Rapid Earthquake Magnitude Estimation for Local Early Warning Systems Using Seismogeodesy

Abstract

Rapid and accurate estimation of earthquake moment magnitude is crucial for early warning systems, for alerting coastal populations vulnerable to tsunamigenic hazards. Most seismic-based estimation approaches introduce time delays that limit applicability near the source, while geodetic approaches have been limited to empirical scaling relationships. We extend a physics-based approach for seismogeodetic moment magnitude (M_wg) estimation initially developed for thrust earthquakes to also include strike-slip and normal fault mechanisms by examining 17 M_w 7.0 to 9.1 earthquakes. We find that considering S-wave propagation is critical for accurately estimating the magnitude of strike-slip events. Radiation pattern (RP) corrections offer substantial benefits for normal fault events but are difficult to compute in real-time. However, RP corrections can be neglected for strike-slip events, while thrust and normal earthquakes are more reliably handled using the previously established seismogeodetic approach, allowing accurate M_wg estimates within about 2–3 min of earthquake initiation in early warning scenarios. We further broaden the seismogeodetic approach by interpolating coseismic windows from collocated GNSS and/or accelerometer stations to stand-alone GNSS stations, thereby increasing the size and geometry of the available network. We present an integrated workflow for rapid M_wg estimation that leverages tectonic information from subduction-zone geometry to inform focal mechanism selection, rather than relying on uncertain hypocentral depths. Our extended approach provides rapid earthquake magnitudes (∼2–3 min after earthquake initiation) for moderate to large events (M_w ≥ 7) with an M_wg accuracy of $\mathit{\pm }$0.2 magnitude units. Our approach is useful for operational environments where timely magnitude estimates are essential.