Exploration
Hamid Reza Baghzendani; Hamid Aghajani; Gholam Hossein Karami
Abstract
Karsts are important sources of groundwater, and it is crucial to determine their water volume and quality. The Ravansar Karst spring in the Kermanshah province is a significant water resource with a substantial water volume in the area. The source of this spring is the carbonate rock unit from the Cretaceous ...
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Karsts are important sources of groundwater, and it is crucial to determine their water volume and quality. The Ravansar Karst spring in the Kermanshah province is a significant water resource with a substantial water volume in the area. The source of this spring is the carbonate rock unit from the Cretaceous period and is affected by tectonic changes and faulting caused by movements related to the Zagros folding. In this work, geophysical methods of microgravity, electrical resistivity, and induced polarization have been utilized to identify the extent of karst development in the limestone units. The minimum residual gravity values are associated with karstification. The field dataset comprised two electrical profiles with the dipole- dipole and pole-dipole arrays. The resistivity and gravity data were inverted using a 2D algorithm based on the least square’s technique with a smoothing constraint. According to the processing and 3D modelling of gravity data; not only cavity-shaped voids and spacious cavity chambers were identified but also sub-structures and micro-karstification in carbonate rocks were detected. The most significant finding from the field survey is the detection of low gravimetric values, indicating relatively large holes and chambers that were previously unknown and inaccessible from ground level. These findings are consistent with known collapse and sediment infill features, as seen in surface sinkholes, cavities, and karstification systems. Geophysical surveys and field surveys show that the holes and karsts in the area are related to tectonic phenomena and faulting and are conduits for transporting water to the Ravansar spring.
H.R Baghzendani; H. Aghajani; M. Solimani
Abstract
Detection of subsurface structures by means of gravity method can be used to determine mass distribution and density contrast of rock units. This distribution could be detected by different geophysical methods, especially gravity method. However, gravity techniques have some drawbacks and can't be always ...
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Detection of subsurface structures by means of gravity method can be used to determine mass distribution and density contrast of rock units. This distribution could be detected by different geophysical methods, especially gravity method. However, gravity techniques have some drawbacks and can't be always successful in distinguishing subsurface structures. Performance of the gravity technique could be further improved by simultaneous combination and introducing additional information from other geophysical data. This study used existing relation between seismic and gravity methods to better clarify subsurface structures. This relationship relates mass distribution of the medium to velocity of wave propagation in that media. This method was applied on an area that consists of three mud volcanoes. After completion of the primary model by forward modeling, mass distribution and analysis of seismic velocity were provided on a 2-D profile. Bouguer anomaly map of gravity data of the area was obtained and negative anomalies were identified. These negative anomalies could be related to the existence of mud volcanoes. A 2-D seismic line was also acquired over the greatest mud volcano, as additional information for direct modeling. The Gardner equation was used for further velocity estimation by density values. This velocity model also compared with seismic velocity analysis for evaluation. The final results indicated that density modeling and the use of seismic velocity model increases the resolution of subsurface structures imaging. Separation of subsurface layers was implemented correctly in the velocity model resulting from gravity data and subsurface discontinuities of the area that become more obvious by this technique.
