Cutten, H.N.C. 1988 Structure of the Cretaceous and Tertiary sediments in the vicinity of the Mohaka, Te Hoe River junction, Western Hawkes Bay. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EDS 115 47 p.
Abstract: The area of investigation is located in Western Hawkes Bay, East Coast, North Island, New Zealand, around the junction of the Mohaka and Te Hoe rivers. The area lies on the western margin of the East Coast Deformed Belt (Walcott 1978a) at the edge of the Forarc Basin of the Accretionary Borderland (Cole & Lewis 1981) of the subducting Pacific Plate. The Mohaka Fault separates Cretaceous and Tertiary sediments from Torlesse greywacke basement of the axial ranges, containing the Ruahine Fault 14 km further west. A fold and fault zone, approximately 8 km wide, lies east of and trends parallel to the Mohaka Fault. Structural analysis of folding of Tertiary rocks within this zone suggests folding is a less competent response to faulting in the underlying basement greywacke. Ngatapa syncline is located immediately east of the Mohaka Fault with an overturned western limb and axial plane which parallels dip of the Mohaka Fault. Dam site Anticline, 4 km further eat, has an overturned eastern limb and is considered to have formed over a steeply dipping reverse basement fault (Dam Site Fault) which is non-emerged and lies beneath the fold. An earlier phase of folding (middle Miocene) indicates a compression direction between NE-SW and EW which is broadly consistent with the movement vector of the Pacific Plate from Miocene to present. Subsequent oblique slip on the Mohaka and Dam Site faults under the same compression regime produced the fold and fault zone which parallels the Mohaka Fault. A scissor fault (Te Hoe Fault) which dies out to the south is postulated and trends NW-SE, oblique to the Mohaka Fault. Late Quaternary river terraces as old as 16 000 years B.P., along the Mohaka River appear undeformed by the Dam Site Fault and the Te Hoe Fault. The Dam Site Fault has the potential for near future seismic movement as it may join the Mohaka Fault (which moved 2-3 times in the last 1800 years) at depth, and certainly lies within the same tectonic regime.
