UNAVCO Leads Tests On Alternate Way to Measure Earthquakes
Tracking the movement of tectonic plates with GPS stations is possible - and (relatively) slow. Collecting multiple position measurements over time shrinks the error bars and improves precision.
However the network of GPS (or multi-constellation GNSS) stations also have an important role to play in earthquake early warning systems, and here the luxury of time evaporates. Stations need to detect and help characterize an earthquake in a matter of seconds in order to assist in generating timely warnings. A UNAVCO team led by Tim Dittmann, along with Jade Morton of the University of Colorado Boulder have been working on a velocity-based geodetic processing technique is complementary to existing approaches to characterize earthquake motions. Read more below and here.
Currently, GPS/GNSS earthquake motion assessment is done by applying real-time corrections to the data. This involves using estimates of current satellite positions and clock errors, along with calculations of the ionosphere’s impact on the satellite signal, to greatly improve precision to within a few centimeters. But there’s another way to approach this problem, and that’s to directly measure the station’s velocity as it moves during an earthquake—which has the advantage of working without relying on external correction information.
The basic principle is that when precise measurements of the oscillating satellite signal are made in rapid succession, most sources of measurement error (like atmospheric conditions or satellite positions) aren’t changing much between consecutive datapoints. Additionally, the velocity of an orbiting GPS satellite is predictable. So instead of calculating the station’s absolute position, you can simply calculate the apparent amount of position change—its velocity—based on the change in the signal. A motionless antenna will measure very little change, but a moving antenna will measure much more. Read more>>>
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