Source-Scaling Comparison and Validation for Ridgecrest, California: Radiated Energy, Apparent Stress, and Mw Using the Coda Calibration Tool (2.6<Mw<7.1)

Abstract

ABSTRACT The determination of accurate apparent stress, radiated energy, corner frequency, and their scaling with magnitude remains one of the most difficult seismological endeavors because of complicated 3D Earth structure, complex rupture, and limited broadband recordings. This study focuses on a comparison of four separate state-of-the-art methods that aim to compare and contrast common events using the well-recorded 2019 Ridgecrest, California, sequence, which was motivated in large part by the U.S. Geological Survey (USGS)/Southern California Earthquake Center (SCEC) Community Stress-Drop Validation Study group (Baltay et al., 2024). For this study, we calibrated the Ridgecrest and surrounding region using the Coda Calibration Tool (CCT) and compared them against recent generalized inversion technique (GIT) results of Bindi et al. (2021) (2.6<Mw<7.1) and two other state-of-the-art methods for moderate-sized events in the sequence (3.5<Mw<5.5). We find excellent agreement between the GIT and coda-derived results over a broad range of magnitudes, and for moderate-size events, we find equally good agreement with source estimates from finite-fault inversion method based on Dreger (1997) and a direct S-wave spectral method by Ji et al. (2024). As found in a recent comparative study in central Italy by Morasca et al. (2022) (3.5<Mw<6.3), we find that CCT and GIT results are in excellent agreement for events ranging between 2.6<Mw<7.1, and relative, weak-motion site terms are also in agreement. Although both approaches observe a modest increase in apparent stress with depth, the overall trend in apparent stress increasing with magnitude is supported by our findings. Finally, upon comparison with other regions, we find that the absolute apparent stress values from Ridgecrest are comparable to central Italy but significantly lower than both eastern Canada and the United Kingdom.