Summary. The quality of marine magnetic anomaly sources is described with the power-density representation of a stochastic model of random temporal and spatial emplacement of the marine magnetic anomaly source in the oceanic crust. Typical values of sea-floor spreading and emplacement parameters define a high-fidelity process of recording and sea-surface detection of the palaeomagnetic field reversals for spreading rates over 20mmyr-'. An analogous stochastic model is developed for the formation of sea-floor topography by normal faulting. It is shown that the random process of normal faulting observed in the inner walls of the FAMOUS rift valley can account for the quality of the adjacent West Rift Mountains topography. Quality, as opposed to quantity, is a degree of excellence, relative nature or kind or character (Concise Oxford Dictionary of Clcrrent English). The signal-to-noise ratio is a measure of quality. In this paper we address the signal-to-noise ratio of sea-floor spreading magnetic anomaly sources. We use a stochastic model of discrete random temporal and spatial emplacement of magnetic source material in a spreading centre that records the ambient geomagnetic field behaviour, and show that the temporal aspect (i.e. the mean frequency of emplacement in a spreading centre) is critical to the quality of sea-floor spreading magnetic anomaly sources. It will be shown that the sea-floor topography generated by a stochastic process of extension or thinning of the brittle crust in response to discrete and random normal faulting in atspreading centre, can be treated as noise. The quality of sea-floor topography can be estimated and expressed in terms of mean fault density and crustal thinning as a measure of the tectonic processes which formed the topography.