Detection of faults position and possible crushed zones by using electrical resistivity and microgravity methods: Applic
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ORIGINAL PAPER
Detection of faults position and possible crushed zones by using electrical resistivity and microgravity methods: Application to the Lar Dam area, Iran Mirsattar Meshinchi Asl & Hamed Jalal Pour & Mahmoud Mehramuz
Received: 10 January 2012 / Accepted: 26 November 2013 # Saudi Society for Geosciences 2013
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.
M. M. Asl (*) : H. J. Pour : M. Mehramuz Department of Geophysics, Science and Research Branch, Islamic Azad University, Tehran, Iran e-mail: [email protected]
Keywords ERT method . Microgravimetry . Fault . Crushed zone
Introduction Resistivity method has been used to diagnose buried canals and used for underground water studies, landslides, and also study of the karstic areas and underground natural and artificial cavities. In this article, the capacity of different geoelectrical methods was studied and compared. Exact examination of geological structure in field surveys of electrical resistivity tomography with high density of measurement points is very suitable (Sasaki 1992; Loke 1999; Griffiths and Barker 1993). The result of electrical sounding interpreted by using the number explanation method of Schlumberger and Wenner sounding as an equivalent multilayer environment and pseudosections transformed to geoelectrical section with layers of actual resistance. In this method, changes of special resistivity were analyzed as an equivalent and continuous multilayer structure (Schulz and Tezkan 1988). A geoelectrical model with actual electric resistivity distribution was offered by using two-dimensional electric sounding inversion of each profile (Loke and Barker 1996; Menke 1989; Bobatchev et al. 1997). Gravimetry method had been used to recognize anomaly position and expansion
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