The Eastern California Shear Zone is bounded by the high heat flow region of the Basin and Range province and the low heat flow region of the Sierra Nevada block. This difference in thermal state influences the rheology of the lower crust/upper mantle, resulting in a viscosity contrast between the two regions. We analyze the effect of such a contrast on the kinematics and dynamics of the shear zone with numerical models. This viscosity contrast drives asymmetric strain accumulation in the upper crust, producing an asymmetric surface velocity field. An additional consequence of this strain pattern is the potential for asymmetric co-seismic displacement during an earthquake. ¿ 2001 American Geophysical Union