Abstract

The long-offset transient electromagnetics (LOTEM) sounding method is a valuable complementary technique for deep seismic exploration as applied to earth crustal investigations. During 1986, two LOTEM surveys were conducted to augment completed seismic investigations for crustal studies in southern West Germany, east of the Rhine graben. Our studies were motivated by the geoscientific activities within the framework of the German Continental Deep Drilling (KTB) project. The survey objectives were (1) to determine the applicability of the LOTEM method to crustal geophysics, (2) to investigate the correlation of resistivity anomalies with velocity anomalies, and (3) to confirm the method and interpretation in an area of known geology with existing geophysical data.The Black Forest and the Urach geothermal area survey results exhibit conductive features in the upper 10 km of the crust which were not previously defined by other geophysical data. Importantly, the results demonstrate a very strong correlation of a low-velocity zone with low electrical resistivity at 5 to 7 km depth within the crystalline basement at both locations.

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