A field test of 3D reflection orientation analysis along a 2D crooked line in northern Finland supplemented with additional cross-spreads

Reflection seismics is indispensable for understanding the structural framework of the crust and providing important constraints on mineral system studies. The non-uniqueness inherent in interpreting data from2D crooked seismic profiles acquired over complex geological structures can be reduced by performing 3D reflector orientation analysis (Calvert, 2017), but this requires good azimuthal coverage, which can be enhanced with the deployment of cross-spreads. A new 70-km long reflection seismic profile was acquired across the Palaeoproterozoic Peräpohja belt in northern Finland to shed new light on its structural framework and contribute to development of the new national mineral exploration program. Single-receiver and single-source acquisition was implemented, resulting in excellent data quality. Survey layout was optimized to extract 3D reflector orientations, and included eight additional cross-spreads extending up to 5 km from the survey line spaced every 7-8 km.

3D reflector orientation analysis was performed for both the inline data (i.e. along the main profile) as well as with the cross-spreads included. The main challenge to processing these data is obtaining an optimal refraction statics solution: in the first pass, a combination of 2D inline statics with 2D statics for each cross-spreads was applied. In the second pass, a 3D tomostatics solution was obtained for the complete dataset. The initial results of the reflection orientation analysis suggests that while the additional effort in acquiring the cross-spreads may not be justified for obtaining the structural image (cross-spreads bring more noisy data), orientation attributes (dip and strike) are better resolved, especially at shallower levels, and where gaps in azimuthal coverage are present (i.e. the profile was too straight). With current acquisition capabilities, cross-spreads can be acquired in a cost-effective manner, yet they should be carefully planted to provide reasonable signal-to-noise ratio data, essential for 3D statics and for the orientation analysis itself.

The new seismic data were acquired as a part of the REPower-CEST “Clean Energy System Transition” project, which received funding by the European Union (number 151, P5C1I2, NextGenerationEU).