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

Investigation of ULF magnetic anomaly before moderate earthquakes

Exploration Geophysics, 2012

Electromagnetic anomalies covering a wide range of frequencies from ultra low frequency (ULF), very low frequency (VLF) up to very high frequency (VHF) have been observed before earthquakes. However, the ULF range emissions provide a greater source of information regarding the earthquake precursor. One of the main techniques of investigating such a precursor is by using a magnetic sensor. In this paper, we have carried out a study of spectral density (magnetic field intensity) and polarization ratio methods to extract earthquake precursory signatures of the ULF data for moderate earthquakes (magnitude Mb = 3.7–4.8), using a three-component induction coil magnetometer installed at Shivaji University, Kolhapur (16.40°N, 74.15°E), India. We have applied a Fast Fourier Transform (FFT) procedure to calculate the spectral density of the ULF time series. We have found enhancement in ULF magnetic field intensity 3 to 5 days before the main shock and this specific enhancement appeared ±3 h a...

Initial results of ultra low frequency magnetic field observations at Agra and their relation with seismic activ ities

Current Science, 2004

Employing search coil magnetometers (f = 0.01–30 Hz) the ultra low frequency (ULF) magnetic field observations have been started at Agra since 13 Se ptember 2002. The analysis of first three months data shows that the amplitudes of the three components (Bx, By and Bz) are low between 0.01 and 0.30 nT normally, which increase to large values between 0.23 and 2.53 nT occasionally. Three cases of largest enhancements in amplitudes are selected and possible causes for the enhancements are examined in terms of magnetospheric ULF emissions (micropulsations) and ULF emissions associated with earthquakes using polarization parameter (Z/X) and magnetic storm index Kp variation. We show that in the three selected cases the amplitude enhancements are associated with moderately large earthquakes that occurred in the neighbouring countries Pakistan and China. In two of the three cases, the precursory enhancements in a mplitudes are identified clearly. The statistical analysis of the data using m...

Geomagnetic Investigation in the Seismoactive area of Narmada-Son Lineament, Central India

J. Ind. Geophys. Union, 2008

Activation of Narmada south fault caused the devastating Jabalpur earthquake (6.0 M) on May 22, 1997. To understand the secular variation of the total geomagnetic field in the vicinity of Narmada south fault, particularly comprising the seismoactive zone of Jabalpur and its adjoining areas in the Narmada-Son Lineament, Central India, tectonomagnetic studies were undertaken by carrying repeat surveys since 2003. The repeat survey area covers a total of 70 observation stations falling in areas of Jabalpur, Mandla, Seoni, Lakhnadon and Narsimhapur in Deccan Trap provinces. Using the Proton Precession Magnetometer of sensitivity 0.1nT, simultaneous measurements of total geomagnetic field were made at all stations and at base station and the process and 2007 bring out secular changes in total geomagnetic fields that seem to be concentrating locally. Results of these observations have shown the anomalous geomagnetic field secular variations in a range of ± 0.06 to ± 9.54 nT at separate stations over the distinct profiles. The anomalies in secular variation of the total geomagnetic field may be related to anomalous accumulation of tectonic stresses and tensions on the fault zones and crustal blocks due to recent geodynamic processes and tectonic setting of the Narmada-Son Lineament.