In a cross-well experiment, the seismic source is located at various positions
in one well and receivers are deployed in the other well. The seismic waves
generated by the source propagate through the medium within the cross-well
region, and are recorded by the receivers.
Each pair of source and receiver generates a seismic trace from
which we can pick the traveltime of the first arrival (or first break).
Therefore, from a cross-well experiment, one can obtain a set of
first arrival traveltimes that are
the functions of receiver depth *r*.
Subscript *i* indicates the source number, and
*N* is the total number of sources used in the experiment.

The medium between two wells is characterized by a slowness model. The slowness model is usually described as a linear superposition of a set of basis functions:

(1) |

12/18/1997