Detection of faults position and possible crushed zones by using electrical resistivity and microgravity methods: Application to the Lar Dam area, Iran

Abstract

The main purposes of this study are to determine the fault position and possible crushed zones, general position and qualitative image of injection curtain, topology of cavities, and weak areas, and also examine deep extension of existing cracks in Berm. Geophysical examinations were performed by using the combination of electrical resistivity and microgravimetry data in Lar Dam. These studies include measurements of 420 electrical soundings with 1,000 m maximum length of current transmitter and measuring 1,081 microgravimetry stations. Also, in order to examine the possible density contrasts, this study discussed three-dimensional modeling by microgravimetry method to obtain Bouguer anomaly and residual anomaly, and determine the edge of residual anomaly. The result of these studies identified four crushed and weak areas with maximum water flight potential. Due to priority and importance degree of geological anomalies, these four weak areas are in the south part of the dam body, north of Berm, south of Berm, and west and southwest of Berm. The observed cracks in Berm are results of Berm subsidence that is due to fault activities or falling developed cavities along faults. It is presented that these cavities which are extended to depth of 70 m can have significant effect on the stability of the dam body.