Colloquium: Yuri Fialko

Yuri Fialko

Professor, Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California San Diego

Abstract:  Major seismogenic faults are often associated with fault zones that have mechanical properties that are distinct from those of the ambient crustal rocks. I will discuss geologic, geodetic and seismic signatures of several fault zones in Southern California, and implications for the fault mechanics. I will also investigate the long-term evolution of stress and strain in a ductile substrate due to a vertical transform fault cutting through the brittle crust, using numerical models that incorporate laboratory-derived power-law rheologies with Arrhenius temperature dependence, viscous dissipation, and conductive heat transfer. For conditions corresponding to the San Jacinto and San Andreas Faults in Southern California, the predicted width of the shear zone in the lower crust is a few kilometers; this shear zone accommodates more than 50% of the far-field plate motion. Coupled thermomechanical models predict a single-layer lithosphere in case of "dry" composition of the lower crust and upper mantle, and a "jelly sandwich" lithosphere in case of "wet" composition. Deviatoric stresses in the lithosphere in our models is relatively insensitive to the host rock composition, the water content, and the far-field loading rate, and are of the order of 100 MPa.