How Often Can Earthquake Early Warning Systems Alert Sites With High‐Intensity Ground Motion?. Issue 2 (27th January 2020)

• Record Type: Journal Article
• Authors: Meier, Men‐Andrin; Kodera, Yuki; Böse, Maren; Chung, Angela; Hoshiba, Mitsuyuki; Cochran, Elizabeth; Minson, Sarah; Hauksson, Egill; Heaton, Thomas
• Is Part Of: Journal of geophysical research. Volume 125:Issue 2(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-01-27
• Subjects: seismology -- earthquake early warning -- seismic hazard -- natural hazards; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2019JB017718
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Although numerous Earthquake Early Warning (EEW) algorithms have been developed to date, we lack a detailed understanding of how often and under what circumstances useful ground motion alerts can be provided to end users. In particular, it is unclear how often EEW systems can successfully alert sites with high ground motion intensities. These are the sites that arguably need EEW alerts the most, but they are also the most challenging ones to alert because they tend to be located close to the epicenter where the seismic waves arrive first. Here we analyze the alerting performance of the Propagation of Local Undamped Motion (PLUM), Earthquake Point‐Source Integrated Code (EPIC), and Finite‐Fault Rupture Detector (FinDer) algorithms by running them retrospectively on the seismic strong‐motion data of the 219 earthquakes in Japan since 1996 that exceeded Modified Mercalli Intensity (MMI) of 4.5 on at least 10 sites ( M w 4.5–9.1). Our analysis suggests that, irrespective of the algorithm, EEW end users should expect that EEW can often but not always provide useful alerts. Using a conservative warning time ( t w ) definition, we find that 40–60% of sites with strong to extreme shaking levels receive alerts with t w > 5 s. If high‐intensity shaking is caused by shallow crustal events, around 50% of sites with strong (MMI~6) and <20% of sites with severe and violent (MMI ≥ 8) shaking receive alerts with t w > 5 s. Our results provide detailed quantitative insight into the expected alerting performance for EEW algorithms under realistic conditions. We also discuss how operational systems can achieve longer warning times with more precautionary alerting strategies. Plain Language Summary: Whether or not Earthquake Early Warning systems can provide useful (i.e., timely and correct) alerts before earthquake shaking begins at a site depends on numerous factors. The hardest hit sites tend to be the ones that are the most difficult to alert because they are typically located close to the epicenter, where the seismic waves arrive first. Sites that are farther away from the epicenter can potentially receive longer warning times, but in these places the alerts may be less important because the shaking is weaker. In this study we run three prominent Earthquake Early Warning algorithms retrospectively on 219 of the largest earthquakes in Japan. We analyze how often and under what circumstances the algorithms can provide useful warnings. We put special emphasis on the challenging sites that receive high shaking intensities. We find that all algorithms can alert a significant fraction even of these difficult cases. Key Points: We run three prominent Earthquake Early Warning algorithms on strong‐motion data from 219 large earthquakes in Japan We evaluate how often, and under what circumstances, useful ground motion alerts can be provided, using a conservative warning time definition 40% to 60% of sites with strong to extreme ground motion get alerts with warning times ≥5 s