Possible seismogenic origin of changes in the ULF EM resonant structure observed at Teoloyucan geomagnetic station, Mexico, 1999-2001
- 1Centro de Geociencias en Juriquilla, UNAM, Apdo Postal 1-742, Centro Queretaro, Querétaro, C.P. 76001, Mexico
- 2Institute of the Physics of the Earth, Moscow, Russia
- 3UAEM, Cuernavaca, Morelos, Mexico
- 4INAOE, Tonantzintla, P.O.51 & 216, C.P. 72000, Puebla, Pue., Mexico
- 5Institute of Space Research, Nat. Acad. Sci. and Nat. Space Agency, Ukraine
Abstract. The 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 λ=29.1°) and its proximity to the equatorial electrojet (λ~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.