When Do We Need Elastic Waveform Inversion for Velocity Model Building? Marine and Land Examples

Full waveform inversion is a widespread data-fitting technique commonly used for velocity model building. In this context, the target input data are low-frequency transmissions and post-critical reflections in a long offset range. These seismic data, associated to diving waves, are highly sensitive and therefore can be used to retrieve the P-wave velocities of the subsurface. However, according to the diffraction theory, the transmission data can be influenced by shear parameter variations in the subsurface which create tuning and interference effects at the low frequencies, notably when the variations are large and occur inside the first Fresnel zone. The elastic interference challenges the applicability of an acoustic waveform inversion approach in a global manner, and despite its relatively low computational costs and practicality, its results have proven mixed. We discuss marine and land seismic data examples, from the Gulf of Mexico and the Middle-East, where elastic waveform inversion provides compelling results superseding the acoustic waveform inversion results.