Viscoelastic-cycle model of interseismic deformation in the northwestern United States

Geophysical Journal International
By: , and 



We apply a viscoelastic cycle model to a compilation of GPS velocity fields in order to address the kinematics of deformation in the northwestern United States. A viscoelastic cycle model accounts for time-dependent deformation following large crustal earthquakes and is an alternative to block models for explaining the interseismic crustal velocity field. Building on the approach taken in Pollitz et al., we construct a deformation model for the entire western United States-based on combined fault slip and distributed deformation-and focus on the implications for the Mendocino triple junction (MTJ), Cascadia megathrust, and western Washington. We find significant partitioning between strike-slip and dip-slip motion near the MTJ as the tectonic environment shifts from northwest-directed shear along the San Andreas fault system to east-west convergence along the Juan de Fuca Plate. By better accounting for the budget of aseismic and seismic slip along the Cascadia subduction interface in conjunction with an assumed rheology, we revise a previous model of slip for the M~ 9 1700 Cascadia earthquake. In western Washington, we infer slip rates on a number of strike-slip and dip-slip faults that accommodate northward convergence of the Oregon Coast block and northwestward convergence of the Juan de Fuca Plate. Lateral variations in first order mechanical properties (e.g. mantle viscosity, vertically averaged rigidity) explain, to a large extent, crustal strain that cannot be rationalized with cyclic deformation on a laterally homogeneous viscoelastic structure. Our analysis also shows that present crustal deformation measurements, particularly with the addition of the Plate Boundary Observatory, can constrain such lateral variations.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Viscoelastic-cycle model of interseismic deformation in the northwestern United States
Series title Geophysical Journal International
DOI 10.1111/j.1365-246X.2010.04546.x
Volume 181
Issue 2
Year Published 2010
Language English
Publisher Wiley
Publisher location Hoboken, NJ
Contributing office(s) Earthquake Science Center
Description 32 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Geophysical Journal International
First page 665
Last page 696
Country United States