Scaling earthquake magnitude in real time with high-rate GNSS peak ground displacement from variometric approach
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ORIGINAL ARTICLE
Scaling earthquake magnitude in real time with high‑rate GNSS peak ground displacement from variometric approach Jianfei Zang1 · Caijun Xu1,2,3 · Xingxing Li1 Received: 31 December 2019 / Accepted: 21 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
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. Keywords Magnitude scaling · Peak ground displacement · Variometric approach · High-rate GNSS
Introduction For earthquake early warning systems or tsunami early warning systems, fast determination of earthquake magnitude plays a key role. Most running systems determine Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10291-020-01013-x) contains supplementary material, which is available to authorized users. * Caijun Xu [email protected] 1
School of Geodesy and Geomatics, Wuhan University, Wuhan 430079, China
2
Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, Wuhan University, Wuhan 430079, China
3
Key Laboratory of Geophysical Geodesy, Ministry of Natural Resources, Wuhan 430079, China
the magnitude based on empirical scaling laws that relate the magnitude to the typical metrics of an initial 2–4 s of P waves. Such metrics inc
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