We show that SV-P reflectivity closely matches P-SV reflectivity; thus, in concept, an SV-P image should be as informative and as valuable as a P-SV image for seismic interpretation purposes. If the dip of rock layering is not severe, the length of the SV raypath involved in SV-P imaging is approximately the same as the length of the SV raypath in P-SV imaging; thus, the important lithology-sensitive V P ∕V S velocity ratio determined with SV-P data should be approximately the same as the V P ∕V S velocity ratio determined with P-SV data. We compare velocities used in P-SV imaging and SV-P imaging to emphasize the equivalence of P-SV and SV-P stacking velocities, and therefore seismic-derived V P ∕V S velocity ratios, obtained with both converted-wave modes. We compare images of P-SV and SV-P data to illustrate the high-quality images that can be made with a SV-P mode. The SV-P data used in these comparisons are recorded by vertical geophones, whereas the P-SV data are recorded by horizontal geophones. In the real-data examples we present, the energy sources that produced the downgoing SV wavefield are vertical-force sources, not horizontal-force sources. A vertical vibrator is used in the first case, and shot-hole explosives are used in the second case. The interpretation technology described here thus introduces the option of extracting valuable S-wave information and images from legacy P-wave data generated by a vertical-force source and recorded with only 1C vertical geophones. We discuss several principles involved in constructing SV-P images from VSP data because of the importance that VSP technology has in calibrating depth-based geology with surface-recorded SV-P data. We emphasize that cautious and attentive data processing procedures are required to segregate SV-P reflections and P-P reflections in VSP data.

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We inverted P-wave amplitude variation with offset and azimuth (AVOAz) data from the Marcellus Shale to obtain fracture parameters that can fully describe the elastic behavior of fractured rocks with overall symmetry of orthorhombic or monoclinic. AVOAz data from two interfaces, (1) the upper interface between top Marcellus and Stafford limestone and (2) the lower interface between base Marcellus and Onondaga limestone, were used for inversion. To check the validity of our inversion results, fracture parameters for the Marcellus Shale were inverted for each interface using Monte Carlo simulation to include uncertainty in our a priori information, i.e., elastic properties of unfractured rocks that are assumed to be known from well logs. Inversion results appeared robust with respect to uncertainties and converge to the same values for the two inversions. Our results were also consistent with singular value decomposition analysis (resolution matrix).

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