Detailed shallow geometry and vertical displacement estimates of the Maleme Fault Zone, New Zealand, using 2D and 3D 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 2D and 3D georadar data using 100 MHz antennae. The 2D data consisted of three parallel georadar lines recorded perpendicular to the axis of the well-defined graben of the Maleme Fault Zone. These ~160 m long lines, which were 7.5 m apart, crossed several fault strands on either side of the graben axis. The processed georadar sections revealed two prominent parallel reflections that originated from the boundaries of Late Pleistocene lacustrine and tephra deposits. Distinct vertical offsets of these reflections allowed us to estimate displacements at individual fault strands across the entire inner graben. The total displacements represented by these offsets was ~10–20 % greater than that inferred from geomorphological studies, thus demonstrating the limitations of surface observations for determining cumulative fault movements. The 3D georadar data set, recorded across an area of ~70×~20 m to one side of the graben axis, provided key details on individual fault strands. For the 3D visualization of fault-related structures, various spatial attribute analyses based on the cosine of the instantaneous phase proved to be useful.