Abstract
Earthquake Early Warning (EEW) predicts future ground shaking based on presently available data. Long ruptures present the best opportunities for EEW since many heavily shaken areas are distant from the earthquake epicentre and may receive long warning times. Predicting the shaking from large earthquakes, however, requires some estimate of the likelihood of the future evolution of an ongoing rupture. An EEW system that anticipates future rupture using the present magnitude (or rupture length) together with the Gutenberg-Richter frequency-size statistics will likely never predict a large earthquake, because of the rare occurrence of ‘extreme events’. However, it seems reasonable to assume that large slip amplitudes increase the probability for evolving into a large earthquake. To investigate the relationship between the slip and the eventual size of an ongoing rupture, we simulate suites of 1-D rupture series from stochastic models of spatially heterogeneous slip. We find that while large slip amplitudes increase the probability for the continuation of a rupture and the possible evolution into a ‘Big One’, the recognition that rupture is occurring on a spatially smooth fault has an even stronger effect. We conclude that an EEW system for large earthquakes needs some mechanism for the rapid recognition of the causative fault (e.g., from real-time GPS measurements) and consideration of its ‘smoothness’. An EEW system for large earthquakes on smooth faults, such as the San Andreas Fault, could be implemented in two ways: the system could issue a warning, whenever slip on the fault exceeds a few metres, because the probability for a large earthquake is high and strong shaking is expected to occur in large areas around the fault. A more sophisticated EEW system could use the present slip on the fault to estimate the future slip evolution and final rupture dimensions, and (using this information) could provide probabilistic predictions of seismic ground motions along the evolving rupture. The decision on whether an EEW system should be realized in the first or in the second way (or in a combination of both) is user-specific.
Highlights
Earthquake Early Warning (EEW) requires fast and robust predictions of earthquake source and ground motion parameters shortly after the initiation of an earthquake
A more sophisticated EEW system could use the present slip on the fault to estimate the final rupture dimensions and future slip evolution, and could provide probabilistic predictions of seismic ground motions along the evolving rupture
The frequencysize statistics of these events are close to the power-law distributions generated by the Gutenberg-and-Richter model (G-R) model; slip series generated from models with large μ, on the other hand, produce smooth ruptures with a higher number of large events, that is, the frequency-size statistics of these series are more similar to the distributions produced by the Characteristic Earthquake model (CE) model (Fig. 3a)
Summary
Earthquake Early Warning (EEW) requires fast and robust predictions of earthquake source and ground motion parameters shortly after the initiation of an earthquake. Generated by the G-R model; slip series generated from models with large μ, on the other hand, produce smooth ruptures with a higher number of large events, that is, the frequency-size statistics of these series are more similar to the distributions produced by the CE model (Fig. 3a) This means that we can use the roughness parameter μ to tune the stochastic models from G-R- to CE-like behaviour. This is in good agreement with, for example, Hillers et al (2007), who found from quasi-dynamic rupture simulations that smooth continuum faults usually tend to have narrow event distributions, and that strong spatial heterogeneity is required to produce spatiotemporal non-uniform seismic behaviour. We assume that μ is a fault-characteristic parameter, which has been determined from previous geological and geophysical studies (e.g., Sagy et al 2007) and is known when the rupture nucleates
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