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WITHDRAWN Guidelines on Using (Uncertain) Macroseismic Data in ShakeMap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WITHDRAWN The U.S. Geological Survey (USGS) collects macroseismic intensity (MI) data from users worldwide through the “Did You Feel It?”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 intensity data operationally. We report here on developing guidelines for incorporating crowdsourced MI data into ShakeMap. We take advantage of our newly developed MI database to reassess the uncertainty of the MI assignment as a function of intensity and the number of responses (n_resp), demonstrating that higher intensities have more uncertainty. This is consistent with the known challenge of assigning higher, damaging intensity levels, even by experts. From an operational perspective, crowdsourced MIs are more consistent at lower intensities and can be readily used automatically. Higher intensities, particularly with few entries per locale, are more uncertain and require further downweighing with respect to other shaking estimates. We approach this problem with two strategies to quantify uncertainties: 1) We analyze MI residuals to understand trends with n_resp, MI, and the source of the MI data (e.g., DYFI, historical, or assigned), then assign MI uncertainties as a function of intensity by adding (heuristically) a constant such that the relative weight of the macroseismic data for a single response approaches that of the GMM contribution. 2) We simulate the rich MI databases using a Monte Carlo approach to ensure that the uncertainty assessments are consistent with the levels of variability observed in the data.

Session: Creating Actionable Earthquake Information Products [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: David

Student Presenter: No

Invited Presentation: 

Authors