Seismic Techniques
Crosshole Seismic Tomography
Outline
Borehole seismic tomography involves the measurement of the travel times of seismic raypaths between two or more boreholes in order to derive an image of seismic velocity in the intervening ground. Data is collected using one hole for the seismic source (normally a sparker) and measuring first-arrival times using strings of hydrophones in the others. Travel times are collected at regular intervals (usually 0.5m to 2m) all the way down the hole(s) for each shot position. This results in a network of overlapping raypaths that can then be used to model the velocity profile. The resulting velocity image is termed a tomogram and enables identification of anomalous velocity zones lying between the boreholes as well as imaging individual velocity layers.
