Article
Palaeoseismic constraints on Holocene surface ruptures along the Ostler Fault, southern New Zealand
New Zealand Journal of Geology and Geophysics
(2011)
Abstract
Palaeoseismic trenching along the central Ostler fault zone reveals the nature and timing of past surface-rupturing earthquakes. A 26 m long trench excavated into a last-glacial (26.5 ka) outwash surface cut by the Ruataniwha strand of the North Central Ostler fault reveals evidence for at least two metre-scale surface displacements in the last c. 8 ka. Detailed logging of colluvial wedge and alluvial stratigraphy, combined with optically stimulated luminescence dating of loess within colluvial packages, provides a maximum bound on the most recent earthquake (MRE) of 2.3–4.5 ka. The MRE resulted in a surface displacement of at least 1.8 m, consistent with an estimated moment magnitude (M) 6.9–7.1 earthquake based on the total 60 km length of the Ostler fault zone. The penultimate event occurred sometime before 4.1–8.4 ka and resulted in a comparable or larger surface displacement. Similar ages from samples collected in previous trenches on the Ostler fault suggest that surface ruptures may persist across kilometre-scale stepovers defined by the active surface trace of the fault. At the trench scale, comparison between dip slip calculated from topographic fault-scarp profiling (7.8 m) and the total offset of exposed outwash gravels (6.0 m) suggests that surface folding immediately adjacent to the fault scarp accommodates roughly 25% of the total slip. Given a previously reported recurrence interval of c. 2–5 ka for the Ostler fault, the presence of only 2–3 palaeoearthquakes on the 26.5 ka outwash surface indicates that additional events likely occurred on nearby fault scarps in an overall complex zone of surface faulting.
Keywords
- earthquake recurrence,
- luminescence dating,
- neotectonics,
- Ostler fault,
- palaeoseismicity,
- seismic hazard,
- Southern Alps
Disciplines
- Geology and
- Geomorphology
Publication Date
2011
DOI
10.1080/00288306.2011.601746
Publisher Statement
Copyright by Informa UK Limited
Citation Information
Amos, C.B., J.J. Lapwood, D.C. Nobes, D.W. Burbank, U. Rieser, and A. Wade (2011) Palaeoseismic constraints on Holocene surface ruptures along the Ostler Fault, southern New Zealand, New Zealand Journal of Geology and Geophysics, v. 54, no. 4, p. 367-378, doi: 10.1080/00288306.2011.601746.