Abstract
Seismo-magnetic anomalies induced from the momentary existence of current and/or high-conductivity materials have been widely reported. The Parkinson vectors derived from 3-component geomagnetic data at 3 stations were obtained via the magnetic transfer function and discussed with respect to the location (23.90°E, 121.07°N) and the depth (15.1 km) of the M 6.2 earthquake on March 27, 2013 in Taiwan. Azimuth distribution constructed from the entire Parkinson vectors during the observation period is utilized to estimate the persistent background (i.e., the coast effect and underlying inhomogeneous tectonic structures) at each station. The normalized background distribution is subtracted from the normalized monitoring distributions computed using the azimuths of the Parkinson vectors within a 15-day moving window to determine the anomalous azimuths of high-conductivity materials. The depth ranges of high-conductivity materials are evaluated when the magnetic transfer function is subjected to the skin effect. The analytical results show that high-conductivity materials appeared in areas (121.25°E, 23.70°N) and about 10 - 25 km in depth. The location of the high-conductivity materials is about 32 km away from the epicenter reported by the Central Weather Bureau and well covers the hypocenter depth. The agreement sheds lights on forecasting locations and hypocenter depths of forthcoming earthquakes via momentary existence of earthquake-related high-conductivity materials.
Highlights
Taiwan is located in the western margin of the Pacificrim seismic zone
One magnetometer was installed at National Chung Cheng University in 2005 to provide potential 3-component flux magnetic data with a 1-minute sampling interval
Seismo-magnetic anomalies have been widely observed and reported in many major earthquakes (Fraser-Smith et al 1990; Bernardi et al 1991; Molchanov et al 1992; Kopytenko et al 1993; Hayakawa et al 1996, 1999, 2000; Kawate et al 1998; Gotoh et al 2002; Hattori et al 2002, 2004a, b, 2013; Liu et al 2006; Molchanov and Hayakawa 2008; Chen et al 2009, 2010, 2011a, 2012, 2013a; Han et al 2011; Wen et al 2012). These anomalies are generally considered to be caused by the momentary existence of electric currents along faults (Yen et al 2004), sudden changes in conductivity (Zeng et al 1995; Merzer and Klemperer 1997) and/or fluctuations in susceptibility near epicenters (Stacey 1962; Nagata 1970; Liu et al 2006; Wen et al 2012) due to the accumulation of earthquake-related stress on nearby rock beds
Summary
Taiwan is located in the western margin of the Pacificrim seismic zone. The Philippine Sea Plate subducts northward beneath the Eurasian Plate along the Ryukyu Trench forming the Okinawa Trough spreading toward northeastern Taiwan (Tsai et al 1977; Wu 1978). Seismo-magnetic anomalies have been widely observed and reported in many major earthquakes (Fraser-Smith et al 1990; Bernardi et al 1991; Molchanov et al 1992; Kopytenko et al 1993; Hayakawa et al 1996, 1999, 2000; Kawate et al 1998; Gotoh et al 2002; Hattori et al 2002, 2004a, b, 2013; Liu et al 2006; Molchanov and Hayakawa 2008; Chen et al 2009, 2010, 2011a, 2012, 2013a; Han et al 2011; Wen et al 2012) These anomalies are generally considered to be caused by the momentary existence of electric currents along faults (Yen et al 2004), sudden changes in conductivity (Zeng et al 1995; Merzer and Klemperer 1997) and/or fluctuations in susceptibility near epicenters (Stacey 1962; Nagata 1970; Liu et al 2006; Wen et al 2012) due to the accumulation of earthquake-related stress on nearby rock beds. Interlaced maps were constructed using anomalous Parkinson vector orientations from the CCU, HLG, and YMM stations, and the experimental epicenter locations were compared with the officially-reported epicenter location to examine the validity and practicability of the proposed analytical method
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