Estimating vertical displacement within the Ngakuru Graben, New Zealand, using 2-D and 3-D georadar

In an attempt to map the shallow geometry of the Maleme Fault Zone (North Island, New Zealand) and estimate vertical displacements of selected fault strands, we have collected 2-D and 3-D georadar data using 100MHz antennas. The 2-D data consisted of three parallel georadar lines recorded perpendicular to the graben axis. These lines, which were 7.5 m apart and -160111 long, crossed several fault strands on either side `of the graben axis. The processed georadar sections showed two prominent subhorizontal reflections that most likely originated, as known from calibration measurements in a nearby outcrop, from Late Pleistocene tephras. Vertical offsets of these reflections and strong diffraction patterns correlated with individual fault strands visible at the surface. This has allowed us to est imate vertical displacements at individual fault strands. The 3-D georadar data set, recorded across a -70 x -20 m area to one side of the graben axis, provides further details associated with stratigraphy and fault zone.