Vessel-based photogrammetric reconstruction of a coastal fault zone integrated with bathymetric data: the case of Amorgos Island

Description

The Mediterranean region is exposed to potentially damaging tectonic and tsunami hazards, with Greece representing Europe's most seismically active country. In particular, the Santorini-Amorgos fault system located in the Aegean extending back-arc region (Aegean Sea, Greece) was the scene of the largest earthquake and subsequent tsunami event in the Aegean Sea in the 20th century, the 1956 Mw 7.8 Amorgos earthquake. However, the causative fault that produced this event is still unidentified. One potential candidate is the Amorgos fault which also structures the southern coast of the Amorgos Island. The related cumulative scarp outcrops both inland up to 700 m of altitude, and offshore down to -700 m and is affected by mass-wasting hazards which was also triggered by the 1956 event, causing the amplification of the tsunami run-ups along the southern Amorgos coast (≥ 20 m).During the AMORGOS 2022 cruise, we complemented the coastal bathymetric survey with the acquisition of photographs of the coast acquired from the front deck of Ifremer's research vessel Europe, cruising at a speed of ~9km/hour. Several acquisitions were performed between 1 and 5 km of distance from the shore, imaging back and forth portions of the coasts extending from a few hundreds of meters to several kilometers in length. By calculating photogrammetric terrain models at different resolutions, and combining them to the coastal bathymetric data acquired both by the vessel and by an underwater autonomous vehicle (AUV IdefX), we intend to build high-resolution model of the entire cumulative fault scarp. These combined datasets would provide new constraints to better characterize the active fault system and mass-wasting hazards in the Aegean region. It could and will also be used to model and thus understand the run-ups of the 1956 tsunami and therefore to better constrain its source.

Abstract

International audience

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