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Alert Optimization of the PLUM Earthquake Early Warning Algorithm for the Western United States

Cochran, Elizabeth S. and Saunders, Jessie K. and Minson, Sarah E. and Bunn, Julian and Baltay, Annemarie and Kilb, Debi and O’Rourke, Colin and Hoshiba, Mitsuyuki and Kodera, Yuki (2022) Alert Optimization of the PLUM Earthquake Early Warning Algorithm for the Western United States. Bulletin of the Seismological Society of America, 112 (2). pp. 803-819. ISSN 0037-1106. doi:10.1785/0120210259.

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We determine an optimal alerting configuration for the propagation of local undamped motion (PLUM) earthquake early warning (EEW) algorithm for use by the U.S. ShakeAlert system covering California, Oregon, and Washington. All EEW systems should balance the primary goal of providing timely alerts for impactful or potentially damaging shaking while limiting alerts for shaking that is too low to be of concern (precautionary alerts). The PLUM EEW algorithm forward predicts observed ground motions to nearby sites within a defined radius without accounting for attenuation, avoiding the earthquake source parameter estimation step of most EEW algorithms. PLUM was originally developed in Japan where the alert regions and ground motions for which alerts are issued differ from those implemented by ShakeAlert. We compare predicted ground motions from PLUM to ShakeMap-reported ground motions for a set of 22 U.S. West Coast earthquakes of magnitude 4.4–7.2 and evaluate available warning times. We examine a range of prediction radii (20–100 km), thresholds used to issue an alert (alert threshold), and levels of impactful or potentially damaging shaking (target threshold). We find optimal performance when the alert threshold is close to the target threshold, although higher target ground motions benefit from somewhat lower alert thresholds to ensure timely alerts. We also find that performance, measured as the cost reduction that a user can achieve, depends on the user’s tolerance for precautionary alerts. Users with a low target threshold and high tolerance for precautionary alerts achieve optimal performance when larger prediction radii (60–100 km) are used. In contrast, users with high target thresholds and low tolerance for precautionary alerts achieve better performance for smaller prediction radii (30–60 km). Therefore, setting the PLUM prediction radius to 60 km balances the needs of many users and provides warning times of up to ∼20 s.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemSouthern California Earthquake Data Center ItemWaveform Data ItemShakeMaps ItemExample ShakeAlert message ItemNational Weather Service (NWS) public forecast zones data
Cochran, Elizabeth S.0000-0003-2485-4484
Saunders, Jessie K.0000-0001-5340-6715
Minson, Sarah E.0000-0001-5869-3477
Bunn, Julian0000-0002-3798-298X
Baltay, Annemarie0000-0002-6514-852X
Kilb, Debi0000-0002-7252-4167
O’Rourke, Colin0000-0001-5403-4685
Hoshiba, Mitsuyuki0000-0001-9701-5986
Kodera, Yuki0000-0002-8071-2360
Additional Information:© 2022 Seismological Society of America. Manuscript received 28 September 2021; Published online 11 January 2022. The authors thank Eric Thompson, Morgan Moschetti, two anonymous reviewers, and Associate Editor Sanjay Singh Bora for thoughtful reviews of this article. This work benefited from discussions with members of the ShakeAlert project team. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Data and Resources: The 20 historical earthquake records used in this analysis were downloaded from the ShakeAlert Testing Event Archive ftp site housed at the Southern California Earthquake Data Center ( The Ridgecrest M 7.1 and 6.4 earthquake records were obtained from the Southern California Earthquake Data Center ( ShakeMaps were obtained via the U.S. Geological Survey ( An example for ShakeAlert message is available at National Weather Service (NWS) public forecast zones data are available at All websites were last accessed in July 2021. The unpublished manuscript by J. K. Saunders, S. E. Minson, and A. S. Baltay (in review). How low should we alert? Examining intensity threshold alerting strategies for earthquake early warning, was submitted to Earth’s Future. The authors acknowledge that there are no conflicts of interest recorded.
Group:Seismological Laboratory
Issue or Number:2
Record Number:CaltechAUTHORS:20220218-46654700
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Official Citation:Elizabeth S. Cochran, Jessie K. Saunders, Sarah E. Minson, Julian Bunn, Annemarie Baltay, Debi Kilb, Colin O’Rourke, Mitsuyuki Hoshiba, Yuki Kodera; Alert Optimization of the PLUM Earthquake Early Warning Algorithm for the Western United States. Bulletin of the Seismological Society of America 2022; 112 (2): 803–819. doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113509
Deposited By: Tony Diaz
Deposited On:19 Feb 2022 00:41
Last Modified:06 Apr 2022 18:54

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