Vol.42-1 ABSTRACT1
AbstractGeomagnetic signals observed at the surface of the earth contain information on underground conductivity structure of the erath. As the geomagnetic transfer function is calculated from the geomagnetic signals and related to the conductivity structure of the earth, it is one of the most useful and efficient methods for geomagnetic inverstigations.In this study,we examined temporal changes of the transfer functions using data obtained mainly by the Geographical Survey Institute in order to detect conductivity changes associated with crustal activities such as occurrence of earthquakes and volcanic activity. Using the geomagnetic data observed at observatories and first order geomagnetic stations, changes in the transfer functions were obtained. The traditional single-station transfer functions of wide period range (from 4 min to 128 min) were calculated. In addition, we calculated the interstation transfer functions which are robust against arttificial magnetic and electric noises. Although we did not find changes in the transfer functions associated with crustal activities at the observatories, we detected temporal changes which were possibly associated with occurrence of a large earthquake at the first order geomagnetic stations using the interstation transfer functions. |