GPS seismometers with up to 20 Hz sampling rate

The large near-field displacements before and during an earthquake are invaluable information for earthquake source study and for the detection of slow/silent earthquakes or pre-seismic crustal deformation events. However, due to bandwidth limitations and saturation current, seismometers cannot measure many of these displacements directly. In a joint experiment between the University of New South Wales (UNSW) and the Meteorological Research Institute (MRI), two Trimble MS750 GPS receivers were used in the Real-Time Kinematic (RTK) mode with a fast sampling rate of up to 20 Hz to test the feasibility of a "GPS seismometer" in measuring displacements directly. The GPS antenna, an accelerometer, and a velocimeter were installed on the roof of a truck capable of simulating shaking due to earthquakes. The simulated seismic waveforms resolved from the RTK time series are in very good agreement with the results from the accelerometer and the velocimeter, after integrating twice and once respectively. Moreover, more displacement information are revealed in the GPS RTK results although they are noisier.