Articles | Volume 12, issue 5
Nat. Hazards Earth Syst. Sci., 12, 1747–1754, 2012
Nat. Hazards Earth Syst. Sci., 12, 1747–1754, 2012

Research article 25 May 2012

Research article | 25 May 2012

Magnetic storm free ULF analysis in relation with earthquakes in Taiwan

S. Wen1, C.-H. Chen2, H.-Y. Yen3, T.-K. Yeh4, J.-Y. Liu5,6, K. Hattori7, H. Peng7, C.-H. Wang2, and T.-C. Shin8 S. Wen et al.
  • 1Institute of Seismology, National Chung Cheng University, Chiayi 621, Taiwan
  • 2Institute of Earth Sciences, Academia Sinica, Taipei 115, Taiwan
  • 3Institute of Geophysics, National Central University, Jhongli 320, Taiwan
  • 4Department of Real Estate and Built Environment, National Taipei University, New Taipei City 237, Taiwan
  • 5Institute of Space Science, National Central University, Jhongli 320, Taiwan
  • 6Center for Space and Remote Sensing Research, National Central University, Jhongli 320, Taiwan
  • 7Graduate School of Science, Chiba University, Inage, Chiba 263-8522, Japan
  • 8Central Weather Bureau, Taipei 10048, Taiwan

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. Seismo-magnetic 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.