VSP pattern recognition in absolute time

A procedure to determine VSP-WD (Vertical Seismic Profiling-While Drilling) first breaks in absolute time is described. By combining a seismic surface source and firing complex seismic pattern unique in time (with a highly accurate surface-downhole time reference system), an automatic downhole procedure for first break detection on the downhole data, even under harsh conditions (low signal to noise ratio), is established. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b).