How GPS Can Keep Track of Earthquakes and Flooding
We usually think of GPS as a way to find out where we are and how to get where we’re going. But over the past couple of years, researchers have discovered that GPS, when combined with sensors such as accelerometers and barometers, can be an important tool for evaluating and possibly predicting earthquakes and flash floods.
At the fall meeting of the American Geophysical Union in December, scientists from the Scripps Institution of Oceanography (SIO) in San Diego, NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, and the National Oceanic and Atmospheric Administration (NOAA) described the way they are doing this by piggybacking on a preëxisting network of hundreds of GPS stations scattered throughout Southern California. At a handful of these stations, originally installed to measure tectonic movement at the boundary between the Pacific Plate and the North American Plate, the researchers have added other meteorological and seismic sensors that make it possible to monitor hazardous events in real time and sometimes even predict them before they happen. The prototype system was tested this past July.
“In recent years, the communication infrastructure between these [GPS] base stations has been gradually updated so we have the opportunity to do more real-time projects such as these,” says Angelyn Moore, a research scientist at JPL.
The meteorological side of the project relies on the fact that ground-based GPS stations are in frequent communication with orbiting satellites above. The amount of time it takes a signal from the satellite to reach the ground can be used to calculate moisture levels in the troposphere. This moisture data, combined with data from barometers and thermometers, can improve the accuracy of predictions about rainfall and flash floods.
Using GPS as a tool to measure storm systems is not new; NOAA has already deployed roughly 300 GPS-equipped ground-based weather stations throughout the country, Moore says. But such a sparse network doesn’t allow for local, just-in-time warnings of flash floods. She adds that in Southern California, where storms have been tracked by infrequently launched weather balloons, the density of the new sensor network makes it possible to track the movement of storm systems in unprecedented detail.
On the seismological side of the project, the researchers have added accelerometers to the base stations, an increasingly popular way to record earthquake motion. While GPS sensors note large changes in ground position, accelerometers pick up small movements. “By combining these two signals together, you get a more complete picture of what ground motion was,” says Doug Given, lead of the earthquake early-warning program at the United States Geological Society, who wasn’t involved in this project.
Yehuda Bock, research geodesist and project lead at SIO, explains that combining GPS and accelerometer data is particularly well suited to rapidly estimating magnitude and other characteristics of earthquakes with magnitudes between 7 and 9, which are difficult to quickly differentiate using traditional seismic methods alone. In addition, Bock says, accelerometers pick up primary or P-waves, which can be used to predict the arrival of the secondary or S-waves that mark the beginning of damaging, violent shaking during an earthquake. This information could be integrated into an early-warning system.
Even just a few seconds of notice before an earthquake could provide enough time to shut down elevators in buildings or keep surgeons from making a fatal cut, although Given of the USGS notes that earthquake warning systems are still an open area of research. Given says his team, working with hundreds of seismometers throughout California, is currently “in the midst of figuring out the proper station locations and algorithms to characterize earthquakes and get information out quickly.”
So far, says Bock, 17 stations in Southern California have been retrofitted with seismological and meteorological sensors, but he hopes to add more stations along the West Coast in the coming months.
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