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On the origin of diverse aftershock mechanisms following the 1989 Loma Prieta earthquake

January 1, 1997

We test the hypothesis that the origin at the diverse suite of aftershock mechanisms Following the 1989 M 7.1 Loma Prieta, California, earthquake is related to the post-main-shock static stress field We use a 3-D boundary-element algorithm to calculate static stresses combined with a Coulomb failure criterion to calculate conjugate failure planes at aftershock locations. The post-main-shock static stress field is taken as the of a sum of a pre-existing stress field and changes in stress due to the heterogeneous slip across the Loma Prieta rupture plane. The background stress field is assumed to be either a simple shear parallel to the regional trend of the San Andreas fault or approximately fault-normal compression A suite of synthetic aftershock mechanisms from the conjugate failure planes is generated and quantitatively compared (allowing for uncertainties in both mechanism parameters and earthquake locations) to well-constrained mechanisms reported in the US Geological Survey Northern California Seismic Network catalogue. We also compare calculated rakes with those observed by resolving the calculated stress tensor onto observed focal mechanism nodal planes, assuming either plane to be a likely rupture plane.

Publication Year 1997
Title On the origin of diverse aftershock mechanisms following the 1989 Loma Prieta earthquake
DOI 10.1111/j.1365-246X.1997.tb05318.x
Authors Debi Kilb, M. Ellis, J. Gomberg, S. Davis
Publication Type Article
Publication Subtype Journal Article
Series Title Geophysical Journal International
Index ID 70019908
Record Source USGS Publications Warehouse