What is sigma of the stress drop?

Fabrice Cotton, Ralph J. Archuleta, & Mathieu Causse

Published 2013, SCEC Contribution #1683

Ground-motion variability is usually divided into between-events variability and within-event variability. The between-events residual represents average source effects (averaged over all azimuths) and reflects the influence of factors such as stress drop and variation of slip in space and time that are not captured by the inclusion of magnitude, style of faulting, and source depth. Using the theory of stationary Gaussian random functions and a simple source Brune’s model we show that there is proportionality between PGA and the stress-drop. According to this relation, the observed between-event PGA variability is a way to evaluate an upper bound of the stress-drop variability for a given region. We show that stress-drop variability derived from the observed between-event ground-motion variability is much lower than those derived from source parameter studies, i,e., those based on corner frequency analysis. This suggests that stress-drop, determined by corner frequency, has greater uncertainty than that implied by the ground-motion data.

Cotton, F., Archuleta, R. J., & Causse, M. (2013). What is sigma of the stress drop?. Seismological Research Letters, 84(1), 42-48. doi: 10.1785/0220120087.