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Journal: |
Journal of Geophysical Research 2019 No.5
clicks:160 |
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Title:
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Author:
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C. J. Ruhl1,2 , D. Melgar3 , A. I. Chung1 , R. Grapenthin4 , and R. M. Allen1 |
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Adress: |
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Abstract:
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Geodetic earthquake early warning (EEW) algorithms complement point‐source seismic
systems by estimating fault‐finiteness and unsaturated moment magnitude for the largest, most damaging
earthquakes. Because such earthquakes are rare, it has been difficult to demonstrate that geodetic
warnings improve ground motion estimation significantly. Here, we quantify and compare timeliness and
accuracy of magnitude and ground motion estimates in simulated real time from seismic and geodetic
observations for a suite of globally distributed, large earthquakes. Magnitude solutions saturate for the
seismic EEW algorithm (we use ElarmS) while the ElarmS‐triggered Geodetic Alarm System (G‐larmS)
reduces the error even for its first solutions. Shaking intensity (Modified Mercalli Intensity, MMI) time series
calculated for each station and each event are assessed based on MMI threshold crossings, allowing us to
accurately characterize warning times per station. We classify alerts and find that MMI 4 thresholds result in
true positive alerts for only 13.7% of sites exceeding MMI 4 with a median warning time of 18.9 s for ElarmS,
while G‐larmS issues true positive alerts for 52.3% of all sites exceeding MMI 4 with a significantly longer
median warning time of 55.8 s. The geodetic EEW system reduces the number of missed alerts for a
threshold of MMI 4 from 48.7% to 19.2% for all sites, but also increases the number of false positive alerts
from 1.2% to 13.4% of all sites. By quantifying increased accuracy in magnitude, ground motion estimation,
and alert timeliness, we demonstrate that finite‐fault geodetic algorithms add significant value, including
better cost savings performance, to point‐source seismic EEW systems for large earthquakes. |
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