Magnitude-period scaling relations for Japan and the Pacific Northwest: Implications for earthquake early warning

Andrew B. Lockman
University of Wisconsin-Madison

Richard M. Allen
University of California, Berkeley

Bull. seism. Soc. Am. 97 (1), 140-150, doi: 10.1785/0120040091

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Scaling relations between the predominant period of P-wave arrivals and earthquake magnitude are explored using datasets from the Pacific Northwest and Japan, and compared to previous observations in southern California (Allen and Kanamori, 2003). While we find the same scaling for events in all three geologically diverse regions, the sensitivity of the predominant period observation to magnitude can be optimized using various frequency bands for different magnitude ranges and in different regions. The ability to estimate the magnitude using just 4 sec of the P-wave offers a methodology for earthquake early warning capable of providing a few seconds of warning even in the epicentral region. While the accuracy of magnitude estimates increases with the number of stations reporting predominant period observations, the most significant improvements require only four stations, at which point the average magnitude error is less than 0.5. Thus seismic hazard mitigation using earthquake early warning does not require a dense regional network. Finally, the ability to estimate the magnitude from the first 4 sec of data, even when the rupture duration is greater, suggests what we term an initiation phase for earthquakes and demonstrates that the beginnings of large earthquakes are distinguishable from those of small earthquakes.

© Richard M Allen