A SIMULTANEOUS INVERSION OF SEISMIC TRAVEL-TIMES AND AMPLITUDES FOR VELOCITY AND ATTENUATION

It is possible to efficiently use traveltime and amplitude information to infer variations in velocity and Q. With little additional computa tion, terms accounting for source radiation pattern and receiver coupl ing may be included in the inversion. The methodology is based upon a perturbation approach to paraxial ray theory. The perturbation approac h linearizes the relationship between velocity deviations and travelti me and amplitude anomalies. Using the technique, we infer the velocity and attenuation structure at a fractured granitic site near Raymond, California. A set of four well pairs are examined and each is found to contain two zones of strong attenuation. The velocity variations cont ain an upper low velocity region corresponding to the uppermost attenu ating zone. The location of these zones agrees with independent well-l og and geophysical data. The velocity and attenuation anomalies appear to coincide with extensively fractured sections of the borehole and m ay indicate fracture zones rather than individual fractures.