M. Finnemore

Recent deformation of Quaternary sediments in the northwest Canterbury Plains, New Zealand, as inferred from GPR and seismic data

A high-resolution seismic reflection survey in the northwest Canterbury Plains, New Zealand, has revealed a network of interconnected faults and folds underneath the seemingly undisturbed flat surface. Known rates of background seismicity in the larger area suggest ongoing deformation in the Plains, despite a lack of convincing surface expression. Ongoing deformation would be seen as disturbance of the uppermost Quaternary sediments. Unfortunately, the resolution of the seismic reflection data falls short in adequately imaging these uppermost sediments. Accordingly, we have collected > 31 kilometers of 50 MHz GPR data to provide complementary images of the uppermost Quaternary sediments. Final images show GPR-facies over the full depth range, indicative of braided river sediments. GPR images together with seismic refraction tomographic images also reveal locations where the youngest Quaternary sediments are deformed. Youngest deformation is observed only where folded Cretaceous-Tertiary and Permian-Triassic units come close to the surface.