Multi-decadal fault creep preceding co-located coseismic slip at the Nankai subduction zone, offshore Japan

Abstract Geometric moment is accumulated and released throughout the earthquake cycle and can be imaged over both co- and inter-seismic time intervals with geodetic data. Recent dynamic earthquake cycle models have shown that substantial coseismic slip may occur in regions that exhibit low levels of moment accumulation during decadal-scale pre-earthquake epochs. We estimate that <1% of the region that slipped coseismically during the 2024 MW = 7.1 Hyuganada Sea (offshore southeastern Japan) earthquake was co-located with a region of pre-event moment accumulation. This stands in contrast with the behavior of the 2011 MW = 9.1 Tohoku-Oki (offshore northeastern Japan) earthquake, where ~98% of the coseismic rupture area was co-located with pre-seismic moment accumulation. This co-location of coseismic slip and pre-seismic moment release proximal to the 2024 Hyuganada Sea earthquake serves as a real-world observation consistent with a novel theoretical prediction and is consistent with a perspective that decadal-scale pre-earthquake coupling estimates may provide snapshots of a highly time-variable fault system behavior, and may not necessarily serve as diagnostic identifiers of regions facing short-term earthquake hazard.