Frequent hikers, boaters and car-traveling out-of-towners have very intimate — perhaps even untoward — relationships with their GPS (global positioning system) devices, typically depending on them as navigational "must haves" and making sure the device is in the car before even the spouse is. In addition to such functions, however, scientists now are considering GPS technology a potential solution in predicting tsunamis.

International organizations currently depend on coastal seismic stations to record deep-sea earthquakes that could cause threatening waves. But, a Wired article last month quoted geophysicist Jeff Freymueller, "data from GPS receivers could provide quicker, more accurate estimates of the magnitude of a tsunami-causing quake," thus prolonging time enough for evacuation.

Freymueller, a geophysicist at the University of Alaska Fairbanks, presented his findings at the American Geophysical Union conference in San Francisco last month.

GPS receivers can measure the movement — slippage — of the ground directly and in real time. As quake magnitude is "a direct function of how much the earth shifts," Freymueller has demonstrated the receivers can obtain precise measurements of a massive quake's severity in as few as 20 minutes. He said, "GPS receivers measure the static displacement of the earth, and after the first few minutes of a quake, that doesn't change much." This is in comparison with seismometers, measure the velocity of the ground and, according the Freymueller, "you have to collect a number of cycles of the important wave in order to get that measurement."

Hand-held GPS devices — such as those used by hikers, boaters and car travelers — employ a network of satellites to pin down a location to within a yard. Surface-mounted units can do much better, and can do so quickly enough that if the data uplink to the Internet, the earthquake can be viewed as it takes place.

Freymueller envisions a new tsunami-warning strategy that would use the seismic and GPS data in tandem to calculate a wave-causing quake's strength soon after its onset; this would enable more accurate computer simulations of the coming wave, allowing more targeted evacuation strategies, according to Freymueller in Wired.

Had an accurate warning system been in place, the Indian Ocean earthquake and tsunami, which on Dec. 26, 2004, killed nearly 300,000 people in Indonesia and neighboring countries, allowed potentially one-to-two hours for evacuation. The earthquake that caused the tsunami "reshaped the landscape of some Indonesian and Indian islands, lifting reefs out of the water, eroding beaches and submerging coconut groves," the Associated Press reported last month, approximately one year after the tragedy. "The giant waves caused ecological damage across Indian Ocean coastlines. But the destruction was mostly localized and overall it pales in comparison to years of rampant development and dynamite fishing, experts say."

If enough GPS units had been mounted throughout Indonesia, according to Freymueller in a recent San Diego Union-Tribune article, "it would have been possible to measure land displacements accurately enough to obtain a decent estimate of the earthquake's magnitude within minutes of its onset."

Wired said:
Seismic measurements of very large quakes like the one that caused last year's Indian Ocean tsunami take several hours to fine-tune, because the moving vibrations must be recorded at a variety of stations in different locations. When the quake that caused the giant Southeast Asian wave first hit, scientists at the PTWC [Pacific Tsunami Warning Center] estimated its magnitude at 8.0, but revised their estimate to 8.5 an hour later. After a few more hours passed, a team at Harvard University pegged the quake at 8.9. The final reading, 9.2, was not agreed upon until months afterward.

Other scientists and experts, Wired noted, are agreeing with Freymueller in tsunami-associated GPS potential: Yehuda Bock, a geologist at the Scripps Institution of Oceanography, has investigated the possibilities of using GPS receivers in tsunami-warning systems, and his results, similar to Freymueller's, indicate the receivers can gauge the ground movements created by tsunami-causing quakes with unprecedented precision and speed; and Peter MacDoran, a GPS expert who works for George Washington University's Space and Advanced Communications Research Institute, wants to make GPS receivers part of disaster-prediction networks to track the movement of tsunami-associated pressure waves in the Earth's atmosphere.

According to Freymueller, planting the receivers every hundred miles in tsunami-prone areas could be done in a matter of months, and each receiver would cost less than $10,000.

References

GPS Could Speed Tsunami Warnings
by Elizabeth Svoboda
Wired, Dec. 20, 2005
http://www.wired.com/news/technology/1,69847-0.html

What lies beneath
by Richard A. Lovett
San Diego Union-Tribune, Nov. 23, 2005
http://www.signonsandiego.com/news/science/20051123-9999-1c23tsunamim.html#

Tsunami still taking toll on environment
by Michael Casey
The Associated Press, Dec. 19, 2005
http://msnbc.msn.com/id/10463953/