Structure of the Mygdonia basin (N. Greece) inferred from MT and gravity data

The area of the Mygdonia basin (N. Greece) comprises the European Seismological Test Site. For that reason, a large number of different geophysical methods have been applied in the area. However, information on the structure below the sediments has not been revealed. MT and gravity data were interpreted in order to identify the deeper structure of the region where the basin is in detail. Gravity data were also used in order to reveal information about the extent of the magmatic intrusions in the area. A three-dimensional gravity model for the broader area of the Mygdonia basin was constructed, based on the interpretation of the gravity data. A buried body of a density less than that of the hosting metamorphic rocks is suggested and is considered as the continuation of the Arnea granite, which outcrops mainly southwards of the studied area. Eight MT soundings were performed in the Mygdonia basin. The frequency range was 128–0.004 Hz, and nine channels were employed for each sounding, with four used as a reference station. The data were processed using both least-square and remote-reference least-square methods. Different types of dimensionality indicators were calculated, resulting in a N65E regional strike. A profile perpendicular to the strike was concluded, and a vertical grid along this line was created using information from d.c.-resistivity measurements for the first 400 m depth. The grid was used as an input to a two-dimensional inversion algorithm (Occam's 2D). The geological model proposed for the basement consists of schists with a thickness of 200 m, and gneisses, which reach a depth of 1200 m. Below these formations, the existence of the granite is suggested from the results of both the MT and gravity data. The depth of the bottom of the granitic body reaches 5 km.