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WITHDRAWN Guidelines on Using (Uncertain) Macroseismic Data in ShakeMap

Description: 

WITHDRAWN The U.S. Geological Survey (USGS) collects macroseismic intensity (MI) data from users worldwide through the “Did You Feel It?” (DYFI) system. DYFI is a primary MI source for USGS ShakeMap, which combines ground motion data with rupture parameters, site conditions, and ground motion models (GMMs) to estimate the spatial distribution of ground shaking. Despite their utility in ShakeMap, the potential for outliers and larger uncertainties makes it challenging to include crowdsourced MI data operationally. We report here on guidelines for incorporating crowdsourced MI data into ShakeMap. We analyzed MI residuals compared to ShakeMaps that were well-constrained by strong-motion data to understand trends with the number of responses per cell (Nresp) and the MI level. We present these trends, which we have adopted for weighting DYFI “stations” in ShakeMap. Crowdsourced MIs are consistent at lower intensities, so we can readily use them automatically. Higher intensities, particularly with few entries per locale, are more uncertain and require further downweighing with respect to other shaking observations. In short, fewer than three responses result in intensities with larger uncertainties and are bias high; with more and more responses, they trend towards unbiased and have lower uncertainties. Higher intensities are more variable, given the same Nresp. Before this, based on heuristics, we only allowed ShakeMaps to employ DYFI stations with Nresp of three or more; our DYFI uncertainty analyses now quantitatively support that assumption. Moreover, based on requests from financial decision-makers who employ DYFI-informed ShakeMaps for insurance, contingency loans, and catastrophe bonds, we aim to generate DYFI-free ShakeMaps for significant events, deliver them online, and store them permanently in USGS’ ComCat archive for escrow purposes. The authoritative maps will continue to use DYFI data because these data significantly reduce the uncertainty in nearly all circumstances, and our new station weighting in ShakeMap more quantitively accounts for DYFI uncertainties as a function of Nresp and the estimated intensity.

Session: Macroseismic Intensity: Past, Present and Future [Poster]

Type: Poster

Date: 4/17/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Vincent

Student Presenter: No

Invited Presentation: 

Poster Number: 21

Authors