Real-time high-precision earthquake monitoring using single-frequency GPS receivers

We present a new method for high-precision real-time earthquake monitoring that focuses on station velocity using single-frequency GPS receivers. By means of GPS absolute velocity determination (AVD), real-time station velocity of millimeter per second precision can be obtained epoch by epoch using the GPS broadcast ephemeris. While the monitoring stations are considered stationary during aseismic time, the coseismic displacement can be instantaneously recorded by the velocity changes. The 1-Hz GPS data at selected stations during the M_w 8.0 Wenchuan earthquake, the M_w 9.0 Tohoku-Oki earthquake and the M_w 6.6 Lushan earthquake are processed with the AVD approach. The results indicate that the phase and amplitude of AVD-derived velocity time series induced by the earthquakes coincide with those derived from post-mission kinematic PPP approach. Even when coseismic displacements at some stations are occasionally not visible in the position time series, the velocity series can still clearly manifest the earthquake displacement signal. With the AVD approach, the precision and reliability of the real-time monitoring can be improved significantly. It is also indicated the velocity series can be used for fast post-earthquake assessment such as rapid determination of earthquake magnitude, locating epicenter, determining seismic wave propagation velocity and other earthquake studies.