A slower fault may produce a smaller preseismic moment rate: Non‐1/tf acceleration of moment rate during nucleation and dependency on the background slip rate

Abstract

A recent global study has revealed that seismicity near the hypocenter prior to large earthquakes, which could be a proxy for preseismic moment rate, accelerates before interplate earthquakes, while it rarely does before intraplate earthquakes. Understanding the amplitude of preseismic deformation is important in assessing the possibility of its detection. For a class of rate‐state friction laws without a characteristic speed‐related parameter (e.g., aging law and slip law), a dimensional analysis has shown that if the moment rate increases more mildly than 1/tf where tf is the time‐to‐failure, then the amplitude of preseismic moment rate is smaller for a smaller quasistatic slip rate. Three‐dimensional numerical simulations have revealed that the aging law yields 1/tf acceleration, while the slip law causes milder acceleration. If the latter is the case, faults with very low long‐term slip rates (e.g., intraplate faults) may have very small preseismic moment rates.