A Lithospheric Seismic Profile in Britain--I Preliminary Results

Abstract

The planning, execution and preliminary results of a major Anglo-German explosion seismic project are presented in this, paper I of a series. This Lithospheric Seismic Profile in Britain (LISPB) was planned as a reversed 1000 km line between two major sea-shot points off Cape Wrath in Scotland and one in the English Channel; additional sea-shots and intermediate land-shots were fired to give reversed and overlapping crustal coverage (to 180400 km distance) along the line. In all, 29 shots were fired and 60 mobile magnetic tape stations recorded three-components of ground 'motion. The resulting 14 crustal and three long-range profiles have observations at intervals of typically 2-4 km. Recordings have been digitized and four examples of filtered, computer-plotted record sections are presented to illustrate data quality. In a preliminary analysis, phase correlations are discussed and some models presented; the latter especially are more relevant to future interpretations than to geological or tectonic problems. However, significant variations in crustal thickness and in the nature of the crust-mantle transition do seem to occur beneath the British Isles.

Geophysical images of the deep crust: the Iapetus suture

“…Moseley (1977), reviewing the variety of conceptual models, pointed out that the results of the lithospheric refraction profile LISPB (Fig. 1), by then becoming available (Bamford et al 1976(Bamford et al , 1978 precluded the existence of any significant remnant of Palaeozoic oceanic crust below northern England. Nevertheless, geologists were able to map the surface expression of the suture, as defined by 'Pacific' versus 'Atlantic' (or 'Baltic') fauna!…”

Local earthquake tomography of Scotland

“…The Lithospheric Seismic Profile in Britain (LISPB) was an Anglo-German explosion seismic project shot in 1974 and designed to study the whole lithosphere below Britain (Bamford et al, 1976). It included three segments of a line running north-south through Scotland and northern England.…”

“…1) The six layer boundaries from the BGS velocity model for Scotland, which is derived from the LISPB active source experiment (Bamford et al, 1976). The seed velocities were those from the BGS model.…”

Seismic Wave Propagation in Stratified Media

“…Early work in seismic refraction in Western countries used very limited numbers of receivers, but latterly the benefits of very much denser recording have been appreciated (see, e.g., Bamford et al, 1976). In Eastern Europe and the USSR, reflection and refraction techniques have been combined in 'Deep Seismic Sounding' (Kosminskaya, 1971), which has closely spaced receivers along profiles which can be hundreds of kilometres long.…”

“…In this way a detailed profile can be built up to considerable range with only a limited number of recording stations. Since studies of deep structure require a detailed knowledge of the shallower regions, multiple shots at a variety of ranges are often fired into the same receiver array so that detailed results can be built up at both large and small ranges (Bamford et al, 1976). Such a procedure also allows a test of the degree of lateral homogeneity along a refraction profile.…”