Active faults and coastal landscapes in Central Japan's back arc after the Mw 7.5 Noto Peninsula earthquake

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

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

On January 1st, 2024, the Mw 7.5 Noto Peninsula earthquake ruptured on a series of coastal offshore reverse faults in the back arc of central Japan. Closest to the rupture, in the northwest, the coastal rocks uplifted as much as 4.4 m. The coastline accordingly moved seaward by up to 200 m creating new wide bedrock platforms that could become marine terraces if they survive erosion and weathering. The Peninsula itself hosts 4767 unique mapped terraces ranging in age from Holocene to 1.02 Ma. The terraces associated with the last two interglacial high stands (ca. 120 and 234 ka) record a tectonic SE-tilting similar to that of the Mw 7.5 earthquake. Older terraces all record a spatially uniform rate of uplift across the Peninsula. The landscape itself does not appear to be equilibrated to this gradient in uplift, with a seemingly disconnected fluvial geometry. We conclude that the faults that caused the most recent earthquake became the dominant structures on the Peninsula around 250 ka and that the Peninsula is in a state of transient equilibration. Most of the faults that ruptured on January 1st track the coast along a marked ramp at ca. 60 m below sea level. This corresponds to the average elevation of sea level over the last 500 kyr. 80 km to the northeast of the Noto Peninsula lies the Island of Sado where marine terraces record a strong southeast tilting similar to the Noto Peninsula. Earlier work suggested that the tilt is driven by a fault lying just offshore of the Oosado coast. The bathymetry reveals a ramp at around -60 m reflecting a geometry similar to the Noto Peninsula. This calls our attention to the often less-studied near-shore, and highlights a potential seismogenic source capable of M7 ruptures.