Possible seismogenic origin of changes in the ULF EM resonant structure observed at Teoloyucan geomagnetic station, Mexico, 1999-2001

Abstract

International audienceThe evolution of the ULF resonant structure observed at Teoloyucan geomagnetic station has been provisionally studied in a possible relation with seismic activity in Mexico in the period 1999-2001. Two resonant lines were observed in the H-component (linear polarization) in the frequency bands fR2=10.2?11.1 mHz and fR2=13.6?14.5 mHz, sometimes accompanied by other harmonics. The source of the observed resonances is possibly related with the geomagnetic location of the station (geomagnetic latitude ?=29.1°) and its proximity to the equatorial electrojet (?~30°). An enhancement of the carrier frequency of both resonances in the period 1 month?2 weeks was found before the strongest EQs. Also, a depression of the resonant structure just a few days before and a few days after some EQs seems to be correlated with seismic activity