The Wednesday Centerfault (7)

This week’s centerfault is a very prominent one that you will know for sure – the Dead Sea Fault. The sinistral strike-slip fault marks the boundary between the Arabian plate and the Sinai. The entire system is more than 600 km long and has accommodated ~107 km of slip since Miocene. Magnitude 7 is no problem for this structure and the recurrence intervalls are short.The seismicity of the fault system is well known thanks to good historical catalogs and a huge amount of archeoseismological and paleoseismological work. Its slip rate is around 4mm/yr. One of the greatest examples of archeoseismological damage comes from Ateret Castle (Vaduum Iacob), being situated close to the northern shore of Lake Galilee (33.00°N, 35.62°E). Here, the walls of the crusader fortress are offset 2.1 m, as it is directly built on the DSF!

Remains of hellenistic walls below the castle show even more offset, revealing the intense earthquake activity there. Archeoseismological damage can be found all along the Dead Sea Transform, since the region is one of the oldest cultural landscapes in the world. Ateret was by far the most impressive example to me (I was so lucky to join the Dead Sea Rift workshop in 2009).

Geological evidence for the fault activity comes from offset alluvial fans, from offset streams and simply from the offset of the geolgical units at both sides of the fault. A kind of special case is the formation of sink holes at the Dead Sea (31.55°N, 35.40°E), which were caused by the lowering sea level. Due to the retreat of salt water, freshwater is able to migrate along the faults, dissolving the salt deposits:

The (probably) most beautiful seismites can be observed further south, close to Mt. Sodom in Wadi Perazim (31.08°N, 35.35°E):

This is just a playground for every earthquake geologist! Download the fieldtrip guide at the IGCP567 homepage!

References:

Ken-Tor, R., Agnon, A., Enzel, Y., Marco, S., Negendank, J. F. W., Stein, M. (2001): Highresolution geological record of historical earthquakes in the Dead Sea basin, Journal of Geophysical Research, 106, 2221-2234.

Marco, S. (2008): Recognition of earthquake-related damage in archaeological sites: Examples from the Dead Sea fault zone, Tectonophysics, 453, 148-156, doi:10.1016/j.tecto.2007.04.011.

Marco, S., Stein, M., Agnon, A. (1996): Long-term earthquake clustering: A 50,000-year paleoseismic record in the Dead Sea Graben, Journal of Geophysical Research, 101 B3, 6179-6191.

Marco, S., Agnon, A., Ellenblum, R., Eidelman, A., Basson, U., Boas, A. (1997): 817-year old walls offset sinistrally 2.1 m by the Dead Sea Transform, Israel, Journal of Geodynamics, 24, 11-20.

Segal, Y., Marco, S., Ellenblum, R. (2003): Intensity and direction of the geomagnetic field on 24 August 1179 measured at Vadum Iacob (Ateret) Crusader fortress, northern Israel, Isr. J. Earth Sci.; 52: 203-208.

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