FAULT CREEP AND INTERSEISMIC DEFORMATION IN THE JAPAN-KURIL SUBDUCTION ZONE

Geodetic measurements of interseismic deformation from subduction zones are routinely used to infer the pattern of megathrust coupling using the so-called back-slip model. Coupled regions might indicate regions in which stress is accumulating on asperities, or they may indicate regions in which creep is suppressed due to stress shadowing from nearby asperities. Alternatively, it has been proposed that in some instances not all of the inferred megathrust coupling is physical, and that long-term, permanent deformation processes affect the geodetic data. Using the back-slip model and geodetic data it is difficult to uniquely resolve actual megathrust coupling from other deformation processes that results in broad deformation similar to that produced by coupling. We propose a physical model of localized fault creep in response to megathrust earthquakes, to investigate whether geodetic measurements in northern Japan can be explained by recoverable strain-accumulation on known asperities on the Japan-Kuril subduction megathrust. In contrast to the kinematic back-slip approach, we model megathrust creep using velocity strengthening friction. We find that a model that includes known M8-class asperities along the megathrust, in addition to two shallow M9-class asperities can explain most of the geodetic measurements in northeast Japan. One of the M9-class asperities corresponds to the 2011 Tohuku-Oki earthquake, while the other is offshore of Hokkaido, updip of the Tokachi-oki earthquake. This model explains most of the observed long-term vertical subsidence during the past century, and other processes such as subduction erosion may not be required to explain the geodetic data. Deformation not explained by our physical subduction zone strain-accumulation model is shorter wavelength than the megathrust coupling signal, and may reflect strain accumulation on onshore faults or other processes.