Approximations to seismic AVA responses: Validity and potential in glaciological applications


Contact
Anja.Diez [ at ] awi.de

Abstract

Amplitude-variation-with-angle (AVA) methods establish the seismic properties of material either side of a reflective interface, and their use is growing in glaciology. The AVA response of an interface is defined by the complex Knott-Zoeppritz (K-Z) equations, numerous approximations to which we typically assume weak interface contrasts and isotropic propagation, inconsistent with the strong contrasts at glacier beds and the vertically transverse isotropic (VTI) fabrics were associated with englacial reflectivity. We considered the validity of a suite of approximate K-Z equations for the exact P-wave reflectivity RP of ice overlying bedrock, sediment and water, and englacial interfaces between isotropic and VTI ice. We found that the approximations of Aki-Richards, Shuey, and Fatti match exact glacier bed reflectivity to within RP±0.05, smaller than the uncertainty in typical glaciological AVA analyses, but only for maximum incident angle θi limited to 30°. A stricter limit of θi≤20° offered comparable accuracy to a hydrocarbon benchmark case of shale overlying gas-charged sand. The VTI-compliant Rüger approximation accurately described englacial reflectivity, to within RP±0.01, and it can be modified to give a quadratic expression in sin2(θi) suitable for curve-matching operations. Having shown the circumstances under which AVA approximations were valid for glaciological applications, we have suggested that their interpretative advantages can be exploited in the future AVA interpretations.



Item Type
Article
Authors
Divisions
Primary Division
Programs
Primary Topic
Peer revision
ISI/Scopus peer-reviewed
Publication Status
Published
Eprint ID
38815
DOI 10.1190/geo2015-0187.1

Cite as
Booth, A. D. , Emir, E. and Diez, A. (2016): Approximations to seismic AVA responses: Validity and potential in glaciological applications , Geophysics . doi: 10.1190/geo2015-0187.1


Share


Citation

Research Platforms
N/A

Campaigns


Actions
Edit Item Edit Item