Surface Displacement and Early Warning Magnitude of the 2025 Dingri, Xizang Ms 6.8 Earthquake Using High-Rate GNSS Observations

Objectives:On January 7, 2025, the Ms 6.8 earthquake in Dingri, Tibet resulted in significant casualties. Rapidly capturing near-field seismic surface deformation and accurately estimating earthquake magnitude are crucial for post-earthquake response and disaster mitigation. The development of BDS-3 precise point positioning, (PPP) B2b technology and the deployment of high-rate global navigation satellite system(GNSS) stations in the seismic region provide valuable observational data for this study. Methods:This study utilizes PPPB2b corrections to process 1 Hz and 50 Hz GNSS data from nine stations for surface deformation monitoring and magnitude estimation. First, PPP-B2b is applied to correct broadcast ephemerides, generating real-time highprecision orbit and clock products. These corrections are then used in PPP to derive ground displacement and seismic waveforms, which are compared with post-processed PPP results. Finally, an investigation is conducted on earthquake magnitude estimation based on GNSS observations. Results:The results show that seismic waveforms derived using B2b-corrected products exhibit root mean square errors of 0.40 cm, 0.41 cm, and 1.34 cm in the east, north, and vertical components, respectively, compared to solutions based on post-processed precise products. This confirms the feasibility of B2b-corrected products for high-rate GNSS seismic deformation monitoring. The earthquake magnitude estimated using B2b-corrected products is 7.16, differing by 0.08 from the post-processed PPP result and by 0.06 from the moment magnitude reported by the United States Geological Survey, demonstrating the effectiveness of B2b precise products for magnitude estimation. Additionally, 50 Hz ultra-high-rate GNSS data reveal that 1 Hz GNSS monitoring exhibit aliasing distortion in near-field seismic waveforms. Considering both network transmission capacity and waveform fidelity, a sampling rate of 5-10 Hz is recommended for seismic monitoring applications. Conclusions:The BDS PPP-B2b technology, in conjunction with ultra-high-rate GNSS, has effectively facilitated the monitoring of surface deformation and the inversion of early warning magnitudes for the Ms 6.8 earthquake in Dingri, Tibet, demonstrating its feasibility and reliability.