Global navigation satellite systems (GNSS) play a significant role in geodynamic applications. Even though tectonic motions are in the order of a few millimeters to centimeters per year, the accuracy of high-end GNSS equipment is well suited to detect such displacements. The magnitude and direction of GNSS station displacements following an earthquake can also provide valuable information on the type of crustal movements encountered which can, in some instances, be used as a component of a tsunami-warning system. In this post, I take a look at data collected at a GNSS station affected by the magnitude 7.8 earthquake that occurred on 25 April 2015 in Nepal.
Station LHAZ, located about 400 miles (640 kilometers) from the epicenter of the earthquake, is the closest GNSS station with publicly available data. Time series of positions were obtained based on the precise point positioning (PPP) methodology, meaning that no base station was required. The figure below shows that, although the distance between LHAZ and the epicenter is quite significant, the station moved approximately 10 centimeters in all directions (latitude, longitude and height) before returning to its original position. It is expected that movements with much larger amplitudes were observed closer to Katmandu, Nepal.
Looking back at data I had processed for previous major earthquakes, station displacements are really impressive. For example, on 27 February 2010, a magnitude 8.8 earthquake occurred approximately 100 km northeast of Concepcion, Chile. Station CONZ, located in the aforementioned city, was able to record GPS observations throughout the event, providing valuable information on the seismic displacements including the response to surface waves. Notice the different scale in the y-axis for the following plot, showing that Concepcion moved by over 3 meters in just a few seconds!
The last example provided here is the 11 March 2011 magnitude 9.0 earthquake off the Pacific coast of Tohoku, Japan. Station MIZU, located at about 135 km from the epicenter, permanently moved in the south-east direction by over 2 meters.
I find these numbers astonishing every time I look at them. Analyzing this data does not help the people who suffered through these tragedies, but researchers are currently looking at ways of predicting earthquakes using GNSS signals… now this would be ground-breaking news!