Post-Miocene faults in Auckland: insights from borehole and topographic analysis

Abstract

Although experiencing some seismicity, the Auckland region is generally considered to be one of New Zealand's most tectonically stable areas. There is a distinct lack of mapped faults in the central Auckland area, yet regional trends indicated by several mapped faults surrounding it suggest that these faults should continue through Auckland. The overprint of Auckland Volcanic Field (AVF) deposits may mask any potential fault traces in the area. We carried out a detailed study of the topography of Auckland concealed beneath the AVF deposits, using borehole and geophysical data, and combined this with structural information gleaned from current topography and exposed geology to identify significant concealed fault offsets. The reliability of each potential fault displacement was determined using pre-defined attributes. The resulting block faulting model for Auckland supports the proposed connection between the position of the Junction Magnetic Anomaly and Auckland volcanism. The identification of several possible faults in the area covered by the AVF might indicate more structural control on volcanism than previously thought.