Real-time magnitude estimation of large earthquakes utilizing combined strong motion and GPS data

The rapid and accurate assessment of the earthquake magnitude has long been a focal point for seismologists. Traditional methods, such as ${\tau }_c$ and P_d, which rely on initial P-wave information for magnitude estimation, often encounter issues of magnitude saturation. In recent years, the development of the $\sqrt{Es}$ method based on strong motion data and the PGD method based on GPS data has provided new solutions to address the saturation problem. In this study, we employ the $\sqrt{Es}$ method in combination with the geodetic PGD method to assess the magnitudes of the California M_w 6.4, M_w 7.1 and the Italy M_w 6.6 earthquakes. In addition, we developed a real-time focal mechanism inversion method based on high-frequency GPS and applied it to the California M_w 7.1 and Japan M_w 9.1 earthquakes. The magnitudes of these earthquakes obtained from individual methods and the composite approach exhibit a commendable concordance with the reported moment magnitudes, demonstrating an average absolute deviation of less than 0.3. Reliable magnitude estimates can be achieved within 60–80 s after the earthquake origin time. Furthermore, the real-time focal mechanism inversion can also provide reliable parameters such as moment magnitude, strike, dip, and rake angle within a short time. Our findings demonstrate that the combined method enhances the robustness of real-time magnitude estimation for early warning of large earthquakes and shows potential for application in tsunami warning systems.