Scaling earthquake magnitude in real time with high-rate GNSS peak ground displacement from variometric approach

Abstract

Peak ground displacement (PGD) derived from high-rate Global Navigation Satellite System (GNSS) can be used to determine, i.e., the estimate or scale the earthquake magnitude in real time without magnitude saturation experienced by seismic sensors at large earthquakes. Compared with relative positioning or Precise Point Positioning (PPP), the variometric approach can calculate station velocity using the broadcast ephemeris and avoiding estimating phase ambiguities. By integration, velocities can be translated into displacements. However, an inaccurate broadcast ephemeris might cause integrated displacements to show nonlinear drifts. Recently developed real-time orbit and clock products used by real-time PPP have higher accuracy and can also be employed by the variometric approach. We evaluate the performance of the variometric approach on magnitude scaling using high-rate GNSS data collected during the 2019 Mw 7.1 Ridgecrest earthquake, the 2016 Mw 7.8 New Zealand earthquake, and the 2017 Mw 6.5 Jiuzhaigou earthquake. The results indicate that a spatial filter cannot correct nonlinear drifts of integrated displacements completely and scaled magnitudes are not stable when the broadcast ephemeris is used. While using the Centre National d’Etudes Spatiales (CNES) real-time ephemeris, we find both the spatial filter and linear filter can correct drifts well and scaled magnitudes have the same accuracy as those of PPP. While comparing different GNSS systems, we find that BDS is superior to GPS and GLONASS in the case of the Jiuzhaigou earthquake because BDS has a better satellite geometry in this region. Compared with single GPS, multi-GNSS can improve satellite geometry and provide more precise seismic displacements when broadcast ephemeris and low sampling precise clocks are used by the variometric method.