Publication 16

Geomagnetic induction studies in Scandinavia - III. Magnetotelluric observations

Alan G. Jones, B. Olafsdottir and J. Tiikkainen

Abstract

In this work, data from two of the instruments of the Munster International Magnetospheric Study (IMS) Scandinavian Magnetometer Array are combined with synoptic telluric field measurements, and the joint data sets are analysed to derive the magnetotelluric response functions for the locations. The data analysis procedures employed, particularly the timing error correction technique, are described in detail. One-dimensional interpretations of the response functions, from both the northern Swedish and the southern Finnish location, are shown to be valid. Accordingly, both first-approximation continuous models and more comprehensive layered-earth models - found by a Monte-Carlo search procedure - acceptable to the response functions are illustrated. The models acceptable to the northern Swedish MT response are almost identical to those acceptable to the previously derived horizontal spatial gradient (HSG) response for the same locale, displaying a monotonically decreasing electrical resistivity with depth, and the existence of a zone of low resistivity in the upper mantle at a depth of around 200 km. For the southern Finnish data however, the acceptable models describe the existence of a lower crustal conducting layer, of around 25 ohm.m, which was suspected from a qualitative analysis of previous work. Inadequate and insufficient long period information for this location preclude a positive identification of a possible electrical asthenosphere beneath southern Finland. However, any such zone cannot be closer to the surface than 150 km.

Source

Journal of Geophysics (Zeitschrift fuer Geophysik), 54, 35-50.

MTNet Home Page Alan's Home Page

Alan G Jones / XX XXX 2010 / alan-at-cp.dias.ie