Earthquake faults recorded in the near-shore bathymetry of Japan's back-arc

Luca Claude Malatesta , Shigeru Sueoka, Nina-Marie Weiss, Boris Gailleton, Sumiko Tsukamoto, Daisuke Ishimura, Naoya Ono Takahashi , Takuya Nishimura, Kyoko Kataoka, Tetsuya Komatsu, Yoshiya Iwasa

The eastern margin of the Sea of Japan is a zone of great seismic and tsunami hazard due to multiple offshore and nearshore reverse faults as shown by the 2024 Mw 7.5 Noto Peninsula Earthquake. Here we compare coseismic deformation of the 2024 Noto Peninsula Earthquake with 4767 individual marine terraces spanning the last Myr. This reveals that the earthquake faults started slipping between 326 and 238 ka. The emerged landscape is still adjusting to it while the nearshore domain already records it, in particular the -60 m trace of the average coastline across eustatic cycles. Applied to nearby Sado Island, these observations reveal the likely location of an active fault that drives its fast deformation. We show that scarps along the currently submerged “average coastline” are more likely to be active faults defining the edge of land.