Uplift-induced marine regression due to the January 1, 2024, earthquake, Noto Peninsula, central Japan

Abstract

Abstract Large earthquakes instantaneously may reshape coastal landforms due to fault zone ruptures that uplift the Earth’s surface. On January 1, 2024, in the northern part of the Noto Peninsula, central Japan, an Mj7.6 (Mw7.5) earthquake occurred that triggered up to ≈ 4 m uplift. To measure the associated marine regression, orthophotos taken before and after the earthquake were analyzed, focusing on two bays on the northwestern Noto Peninsula where the largest uplift occurred. In response to the uplift, the shoreline retreated seaward (i.e., marine regression) by up to ≈ 200 m. The total area of the coastal plains increased by ≈ 0.46 km2; thus, all fishing ports in the bays dried up and were unable to function. The maximum shoreline extension occurred in the midsections of the two bays; however, shoreline extension at the edges of the bays was < 20 m, which possibly reflects the shoreface topography and sea depth before the uplift. The earthquake-induced uplift of the previously undersea rocks formed new coastal plains, which extended the total length of the rivers. Consequently, sandy beaches at two river mouths were no longer available as shoreline sediment sinks. Because of this, coastal landforms may need a long time to regain stable topographies after earthquakes.