Document Type
Article
Publication Date
4-2012
Keywords
Strata and fault relationships, surface-faulting events, surface-rupture recurrence interval
Abstract
Abstract Strata and fault relationships revealed in five trenches excavated across the recent trace of the Alpine fault at the Haast, Okuru, and Turnbull Rivers, South Westland, New Zealand, record the three most recent surface-faulting events. Using back-stripping techniques to remove the three faulting events and the sedimentary units associated with the faulting restores the cross-sections to gravel-bed floodplains at the Haast and Okuru Rivers, at about A.D. 750. Horizontal and vertical offsets of stream channels and terrace risers reveal characteristic displacements of about 8–9 m dextral and up to 1 m vertical per event. Cumulative dextral displacement is 25 ± 3 m in the past three events. The most recent surface-rupture event was probably in A.D. 1717, and the next prior events were about A.D. 1230 ± 50 and about A.D.750 ± 50. The timing of these events is consistent with past large-great earth- quakes on the southern section of the Alpine fault inferred from off-fault data, but there are fewer events identified in trenches. Our three-event dataset indicates the aver- age surface-rupture recurrence interval for the South Westland section of the fault is about 480 years, much longer than the current elapsed time of 295 years. Therefore, the Alpine fault in South Westland may not be close to rupture as is often speculated.
Publication Title
Bulletin of the Seismological Society of America
Volume
102
Issue
2
First Page
620
Last Page
638
Required Publisher's Statement
Published by the Seismological Society of America
DOI: 10.1785/0120110177
Recommended Citation
Berryman, K., Cooper, A.F., Norris, R.J., Villamor, P., Sutherland, R., Wright, T., Schermer, E.R., Langridge, R., and Biasi, G., Late Holocene Rupture History of the Alpine Fault in South Westland, New Zealand, Bulletin Seismological Society of America 102:2, p 620-638, 2012 © Seismological Society of America
Subjects - Topical (LCSH)
Faults (Geology)--New Zealand--Westland District; Geomorphology--New Zealand--Westland District; Event stratigraphy--New Zealand--Westland District
Geographic Coverage
Westland District (N.Z.)
Genre/Form
articles
Type
Text
Language
English
Format
application/pdf
