Geodetic Observations of Weak Determinism in Rupture Evolution of Large Earthquakes

• Published in: Journal of geophysical research. Solid earth Vol. 123; no. 11; pp. 9950 - 9962
• Main Authors: Goldberg, D. E., Melgar, D., Bock, Y., Allen, R. M.
• Format: Journal Article
• Language: English
• Published: United States 01.11.2018
• Subjects: determinism; earthquake magnitude; GNSS; earthquake magnitude; GNSS; determinism
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2018JB015962

The moment evolution of large earthquakes is a subject of fundamental interest to both basic and applied seismology. Specifically, an open problem is when in the rupture process a large earthquake exhibits features dissimilar from those of a lesser magnitude event. The answer to this question is of importance for rapid, reliable estimation of earthquake magnitude, a major priority of earthquake and tsunami early warning systems. Much effort has been made to test whether earthquakes are deterministic, meaning that observations in the first few seconds of rupture can be used to predict the final rupture extent. However, results have been inconclusive, especially for large earthquakes greater than Mw7. Traditional seismic methods struggle to rapidly distinguish the size of large‐magnitude events, in particular near the source, even after rupture completion, making them insufficient to resolve the question of predictive rupture behavior. Displacements derived from Global Navigation Satellite System data can accurately estimate magnitude in real time, even for the largest earthquakes. We employ a combination of seismic and geodetic (Global Navigation Satellite System) data to investigate early rupture metrics, to determine whether observational data support deterministic rupture behavior. We find that while the earliest metrics (~5 s of data) are not enough to infer final earthquake magnitude, accurate estimates are possible within the first tens of seconds, prior to rupture completion, suggesting a weak determinism. We discuss the implications for earthquake source physics and rupture evolution and address recommendations for earthquake and tsunami early warning. Key Points GNSS observations in addition to seismic observations are critical to rapid and reliable earthquake magnitude estimates GNSS‐derived displacements can reliably estimate earthquake magnitude prior to rupture completion Evidence of weak determinism suggests that near‐fault instrumentation is the best method for improving rapid magnitude estimations