Short Note Possibility of Biases in the Estimation of Earthquake Recurrence and Seismic Hazard from Geologic Data

Aseismic deformation is an integral part of the earthquake process and may lead to systematic biases in the estimation of earthquake size, recurrence, and attendant strong ground motions in seismic hazard analyses founded on the geologic description of the locations, lengths, and slip rates of active faults. Observations are reviewed and presented to suggest that large earthquakes systematically rupture to increasingly greater depths below the seismogenic layer and that the portion of slip on faults accommodated by aseismic processes may be inversely related to the length of rupture expected to occur on them. If so, the expected seismic moment per unit area of earthquakes on mapped faults may be systematically overestimated as a function of rupture length when derived from regressions of seismic moment and aftershock area, and estimates of seismic moment rate derived from geologic measures of fault offset might be systematically overestimated as an inverse function of the length of rupture expected to recur on a fault.