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Migration of reflector orientation attributes in deep seismic profiles: evidence for decoupling of the Yilgarn Craton lower crust

Abstract. Interpretation of deep seismic data is challenging due to
the lack of direct geological constraints from drilling and the more limited
amount of data available from 2-D profiles in comparison to hydrocarbon
exploration surveys. Thus other constraints that can be derived from the
seismic data themselves can be of great value. Though the origin of most
deep seismic reflections remains ambiguous, an association between seismic
reflections and crustal strain, e.g. shear zones, underlies many
interpretations. Estimates of the 3-D orientation of reflectors may help
associate specific reflections, or regions of the crust, with geological
structures mapped at the surface whose orientation and tectonic history are
known. In the case of crooked 2-D onshore seismic lines, the orientation of
reflections can be estimated when the range of azimuths in a common midpoint
gather is greater than approximately 20∘, but integration of these
local orientation attributes into an interpretation of migrated seismic data
requires that they also be migrated. Here we present a simple approach to
the 2-D migration of these orientation attributes that utilizes the apparent
dip in reflections on the unmigrated stack and maps reflector strike, for
example, to a short linear segment depending on its original position and a
migration velocity. This interpretation approach has been applied to a
seismic line shot across the Younami Terrane of the Australian Yilgarn
Craton and indicates that the lower crust behaved differently from the
overlying middle crust as the newly assembled crust collapsed during the
Late Archean. Some structures related to approximately east-directed
shortening are preserved in the middle crust, but the lower crust is
characterized by reflectors that suggest N-NNE-oriented ductile flow.
Deployment of off-line receivers during seismic acquisition allows the
recording of a larger range of source-receiver azimuths and should produce
more reliable future estimates of these reflector attributes.
