Real‐Time Seismogeodetic Earthquake Magnitude Estimates for Local Tsunami Warnings

Abstract

Tsunamis are a devastating natural, high-fatality hazard (Bryant, 2008). Because most tsunamis are generated by earthquakes, the first indication of a potentially life-threatening tsunami is the earthquake itself. Effective tsunami warning systems must therefore detect, locate, and estimate the magnitude of the causative earthquake to infer tsunamigenic potential, and warn coastal populations as soon as possible after initiation of fault rupture. Rapid characterization of the earthquake focal mechanism also aids in inferring tsunamigenic potential Melgar et al., 2016). Most tsunamis originate from Earth's subduction zones due to thrust faulting although earthquakes with other source mechanisms have also generated tsunamis (Elbanna et al., 2021;Scott, 2021). For example, the 2012 𝐴𝐴 𝐴𝐴𝑤𝑤 8.6 predominantly strike-slip intraplate event off Sumatra, Indonesia (Satriano et al., 2012), generated a tsunami that was recorded at sea-level stations as far as 4,800 km from the epicenter and by ocean bottom pressure sensors (i.e., DART buoys) in the Indian Ocean (Wang et al., 2012). Similarly, the 2009 𝐴𝐴 𝐴𝐴𝑤𝑤 8.1 Samoa earthquake was a normal faulting, outer-rise type event that produced a sizable tsunami with 189 fatalities (Okal et al., 2010).Current warning systems are well-developed for basin-wide and regional tsunamis. For earthquakes over 𝐴𝐴 𝐴𝐴𝑤𝑤 8.0, they rely mainly on long period (>∼300 s) seismic data recorded by broadband seismometers at distances greater than ∼500 km from the epicenter. However, for large tsunamigenic events, ground motions can exceed the dynamic range of a seismometer and result in a clipped record if measured too close to the seismic rupture. Therefore, tsunami warnings to the coastal communities located closest to the earthquake rupture may not be issued in a sufficiently timely manner. Another serious challenge for tsunami warning is the identification of tsunami