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Published November 1, 1999 | Published
Journal Article Open

Stress loading from viscous flow in the lower crust and triggering of aftershocks following the 1994 Northridge California, earthquake

Abstract

Following the M_w 6.7 Northridge earthquake, significant postseismic displacements were resolved with GPS. Using a three-dimensional viscoelastic model, we suggest that this deformation is mainly driven by viscous flow in the lower crust. Such flow can transfer stress to the upper crust and load the rupture zone of the main shock at a decaying rate. Most aftershocks within the rupture zone, especially those that occurred after the first several weeks of the main shock, may have been triggered by continuous stress loading from viscous flow. The long-term decay time of aftershocks (about 2 years) approximately matches the decay of viscoelastic loading, and thus is controlled by the viscosity of the lower crust. Our model provides a physical interpretation of the observed correlation between aftershock decay rate and surface heat flow.

Additional Information

© 1999 by the American Geophysical Union. Received April 14, 1999; revised June 14, 1999; accepted June 17, 1999. This research was supported by the Southern California Earthquake Center. SCEC contribution 465. This also represents contribution number 8622 of the Division of Geological and Planetary Sciences, California Institute of Technology.

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