SAN FRANCISCO — No one can predict the exact time and location of an impending earthquake, and efforts to use satellites to detect imminent temblors often have been dismissed by geologists. Nevertheless, scientists say that sophisticated sensors and intricate computer models offer evidence that space-based instruments operating in concert with ground-based networks can help to reveal the intense stress on a fault line that occurs before a serious quake.
NASA’s most ambitious earthquake forecasting mission is Deformation, Ecosystem Structure and Dynamics of Ice, or DESDynI, a comprehensive effort to monitor changes in the Earth’s surface that signal earthquakes, landslides or volcanoes in addition to evaluating the impact of climate change on ice sheets. That mission, which is tentatively scheduled for launch in 2017, will include two satellites operating in different orbits. One will carry an L-band interferometric synthetic aperture radar to provide 3-D imagery of the Earth’s surface. The other will house a multibeam laser altimeter to measure vegetation, said Paul Rosen, DESDynI project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
The synthetic aperture radar is the key earthquake-monitoring tool. During each orbit, the instrument will use radar waves to create a 3-D map of the ground and reveal changes over time. “By making these repeated measurements, we can see the shape of the Earth change as plate tectonics causes deformation,” Rosen said. “If an event occurs, we can see changes to a millimeter scale. That will help us to understand what happens when earthquakes occur and to look for precursor signals.”
In preparation for that mission and to bolster ongoing efforts to better understand earthquake dynamics, JPL scientists are using a synthetic aperture radar on a Gulfstream 3 aircraft operating from NASA’s Dryden Flight Research Center in Edwards, Calif., to map California’s fault lines. The radar, which is located in a pod underneath the plane, is being used to make detailed 3-D maps of the San Andreas, Hayward and nearby faults. As scientists gain insight into the structure and movement along those faults, they can offer better information on the risk of earthquakes in specific areas, said JPL scientist Eric Fielding.
Looking for movement on the Earth’s surface, however, is not the only technique being studied for signs of an impending earthquake. When intense pressure builds in the rocks that form the Earth’s crust, those rocks effectively turn into a battery that emits an electronic charge. That charge produces a signal, explains Friedemann Freund, a scientist at the NASA Ames Research Center in Mountain View, Calif., who has been investigating this phenomenon for more than a decade. Sophisticated sensors may be able to detect signals generated at the Earth’s surface by looking for anomalies in infrared emissions on the ground or at perturbations in the ionosphere above the region.
“Once we understand the many processes involved, we can use a combination of space assets and ground networks to forecast earthquakes,” Freund said. To detect the subtle and often fleeting signs that an earthquake is likely to occur in the days or weeks ahead, it will be crucial to combine different instruments capable of detecting different signs that high levels of stress are building underground, he added.
When all or most of those instruments points to a large increase in underground stress, there is a good chance of an earthquake. However, even when pressure reaches very high levels, there is always a chance that tectonic plates will slide past one another without producing a serious earthquake, Freund said.
Companies already are deploying the initial elements of an earthquake forecasting network. QuakeFinder of Palo Alto, Calif., a division of Stellar Solutions, has established ground stations throughout California to detect electromagnetic radiation. Open Hazards Group of Davis, Calif., has created a Web site to offer public information on the risk of earthquakes and other events. As more information is available from satellite and ground-based sensors, it will be folded into the Open Hazards forecasts, said John Rundle, company chairman and a professor at the University of California, Davis.
Scientists at Surrey Satellite Technology Ltd. (SSTL) of Guildford, England, are drafting plans for a constellation of earthquake-alert satellites. “The first phase is to identify potential earthquake precursors which could be detected from space with sufficient timeliness before the event to allow a warning or forecast to be issued,” according to Kathryn Graham, mission concepts team leader for SSTL, which was purchased last year by the Astrium space division of Europe’s largest aerospace company, EADS. “Once this phase is complete, we will identify the payloads required to detect these precursors and finally assess which of these could be accommodated on small satellite platforms.”
Stuart Eves, SSTL principal engineer, added, “In an ideal world, the aim would be to combine inputs from both infrared sensors and the radio frequency monitoring to provide confirmation that some form of event may be imminent, but as yet we don’t have enough evidence to say whether these effects occur in association with all earthquakes.”