http://www3.geosc.psu.edu/~jte2/references/link053.pdf

The role of salt in fold-and-thrust belts

SUMMARY

In the Hellenic Trench south of Crete convergence between the southern Aegean Sea and Africa occurs at a rate of at least 60 mm yr-1. Previously published first motion fault plane solutions show a variety of different fault orientations and types, but are not well constrained. Furthermore, the lack of reliable focal depths for these earthquakes has obscured any simple pattern of deformation that might exist. Nonetheless, the mechanisms of these earthquakes have strongly influenced views of the tectonics in the Hellenic Trench. We have improved estimates of the fault parameters and focal depths for 14 of these earthquakes, using long-period P- and SH-waveforms. The earthquake mechanisms fall into four groups: (a) normal faults with a N-S strike in the over-riding material above the subduction zone; (b) low-angle thrusts with an E-W strike at a depth of about 40 km; (c) high-angle reverse faults with the same strike but shallower focal depths than (b); (d) events within the suducting lithosphere with approximately E-W P axes. The thrusting in groups (b) and (c) is probably the mechanism by which the sediments of the Mediterranean Sea underplate and uplift Crete. These events have slip vectors in the direction 025 ± 12° which represents the convergence direction between Crete and Africa along the SW-facing boundary of the Hellenic Trench. One of the events in group (d) occurred beneath the Mediterranean Ridge and involved high-angle reverse faulting with a WNW-ESE P axis: almost perpendicular to the direction of shortening deduced from folds at the surface. The Mediterranean Sea floor in this region appears to be in a state of E-W compression, for reasons that are not clear.

Earthquake mechanisms in the Hellenic Trench near Crete

Strain distribution over the east Mediterranean ridge: A synthesis incorporating new Sea-Beam data

Rate of outward growth of the Mediterranean ridge accretionary complex

Tectonics of the hellenic trench: A synthesis of sea-beam and submersible observations

Summary A Seabeam survey of the Hellenic Trench in 1978 was followed by a submersible survey in 1980. Fifteen dives were completed between 1500 and 3000 m covering 58 km on the bottom and obtaining 48 samples. Thus, the Hellenic Trench is probably now the most intensively studied trench as previous work included seismic reflection, dredging, coring, bottom photography, side-scan sonar and drilling. Because of the high sedimentation rate and the relatively shallow depth, we did not expect outcrops except along faults and in canyons. Active tectonics with numerous faults and folds have been observed. But we have also discovered vertical cliffs with hard rock exposure over a depth range of 1000–1500 m. In this paper, we discuss the nature of the hard rock outcrops observed both on the inner wall and on two hills that we interpret as diapirs. We conclude that at least part of these hard rocks are probably Messinian evaporites and concentrate on the tectonic role of this evaporitic layer in the Hellenic subduction. It is likely that the evaporites do not subduct but tend to pile up in the trench, to form a floating evaporitic basin.

Subduction in the Hellenic Trench: probable role of a thick evaporitic layer based on Seabeam and submersible studies

Active deformation of the sea-floor of the Hellenic trench has been observed using the Cyana SP-3000 submersible. The strain pattern observed on a scale of a few kilometers is similar to the one deduced from an analysis of Seabeam morphological maps on a scale of tens of kilometers. The overall strain pattern is compatible with subduction of the Mediterranean sea-floor toward the northeast. It is characterized by underthrusting in the Western Ionian branch and left-lateral strike-slip faulting in the Eastern Strabo branch.

D. Karig

Papers

Subduction in the Hellenic Trench: probable role of a thick evaporitic layer based on Seabeam and submersible studies

Active Tectonics in the Hellenic Trench

Geochemical processes influencing suspended particulate and bottom sediment composition in Lake Michigan