Strong‐Motion Seismogeodesy by Deeply Coupling GNSS Receivers with Inertial Measurement Units.

Global navigation satellite system (GNSS) displacements at near‐source stations can be biased in both amplitude and phase due to fierce earthquake strike. We propose to inject inertial measurement unit (IMU)‐recorded ground motions into GNSS receivers to compensate their phase‐lock loops (PLLs) for seismic motion stress, aiming at keeping steady carrier‐phase tracking. We use a shake table to replay an acceleration record (0.5–2.0 g) from the 2008 Mw7.9 Wenchuan earthquake to test this IMU‐augmented PLL: It achieves a 1.9‐mm amplitude error (RMS) and an 8.0‐ms phase lag against the shake table's recordings, while the conventional PLL languishes to 6.0 mm and 56.5 ms, respectively. Moreover, the IMU‐augmented PLL enables a six‐degree‐of‐freedom integration among the GNSS and IMU data, where the displacement amplitude error and phase lag decline further to 0.9 mm and 3.5 ms, respectively. We believe that the IMU‐augmented GNSS receivers are ideal strong‐motion seismograph to capture trustworthy broadband displacements in the near fields. Plain Language Summary: Understanding the origin and mechanism of destructive earthquakes is predicated on the faithful recordings of their induced ground displacements near the significantly deformed epicentral regions. Global navigation satellite system (GNSS) receivers have been recognized as the best tool to measure the large epicentral 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 complete and accurate displacement waveforms in case of strong ground motions, since their carrier‐phase tracking becomes unstable 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 subcentimeter to millimeter level by about 70% when the ground accelerations reach up to twice the gravitational acceleration. We believe that this advanced GNSS receiver will be an excellent strong‐motion seismometer in recording displacements directly at a few millimeter resolution without missing or distorting any earthquake signals, even in case of fierce ground motions. Key Points: A new GNSS receiver architecture is developed by embedding both accelerometer and gyroscope to capture fierce seismic displacementsGNSS displacement error and phase lag are both reduced by 70% and 85% to 2 mm and 8.0 ms, respectively, compared to conventional receiversSix‐degree‐of‐freedom seismogeodesy is achieved with the displacement error and phase lag reduced further to 0.9 mm and 3.5 ms, respectively [ABSTRACT FROM AUTHOR]