Summary Magnetotelluric soundings from 30 sites on the Hikurangi Margin have been used to image the electrical resistivity structure associated with the subduction of the Pacific Plate beneath the Australian Plate along the east coast of the North Island of New Zealand. The data are generally 2‐D in nature and exhibit a strike orientation that is compatible with the observed tectonic strike of the margin. 1‐D inversions of invariant impedance responses from sites on a transect parallel to this orientation yield an electrical structure that correlates with both the near‐surface geology and the results of a seismic refraction profile. 2‐D inversion and forward modelling of responses from a transect across the margin not only clearly identify surface conductive sediments associated with the outer forearc region but also suggest the possibility of a thin conductive zone immediately above the plate interface. The conductive layer is coincident with a low‐velocity region identified by seismic results and has been interpreted as being due to subducted sediments.

SUMMARY Mean hourly values of the horizontal and vertical components of the geomagnetic field at six observatories on the Iberian Peninsula were analysed to study seasonal and spatial behaviour of the solar and lunar (ionospheric and oceanic) daily geomagnetic variations. The results are tabulated and their characteristics are discussed. The influence of local oceanic effects on the lunar oceanic contribution at the peninsular observatories is noted. In particular, the spatial behaviour of the lunar oceanic contribution is considered. Whereas the mean value for the Peninsula is consistent with that expected according to an existing model for electric currents in the eastern Atlantic Ocean, individual values are not. The influence of tide in the Mediterranean Sea, of water currents in the Strait of Gibraltar and of local effects in the Atlantic Ocean is proposed as the reason for this behaviour.

Magnetotelluric (MT) soundings have been made at 14 sites along a traverse of the Wairarapa region at the southwest end of the active Hikurangi margin. Joint inversion of direct current resistivity soundings and the MT data indicates that the MT data are unaffected by static-shift. Analysis of the dimensionality of the data suggests that the transverse electric (TE) mode data (derived from an electric field parallel to the strike of the margin) may be distorted by 3D effects arising from the presence of Cook Strait and the non-continuity of structure along the margin. 2D inversion of the more robust transverse magnetic (TM) mode responses has therefore been used to derive a model of electrical resistivity structure beneath the transect. This shows the existence of two depressions containing lowresistivity sediments separated by a more resistive region which is inferred to correlate with a spur of Mesozoic greywacke extending north from the Aorangi Mountains. The same features were previously identified from gravity data. The thickness of sediments adjacent to the Wairarapa Fault is of the order of 3-4 km, whereas that in the western arm of the Wairarapa trough is c. 2-3 km. The resistivity structure of the southwest end of the Hikurangi margin is more complex than the structure determined farther north along the margin.

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