Active tectonics west of New Zealand's Alpine Fault: South Westland Fault Zone activity shows Australian Plate instability

Abstract

The 300 km long South Westland Fault Zone (SWFZ) is within the footwall of the Central Alpine Fault (<20 km away) and has 3500 m of dip‐slip displacement, but it has been unknown if the fault is active. Here the first evidence for SWFZ thrust faulting in the “stable” Australian Plate is shown with cumulative dip‐slip displacements up to 5.9 m (with 3 m throw) on Pleistocene and Holocene sediments and gentle hanging wall anticlinal folding. Cone penetration test (CPT) stratigraphy shows repeated sequences within the fault scarp (consistent with thrusting). Optically stimulated luminescence (OSL) dating constrains the most recent rupture post‐12.1 ± 1.7 ka with evidence for three to four events during earthquakes of at least Mw 6.8. This study shows significant deformation is accommodated on poorly characterized Australian Plate structures northwest of the Alpine Fault and demonstrates that major active and seismogenic structures remain uncharacterized in densely forested regions on Earth.

A 2000 Yr Paleoearthquake Record along the Conway Segment of the Hope Fault: Implications for Patterns of Earthquake Occurrence in Northern South Island and Southern North Island, New Zealand

“…These latter, smaller magnitude events would not be recorded in paleoseismic trenches, but may be recovered in offfault records of lake seismites [DePascale et al, 2014;Howarth et al, 2018]. Given the fact that these records of lake seismites are off-fault records of Alpine fault seismicity, it remains possible that these seismities represent earthquakes with sources on faults adjacent to the Alpine fault, of which many have been documented [e.g., Cox et al, 2012;DePascale et al, 2016]. We denote this uncertainty as a more transparent box for possible-sequence 3 on Figure 7.…”

Heterogeneity in Microseismicity and Stress Near Rupture‐Limiting Section Boundaries Along the Late‐Interseismic Alpine Fault

“…We observe no seismicity clearly associated with the steeply SE‐dipping South Westland Fault Zone (SWFZ, Figure 2), which De Pascale et al. (2016) suggested to represent a major source of seismic hazard within the Australian Plate due to the large, accumulated offsets on it farther north.…”

Structure and kinematics of active faulting in the northern domain of Western and Central Alborz, Iran and interpretation in terms of tectonic evolution of the region

“…In arid regions (e.g., the Wadi Araba basin in Egypt; the Gobidesert in NW China; the Lut desert in eastern and southern Iran), we can describe the faults with a level of detail that is not possible in the humid region. However, in the humid area, most of the tectonic geomorphic features are obscured due to the dense vegetation, as are forest covers (e. g., Tsereteli et al, 2016;De Pascale et al, 2016;Chen et al, 2015;Selim et al, 2013;Goswami et al, 2009). Therefore, studies of the active tectonics in the region with dense vegetation-forest as the Alborz, have to involve lots of field visits, an approach described here.…”