Analogue model study of electromagnetic induction in the Newfoundland region

Abstract

The behaviour of magnetic field variations over the Newfoundland, Canada region is studied using a scaled laboratory analogue model. The model source frequencies used simulate periods of 100 s, 300 s, 900 s, and 1800 s in the geophysical scale. Contour views of in-phase and quadrature-phase parts of the three magnetic field components for two orthogonal source field polarizations for 100 s and 1800 s period variations are shown. Large anomalous in-phase and quadrature model magnetic fields are observed over the Strait of Belle Isle and Cabot Strait for all four periods studied, with the anomalous fields reaching maxima when the skin depth is of the order of six times the depth of the strait. The “cape effect”, that is, the large field enhancements due to deflection of induced current at capes, is observed for all four periods. Enhanced fields are observed at the continental shelf edge for 1800 s variations, but not for 100 s variations. A general shift in the anomalous field from the in-phase to the quadrature part for all three magnetic components is found for increasing period. The magnitudes and directions of inter-station induction arrows and single station induction arrows are studied. The two types of induction arrows differ when an anomalous horizontal magnetic field is present. This is especially evident near the coastline for a period of 100 s. For all periods studied, the in-phase induction arrows point towards the nearest and largest current concentrations. In traversing the coastline, the single station quadrature arrows reverse direction for the 100 s period, but not for the 1800 s period. The model results indicate that there is no preference for using either single station or inter-station induction arrows with respect to minimizing the effects due to coastal variations for inland locations. Further, the model results show that for periods studied, 100 s–1800 s the coastal effects would not produce serious perturbations to the field measured over crustal anomalies within the central regions of Newfoundland.