Last week Dominique Similox-Tohon and Manuel Sintubin demonstrated that fault activity has occurred on the Isparta Cay lineament, although evidence for historical fault activity has not been found. It's apparent in satellite image that the Isparta Cay lineament continues into the Quaternary Canakli depression, but this lineament is rather undetectable in the landscape. We therefore used a geophysical method called electrical resistivity profiling to image the subsurface. Kris Vanneste, a specialist in this technique, joined the team with equipment provided by the Royal Observatory of Belgium.
The principle of electrical resistivity profiling--also called electrical tomography--is based on the differences in subsurface materials' resistivity. Materials such as clays are good conductors with low resistivity, while materials such as limestone are good isolators with high resistivity. Profiling consists of setting up an array of electrodes with a certain spacing (we applied a spacing of 3 to 5 meters) connected to a control and measuring device. For each measurement, two of the electrodes introduce an electrical current in the ground while two others measure the potential.
Although this geophysical method looks rather simple, failure often lies in small details as we also experienced this week. One entire day was lost when we learned that batteries not fully charged lead to the complete failure of an entire profiling session. Other strange errors may appear on the screen, such as when a goat has eaten one of your connector cables!
We performed six profiles in the Canakli depression about ten kilometers south of Sagalassos. The expected lineament didn't show up at all in our preliminary analysis. However, a new fault scarp was detected. The limestone front north of the depression is apparent on a number of profiles as a very sharp and straight, steeply south-dipping contact between high-resistivity material (limestone) in the north and low-resistivity material (clay) in the south. Strikingly, this Canakli fault has the same orientation as the Sagalassos fault, itself an orientation that is not at all the rule in this part of Turkey.
The team performed another electrical resistivity profiling in the Basköy area where a travertine escarpment is present. Again the question arose whether or not these travertine deposits are related to an active fault. We shot this profile along a steep irrigation channel, hoping that farmers would not use it that day. (Water and electricity do not really match, but we were lucky!) The measurements look promising, but nothing can be said yet about the deeper architecture of the travertines at Basköy.