THE EFFECT OF LOADING RATE ON STATIC FRICTION AND THE RATE OF FAULT HEALING DURING THE EARTHQUAKE CYCLE

The seismic cycle requires that faults strengthen (heal) between earth quakes, and the rate of this healing process plays a key role in deter mining earthquake stress drop(1-4), rupture characteristics(5,6) and s eismic scaling relations(2-4,7). Frictional healing (as evidenced by i ncreasing static friction during quasi-stationary contact between two surfaces(1,8-12)) is considered the mechanism most likely to be respon sible for fault strengthening(2,3,13,14). Previous studies, however, h ave shown a large discrepancy between laboratory and seismic (field) e stimates of the healing rate(2-4,14,15); in the laboratory, rock frict ion changes by only a few per cent per order-of-magnitude change in sl ip rate, whereas seismic stress drop increases by a factor of 2 to 5 p er order-of-magnitude increase in earthquake recurrence interval, But in such comparisons, it is assumed that healing and static friction ar e independent of loading rate, Here, I summarize laboratory measuremen ts showing that static friction and healing vary with loading rate and time, as expected from friction theory(16-18). Applying these results to seismic faulting and accounting for differences in laboratory, sei smic and tectonic slip rates, I demonstrate that post-seismic healing is expected to be retarded for a period of several hundred days follow ing an earthquake, in agreement with recent findings from repeating ea rthquakes(13,14,19,20).