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The December 5, 2024 Offshore Cape Mendocino Earthquake: Response to Earthquake Early Warning in an Earthquake Experienced Region

Description: 

On Thursday, December 5, 2024 at 10:44 AM an earthquake of magnitude 7 occurred in the Pacific Ocean approximately 70 miles southwest of Ferndale California generating up to MMI VIII intensities in some locations onshore. The earthquake was in the Mendocino triple junction region, an area of frequent large earthquakes. This earthquake generated 16,825 felt reports in the US Geological Survey’s ‘Did You Feel It?’ system and 1,808 validated responses to the earthquake early warning (EEW) supplemental questionnaire. This earthquake was the largest to occur in the United States for which EEW data has been generated and in an area in which many people have experienced significant earthquakes in the past. As data on human behavioral response has been collected over the past decade, the question arose as to whether behavioral response, assessments of the usefulness of EEW and perceptions regarding this briefest of all hazard warnings differed from previous data in the US and elsewhere.

Preliminary results suggest that on many dimensions, response and assessments of usefulness were similar to results from previous assessments of behavioral response to EEW alerts including, alert medium (mobile devices), locations where the alert was received (inside a building), general evaluations of usefulness (useful) and the preference for alerts only for events that disrupt ongoing activities. EEW response behavior was consistent with other alert situations in that those who received alerts before they experienced shaking were more likely to report mentally bracing for an earthquake, moving away from potential hazards and far less likely to have reported taking no action at all. Also consistent was that drop, cover and hold on was not particularly salient and characterized just 6.9% of those who received the alert before experiencing shaking. Neither alert nor earthquake experience had large impacts on behavioral response though those who reported having experienced previous earthquakes were more likely to respond actively or indicate an awareness of earthquake hazards than those who reported no previous earthquake experience.

Session: Adventures in Social Seismology: Ethical Engagement, Earthquake Early Warnings, Operational Forecasts, and Beyond - II

Type: Oral

Date: 4/15/2025

Presentation Time: 10:30 AM (local time)

Presenting Author: James

Student Presenter: No

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