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Yogeshwar, P. and Tezkan, B. (2018). Analysing two-dimensional effects in central loop transient electromagnetic sounding data using a semi-synthetic tipper approach. Geophys. Prospect., 66 (2). S. 444 - 457. HOBOKEN: WILEY. ISSN 1365-2478

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Abstract

We present a simple and feasible approach to analyse and identify two-dimensional effects in central loop transient electromagnetic sounding data and the correspondingly derived quasi two-dimensional conductivity models. The proposed strategy is particularly useful in minimising interpretation errors. It is based on the calculation of a semi-synthetic transient electromagnetic tipper at each sounding and for each observational transient time point. The semi-synthetic transient electromagnetic tipper is derived from the measured vertical component of the induced voltage and the synthetically calculated horizontal component. The approach is computationally inexpensive and involves one two-dimensional forward calculation of an obtained quasi two-dimensional conductivity section. Based on a synthetic example, we demonstrate that the transient electromagnetic tipper approach is applicable in identifying which transient data points and which corresponding zones in a derived quasi two-dimensional subsurface model are affected by two-dimensional inhomogeneities. The one-dimensional inversion of such data leads to false models. An application of the semi-synthetic transient electromagnetic tipper to field data from the Azraq basin in Jordan reveals that, in total, eight of 80 investigated soundings are affected by two-dimensional structures although the field data can be fitted optimally using one-dimensional inversion techniques. The largest semi-synthetic tipper response occurs in a 300 m-wide region around a strong lateral resistivity contrast. The approach is useful for analysing structural features in derived quasi two-dimensional sections and for qualitatively investigating how these features affect the transient response. To avoid misinterpretation, these identified zones corresponding to large tipper values are excluded from the interpretation of a quasi two-dimensional conductivity model. Based on the semi-synthetic study, we also demonstrate that a quantitative interpretation of the horizontal voltage response (e.g. by inversion) is usually not feasible as it requires the exact sensor position to be known. Although a tipper derived purely from field data is useful as a qualitative tool for identifying two-dimensional distortion effects, it is only feasible if the sensor setup is sufficiently accurate. Our proposed semi-synthetic transient electromagnetic tipper approach is particularly feasible as an a posteriori approach if no horizontal components are recorded or if the sensor setup in the field is not sufficiently accurate.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Yogeshwar, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Tezkan, B. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-197474
DOI:	10.1111/1365-2478.12520
Journal or Publication Title:	Geophys. Prospect.
Volume:	66
Number:	2
Page Range:	S. 444 - 457
Date:	2018
Publisher:	WILEY
Place of Publication:	HOBOKEN
ISSN:	1365-2478
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language INVERSION; BASIN Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/19747