SCEC/USGS Community Stress‐Drop Validation Study: How Spectral Fitting Approaches Influence Measured Source Parameters
Elizabeth Cochran, Annemarie Baltay, Shanna Chu, Rachel Abercrombie, Dino Bindi, Xiaowei Chen, Grace Parker, Colin Pennington, Peter Shearer, & Daniel TrugmanPublished 2024, SCEC Contribution #14189
Spectral 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 and corner frequency 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 the long period level, corner-frequency and spectral stress drop 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 long period level and corner frequency can largely be attributed to whether a spectrum is consistent with the smooth function of an idealized simple crack model. The trade‐off between long period level and corner frequency 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 long period level and somewhat higher corner frequency 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.
Citation
Cochran, E., Baltay, A., Chu, S., Abercrombie, R., Bindi, D., Chen, X., Parker, G., Pennington, C., Shearer, P., & Trugman, D. (2024). 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/10.1785/0120240140. https://pubs.geoscienceworld.org/ssa/bssa/article/115/3/760/650721/SCEC-USGS-Community-Stress-Drop-Validation-Study
Related Projects & Working Groups
Stress Drop Community Validation Study
