Active Tectonic and Paleoseismic Investigation of the Lower Mikonui Valley in Westland, New Zealand
Thesis DisciplineEngineering Geology
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
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.