Summary The object of this paper is to discuss some of the unknown or little-known relationships between surface structure and deep displacements in the well-exposed Zagros orogenic belt of south-west Iran, which can be divided into three major structural belts. The subjective nature of all inferences about deep structure in the absence of seismic data supported by deep borehole evidence is accentuated. Only at relatively shallow depths where the rock succession is well known can concealed structure be predicted with confidence from surface geology alone.

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We present interferometric imaging at 33 GHz of the Corona Borealis supercluster, using the extended configuration of the Very Small Array. A total area of 24 deg2 has been imaged, with an angular resolution of 11 arcmin and a sensitivity of 12 mJy beam−1. The aim of these observations is to search for Sunyaev–Zel'dovich (SZ) detections from known clusters of galaxies in this supercluster and for a possible extended SZ decrement due to diffuse warm/hot gas in the intercluster medium. Hydrodynamical simulations suggest that a significant part of the missing baryons in the Local Universe may be located in superclusters. The maps constructed from these observations have a significant contribution from primordial fluctuations. We measure negative flux values in the positions of the 10 richest clusters in the region. Collectively, this implies a 3.0σ detection of the SZ effect. For two of these clusters, A2061 and A2065, we find decrements of approximately 2σ each. Our main result is the detection of two strong and resolved negative features at −70 ± 12 mJy beam−1 (−157 ± 27 μK) and −103 ± 10 mJy beam−1 (−230 ± 23 μK), respectively, located in a region with no known clusters, near the centre of the supercluster. We discuss their possible origins in terms of primordial cosmic microwave background (CMB) anisotropies and/or SZ signals related either to unknown clusters or to a diffuse extended warm/hot gas distribution. Our analyses have revealed that a primordial CMB fluctuation is a plausible explanation for the weaker feature (probability of 37.82 per cent). For the stronger one, neither primordial CMB (probability of 0.38 per cent) nor SZ can account alone for its size and total intensity. The most reasonable explanation, then, is a combination of both primordial CMB and SZ signal. Finally, we explore what characteristics would be required for a filamentary structure consisting of warm/hot diffuse gas in order to produce a significant contribution to such a spot taking into account the constraints set by X‐ray data.

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We present Very Small Array (VSA) observations (centred on ≈34 GHz) on scales ≈20 arcmin towards a complete, X‐ray flux‐limited sample of seven clusters at redshift z < 0.1. Four of the clusters have significant Sunyaev–Zel'dovich (SZ) detections in the presence of cosmic microwave background (CMB) primordial anisotropy. For all seven, we use a Bayesian Markov Chain Monte Carlo (MCMC) method for inference from the VSA data, with X‐ray priors on cluster positions and temperatures, and radio priors on sources. In this context, the CMB primordial fluctuations are an additional source of Gaussian noise, and are included in the model as a non‐diagonal covariance matrix derived from the known angular power spectrum. In addition, we make assumptions of β‐model gas distributions and of hydrostatic equilibrium, to evaluate probability densities for the gas mass (Mgas) and total mass (Mr) out to r200, the radius at which the average density enclosed is 200 times the critical density at the redshift of the cluster. This is further than has been done before and close to the classical value for a collapsed cluster. Our combined estimate of the gas fraction (fgas=Mgas/Mr) is 0.08+0.06−0.04 h−1. The random errors are poor (note, however, that the errors are higher than would have been obtained with the usual χ2 method on the same data) but the control of bias is good. We have described the MCMC analysis method specifically in terms of SZ but hope the description will be of more general use. We find that the effects of primordial CMB contamination tend to be similar in the estimates of both Mgas and Mr over the narrow range of angular scales we are dealing with, so that there is little effect of primordials on fgas determination. Using our Mr estimates we find a normalization of the mass–temperature relation based on the profiles from the VSA cluster pressure maps, which is in good agreement with recent M–T determinations from X‐ray cluster measurements.