Dr. Pritam Yogeshwar

 

Dissertation Title

A resistivity-depth model of the central Azraq basin area, Jordan: 2D forward and inverse modeling of time domain electromagnetic data

Supervisor: Prof. Dr. Bülent Tezkan
Advisor: Dr. Roland Martin

Abstract

The focus of this thesis is the geophysical exploration of the central part of the Azraq basin in the northeastern desert of Jordan. In addition to common 1D inversion techniques, further 2D forward modeling strategies and a rarely used 2D inverse modeling scheme are applied to transient electromagnetic data. The Azraq area is of potential interest for palaeoclimatical and archaeological research in the frame of the interdisciplinary Collaborative Research Centre 806, entitled “Our Way to Europe” (CRC 806). The project investigates the history of modern human, particularly population movements in the past 190,000 years before present.

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The center of the Azraq basin is covered by a 10 km x 10 km mudflat consisting thick sedimentary deposits. To provide the basis for probable future drilling projects within the CRC 806, a 7 km and a 5 km long transects were investigated in the mudflat area. An extensive survey was conducted consisting of 150 recorded central loop transient electromagnetic (TEM) sounding locations. The electrical resistivity tomography (ERT) was applied as a complementary method to validate the TEM results. Common 1D inversion techniques are applied to interpret the TEM field data and to investigate the uncertainty of the inverse models. The results are patched together to quasi 2D resistivity-depth sections. The derived quasi 2D sections are consistent and provide a detailed image of the subsurface electrical resistivity distribution down to approximately 100 m depth. The results identify a resistive buried basalt layer in the periphery of the mudflat and a resistivity increase inside the high conductive mudflat sediments, which obviously corresponds to the layer below. The subsurface models are in excellent agreement with lithological borehole data and the geological information. Moreover, a transition zone from moderate to very low resistivities is observed, which is of interest for the groundwater management in Azraq. To verify the derived 1D inverse models, a detailed 2D modeling study is performed. Although the subsurface resistivity structure varies significantly along both investigated transects, the study demonstrates that a 1D inversion is sufficient to interpret the TEM data. Due to reduced data quality at late transient times for a few sounding locations, the deep resistivity contrast inside the mudflat is not well resolved in those zones. Further systematical 2D forward modeling shows that the resistivity increase is in general required to fit the TEM field data. The 2D forward modeling approach is based on the prior selection of a model and, therefore, does not provide an independent validation of the subsurface resistivity distribution. For this reason, a rarely applied 2D TEM inversion scheme is used to interpret the field data. The obtained 2D inverse models reveal a remarkable agreement with the quasi resistivity-depth sections, which are derived from the 1D results. Moreover, the unsatisfactory resolved deep resistivity contrast below the mudflat is reconstructed by using a-priori information, which is integrated into the parameterization of the model. Accordingly, the 2D inversion provides a strong independent validation of the subsurface resistivity distribution.

 

Education

2014: Ph.D. in Geophysics

2010 – 2014: Ph.D. student at the Institute of Geophysics and Meteorology, University of Cologne

2010: M.Sc./Diploma in Geophysics, University of Cologne

M.Sc. thesis:Grundwasserkontamination bei Roorkee/ Indien: 2D Joint Inversion von Radiomagnetotellurik und Gleichstromgeoelektrik daten. Institut für Geophysik and Meteorologie.”

2006 2010: Student assistant at the institute of Geophysics and Meteorology, University of Cologne.

 

Fieldwork

RMT and ERT survey in Roorkee – North India

Detection of fresh groundwater bodies offshore Israel using the LOTEM method

TEM and RMT survey near Thessaloniki, Greece

TEM, ERT and RMT survey in the Azraq Basin, Jordan

 

Publications

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