Transmission effects of localized variations of Earth's visco-acoustic parameters

Introduction

Localized heterogeneities in the subsurface cause amplitude and travel-time distortions of seismic reflections from underlying reflectors. These distortions are problematic to imaging and AVO analysis. The distortions come in almost regular patterns and usually are recognizable by V-shaped trajectories in the midpoint-offset domain (X-shapes for split-spread acquisition geometry). These distortions can be used to find the locations of the anomalies, which can reveal valuable information for interpreters such as fault locations (Hatchell, 2000). Moreover, they can be used to invert for velocity and absorption anomalies. The analyses of several authors Vlad (2005), Hatchell (2000) and Harlan (1994) have considered mostly velocity anomalies, which cause focusing and defocusing effects.

In this report, we stress that absorption must be considered in the analysis of these distortions. A seismic amplitude inversion that disregards absorption is likly to be biased, especially if velocity perturbations of interest are less than $4\%$. We examine the relative impact of localized velocity anomalies versus absorption anomalies on seismic amplitude.

Transmission effects of localized variations of Earth's visco-acoustic parameters