Variations in rupture process with recurrence interval in a repeated small earthquake

IN theory and in laboratory experiments, friction on sliding surfaces such as rock, glass and metal increases with time since the previous episode of slip1. This time dependence is a central pillar of the friction laws widely used to model earthquake phenomena2,3. On natural faults, other properties, such as rupture velocity4,5, porosity and fluid pressure6-11, may also vary with the recurrence interval. Eighteen repetitions of the same small earthquake, separated by intervals ranging from a few days to several years, allow us to test these laboratory predictions in situ. The events with the longest time since the previous earthquake tend to have about 15% larger seismic moment than those with the shortest intervals, although this trend is weak. In addition, the rupture durations of the events with the longest recurrence intervals are more than a factor of two shorter than for the events with the shortest intervals. Both decreased duration and increased friction are consistent with progressive fault healing during the time of stationary contact. © 1994 Nature Publishing Group.