HR: 0800h
AN: GP41D-05    [Abstracts]
TI: Anomalous geomagnetic variations associated with Parkfield (Ms=6.0, 28-SEP-2004, California, USA) earthquake
AU: * Kotsarenko, A A
EM: kotsarenko@geociencias.unam.mx
AF: Centro de Geociencias, UNAM, Carretera QRO-SLP, km 15 Campus UNAM, Juriquilla, Queretaro, Mexico,
AU: Pilinets, S A
EM: pulse@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Mexico D.F., Mexico
AU: Perez Enriquez, R
EM: roman@geociencias.unam.mx
AF: Centro de Geociencias, UNAM, Carretera QRO-SLP, km 15 Campus UNAM, Juriquilla, Queretaro, Mexico,
AU: Lopez Cruz Abeyro, J A
EM: lcabeyro@geociencias.unam.mx
AF: Centro de Geociencias, UNAM, Carretera QRO-SLP, km 15 Campus UNAM, Juriquilla, Queretaro, Mexico,
AB: Analysis of geomagnetic and telluric data, measured at the station PRK (Parkfield, ULF flux-gate 3-axial magnetometer) 1 week before (including) the day of the major EQ (EarthQuake, Ms=6.0, 28-SEP-2004, 17:15:24) near Parkfield, California, USA, are presented. Spectral analysis reveal the ULF geomagnetic disturbances observed the day before the event, Sep 27, at 15:00- 20:00 by UT, and at the day of the EQ, Sep 28, at 11:00-19:00. Filtering in the corresponding frequency band f = 0.25-0.5 Hz gives the following estimations of the amplitudes of the signals: up to 20 pT for the magnetic channels and 1.5 mkV/km for the telluric ones. Observed phenomena occurs under quiet geomagnetic conditions (|Dst|<20 nT); revision of the referent stations data situated far away from the EQ epicenter (330 km) does not reveal any similar effect. Moreover, the Quake Finder research group (http:www.quakefinder.com) received very similar results (ELF range instrument, placed about 50 km from the EQ epicenter) for the day of the EQ. Mentioned above suggests the localized character of the source, possibly of the ionosphere or tectonic origin rather than of magnetosphere. Comparative analysis of the mentioned 2 stations show that we observed the lower-frequency part of the ULF- ELF burst, localized in the frequency range 0.25-1 Hz, generated 9 hours before the earthquake. Acknowledgements. The authors are grateful to Malcolm Johnston for providing us with the geomagnetic data.
DE: 0468 Natural hazards
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 6914 Electromagnetic noise and interference
DE: 6974 Signal processing (0674)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly