f Crosshole reflection imaging at a borehole test site

Although crosshole first arrival travel-time tomography is now a relatively routine procedure, there are very few examples of field data studies involving imaging based on the full wavefield or indeed any part of the data other than the first arrival. This is in spite of the existence of several imaging algorithms which aim to provide increased resolution of geological structure using later, scattered energy. The main problem is that even in apparently high-quality datasets the requisite later phases are often obscured by strong tube waves and other types of 'noise' in the form of arrivals which are not taken into account by these algorithms. In this paper, we describe a crosshole reflection seismic experiment carried out at a borehole seismic test site at Whitchester, Northumberland, England. It is a good illustration of various problems that may be encountered in the acquisition and processing of reflection crosshole seismic data. The validity of reflection imaging is investigated with the aid of full elastic wave equation synthetic data.