Abstract
This study uses a network that is comprised of 10 total intensity magnetometers to detect azimuthal propagation of seismo-magnetic emission waves during 26 earthquakes that occurred between July 2007 and December 2008 in Taiwan. The propagation azimuth and phase velocity of the seismo-magnetic waves are calculated using frequency wavenumber analysis at the ultra low frequency of 0.05 Hz every 30 min. We superimpose the derived azimuths within a moving window of 30 days as the monitored distributions, and the entire dataset as the background distribution. We also find the propagation azimuths of the seismomagnetic anomalies of each earthquake by subtracting the background from the monitored distributions. The results show that frequency wavenumber analysis can be applied to evaluate azimuthal propagation of seismo-magnetic emission waves using a scalar of geomagnetic total intensity fields. The success detection rate of seismo-magnetic anomalies increases from 62% of the 26 earthquakes to 77% using the surface magnetic anomalous reference tip (SMART) to substitute the epicenters. Meanwhile, the odds proportions between the azimuths of the seismomagnetic emission waves towards and away from SMART reveal the associated anomalous propagation.
Highlights
Geomagnetic anomalies within a wide frequency range from direct current (DC) to very low frequency (VLF) that are associated with large earthquakes have been studied intensively [Hayakawa and Fujinawa 1994, Hayakawa 1999, Hayakawa and Molchanov 2002]. Fraser-Smith et al [1990] CHEN ET AL.generated by an earthquake during a seismogenic process, it would be possible to estimate the direction of a forthcoming earthquake using the FK analysis.In the present study, standard FK analysis is applied to analyze geomagnetic total intensity fields, which are scalars recorded by a network of 10 magnetometers (Table 1) in Taiwan, to determine the directions of SMEWs before large earthquakes (Figure 1)
This study uses a network that is comprised of 10 total intensity magnetometers to detect azimuthal propagation of seismo-magnetic emission waves during 26 earthquakes that occurred between July 2007 and December 2008 in Taiwan
The results show that frequency wavenumber analysis can be applied to evaluate azimuthal propagation of seismo-magnetic emission waves using a scalar of geomagnetic total intensity fields
Summary
Geomagnetic anomalies within a wide frequency range from direct current (DC) to very low frequency (VLF) that are associated with large earthquakes have been studied intensively [Hayakawa and Fujinawa 1994, Hayakawa 1999, Hayakawa and Molchanov 2002]. Fraser-Smith et al [1990]. Geomagnetic anomalies within a wide frequency range from direct current (DC) to very low frequency (VLF) that are associated with large earthquakes have been studied intensively [Hayakawa and Fujinawa 1994, Hayakawa 1999, Hayakawa and Molchanov 2002]. Standard FK analysis is applied to analyze geomagnetic total intensity fields, which are scalars recorded by a network of 10 magnetometers (Table 1) in Taiwan, to determine the directions of SMEWs before large earthquakes (Figure 1). A statistical study of 26 earthquakes (Mw >4.3; Table 2) is carried out, which were retrieved from the broadband array in Taiwan [Kao et al 2002, Liang et al 2003, 2004] for the seismology for the period from July to December 2008. Filtered seismic data, where the distance between every two stations is smaller than the wavelength of a single wave
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