Tomographic velocity imaging can be applied to any form of microseismic or transmission seismic data, including crosshole, VSP, critical refraction and cross gallery. It is also applicable to reflection data for known reflector geometries or reflectors imaged by migration.
The illustration shows a model study of crosshole transmission imaging of an anomalous body. The lefthand window contains the tomogram and interpretation of the outline of the body and a deeper interface. The righthand window shows the misfit in milli-seconds between the data and the traveltimes through the tomogram.
In this application crosshole transmission data were acquired in a metamorphic sequence. The right hand window shows the interactive interpretation of a shot gather. The trace data have been processed to remove tube waves that were prevalent at this site.
The transmission velocity tomogram on a vertical section is shown on the left with the ray paths from one shot gather overlain for illustration. Low velocity, cooler colour, regions may be interpreted as zones of fracturing.