly apparent -- a realization that throughout history has come too late.

A Papua, New Guinea tsunami in 1998 killed some 3,000 people. It resulted from a 7.1 magnitude earthquake 15 miles offshore that was followed within 10 minutes by a wave estimated to be 40 feet tall. One of the worst tsunami disasters in history engulfed whole villages along Sanriku, Japan in 1896, when a wave more than seven-stories tall drowned 26,000 people. The powerful 1964 Alaskan earthquake triggered a tsunami that killed 11 people as far away as northern California.

To improve the detection of tsunamis, and possibly save lives, a consortium of agencies has deployed seafloor seismic sensors -- one off the coast of Monterey last May and three others near Alaska three weeks ago.

The devices sense pressure differences. If a tsunami passes above, the added weight of the water -- even as little as 1 cm -- is registered. Normal wind waves, which have a much shorter period than tsunamis, are filtered out. If a tsunami is detected, data is uploaded from an onboard computer chip, via sound signals, to a "hydrophone" that is attached to a buoy at the surface.

The buoy sends the data to the Geostationary Operational Environmental Satellite, orbiting in a fixed perch above the planet. From there, the information is downloaded to ground-based computers.

The system, called the Deep Ocean Assessment and Reporting of Tsunamis program (DART), is the latest component of the Tsunami Warning System -- a cooperative venture of 26 states and countries that monitor seismic activity and tidal stations throughout the Pacific Basin. Warnings are issued from bases in Hawaii and Alaska.

The October 16 earthquake was detected by the sensor off the coast of Monterey. However, instead of a tsunami, the device sensed a pressure change when it was lifted from below by seismic waves.

"Although there was no tsunami produced by the 7.0 earthquake, it did trigger the buoy and gave us an unexpected test of the system," said Eddie Bernard, director of the Pacific Marine Environmental Laboratory in Seattle, Wash. "The buoy system performed as designed."

Bernard said the device was able to distinguish the short duration of the event from a tsunami, which would have lasted longer. "When our people at the warning center saw it, they realized it was a seismic wave."

Had DART detected a tsunami, Bernard said a warning could have been issued immediately.

Existing measurements can only tell whether or not there is a tsunami, and when it might strike. The new system will enable scientists to predict the duration of the event, which in some cases can be a series of waves lasting several hours. Bernard also expects DART to do a much better job predicting the height of tsunamis. The improvements will help emergency managers decide who to evacuate and how long to keep them away from coastal areas.

In the past, warnings have been issued for tsunamis that turned out to be inconsequential. This is worrisome for emergency managers who fear such false alarms may cause public apathy when successive warnings are posted.

"Our hope is to eliminate false alarms with these buoys," Bernard said.