Self-organization of elastic moduli in the rock above blind faults

Abstract

[1] Distributed anelastic deformation accommodates long-term motion in the “lid” region above blind faults. The flowing sequence of cyclic processes may lead to self-organization within lids composed of quartz-rich clay-bearing sedimentary rocks. Coseismic slip on the deep fault imposes strain and displacement on the lid. Sufficient strain brings the lid to frictional failure, producing distributed cracks. Cracked lid becomes increasing elastically compliant over many seismic cycles. The lid tends to evolve so that coseismic displacement barely causes frictional failure; hence, only a few new cracks open within the lid. However, this process cannot increase crack porosity and decrease the shear modulus below values where the material would readily compact under lithostatic pressure. Accumulating sedimentary rocks provide a convenient proxy for this limit. Numerical modeling indicates that the (geodetic) coseismic displacement above a compliant lid is much of the total geodetic displacement that would be observed over a full cycle. Stresses within the lid relax by ductile creep at nearly constant strain with only modest geodetic displacement >100 year after the earthquake for a 1000 year cycle.