Anomalous geomagnetic disturbances induced by catastrophic tsunamigenic earthquakes in the region of Indonesia
Analysis of geomagnetic variations registered by the stations of the North-Caucasian geophysical observatory (the Elbrus volcanic area) has been fulfilled. Anomalous "quasi-harmonic" magnetic disturbances have been distinguished which were observed during all the stages of development of catastrophic tsunami-producing earthquakes in the area of Indonesia and morphologic effects in variation structure of geomagnetic field of the Earth have been described. Experimental results cited permit to obtain general idea on geomagnetic activity and some features of induced geomagnetic disturbances which we refer to tsunami-producing earthquakes. In all the observed cases seismic events occurred under the conditions of specific ratios between the components of magnetic field; it has been found that in the structure of magnetic variations we succeeded to distinguish ultra-low-frequency quasi-harmonic wave forms of geomagnetic disturbances reflecting the conditions of preparation and development of tsunami-producing earthquake in the studied region. We do not consider in the paper the forecast of tsunamiproducing earthquakes because even if we can distinguish in geomagnetic field some specific indications, in the source preceding the start of seismic event its coordinates and time in the source are left uncertain so far.