Earthquake earthquake early warning considerations during aftershock sequences

Jessie K. Saunders, & Allen L. Husker

Published September 8, 2024, SCEC Contribution #13736, 2024 SCEC Annual Meeting Poster #025 (PDF)

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We analyze earthquake catalog information for several recent large-magnitude global earthquakes to evaluate how frequently earthquake early warning (EEW) alerts could be issued during aftershock sequences using the current alerting strategies for the ShakeAlert EEW system for the West Coast of the United States. ShakeAlert takes a threshold-based approach to EEW. Public alerts are issued for non-damaging shaking intensity thresholds and smaller magnitude thresholds in order to increase warning times and avoid missing alerts to locations that experience higher intensities. The number of aftershocks that occur during the days following a major earthquake can be substantial and lead to much higher rates of EEW alerts than the public usually receives. We find that some locations could be issued dozens of alerts (and sometimes over a hundred alerts) during the first month following a major earthquake depending on the alert threshold used, where the number of alerts increases if we consider ShakeAlert’s magnitude estimation uncertainties relative to catalog source values. The locations that are issued the most alerts are those that experienced damage from the mainshock and thus are vulnerable to additional damage from aftershocks. However, many of these alerts are likely to be late relative to the expected onset of shaking, limiting the utility of EEW alerts in these areas. Our results motivate a need to discuss whether ShakeAlert’s public alert thresholds should be adjusted for a few weeks following a major earthquake to prevent alert fatigue during aftershock sequences.

Key Words
Earthquake early warning, aftershock sequences

Citation
Saunders, J. K., & Husker, A. L. (2024, 09). Earthquake earthquake early warning considerations during aftershock sequences. Poster Presentation at 2024 SCEC Annual Meeting.


Related Projects & Working Groups
Seismology