Appendix Chapter 2 Marine Geological Survey

Appendix Chapter 2 Marine Geological Survey

Chapter 2.3.1

The marine geological survey in the Kos-Nisyros area took place between 1997 and 2001. The first seafloor bathymetric survey was carried out 1997 with the Greek R/V AEGAEO (Fig. 1) of the Hellenic Centre for Marine Research (NCMR), followed by three successive cruises, as part of the GEOWARN scientific program. These used the “swath multibeam system” which sends out an array of sound pulses in a fan shape and returns depths from underneath the ship and from either side as well. During the first mission, the area of Nisyros island and the surrounding small islets has been mapped using the SEABEAM 1180 (180 kHz) system, for depths <500m. The other two missions mapped the whole area of Kos-Nisyros-Tilos using the SEABEAM 2120 (20 kHz) system, for depths >500 m. A complete coverage of 3,500 km2 from very shallow depths to depths ~2,200 m has been mapped, operating for 12 days total with an average speed of 10 knots.

The submersible THETIS (Fig. 2) was used for detailed investigation of the seafloor down to 300 m depth.

Fig. 1 Research vessel AEGAEO from HCMR. Photo V. Dietrich

Fig. 2 Submersible THETIS ready for diving. Photo P. Nomikou

Structural analysis of the area both onshore and offshore permitted the distinction of the faults in major and secondary structures, based on their throw >200m or less (Nomikou, 2004). These faults have been projected on the topographic map of the area together with their main kinematic character of relative vertical motion, with dentitions on the subsiding blocks (Fig. 3).

In addition, a single channel seismic-reflection profiling system with an air-gun as an energy source was used to survey the area between Kos, Yali and Nisyros. The penetration of the air gun shooting reached only 50 to 300 m, due to the existence of volcanic domes in the area and the shallow water depth.

The second surveys from 1999-2001 provided a large number of lithoseismic profiles, throughout marine area of the Kos-Yali-Nisyros-Tilos volcanic field, using not only single channel air-gun system but multi channel air-gun system of 24 channel steamer with 2 air-guns. These data complete our knowledge about the tectonic structure of the area.

The resultant bathymetric map was combined with onshore topographic maps of the islands to produce a synthetic topographic map of the entire area both onshore and offshore (Fig. 3).

Fig. 3 Synthetic tectonic map of Kos-Nisyros-Tilos Volcanic field based on data obtained from multi-beam bathymetric surveys and combined with onshore hypsometric data. 1: Eastern Kos Basin, 2: Western Kos Basin, 3: Western Nisyros Basin, 4: Southern Nisyros Basin, 5: Tilos Basin, 6: Pachia-Pergousa Basin, 7: Yali-Nisyros Basin. Source: Nomikou 2004, Nomikou et al. 2004, Nomikou and Papanikolaou 2010b.

2.4.1 Marine Geological Survey

The marine geological survey in the Kos-Nisyros area took place between 1997 and 2001. The first seafloor bathymetric survey was carried out 1997 with the Greek R/V AEGAEO of the Hellenic Centre for Marine Research (NCMR), followed by three successive cruises, as part of the GEOWARN scientific program. These used the “swath multibeam system” which sends out an array of sound pulses in a fan shape and returns depths from underneath the ship and from either side as well. During the first mission, the area of Nisyros island and the surrounding small islets has been mapped using the SEABEAM 1180 (180 kHz) system, for depths <500m. The other two missions mapped the whole area of Kos-Nisyros-Tilos using the SEABEAM 2120 (20 kHz) system, for depths >500 m. A complete coverage of 3,500 km2 from very shallow depths to depths ~2,200 m has been mapped, operating for 12 days total with an average speed of 10 knots.

The submersible THETIS was used for detailed investigation of the seafloor down to 300 m depth.

Figs. 2.3 a: Research vessel AEGAEO from HCMR and b: the submersible THETIS ready for diving Photos P. Nomikou

Structural analysis of the area both onshore and offshore permitted the distinction of the faults in major and secondary structures, based on their throw >200m or less (Nomikou, 2004). These faults have been projected on the topographic map of the area together with their main kinematic character of relative vertical motion, with dentitions on the subsiding blocks (Fig. 2.4).

In addition, a single channel seismic-reflection profiling system with an air-gun as an energy source was used to survey the area between Kos, Yali and Nisyros. The penetration of the air gun shooting reached only 50 to 300 m, due to the existence of volcanic domes in the area and the shallow water depth.

The second surveys from 1999-2001 provided a large number of lithoseismic profiles, throughout marine area of the Kos-Yali-Nisyros-Tilos volcanic field, using not only single channel air-gun system but multi channel air-gun system of 24 channel steamer with 2 air-guns. These data complete our knowledge about the tectonic structure of the area.

The resultant bathymetric map was combined with onshore topographic maps of the islands to produce a synthetic topographic map of the entire area both onshore and offshore (Fig. 2.4).

Fig. 2.4 Synthetic tectonic map of Kos-Nisyros-Tilos Volcanic field based on data obtained from multi-beam bathymetric surveys and combined with onshore hypsometric data. 1: Eastern Kos Basin, 2: Western Kos Basin, 3: Western Nisyros Basin, 4: Southern Nisyros Basin, 5: Tilos Basin, 6: Pachia-Pergoussa Basin, 7: Yali-Nisyros Basin. Source: Nomikou 2004, Nomikou et al. 2004, Nomikou and Papanikolaou 2010b.