Abstract:
This paper presents the results of a magnetovariational study undertaken over a basalt-covered region of western India which has been experiencing a swarm of seismic activity since early 1986. The most striking feature of the transient variations is the anomalous enhancement of the east-west (Y) component at stations bounding the seismically active belt. From the nature of the horizontal transfer functions and the anomalous induction arrows, it is inferred that this behaviour is related to the presence of a resistive body embedded in a north-south-oriented conductive belt. Consistent with an evolutionary model of Deccan volcanism and other geophysical data, it is suggested that the central resistive block coincident with the concentrated belt of earthquake epicentres represents either a dormant volcanic plug or a plutonic body rooted in upwarped conducting mantle. To account for the phase relationship between the anomalous Y variations and the normal north-south (X) variations, it is proposed that the upwarped asthenosphere, with its associated high geothermal anomaly, acts as a conducting path to channel induced current from the region of the Cambay triple junction located towards the northwest of the array. The existence of the strong induced currents in the region of the triple junction conforms with the induction arrow pattern observed at the array stations.
