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Real-time forecasts of tomorrow's earthquakes in California


Despite a lack of reliable deterministic earthquake precursors, seismologists have significant predictive information about earthquake activity from an increasingly accurate understanding of the clustering properties of earthquakes1,2,3,4. In the past 15 years, time-dependent earthquake probabilities based on a generic short-term clustering model have been made publicly available in near-real time during major earthquake sequences. These forecasts describe the probability and number of events that are, on average, likely to occur following a mainshock of a given magnitude, but are not tailored to the particular sequence at hand and contain no information about the likely locations of the aftershocks. Our model builds upon the basic principles of this generic forecast model in two ways: it recasts the forecast in terms of the probability of strong ground shaking, and it combines an existing time-independent earthquake occurrence model based on fault data and historical earthquakes5 with increasingly complex models describing the local time-dependent earthquake clustering1,2. The result is a time-dependent map showing the probability of strong shaking anywhere in California within the next 24 hours. The seismic hazard modelling approach we describe provides a better understanding of time-dependent earthquake hazard, and increases its usefulness for the public, emergency planners and the media.

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Figure 1: Maps of California, showing the probability of exceeding MMI VI over the next 24-h period.
Figure 2: Hazard maps calculated for four 24-hour intervals in the vicinity of the 1992 Landers ( M = 7.3) earthquake.
Figure 3: Calculated and observed rates of events M ≥ 4 in 24-hour intervals following mainshocks occurring between 1988 and 2002 in southern California.


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We are very grateful for the reviews from E. Field, D. Jackson, R. Simpson and A. Cornell. The work was supported by the Southern California Earthquake Center, ETH Zurich and the US Geological Survey.Author Contributions This work was completed as part of the PhD thesis of M.C.G. under the supervision of S.W. at ETH-Zürich. L.M.J. and P.A.R. provided significant contributions to the model development.

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Correspondence to Matthew C. Gerstenberger.

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Supplementary Methods

In this section, the methodology for creating the real-time hazard maps is fully developed. Each step from the data collection, definition of an aftershock sequence to the hazard calculation is detailed. (PDF 502 kb)

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Gerstenberger, M., Wiemer, S., Jones, L. et al. Real-time forecasts of tomorrow's earthquakes in California. Nature 435, 328–331 (2005).

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