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The Plum Earthquake Early Warning Algorithm: A Case Study of Two West Coast, USA, Datasets

Debi Kilb, Julian Bunn, Jessie K. Saunders, Elizabeth S. Cochran, Sarah E. Minson, Annemarie S. Baltay, & Colin O'Rourke

Published August 7, 2020, SCEC Contribution #10305, 2020 SCEC Annual Meeting Poster #059

The PLUM (Propagation of Local Undamped Motion) earthquake early warning (EEW) algorithm differs from typical source-based EEW algorithms in that it forward-predicts shaking directly from observations. We apply PLUM to two retrospective datasets: 558 M3.5+ earthquakes within California, Oregon, and Washington (2012-2017), and a test suite of historical and other signals (1999-2014). We compute Modified Mercalli Intensity (MMI) using velocity and acceleration data, and leverage co-located sensor data to avoid problematic signals. We favor a two-station alerting method, using MMI trigger thresholds of 4.0 and 3.0 for the first and second stations, respectively. This configuration reduces the detection of M<4 events (where alerts for MMI4+ shaking are usually too late) without significantly increasing detection latencies of M5+ events. Based on existing station density, of the 558 M3.5+ earthquakes only 85 are theoretically detectable. PLUM correctly detected 79 events, with detection times of 1.5-37s (mean 8.0s; median 5.8s). Detection times do not include telemetry latencies or the time required to communicate alerts to people. No false alerts were issued at the MMI4+ level. PLUM detected all 10 of the theoretically detectable M5+ events. These included the 2014 M6.8 event ~100 km offshore that was problematic for other EEW algorithms. Of the 79 detected events, however, only two have the potential to provide timely warnings to regions of MMI4+ shaking: the 2014 M6.8 offshore earthquake and the M6.02 2014 Napa earthquake. For the test suite data, PLUM correctly identified 14/15 theoretically detectable M5+ local events and had a 100% success rate avoiding calibration pulses, anomalous signals, and regional and teleseismic events. We conclude PLUM can provide reliable EEW strong-motion alerts in regions where the seismic station network is dense (inter-station spacing ≤30 km), and is a promising candidate for integration into the U.S. ShakeAlert EEW system.

Key Words
earthquake early warning (EEW), ShakeAlert, California, Washington, Oregon, PLUM, seismic network, earthquake, Cascadia, San Andreas Fault, earthquake preparedness.

Kilb, D., Bunn, J., Saunders, J. K., Cochran, E. S., Minson, S. E., Baltay, A. S., & O'Rourke, C. (2020, 08). The Plum Earthquake Early Warning Algorithm: A Case Study of Two West Coast, USA, Datasets. Poster Presentation at 2020 SCEC Annual Meeting.

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