Strong-motion seismogeodesy by deeply coupling GNSS receivers and inertial measurement units

Understanding the origin and mechanism of destructive earthquakes is predicated on the faithful recordings of their induced ground displacements near the clearly deformed epicentral regions. Global Navigation Satellite System (GNSS) receivers, such as the GPS sort, have been recognized as the best, if not the only reliable, tool to measure such large displacements. This is achieved within the GNSS receivers by continuously tracking the satellite carrier-phase signals. However, GNSS receivers are likely to lose their fidelity in recording the complete and accurate displacement waveforms in case of fierce ground motions, since their carrier-phase tracking becomes instable when strained by such persistent and high dynamic stress. We hence developed an advanced GNSS receiver architecture where the dynamic stress suffered by the carrier-phase tracking components is compensated for by an embedded inertial measurement unit consisting of one accelerometer and one gyroscope. In this case, the carrier-phase signals can be tracked steadily by GNSS receivers, and the displacement accuracy can be improved from sub-centimeter to millimeter level by about 70% when the ground accelerations reach twice the gravitational acceleration. We believe that this advanced GNSS receiver will be an excellent strong-motion seismometer recording displacements directly at a few millimeter accuracy without missing any earthquake signals, even in case of fierce ground motions.