Tilting of active folds and faults in the Manawatu region, New Zealand: Evidence from surface drainage patterns

Abstract

We examine the drainage system on four anticlinal ridges in Manawatu that affect a mid‐Quaternary (c. 300 000 yr old) marine horizon. The folds are all located above buried, west‐dipping, reverse faults in the basement that are c. 15–20 km long and capable of generating earthquakes of c. M_W 6.5–7.0. The drainage systems allow us to distinguish a regional tectonic tilt from the normal plunge of an anticline axis towards its end. We estimate tilt rates of around 4 × 10^‐8 rad/yr towards the south averaged over the last c. 300 000 yr. The regional tilting is related to the development and southward migration of the Pliocene‐Pleistocene depocentre in the offshore South Wanganui Basin.