Digital archive of ephemerally preserved sedimentary structure in surf zone uplifted by the 2024 Noto Peninsula Earthquake

The surf zone is a dynamic coastal area characterising the physical environment of sandy beaches. However, direct, non-disturbing field observations of the highly variable sedimentary history of surf zones have been almost impossible in the past. The lack of on-site observations has limited our understanding of the morphological behaviour and inherent dynamics. In contrast, surf-zone stratigraphy was uplifted onto land on a time scale of seconds at the Kaiso Coast, Japan, by the Noto Peninsula Earthquake on 1 January 2024. The structure of unsolidified sediments covering the bar-trough zone to the foreshore (hereafter referred to as the surf zone) has been instantaneously preserved as it was without post-event interference except for the top layer. This extraordinary natural experiment enables us to explore the present-day sedimentary architecture formed beneath the surf zone under high-wave conditions. Here, we show the results of a large-scale trenching survey of the uplifted stratigraphy that covers the surf zone, including the breaker zone. A high-resolution photogrammetric digital archive of the sedimentary structure of the ephemerally preserved stratigraphy that was instantaneously uplifted by the earthquake was constructed, which provides an ideal basis for interpreting the spatiotemporal evolutionary history of bedforms within the surf zone. The spatially continuous orthoimages, covering a total of over 500 m, identified the development and transition of various sedimentary structures that were previously estimated but not fully evidenced in the real field. The combination of multiple trench surveys, aligned in both cross-shore and alongshore directions, allows for quasi-three-dimensional observations. This pioneering archive provides a unique opportunity for anyone to freely observe in detail the recent sedimentary structures as if they were there. Together with the wave and tidal observation records prior to the uplift, the comprehensive archive provides vital information to gain essential physical insights into the evolutionary sequences.