On the tectonoelectric zonation in the Hellenic Arc.
PHYS CHEM EARTH PT A
307 - 313.
Geotectonic, seismotectonic and in-situ stress measurements in Greece indicate a zonation parallel to the active Hellenic arc. The raised question is, whether a similar zonation is characteristic of the geoelectrical structure and if the experimental ratio, R, of the time-averaged absolute values of the electric field variations comprises a competent indicator for the distinction of electric zones. In the present work, the magnetotelluric (MT) impedance tensor, measured at different sites in Greece, is further analyzed assuming that results from the galvanic distortion of the regionally induced electric field at a homogeneous or horizontally layered Earth due to near surface local inhomogeneities. From the comparison of the calculated ratio, R, with the respective experimental values, it is concluded that this ratio is strongly depended on local inhomogeneities.Furthermore, the geoelectrical anisotropy at these sites is investigated using the magnetotelluric representation of Mohr circles. Through this analysis, generalized local and regional strike-directions are estimated at each site, assuming a regional 2D-geoelectric structure aggravated by near surface local 3D-bodies of anomalous conductivity. The concepts of local and regional strikes are clarified in cases where the impedance tensor is singular, i.e. strong polarization of the measured electric field exists. It is concluded that the local strike is solely defined from the influence of the local inhomogeneities. On the contrary, the regional strike-direction is compatible, in a generalizing sense, with the direction designated by the major axes of the isoseismal curves drawn for earthquakes with epicenters in the vicinity of the measuring site. (C) 2000 Elsevier Science Ltd. All rights reserved.
|Title:||On the tectonoelectric zonation in the Hellenic Arc|
|Keywords:||EARTH PRECEDING EARTHQUAKES, 3-DIMENSIONAL BODIES, GALVANIC DISTORTION, PHYSICAL-PROPERTIES, ELECTRIC-FIELD, LAYERED EARTHS, MOHR CIRCLES, TENSOR|
|UCL classification:||UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Institute for Risk and Disaster Reduction|
Archive Staff Only