Active audiomagnetotellurics on Milos (Greece) for determination of electrical conductivity distribution and their correlation to geothermal anomalies
The aim is to evaluate the extension of the geothermal anomaly in the subsurface. Due to very low resistivities of less than 1ohm.m and due to the limited transmitter-receiver separation the sounding depth for the active system is limited to approximately 2000 m. Comparison with well logs shows that it is possible to assign an increase of resistivity at depths of 200-500 m to the top of the crystalline basement at many sites. AAMT far-field data and long period MT data fit well and can be used for a common interpretation with a frequency range of more than six decades. Good agreement of measurements made with orthogonal transmitter dipoles seems to justify the one-dimensional interpretation. Differences in the resistivity of poorly conducting layers obtained by passive AMT measurements of other groups and by AAMT can be explained by vertical current components appearing with a grounded electric dipole as source. A short discussion of the so called coast effect depending on the MT frequency used is also given as a support for the MT groups. Finally the crystalline basement surface as found by AAMT is compared with the gravity measurements for a profile across the Zephiria graben.
Bibliographic Reference: EUR 12129 EN (1990) 139 pp., MF, ECU 8
Record Number: 199010217 / Last updated on: 1994-12-01
Original language: en
Available languages: en