Shallow Shear Wave Reflections: What Can the Amplitude Tell Us and How?

Shallow shear-wave reflection method at present is entirely restricted to the use of reflection time information. The average velocity is estimated from the travel time, whether in stacking velocity analysis, tomographic inversion, or in other processing schemes. Use of reflection amplitude has remained challenging primarily due to source and receiver effects camouflaging geologically meaningful amplitude perturbation. We have found ways to improve amplitude fidelity and reduce the effect of source and receiver coupling variations. When tested on real field data, shear-wave reflection amplitude as a function of incidence angle is found to provide useful near-surface interfacial information. Moreover, when frequency-dependent reflection amplitudes are looked at using the pertinent theories of poroelasticity, we find that those reflection amplitudes seem to contain even further information about the flow properties and the state of stress in the near-surface. These information are crucial to diverse practical applications.