Cochran, Elizabeth S.Baltay, AnnemarieChu, ShannaAbercrombie, Rachel E.Bindi, DinoChen, XiaoweiParker, Grace A.Pennington, ColinShearer, Peter M.Trugman, Daniel T.2025-04-232025-04-232024-12-17E.S. Cochran, A. Baltay, S. Chu, R.E. Abercrombie, D. Bindi, X. Chen, G.A. Parker, C. Pennington, P.M. Shearer, D.T. Trugman. "SCEC/USGS Community Stress-Drop Validation Study: How Spectral Fitting Approaches Influence Measured Source Parameters" Bulletin of the Seismological Society of America. https://doi.org/10.1785/01202401400037-11061943-3573https://hdl.handle.net/2144/50148Spectral source parameters used to estimate an earthquake’s stress drop (Δσ) can vary significantly across measurement approaches. The Statewide California Earthquake Center/U.S. Geological Survey Community Stress-Drop Validation Study was initiated to compare source parameter estimates, focusing initially on a dataset from the 2019 Ridgecrest earthquake sequence. As part of that validation effort, here we focus on one potential source of uncertainty: whether spectral fitting approaches alone, applied to a common set of spectra from the 2019 Ridgecrest sequence result in different source parameter estimates. By using a common set of benchmark spectra analyzed across a consistent frequency band of 1–40 Hz, we eliminate many sources of variability. A subgroup of validation study participants volunteered to estimate the low-frequency displacement (Ω0) and corner frequency (fc) by fitting a smooth function to benchmark displacement spectra. Participants used linear- or log-sampled spectra, assumed a Brune or Boatwright spectral model, and applied different misfit criteria. We compare 17 approaches used to estimate Ω0, fc, and Δσ for 54 earthquake spectra. Our results reveal that 35% of events have Δσ estimates within a factor of two, whereas others exhibit variations exceeding an order of magnitude. The variability in Ω0 and fc can largely be attributed to whether a spectrum is consistent with the smooth function of an idealized simple crack model. The trade-off between Ω0 and fc may be more pronounced when using linearly sampled spectra, as higher frequency spectral bumps control the fits. As expected, methods that assumed a Boatwright model tended to have lower Ω0 and somewhat higher fc compared to those assuming a Brune model, although resulting Δσ estimates are similar. When compared to the overall validation study results, the fitting approach alone may account for between 5% and 90% (25% on average) of the total variability in spectral Δσ.enGeophysicsCivil engineeringGeochemistry & geophysicsArticle10.1785/01202401400000-0003-2485-4484 (Cochran, Elizabeth S)0000-0002-6514-852X (Baltay, Annemarie)0000-0001-5974-183X (Chu, Shanna)0000-0003-4515-5420 (Abercrombie, Rachel E)0000-0002-8619-2220 (Bindi, Dino)0000-0001-6362-3297 (Chen, Xiaowei)0000-0002-9445-2571 (Parker, Grace A)0000-0002-1474-9368 (Pennington, Colin)0000-0002-2992-7630 (Shearer, Peter M)0000-0002-9296-4223 (Trugman, Daniel T)1039131