Tectonic weak zones determined by magnetotellurics along the CEL-7 deep seismics profile

Abstract

In the contact zone of three tectonic units (Pannonian Basin, Eastern Alps and Dinarides), in a complicated — basin and range — geological situation magnetotelluric deep soundings were carried out along a 140 km long profile (CELEBRATION-007) with a site distance of 2 km. In this area deep fractures of the Basin run together in NE-SW direction.

In the paper various magnetotelluric images completed with gravity and magnetics are provided. In the traditional magnetotelluric approach, the structural indication of the TM and TE mode magnetotelluric sounding curves is clearly separated. The TM mode curves well express the resistive basement structure, already known from dense boreholes and detailed seismic exploration. The TE mode curves on the other hand (together with the induction vectors of very low values) definitely show the conductive root of the deep fractures, where the ductile materials are assumed to be raised into a very shallow depth of about of 8 km. The high heat flow of the area (about 100 mW/m²), which explains the shallowness of the conductive asthenosphere is also well indicated. The asthenosphere has more Alpine character in the NW part of the profile (its depth is about 80 km) and it is at smaller (about 50 km) depth in the SE part of the profile, due to the higher heat flow near the extensional Drava Basin. The induction vectors are also separated into two characteristic regions, according to their general direction, influenced by both local and remote effects.

A strong correlation is shown between magnetotelluric and gravity inversion results. A joint interpretation of magnetotelluric, gravity, magnetic results provide a quite comprehensive interpretation about the deep geological structures in SW-Hungary.