New Insights from Lidar, Central Alpine Fault, New Zealand

RESEARCH

Scale dependence of oblique plate-boundary partitioning: New insights from LiDAR, central Alpine fault, New Zealand

Nicolas C. Barth1*, Virginia G. Toy1, Robert M. Langridge2, and Richard J. Norris1 1DEPARTMENT OF GEOLOGY, UNIVERSITY OF OTAGO, P.O. BOX 56, DUNEDIN, NEW ZEALAND 2GNS SCIENCE, P.O. BOX 30-368, LOWER HUTT, NEW ZEALAND

ABSTRACT

We combine recently acquired airborne light detection and ranging (LiDAR) data along a portion of the Alpine fault with previous work to defi ne the ways in which the plate-boundary structures partition at three different scales from <106 to 100 m. At the fi rst order (<106–104 m), the Alpine fault is a remarkably straight and unpartitioned structure controlled by inherited and active weakening processes at depth. At the second order (104–103 m), motion is serially partitioned in the upper ~1–2 km onto oblique-thrust and strike-slip fault segments that arise at the scale of major river valleys due to stress perturbations from hanging-wall topographic variations and river incision destabilization of the hanging-wall critical wedge, concepts proposed by previous workers. The resolution of the LiDAR data refi nes second-order mapping and reveals for the fi rst time that at a third order (103–100 m), the fault is parallel-partitioned into asymmetric positive fl ower structures, or fault wedges, in the hanging wall. These fault wedges are bounded by dextral-normal and dextral-thrust faults rooted at shallow depths (<600 m) on a planar, moderately southeast-dipping, dextral-reverse fault plane. The fault wedges have widths of ~300 m and are bounded by and contain kinematically stable fault traces that defi ne a surface-rupture hazard zone. Newly discovered anticlinal ridges between fault traces indicate that a component of shallow shortening within the fault wedge is accommodated through folding. A fault kinematic analysis predicts the fault trace orientations observed and indicates that third-order fault trace locations and kinematics arise independently of topographic controls. We constructed a slip stability analysis that suggests the new strike-slip faults will easily accommodate displacement within the hanging-wall wedge, and that thrust motion is most easily accommodated on faults oblique to the overall strike of the Alpine fault. We suggest that the thickness of footwall sediments and width of the fault damage zone (i.e., presence of weaker, more isotropic materials) are major factors in defi ning the width, extent, and geometry of third-order near-surface fault wedges.

LITHOSPHERE; v. 4; no. 5; p. 435–448 | Published online 11 July 2012 doi: 10.1130/L201.1

INTRODUCTION Airborne LiDAR data were collected in July with aerial photo interpretation and decades 2010 in a 1.5-km-wide by 34-km-long swath of previous geologic mapping, we explore the In the past 10 yr, airborne light detec- encompassing a portion of the heavily vegetated signifi cance of several orders of magnitude of tion and ranging (LiDAR) technology has Alpine fault (the major plate-boundary structure shallow transpressional partitioning observed been demonstrated to be an effective tool for in the South Island of New Zealand; Fig. 1) to on the oblique-slip central Alpine fault and pro- identifying active faults and assessing seis- better understand seismic hazards in the region. pose a new model for the geometry of structures mic hazards in a wide range of environments, The LiDAR survey extends roughly between observed at 103–100 m scales. including urban areas (northern Taiwan—Chan the townships of Franz Josef (which straddles et al., 2007; Houston, Texas—Engelkemeir a known surface trace of the Alpine fault) and GEOLOGIC AND TECTONIC SETTING and Khan, 2008), grassland and scrub (Cali- Whataroa. Within the study area, ~75% of fornia—Arrowsmith and Zielke, 2009; Zielke the terrain is covered by dense temperate rain The Alpine fault is the ~850-km-long et al., 2010; Hunter et al., 2011), and densely forest, with the remaining 25% dominated (~600 km onshore) major active transpressive vegetated forests (Washington—Harding and by lightly populated active river fl oodplains. plate-boundary structure in the South Island Berghoff, 2000; Haugerud et al., 2003; Cali- Within the latter, any evidence for a surface rup- of New Zealand (Fig. 1). It currently accom- fornia—Zacha riasen and Prentice, 2008; Slo- ture of the most recent Alpine fault earthquake modates ~75% of total motion between the venia—Cunningham et al., 2006). In particular, in A.D. 1717 (Yetton, 1998; Yetton et al., 1998) Pacifi c and Australian plates (Berryman et al., the ability of LiDAR to image the land surface has already been erased. The prospect of a 30% 1992; Norris and Cooper, 2001; Sutherland beneath thick vegetative covers at a resolution chance of a surface-rupturing, M ~8 Alpine fault et al., 2006; Barnes, 2009; Langridge et al., of centimeters to meters has allowed the topo- earthquake in the next 50 yr (Sutherland et al., 2010). Along with the North Anatolian fault in graphic features of these landscapes to be exam- 2007; Berryman et al., 2012a) poses a signifi cant Turkey and the San Andreas fault in California, ined in revolutionary new ways. national hazard to the country of New Zealand, the Alpine fault is commonly cited as one of the and better understanding of surface rupturing major continental strike-slip faults in the world along the fault is sorely needed. By incorpo- (e.g., Frankel and Owen, 2013; Molnar and *Email: [email protected] rating interpretations of the new LiDAR data Dayem, 2010; Sylvester, 1988).

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/4/5/435/3050629/435.pdf by guest on 28 September 2021 BARTH ET AL.

fault has a relatively straight and uncomplicated 1997). Negative surface slopes (i.e., toward the 170°E surface expression, the central section exhibits range) are only likely to occur where deep inci- AUSTRALIAN sequences of transpressional oblique-thrust and sion by rivers has taken place, hence the close strike-slip faults (Fig. 2B) dubbed “serial par- relationship to valleys. Other prominent exam- PLATE titioning” by Norris and Cooper (1997, 1995). ples of abandoned thrusts of the Alpine fault are These zigzag sequences of north-northeast– at Ward Hill near Paringa, 60 km southwest of striking, thrust/dextral-thrust faults and east- the study area (Simpson et al., 1994), and near northeast–striking, dextral faults repeated over Simon Slew and Robinson Creek, 85 km south- T lengths of 1–10 km have been interpreted to west of the study area (Department of Geology, UL FA form as a result of an angle of obliquity of 16° University of Otago, 2012, Alpine fault map NE N between the 071°-trending relative Pacifi c-Aus- Web site). PI ALPINEAL FAULT tralian plate-motion vector (DeMets et al., 1994) It should be emphasized that despite the 45°S resolved on the 055°-striking central Alpine complex surface-rupture patterns, all evidence PACIFIC fault, as well as local stress fi eld perturbations suggests the fault is a single planar structure at 300 km due to topographic effects of a steep range depths greater than 500–1000 m, and that shal- PLATE front with deeply incised river valleys (Norris low partitioning does not appear to hinder the and Cooper, 1997, 1995). Norris and Cooper propagation of earthquakes through this region Figure 1. Tectonic setting of New Zealand (1995) constructed transpressional sandbox (Norris and Cooper, 1995). Along its entire showing major plate-boundary structures and experiments simulating the Alpine fault with onshore length, the fault exhibits no step-overs light detection and ranging (LiDAR) study area and without valleys to support the topographic or discontinuities in the fault plane greater than overlain on bathymetric and topographic data infl uence on serially partitioned fault segments. 1 km, at depth (Sutherland et al., 2007). Active compiled by the National Institute of Water and Serial partitioning here is confi ned to the upper faults within the Western Province are rare in Atmospheric Research of New Zealand. ~1–2 km of the crust along ~100 km of the cen- the central Alpine fault zone (Cox and Bar- tral Alpine fault. rell, 2007). As the Alpine fault dips shallowly An alternate geometry, parallel partitioning, to moderately southeast with depth, fault traces In the study area, the Alpine fault is the in which oblique motion is accommodated on south and east of the Alpine fault are rooted geologic boundary between the granitic parallel-striking thrust and strike-slip faults, within the base of the Pacifi c plate (the main and gneissic Western Province (Australian is more common globally (e.g., Molnar and Alpine fault plane). Thus, the main trace of the plate) and gneissic and schistose rocks (Alpine Dayem, 2010; McCaffrey, 1996, 1992; Went- Alpine fault tends to correspond to the most Schist and Alpine Schist–derived mylonites) of worth and Zoback, 1989). Parallel partitioning basinward (basal) fault trace, which still accom- the Pacifi c plate (Reed, 1964; Cox and Barrell, has been documented in detail on the Alpine modates the most slip at the surface, with parti- 2007), across which 480 km of cumulative strike- fault offshore Fiordland by Barnes et al. (2005), tioning occurring only in the hanging wall. slip motion has taken place (Wellman[1949] in where multiple fault splays ~1–2 km apart are Typical exposures along the central Alpine Benson, 1952). Dip-slip rates vary along strike interpreted to link into a single through-going fault (e.g., Hare Mare Creek, 4 km southwest of of the Alpine fault. Only its central part experi- fault at depth. At Darnley and Gaunt Creeks study area; Gaunt Creek) consist of Pacifi c plate ences very high hanging-wall uplift rates, giv- in the LiDAR study area, structural mapping fault rocks thrust obliquely over fl uvio-glacial ing rise to the Southern Alps. In the vicinity of by Easterbrook (2010) revealed two subverti- sedi ments on the Australian plate. The Pacifi c the LiDAR study area, the fault is a relatively cal hanging-wall dextral faults thought to root plate section typically consists of a centimeter- planar, moderately southeast-dipping, dextral- into a southeast-dipping, dextral-thrust fault at thin ultracataclastic clay gouge, a 20–30-m-thick reverse fault accommodating ~27 mm/yr of shallow depths to form an ~200-m-wide zone hydrothermally altered, highly fractured fault strike-slip motion and up to ~10 mm/yr of dip- of parallel partitioning. These two examples in rock (commonly referred to as “cataclasite”), slip motion (Norris and Cooper, 2001; Little Easterbrook’s study are the fi rst suggestion of and a sequence of progressively less-fractured et al., 2005; Sutherland et al., 2006). The fault is parallel partitioning on the central Alpine fault ultramylonite, mylonite, protomylonite, and thought to rupture in large to great (M ~8) earth- in the same area where serial partitioning was paragneissic Alpine Schist (Norris and Cooper, quakes with a mean long-term recurrence inter- previously identifi ed. A requirement of serial 2007; Sibson et al., 1981; Wellman, 1955). The val of ~300 yr, and it last ruptured in A.D. 1717 partitioning is that equal amounts of slip are zone of intense fracturing (i.e., damage zone) (Wells et al., 1999; Yetton, 1998; Yetton et al., accommodated on sequenced thrust and strike- associated with the Alpine fault is typically 1998; Sutherland et al., 2007; Berryman et al., slip fault segments, whereas varying degrees of on the order of 100 m in width on the Pacifi c 2012a). In terms of single-event displacement, slip partitioning are possible between parallel- plate (e.g., Cooper and Norris, 1994; Norris and Alpine fault earthquake events have generated partitioned thrust and strike-slip faults. Cooper, 1997; Wright, 1998). These rocks are 6–9 m of dextral displacement and throw of up Imbricate out-of-sequence thrusts form as especially prone to near-surface faulting and to 2 m (Cooper and Norris, 1995; Yetton and rapid river incision reduces the wedge taper slope failure (Korup, 2004). Nobes, 1998; Berryman et al., 2012b). Evidence below its critical value so that they internally The Alpine fault outcrops at the foot of the from fault trenches and tree-ring chronologies imbricate (Norris and Cooper, 1997). The steep western range front of the Southern Alps. suggest that at least 375 km strike-length of best known example of this is the Waikukupa Some of the highest peaks (~3000 m) along the fault ruptured in the A.D. 1717 earthquake River–Hare Mare Creek thrust system, where the main divide of the Southern Alps occur (Wells et al., 1999). the wedges can be >1 km wide. A 30°-dipping adjacent to the high-uplift region around Franz The Alpine fault forms a particularly striking basal plane requires a negative surface slope to Josef; these are found at a distance of ~15 km lineament visible from space, extending for hun- render the wedge subcritical and therefore likely southeast of the surface trace of the Alpine fault. dreds of kilometers (Fig. 2A). While much of the to imbricate in this way (Norris and Cooper, Fast-fl owing mountain rivers in steep-walled

436 www.gsapubs.org | Volume 4 | Number 5 | LITHOSPHERE

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/4/5/435/3050629/435.pdf by guest on 28 September 2021 Scale dependence of oblique plate-boundary partitioning, Alpine fault, New Zealand | RESEARCH

170°E 1 6 4 43°S 72°E 42 A <10 –10 m °S B & C

100 km 170°E 44°S 172°E 43 °S

170.2°E 17 43 0 4 3 .3 .4°E B 10 –10 m °S

Dextral- thrust

1 43.4°S 43.3°S 4 km Thrust 70.2°E 17 0. Dextral 4°E

170.2° 1 3 0 43.3 70.4° C 10 –10 m E °S WHATAROA E Waitangi-taona Docherty River

43. 4° Creek Potters Creek McCulloughs Creek S FRANZ JOSEF Matainui Creek

Waitangi-taona Darnley Creek River Arthur Creek Gaunt Creek Waiho Tartare River 37.5 mm/yr Stream 251.4° Whataroa NUVEL-1A River Australian-Pacific plate-motion vector 43.4°S 1 1 4 km 7 70 0.2°E .4°E

Figure 2. (A) Extent of the onshore trace of the Alpine fault (arrows) visible from topography. Notice the straightness of the Alpine fault at this scale (<106–104 m). All images in this fi gure utilize a hillshade derived from the Land Information New Zealand 100 m digital elevation model. Illumination is from the northwest. (B) Major serially partitioned (oblique-) thrust and strike-slip faults mapped from fi eld, aerial photographic, and light detection and ranging (LiDAR) data (refi ned after Norris and Cooper, 1995). Serially partitioned segments are of the order of 104–103 m in length. The strike-slip faults occur at the scale of the major river valleys and can be thought of as passive linkage structures necessitated by tears in the basal fault plane in the near surface. (C) All fault traces identifi ed in this study (n = 268) mapped at 103–100 m scale from LiDAR data, fi eld checking, and previous work. Local Australian-Pacifi c plate-motion vector is from NUVEL-1A (DeMets et al., 1994). Towns of Franz Josef and Whataroa are denoted in capital letters. Location names are those referred to in Figure 4.

glaciated river valleys exit the Southern Alps and early or mid–Last Glacial Maximum (LGM), METHODS cross the Alpine fault at elevations of ~100 m ca. 27,000–20,000 yr B.P., which covered most onto wide and active river fl oodplains lined with of the range front of the Southern Alps in ice LiDAR data used in this study were collected widespread glacial moraine deposits attributed (Barrell, 2011; Cox and Barrell, 2007; Suggate, by NZ Aerial Mapping Limited using an Optech to as many as fi ve major middle to late Pleisto- 1990). A high annual precipitation of 5000 mm ALTM3100EA instrument fl own from ~1200 m cene glacial advances (Barrell, 2011). The most allows a dense temperate rain forest to fl ourish altitude. Data were collected in six overlap- recent widespread glacial advance dates to the west of the main divide. ping swaths, ~780 m wide (for a total width of

LITHOSPHERE | Volume 4 | Number 5 | www.gsapubs.org 437

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/4/5/435/3050629/435.pdf by guest on 28 September 2021 BARTH ET AL.

~1.5 km), to increase the point counts through The features were sorted into several shape- mapped fault traces are indeed faults, and they the dense podocarp rain forest. Positional accu- files utilizing a hierarchy of confidence in have also allowed us to identify 1–2-m-wide lin- racy of data points is ±0.30 m horizontally and interpretation of fault traces. Factors such as ear troughs in Riedel shear orientations below ±0.15 m vertically. A 2-m-resolution bare-earth defi nitive offsets, adjacency to anticlinal ridges, the resolution of the LiDAR data. In addition, digital elevation model (DEM), 2 m hillshade, scarps on millennially inactive glacial or fl uvial trenching of a north-striking fault trace at Gaunt and 0.5 m contour lines generated from the last surfaces, particularly well-defi ned range-front Creek confi rmed the existence of a multi-event returns (i.e., ground returns) of the LiDAR data lineaments, signs of disequilibrium erosion, thrust fault (De Pascale and Langridge, 2012). were used in this study. These data were incor- and otherwise atypical geomorphology best We recognize eight 104–103-m-scale serially porated into a geographic information system explained by the presence of a fault were used partitioned segments in the LiDAR coverage (GIS) geodatabase along with Land Information to qualitatively rank individual features as “fault area. The mapped segments are largely concor- New Zealand (LINZ) Topo 50 topographic map trace,” “probable fault trace,” or “lineament” (in dant with the regional-scale serial-partitioned sheets, and georeferenced geologic maps and order of decreasing confi dence). After several segments mapped by Norris and Cooper (1995), structural data collected previously by research- iterations, comparisons with previous work, and with the exception of a new well-defi ned 3.5-km- ers from the University of Otago and GNS some fi eld checking, this classifi cation was sim- long strike-slip segment between Docherty Science (Cox and Barrell, 2007). Orthophotos plifi ed into fault trace and lineament shapefi les. Creek and Franz Josef Township (Fig. 2B). taken at the same time as the LiDAR run were An effort was also made to defi ne the primary Our mapping also shows a clearer link between also incorporated into the geodatabase and were slip zone—the fault trace (or traces) that has serial-partitioned segments and major river most helpful for identifying linear cultural fea- accommodated the majority of surface-rupture valleys than these authors were able to make tures, such as roads and trails, which could be slip at any point along strike. previously; the southwestern ends of oblique- mistaken for natural features. ArcMap computer thrust segments correlate to the southwest- software was used to create polyline and poly- RESULTS ern side of major river valleys (e.g., Docherty gon shapefi les of features of interest, including Creek, Waiho River, Waitangi-taona River, and fault traces, anticlinal ridges, lineaments, fault Fault Traces Whataroa River). The overall strikes of oblique- offset features, landslides, river terraces, and thrust segments are 030°–053° (048° average), glacial features. Interpretation was initially per- In total, 268 fault traces were identifi ed within and those of strike-slip segments are 068°– formed without reference to previous geologic the LiDAR coverage area in a 200–800-m-wide 088° (082° average). Thrust segments tend to be information, using only the LiDAR data and zone along the range front (Fig. 2C) for a total longer, although the longest strike-slip segment orthophotos, to eliminate potential bias. fault trace length of 68.9 km. We compared our south of Whataroa Township is ~5 km long. Special care was taken in the interpretation results to a compilation of Alpine fault traces A rose diagram of 103–100-m-scale fault of fault traces, especially since regional fracture mapped by researchers at the University of traces weighted by fault length gives thrust and patterns and Alpine Schist/mylonite foliations Otago’s Department of Geology (publicly avail- dextral-thrust maxima at 040°–045°, oblique are known to have similar strikes to expected able through their Web site). We found 12.4 km maxima at 060°–065°, and dextral maxima fault traces (Hanson et al., 1990). Low-angle of the total fault length in this study had been at 070°–075° (Fig. 3); when combined with range-front dextral thrusts, which commonly previously identifi ed as “accurate” (±50 m) and structural measurements, these maxima are form the most basinward Alpine fault trace that, by length, 82% of the LiDAR-mapped interpreted as thrust/dextral-thrust, oblique, (e.g., Waikukupa thrust, Hare Mare Creek, and traces are new. Only 4.2 km (6%) of the fault and dextral fault sets, respectively. Range-front Gaunt Creek), consist of highly fractured fault traces southeast of the range front were previ- dextral-thrust fault traces are typically curvi- rocks and incoherent fl uvio-glacial deposits ously identifi ed. linear and are expressed as poorly preserved thrust over unconsolidated fl uvio-glacial gravel Mean trace length is 260 m, with a few traces west- to northwest-facing, 20-m-high scarps. deposits. These fault traces can be subtle fea- longer than 1 km. Many ends of fault traces are Dextral-normal fault traces within 100–1000 m tures due to the low angle at which the fault covered or have been removed by slope failure of the range front are expressed as linear or cur- plane intersects topography, and they are com- or creek erosion and aggradation, suggesting the vilinear, 1–10-m-high, south- to southeast-facing monly obscured by deposits from slope failures fault traces would have been longer and more scarps or 10-m-wide symmetrical troughs. These prompted by tectonic oversteepening, fl uvial continuous at the time they ruptured. Some dextral-normal traces have not been identifi ed undercutting, and earthquake ground motion fault traces extend off the LiDAR-mapped prior to this study, but they are thought to be in highly fractured rock. Dextral-thrust fault area, suggesting there are places where extend- coincident with east-west–striking clay gouge– traces are characterized by 20–40-m-high over- ing the coverage farther southeast may reveal cored faults observed in Docherty Creek (e.g., steepened range-front topographic steps onto more fault traces. However, in most places, the Norris and Cooper, 1995), which dip 70°–90°S river fl oodplains or alluvial fans. In contrast, LiDAR imagery covers the full width of surfi - with groove lineations raking 20°–60° from the high-angle dextral and dextral-normal faults cial structures we infer to be part of the Alpine west, indicating dextral-normal slip. have well-defi ned traces due to the high angle at fault surface damage zone. We observe no fault Dextral stream channel offsets are typically which the fault plane intersects topography and traces within the interfl uves northwest of the ambiguous along the range-front dextral-thrust relative protection from fl uvial erosion in the range front and see that fault traces tend to occur traces. Alluvial fans have a tendency to defl ect interfl uves. These fault traces are characterized at low elevations north or west of the steepest streams to the southwest (apparently sinistrally) by sharp linear or curvilinear scarps, 1–10 m portion of the range-front step. Fault mapping as the highest part of the fan is shifted to the high, or symmetrical troughs. While the strike- across the whole width of the central Southern northeast relative to the mouth of the valley. slip–dominant fault scarps are the most striking, Alps by Cox et al. (2012) also showed a relative The more rangeward faults have identifi able it is emphasized that they have not necessarily absence of faults 5–10 km southeast of the study dextral offsets of creeks, particularly in the area accommodated the most movement or are a area. Field investigations west of the Whataroa west of the Whataroa River and near Darnley product of the youngest surface ruptures. River have allowed us to confi rm that LiDAR- Creek, in part due to the creeks having deeply

438 www.gsapubs.org | Volume 4 | Number 5 | LITHOSPHERE

N to east-northeast–striking dextral-thrust faults to Thrust and dextral-thrust east-striking dextral-normal faults. Thrust fault Average strike of the Alpine fault traces still bound the basinward side of the fault wedge on this strike-slip segment. From Gaunt Oblique Creek toward Matainui Creek, north-northeast–

Dextral striking thrust faults transition to east-striking dextral faults along the range front. More rangeward dextral faults strike northeast, effectively “cutting the corner.” Note that the width of the fault wedge (and density of faults) is greatest at the serially partitioned transition.

Fault traces Lineaments n = 268 Length weighted ∑ = 68.9 km In addition to fault traces, 175 lineaments 5° binning were identifi ed (Fig. 5). Most of these are more rangeward than the fault traces and cut topogra- Figure 3. Rose diagram of 268 fault trace azimuths weighted by length phy steeply, frequently as strikingly linear drain- with 5° binning. Total fault trace length is 68.9 km. Maxima are interpreted from structural measurements. Arrow denotes average strike of ages. We found that lineaments (100–500 m the Alpine fault (055°). long) revealed in the LiDAR imagery within 1 km of the Alpine fault have similar orientations and abundances to large-scale regional lin- incised channels on both sides of fault traces. Anticlinal ridges are parallel to the trace of the eaments within 7.5 km east of the Alpine fault The LiDAR study area illustrates the complica- main dextral-normal fault. near Franz Josef and Fox Glacier compiled from tions in determining offset rates on faults with The region between Franz Josef Township aerial photographs by Hanson et al. (1990). multiple rupture planes in the near surface. It and Tatare Stream (Fig. 4C) is characterized by Hanson et al. (1990) identifi ed three orientation is common to observe several parallel major en echelon strike-slip faults that curve into par- sets of lineaments: a 025°-trending set parallel traces; these may have been active at different allelism with the rear of the fault wedge such to the strike of the foliation in the Alpine Schist, times and may have accommodated different that the overall character is similar to parallel a minor set trending 130°, possibly related to com ponents of strike-slip and dip-slip motion. partitioning. The basinward side of the fault extension fractures, and an east-west–trend- Thus, a slip rate determined from one of these wedge is dominated by oblique-thrust faults, ing set of dextral faults with late normal dis- traces would not be representative of the entire and the rangeward side is dominated by dextral- placement. The structures in both studies are rupture history. normal faults. The range-front thrust faults have similar in orientation despite the fact that the small apparent dextral offsets where they cross bulk of the area examined by Hanson et al. was Characteristic Fault Geometries two small drainages, which correspond to dex- in the Alpine Schist, which is the proto lith of tral faults. This behavior is comparable to that the Alpine fault mylonites that underlie most Characteristic transpressional fault geom- generated in sandbox experiments conducted of the study area described herein. We fi nd etries observed in this study are highlighted by Norris and Cooper (1995) using a rigid that structures parallel to the Alpine fault and in Figure 4. McCulloughs Creek and Darnley indenter and ignoring the effects of topography. mylonitic foliation are more dominant in our Creek (Figs. 4A and 4B) are both examples of The dextral faults have increasing down-to-the- data set than in this previous study (Fig. 4). parallel partitioning in which a 100–300-m-wide southeast displacement as the faults approach The dominant strike (035°) is slightly more fault wedge is bounded by a basinward oblique parallelism with the rear of the fault wedge. parallel to the Alpine fault than was observed thrust and a rangeward dextral-normal fault At Arthur Creek, two major fault traces are by Hanson et al. (1990), likely indicating a rooted on a southeast-dipping Alpine fault observed dextrally offsetting stream channels clockwise rotation toward parallelism with the plane. At McCulloughs Creek, the terrace riser on the longest strike-slip serially partitioned Alpine fault with decreasing distance from the north of the creek is offset ~100 m dextrally segment in the study area. Well-defi ned east- fault. This is consistent with dextral shear hav- and 10 m down-to-the-southeast along the northeast–striking anticlinal ridges (compared ing been accommodated in the ductile shear dextral-normal fault. A complex array of nor- to more northeasterly striking anticlinal ridges zone at depth with concurrent foliation devel- mal faulting occurs in the southeastern half of on thrust segments) accommodated limited opment. For shear strains >5 as measured by the fault wedge, while the northwestern half is shortening on the basinward side of fault traces. Norris and Cooper (2003), the angle between dominated by three en echelon anticlinal ridges, No thrust traces were identifi ed here. Fault foliation and the shear zone should be <10°. clearly defi ned from LiDAR-derived contour traces here record the most cumulative dextral data, that comprise the axis of the anticlinal fault displacement preserved from offset features Anticlinal Ridges wedge. At Darnley Creek in the Waitangi-taona anywhere in the LiDAR study area. Valley, a curvilinear thrust trace and a linear The Docherty Creek–Waiho River and Gaunt Anticlinal ridges associated with near-sur- 10–25 m down-to the-southeast dextral-normal Creek–Matainui Creek regions (Figs. 4E and 4F) face Alpine fault deformation have not been trace bound the fault wedge. To the north, the are on transitions between near-orthogonally previously identifi ed within the study area. We dextral-normal fault offsets two stream chan- striking thrust and strike-slip serially partitioned mapped 100 anticlinal ridges with characteristic nels, whereas to the south. it devolves into segments. From Docherty toward the Waiho strikes 0°–15° counterclockwise to the nearest 75-m-long en echelon dextral-normal traces. River, northeast-striking thrust faults transition fault trace strike (Fig. 6). The resolution of the

LITHOSPHERE | Volume 4 | Number 5 | www.gsapubs.org 439

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/4/5/435/3050629/435.pdf by guest on 28 September 2021 BARTH ET AL.

A B Norris and Cooper, 2007; Toy et al., 2008). 500 m Darnley Uncemented clay gouge zones outcrop through- Creek out this exhumed sequence (Reed, 1964; Sibson et al., 1979), including at the contact of hanging- wall cataclasite on footwall gravel. We assume McCulloughs the gouge zones developed during near-surface Creek fault slip since they have not been affected by hydrothermal cementation. Their mean orientation (Fig. 7) is 030°/40°SE, but dips ranging from 30° to 50° are common. Additionally, the 500 m mylonitic foliation in the hanging wall, which has an average orientation of 055°/50°SE (Norris C D and Cooper, 2007), presents a strong mechani- 500 m 500 m Arthur cal anisotropy, and brittle faults should therefore Creek parallel it. The dominant orientation of the brittle part of the fault at depth (below near-surface complexities) can be explained in this way. However, in the ~10 well-exposed thrust segments of the fault, the boundary between FRANZ JOSEF hanging-wall cataclasite and footwall gravel commonly dips more shallowly (~30°) than the mylonites that overlie it. This may be due in part to near-surface stress control, as this shallower orientation has a dip similar to that predicted E F Matainui for thrust faults in the near surface, where a Creek principal stress is likely to be vertical (Ander- son, 1951). It may also be related to collapse of the overthrust material toward the free surface. Docherty By the same principle, we expect strike-slip Creek faults to be near vertical. Reassuringly, steeply 500 m S-dipping, E-W–striking clay gouge zones with Key (sub)-horizontal striae have been observed in a (Oblique)-thrust fault number of places in the hanging-wall sequence (Dextral)-normal fault (Fig. 6A; Gaunt Creek—Toy, 2007; Darnley 500 m Strike-slip fault Creek—Easterbrook, 2010; Docherty Creek Anticlinal ridge and Waikukupa River—Norris and Cooper, Figure 4. Key examples of characteristic geometries revealed by light detection and ranging (LiDAR) 1995, 1997). These vertical features are easily data. Fault motion is inferred based on LiDAR data and limited fi eld data. Fault and fold interpre- eroded in creek sections and do not outcrop as tations are overlain on 2 m LiDAR hillshade map. Grid north is toward the top of the fi gure in all commonly as thrusts, and so they are under- views. Refer to Figure 2C for locations. (A–B) McCulloughs Creek and Darnley Creek sites illustrate represented in the compilation of gouge zone third-order parallel partitioning on a second-order thrust segment. (C) The Franz Josef area is char- orientations (Fig. 7A). acterized by en echelon fault partitioning. (D) Arthur Creek illustrates fault patterns on a second- order strike-slip segment. (E) Docherty Creek–Waiho River and (F) Gaunt Creek–Matainui Creek are By combining fault strikes from LiDAR on transitions from thrust to strike-slip segments. with corresponding fi eld observations of characteristic fault dips and striae on faults, we hypothesize a set of likely orientations and slip LiDAR reveals that anticlinal ridges are com- uplifted asymmetric anticlinal structure associ- vectors for the major groups of faults identifi ed posed of smaller-scale en echelon anticlines, ated with hanging-wall near-surface Alpine fault in the LiDAR data (Table 1). If faults of these which could indicate development in a step- deformation has been identifi ed near Paringa, orientations bound semirigid crustal blocks, wise manner (e.g., Fig. 4A). The majority of ~60 km south of the study area (Simpson et al., their intersections must approximately parallel anticlinal ridges cluster around a strike of 055° 1994; Adams, 1979; Suggate, 1968). the fault slip vectors in order to maintain geo- (the average strike of the Alpine fault), with a metrical continuity. For a slip vector parallel to minority approaching a strike of 085°, i.e., close Fault Kinematic Analysis the NUVEL-1A plate-motion vector trending to the average strike of strike-slip fault traces 071° (DeMets et al., 1994), some fault orien- in this study. In the fi eld, we observed one of We used the fi eld data to predict dips for tations are thus further constrained so a single these anticlinal ridges near Arthur Creek, west the lineaments identifi ed as fault traces. The slip vector orientation (15°→071°) can lie within of the Whataroa River (Fig. 4D). It consists of hanging-wall sequence of fault rock, consist- them, as indicated in Table 1 and Figure 7B. Whataroa-derived bedded river terrace deposits ing of mylonites and cataclasites developed From Figure 7B, it is also apparent that it is folded into an asymmetric anticline with a mod- during ductile and then brittle shear at depth on diffi cult for such geometrical continuity to be erately dipping northwest limb and shallowly the Alpine fault, is exposed in stream sections maintained during coeval slip on reverse faults dipping southeast limb. A comparable recently to the southeast of the most recent trace (e.g., and faults of any other type. This may induce

440 www.gsapubs.org | Volume 4 | Number 5 | LITHOSPHERE

NNdeep fault zone, and so the surface structures A B are constrained to an average strike similar to the deep regional structure and are required to accommodate oblique motion.

Fault Stability and Slip Tendency Analysis

We now consider the relative slip tendency of faults with the orientations indicated in Table 1. The orientation of the modern stress fi eld around the Alpine fault has been estimated by a variety of methods (e.g., geodetics—Pear- son, 1994; inversion of postglacial fractures— Lineaments Lineaments Norris and Cooper, 1986), most of which nn = 175 = 788 give S (maximum horizontal compressive 5° binning 10° binning Hmax This study Hanson et al. (1990) stress) trending 115° to 125°. The only three- dimensional solutions come from inversions Figure 5. Lineaments (excludes fault traces). (A) Rose diagram (this study) showing azimuths of of earthquake focal mechanisms (Boese et al., 175 lineaments with 5° binning. (B) Rose diagram redrawn from Hanson et al. (1990) showing the 2012; Leitner et al., 2001, their fi g. 2.5), who azimuths of 788 lineaments with 10° binning. Lineaments from Hanson et al. were traced from aerial photography of an area bounded by the Alpine fault, the Fox and Waiho Rivers, and ~7.5 km derived a stress tensor for the central section of east of the Alpine fault. the Alpine fault between approximately Hari σ Hari and Haast where 1 (maximum principal → σ compressive stress) trends ~10° 118° and 3 N (minimum principal compressive stress) trends toward 220°. We take this as representative of the large-scale stress fi eld, noting that it is likely to be signifi cantly perturbed near the surface due to topography. We evaluated the tendency of any particular fault orientation to slip by calculating the rela- Figure 6. Rose diagram of 100 anticlinal ridge tionship between the static coeffi cient of friction axes with 5° binning. μ ( s) and the ratio of maximum and minimum σ σ principal stresses (R = 1/ 3) at which slip will occur. This is accomplished by resolving the components of shear stress (τ) and normal stress σ ( n) on the fault plane for various R, and then Anticlinal ridges τ σ applying the limiting condition for failure, / n n = 100 μ 5° binning > s (Collettini and Trippetta, 2007), for a range μ of s. This calculation was performed iteratively for increasing values of R until this limiting condition was met, using a simple MATLAB script. σ σ σ the fault to partition into the other orientations 7C shows a predicted fault system geometry. Note that we assume that 2 = ½ ( 1 + 3) but σ σ as it approaches the free surface. We present a Most of the subsidiary fault orientations in this obtain similar results if 2 ~ 3. three-dimensional model for the geometry of case strike parallel to fault traces identifi ed in The results (Fig. 8) indicate that steeply dip- interlinked fault segments with these orienta- the LiDAR data set (e.g., P-shear at 038°/52°SE ping (i.e., strike-slip) faults have a greater ten- tions in the Discussion section. is similar to the group of faults with strikes dency to slip than other orientations indicated An alternate model for likely fault orienta- 040°–045°; R-shear at 075/42SE is similar to in Table 1. This is apparent from the fact that, tions can be constructed based on the idea of a the group of faults with strikes 070°–075°). for a comparable ratio of principal stresses, a characteristic Riedel shear geometry. In natu- Therefore, many of the faults identifi ed in the strike-slip fault will slip even if its frictional μ ral situations, the elastic stress fi eld generated LiDAR data could have initiated as part of a strength ( s) is over twice that of any of the in the material surrounding a slipping fault, Riedel shear system arising independently of predicted thrust or oblique-thrust fault orienta- particularly within a relatively unconsolidated topographic and river incision effects. How- tions. On the other hand, there is little differ- (structurally weak) sequence above a basement ever, this system of faults cannot intersect par- ence in the strength of the various thrust and fault, results in formation of a system of linked allel to the slip vector, so it is geometrically oblique-thrust fault orientations indicated by faults with characteristic geometry (Cloos, destabilized by ongoing slip. Internal defor- the LiDAR analysis when expressed in this way. 1928; Riedel, 1929). Using this characteristic mation of Riedel shear–bounded blocks by For comparison purposes only, we also evalu- fault geometry, for a main fault orientation of folding could allow shear to continue on these ated a fault with the average strike of the Alpine 055°/45°SE (Norris and Cooper, 2007) and a structures. In either case, it is important to real- fault overall, and dip parallel to the exhumed slip vector parallel to the DeMets et al. (1994) ize that displacement within the near-surface mylonitic foliation (055°/45°SE). This structure Pacifi c-Australian plate-motion vector, Figure fault zone is controlled by slip/creep on the has even lower tendency to slip than any of the

LITHOSPHERE | Volume 4 | Number 5 | www.gsapubs.org 441

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/4/5/435/3050629/435.pdf by guest on 28 September 2021 BARTH ET AL.

Figure 7. Equal-area lower-hemi- Kamb contours R’ folds sphere projections illustrating A C.I. = 2.0 sigma B C (A) poles to gouge zones measured within the central Alpine D fault zone (black dots); Kamb U contour interval (C.I.) = 2.0, n = 224; (B) orientations of faults D D U U D interpreted from combined light U P detection and ranging (LiDAR) and ﬁ eld data (black great circles); Y slip vector for three of the fault sets is indicated by gray dot; and R (C) expected orientations of faults n =224 in a Riedel shear system around a mean Alpine fault plane (Y-shear) orientation of 055°/45°SE. Dashed great circle indicates hinge plane of associated folds. Arrows and D/U (down/up) show shear sense. Arrow outside plot shows trend of plate-motion vector. In B and C, gray bars outside circle illustrate strikes of main groups of faults interpreted from the LiDAR data.

structures we derived from the LiDAR analysis. TABLE 1. ORIENTATIONS OF FAULT GROUPS EVIDENT IN LiDAR DATA, This result suggests that new strike-slip faults WITH DIPS CONSTRAINED BY FIELD OBSERVATIONS AS STATED IN THE TEXT will easily accommodate displacement within Orientation of fault plane Orientation of slip vector (strike/dip) (plungeàtrend) the hanging-wall wedge, and that thrust motion à is most easily accommodated on faults oblique Major thrust segments; near surface 040°–045°/30°SE 15° 071° Major reverse segments at greater depths 040°–045°/50°SE 30°à071° to the overall strike of the Alpine fault. The rela- Major strike-slip segments 070°–075°/90° 15°à071° tive tendency of these fault orientations to slip Oblique segments 060°–065°/60°SE 15°à071° is consistent with the formation of a partitioned fault system in the near-surface to accommodate oblique motion away from a nonideally oriented fault plane, and with our observations that fault 0.8 traces in this study are reactivated during mul- 070°-075°/90° tiple earthquake rupture events. 0.7 As noted previously, it is unlikely that the local stress tensor around the faults is the same as 0.6 that derived at depth by Boese et al. (2012) and Leitner et al. (2001), due to variations in topog- 0.5 040°-045°/50°SE n

σ 040°-045°/30°SE

raphy and therefore in the orientation of the free / surface. The anisotropic strength of the strongly τ 0.4 =

s 060°-065°/60°SE060°-065°/60°SE foliated mylonites will also infl uence fault ori- μ 055°/45°SE entations and slip tendency. Furthermore, it 0.3 is possible that the stress tensor is perturbed by the existing faults, so that a heterogeneous 0.2 070°-075°/90° stress distribution allows slip on all fault orien- 040°-045°/50°SE 040°-045°/30°SE tations, despite their varying strengths. Essen- 0.1 060°-065°/60°SE tially, kinematic constraints mean that slip has 055°/45°SE to occur on these faults, and stresses will locally 0 0 10 20 30 40 50 60 70 80 90 100 rotate to allow this. Small-scale stress variations R = σ /σ should be more thoroughly evaluated in the 1 3 future by combining numerical models with in μ Figure 8. Plot illustrating relationship between frictional strength ( s) situ measurements derived from future borehole σ σ and ratio of principal stresses (R = 1/ 3) to cause slip on faults with the measurements . orientations illustrated in Figure 7B, and for the average orientation of the Alpine fault (055°/45°SE). Gray fi eld indicates thrust faults; diagonal DISCUSSION hatched fi eld indicates strike-slip faults.

First-Order Controls on the Alpine Fault within the Zealandia continent that could be as gressively weakening discontinuity. The fault The Alpine fault is thought to have localized old as Paleozoic (Sutherland et al., 2000). zone only displays time-averaged dominantly on an inherited Eocene (ca. 45 Ma) passive mar- The ﬁ rst-order structure (<106–104 m) of brittle behavior in the upper ~8 km (Toy et al., gin that separated continental and oceanic litho- the central Alpine fault is thus simply imposed 2010). Beneath this, viscous creep predomi- sphere (Sutherland et al., 2000). The Eocene rift by the fact it experiences a component of rapid nates within a ductile shear zone that contin- boundary exploited Cretaceous oceanic trans- dip-slip motion throughout the continental ues to the base of the quartzofeldspathic crust form faults and a major crustal discontinuity upper crust of the South Island along a pro- at ~35 km (Little et al., 2005). Ductile shear

442 www.gsapubs.org | Volume 4 | Number 5 | LITHOSPHERE

results in development of a >1-km-thick zone to the southwestern side of major river val- dip from 30° at low elevations to horizontal at of metamorphic tectonites with fi ner grain leys, such as at Docherty Creek, Waiho River, the highest terminus (Norris and Cooper, 1997). size than the protolith (i.e., mylonites; Sibson, Waitangi-taona River, and Whataroa River. At Detailed fi eld mapping by Norris and Cooper 1977). Total simple shear strains range up to γ these same transitions, active strike-slip traces (1995) at Docherty Creek has shown that from = 180–220, so a planar fabric is well developed do not extend past the oblique-thrust segments south to north, the oblique-thrust segment bends parallel to the shear-zone boundaries (Norris into the hanging wall, indicating that strike-slip from a northeast-striking, moderately dipping and Cooper, 2003; Ramsay, 1980). Hot hang- movement is limited to the section between the orientation to a north-northeast–striking, shal- ing-wall rock is uplifted relative to the footwall offset oblique thrusts. This clearly supports lowly dipping orientation while becoming by shear displacement on the fault faster than the concept of strike-slip segments as linkage more dip-slip in nature to the north. In addition diffusive cooling can occur, resulting in advec- structures between (and only between) tears in to topographic controls, we propose that this tion of hanging-wall isotherms across the duc- the basal fault plane. The LiDAR data there- greater amount of thrusting over footwall sedi- tile shear zone (Koons, 1987). This results in fore provide strong support for the basic idea ments on the northern end of the oblique-thrust thermal weakening and localization of ductile of serial partitioning proposed by Norris and segments might also signifi cantly infl uence shear, so that both dip-slip and strike-slip com- Cooper (1995, 1997). Slip on the strike-slip fault dip. With the decreasing dip of the basal ponents of relative plate motions are focused on segments should thus depend on (and be equal thrust as it progressively overthrusts footwall a single structure dipping 40°–60°SE (Norris to) slip on the oblique-thrust segments in the sediments, it becomes harder to accommodate and Cooper, 2007; Koons et al., 2003), a rea- manner oceanic transform faults are dependent oblique motion and likely encourages a rotation sonably unfavorable orientation for slip accord- on oceanic-ridge spreading. As such, the strikes in fault strike or parallel partitioning. The geom- ing to an Andersonian view of fault mechanics of the strike-slip segments would be expected etry from DFDP-1 and our observations suggest (Anderson, 1951). Transient high stresses and to be close to the azimuth of the plate-motion that the serial partitioning described by Norris high strain rates due to loading around a very vector accommodated on the Alpine fault. and Cooper (1995) may be rooted considerably narrow fault tip at the base of the seismogenic The average strike-slip segment strike of 082° shallower than the 4 km maximum depth they zone contribute to keeping the shear zone local- might locally indicate an 11° clockwise rotation calculated as the limit of stress fi eld perturbation ized within the deforming lower crust (Ellis of the slip vector from the 071° plate-motion due to surface topography. et al., 2006). vector, which would be consistent with obser- The ductilely sheared rocks are progressively vations of greater obliquity and higher uplift Third-Order Geometry of the Central exhumed up dip of the fault zone during suc- rates along the central Alpine fault. Oblique- Alpine Fault from the LiDAR Study Area cessive earthquakes. At depths where viscous thrust segments tend to be longer because they creep no longer predominates (<~8 km), brittle are continuous at depth with a 055°-striking Our LiDAR-interpreted fault traces allow shear remains localized within the exhumed dextral-reverse fault plane. The strike-slip seg- us to reliably document a surface-rupture zone shear-zone rocks, parallel to the boundaries of ments are tears within this surface constrained on the central Alpine fault for the fi rst time. By this zone at depth. This occurs because cohe- to an average 082° strike. The amount of rota- combining fault traces revealed in the LiDAR sion parallel to the well-developed shear-zone tion of the oblique thrust adjacent to these tears, imagery with fi eld observations, we can identify boundary-parallel foliation in the micaceous and hence the length of the strike-slip segment, a smaller scale of parallel partitioning super- mylonites is lower than in any surrounding is related to the amount of westward thrusting, imposed on the second-order serial partitioning. rocks. Consequently, brittle Mohr-Coulomb which in turn is constrained by the spacing of Although Norris and Cooper (1997) defi ned failure is most likely to occur parallel to the major river valleys (~10–15 km) and by the serial and parallel partitioning, they proposed existing fabric (cf. Allen and Shaw, 2011). The 082° average strike of the tears. them as alternative geometries for the accom- end result is a fault zone that fails parallel to Recent drill core recovered from the Deep modation of near-surface oblique motion. Here, the inherited mylonitic foliation, which dips Fault Drilling Project (DFDP-1) at Gaunt we demonstrate that they coexist at different 50°–60°SE. Creek has revealed that where the basal fault scales along the same fault zone. is thrust over gravels at 90 m depth, it dips 30° We confi rm that active faults within the Second-Order Controls on the Central (DFDP-1A). Dip increases to >30° in another Western Province (Australian plate) are rare Alpine Fault hole (DFDP-1B) 100 m away, where the hang- in the central Alpine fault zone. As the Alpine ing-wall Pacifi c plate fault rocks are juxtaposed fault dips shallowly to moderately south- At a second order (104–103 m), the cen- against the footwall Australian plate fault rocks east with depth, fault traces south and east of tral section of the Alpine fault (where uplift at a depth of ≤130 m (Sutherland et al., 2011). the Alpine fault are rooted within the base of the rates are high) is partitioned along strike into There may be similar dramatic changes in the dip Pacifi c plate (the main Alpine fault plane). sequenced (i.e., serial) oblique-thrust and of the fault plane over a short distance elsewhere Thus, the main trace of the Alpine fault tends to strike-slip segments. These arise in the upper where the fault changes from placing basement- correspond to the most basinward (basal) fault <1–2 km when stress perturbations from on-basement to basement-on-sediment in the trace, which still accommodates the most slip hanging-wall topographic variations (a steep near surface. The fault dip should continue to at the surface, with partitioning occurring only range front with deeply glaciated valleys and shallow with progressive overthrusting into in the hanging wall. high peaks) on a dipping oblique-slip struc- these unconsolidated sediments. Consequently, The dynamic landscape only records a fracture exceed the strength contrast imposed by the thickness of footwall sediments will have tion of the expected horizontal and vertical dis- the anisotropic tectonite fabric (Norris and a large control on the width of the fault wedge placements expected on the Alpine fault in this Cooper, 1995, 1997). Our mapping illustrates a in the hanging wall at scales ≤103 m. This is area (~27 mm/yr and ~10 mm/yr, respectively). clear link between serial-partitioned segments observed for the Waikukupa thrust of the Alpine Glacial trimline and moraine crest elevations and major river valleys, with the southwestern fault, ~4 km southwest of the study area, where indicate extensive glaciation in this area during ends of oblique-thrust segments correlating exposures document decreases in basal thrust the Last Glacial Maximum (LGM). Because ice

LITHOSPHERE | Volume 4 | Number 5 | www.gsapubs.org 443

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/4/5/435/3050629/435.pdf by guest on 28 September 2021 BARTH ET AL.

would have completely covered the range front fault traces of note in the strongly anisotropic quake cycles, the oblique plate-boundary move- here (Cox and Barrell, 2007), all fault traces are mylonites and Alpine Schist, which have com- ment gradually transports them up the basal presumed to be post-LGM in age. Near Arthur parably high rock mass strengths, and we expect oblique-thrust plane. This causes the fault Creek (Fig. 4D), incised channel offsets associ- the rear of the fault wedge to generally correlate wedge to narrow until new dextral-normal faults ated with well-preserved fault scarps protected with the faultward transition to less anisotropic form farther back. Whatever the mechanics, the from the Whataroa River and glacial scouring fault-damaged rocks (i.e., the damage zone). basal fault is usually still oblique and accommo- record about half of the expected strike-slip The width of the fault wedge toward the range dates the most slip (Norris and Cooper, 2007). motion since the Last Glacial Maximum; most will therefore be limited by the thickness of the localities are ambiguous or record signifi cantly damage zone. Additional Third-Order Controls on the less displacement. Fault offsets of post-LGM The result is a near-surface (~300 m scale) Central Alpine Fault surfaces require most of the accumulated dis- asymmetric positive fl ower structure, or fault placement during this time to have occurred wedge, rooted on a planar, moderately south- It is expected for the near-surface structure on the basinward fault traces, which are espe- east-dipping, dextral-reverse fault plane at depth of the Alpine fault to vary throughout glacial cially prone to fl uvial erosion and slope failures. (Fig. 9). Most fault movement at depth probably and interglacial periods. Removal of sediments If we characterize the central Alpine fault as a occurs on a narrow fault core, 1–2 m wide, and due to glacial abrasion could act to reduce the 055°-striking, 50° southeast-dipping fault with it is only in the upper ~300 m that partitioning width of the fault wedge, as a thinner sedi- an 071°-trending slip vector and a >8-km-deep into the transpressional fl ower structures occurs. ment package would give less distance for the brittle-viscous transition (Boese et al., 2012; This fault wedge is bounded by a basal dextral fault plane to rotate to a lower dip. The mass O’Keefe, 2008), then we would expect at least thrust that tends to shallow as it overthrusts of extensive ice cover during a glaciation would 22 km of displacement to have been accom- unconsolidated sediments in the footwall and serve to lessen the stress perturbations caused modated within brittle fault rocks when they dextral-normal faults that bound its rear. Within by the deep valleys cut into the hanging wall, arrive at the surface. Surface exposures of the the fault wedge, dextral-thrust faults concentrate potentially signifi cantly enough to reduce the Alpine fault thrust over sediments (e.g., Gaunt along the front of the fault wedge and dextral- development of a serially partitioned fault Creek, Hare Mare Creek, Stony Creek, and normal faults along the rear, consistent with zone. Extensive postglacial aggradation of river Martyr River) commonly show discontinuous extrusion of the fault wedge (Fig. 9). The fault and glacial sediment would promote a wider excised clay gouges and ultracataclasites adja- wedge itself consists of incohesive sediments near-surface fault zone as the fault shallowly cent to an active 1–10-cm-thick continuous and semicohesive fault rocks. We propose that overthrusted a thicker sediment package in the gouge zone composed of recycled gouge and the width of the fault wedge is roughly con- footwall, and more sediment was available to reworked glacial till and fl uvioglacial gravels. trolled by the depth to basement in the footwall be incorporated in a “bulldozed” fault wedge. Conversely, the fault gouges in the fault core at and the width of fault-damaged rock in the Periods of degradation should focus the width depth were formed as a result of hydrothermal hanging wall. of surface ruptures by rendering oblique-thrust processes (Warr and Cox, 2001) during >17 km The fault wedge deforms by both discrete wedges subcritical, as previously discussed by of displacement and are smectite rich. These faults and distributed folds (Fig. 9). The reso- Norris and Cooper (1995, 1997). gouges are frictionally weak and therefore lution of the LiDAR data reveals that anticlinal At fi rst glance, the predominance of range- easily accommodate localized fault slip (Boul- ridges are composed of smaller-scale en echelon ward facing dextral-normal scarps on a trans- ton et al., 2012). However, when the fault plane anticlines with a left-stepping sense, opposite to pressive plate boundary may seem counter- begins to overthrust sediments, the weak fault what would be predicted for anticlines produced intuitive. Late-stage uphill-facing normal fault gouges developed at depth during accumulated during dextral wrench tectonics (e.g., Sylvester, scarps are also ubiquitous in the Charwell displacement are abraded along their displaced 1988), suggesting they are more closely related region of the Hope fault in the northern South contact with footwall sediments (the incipient to transpression and fault wedge geometry. Island, despite the fact that the fault accom- fault plane), and a new gouge is formed from Strengthening of the basal oblique thrust as it modates predominantly strike-slip transpres- older fault gouges and footwall sediments. approaches the surface could result in a displace- sive motion (Eusden et al., 2005). Eusden et al. These new gouges will be frictionally stronger ment gradient on the basal plane and cause some (2005) proposed a model in which a 1-km-wide than those inherited from depth. Consequently, shortening to be distributed as folding between fault wedge is extruded between thrust and we expect an increase in frictional resistance to the two fault planes bounding the fault wedge. normal faults, and then collapses to produce a shear on the basal thrust in the near surface (Fig. The average fold axis trend is 055°–060°, i.e., secondary wedge comprising late normal faults 9C). In particular, a component of the strike-slip slightly oblique to the overall fault wedge ori- in a 2-km-wide wedge in an unsupported hang- plate motion is unable to be accommodated on entations of ~048°. A similar analog is observed ing wall. In contrast to observations on the the high-friction, low-angle surfaces and so is on a large scale along the Hikurangi subduction Hope fault, we fi nd that no obvious crosscut- partitioned onto the fault traces at the rear of the zone on the east coast of the North Island, where ting relationships exist between the observed wedge (e.g., nonthermally weakened model of regional folds and strike-slip faults within the fault traces to suggest the near-surface fault Koons et al., 2003). Thus, deformation becomes accretionary prism trend parallel to the trench to zone has evolved (i.e., partitioning has evolved distributed into the lower rock mass strength indicate trench-perpendicular shortening despite with time). We suggest that normal-motion materials in the adjacent footwall and fault rock the overall oblique displacement (e.g., Lamb traces observed on the central Alpine fault arise wedge above (which is highly fractured due and Vella, 1987). The anticlines in our study are purely geometrically to accommodate a more- to off-fault damage developed at low confi n- not produced by classic wrench tectonics, but or-less stable extruding fault wedge consisting ing pressures). New faults form in the hanging by the kinematics of parallel-partitioned oblique of incohesive sediment and semicohesive fault wall to accommodate the deformation, which thrust wedges. rocks. These traces are thus coseismic and not are expected to have the three orientations of While the wedge-bounding dextral-normal postseismic collapse features as on the Hope faults in Figure 7B. We observe relatively few faults are kinematically stable over many earth- fault. The predominantly strike-slip nature of

444 www.gsapubs.org | Volume 4 | Number 5 | LITHOSPHERE

PLAN VIEW OBLIQUE VIEW

Average strike A 048° of the Alpine Fault PACIFIC is 055° N PLATE AUSTRALIAN PLATE 048° Overall relative plate motion

Basal thrust AUSTRALIAN

Strike-slip PLATE FAULT PACIFIC WEDGE PLATE 100 m

PLAN VIEW

251° Overall relative plate motion 270° Basal thrust 214° Strike-slip

B Fluvioglacial C sediments

Strong Fault gouge: Mylonite -Strong Fluvial/glacial/marine Weakest Damage zone -Higher friction sediments Ultramylonite -Result of ~3 km displacement ??? Cataclasite Weak Fault gouge: Western Province -Weak Damage zon Strong -Lower friction -Result of >20 km 100 m displacement e

Figure 9. Geometric models. (A) Oblique three-dimensional model based on geometry near Franz Josef (Fig. 4C). Topographic profi le is derived from the light detection and ranging (LiDAR) digital elevation model. The relative sizes of the arrows show how slip is partitioned relative to a stationary Australian plate. Lines on fault planes show expected slip vectors from fi eld data and calculations. Plan views show expected slip vector partitioning on the fault wedge boundaries (does not account for deformation within the fault wedge). (B) Fault-perpendicular cross section through front of model in A showing fault wedge structure. (C) Conceptual model showing relative strengths of materials. Note the signifi cance of the depth to basement in the footwall for controlling the basal fault dip and the width of the fault damage zone for controlling the width of the fault wedge.

LITHOSPHERE | Volume 4 | Number 5 | www.gsapubs.org 445

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/4/5/435/3050629/435.pdf by guest on 28 September 2021 BARTH ET AL.

many of the apparently “normal” traces here advection and exhumation cause localization of ACKNOWLEDGMENTS also argues against a collapse mechanism. The oblique slip on a single, relatively planar, mod- fact that some of these fault scarps have faces erately to steeply southeast-dipping shear zone We acknowledge the New Zealand Natural Haz- greater than 10–15 m high, and a characteristic at depth (Ellis et al., 2006; Koons et al., 2003). ards Research Platform for funding this study. earthquake here generates <1.5 m throw, sug- This orientation is inherited above the brittle- We wish to thank Will Ries at GNS Science gests that once established, reactivation of these viscous transition due to the anisotropic fabric for his work processing the light detection and faults is preferred over formation of new faults developed at depth. Development of weak clay ranging (LiDAR) data. We thank Rupert Suther- (as also demonstrated independently in our minerals and associated high fl uid pressures land for helpful comments. This manuscript was slip tendency analysis). This suggests that the contribute to a localized fault zone in the upper greatly improved by critical and constructive fault confi guration has been more-or-less stable crust (Warr and Cox, 2001). Consequently, reviews by Mike Oskin and Kate Scharer, and since the LGM. We predict future earthquake at fi rst order, the structure has a remarkably editorial comments by Eric Kirby. surface ruptures will appear on or near known straight and continuous surface expression with fault traces. no step-overs greater than 1 km (Sutherland Second- and third-order structures are et al., 2007). REFERENCES CITED dependent on the fi rst-order controls of geom- At the second order (104–103 m), the cen- etry, continuity, and plate-motion kinematics of tral section of the Alpine fault (where uplift Adams, C.J.D., 1979, Age and origin of the Southern Alps, in Walcott, R.I., and Cresswell, M.M., eds., The Origin the fault at depth. The third-order structure of a rates are high) is partitioned along strike into of the Southern Alps: Bulletin of the Royal Society of given area is strongly infl uenced by its position sequenced (i.e., serial) oblique-thrust and New Zealand, v. 18, p. 73–78. Allen, J.L., and Shaw, C.A., 2011, Seismogenic structure of on a second-order serially partitioned segment strike-slip segments that arise due to stress a crystalline thrust fault: Fabric anisotropy and coeval because the orientation of the basal thrust or perturbations from hanging-wall topographic pseudotachylyte–mylonitic pseudotachylyte in the strike-slip segment will have an infl uence on variations in a transpressional regime on a Grizzly Creek shear zone, Colorado, in Fagereng, A., Toy, V.G., and Rowland, J., eds., Geology of the Earth- the geometry of the near-surface fault wedge. dipping structure (Norris and Cooper, 1995, quake Source: A Volume in Honour of Rick Sibson: Third-order transpressional fl ower structures 1997). Imbricate thrusts at this scale form as Geological Society of London Special Publication 359, are most obvious on oblique-thrust segments a result of rapid river incision reducing the p. 135–151. Anderson, E.M., 1951, The Dynamics of Faulting and Dyke (e.g., McCulloughs Creek, Darnley Creek, wedge taper below its critical value (Norris Formation: Edinburgh, UK, Oliver and Boyd, 206 p. and Franz Josef), while strike-slip segments and Cooper, 1997) and/or decreasing dip of the Arrowsmith, J.R., and Zielke, O., 2009, Tectonic geomorphology of the San Andreas fault zone from high resolution host fault wedges bounded by parallel strike- basal thrust as it progressively overthrusts foot- topography: An example from the Cholame segment: slip faults (e.g., near Arthur Creek and upper wall sediments. Geomorphology, v. 113, p. 70–81, doi:10.1016/j.geomorph Waitangi-taona River). In this sense, there is a At the third order (103–100 m) asymmetric .2009.01.002. Barnes, P.M., 2009, Postglacial (after 20 ka) dextral slip rate hierarchy of infl uences on fault segmentation positive fl ower structures in the hanging wall of the offshore Alpine fault, New Zealand: Geology, v. 37, from continuous fault planes and shear zones are bounded by parallel-partitioned dextral-nor- p. 3–6, doi:10.1130/G24764A.1. at depth (<106–104 m length scales) to zones of mal and thrust faults rooted at shallow depths Barnes, P.M., Sutherland, R., and Delteil, J., 2005, Strike- slip structure and sedimentary basins of the southern 3 0 partitioned faults in the near surface (10 –10 m (<600 m) on a planar, moderately southeast- Alpine fault, Fiordland, New Zealand: Geological Soci- length scales). dipping, dextral-reverse fault plane. These ety of America Bulletin, v. 117, p. 411–435, doi:10.1130 /B25458.1. The near-surface complexity in this region parallel-partitioned fault wedges form with Barrell, D.J.A., 2011, Quaternary glaciers of New Zealand, in has formed despite paleoseismic evidence that characteristic widths of 200–600 m bounded by Ehlers, J., et al., eds., Quaternary Glaciations—Extent the Alpine fault ruptures during one through- and containing kinematically stable fault traces. and Chronology: Amsterdam, Elsevier, p. 1047–1064. Benson, W.N., 1952, Meeting of the Geological Division of going ~M 7–8 event every ~100–500 yr (Wells Likely influences on third-order structure the Pacifi c Science Congress in New Zealand, February et al., 1999; Yetton, 1998; Yetton et al., 1998; include thickness of footwall sediments, width 1949, Interim Proceedings of the Geological Society of Sutherland et al., 2007; Berryman et al., 2012a). of the fault damage zone, increases in friction America, 1950, p. 11–13. Berryman, K.R., Beanland, S., Cooper, A.F., Cutten, H.N., The complexity therefore illustrates that during on the basal fault with increasing overthrusting Norris, R.J., and Wood, P.R., 1992, The Alpine Fault, these large to great oblique-motion fault rup- (due to abrasion of fault rocks), a decrease in New Zealand: Variation in Quaternary structural style and geomorphic expression: Annales Tectonicae, Spe- tures rooted in basement, slip does not remain basal fault dip in the near surface, sea level, glacial issue, supplement to v. 6, p. 126–163. localized when the fault propagates through cial cycles of sedimentation, abrasion, and ice Berryman, K.R., Cochran, U.A., Clark, K.J., Biasi, G.P., Lang- unconsolidated surfi cial sediment and fault- cover, and changes in stress orientations toward ridge, R.M., and Villamor, P., 2012a, Twenty-four surface-rupturing earthquakes over 8000 years on the damaged rock under low confi ning pressures. a free surface. Alpine fault, New Zealand: Science (in press). Near-surface complexity in the upper 1 km of A fault kinematic analysis can predict the Berryman, K.R., Cooper, A., Norris, R., Villamor, P., Suther- the crust here is insuffi cient to halt earthquake orientations of fault traces observed and indi- land, R., Wright, T., Schermer, E., Langridge, R., and Biasi, G., 2012b, Late Holocene rupture history of the rupture propagation (as proposed at different cates that topography is not a signifi cant factor Alpine fault in South Westland, New Zealand: Bulletin scales by Sutherland et al., 2007; Norris and at this scale. Most fault traces observed have of the Seismological Society of America, v. 102, p. 620– 638, doi:10.1785/0120110177. Cooper, 1995). large offsets, indicating they are the product Boese, C.M., Townend, J., Smith, E., and Stern, T., 2012, of many surface-rupturing earthquakes. A slip Microseismicity and stress in the vicinity of the Alpine CONCLUSIONS tendency analysis confi rms the fault trace ori- fault, central Southern Alps, New Zealand: Journal of Geophysical Research, v. 117, 20 p., doi:10.1029 entations are stable and are expected to accom- /2011JB008460. We used LiDAR data to contribute to a struc- modate repeated slip. Despite the multiplicity Boulton, C.J., Carpenter, B.M., Toy, V., and Marone, C., 2012, tural hierarchy of along-strike observations on of near-surface traces, most displacement still Physical properties of surface outcrop cataclastic fault rocks, Alpine fault, New Zealand: Geochemistry Geo- the Alpine fault. occurs on a basal slip surface that preserves the physics Geosystems, v. 13, no. 1, 13 p. At the fi rst order (<106–104 m), the Alpine hanging-wall fault rock sequence. We predict Chan, Y.C., Chen, Y.G., Shih, T.Y., and Huang, C., 2007, Charac- terizing the Hsincheng active fault in northern Taiwan fault is a kinematically driven system in which future earthquake surface ruptures will appear using airborne LiDAR data: Detailed geomorphic fea- seismic loading and thermal weakening by on or near fault traces identifi ed in this study. tures and their structural implications: Journal of Asian

446 www.gsapubs.org | Volume 4 | Number 5 | LITHOSPHERE

Earth Sciences, v. 31, p. 303–316, doi:10.1016/j.jseaes near Truckee, California: Bulletin of the Seismologi- Ramsay, J.G., 1980, The crack-seal mechanism of rock .2006.07.029. cal Society of America, v. 101, no. 3, p. 1162–1181, doi: deformation: Nature, v. 284, p. 135–139, doi:10.1038 Cloos, H., 1928, Experimente zur inneren tektonik: Central- 10.1785/0120090261. /284135a0. blatt für Mineralogie, Abt. B, p. 609–621. Koons, P.O., 1987, Some thermal and mechanical conse- Reed, J.J., 1964, Mylonites, cataclasites, and associated rocks Collettini, C., and Trippetta, F., 2007, A slip tendency analysis quences of rapid uplift: An example from the Southern along the Alpine fault, South Island, New Zealand: to test mechanical and structural control on aftershock Alps, New Zealand: Earth and Planetary Science Let- New Zealand Journal of Geology and Geophysics, v. 7, rupture planes: Earth and Planetary Science Letters, ters, v. 86, p. 307–319. p. 645–684. v. 255, p. 402–413, doi:10.1016/j.epsl.2007.01.001. Koons, P.O., Norris, R.J., Craw, D., and Cooper, A.F., 2003, Riedel, W., 1929, Zur Mechanik geologischer Brucherschei- Cooper, A.F., and Norris, R.J., 1994, Anatomy, structural evolu- Infl uence of exhumation on the structural evolution nungen: Zentralblatt für Mineralogie, Geologie, und tion, and slip rate of a plate-boundary thrust: The Alpine of transpressional plate boundaries: An example Palaeontologie, v. 1929B, p. 354–368. fault at Gaunt Creek, Westland, New Zealand: Geologi- from the Southern Alps, New Zealand: Geology, v. 31, Sibson, R.H., 1977, Fault rocks and fault mechanisms: Jour- cal Society of America Bulletin, v. 106, no. 5, p. 627–633, no. 1, p. 3–6, doi:10.1130/0091-7613(2003)031<0003: nal of the Geological Society of London, v. 133, no. 3, doi:10.1130/0016-7606(1994)106<0627:ASEASR>2.3.CO;2. IOEOTS>2.0.CO;2. p. 191–213, doi:10.1144/gsjgs.133.3.0191. Cooper, A.F., and Norris, R.J., 1995, Displacement on the Korup, O., 2004, Geomorphic implications of fault zone Sibson, R.H., White, S.H., and Atkinson, B.K., 1979, Fault rock Alpine fault at Haast River, South Westland, New Zea- weakening: Slope instability along the Alpine fault, distribution and structure within the Alpine fault zone: land: New Zealand Journal of Geology and Geophysics, South Westland to Fiordland: New Zealand Journal of A preliminary account, in Walcott, R.I., and Cresswell, v. 38, no. 4, p. 509–514. Geology and Geophysics, v. 47, p. 257–267, doi:10.1080 M.M., eds., The Origin of the Southern Alps: Bulletin Cox, S.C., and Barrell, D.J.A. (compilers), 2007, Geology of /00288306.2004.9515052. of the Royal Society of New Zealand, v. 18, p. 55–65. the Aoraki Area, Scale 1:250,000: Lower Hutt: GNS Sci- Lamb, S.H., and Vella, P., 1987, The last million years of defor- Sibson, R.H., White, S.H., and Atkinson, B.K., 1981, Struc- ence: Institute of Geological & Nuclear Sciences Geo- mation in part of the New Zealand plate-boundary ture and distribution of fault rocks in the Alpine fault logical Map 15, scale 1:250,000, 71 p. + 1 folded map. zone: Journal of Structural Geology, v. 9, no. 7, p. 877– zone, New Zealand, in McClay, K.R., and Price, N.J., Cox, S.C., Stirling, M.W., Herman, F., Gerstenberger, M., and 891, doi:10.1016/0191-8141(87)90088-5. eds., Thrust and Nappe Tectonics: The Geological Soci- Ristau, J., 2012, Potentially active faults in the rapidly Langridge, R.M., Villamor, P., Basili, R., Almond, P., Martinez- ety of London Special Publications, v. 9, p. 197–210, eroding landscape adjacent to the Alpine fault, central Diaz, J.J., and Canora, C., 2010, Revised slip rates for doi:10.1144/GSL.SP.1981.009.01.18. Southern Alps, New Zealand: Tectonics, v. 31, 24 p., the Alpine fault at Inchbonnie: Implications for plate Simpson, G.D.H., Cooper, A.F., and Norris, R.J., 1994, Late doi:10.1029/2011TC003038. boundary kinematics of South Island, New Zealand: Quaternary evolution of the Alpine fault zone at Paringa, Cunningham, D., Grebby, S., Tansey, K., Gosar, A., and Kastelic , Lithosphere, v. 2, p. 139–152, doi:10.1130/L88.1. South Westland: New Zealand Journal of Geology V., 2006, Application of airborne LiDAR to mapping Leitner, B., Eberhart, P.D., Anderson, H., and Nabelek, J.L., and Geophysics, v. 37, p. 49–58, doi:10.1080/00288306 seismogenic faults in forested mountainous terrain, 2001, A focused look at the Alpine fault, New Zealand: .1994.9514600. southeastern Alps, Slovenia: Geophysical Research Seismicity, focal mechanisms and stress observa- Suggate, R.P., 1968, The Paringa Formation, Westland, New Letters, v. 33, 5 p., doi:10.1029/2006GL027014. tions: Journal of Geophysical Research, v. 106, no. B2, Zealand: New Zealand Journal of Geology and Geo- DeMets, C., Gordon, R.G., Argus, D.F., and Stein, S., 1994, p. 2193–2220, doi:10.1029/2000JB900303. physics, v. 11, p. 345–355. Effect of revision to the geomagnetic reversal time Little, T.A., Cox, S., Vry, J.K., and Batt, G., 2005, Variations Suggate, R.P., 1990, Late Pliocene and Quaternary glaciations scale on estimates of current plate motions: Geophysi- in exhumation level and uplift-rate along the oblique- of New Zealand: Quaternary Science Reviews, v. 9, cal Research Letters, v. 21, p. 2191–2194, doi:10.1029 slip Alpine fault, central Southern Alps, New Zea- p. 175–197. /94GL02118. land: Geological Society of America Bulletin, v. 117, Sutherland, R., Davey, F.J., and Beavan, J., 2000, Plate bound- Department of Geology, University of Otago, 2012, Alpine p. 707–723. ary deformation in South Island, New Zealand, is related fault maps: http://www.otago.ac.nz/geology/research McCaffrey, R., 1992, Oblique plate convergence, slip vec- to inherited lithospheric structure: Earth and Planetary /structural_geology/alpinefault/index.html#alpine_fault tors, and forearc deformation: Journal of Geophysical Science Letters, v. 177, p. 141–151, doi:10.1016/S0012 _maps (accessed May 2012). Research, v. 97, p. 8905–8915, doi:10.1029/92JB00483. -821X(00)00043-1. De Pascale, G.P., and Langridge, R.M., 2012, New on-fault McCaffrey, R., 1996, Slip partitioning at convergent plate Sutherland, R., Berryman, K.R., and Norris, R.J., 2006, Qua- evidence for a great earthquake in 1717, central Alpine boundaries of SE Asia, in Hall, R., and Blundell, D., ternary slip rate and geomorphology of the Alpine fault, New Zealand: Geology, v. 40, doi:10.1130/G33363.1 eds., Tectonic Evolution of Southeast Asia: Geological fault: Implications for the kinematics and seismic (in press). Society of London Special Publication 106, p. 3–18. hazard in southwest New Zealand: Geological Soci- Easterbrook, L., 2010, The Alpine Fault Zone along the Molnar, P., and Dayem, K.E., 2010, Major intracontinental ety of America Bulletin, v. 118, p. 464–474, doi:10.1130 Waitangi-taona River, West Coast, New Zealand [M.Sc. strike-slip faults and contrasts in lithospheric strength: /B25627.1. thesis]: Dunedin, New Zealand, University of Otago, Geosphere, v. 6, p. 444–467, doi:10.1130/GES00519.1. Sutherland, R., Eberhart-Phillips, D., Harris, R.A., Stern, T., 211 p. Norris, R.J., and Cooper, A.F., 1986, Small-scale fractures, Beavan, J., Ellis, S., Henrys, S., Cox, S., Norris, R.J., Ellis, S., Beavan, J., Eberhart-Phillips, D., and Stöckhert, B., glaciated surfaces, and recent strain adjacent to the Berryman, K.R., Townend, J., Bannister, S., Pettinga, 2006, Simplifi ed models of the Alpine fault seismic cycle: Alpine fault, New Zealand: Geology, v. 14, p. 687–690, J., Leitner, B., Wallace, L., Little, T.A., Cooper, A.F., Yet- Stress transfer in the mid-crust: Geophysical Journal doi:10.1130/0091-7613(1986)14<687:SFGSAR>2.0.CO;2. ton, M., and Stirling, M., 2007, Do great earthquakes International, v. 166, p. 386–402, doi:10.1111/j.1365-246X Norris, R.J., and Cooper, A.F., 1995, Origin of small-scale occur on the Alpine fault in central South Island, New .2006.02917.x. segmentation and transpressional thrusting along the Zealand?, in Okaya, D., Stern, T., and Davey, F., eds., A Engelkemeir, R.M., and Khan, S.D., 2008, LiDAR mapping of Alpine fault, New Zealand: Geological Society of Amer- Continental Plate Boundary: Tectonics at South Island, faults in Houston, Texas, USA: Geosphere, v. 4, no. 1, ica Bulletin, v. 107, p. 231–240, doi:10.1130/0016-7606 New Zealand: American Geophysical Union Geophysi- p. 170–182, doi:10.1130/GES00096.1. (1995)107<0231:OOSSSA>2.3.CO;2. cal Monograph 175, p. 235–251. Eusden, J.D., Pettinga, J.R., and Campbell, J.K., 2005, Norris, R.J., and Cooper, A.F., 1997, Erosional control on the Sutherland, R., Townend, J., Toy, V.G., Cox, S.C., Prior, D., Structural collapse of a transpressive hanging-wall structural evolution of a transpressional thrust complex and Eccles, J.D., 2011, Operations Summary and Pre- fault wedge, Charwell region of the Hope fault, South on the Alpine fault, New Zealand: Journal of Structural liminary Findings from the First Phase of the Deep Island, New Zealand: New Zealand Journal of Geology Geology, v. 19, p. 1323–1342, doi:10.1016/S0191-8141 Fault Drilling Project (DFDP-1), Alpine Fault, New and Geophysics, v. 48, p. 295–309. (97)00036-9. Zealand, Abstract T41C-03 presented at 2011 Ameri- Frankel, K.L., and Owen, L.A., 2013, Transform plate margins Norris, R.J., and Cooper, A.F., 2001, Late Quaternary slip rates can Geophysical Union Fall Meeting, San Francisco, and strike-slip fault systems, in Shroder, J., ed., Trea- and slip partitioning on the Alpine fault, New Zealand: 5–9 December. tise on Geomorphology: Tectonic Geomorphology, v. 5 Journal of Structural Geology, v. 23, no. 2–3, p. 507–520, Sylvester, A.G., 1988, Strike-slip faults: Geological Soci- (in press). doi:10.1016/S0191-8141(00)00122-X. ety of America Bulletin, v. 100, no. 11, p. 1666–1703, Hanson, C.R., Norris, R.J., and Cooper, A.F., 1990, Regional Norris, R.J., and Cooper, A.F., 2003, Very high strains recorded doi:10.1130/0016-7606(1988)100<1666:SSF>2.3.CO;2. fracture patterns east of the Alpine fault between the in mylonites along the Alpine fault, New Zealand: Impli- Toy, V.G., 2007, Rheology of the Alpine Fault Mylonite Zone: Fox and Franz Josef Glaciers, Westland, New Zealand: cations for the deep structure of plate boundary faults: Deformation Processes at and Below the Base of the New Zealand Journal of Geology and Geophysics, v. 33, Journal of Structural Geology, v. 25, p. 2141–2157, Seismogenic Zone in a Major Plate Boundary Struc- p. 617–622. doi:10.1016/S0191-8141(03)00045-2. ture [Ph.D. thesis]: Dunedin, New Zealand, University Harding, D.J., and Berghoff, G.S., 2000, Fault scarp detec- Norris, R.J., and Cooper, A.F., 2007, The Alpine fault, New of Otago, 629 p. tion beneath dense vegetation cover: Airborne LiDAR Zealand: Surface geology and fi eld relationships, in Toy, V.G., Prior, D.J., and Norris, R.J., 2008, Quartz fabrics mapping of the Seattle fault zone, Bainbridge Island, Okaya, D., Stern, T., and Davey, F., eds., A Continen- in the Alpine fault mylonites: Infl uence of pre-existing Washington State, in Proceedings of the American tal Plate Boundary: Tectonics at South Island, New preferred orientations on fabric development during Society of Photogrammetry and Remote Sensing Zealand: American Geophysical Union Geophysical progressive uplift: Journal of Structural Geology, v. 30, Annual Conference: Washington, D.C., p. 1–11. Monograph 175, p. 157–175. p. 602–621, doi:10.1016/j.jsg.2008.01.001. Haugerud, R.A., Harding, D.J., Johnson, S.Y., Harless, J.L., O’Keefe, B.C., 2008, Microseismicity of the Central Alpine Toy, V.G., Craw, D., Cooper, A.F., and Norris, R.J., 2010, and Weaver, C.S., 2003, High-resolution LiDAR topog- Fault Region, New Zealand [M.Sc. thesis]: Wellington, Thermal regime in the central Alpine fault zone, New raphy of the Puget Lowland, Washington—A bonanza New Zealand, University of Victoria, 124 p. Zealand: Constraints from microstructures, biotite for earth science: GSA Today, no. 6, p. 4–10, doi:10.1130 Pearson, C., 1994, Geodetic strain determinations from the chemistry and fluid inclusion data: Tectonophysics, /1052-5173(2003)13<0004:HLTOTP>2.0.CO;2. Okarito and Godley-Tekapo regions, central South v. 485, p. 178–192, doi:10.1016/j.tecto.2009.12.013. Hunter, L.E., Howle, J.F., Rose, R.S., and Bowden, G.W., Island, New Zealand: New Zealand Journal of Geology Warr, L.N., and Cox, S., 2001, Clay mineral transformations 2011, LiDAR-assisted identifi cation of an active fault and Geophysics, v. 37, p. 309–318. and weakening mechanisms along the Alpine fault,

LITHOSPHERE | Volume 4 | Number 5 | www.gsapubs.org 447

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/4/5/435/3050629/435.pdf by guest on 28 September 2021 BARTH ET AL.

New Zealand, in Holdsworth, R.E., Strachan, R.A., Wright, C.A., 1998, Geology and Paleoseismology of the Zachariasen, J., and Prentice, C.S., 2008, Detailed Map- Magloughlin, J.F., and Knipe, R.J. eds., The Nature Central Alpine Fault, New Zealand [M.Sc. thesis]: ping of the Northern San Andreas Fault Using LiDAR and Tectonic Signiﬁ cance of Fault Zone Weakening: Dunedin, New Zealand, University of Otago, 260 p. Imagery: U.S. Geological Survey Final Technical Report Geological Society of London Special Publication 186, Yetton, M.D., 1998, Progress in understanding the paleoseis- 05HQGR0069, 47 p. p. 85–101. micity of the central and northern Alpine fault, West- Zielke, O., Arrowsmith, J.R., Ludwig, L.G., and Akciz, S.O., Wellman, H.W., 1955, The Geology between Bruce Bay and land, New Zealand: New Zealand Journal of Geology 2010, Slip in the 1857 and earlier large earthquakes Haast River, South Westland: New Zealand Geological and Geophysics, v. 41, no. 4, p. 475–483. along the Carrizo Plain, San Andreas Fault: Science, Survey Bulletin 48, 46 p. Yetton, M.D., and Nobes, D.C., 1998, Recent vertical offset and v. 327, no. 5969, p. 1119–1122, doi:10.1126/science Wells, A., Yetton, M.D., Duncan, R.P., and Stewart, G.H., 1999, near-surface structure of the Alpine fault in Westland, .1182781. Prehistoric dates of the most recent Alpine fault earth- New Zealand, from ground penetrating radar proﬁ ling: quakes, New Zealand: Geology, v. 27, p. 995–998, doi: New Zealand Journal of Geology and Geophysics, v. 41, MANUSCRIPT RECEIVED 13 JANUARY 2012 10.1130/0091-7613(1999)027<0995:PDOTMR>2.3.CO;2. no. 4, p. 485–492, doi:10.1080/00288306.1998.9514825. REVISED MANUSCRIPT RECEIVED 12 MAY 2012 Wentworth, C.M., and Zoback, M.D., 1989, The style of late Yetton, M.D., Wells, A., and Traylen, N.J., 1998, Proba- MANUSCRIPT ACCEPTED 17 MAY 2012 Cenozoic deformation at the eastern front of the Cali- bility and Consequences of the Next Alpine Fault fornia Coast Ranges: Tectonics, v. 8, no. 2, p. 237–246, Earthquake: Earthquake Commission New Zealand doi:10.1029/TC008i002p00237. Research Report 95/193. Printed in the USA

448 www.gsapubs.org | Volume 4 | Number 5 | LITHOSPHERE

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/4/5/435/3050629/435.pdf by guest on 28 September 2021