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B. Dando, F. J. Simons
Earthquake early warning systems save lives. It is of great importance that networked systems of
seismometers be equipped with reliable tools to make rapid determinations of earthquake magnitude in the few to tens of seconds before the damaging ground motion occurs. A new fully automated algorithm based on the
discrete wavelet transform detects as
well as analyzes the incoming first arrival with unmatched accuracy and precision, estimating the final
magnitude to within a single unit from the first few seconds of the P wave.
The curious observation that such brief segments of the seismogram may contain information about the final
magnitude even of very large earthquakes, which occur on faults that may rupture over tens of seconds, is
central to a debate in the seismological community which we hope to stimulate but cannot attempt to address
within the scope of this paper.
Wavelet coefficients of the seismogram can be determined extremely rapidly and efficiently by the fast lifting
wavelet
transform. Extracting amplitudes at individual scales is a very simple procedure, involving a mere handful of
lines of computer code. Scale-dependent thresholded amplitudes derived from the wavelet transform of the first
3--4 seconds of an incoming seismic P arrival are predictive of earthquake magnitude, with errors of one
magnitude unit for seismograms recorded up to 150 km away from the earthquake source.
Our procedure is a simple yet extremely efficient tool for
implementation on low-power recording stations. It provides an accurate and precise method of autonomously
detecting the incoming P wave and predicting the magnitude of the source from the scale-dependent
character of its amplitude well before the arrival of damaging ground motion. Provided a dense array of
networked seismometers exists, our procedure should become the tool of choice for earthquake early warning
systems worldwide.
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