HR: 0800h
AN: G11A-0775    [Abstracts]
TI: Incorporation of Complex Rheologies Into Models of Interseismic Displacements
AU: * Hetland, E A
EM: eah@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: Hager, B H
EM: bhhager@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AB: The standard viscoelastic model of interseismic displacements near strike-slip faults was first proposed by Savage and Prescott in 1978 (SP78). This model has been widely used to model data and is a powerful tool to guide intuition about interseismic displacements. The model of SP78 provides the displacements throughout a seismic cycle due to an infinitely long strike-slip fault periodically breaking an upper elastic layer overlying a Maxwell linear viscoelastic half-space. The model of SP78 has fairly stringent assumptions, such as 1) that the upper seismogenic layer is elastic, 2) that the aseismic lower region can be considered a half-space, 3) that the anelastic half-space behaves simply, 4) that the shear moduli in the upper layer and half-space are identical, 5) that successive ruptures are infinite in length and 6) they occur regularly in time with constant coseismic displacement, and 7) that the system is in a cycle-invariant state, where the displacements throughout the interseismic period do not depend on the particular cycle (often referred to as a mature or steady-state). These assumptions are likely not applicable to the crust and upper mantle. For example, the shear modulus of the seismic and aseismic regions is not uniform and recent studies of postseismic relaxation have indicated that the anelastic region of the Earth has a much richer time dependence than the single exponential decay predicted by Maxwell viscoelasticity. Additionally, recent paleoseismological studies have indicated that rarely do earthquakes occur periodically. When earthquakes repeat irregularly the assumption that crustal deformation is cycle-invariant is likely inappropriate. We have extended the model of SP78 to more general earthquake rupture histories and a wider suite of linear viscoelastic rheologies of the seismic and aseismic layers. While the general model we propose is still too simple to model geodetic data with high spatial coverage, it is rich enough to be used to build intuition about interseismic displacements assuming irregular earthquake histories and complex rheologies. Finally, the method we propose can be applied to existing 3D models of finite ruptures that utilize the Correspondence Principle.
DE: 8199 General or miscellaneous
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 3210 Modeling
DE: 1236 Rheology of the lithosphere and mantle (8160)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting