The Community Stress-Drop Validation Study-Part I: Source, Propagation, and Site Decomposition of Fourier Spectra

As part of the community stress-drop validation study initiative, we apply a spectral decomposition approach to isolate the source spectra of 556 events occurred during the 2019 Ridgecrest sequence (Southern California). We perform multiple decomposi-tions by introducing alternative choices for some processing and model assumptions, namely: three different S -wave window durations (i.e., 5 s, 20 s, and variable between 5 and 20 s); two attenuation models that account differently for depth dependencies; and two different site amplification constraints applied to restore uniqueness of the solu-tion. Seismic moment and corner frequency are estimated for the Brune and Boatwright source models, and an extensive archive including source spectra, site amplifications, attenuation models, and tables with source parameters is disseminated as the main product of the present study. We also compare different approaches to measure the precision of the parameters expressed in terms of 95% confidence intervals (CIs). The CIs estimated from the asymptotic standard errors and from Monte Carlo resam-pling of the residual distribution show an almost one-to-one correspondence; the approach based on model selection by setting a threshold for misfit chosen with an F -ratio test is conservative compared to the approach based on the asymptotic standard errors. The uncertainty analysis is completed in the companion article in which the out-comes from this work are used to compare epistemic uncertainty with precision of the source parameters.

Automated summary

In this study, a spectral decomposition approach is utilized to isolate the source spectra of 556 events that occurred during the 2019 Ridgecrest sequence. Multiple decompositions are performed by introducing alternative choices for various processing and model assumptions. Estimates of seismic moment and corner frequency are obtained, and a comprehensive archive of source spectra, site amplifications, attenuation models, and source parameters is made available. Different approaches to measure the precision of the parameters are compared.