Rate of co‐seismic strain release in the northern South Island, New Zealand

Pearson, Chris

doi:10.1080/00288306.1993.9514565

Cited by 9 publications

(5 citation statements)

References 26 publications

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“…Figure 8 shows the results of strain determinations located near the study area. For all of these networks, the principal axes of horizontal contraction are within 2 SE of 110" Similar orientations have been reported for the geodetu strain determinations for the Haast area immediateh southwest of the study area (Pearson 1991) and from summed moment tensors for large historic earthquakes on the Marlborough faults (Pearson 1993). The fact that the principal axes of horizontal contraction shown in Fig.…”

Section: The Godley Earthquake Of 1984supporting

confidence: 52%

Geodetic strain determinations from the Okarito and Godley‐Tekapo regions, central South Island, New Zealand

Pearson

1994

New Zealand Journal of Geology and Geophysics

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This paper presents geodetic strain rate determinations from the Okarito area of South Westland aid the Godley Valley region in western Canterbury.In the Okarito area, the triangulation network extends from c. 10 km west of the Alpine Fault to 1 km east of the fault. To examine the distribution of strain about the fault, 1 broke the data into two subnetworks. One of the networks includes all stations located west of the Alpine Fault, and the other includes two stations located west of the fault and two stations located near the fault on the east.Geodetic strain rates for the two networks are similar. In the western network, the maximum (engineering) shear strain rate is 0.85 ± 0.15 µrad/yr and the azimuth of principal axis of relative contraction is 119° ± 4, whereas in the e.istern network the maximum (engineering) shear strain rate is 0.62 ± 0.11 µrad/yr and the azimuth of the principal axis of relative contraction is 115° ± 6. Errors are to the 1 SE level of confidence. Results of the strain determinations indicate that high shear strain rates are not restricted to networks that cross the surface trace of the Alpine Fault.In the Godley Valley, the maximum (engineering) shear strain rate is 0.28 ± 0.14 urad/yr and the azimuth of the principal axis of relative contraction is 116° ± 14, similar to other measurements from the eastern side of the Alps. The strain rate from the northern half of the area is much higher, however. A subnetwork extending from the northern end of the Godley Valley (within a few kilometres of the Main Divide) to the confluence with the Macauley River gives 0 62 ± 0.19 for the maximum (engineering) shear strain rate and 92° ± 9 for the azimuth of the principal axis of relative contraction. The Godley earthquake of 1984, with a moment magnitude of 6.1, occurred within a few kilometres of the subnetwork and may possibly have affected the results.The azimuth of the principal axis of relative contraction is within ±2 SE of 110° for the whole central Southern Alps. This direction is consistent with transpressional movement on the Alpine Fault and the NUVEL-1 relative plate motion vectors for the Pacific-Australian plate pair.

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Section: The Godley Earthquake Of 1984supporting

confidence: 52%

Geodetic strain determinations from the Okarito and Godley‐Tekapo regions, central South Island, New Zealand

Pearson

1994

New Zealand Journal of Geology and Geophysics

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“…Farther north, at the transition between continental collision and subduction on the Hikurangi Trench, the plate boundary zone broadens and the Alpine fault is joined by the Marlborough faults, a series of major northeast-southwest trending strike-slip faults that accommodate most of the relative plate motion [e.g., Berryman et al, 1992]. The Hope fault, the southernmost of the recognized Marlborough faults, is also the most active, with slip rates of 20-25 mm/yr, which is more than twice the rate for any of the northern faults Historical seismic activity in the South Island is concentrated on the Marlborough faults and adjacent areas northwest of the Alpine fault, where five magnitude 7 or greater earthquakes have occurred since 1840 [Anderson et al, 1993;Pearson, 1993]. There are no historically recorded large earthquakes on the Alpine fault itself [Eiby, 1968a, b].…”

Section: Tectonicsmentioning

confidence: 99%

“…In the single-fault twodimensional model, the Alpine fault was treated as an infinitely long, 50 ø dipping fault locked between the surface and 12-km depth, with the full NUVEL-1A plate velocity resolved onto the freely slipping fault plane below 12 km. The 50 ø dip is based on numerous measurements by Sibson et al [1979], while the 12-km locking depth is a reasonable estimate for the seismogenic thickness in this part of the South Island [Pearson, 1993]. Slip rates were taken to be 18 mm/ W'"'----•.…”

Section: Dislocation Models For the Alpine Faultmentioning

confidence: 99%

Strain distribution across the Australian‐Pacific plate boundary in the central South Island, New Zealand, from 1992 GPS and earlier terrestrial observations

Pearson¹,

Beavan²,

Darby³

et al. 1995

J. Geophys. Res.

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As part of a geodetic experiment aimed at understanding the deformation associated with the Australian‐Pacific plate boundary in the South Island of New Zealand, in 1992 we reoccupied using Global Positioning System (GPS) techniques a first‐order triangulation and trilateration network established in 1978 between Christchurch on the east coast and Hokitika on the west. The network crosses the South Island a few tens of kilometers southwest of the region where the plate boundary changes from a single, throughgoing oblique slip fault, the Alpine fault, to a series of subparallel strike‐slip faults, the Marlborough faults. The GPS data have been analyzed as daily network solutions, with about 12 stations in each solution. RMS repeatabilities for stations with multiple occupations are 4 mm, 8 mm, and 15 mm in the north, east, and vertical components, respectively. The observed strain across the network is consistent with the entire NUVEL‐IA Pacific‐Australia plate velocity being accommodated on land across this part of the South Island. Shear strain rates derived from the GPS and terrestrial data show that the highest strain rate (> 0.4 μrad/yr) occurs in the region of the Southern Alps and Alpine fault. This rate is about two thirds of the rate predicted from the NUVEL‐IA plate velocity model assuming that all the plate boundary deformation occurs across this region, implying that about two thirds of the plate motion is accommodated in the vicinity of the Alpine fault. Significant shear strain rates greater than 0.2 μrad/yr are also observed farther east, particularly in the region of the Porters Pass‐Amberley fault zone, demonstrating that this zone accommodates a significant part of the plate boundary deformation. Using dislocation modeling, we show that the variation in fault‐parallel shear strain rates across the Alpine fault is reasonably consistent with a nonoptimized dislocation model involving a 50° dipping fault that is presently locked to a depth of ∼12 km. One explanation for this observation is that the upper ∼12 km of the crust in this area is storing most of the right‐lateral shear component of the relative plate motion as elastic energy that will be released in a future major earthquake. The variation in the other component of shear strain, which may be interpreted as fault‐normal relative contraction, is not explained by a simple dislocation model, implying that the normal component of plate motion is taken up in other ways.

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“…However, definitive evidence for active fault slip and slip-rates within the central Southern Alps is lacking-probably due to extreme erosion rates and consequent lack of preserved tectonic features. The presence of elevated topography and earthquakes provides indirect yet strong evidence that at least some of the observed contemporary deformation must be permanent in this region (Pearson 1993;Leitner et al 2001). Estimated uplift and exhumation rates vary across the Southern Alps, from c. 1 mm/yr in the southeast near Lake Pukaki (beneath the seismic line), to c. 6-10 mm/yr immediately adjacent to the Alpine Fault where the rainfall and erosion rates are much higher (e.g.…”

Section: Tectonic Settingmentioning

confidence: 99%

Upper crustal structure beneath the eastern Southern Alps and the Mackenzie Basin, New Zealand, derived from seismic reflection data

Long

Cox

Bannister

et al. 2003

New Zealand Journal of Geology and Geophysics

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Rate of co‐seismic strain release in the northern South Island, New Zealand

Cited by 9 publications

References 26 publications

Geodetic strain determinations from the Okarito and Godley‐Tekapo regions, central South Island, New Zealand

Geodetic strain determinations from the Okarito and Godley‐Tekapo regions, central South Island, New Zealand

Strain distribution across the Australian‐Pacific plate boundary in the central South Island, New Zealand, from 1992 GPS and earlier terrestrial observations

Upper crustal structure beneath the eastern Southern Alps and the Mackenzie Basin, New Zealand, derived from seismic reflection data

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