On the use of geomagnetic indices and ULF waves for earthquake precursor signatures

Abstract

Ultralow frequency (ULF: 0.001–5 Hz) magnetic records have recently been used in the search for short‐term earthquake prediction methods. The separation of local and global effects in the magnetic records is the greatest challenge in this research area. Geomagnetic indices are often used to predict global ULF magnetic behavior where it is assumed that increases in a geomagnetic index correspond with an increase in ULF power. This paper examines the relationships between geomagnetic indices and ULF power, spectral polarization ratio, and the relationship between the spectral polarization ratio and solar wind parameters. The power in the ULF, Pc3‐5 bands (10–600 s), shows a linear correlation coefficient of 0.2 with the Kp magnetic activity index. The correlation varies with magnetic local time (MLT) and latitude. The correlation coefficient is inversely related to the integrated power in the ULF Pc3 band (10–45 s) over MLT and magnetic latitude. The ratio of spectral powers Z(ω)/G(ω) is discussed and shown to be a promising parameter in the search for earthquake precursor signals in ULF records.