Geodetic Observations of Weak Determinism in Rupture Evolution of Large Earthquakes

Abstract

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 M w7. 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.

Earthquakes Within Earthquakes: Patterns in Rupture Complexity

“…We have shown that the statistical properties of the subevent moment relative to the main event moment may be utilized for early magnitude estimates. Our results do not imply that earthquakes are deterministic in the sense that early nucleation is indicative of the entire evolution of rupture (Beroza & Ellsworth, 1996;Goldberg et al, 2018;Iio, 1995;Meier et al, 2017;Melgar & Hayes, 2017), but rather that we can exploit the patterns in earthquake complexity to statistically infer the future number and size of subevents from the first subevent. Our results are mostly practical for strike-slip events that tend to have shorter duration subevents.…”

“…Furthermore, there is not yet an implementation of real-time source time function inversion, which would require an a priori knowledge of the source location and P wave Green's function (the latter can be precomputed and efficiently searched in databases). Goldberg et al (2018) and Minson et al (2018) indicate that, at best, magnitude estimates are slightly lower but track the evolution of cumulative moment release (green curve in Figure 4b). The advantage of using the scaling provided described in this paper is therefore a speed up, in the Palu example, of the duration of observation required to produce a final magnitude estimate by about 10 s from current methods.…”

“…Whether earthquake complexity reflects underlying organization or randomness is a fundamental issue in earthquake physics and predictability. Recent work has suggested that organization in earthquake complexity permits a sense of determinism whereby observations made in a short period of time at the beginning of an earthquake may be used to infer the overall event size and style (Olson & Allen, 2005;Melgar & Hayes, 2017;Goldberg et al, 2018;Allen & Melgar, 2019). Previous studies have found that early P wave arrivals carry information about the overall earthquake size (Iio, 1995;Beroza & Ellsworth, 1996;Allen & Kanamori, 2003;Olson & Allen, 2005), but such correlations bear large uncertainties that necessitate additional information, such as attenuation parameters, in order to conduct meaningful early magnitude estimation (Wu et al, 2006;Colombelli et al, 2014;Noda & Ellsworth, 2016).…”

Peak Ground Displacement Saturates Exactly When Expected: Implications for Earthquake Early Warning

“…More recently, Leyton et al () analyzed seismic and geodetic waveforms from earthquakes in the Chilean subduction zone, finding that EEW source characterization can be significantly improved using extended measurement time windows, which is inconsistent with the notion of rupture determinism. While these studies suggest that a purely deterministic rupture mechanism can likely be ruled out, a weak or probabilistic form of determinism may still be observed in some instances through careful analysis of seismic or geodetic data (Goldberg et al, ; Melgar & Hayes, ; Olson & Allen, ).…”

Weak Near‐Field Behavior of a Tsunami Earthquake: Toward Real‐Time Identification for Local Warning

“…Consider the STFs of the events that have similar magnitudes to the Mentawai earthquake (Figure e). The protracted duration of the tsunami earthquake and slow growth to final PGD (Figure a; Goldberg et al, ), produced by the slow rupture of low rigidity rocks, leads to a low‐stress drop rupture (Ye et al, ; Yue et al, ) with a source spectrum (Figure f) that has a much lower corner frequency for tsunami earthquakes. It also leads to a larger coseismic slip for the given earthquake magnitude, as slip is inversely proportional to rigidity with respect to seismic moment.…”