Coast uplifted by nearby shore-parallel active submarine faults during the 2024 Mw 7.5 Noto Peninsula earthquake

An Mw 7.5 earthquake occurred at 16:10 JST on January 1, 2024 at a depth of 16 km on the Noto Peninsula, central Japan. This earthquake was the second-largest intraplate earthquake recorded in Japan during 120 years of seismic observation, and it caused approximately 100 km of coastal seafloor emergence along the peninsula's northern coast. Herein, we mapped the emergence of this coastal seafloor and measured the uplift along the coast. The movement of the coastline led to the emergence of approximately 4.4 km2 of seafloor, which is continuous and probably the longest in the world. We determined the uplift distribution along the coast using the white remains of a reddish seaweed called Corallina pilulifera. Its upper limit exhibited a distinct horizontal line, effectively representing the uplift amount throughout the peninsula. Two large, uplifted regions were identified, around Cape Saruyama (5.21 m) in the west and Cape Kurasaki (2.70 m) in the north. Although active offshore submarine faults have been extensively researched, the fault traces remain poorly defined because they are primarily interpreted from seismic reflection profiles. We identified the distribution of active submarine faults using anaglyph-type stereoscopic images, confirming the subsurface deformation structure seen through the seismic reflection profiles. The main fault trace is primarily straight and contiguous with the nearby north coast. The uplift amount is greater near the active fault traces on the north side and diminishes sharply with increasing distance from these faults, indicating a southward tilt of surface uplift related to the active submarine faults.