The KRISP-94 magnetotelluric survey of early 1995: first results

In early 1995, high-quality, broad-band (10(-2)-10(4) s) magnetotelluric (MT) data were collected at 20 sites in southern Kenya. These sites were located to lie along pre-existing geophysical profiles along which seismic and gravity data had previously been acquired in 1994. Transient electromagnetic soundings (TEM) were also performed in order to facilitate removal of static shift effects from the MT data. Preliminary analyses of the MT transfer functions before and after static shift correction are presented, together with a review of those lithospheric processes which may plausibly exert an influence on the geoelectric signature, particularly in the context of a rift environment. Consideration of both the regional geology and induction anew transfer functions implies the importance of two principal strike directions, one delineated by the faulting bounding the N-S-trending lift, the other controlled by a continental-scale, Proterozoic, NW-SE fault fabric. The western boundary of the rift appears more sharply imaged than the eastern margin, with the onset to conductivity enhancement enigmatically offset to the west of the Nguruman fault bounded western flank. Significantly enhanced conductivities are implied in the vicinity of the rift below the Chyulu Hills.