Observational analysis of correlations between aftershock productivities and regional conditions in the context of a damage rheology model

Wenzheng Yang, & Yehuda Ben-Zion

Published 2008, SCEC Contribution #1159

Aftershock sequences are commonly observed but their properties vary from region to region. Ben-Zion and Lyakhovsky (2006) developed a solution for aftershocks
decay in a damage rheology model. The solution indicates that the productivity of aftershocks decreases with increasing value of a non-dimensional material parameter R
given by the ratio of timescale for brittle deformation to timescale for viscous relaxation. The parameter R is inversely proportional to the degree of seismic coupling and is expected to increase primarily with increasing temperature, and also with increasing thickness of sedimentary cover. To test these predictions we use aftershock sequences from several southern California regions. We first analyze properties of individual
aftershock sequences generated by the 1992 Landers and 1987 Superstition Hills earthquakes. The results show that the ratio of aftershock productivities in these sequences spanning 4 orders of event magnitudes is similar to the ratio of the average heat flow in the two regions. To perform stronger statistical tests we systematically
analyze the average properties of stacked aftershock sequences in five regions. In each region we consider events with magnitudes between 4.0 and 6.0 to be mainshocks. For each mainshock, we consider events to be aftershocks if they occur in the subsequent 50 days, within a circular region that scales with the magnitude of the mainshock, and in the magnitude range between that of the mainshock and 2 units lower. This procedure produces 28-196 aftershock sequences in each of the five regions. We stack the aftershock sequences in each region and analyze the properties of the stacked data. The results indicate that the productivities of the stacked sequences are inversely correlated with the heat flow and thickness of sedimentary cover, in agreement with the damage model predictions. Using the observed ratios of aftershock productivities along with simple expressions based on the damage model, we estimate the relative values of the material parameter R and seismic coupling coefficient in the different regions. The employed methodology for estimating the seismic coupling of fault systems can be useful for seismic hazard studies.

Citation
Yang, W., & Ben-Zion, Y. (2008). Observational analysis of correlations between aftershock productivities and regional conditions in the context of a damage rheology model. Geophysical Journal International, 177, 481-491. doi: 10.1111/j.1365-246X.2009.04145.x.