Australia: The Land Where Time Began

A biography of the Australian continent 

The Central Alpine Fault, New Zealand, New On-Fault Evidence of a Great Earthquake in AD 1717

The major plate boundary structure between the Australian Plate and the Pacific Plate that is onshore in New Zealand is the Alpine Fault, which is dextral-reverse. This is the first study of the central portion of the  central segment that is 200 km long that has provided on-fault evidence of the most recent event (MRE). Lidar (light detection and ranging) data was used, coupled with field mapping, to allow the recognition of the main trace of the Alpine Fault to the north of Gaunt Creek, South Island, as being a fault scarp striking to the north. Evidence of repeated thrust fault movement in the Late Holocene was revealed by the enhancement of a natural exposure. A distinct clay fault-gouge layer, that is 5-50 cm thick, characterises the north-northwest-striking fault zone, that is juxtaposed to a hanging wall bedrock (mylonites and cataclasites) over footwall colluvium from the Late Holocene that is unconsolidated. A strath terrace cuts the bedrock and above it is a alluvial terrace, about 5,400 BP (calibrated 14C years), which has been repeatedly faulted and which is overlain conformably by undeformed alluvium and colluvium from the Late Holocene. At the base of the scarp an unfaulted peat is buried by post-MRE alluvium yielding a calibrated 2σ radiocarbon age of AD 1710-1930, which dates the MRE as post-1709. The data obtained by the authors1 is consistent with the sparse on-fault data, and validated off-fault records suggesting an AD 1717 event that had a moment magnitude of Mw 8.1 ± 0.1, that is based on a surface rupture that is 380 km long. The fault has not ruptured for about 300 years so is believed likely to be approaching the end of its seismic cycle, suggesting it poses a significant seismic hazard to New Zealand.

Sources & Further reading

  1. De Pascale, G.P., and R.M. Langridge. "New on-Fault Evidence for a Great Earthquake in A.D. 1717, Central Alpine Fault, New Zealand." Geology 40, no. 9 (September 1, 2012 2012): 791-94.

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Tsunamis - New Zealand's Underrated Hazard

Author: M. H. Monroe
Last Updated 04/07/2013
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