USING SLICKENSIDES TO UNDERSTAND FAULT MECHANICS ON THE ACTIVE WADI ARABA FAULT, JORDAN

The Wadi Araba fault (WAF) is one of the main strike-slip faults in the Dead Sea Transform plate boundary, which separates the Arabian plate on the east from the Sinai subplate on the west. Structural orientation data were collected from slickenside striations on the fault plane exposed in the area of the intersection of the NE-trending, strike-slip WAF and the dip-slip Khunayzira at the south end of the Dead Sea basin. These slickenlines are best observed in the polished pebbles of the upper Pleistocene conglomerates exposed within the deep incisions of the Wadi Khunayzira and Wadi An Nakhbar streams and provide evidence for multiple faulting mechanisms. Oriented pebbles were collected from the fault plane in order to study the formation sequence of the striations. Detailed generation data for the lineations were obtained from SEM and high magnification petrographic microscopic images of the striated pebble surfaces. Analyses of the cross-cutting relationship between the striations observed in these images indicate three principle directions of movement on the fault plane oriented N16E, 76SE. One motion is predominantly strike-slip with a rake orientation of 3°N. The second direction is nearly pure dip-slip with an orientation of 88°S. The third direction indicates right-reverse slip oriented 22°N. Our analyses of the striated pebble surfaces suggest that the most recent faulting on this fault plane was the oblique movement. These data indicate that the fault is oriented within in a present-day stress field that allows for both dip slip and strike slip on the fault over a very short period of time. Faulting associated with several historical earthquakes over the past 1500 years has ruptured this segment of the WAF as is indicated by offset archaeological ruins located 10 km south of the site for this study area. Because repeated motion on this fault plane would obliterate earlier faulting events, only the last few slips are preserved on the polished pebbles. Our preliminary results suggest that the past several earthquakes have had vastly different focal plane mechanisms.