Previously Unknown Fault Shakes New Zealand's South Island

Eos, Vol. 91, No. 49, 7 December 2010

Volume 91 number 49 7 DECEMber 2010 EOS, Transactions, American Geophysical Union pages 469–488

trace greater than 29 kilometers long (Fig- Previously Unknown Fault Shakes ure 1a). Using data from New Zealand national and strong-motion seismic net- works, New Zealand seismologists have New Zealand’s South Island identified a reverse faulting component in the overall rupture sequence [Gledhill et al., PAGES 469–470 Fault about 100 kilometers north of the city. 2010]. As of mid-November, the region has Moment tensor solutions indicate that the experienced thousands of aftershocks of At 4:35 A.M. local time on 4 September Darfield earthquake main shock is associ- local magnitude (ML) greater than 2, includ- (1635 UTC, 3 September), a previously unrec- ated with almost purely dextral strike-slip ing 12 aftershocks of ML greater than 5.0, ognized fault system ruptured in the Canter- displacement on a subvertical, nearly east- with decreasing frequency in approximate bury region of New Zealand’s South Island, west striking fault plane. The event pro- accordance with current theories of after- producing a moment magnitude (Mw) 7.1 duced a dextral strike-slip surface rupture shock decay. earthquake that caused widespread damage throughout the area. In stark contrast to the 2010 Mw 7.0 Haiti earthquake, no deaths occurred and only two injuries were reported despite the epicenter’s location about 40 kilometers west of Christchurch (population ~386,000). The Canterbury region now faces a rebuilding estimated to cost more than NZ$4 billion (US$2.95 billion). On the positive side, this earthquake has provided an opportunity to document the dynamics and effects of a major strike-slip fault rupture in the absence of death or seri- ous injury. The low-relief and well-maintained agricultural landscape of the Canterbury Plains helped scientists characterize very sub- tle earthquake-related ground deformation at high resolution, helping to classify the earthquake’s basic geological features [Quigley et al., 2010]. The prompt mobilization of col- laborating scientific teams allowed for rapid data capture immediately after the earthquake, and new scientific programs directed at developing a greater understanding of this event are under way. Fig. 1. (a) Digital elevation map of Canterbury region showing location of Greendale Fault and The September 2010 Darfield (Canterbury) other tectonically active structures relative to selected urban centers. Red lines are active faults, Earthquake and green lines are active folds (data from Forsyth et al. [2008] (see www.gns.cri.nz, search word “QMAP Christchurch”) and GNS Science Active Faults Database). Blue squares are GeoNet The epicenter of the earthquake was national strong-motion network sites, and purple squares are Canterbury regional strong-motion approximately 10 kilometers southeast of network sites. Locations of sites in Figures 1e and 1f are shown on map. A PDF of the fault the town of Darfield (Figure 1a) with a focal map is available at http://www.drquigs.com and http://www.geonet.org.nz. (b) Failure of an depth of 10.8 kilometers [Gledhill et al., unsupported wall in Christchurch. (c) Linear trend of sand boils in a liquefaction-affected part 2010] within the Canterbury Plains, an area of Christchurch. (d) Mapped location of Greendale Fault, showing a pattern of similarly oriented of moderately low historical seismicity just faults and relative fault movement (arrows denote relative motion of area north of fault, with U representing up (the hanging wall of the secondary thrust component) and D representing east of the Southern Alps foothills. The pre- down (the footwall of the secondary thrust component), although the centroid moment tensor vious largest earthquake to affect Christ- “beachball” diagram for this earthquake (http://www.globalcmt.org) shows that the majority of church was the 1888 M 7–7.3 North Canter- motion on the fault is strike-slip). (e) Greendale Fault surface rupture patterns and dextral offset bury earthquake, which ruptured the Hope of irrigation channels. (f) Partial diversion of the Hororata River because the northeast side of the Greendale Fault has moved down at this location. (g) Unwrapped differential interferometric synthetic aperture radar (InSAR) image of coseismic ground deformation from Advanced Land By M. Quigley, P. Villamor, K. Furlong, Observing Satellite phased array type L-band synthetic aperture radar (ALOS/PALSAR) ascend- J. Beavan, R. Van Dissen, N. Litchfield, ing track 336 between 11 March 2010 and 11 September 2010, with the mapped surface rupture T. Stahl, B. Duffy, E. Bilderback, D. Noble, overlaid. ALOS processing by Sergey Samsonov, University of Western Ontario, London, Canada. D. Barrell, R. Jongens, and S. Cox ALOS data used with permission. Eos, Vol. 91, No. 49, 7 December 2010

The shallow depth and proximity of the earthquake to Christchurch resulted in felt intensities of as much as IX on the Modi- fied Mercalli (MM) Intensity Scale, although most were MM VIII or less. Extensive damage occurred to unreinforced masonry buildings throughout the region (Figure 1b), but no buildings totally collapsed. The earthquake struck early in the morning, mini- mizing human exposure to hazards such as exterior wall and parapet collapses onto nor- mally busy sidewalks. Nonetheless, many thousands of brick chimneys collapsed throughout the region. Extensive liquefaction, differential subsidence, and lateral spreading occurred in areas close to major Fig. 2. Lidar (light detection and ranging) hillshade (illuminated from the northwest) digital eleva- streams and rivers throughout Christchurch, tion map of a short section of the central Greendale Fault, showing characteristic left stepping rup- Kaiapoi, and Tai Tapu (Figure 1c). In these ture pattern and right-lateral offsets of farm roads and fences. Lidar from NZ Aerial Mapping Limited. areas, as well as near the fault trace, some homes were rendered uninhabitable by the and irrigation channels, which provided an NW striking western portion of the fault earthquake and resulting liquefaction. Parts invaluable wealth of fault displacement mark- resulted in partial diversion of the Hororata of the city were without water and power for ers. Progressive iterations of maps of the sur- River (Figure 1f). The gross morphology of several days following. Slow ground settle- face rupture features were made available to the fault is that of a series of EW striking, ment has continued to affect liquefaction- the public online and presented to local and NE stepping surface traces (Figure 1d) that prone areas. regional councils and landowners. Airborne in detail consist of ESE trending fractures lidar (light detection and ranging) was flown with right-lateral displacements, SE trend- An ML 5.1 aftershock on 8 September located about 7 kilometers southeast of over a roughly 20-kilometer-long section of the ing extensional fractures, SSE to south trend- the city center at a depth of approximately fault rupture (Figure 2) 6 days after the event. ing fractures with left-lateral displacements, 6 kilometers caused further damage to previ- As a consequence, a spectacular data set of and NE striking thrusts and folds (Figure 1e). ously compromised structures. fault displacement, buckling, and detailed frac- Offsets as small as 1–5 centimeters were ture patterns was captured over the full length mapped due to the numerous straight fea- A Rapid and Coordinated Scientific of the surface rupture. Fault data continue to tures (e.g., roads, fences) crossing the fault. Response be analyzed by GNS and UC personnel. Ongoing research and mapping of deforma- Scientists working on GeoNet, a New tion will provide additional constraints on Immediately following the earthquake, Zealand–based geological hazard monitor- the spatial pattern of surface rupture. Earth scientists from the University of Can- ing system operated by GNS for New Zealand’s The Greendale Fault ruptured primarily terbury (UC) in Christchurch rushed to Earthquake Commission (EQC), deployed por- across gravelly alluvial plains abandoned by inspect earthquake damage in the city and table earthquake recorders the day after the rivers at the end of the last glaciation, about provide immediate information to the public main shock and have been continuously pro- 16,000 years ago [Forsyth et al., 2008]. No via media. Within 3 hours of the earthquake cessing seismological data since the event. evidence of previous faulting had been rec- a reconnaissance and response team led by A GNS-led team used GPS to resurvey more ognized, either prior to the earthquake or in scientists from the UC Active Tectonics team than 80 existing survey marks within 80 kilo- retrospective examination of pre-earthquake and GNS Science (GNS) had been deployed. meters of the rupture starting 3 days after the aerial photographs. However, thorough cul- By 9:30 A.M. the UC reconnaissance team event; the 45 marks closest to the main shock tivation of the Canterbury Plains following located the first evidence for ground surface were resurveyed 2 weeks later. GNS is working the arrival of Europeans in the mid-1800s fault rupture and began to assess local haz- with overseas colleagues to collect and pro- has subdued some detail of the original river ards and conduct detailed measurements of cess interferometric synthetic aperture radar channel form. Coupled with the possibility fault offsets across roads and fences. GNS (InSAR) data from both Japanese and Euro- that previous earthquakes may not have pro- scientists undertook a helicopter reconnais- pean satellites; some of the early images have duced significant surface rupture, the long- sance flight to define the limits of obvious produced very high quality maps of surface term earthquake history of the Greendale surface deformation and photograph key fea- displacements (Figure 1f) [Beavan et al., 2010]. Fault is difficult to assess. tures. Another team of UC staff and students, The InSAR data are being combined with GPS, aided later by colleagues from other organi- geological, and seismological data to develop What Are Earth Scientists Doing Now? zations, began mapping liquefaction features rupture models. in and around Christchurch. By the end of Together with research partners in New the day, a first approximation of the surface Characteristics of the Surface Fault Rupture Zealand and abroad, several UC- and GNS-led rupture length and general damage patterns research programs have been initiated fol- had been established throughout the region, The zone of identified surface rupture lowing the earthquake. High-precision GPS which formed the basis for planning the sci- extends from about 4 kilometers west- surveying and measurement of fault offsets entific documentation of the event. northwest (WNW) of the hamlet of Green- continues, with an emphasis on refining the The rapid collaborative scientific response dale for about 29 kilometers to an eastern characteristics of the surface rupture. Struc- ensured that fault deformation features were tip roughly 2 kilometers NW of the town of tural analysis of fault fracture arrays is provid- accurately documented before they were Rolleston (Figures 1a and 1d). The fault, ing insights into fault behavior and kinemat- removed by land remediation. The fault not previously recognized, has been named ics. Repeat surveying of markers across the was mapped in detail over the following the Greendale Fault. High-quality observa- Greendale Fault, conducted at weekly inter- 2 weeks using a variety of methods, rang- tions and measures of offsets and fracture vals, helps document postrupture relaxation ing from tape and compass to Global Posi- patterns reveal more than 4 meters of right- and/or ongoing fault growth. Reoccupation of tioning System (GPS) surveys and terrestrial lateral displacement (Figures 1e and 2). Ver- pre-earthquake survey points, combined with laser scanning. The fault rupture occurred tical offsets of up to approximately 1 meter GPS and InSAR studies, will provide high- entirely in a region with numerous linear occur at constraining or releasing bends. resolution data sets relevant to characterizing features such as roads, fences, hedgerows, Oblique northeast-side down slip on the the earthquake source. Eos, Vol. 91, No. 49, 7 December 2010

The earthquake has provided seismologists peak ground acceleration variability. Col- (Canterbury) earthquake: Geodetic observations with an exceptional set of near-source strong- laborative efforts to link remote sensing, and preliminary source model, Bull. N. Z. Soc. motion data from the GeoNet national strong- seismological, and geological data to fault Earthquake Eng., in press. motion network and the Canterbury regional rupture propagation models are providing Cousins, J., and G. McVerry (2010), Overview of strong-motion data from the Darfield earthquake, strong-motion network (Figure 1a). The sta- intriguing insights into the rupture dynamics Bull. N. Z. Soc. Earthquake Eng., in press. tion nearest the rupture recorded peak ground of this earthquake and continental strike-slip Forsyth, P. J., D. J. A. Barrell, and R. Jongens accelerations greater than those of gravity earthquakes in general. (2008), Geology of the Christchurch area, Geol. [Cousins and McVerry, 2010], and understand- Map 16, 1 sheet + 67 pp., 1:250,000, GNS Sci., ing why accelerations diminished over small Acknowledgments Lower Hutt, New Zealand. distances is important for understanding the Gledhill, K., et al. (2010), The Darfield (Canterbury) future seismic hazard throughout this region. Field mapping in the weeks following the Mw 7.1 earthquake of September 2010: Preliminary Seismologists are currently working on earthquake would not have been possible seismological report, Bull. N. Z. Soc. Earthquake Eng., in press. better defining the rupture’s evolution using without the dedicated efforts of many GNS Sci- Quigley, M., et al. (2010), Surface rupture of the inversion methods and recently developed ence staff and students and staff at the Univer- Greendale Fault during the Mw 7.1 Darfield (Can- source-tracking methods. Landslide map- sity of Canterbury’s Department of Geologi- terbury) earthquake, New Zealand: Initial find- ping and monitoring programs are in place. cal Sciences. GeoNet provided an invaluable ings, Bull. N. Z. Soc. Earthquake Eng., in press. Geophysical surveys (seismic and ground- resource of rapid information on earthquake penetrating radar), fault trenching, and exca- for researchers and the public. We would Author Information vations of areas that experienced liquefac- also like to thank the landowners for gracious tion during this earthquake are being con- access to the fault trace and other field sites M. Quigley, Department of Geological Sciences, ducted to investigate the subsurface geom- during this stressful period. Personnel from University of Canterbury, Christchurch, N. Z.; E-mail: etry and earthquake history of the newly GNS Science, Land Information New Zealand, mark.quigley@canterbury.ac .nz; P. Villamor, GNS Sci- discovered Greendale Fault. Mapping of tree University of Otago, and Victoria University par- ence, Lower Hutt, N. Z.; K. Furlong, Department of Geosciences, Pennsylvania State University, University damage is providing insights into the extent ticipated in postearthquake GPS surveys. We Park; J. Beavan, R. Van Dissen, and N. Litchfield, GNS to which coseismic shaking, changes in thank Duncan Agnew for reviewing this article. Science; T. Stahl, B. Duffy, E. Bilderback, and D. Noble, water table, and damage by faulting of root Department of Geological Sciences, University of systems played a role in generating observed References Canterbury; and D. Barrell, R. Jongens, and S. Cox, GNS patterns of forest destruction. Mapping of Science, Dunedin, N. Z. displaced boulders is providing data rele- Beavan, J., S. Samsonov, M. Motagh, L. Wallace, vant to understanding the factors influencing S. Ellis, and N. Palmer (2010), The Mw 7.1 Darfield

briefing that the evidence presented in the paper has not yet won him over. He said it is NEWS an exceptional result that “will require exceptional evidence to support it.” Benner said he would like to see further research, including radioactive isotope labeling experiments. New Type of Bacterium NASA Astrobiology Institute director Carl Expands Possibilities of Life, Scientists Indicate Pilcher, who was not on the briefing panel, told Eos the finding is “huge. It’s not find- PAGE 471 arsenic lies just below phosphorus and is ing silicon-based life, and it’s not finding similar to it in some ways. The research non-carbon-based life, but it is finding life in Leading up to NASA’s 2 December news team isolated the bacterium from mud from which one of the six essential elements has briefing about a new astrobiology find- Mono Lake, Calif., and substituted arsenic been replaced,” he said, adding that he is ing, segments of the blogosphere had run for phosphorus. “Exchange of one of the even more excited about where the finding wild with speculation that the agency major bio-elements may have profound evo- might lead. “When you make a discovery that would announce that it has found life else- lutionary and geochemical significance,” the is this profound about the nature of life, you where. Although some bloggers and readers team indicates in a paper published online are going to learn all kinds of other things as may have been disappointed in the actual by Science on 2 December (Science Express, the scientific community follows up.” announcement, scientists at the briefing at doi:10.1126/science. 1197258) . “While certainly being able to announce the NASA headquarters in Washington, D. C., At the briefing, James Elser, professor, discovery of an extraterrestrial would be an said the finding of a bacterium that can Arizona State University, Tempe, said the incredible announcement, we feel that from grow by using arsenic instead of phosphorus finding of an organism that thrives on arse- our perspective and our understanding of biol- is “phenomenal,” with broad implications nic could lead to research that could have ogy here on Earth,” said Mary Voytek, direc- for searching for life on Earth and elsewhere practical implications on Earth, including tor of NASA’s Astrobiology Program, “this is a and for other areas of research on Earth. looking into the possibility of whether such a phenomenal finding. We are talking about Felisa Wolfe-Simon, a NASA Astrobiology an organism could be useful in wastewater taking the fundamental building blocks of life Research Fellow in residence at the U.S. Geolog- treatment, in the development of an alterna- and replacing one of them with a perhaps not ical Survey in Menlo Park, Calif., led a team that tive bioenergy, and in serving as a replace- unpredicted, but another, compound.” discovered and experimented on the microbe, ment for dwindling phosphorus supplies. Voytek added that she is sorry if those known as strain GFAJ-1 of the common bacteria Pamela Conrad, an astrobiologist with hoping for ET are disappointed. “But there group Gammaproteobacteria. Noting that life is NASA’s Goddard Space Flight Center, Green- are lots of other people who see this as a mostly composed of carbon, hydrogen, nitro- belt, Md., and deputy principal investigator huge finding and a significant finding that gen, oxygen, sulfur, and phosphorus, she said, of an investigation flying on the Mars Sci- is going to lead to new areas of reseach “If there is an organism on Earth doing some- ence Laboratory in 2011, said the finding and will fundamentally change how we thing different, we’ve cracked open the door to “is delightful because it makes me have to define life and therefore how we will look what is possible for life elsewhere.” expand my notions of what environmental for it. Maybe we will be able to find ET now, Wolfe-Simon said she had come up with constituents might enable inhabitability.” because we have more information about the idea of testing the substitution of arse- However, Steven Benner, distinguished fel- what we might be looking for.” nic for phosphorus used by an organism by low at the Foundation for Applied Molecu- thinking about the periodic table, where lar Evolution, Gainesville, Fla., said at the —Randy Showstack, Staff Writer