Fault Kinematics and Surface Deformation Across a Releasing
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Fault kinematics and surface deformation across a releasing bend during the 2010 MW 7.1 Darfi eld, New Zealand, earthquake revealed by differential LiDAR and cadastral surveying Brendan Duffy1,†, Mark Quigley1, David J.A. Barrell2; Russ Van Dissen2, Timothy Stahl1, Sébastien Leprince3, Craig McInnes4, and Eric Bilderback1 1Department of Geological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand 2GNS Science, PO Box 30-368, Lower Hutt 5040, New Zealand 3Division of Geological and Planetary Sciences, California Institute of Technology, MC 170-25 1200 E. California Blvd., Pasadena, California 91125, USA 4Fox and Associates–Consulting Surveyors, 333 Harewood Road, Christchurch 8053, New Zealand ABSTRACT INTRODUCTION LiDAR survey fl own 5 months before the earth- quake was partly overlapped by LiDAR fl own a Dextral slip at the western end of the Over the past 10 years or so, documentation few days after the earthquake. Also, a cadastral east-west–striking Greendale fault during of earthquake fault surface rupture by well-es- survey was conducted 1 month before the earth- the 2010 MW 7.1 Darfi eld earthquake trans- tablished fi eld methods, including geological/ quake on a property through which the Green- ferred onto a northwest-trending segment, geomorphological mapping and geodetic sur- dale fault subsequently ruptured for ~2 km. across an apparent transtensional zone, here veying, has increasingly been supplemented by Rupture of the Greendale fault also temporarily named the Waterford releasing bend. We technologies such as interferometric synthetic diverted the course of the Hororata River. In this used detailed surface mapping, differential aperture radar (InSAR) (e.g., Reigber et al., study, we mapped the earthquake-induced fl ood, analysis of pre- and postearthquake light de- 1997; Price and Burgmann, 2002; Beavan et al., analyzed pre- and postearthquake LiDAR sur- tection and ranging (LiDAR), and property 2010a) and light detection and ranging (LiDAR ) veys, and undertook postearthquake cadastral boundary (cadastral) resurveying to produce (e.g., Hudnut et al., 2002; Quigley et al., 2012). resurveying of property boundaries, to further high-resolution (centimeter-scale) estimates In combination, these methods provide an op- aid understanding of the surface deformation of coseismic ground-surface displacements portunity to examine fault deformation and and displacement across the Greendale fault. across the Waterford releasing bend. Our kinematics in unrivaled detail and precision. These data sets span a zone where the fault strike results indicate that the change in orienta- Contemporary surface-rupture events, in favor- changed by ~40°, and they have allowed us to tion on the Greendale fault incorporates ele- able land-surface settings, provide primary characterize this fault bend in remarkable de- ments of a large-scale releasing bend (from evidence for the style and kinematics of fault tail. Documentation of this detail is the focus of the viewpoint of westward motion on the defor mation, and documentation of their char- this paper. south side of the fault) as well as a smaller- acter provides an invaluable interpretive ana- scale restraining stepover (from the view- logue for structural and kinematic studies of THE DARFIELD EARTHQUAKE point of southeastward motion on the north prehistoric fault deformation. side of the fault). These factors result in the The 2010 Darfi eld earthquake in Canterbury, New Zealand lies astride the boundary be- Water ford releasing bend exhibiting a de- New Zealand (Fig. 1), caused surface rupture of tween the Pacifi c and Australian plates, at a lo- crease in displacement to near zero at the the Greendale fault across a low-relief alluvial cation where they converge obliquely at rates of change in strike, and the presence within plain. The plain is an intensively farmed agricul- 30–50 mm/yr (DeMets et al., 2010) (Fig. 1A). the overall releasing bend of a nested, local- tural region and contains a multitude of straight Continental collision across the South Island ized restraining stepover with contractional lines in the form of roads, fences, and ditches drives uplift of the Southern Alps (Norris and bulging. The exceptional detail of surface that provided ideal piercing points for quantify- Cooper, 2001) and is expressed by varying deformation and kinematics obtained from ing fault rupture (Barrell et al., 2011; Quigley rates and styles of active deformation across this contemporary surface-rupture event il- et al., 2012; Villamor et al., 2012). Quigley et al. Canterbury (Pettinga et al., 2001; Campbell lustrates the value of multimethod investiga- (2012) took advantage of these piercing points et al., 2012). The rupture of a fault network tions. Our data provide insights into strike- to undertake detailed fi eld mapping and, in beneath the Canterbury Plains, eastern South slip fault bend kinematics, and into the combination with evaluation of LiDAR fl own Island, on 4 September 2010 generated the MW potentially subtle but important structures after the earthquake, were able to quantify 7.1 Darfi eld earthquake (Beavan et al., 2010b; that may be present at bends on historic and fault offsets to high precision. Serendipitously, Gledhill et al., 2010, 2011; Beavan et al., 2012), prehistoric rupture traces. two high-quality geodetic data sets had been which caused widespread ground shaking and acquired prior to the earthquake, in the vicin- damage (Cubrinovski et al., 2010; Gledhill †E-mail: [email protected] ity of the western end of the Greendale fault. A et al., 2010; Quigley et al., 2010a, 2010b, 2013; GSA Bulletin; March/April 2013; v. 125; no. 3/4; p. 420–431; doi: 10.1130/B30753.1; 7 fi gures; 3 tables. 420 For permission to copy, contact [email protected] © 2013 Geological Society of America Fault interactions at a releasing bend 165° E 170° E 175° E 180° 175° W fault trace, the strike change between the West Kermadec and Central segments is transtensional in na- 35° S 500 km Trench 35° S ture (Quigley et al., 2012), so the zone across which the strike change occurs is referred to 48F here as the Waterford releasing bend, taking Australian its name from a nearby farm. Dextral displace- plate ment of up to ~5.3 m on the Central segment 44F decreases to ~1.2 m on the West segment (Quig- 40° S ley et al., 2012). The West segment displayed Hikurangi 40° S Trough a notably south-side-up vertical component of F offset (~1.5 m), which caused temporary partial 39 avulsion of the Hororata River (Quigley et al., Region affected 2010b; Barrell et al., 2011) (Fig. 2). Seismic Chch by earthquake Puysegur Alpine Fault Ash (Fig. 1B) source models indicate that the Greendale fault trench rupture proceeded bilaterally from the vicinity 45° S Canterbury Plains Pacific 45° S of the Water ford releasing bend, which itself lies A Southern Alps plate close to the intersection of the Greendale fault 165° E 170° E 175° E 180° 175° W with the northeast-southwest–striking Charing Cross reverse fault, on which the Darfi eld earth- quake was initiated (Fig. 2) (Holden et al., 2011; Beavan et al., 2012). Regional METHODS shortening Christchurch Flood Mapping Darfield We mapped the extent of avulsion-induced postearthquake fl ooding (Figs. 2 and 3) by digi- Fig. 2 ^ tizing fl ooded areas seen in a set of overlapping oblique aerial photographs taken ~12 h after the ^ Earthquake epicentre Darfield eq. surface rupture earthquake. We georeferenced the photographs Darfield eq. blind rupture using ArcGIS software with reference to digi- Post-Darfield eq blind ruptures tal topographic maps and pre-earthquake digital 20 km Other active faults and folds B orthophotos. Figure 1. Regional setting. (A) New Zealand plate boundary and Cadastral Surveys relative motion vectors (mm/yr) between the Australian and Pacifi c plates (DeMets et al., 2010). Canterbury Plains form the low relief Cadastral surveys have been used to docu- east of the Southern Alps in the central South Island. Ash—Ash- ment surface displacements resulting from burton; Chch—Christchurch. (B) Location of the Greendale fault the Chi-Chi earthquake in Taiwan (Lee et al., west of Christchurch in mid-Canterbury. The extent of surface 2006, 2010, 2011). A cadastral property sur- rupture is from Quigley et al. (2012), and extents of blind ruptures vey done about 1 month before the earthquake are from Beavan et al. (2012). Known active (i.e., late Quaternary) in New Zealand spanned the northern half of faults and folds are based on GNS Science QMAP data sets (Cox and the West segment of the Greendale fault. Base- Barrell, 2007; Forsyth et al., 2008). Regional shortening direction is line surveying employed a Trimble R8 Global from Sibson et al. (2011). Navigation Satellite System (GNSS) real-time kinematic (RTK), and the survey was adjusted in “12d Model” software using simple loops and Van Dissen et al., 2011). Geodetic modeling Mesozoic graywacke rock, and propagated to the Bowditch adjustment method (Bowditch, has revealed that this single earthquake event the surface through a surfi cial 1–1.5-km-thick 1808). The survey was fi xed relative to local consisted of an interlinked succession of rup- cover of post–mid-Cretaceous sedimentary benchmarks by locating the RTK base station tures on several fault structures (Figs. 1B and 2) strata, including as much as 500 m of Qua- on a buried iron tube witness mark that was es- (Beavan et al., 2012). All remained blind, apart ternary fl uvial gravels (Browne et al., 2012; tablished relative to three local benchmarks in from the Greendale fault, which produced an Jongens et al., 2012). 2004. The fl at, unforested farmland provided a ~30-km-long surface rupture, predominantly The Greendale fault is composed of three favorable global positioning system (GPS) envi- strike slip with dextral sense (Quigley et al., geometric segments, each named for their rela- ronment, so the baseline survey over the survey 2010a, 2010b, 2012; Barrell et al., 2011).