Determination of Poisson's ratio from pre-critical wide-angle seismic reflection data from the BABEL project

Abstract

S U M M A R YThe pre-critical wide-angle seismic reflection data collected during the BABEL survey using multireceiver spreads contain high-amplitude P-wave and modeconverted S-wave reflected arrivals. The two phases can be partially separated and their signal-to-noise ratio emphasized by exploiting the multifold nature and the increased sensitivity of velocity analysis afforded by these data to produce zero-offset-corrected stacked sections. Using these sections, a method has been developed to derive estimates of Poisson's ratio by optimizing the cross-correlation of P-wave and S-wave arrivals, and hence to constrain petrological models of the crust sampled by these data. Although the apparently high degree of temporal and spatial resolution of reflected arrivals that are visible within the stacked sections must be reduced to achieve a satisfactory degree of correlation robustness, the results shed some light on crustal petrology, and concur with existing estimates of Poisson's ratio for the Baltic shield.

Processing of pre-critical wide-angle seismic reflection data from the BABEL project

“…At the larger offsets, S-wave energy is produced at conversions at or near the seabed and can be successfully recorded. The S-wave energy can be treated in the same manner as the P-wave energy, and the combination of P and S may be used to derive information about the physical properties of the crust, such as Poisson's ratio (Law et al 1992). However, the finite offset gap between the wide-angle and normal-incidence data used here precludes their use as the basis for amplitude versus offset analysis (Lindsey 1992).…”

“…For example, the dips and thicknesses of tens of northward-dipping reflections within the lower crust just south and updip of clear mantle reflections have been confidently modelled using both ray-tracing and reflectivity methods (Lindsey & Snyder 1994). These models complement the more regional models developed from single-receiver stations recording the same shots at similar and larger offsets (BABEL Working Group 1993;Meissner et al 1992).…”

“…Refracted and reflected S-wave energy, as well as P-wave energy, was recorded. The object of processing and subsequent analysis was to use these 'pre-critical' data sets to merge the information about reflector geometries obtained from the normal-incidence reflection profiles with velocities obtained from regional, long-offset data collected along the same survey lines (also see Law, Snyder & Singh 1992;Matthews, Graham & Long 1992;McBride ei al. 1993;Lindsey & Snyder 1994).…”