The Next M ~6 Event in Parkfield Implied by a Physical Model Linking Interseismic, Coseismic, and Postseismic Phase

Determination of the constitutive frictional parameters is crucial for describing the dynamic behaviors of natural faults. In this study, we explore the along‐strike variation in fault friction along the San Andreas Fault in Parkfield, where characteristic M 6 earthquakes occur nearly every 25 years. Using displacement data measured over decades encompassing the interseismic, coseismic, and postseismic phase of the 2004 M 6 event, which involve inherent fault rheological responses to tectonic loading, we construct a physical model based on the rate‐dependent friction law to describe the fault slip and stress evolution. Our modeled friction rate parameter is consistent with available laboratory measurements using fault cores collected from the San Andreas Fault Observatory at Depth. Based on the physical model linking interseismic, coseismic, and postseismic phase, we predict that the 25‐year slip deficit following the 2004 M 6 earthquake will predominantly accumulate in the area to the south of the 2004 event hypocenter, with an energy equivalent to a M 6.0 event. Together with the slip deficit accumulated over the 25 years prior to the 2004 event that was unreleased by this event, the total slip deficit amounts to a moment magnitude of M 6.35 ± 0.11, suggesting the upper limit of the seismic release level until 2029. The proposed model (1) involves only two free quantities (the friction rate parameter and velocity coefficient used to determine the effective normal stress); (2) is well constrained by available interseismic, coseismic, and postseismic displacement data; and (3) highlights along‐strike variations in the fault friction.