Deep Seismic Reflection Profiling Onshore United Kingdom

Abstract

Over the last few years the Deep Geology Unit of the Institute of Geological Sciences (IGS), with the support of the Natural Environment Research Council's (NERC) Deep Geology Committee, has been acquiring and interpreting seismic reflection data of six seconds, or greater, two-way travel time (TWTI). The purpose of the work is to study the continental crust beneath the UK landmass particularly at levels deeper than those examined on a routine basis by exploration companies. This account discusses some details of individual surveys and presents notes on field parameters, data quality and factors affecting data quality, and interpretation. In general, interpretation work, supplemented by data from relatively shallow reflection surveys and borehole information is showing a consistency of seismic structure of the Earth's crust beneath Britain despite the relatively scattered nature of the data points. The seismic lines themselves, ranging in length from 1.5 to 30 km, have been shot in various, widely separated parts of the country. Not all of the data available to the Unit is discussed in this paper for reasons of confidentiality, but all data has been taken into account in discussion of recommendations for deep data acquisition. Three principal approaches have been used to acquire data: (1) Lines commissioned by IGS, some on behalf of NERC, and shot by a commercial seismic prospecting company. (2) Lines shot by IGS using in-house equipment but processed commercially. (3) Lines shot as commercial hydrocarbons surveys but with record length increased using funds provided by IGS and NERC. The first approach is the most effective in that choice of location and energy source are determined by Deep Geology Unit; speed of data acquisition is a great advantage but the method is expensive (the cost is variable depending on the energy souree used). The second approach is less expensive and allows choice of location, but an explosive energy source is necessary at present; this involves drilling shotholes and therefore a relatively slow rate of data acquisition. The third approach is relatively inexpensive because the cost is limited virtually to the extra processing required. Disadvantages are that there is no control by Deep Geology Unit over acquisition techniques and location. The individual surveys are not illustrated by seismic sections. However, the Deep Geology Unit will inform enquirers which surveys are on open file.