GPS Seismometer and its Signal Extraction

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 none of the current seismometers can measure large near-field displacements directly. Two Leica CRS1000 GPS receivers have been used in the Real-Time Kinematic (RTK) mode with a fast sampling rate of 10Hz to test the feasibility of using a GPS receiver as a seismometer that can measure large displacements directly. Though both the 2.3Hz and 4.3Hz sine signal of 12.7mm amplitude used in the experiment to simulate seismic waves can be resolved easily from the power spectrum of the RTK time series (even for the height component), the time series itself is very noisy due to the effects of atmospheric biases, multipath, receiver noise, etc. In order to develop an operational GPS seismometer an adaptive Finite-duration Impulse Response (FIR) filter, based on a least-mean-square (LMS) algorithm, has been designed to successfully derive a relatively noise-free seismic signal in real-time from the high-rate RTK GPS results. Several configurations of the adaptive filter are discussed.