Constraints on correlation between the anomalous behaviour of electromagnetic normalized functions (ENF) and the intermediate depth seismic events occurred in Vrancea zone (Romania)

摘要

This paper is focused on a specific methodology able to emphasize the correlation between anomalous behaviour of electromagnetic normalized functions and intermediate depth seismic events which have occurred in the Vrancea zone and pointing out the main constraints related to them. The lithospheric conductivity changes produced prior to and during an earthquake, as a sequence of the dehydration of the rocks, associated with rupturing processes and fluid migration through faulting systems developed inside and close vicinity to foci, could be detected by means of the peculiar features of the electromagnetic normalized functions taken throughout the frequency range DC-10~(-2) Hz. Some experiments have been dedicated to assess the robustness of a methodology using electromagnetic data acquired over a span of several years. It means that the real-time selected electromagnetic normalized functions complying with temporal invariability criterion for a 2D geoelectric structure in non-seismic condition have been analysed taking into consideration just their daily mean distribution versus seismic events recorded simultaneously. As this methodology emphasizes the conductivity changes prior to a seismic event, it becomes an interesting subject for studying anomalous behaviour of electromagnetic normalized functions against their normal variation as possible precursors of earthquakes triggered in the Vrancea zone.