The long recurrence intervals of small repeating earthquakes may be due to the slow slip rates of small fault strands

Observations since 1998 have revealed that repeating earthquakes, and particularly small repeating earthquakes, occur less often than expected given their seismically derived slip and the regional fault slip rate. Here we test the hypothesis that small repeaters occur infrequently because they occur on fault segments or strands with low slip rates. We analyze the recurrence interval-moment scaling of earthquake sequences near Parkfield, California. We find that closely spaced sequences, which likely occur on the same fault strand and respond to the same slip rate, follow a M1/30 scaling consistent with seismic slip rates while widely spaced sequences, which likely occur on different strands, follow a M0.170 scaling consistent with the previous counterintuitive observations. These results suggest that spatially varying slip rates could create the M0.170 recurrence interval scaling, though we cannot exclude other explanations.