An interpretation technique for superimposed induction anomalies

Autor: B. Siemon
Rok vydání: 1997
Předmět:
Zdroj: Geophysical Journal International. 130:73-88
ISSN: 1365-246X
0956-540X
DOI: 10.1111/j.1365-246x.1997.tb00989.x
Popis: SUMMARY A salt dome in a trough region of the North German Basin was investigated with electromagnetic methods. A full set of excellent magnetovariational and gnetotelluric sites by robust statistical frequency analysis in the period range d pulsations. The transfer functions are related to a fixed reference site at a great distance from the salt dome. The results are presented using induction arrows and principal axes of the magnetic or telluric field. They show the superimposed influence of additional conductivity anomalies in the surrounding area: the North German Conductivity Anomaly, the Gifhorn Jurassic Trough, and two neighbouring salt domes (Wesendorf and Vorhop). Assuming that the mutual inductive couplings between these anomalies are not too strong, which is demonstrated, each anomaly was interpreted individually. To obtain a suitable data set belonging to a single anomaly, the transfer functions of the others had to be subtracted from the field data. This was carried out in four steps: ( 1) the transfer functions belonging to preliminary salt dome models were derived with 3-D numerical model calculations; (2) after the subtraction of this 3-D model data from the anomalous field data, 2-D numerical model calculations were used for finding the model of the Gifhorn Trough; (3) the salt domes were modelled again in 3-D using a 2-D reduced data set, which was derived by subtracting the 2-D model data from the anomalous field data; (4) the anomalous transfer functions of all the induction models were subtracted from the anomalous field data for interpreting the remaining data. An interpretation procedure was developed for explaining induction data belonging to weakly coupled induction anomalies. This procedure may also be useful in the case of strong inductive couplings, providing an initial 3-D model for more sophisticated and time-intensive model calculations that take all the anomalies into account.
Databáze: OpenAIRE
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