Last November, a violent earthquake dubbed Denali ripped up roads and shook buildings in Alaska. Though registering a memorable 7.9 on the Richter scale, the event may end up in the history books more for its help in proving that the constellation of GPS satellites in the ionosphere could be used to map seismic waves moving across the earth’s surface.
The ionosphere is a region filled with charged particles blanketing the earth. And GPS navigation signals sent to earth from orbiting satellites are frequently interrupted by fluctuations in the ionosphere that cause signal delays, errors and service lockouts.
Using a number of GPS receivers across California, the scientists detected a distinct wavefront moving through the ionosphere as a result of the seismic wave moving across the surface of the earth during the Denali earthquake. They did this by measuring the small shifts in GPS signal transmission times caused as the GPS messages passed through the ionosphere.
With improvements to the technique, they hope to use it to detect earthquakes in areas not covered by current detectors, such as deep in the ocean or near islands.
With the number of satellites set to double under the Galileo programme – a joint EU-ESA navigation system – the team predicts it can obtain much more precise maps of the ionosphere. Their hope is that a seismic detection service based on ionospheric measurements may one day supplement existing resources in Europe and elsewhere.