HR: 16:50h
AN: S34C-04 INVITED    [Abstracts]
TI: Mojave Compliant Zone Structure and Properties: Constraints from InSAR and Mechanical Models
AU: * Hearn, E H
EM: ehearn@eos.ubc.ca
AF: University of British Columbia, Department of Earth and Ocean Sciences, Vancouver, BC V6T 1Z4, Canada
AU: Fialko, Y
EM: yfialko@ucsd.edu
AF: University of California at San Diego, SIO/IGPP 225, La Jolla, CA 92093, United States
AU: Finzi, Y
EM: yfinzi@eos.ubc.ca
AF: University of British Columbia, Department of Earth and Ocean Sciences, Vancouver, BC V6T 1Z4, Canada
AB: Long-lived zones with significantly lower elastic strength than their surroundings are associated with active Mojave faults (e.g., Li et al., 1999; Fialko et al., 2002, 2004). In an earthquake these weak features concentrate strain, causing them to show up as anomalous, short length-scale features in SAR interferograms (Fialko et al., 2002). Fault-zone trapped wave studies indicate that the 1999 Hector Mine earthquake caused a small reduction in P- and S-wave velocities in a compliant zone along the Landers earthquake rupture (Vidale and Li, 2003). This suggests that coseismic strain concentration, and the resulting damage, in the compliant zone caused a further reduction in its elastic strength. Even a small coseismic strength drop should make a compliant zone (CZ) deform, in response to the total (not just the coseismic) stress. The strain should be in the sense which is compatible with the orientations and values of the region's principal stresses. However, as indicated by Fialko and co-workers (2002, 2004), the sense of coseismic strain of Mojave compliant zones was consistent with coseismic stress change, not the regional (background) stress. Here we use finite-element models to investigate how InSAR measurements of Mojave compliant zone coseismic strain places limits on their dimensions and on upper crustal stresses. We find that unless the CZ is shallow, narrow, and has a high Poisson's ratio (e.g., 0.4), CZ contraction under lithostatic stress overshadows deformation due to deviatoric background stress or coseismic stress change. We present ranges of CZ dimensions which are compatible with the observed surface deformation and address how these dimensions compare with new results from damage-controlled fault evolution models.
DE: 7200 SEISMOLOGY
DE: 8020 Mechanics, theory, and modeling
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8164 Stresses: crust and lithosphere
SC: Seismology [S]
MN: 2007 Fall Meeting