ACTIVE FAULTS OCCURRENCE ON LAR DAM AREA and ANALYSES OF POSSIBLE PROBLEMS

Few active faults exist around the Lar dam in the northeast of Tehran, the capital of Iran. There are various kinds of active faults situated adjacent or under dam body. Main active faults located under dam foundation and abutments their types and mechanism are considered based on geological information, boreholes Geological logs correlation and array of ancient, young sinkholes. Geological information is drainage system displacement, change of composition and color of lava caused by fault observed from satellite images and field works. Correlation of boreholes geological logs located on dam axis is discussed. Findings show that the displacement of layers by fault is about 20 and 40m under dam foundation. Young and ancient sinkholes array left and right bank of dam is located on faults strike. As a result of this research it is distinguished that active faults occurrence under the dam foundation and abutments created major problems after dam refilling and will be creating problems in future that the descriptions are as follows: 1-Uncontrollable discharge water (maximum 10 m3 /s) from left abutment involves crushed zone of fault and karstifican zone that is impacted by fault mechanism. 2- Uncontrollable discharge water that considered partly infiltrate into right bank of Dam Lake where sinkholes located on faults strike. 3- Occurrence of two faults under dam foundation and observation of displaced layers about 20 and 40m indicated that movement of faults will be creating unstable situation for dam body. However it is possible that during the earthquakes and sudden movements of the faults, failure of dam body takes place.