Study on noise in simultaneous geomagnetic difference data caused by the effect of S_q local-time variation

Introduction It is well known that the local geomagnetic field would change during the pregnancy of an earthquake, which may be associated with the change of the electromagnetic impedances of the crust medium. This phenomenon has been paid attention for a long time and up to now a lot of work both in observation and theory of tectonomagnetism has been carried out and much progress has been achieved (Stacey, 1964; Johnston, 1978; QI, 1977; Rikitake et al, 1980; Shapiro and Ab-dullabekov, 1982…

Study on noise in simultaneous geomagnetic difference data caused by the effect of Sq local-time variation

A new concept is suggested on tectonomagnetic research about the noise in simultaneous geomagnetic difference data caused by the effect of Sq local-time variation, together with the method of theoretical calculation. The level of the noise and its contribution to the total noises of the differences data are analyzed. The result indicates that the noise increases linearly with the increase of the distance between the two stations in the range of 40° longitude-difference, and its increasing rate is about 0.4 nT/(°) at latitude 40°N. The example calculated at a pair of sites with longitude-difference 0.357°, shows that the noise is about one fifth of the total noises of the difference data on geomagnetic quiet-day.