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

Wenzheng Yang, & Yehuda Ben-Zion

Published 2009, SCEC Contribution #1299

Aftershock sequences are commonly observed but their properties vary from region to region. Ben-Zion and Lyakhovsky 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 existence of sedimentary rocks at seismogenic depth. To test these predictions, we use aftershock sequences from several southern California regions. We first analyse 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 four 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 analyse 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 main shocks. For each main shock, we consider events to be aftershocks if they occur in the subsequent 50 d, within a circular region that scales with the magnitude of the main shock and in the magnitude range between that of the main shock 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 analyse the properties of the stacked data. The results indicate that the productivities of the stacked sequences are inversely correlated with the heat flow and existence of deep sedimentary covers, 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 in different regions can be useful for seismic hazard studies.

Yang, W., & Ben-Zion, Y. (2009). Observational analysis of correlations between aftershocks productivities and regional conditions in the context of a damage rheology model. Geophysical Journal International, 177, 481-490. doi: 10.1111/j.1365-246X.2009.04145.x.