Conference abstract on seismic reflector orientation analysis from the Yilgarn Craton (Western Australia):
Interpretation of seismic data in hard rock areas is challenging due to lack of direct geological constraints from drilling and the more limited data available typically available from sparse 2-D profiles in comparison to hydrocarbon exploration surveys. Estimates of the 3D orientation of reflectors can help associate specific reflections, or regions of the crust, with geological structures mapped at the surface whose orientation and tectonic history are known. Here we present a method analogous to semblance velocity analysis that utilizes varying source-receiver azimuths to derive continuous estimates of 3-D reflector orientations along onshore 2-D reflection profiles. For each zero-offset time within a common depth point supergather, the semblance is calculated along 3-D travel time curves, and the dip and strike of the most coherent reflection is determined. Relative errors in these angles are derived from the range of travel time curves that have semblance values greater than a specified fraction, for example 90%, of the maximum. The potential of the method is illustrated using a section from line 10GA-YU1 from the Youanmi Terrane of the Yilgarn Craton in Australia in which the original field data have been replaced with synthetic in-line and cross-line reflections. Reflector orientations are generally well recovered where the range of available source-receiver azimuths is greater than 20o, but the method fails at lower ranges where the seismic line is almost linear, a behavior that is also observed in analysis of field data. When this approach is applied to data from the 2019 seismic survey around Kalgoorlie in the Eastern Goldfields, the orientations of both moderately dipping volcanic stratigraphy and faults are recovered. Integration of these local orientation attributes into an interpretation of migrated seismic data requires that the orientations also be migrated. We use a simple approach to the 2-D migration of these attributes that utilises the apparent dip of 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. Deployment of off-line receivers during future seismic acquisition will allow the recording of a larger range of source-receiver azimuths that can produce more reliable estimates of these reflector attributes than is possible with the limited range of azimuths available from standard 2-D crooked-line acquisition.
This Abstract was submitted/presented to the Target 2023 Conference 28 July (https://6ias.org/target2023/)
