Banging around Britain

The Birps Atlas
September 15, 1995

My dictionary definition of an atlas is a "collection of maps, usually in book form or a book of charts and graphs". The Birps atlas then, is much more than an atlas. Instead of comprising maps of the earth's surface, it includes cross sections taken along offshore profiles around the United Kingdom that extend from sea level down to about 40km. However, it does much more even than that.

Birps stands for British Institutions Reflection Profiling Syndicate. Reflection profiling is a marine-based geophysical technique used by academics and industrialists alike to determine the sequence of rock types below the sea floor. A specially designed survey ship tows behind it an array of "sources" typically 70m wide and 50m long. The sources are air guns pre-programmed to fire in sequence as the ship sails along. They float about 10m below the surface. Behind the air gun sources, a "streamer" (so called because of its ribbon-like appearance) of detectors or hydrophones collects data and sends it back to the on-ship computers. The air guns produce regular explosions in the water, that, as the ship moves along, occur at precisely known locations. The shock waves from these explosions travel as sound (seismic) waves down through the water to the sea bed. Some are reflected at this water sediment boundary, and return to the hydrophone detectors in the streamer floating 10-15m below the sea surface. Other parts of the seismic signals penetrate the sediment and are reflected at deeper boundaries. The deeper the boundary reflecting the seismic energy, the longer the detector streamer needs to be in order to detect the return signal.

Processed data from some 12,000 km of seismic profiling are presented in a series of envelopes in the Birps atlas. The accompanying book provides a potted history of the Birps project, the techniques of data acquisition and interpretation, summaries of the geological interpretations from each region and a comprehensive bibliography.

In the eight years of the Birps project (1981-88) the lithosphere (crust and upper mantle) around the British Isles has become the most intensively studied region by this method in the world. The spin-offs from the project have been immense. Over 200 academic publications have been produced, several research students have been trained by being involved to some degree in the project, and our understanding of the complex and varied geological history of the UK has been enhanced immeasurably. The key points from the interpretation of each seismic profile are summarised in the accompanying book, with references to fuller discussion texts.

The Birps atlas is a brave attempt at a comprehensive but "user-friendly" reference for the student and expert alike. It certainly comprises an awesome data set, that has been processed in a logical and consistent way. This is a luxury rarely available to the user of geophysical data except in very localised areas. Geoscientists studying the tectonic history of the UK will doubtless find this an invaluable resource. The authors also intend the atlas to be useable by students and teachers of British geological evolution. The seismic profiles can obviously be used at any level, from the general perspective of learning to identify geological features such as faults, to researchers wishing to reinterpret the data following new theories. I feel that the atlas succeeds in its objectives. It goes further, too. This impressive work illustrates perfectly the need for realistic resources to be made available for major scientific projects in this country. In this case, funding was forthcoming from industry as well as traditional academic sources, but the benefits to both communities have been enormous.

Hazel Rymer is Royal Society university research fellow, department of earth sciences, Open University.

The Birps Atlas: Deep Seismic Reflection Profiles around the British Isles

Author - Simon Klemperer and Richard Hobbs
ISBN - 0521 41828 3
Publisher - Cambridge University Press
Price - £85.00
Pages - 124

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