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Post Info TOPIC: Alpine Fault
Blobrana


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Title: New on-fault evidence for a great earthquake in A.D. 1717, central Alpine fault, New Zealand
Authors: G.P. De Pascale and R.M. Langridge

The dextral-reverse Alpine fault is the major onshore plate-boundary structure between the Australian and Pacific plates in New Zealand. No previous study of the central portion of the 200-km-long central segment has provided on-fault evidence for the most recent event (MRE). Using lidar (light detection and ranging) data coupled with field mapping, we recognized the main trace of the Alpine fault north of Gaunt Creek (South Island) as a north-striking fault scarp. We enhanced a natural exposure that revealed evidence for repeated late Holocene thrust fault movement. The north-northwest-striking fault zone is characterized by a distinct 5-50-cm-thick clay fault-gouge layer juxtaposing hanging-wall bedrock (mylonites and cataclasites) over unconsolidated late Holocene footwall colluvium. The bedrock is cut by a strath terrace and overlain by mid-Holocene (ca. 5400 calibrated 14C yr B.P.) alluvial terrace, which has been faulted repeatedly and is conformably overlain by undeformed late Holocene colluvium and alluvium. An unfaulted peat at the base of the scarp is buried by post-MRE alluvium and yields a calibrated 2Sigma radiocarbon age of A.D. 1710-1930, which dates the MRE as post-1709. Our data are consistent with sparse on-fault data, and validate earlier off-fault records that suggest an A.D. 1717 MRE. The 1717 event had a moment magnitude of Mw 8.1 ± 0.1, based on the 380-km-long surface rupture. Because the fault has not ruptured for ~300 yr, it is likely approaching the end of its seismic cycle and poses a significant seismic hazard to New Zealand.

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Blobrana


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Alpine Fault study co-authored by University of Nevada, Reno's Glenn Biasi shows new evidence for regular magnitude 8 earthquakes

A new study published in the prestigious journal Science, co-authored by University of Nevada, Reno's Glenn Biasi and colleagues at GNS Science in New Zealand, finds that very large earthquakes have been occurring relatively regularly on the Alpine Fault along the southwest coastline of New Zealand for at least 8,000 years.
The Alpine Fault is the most hazardous fault on the South Island of New Zealand, and about 80 miles northwest of the South Island's main city of Christchurch.
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Blobrana


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New research out today reveals that the Alpine Fault - a strike-slip fault running almost the entire length of the South Island - is surprisingly "well-behaved" in its regularity.
But good behaviour, in a scientific sense, may not bring much comfort to South Islanders.
In earthquake terms, the 850km-long fault is remarkably consistent, rupturing on average each 330 years, at intervals ranging from 140 years to 510 years.
The last major quake on the fault occurred 295 years ago, according to the GNS Science researchers who have compiled an 8000-year timeline of 24 major quakes on the fault from sediments at Hokuri Creek, near Lake McKerrow in north Fiordland.
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