Magnetic storm free ULF analysis in relation with earthquakes in Taiwan

Abstract

Abstract. Despite early optimism, pre-earthquake anomalous phenomena can be determined by using enhanced amplitude at the ultra-low-frequency range from geomagnetic data via the Fourier transform. In reality, accuracy of the enhanced amplitude in relation to earthquakes (deduced from time-varied geomagnetic data) would be damaged by magnetic storms and/or other unwanted influences resulting from solar activity and/or variations in the ionosphere, respectively. We substitute values of the cross correlation between amplitudes, summarized from the earthquake-related (0.1-0.01 Hz) and the comparable (0.01-0.001 Hz) frequency bands, for isolated amplitude enhancements as indexes of determination associated with seismo-magnetic anomalies to mitigate disturbance caused by magnetic storms. A station located about 300 km away from the others is also taken into account to further examine whether changes of the cross correlation values are caused by seismo-magnetic anomalies limited within local regions or not. Analytical results show that the values suddenly decrease near epicenters a few days before and after 67 % (= 6/9) of earthquakes (M > = 5) in Taiwan between September 2010 and March 2011. Seismomagnetic signals determined by using the values of cross correlation methods partially improve results yielded from the Fourier transform alone and provide advantageous information of earthquake locations.

Ultra low frequency (ULF) electromagnetic anomalies associated with large earthquakes in Java Island, Indonesia by using wavelet transform and detrended fluctuation analysis

“…Some ULF monitoring systems all over the world have registered anomalous ULF electromagnetic signals preceding moderate-large EQs (e.g., Kopytenko et al, 1990;Fraser-Smith et al, 1990;Hayakawa et al, 1996Hayakawa et al, , 2007Nagao et al, 2000;Uyeda et al, 2002;Hattori, 2004;Hattori et al, 2004aHattori et al, , b, 2013Schekotov et al, 2006;Hirano and Hattori, 2011;Chen et al, 2010;Han et al, 2011;Wen et al, 2012). Hattori (2004) found that the appearance of ULF electromagnetic anomalies prior to an EQ is related to its magnitude and the epicentral distance.…”

Evaluation of seismo-electric anomalies using magnetic data in Taiwan

“…Recognition of anomalous pre-earthquake phenomena has been reported for major earthquakes since 1990 (Fraser-Smith et al, 1990;Bernardi et al, 1991;Molchanov et al, 1992;Kopytenko et al, 1993;Lin and Zeng, 1992;Hayakawa et al, , 1999Hayakawa et al, , 2000Kawate et al, 1998;Gotoh et al, 2002;Hattori et al, 2002Hattori et al, , 2004aHattori, 2004;Liu et al, 2006;Molchanov and Hayakawa, 2008;Chen et al, , 2011Han et al, 2011;Wen et al, 2012). These reports indicate that geomagnetic anomalies prior to earthquakes are caused by either momentary existence of earthquake-related high conductivity materials or the movement of electric current along faults (Zeng et al, 1995;Merzer and Klemperer, 1997;Yen et al, 2004).…”

Typhoon-Induced Magnetic Disturbances: Cases in the Western Pacific

“…Night time (20:00 -4:00 local time) geomagnetic data were utilized to reduce the complex disturbances from solar activity (Wen et al 2012). Eight-hour data were transformed into the frequency domain using a 1-hour time span via the fast Fourier transform.…”

“…Variations in the geomagnetic field generally result from solar activities on a worldwide scale, and have an impact on nearby observation stations on a local scale (Wen et al 2012). It is possible to determine local impacts when data recorded by a remote station are also taken into consideration.…”