Sedimentological characteristics of Mass Transport Deposits (MTDs) triggered by the Amorgos 1956 earthquake: sediment provenance and geochemical elements

Abstract

The 1956 Amorgos earthquake, with a magnitude of Ms = 7.5, caused a destructive tsunami in the Central Aegean Sea. Two gravity cores were collected south of Amorgos and Anafi Islands, respectively, confirming submarine landslide deposits linked to the 1956 earthquake. The 1956 Mass Transport Deposits (MTDs) vary in thickness from 55 to 100 cm in the cores. The predominant fraction of the sediments is clay, followed by sand (in the core next to Amorgos Isl.), while silt registers a maximum of 26% of total in the sediments. These MTDs are characterized by their grey color, erosional surfaces and their flows are mostly cohesive. Additionally, values of gamma density, P-wave velocity and magnetic susceptibility are higher compared with the above and underlying sediments. They are referred to as lithoclastic, with a lack of foraminiferal material and calcite dilution and presenting low values of strontium (Sr) and Sr/Rb ratio. All physical and chemical signatures can distinguish the MTD deposit during 1956 from the above and underlying sediments. Finding deposits with similar characteristics in the wider area can be attributed to this event and offer a better understanding of the extent of the multiple and simultaneous MTDs during this particular occurrence of seismic activity. The area is vulnerable to mass flows, as cores are composed of turbiditic layers before and after this event, which are likely the result of the high seismicity. Further study is required to reveal which conditions are conducive for the remobilization of the sediments. The area displays very low hemipelagic sedimentation and sedimentation processes mainly consist of Mass Transport Deposits and turbidites.

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