Correlation between crustal high conductivity zones and seismic activity and the role of carbon during shear deformation

Abstract

The electrical conductivity of the lower crust is anomalously high in many locations around the world. Well‐interconnected grain boundary carbon not only has the potential for increasing the electrical conductivity of the rock but also would be expected to reduce its shear strength. We report a new analysis of field observations and new laboratory measurements consistent with deep carbon‐bearing rocks causing observed high conductivities and crustal weaknesses associated with increased seismicity. The field data indicate a correlation between the depths to a zone of high electrical conductivity observed in Transdanubia in Hungary, earthquake focal depths, and zones of high seismic attenuation. The laboratory triaxial deformation experiments show that progressive shearing of a fracture in carbon‐bearing rock can result in a weaker more electrically conductive fracture. These results provide strong evidence for the role of carbon at depth in both electrical conduction and seismotectonics, explaining the correlation between mid‐crustal high reflectivities and high conductivities observed at many locations worldwide.