Can compliant fault zones be used to measure absolute stresses in the upper crust?

Elizabeth H. Hearn, & Yuri Fialko

Published 2009, SCEC Contribution #1232

Geodetic and seismic observations reveal long-lived zones with reduced elastic moduli along active faults (e.g., Li et al., 1999;<br/>Fialko et al., 2002; Peng et al., 2003; Hamiel and Fialko, 2007). These fault zones localize strain from nearby earthquakes, consistent with an elastic response of a compliant layer (Fialko et al., 2002; Fialko, 2004). Fault-zone trapped wave studies document that the 1999 Hector Mine earthquake caused a small reduction in P and S wave velocities along the Johnson Valley Fault (Vidale and Li, 2003), further softening a permanent compliant structure associated with the fault. Such softening should produce a measurable deformation contribution in response to background (tectonic) stresses, rather than the coseismic stress change.<br/><br/>Here, we investigate how deformation of compliant zones in the Mojave Desert can be used to place limits on crustal stresses. We find that gravitational contraction should cause these zones (and their surroundings) to subside by several centimeters, unless they are essentially incompressible, elastically anisotropic, or both. Strain of the Camp Rock and Pinto Mountain fault zones during the Hector Mine and Landers earthquakes suggests that background deviatoric stresses in the Mojave upper crust are broadly consistent with Mohr-Coulomb theory (with mu >= 0.7). Uncertainties in the compliant zone properties and geometry preclude more precise estimates of crustal stresses. With improved imaging of the geometry and elastic properties of compliant zones, and with precise measurements of their coseismic strain, the modeling approach we describe here could provide robust estimates of absolute crustal stress.

Hearn, E. H., & Fialko, Y. (2009). Can compliant fault zones be used to measure absolute stresses in the upper crust?. Journal of Geophysical Research, 114. doi: 10.1029/2008JB005901.