Interval Anisotropic Parameter Estimation Using Velocity-independent Layer Stripping
Moveout analysis of long-spread P-wave data is widely used to estimate the key time-processing parameter η in layered VTI media. Inversion for interval η values, however, suffers from instability caused by the tradeoff between the effective moveout parameters and by the subsequent error amplification during Dix-type layer stripping. Here, we propose an alternative approach to interval parameter estimation based on the velocity-independent layer-stripping method of Dewangan & Tsvankin (2006). This method makes it possible to compute the interval moveout in a layer of interest without knowledge of the medium parameters in the overburden. Then the interval traveltimes are inverted for the normal-moveout velocity (Vnmo) and η using the single-layer nonhyperbolic moveout equation. Thus, the layer stripping of η in the conventional method is replaced by the much more stable stripping of reflection traveltimes. We also develop the 3D version of the layer-stripping method and apply it to interval parameter estimation for orthorhombic media using wide-azimuth P-wave data. The superior accuracy and stability of our algorithm is illustrated on ray-traced synthetic data for typical layered VTI and orthorhombic models. Even small correlated noise in reflection traveltimes produces substantial distortions in the effective η, and for some models, even in the effective Vnmo. As a result, the inter val η values estimated by the conventional Dix-type method may be highly inaccurate. In contrast, the output of our layer-stripping algorithm proves to be insensitive to mild correlated traveltime errors. The algorithm is also tested on wide-azimuth P-wave reflection data recorded above a fractured reservoir at Rulison field in Colorado. The interval moveout parameters estimated by the velocity-independent layer stripping in the shale layer above the reservoir are more plausible and stable than those obtained by the Dix-type method.
Non‐hyperbolic moveout inversion of wide‐azimuth P‐wave data for orthorhombic media
The azimuthally varying non‐hyperbolic moveout of P‐waves in orthorhombic media can provide valuable information for characterization of fractured reservoirs and seismic processing. Here, we present a technique to invert long‐spread, wide‐azimuth P‐wave data for the orientation of the vertical symmetry planes and five key moveout parameters: the symmetry‐plane NMO velocities, V(1)nmo and V(2)nmo, and the anellipticity parameters, η(1), η(2) and η(3). The inversion algorithm is based on a coherence operator that computes the semblance for the full range of offsets and azimuths using a generalized version of the Alkhalifah–Tsvankin non‐hyperbolic moveout equation.
The politics of becoming bodies: Sex, gender and intersubjectivity in motion
Abstract This paper presents readers with one (research) story about (sexed and gendered) bodies not as objects with inherent boundaries and properties but as material-discursive phenomena. In telling such a story I examine the role that the screendance, Becoming Bodies , has played in knowledge production and argue for a less ontologically ‘old fashioned’ view of what counts as ‘evidence’. Throughout the paper I draw from a range of feminisms: biological, phenomenological, poststructural, psychoanalytical, and post humanist and performative scholarship of sex and gender. These discourses contest nature/nurture, male/female, body/mind dualisms, and take the political and ethical view that bodies are not neutral; that sex and gender, being a woman or a man are both socially and biologically constructed forms of identity (similar to class and race) that are acquired and learned through socio-cultural regimes of discipline and intersubjective bodily practices. Building on this dynamic and developmental bio-psycho-social view I discuss selected aspects of interview data: (1) the material-discursive tensions and contradictions of sexing and gendering bodies and (2) troubling the intersubjective implications of this for clinical practices.