A team of European and American scientists found a new use for global positioning systems (GPS) technology: detecting one of the humanity's most powerful adversaries – earthquakes. The research could help worldwide efforts to mitigate the damage caused by these natural disasters.
Last November a violent earthquake dubbed Denali ripped up roads and shook buildings in Alaska (USA). 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 high above us in the ionosphere could be used to map seismic waves moving across the earth's surface.
|GPS receivers and 'piercing points' for ionospheric measurements from the Denali earthquake|
The research team from the Institut de Physique du Globe de Paris (FR), together with colleagues from the California Institute of Technology (USA), published their paper entitled ‘Ionospheric remote sensing of the Denali earthquake Rayleigh surface waves' in the scientific journal Geophysical Research Letters .
The ionosphere is a region filled with charged particles blanketing the earth which are known to interfere with radio waves. GPS navigation signals sent to earth from orbiting satellites are frequently interrupted by fluctuations in the ionosphere, so-called ‘ionospheric scintillations', causing signal delays, errors and service lockouts, according to a European Space Agency (ESA) statement. The Agency helped to produce this research through its pilot project on space weather applications.
The Franco-American scientists took a problem and turned it to their advantage. They used the networks of GPS receivers in place across California to measure smaller-than-ever shifts in GPS signal transmission times caused as the messages pass through the ionosphere.
EU quake initiatives
Applying what was already known about Rayleigh waves – the largest type of seismic wave moving across the earth's surface during an earthquake – to the data collected from the Denali quake, the team was able to detect a distinctive wavefront moving through the ionosphere. According to the authors of the research, the signals were weak and not continually sampled, but nevertheless showed a clear pattern consistent with models of seismic behaviour. With improvements to the technique, they hope to use it to detect quakes 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.
One such resource is the Euro-Mediterranean Disaster Information Network (EU-MEDIN) which, through better co-operation between policy-makers and stakeholders, aims to improve pre-disaster planning and prevention programmes. This includes creating a better understanding of the events leading up to earthquakes and how to improve building techniques and engineering practices to resist them, as well as furthering knowledge of the socio-economic costs and impacts of earthquakes. More information about EU research activities in this field can be found in a new publication ‘Research on Natural Disasters: Management, Assessment, Prevention, Mitigation' produced by the Research DG's Environment Directorate.
ESA, EU sources