Investigations of the seismomagnetic effect in the geomagnetic diurnal variations
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In this paper we attempt to abstract seismomagnetic signals from geomagnetic diurnal variations of three components in quiet days before and after great earthquakes. The method employed here is to examine the ratio of apparent depths between two geomagnetic observatories using the single-stationZ/H method. We first estimate the apparent depth for the period of 24 h for two observatories which are located at almost the same latitude. Then we analyse the time changes of the apparent-depth-ratio between these stations. In the interval of 1962–1988, the time variation of apparent-depth-ratio between the Beijing and Lanzhou observatories seems to be related to the three great earthquakes occurred near Beijing. Roughly speaking, the anomalous change in apparent-depth-ratio appears to be positive before earthquake, and appears to be negative after earthquake.
Key wordsgeomagneticSq field single-stationZ/H method deep conductivity seismomagnetic effect
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