[J04-2] Geohazard early warning systems II

[J04-2-03] Seismogeodesy for Rapid Earthquake Magnitude Estimation

^○Dara Goldberg¹, Yehuda Bock¹, Diego Melgar² (1.University of California, San Diego, La Jolla, California, United States of America, 2.University of California, Berkeley, Berkeley, California, United States of America)

Earthquake magnitude is a concise metric that provides invaluable information about the destructive potential of a seismic event. Rapid magnitude estimation for earthquake and tsunami early warning relies on near-field seismic and geodetic instruments. However, seismic instruments experience well-documented complications at long periods, which hinders accurate and timely estimates of ground displacement. As such, the relation between ground motions measured with strong-motion accelerometers (broadband seismometers clip in the near field of large earthquakes) and magnitude saturates, leading to underestimation of earthquake magnitude. However, ground motions measured with GNSS do scale with magnitude without saturation [Crowell et al., 2013; Melgar et al., 2015]. Therefore, we supplement high frequency strong-motion accelerations with Global Navigation Satellite System (GNSS) long-period displacement observations to better inform rapid response. We refine magnitude scaling relations using peak ground displacement (PGD) by adding a large GNSS dataset of earthquakes in Japan. We demonstrate that seismogeodesy, the optimal combination of GNSS and seismic instrumentation, improves the sensitivity of displacement time series compared to GNSS alone. This not only means that ground motion can be detected at farther stations, but also that smaller seismic arrivals (i.e. P-waves) become visible in the displacement time series. P-wave amplitude (Pd) has been examined as an early indicator of earthquake magnitude. Relations between Pd and magnitude using seismic-only instruments also appear to suffer from saturation, while seismogeodetic data has been demonstrated to eliminate saturation [Meier et al., 2016, Crowell et al., 2013]. We create seismogeodetic displacements by combining the GNSS dataset with Japanese KiK-net and K-net accelerometer data to explore the potential of seismogeodesy for magnitude scaling using P-wave amplitude with several seconds of data.