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Stress Loading From Viscous Flow in the Lower Crust and Triggering of Aftershocks Following the 1994 Northridge, California, Earthquake

Jishu Deng, Kenneth W. Hudnut, Michael Gurnis, & Egill Hauksson

Published 1999, SCEC Contribution #465

Following the Mw 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 after-shock decay rate and surface heat flow.

Citation
Deng, J., Hudnut, K. W., Gurnis, M., & Hauksson, E. (1999). Stress Loading From Viscous Flow in the Lower Crust and Triggering of Aftershocks Following the 1994 Northridge, California, Earthquake. Geophysical Research Letters, 26(21), 3209-3212.