My master project is about the effect of faults on ground water table in Tehran plain, has been fulfilled at the University of Shahid Beheshti (Tehran, Iran).
The study area is located at the foot of the southern slope of uplifting Alborz Mountains where basically filled by the fluvial sediments of Quaternary; groundwater flow in the unconsolidated sediments is traditionally described as following a potentiometric surface from N-NW to S-SE.
Structures (faults and folds) within the area parallel to the general trend of the Alborz (E-W), and their density decreases toward south.
Mountain front sinuosity and valley floor ratio indexes were used to classify the relative tectonic activity of the area. They imply that the region is tectonically active and young. Study of landforms including alluvial fans and those associated with active faulting indicate that tectonic activity is transforming from North Tehran Thrust front into the pediment front.
This study introduces, the first time, a set of faults F47 (F47a, F47b, F47c, F47d), F46, F45, and F44a. Analysis of the faults mechanism indicates new facts about deformation within the study area.
- F47 fault set (attitude: ~N50E, 85 NW) first developed as T or R fracture in a sinistral simple shear zone between North Tehran Thrust and Niavaran Thrust. Continuation of deformation caused later dextral displacement of about 150-500m along the faults and their anti-clockwise rotation. Further block rotation has moved these into the compressive zone of deformation during the latest stage of activity, which caused reverse dip-slip displacements of about 1 m. This stage of activity occurred before deposition of the upper part of C Formation according to startigraphic evidences.
As the activity of this fault set is related to the movement along the North Tehran Thrust, it is therefore suggesting the latest activity of the North Tehran Thrust before deposition of the upper part of C Formation.
- Hydrogeologic and hydrologic studies are including investigation of the water table profiles across North Rey, South Rey and Kahrizak Faults, and hydrographs for major rivers and 36 wells for a period of nine years monthly observation.
According to my findings, North Tehran Thrust behaves as a barrier and obstructs recharges the southern aquifer. Numerous spring and seepages present along the North Tehran Thrust and an increase of drainage density in Karaj Formation in the hanging wall of the thrust verify this explanation.
Compartmentalization of ground water in the vicinity of main faults has been explored too.
Hydrographs for observation wells along with the water table profiles indicate that the North Rey, South Rey and Kahrizak Faults act as a barrier against ground water flow. The North Rey Fault appears to be impermeable at depth but more permeable near the surface. It acts very much like surface dams, holds back water until a certain elevation above which the water spills over the top.