Dead Sea Transform
The Dead Sea Transform 'fault system, also sometimes referred to as the Dead Sea Rift', is a series of faults that run for about 1,000 km from the Marash triple junction to the northern end of the Red Sea Rift. The fault system forms the transform boundary between the African plate to the west and the Arabian plate to the east. It is a zone of left lateral displacement, signifying the relative motions of the two plates. Both plates are moving in a general north-northeast direction, but the Arabian plate is moving faster, resulting in the observed left lateral motions along the fault of approximately 107 km at its southern end. A component of extension is also present in the southern part of the transform, which has contributed to a series of depressions, or pull-apart basins, forming the Gulf of Aqaba, Dead Sea, Sea of Galilee, and Hula basins. A component of shortening affects the Lebanon restraining bend, leading to uplift on both sides of the Beqaa valley. There is local transtension in the northernmost part of the fault system, forming the Ghab pull-apart basin. The southern part of the fault system runs roughly along the political border of Lebanon and Israel on its western side, and southern Syria and Jordan on the eastern side.
Tectonic interpretation
The DST fault system is generally considered to be a transform fault that has accommodated a 105 km northwards displacement of the Arabian plate. This interpretation is based on observation of offset markers, such as river terraces, gullies and archaeological features, giving horizontal slip rates of several mm per year over the last few million years. GPS data give similar rates of present-day movement of the Arabian plate relative to the Africa plate. It has also been proposed that the fault zone is a rift system that is an incipient oceanic spreading center, the northern extension of the Red Sea Rift.Development
The Dead Sea Transform began to form during the Late Eocene with epeirogenic movement in the region, with the start of the faulting phase beginning in the Oligocene and continuing into the Miocene. During the Early to Middle Miocene, there was a change in plate motions, and rifting stopped in the Gulf of Suez Rift. The initial phase of northward propagation reached as far as southernmost Lebanon and was followed by a period in the Late Miocene where continuing displacement across the plate boundary was taken up mainly by shortening in the Palmyra fold belt. A total displacement of 64 km has been estimated for this early phase of motion. In the Pliocene the DST propagated northwards once more through Lebanon into northwestern Syria before reaching the East Anatolian Fault.Sections
Southern section
The southern section of the DST is about 400 km long, extending from the spreading center in the Red Sea at southern end of the Gulf of Aqaba to just north of the Hula basin in southernmost Lebanon.Gulf of Aqaba
The Gulf of Aqaba was created by movement on four left-stepping strike-slip fault segments in a diagonal stepwise sequence known as echelon formation. In the areas where these segments overlap, pull-apart basins have developed, forming three bathymetric lows known as the Daka Deep, the Aragonese Deep and the Elat Deep. Parts of three of these faults ruptured during the 1995 Gulf of Aqaba earthquake.Wadi Arabah
The Wadi Arabah segment of the DST extends for about 160 km from the Gulf of Aqaba to the southern end of the Dead Sea. Some researchers have further broken down this segment, recognising two separate segments, Avrona and Arava. The Avrona fault extends from the northern part of the Gulf of Aqaba for about 50 km along the Arava Valley. The Arava fault runs from just north of the Avrona fault segment for about 100 km.A slip rate of 4 ±2 mm per year has been estimated from the offset of gullies across the fault. Four major earthquakes are well documented to have occurred due to movement on this fault in the last 1,000 years, in 1068, 1212, 1293 and 1458.
Dead Sea basin
The Dead Sea is formed in a pull-apart basin due to the left-stepping offset between the Wadi Arabah and Jordan Valley segments. The part of the basin with a sedimentary fill of more than 2 km is 150 km long and 15–17 km wide in its central part. In the north, the fill reaches its maximum thickness of about 10 km. The sequence includes Miocene fluvial sandstones of the Hazeva Formation overlain by a sequence of Late Miocene to early Pliocene evaporites, mainly halite, the Sedom Formation, and a lacustrine to fluvial sequence of Pliocene to recent age.The Dead Sea basin is of particular interest due to its title as the lowest land-based elevation on Earth. Other qualities that make the Dead Sea basin unique is the apparent lack of earthquakes in the middle of the basin, an occurrence that is common amongst pull-apart basins as the transform fault tries to accommodate the left-stepping offset, a process that could be described as the fault trying to smooth itself into a more linear feature with no step-overs. The earthquakes are also much deeper than other transform earthquakes throughout the world. The basin also has a very low heat flow compared to other strike-slip faults like the San Andreas Fault. A hypothesis of why the Dead Sea basin has unique earthquake locations, earthquake depths, and a lower heat flow is the "drop-down" or damage rheology hypothesis. This hypothesis states that a heavy magmatic piece of lithosphere has lodged itself in the Moho boundary near the center of the Dead Sea, partitioning stress to the edges of the basin and allowing deeper earthquakes. This could explain the rhombohedral shape of the Dead Sea and the exceptional depth of the basin.