Earthquakes, "young" faults, and landscape in Japan's back-arc

Malatesta, L. C.*; 塚本 すみ子*; 末岡 茂   ; 小松 哲也  ; 高橋 直也*; 石村 大輔*; 片岡 香子*; 西村 卓也*; Weiss, N.-M.*; Keum, D.*; Bonerath, V.*; Norton, K.*; Gailleton, B.*; 岩佐 佳哉*

Malatesta, L. C.*; Tsukamoto, Sumiko*; Sueoka, Shigeru; Komatsu, Tetsuya; Takahashi, Naoya*; Ishimura, Daisuke*; Kataoka, Kyoko S.*; Nishimura, Takuya*; Weiss, N.-M.*; Keum, D.*; Bonerath, V.*; Norton, K.*; Gailleton, B.*; Iwasa, Yoshiya*

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. The 2024 Mw 7.5 Noto Peninsula Earthquake highlights this hazard. It resulted from the combined rupture of multiple adjacent faults. The specific hazard caused by each fault in the back-arc is however difficult to assess owing to long earthquake recurrence intervals. Diagnostic fingerprints in the landscape, onshore and offshore, can reveal clues and augment our understanding of the local earthquake cycle. Here, we compare coseismic deformation of the 2024 Noto Peninsula Earthquake with 4,767 individual marine terraces attributed to 16 successive sea-level stages over the last Myr. This reveals that the reverse faults responsible for the quake were reactivated and started slipping between 326 and 238 ka. The emerged landscape is still adjusting to it while nearshore underwater scarps mark the active faults. Applied to nearby Sado Island, these observations reveal the likely location of an active fault that drives its fast deformation. Active faults defining the edge of uplifting land are likely found in the near shore domain, drowned by the current sea-level high stand. New luminescence dating constraints on uplifted marine terraces further quantify the rate of deformation on Noto. These ages are in the final phase of analysis at the time of writing. Preliminary results appear to largely confirm the existing morphostratigraphic assumptions for the 120 ka terrace of Noto and a recurrence interval for 2024 Mw 7.5-type earthquake on the order of 2 kyr.