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Toward Earthquake Early Warning in Northern California
Gilead Wurman
Richard M. Allen
Peter Lombard
University of California, Berkeley
J. Geophys. Res., 112, B08311, doi:10.1029/2006JB004830, 2007.
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Abstract
Earthquake Early Warning systems are an approach to earthquake hazard mitigation
which takes advantage of the rapid availability of earthquake information to quantify the
hazard associated with an earthquake and issue a prediction of impending ground motion
prior to its arrival in populated or otherwise sensitive areas. One such method,
Earthquake Alarm Systems (ElarmS) has been under development in southern California
and, more recently, in northern California. Event magnitude is estimated using the peak
amplitude and the maximum predominant period of the initial P-wave. ElarmS
incorporates ground motion prediction equations and algorithms from ShakeMap for
prediction of ground motions in advance of the S-wave arrival. The first peak ground
motion estimates are available one second after the first P-wave trigger, and are updated
each second thereafter for the duration of the event. The ElarmS methodology has been
calibrated using 43 events ranging in size from ML 3.0 to Mw 7.1 which occurred in
northern California since 2001. We present the first implementation of ElarmS in an
automated, non-interactive setting, and the results of 8 months of non-interactive
operation in northern California. Between February and September of 2006, ElarmS
successfully processed 75 events between Md 2.86 to Mw 5.0. We find that the ElarmS
methodology processed these events reliably and accurately in the non-interactive setting.
The median warning time afforded by this method is 49 seconds at the major population
centers of the Bay Area. For these events the magnitude estimate is within an average of
0.5 units of the network-derived magnitude, and the ground motion prediction from
ElarmS is within an average of 0.1 units of the observed Modified Mercalli Intensity.
© Richard M Allen
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