Stress differences and their role in identifying earthquake source process properties at different tectonic environments

Abstract

We investigated stress change parameters during ruptures for earthquakes globally with M_w ≥ 6.0 from 1991 to 2023. Employing a formulation and alternative graphical method, we analyzed variations between initial and final stresses as compared to frictional stress during rupture. Our goal was to assess the validity of Orowan’s model (final stress equals frictional stress) across different environments, crucial for recurrent source studies. Our findings reveal significant deviations among event types: reverse-type events diverge slightly from Orowan’s model, while normal events show even larger discrepancy. Strike-slip events exhibit a blend of stress difference mechanisms, with around 30% displaying overshoot (final stress smaller than average frictional stress). The partial stress drop (final stress larger than average frictional stress) percentage for reverse and normal types indicates that approximately 21–23% of the available stress for rupture was not relieved. Our results suggest that partial stress drop is a widespread phenomenon across all event types. This observation implies higher energy at higher frequencies than expected for an ω² frequency decay in the source spectra (Brune, 1976), potentially leading to underestimation of expected damaging accelerations. Our observations underscore the complexity of stress dynamics during earthquakes, with potential implications for energy release and damaging effects.