Crustal and upper mantle electrical conductivity structure in Southern Scotland

Abstract

Magnetotelluric measurements were made during 1978-79 at nine sites on a linear traverse across South Scotland, extending from Kinloch Rannoch in the Highlands to Borthwickbrae in the Southern Uplands. Both one-and two-dimensional modelling of the apparent resistivities and phases indicate the existence of a low resisitivity (-75 a m ) zone at 20-90 km depth beneath the Southern Uplands rising closer to the surface beneath the Midland Valley to the north. A zone of slightly higher resistivity (500s2m), but still relatively conducting compared to the surrounding structure, is shown to exist beneath the Highlands. The real part of the ratio of vertical to horizontal magnetic fields is shown to be suitably modelled by a combination of induction and conduction.

The problem of current channelling: A critical review

“…However, the shorter period vectors (40-1000 s, the vectors at 750 s are shown in Figure 19b) displayed effects which are not compatible with a single crustal conducting anomaly, and agree qualitatively with the interpretation of Green ( 1975) that north of the Southern Uplands Fault, in the Midland Valley of Scotland, the depth to a conducting layer is less than beneath the Southern Uplands. These GDS observations are in total accord with both the 1D (Jones and Hutton, 1979b) and the 2D (Ingham and Hutton, 1982) interpretations of the MT observations -the most acceptable 2D model is illustrated in Figure 20. Analogue model studies of the whole of the British Isles and Eire have been undertaken by Dosso et al (1980) and Nienaber et al (1981), but, because of the modelling restrictions involved, were concerned only with the relatively long periods of 33 min to 11 hr.…”

“…A synoptic GDS magnetometer array study (Hutton et al, 1977;Jones, 1977;Hutton and Jones, 1980;Hutton et al, 1981), using Gough-Reitzel variometers, was followed up by two complete single station short period (10-1000s) MT and GDS experiments (Jones, 1977;Jones and Hutton, 1979a, b;Ingham and Hutton, 1982). The long period induction vector responses, of around 2000 s and greater, were in general agreement with those of Edwards et al (1971): Figure 19a.…”

“…Hence, for short 3D bodies, preferential interpretation of the B-polarisation (1971) ant. Hutton (1979a, b) Ingham andHutton (1982) ant. Dupis and Thera (1982) Summers (1981) Hebert (1983 ant.…”

Exploration of geothermal structure in Puga geothermal field, Ladakh Himalayas, India by magnetotelluric studies

“…As a preliminary step to two-dimensional inversion, the effective average impedance (Z aav = 0.5 (Z ij À Z ji ); Berdichevsky and Dmitriev, 1976) which are rotationally invariant in the surface plane is used to generate 1-D layered models. Similarly, the average impedance data have been used to generate 1-D models to provide useful results (Ingham and Hutton, 1982;Sule and Hutton, 1986;Livelybrooks, 1986) and works well with many 2-D structures. One-dimensional inversion of the data is carried out initially with Occam linearized inversion scheme (Constable et al, 1987) and then Marquardt (Marquardt, 1963) inversion scheme.…”

The use of invariant impedances in magnetotelluric interpretation

“…For example, Ingham & Hutton (1982) modelled apparent resistivity and phase curves calculated from the impedance Z,, = 0.5(ZXy -ZYJ.…”