Application of Concurrent Full Waveform Inversion for Elastic Properties Using Rayleigh and Body Waves in Data from the Arid 2D Land Model

Abstract

In areas of complicated near-surface structures, estimation of an accurate near-surface velocity is challenging and this usually results in a distorted image of deeper targets. Surface waves have strong energy and decay exponentially with the depth, but they usually have high signal-to-noise ratios. Surface waves are strongly depending on S-wave velocities and also include information of P-wave velocity, density and attenuation of both P- and S-waves. Conventional inversion based on dispersion curves can only produce 1D S-wave velocity model. Full waveform inversion of surface waves breaks this limitation and can provide 2D or 3D high resolution near surface S-wave velocity, and reasonable P-wave velocity and density as well. Envelope of seismogram contains effective lower frequencies information which usually is not available in the seismogram. Combined with a multi-frequency strategy, cascadeded inversion of envelope-based and waveform-based misfit functions of both Rayleigh and body waves can reduce cycle skipping for FWI and estimate models with high resolution. This is due to the broader frequency bandwidth and composite contributions from Rayleigh waves and body waves. We test this method on the Arid 2D model, a typical near surface structure designed to include challenges in land seismic processing. Due to the high sensitivity to S-wave velocity and strong energy of Rayleigh waves, concurrent FWI of Rayleigh and body waves using cascaded envelope and waveform inversion produces S-wave velocity model with highest resolution. The resolution of P-wave velocity and density is lower than that of S-wave velocity. The small low velocity anomalies and faults at very shallow depths in the P- and S-wave velocity models are clearly defined. The low velocity structures at greater depths are better inverted in the S-wave velocity than in the P-wave velocity.