The mountains of southern Europe that fringe the
Mediterranean Sea and run generally in an east-west direction are of the
folded type generated by collision of the northward-moving
African Plate with the
Eurasian Plate. Where the northern edge of the African Plate is being
subducted in an irregular line a second
orogeny occurs that is not entirely understood. The mountains of
Italy and
Greece are a combination of folded mountains and
fault-block mountains running in a northwest–southeast direction. The Hellenic Subduction carries the leading edge of the African Plate under the
Aegean Sea Plate at the
Hellenic Trench. It follows an arc around the outer edge of the Peloponnese and Crete. The subduction on the west is to the northeast, on the east to the northwest, and north in the center. The average direction is N 21° E. In the islands and southern Greece a
fault-block mountain orogeny prevails due to a double set of crustal movements. On the one hand the Aegean Sea Plate is being raised by the subduction. On the other hand, north–south extensional movements, yet unexplained, are pulling the plate apart, creating normal
extensional faults and generating a parallel sequence of
horsts and
grabens, or
rift valleys, running in a north–south direction. Mount Taygetus is a limestone
horst bordering the
Eurotas Rift Valley. Below its eastern face is the Sparta fault, a
normal fault striking perpendicular to the direction of extension.
Footwall scarps are visible on the eastern side of Taygetus at the base of its spurs. They result from sudden slippages of the hanging wall in the direction of the dip, causing earthquakes. Single earthquakes result in 1–12 m of scarp. The Sparta fault is zig-zag in strike, varying between N 170° E and N 140° E. The maximum slippage has been 10–12 m in three increments. The earthquake of 464 BC, which levelled Sparta, resulted from a slippage of 3–4 m over a length of 20 km of the fault. The slip rate has been about 1 mm per year suggesting an average interval between earthquakes of 3000 years. ==Ecology==