GPS seismometers with up to 20Hz 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 quakes or pre-seismic crustal deformation events. However current seismometers cannot measure large near-field 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 20Hz to test the feasibility of a “GPS seismometer ” in measuring displacements directly. The GPS antenna, an accelerometer, and a velometer were installed on the roof of an earthquake shake-simulator truck. The simulated seismic waveforms resolved from the RTK time series are in very good agreement with the results from the accelerometer and the velometer, after integrating twice and once respectively. Moreover, more displacement information are revealed in the GPS RTK results although they are noisier. In order to develop an operational GPS seismometer network, implementation issues such as the layout of reference and rover stations, noise reduction using measurements from adjacent days, correlation between measurements, data communication, etc., are briefly discussed. 1