Recent Gravitative Mass Movements in a Highly Tectonic Arc: The Hellenic Arc

G. Ferentinos, G. Papatheodoroy, V. Lycousis

The Hellenic arc is located within one of the world's most seismically active areas and has experienced extreme tectonism through Tertiary and Quaternary time. This tectonic activity controls fragmentation of the crust and formation of deep and shallow grabens, influences rates of uplift and subsidence, and determines sediment supply and depocenters.

This paper discusses the various types of gravitative mass movements detected in selected environments of the Hellenic arc and examines the causes. The areas surveyed were the Sporades and Corinth grabens in the back arc basin, the Zante-Cephalonia shelf in the inner slope of the Hellenic trench, and the Kythera ridge in the outer island arc.

The various types of gravitative mass movements that have been documented include (1) surficial sediment creep in slopes ranging from 1° to 2°, resulting in folding and faulting of the surficial sediments; (2) deep-seated creep, resulting in active faulting with uphill-facing scarps in slopes ranging from 3° to 4°; (3) translational and rotational slides in slopes ranging from 2° to 30°; (4) debris/mud flows in slopes ranging from 1° to 40°; and (5) turbidity currents. Turbidity currents caused by the discharge of red mud wastes have been detected flowing in slopes between 0.5° and 8° up to a distance of 17 km.

The mechanisms responsible for the initiation of these mass movements are: sloping sea bed, thick accumulations of Pliocene-Quaternary sediments, present-day high rates of sedimentation, closely spaced active faults, active faulting and folding, active diapirism, and seismic activity.

Based on the slope gradient, the geotechnical properties of the sediment, and the maximum expected peak ground acceleration, the sea floor all over the Hellenic arc is, in general, conducive to gravitative mass movements.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.