JOURNAL OF THE BALKAN GEOPHYSICAL
SOCIETY, Vol. 1, No 4, November 1998, p. 60-74, 10 figs.
of Sousaki geothermal Area (Greece)
deduced from two-dimensional
D. Galanopoulos*, E.
Lagios*, G.J.K. Dawes**, B.A. Hobbs**
* Department of
Geophysics and Geothermy, University of Athens, Panepistimiopolis-Ilissia,
157 84 Athens, Greece
** Department of Geology and Geophysics,
University of Edinburgh, Grant Institute, West Mains Road, Edinburgh
EH9 3JW, UK
(Received 7 April 1998; accepted
12 October 1998 )
short period (0.075-42 s) Magnetotelluric (MT) survey was carried
to investigate the geoelectric crustal structure of Sousaki geothermal
area in Greece. The MT data were initially processed and analysed
by Lagios (1992) and Tzanis and Lagios (1993). They suggested that
the crustal structure below Sousaki, comprises a complex geoelectric
domain of intersecting conductive fault zones and resistive blocks
which may include igneous intrusions. Their results were based on
one dimensional (1-D) MT models, and thus to determine such a complex
structure at least two dimensional (2-D) modelling should be undertaken.
This was the main task of the present study. An attempt to construct
a three dimensional (3-D) model for this area was proved unsuccessful
due to difficulties in the design of the actual model grid. The
MT data were finally modelled using a 2-D forward modelling technique.
The adopted 2-D MT model concerns the top 2 km of upper crust and
provides a different structure with that derived by the 1-D models.
This was attributed to the presence of regional 2-D or local 3-D
structures. The 2-D model is consistent with the geology and tectonics
of Sousaki. The low resistivities (2.5-5 ohm-m) observed within
the uppermost 100 m seem to be compatible with the Plio-Pleistocene
marls and volcanics. The very low resistivities (0.5-1 ohm-m) observed
at greater depths (0.5-1.5 km) are probably related to hydrothermally
altered ophiolites. The low resistivities observed in the area combined
with the various superficial thermal manifestations, make up a significant
evidence for the existence of a geothermal field. The three major
fractured zones identified in this area are probably those which
should allow the rainwater and the geothermal fluids to flow and
ensure the hydraulic continuation of the Earth’s surface with the
top weathered zone of the limestone or ophiolitic basement.
Key words: Geothermal
Exploration, 2-D Magnetotellurics, Sousaki, Hellenic Volcanic Arc.