Application of polarization ellipse technique for analysis of ULF magnetic fields from two distant stations in Koyna-Warna seismoactive region, West India

摘要: Abstract. A new approach is developed to find the source azimuth of ultra low frequency (ULF) electromagnetic (EM) signals believed be emanating from well defined seismic zone. The method test applied on magnetic data procured seismoactive region Koyna-Warna, known for prolonged reservoir triggered seismicity. Extremely low-noise, high-sensitivity LEMI-30 search coil magnetometers were used measure simultaneously vector field in range 0.001–32 Hz at two stations, one located within and another ~100 km away active During observation campaign extending 15 March 30 June 2006 earthquakes (EQs) magnitude (ML>4) occurred, which are searched presence precursory EM signals. Comparison polarization ellipses (PE) parameters formed by components measurement select bands, allows discrimination seismo-EM natural background ULF magnetospheric/ionospheric origin. corresponding spectral bands dominated fields define PE plane any instant contains fields. Intersection lines such planes distant stations clutter region. Approximating magnetic-dipole configuration source, along intersection suggest that align NNW-SSE direction. This direction coincides with orientation nodal normal fault mechanism largest EQs recorded during campaign. More significantly correspondence this tectonic controlled trend local seismicity, it has been surmised high pressure fluid flow facilitate may also electrokinetic effect.