Abstract
Perturbation of the steady current by a spherical resistivity anomaly embedded in a uniform medium is investigated for three typical models representing an anomalous area caused by dilatancy in the crust. The current is spatially uniform for one model and approximately uniform in the vicinity of the anomaly for other ones. Changes in amplitude and direction of the electric field seem to be observable at measuring sites near the anomalous area if the area is located very close to the earth's surface. The results are applicable to the electric field induced in the crust by fluctuations of the geomagnetic field if the period of variations is not very rapid so that the induced electric field can be treated as a uniform one in the upper crust. Thus a possibility of detecting changes in resistivity associated with shallow earthquakes by measuring the magnetotelluric fields is suggested from a theoretical consideration.
