• Arkoprovo Biswas

      Articles written in Journal of Earth System Science

    • A practical solution in delineating thin conducting structures and suppression problem in direct current resistivity sounding

      Shashi Prakash Sharma Arkoprovo Biswas

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      In hard rock areas, conventional apparent resistivity measurement using Schlumberger resistivity sounding fails to detect thin conducting structures (2-D and 3-D fractures filled with groundwater and mineral aggregate) concealed at a large depth. In the present study, an attempt is made to way-out the detection problem of deep seated thin conducting layer. It is proposed to study the apparent conductance simultaneously with resistivity sounding to detect such conductive zones qualitatively. Apparent conductance is defined as the magnitude of current flowing in the subsurface for a unit applied voltage through current electrodes. Even though such measurement is of qualitative importance, it gives extremely valuable information for the presence of conductive zones at depth in challenging hard rock terrain. It has been observed that apparent conductance increases significantly when groundwater bearing fractures and conductive bodies are encountered in the subsurface. Field data from different locations are presented to demonstrate the efficacy of such measurement. The measurement assists to the conventional resistivity sounding for successful prediction of groundwater zones at large depth in different hard rock areas and is of enormous importance. The approach is also used for possible solution of suppression problem in the DC resistivity sounding when intermediate layer is not reflected in the resistivity sounding curve. Finally, the approach can be used together with resistivity sounding to solve many practical problems.

    • Resolution of multiple sheet-type structures in self-potential measurement

      Arkoprovo Biswas Shashi Prakash Sharma

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      The resolution of self-potential anomalies due to closely spaced multiple sheet-like bodies by the potential difference and potential gradient is studied in this paper. Self-potential anomalies due to several synthetic models were inverted through a very fast simulated annealing (VFSA) global optimization. Increase in depth to the top, polarization constant and depth extent of the body decreases resolution at a particular target separation. It has been observed that depth to the top and separation between two targets play an important role in the resolution. Vertical sheets at equal depth can be resolved in the potential difference measurement only if they are separated by at least four times their depth, while they can be resolved in the gradient method, if they are separated by twice the depth. Resolution using potential difference becomes more difficult for dipping sheets, although the potential gradient method can resolve them efficiently. Efficacy of potential gradient data in the inversion is demonstrated in the study using synthetic data as well as field measurement from South Purulia Shear Zone related with uranium investigation.

    • Magnetic susceptibility investigation of the saline water intrusion problem: The LAMP-BHU protocol

      VIRENDRA RANA PRASHANT KUMAR SAYANDEEP BANERJEE ARKOPROVO BISWAS

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      A protocol is presented to perform bulk magnetic susceptibility (BMS) analysis of simulated seawater/saline water using MFK2-FA Multi-Function Kappabridge instrument at Laboratory for Analyses of Magnetic and Petrofabric (LAMP), BHU to obtain a correlation between BMS and hydrogeological data such as salinity and conductivity. This LAMP-BHU Protocol involves the preparation of simulated saline water. It has been developed after BMS measurement of 20 simulated seawater samples in different frequencies, i.e., F1 (976 Hz), F2 (3904 Hz), and F3 (15616 Hz) to prepare a standard data. This standard data is further validated with field data. Fourteen water samples are collected from the field, and hydrogeological data (salinity and conductivity) and BMS at three different frequencies were measured. Further linear regression analysis is performed on the measured data. This protocol yields efficient results with F3, followed by F1 and F2 having an R$^{2}$ value of 0.84, 0.60, and 0.54, respectively, for salinity, and 0.79, 0.51, and 0.40, respectively, for conductivity. Salinity and conductivity are showing a negative trend with all the frequencies. This protocol enables to delineate saline water intruded zone or extent of saline intrusion using BMS analysis. The proposed protocol is a rapid and efficient mode of determination of the saline water intruded zones in the coastal aquifers for prioritisation of groundwater assets facilitating freshwater availability in coastal areas.

      $\bf{Highlights}$

      $\bullet$ Protocol is developed for Saline water intrusion studies using magnetic susceptibility measurements.

      $\bullet$ Magnetic susceptibility, salinity and conductivity was measured for simulated and field samples.

      $\bullet$ Inverse relationship observed between magnetic susceptibility w.r.t. salinity and conductivity.

      $\bullet$ High frequency magnetic susceptibility provides better results for gradual increase in salinity.

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