Active Tectonic and Paleoseismic Investigation of the Lower Mikonui Valley in Westland, New Zealand
Type of content
Publisher's DOI/URI
Thesis discipline
Degree name
Publisher
Journal Title
Journal ISSN
Volume Title
Language
Date
Authors
Abstract
This study investigates an active southeast-dipping reverse fault mapped in the lower reaches
of the Mikonui River in Westland, New Zealand. The fault, referred to as the Lower Mikonui
Fault, and the nearby Flagstaff Fault, are mapped as splays of the South Westland Fault.
Field investigations for this study have included geological and geomorphological mapping,
shallow depth hand auger hole logging and MSAW surveying. These have been combined with
previous data from mining reports and borelog collections conducted in the Mikonui Valley to
map local geology associated with the Lower Mikonui Fault, Flagstaff Fault, and South
Westland Fault in this area.
Optically Stimulated Luminescence (OSL) dating has been used to provide age constraints of
the rupture history of the active Lower Mikonui Fault from an excellent exposure along the
east bank of the lower Mikonui River. A reconstruction of the fault’s Late Quaternary
deformation, paleoseismicity and current hazard potential have been created which indicate
at least three ruptures in the last ~60,000 years, each with ~1m of vertical displacement and
an average dip slip rate of 0.15±0.05 mm/yr. The Lower Mikonui Fault is estimated to be
capable of at least 6.8±0.5 M earthquakes.
A new location in the Mikonui Valley for the main splay of the South Westland Fault is
proposed, which strongly implies that the South Westland Fault and Hohonu Fault are the
southern and northern parts of a single, longer, fault zone structure. The Lower Mikonui Fault
and the Flagstaff Fault are interpreted as splays of the South Westland/Hohonu Fault Zone.