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National Seismic Hazard Model for New Zealand: 2010 Update

by Mark Stirling, Graeme McVerry, Matthew Gerstenberger, Nicola Litchfield, Russ VanDissen, Kelvin Berryman, Philip Barnes, Laura Wallace, Pilar Villamor, Robert Langridge,Geoffroy Lamarche, Scott Nodder, Martin Reyners, Brendon Bradley, David Rhoades,

Warwick Smith, Andy Nicol, Jarg Pettinga, Kate Clark, and Katrina Jacobs

Abstract A team of earthquake geologists, seismologists, and engineering seis-mologists has collectively produced an update of the national probabilistic seismichazard (PSH) model for New Zealand (National Seismic Hazard Model, or NSHM).The new NSHM supersedes the earlier NSHM published in 2002 and used as the hazardbasis for the New Zealand Loadings Standard and numerous other end-user applica-tions. The new NSHM incorporates a fault source model that has been updated withover 200 new onshore and offshore fault sources and utilizes new New Zealand-basedand international scaling relationships for the parameterization of the faults. The dis-tributed seismicity model has also been updated to include post-1997 seismicity data,a new seismicity regionalization, and improved methodology for calculation of theseismicity parameters. Probabilistic seismic hazard maps produced from the newNSHM show a similar pattern of hazard to the earlier model at the national scale, butthere are some significant reductions and increases in hazard at the regional scale. Thenational-scale differences between the new and earlier NSHM appear less than thoseseen between much earlier national models, indicating that some degree of consis-tency has been achieved in the national-scale pattern of hazard estimates, at leastfor return periods of 475 years and greater.

Online Material: Table of fault source parameters for the 2010 national seismic-hazard model.

Introduction

Probabilistic seismic hazard models need to be updatedand improved with new data and methods whenever a sig-nificant improvement can be made. However, the scale andcomplexity of the task of updating a national-scale model issuch that successive updates are often spaced by many years.We hereby document a major update of the national probabi-listic seismic hazard (PSH) model for New Zealand (NationalSeismic Hazard Model, or NSHM). The new NSHM super-sedes the earlier NSHM developed in 2000 (Stirling et al.,2002) and used as the hazard basis for the New ZealandLoadings Standard (Standard New Zealand, 2004) andnumerous other end-user applications. The update of theNSHM is largely focussed on the source models, while thechoice of ground motion prediction equations and overallPSH methodology used in the earlier NSHM have been pre-served. The source model still comprises fault and distributedseismicity components, but over 200 new onshore andoffshore fault sources (offshore faults were only minimallyconsidered in the earlier NSHM) and 11 additional years ofseismicity data have been included in the new NSHM. Thenew NSHM is the product of a large team of earthquake

geologists, seismologists, and engineering seismologists re-flecting the large multidisciplinary team-orientated approachto seismic hazard modeling that has evolved in New Zealandover the last decade.

Finally, it is important to note that this 2010 updateof the NSHM was completed prior to the occurrence of theMw 7.1, 4 September 2010 Darfield, and Mw 6.2, 22February 2011 Christchurch earthquakes. While the Green-dale fault, source of the Darfield earthquake, has been addedto the fault source model, the large data set of earthquakesand strong-motion records from the two events have not beenincluded in the model. Modeling of the aftershock-derived,time-dependent hazard for the region of the two earthquakesis the focus of considerable effort at the present time and willrepresent a significant follow-up to this update of the NSHM.

General Approach

The probabilistic seismic hazard analysis (PSHA) meth-odology of Cornell (1968) forms the generic basis forthe NSHM. The steps undertaken for our PSHA were to

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Bulletin of the Seismological Society of America, Vol. 102, No. 4, pp. 1514–1542, August 2012, doi: 10.1785/0120110170

(1) use geologic data and the historical earthquake record todefine the locations of earthquake sources and the likelymagnitudes and frequencies of earthquakes that may be pro-duced by each source, and (2) estimate the ground motionsthat the sources will produce at a grid of sites that covers theentire region.

Source Models

As is standard practice for PSH models, we use thecombination of a fault source model and distributed sourcemodel as input to the NSHM. The fault source model uses thedimensions and slip rates of mapped fault sources to developa single characteristic earthquake (magnitude and frequency)for each fault source, while the spatial distribution ofhistorical seismicity is used to develop Gutenberg–Richtermagnitude–frequency estimates for the distributed seismicitymodel Gutenberg–Richter (1944). The two source modelstherefore combine to provide magnitude–frequency esti-mates from data representing a spectrum of time scales (pre-historic to historic) and magnitudes. The following FaultSources and Distributed Earthquake Sources sections de-scribe the data and methodology used to develop the sourcemodels. In construction of the fault and distributed seismicitymodels, we limit our attention to providing mean or preferred

parameters for the sources. In doing so we follow the sameapproach taken in the earlier NSHM.

Fault Sources

The fault source model has been substantially updatedfrom that of the earlier NSHM (Fig. 1). New onshore geolog-ical mapping and interpretations, combined with a substan-tial contribution of offshore fault sources, have resulted in theaddition of over 200 new sources and the revision of many ofthe existing sources.

The distribution of fault sources is shown in Figures 1b,2, and 3, and the mean or preferred parameters and keyreferences for each source are listed and indexed in ⒺTable S1 (available in the electronic supplement to thispaper). The fault sources shown on Figures 1b, 2, and 3 aregeneralizations of mapped fault traces, which is appropriatefor regional-scale PSHA. All fault sources are modeled as dis-cretized planes and assigned a general dip and dip direction(Ⓔ see Table S1 in the supplement). The dips are eitherobtained from seismic-reflection profiles (where available)or inferred by taking into account surface exposures, surfacegeology or geomorphology (e.g., fold geometries), and withconsideration of other fault geometries within similar tec-tonic settings. The model also includes nine blind faults

Figure 1. Comparison of the active fault sources in the earlier NSHM of (a) Stirling et al. (2002) model, and (b) those of the new model.The fault sources are shown (black lines), along with the upper edges of subduction interface sources (blue lines), and relative plate motionrate between the Australian and Pacific plates in the center of the country (black arrow).

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(upper edges inferred to be at 1 km depth), and 13 subductioninterface sources. The depth to the base of the faults is gen-erally obtained from the depth distribution of seismicity (seeDistributed Earthquake Sources section). Most fault basesare in the depth range 10–20 km, but notable variations in-clude the westward deepening of faults interpreted to splayfrom the Hikurangi subduction interface (faults in the Hikur-angi subduction margin forearc, Barker et al., 2009; Wallaceet al., 2009; Mountjoy and Barnes, 2011), shallow depths(∼8 km) within thin, hot crust of the Taupo rift (Bryan et al.,1999), and the ∼35 km deep transition between the the Wair-arapa fault and Hikurangi subduction interface (see sourceindex 345 in Ⓔ Table S1 in the supplement; Darby andBeanland, 1992; Rodgers and Little, 2006).

Fault Source Parameterization. For simplicity of modelingthe large number of fault sources, we use a characteristic ormaximum magnitude model (e.g., Youngs and Coppersmith,1985; Wesnousky, 1994; Stirling et al., 1996) to estimate thelikely maximum magnitude (Mmax) and recurrence intervalof Mmax for each fault source. We therefore assume thatearthquakes smaller in size than the Mmax are modeled fromthe distributed seismicity model, as was the case in the earlier

NSHM (Stirling et al., 2002). However, our methods ofdeveloping these earthquake parameters have been sub-stantially updated from the earlier approach developed byStirling et al. (1998) and again applied in Stirling et al.(2002).Mmax is calculated from three regressions of momentmagnitude (Mw) on fault area (A, in km2). Equation (1) is forglobal plate boundary strike-slip faults, and equations (2) and(3) are regression equations for New Zealand earthquakes.The equation of Hanks and Bakun (2002):

Mw � 3:07� 4=3 logA; (1)

is used for the Alpine fault (seeⒺ type index 1 in Table S1 inthe supplement). The equation given in Villamor et al.(2007):

Mw � 3:39� 1:33 logA; (2)

is used for normal faults in volcanic and rift environments(faults in and west of the Havre trough–Taupo rift) or in-ferred shallow normal faults (faults in the eastern RaukumaraPeninsula, Fig. 3a; see Ⓔ type index 2 in Table S1 in the

Figure 2. (a) Groupings of active fault sources into domains or regions they occupy in New Zealand. K–M F, Kapiti–Manawatu faults;MFS, Marlborough fault system. (b) Sites where paleoearthquake information has been collected. Onshore (yellow) sites are trenches andtrenchlike natural exposures; offshore (orange) sites are high resolution seismic-reflection profiles. Only the upper plate (noninterface) activefaults are shown on these figures.

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Figure 3. Active fault sources used as inputs for the probabilistic seismic hazard analysis (PSHA). The numbers beside each fault cor-respond to the number inⒺ Table S1 (see supplement). The county is split into five maps: (a), (b), (d), and (e) are at the same scale, but (c) isat a larger scale to see the dense faults in the Havre trough–Taupo rift. Domain boundaries are shown in white, and white numbers refer to thedomain number. AR, Axial Ranges; BoP, Bay of Plenty; CH, Caswell high; CR, Chatham Rise; CS, Cook Strait; Fi, Fiordland; HT, Havretrough; KI, Kapiti Island; KR, Kaikoura Ranges; RP, Raukumara Peninsula; SA, Southern Alps; SW, South Westland; TR, Taupo rift; WBa,Wanganui basin; WBi, Wanganui Bight. (f) shows the detail of fault sources in the Wellington region, and (g) is an example area that showsthe relationship between active fault traces (red) and fault sources (black). The fault sources are numbered according to Ⓔ Table S1 (seesupplement). (Continued)


supplement). Lastly, the equation given in Stirling et al.(2008),

Mw � 4:18� 2=3 logW � 4=3 logL; (3)

is used for all remaining faults (Ⓔ see type index 3 inTable S1 in the supplement); L is fault length in kilometers,and W is fault width in kilometers). Equations (2) and (3)were developed in unpublished, peer-reviewed studies (Ber-ryman et al., 2001; Villamor et al., 2001) but were first pub-lished in the associated references shown previously.Recurrence interval T in years is calculated from

T � D=SR; (4)

where D is single-event displacement (mm), and SR is sliprate (mm=yr). Displacement is calculated from seismicmoment M0 by the equation of Aki and Richards (1980):

M0 � μLWD; (5)

where μ is rigidity modulus (assumed to be 3×1011 dyn=cm2), L is fault length in centimeters, W is faultwidth in centimeters (note different units from L and Win equation 3), and D is single-event displacement in centi-meters. M0 is calculated from Mw by the equation of Hanksand Kanamori (1979):

logM0 � 16:05� 1:5Mw: (6)

Figure 3. Continued.






The calculated (equations 1–6) values of D and T werecompared with those derived from paleoseismic studies. Ifthey differed significantly, the fault length (L) was adjustedby shortening at segment boundaries, or lengthening by com-bining contiguous surface traces, until the mean calculatedvalues overlapped the paleoearthquake values. The previousresult was achieved through an expert panel review process,in which experts with extensive local knowledge (most ofwhom are coauthors) provided reality checks of the calcu-lated values. This was initially achieved by four days ofround-table meetings, in which every fault source wasreviewed by the panel in series, and later by extensive reviewof several draft versions of the fault source model. Thereview process was completed in mid-2010.

All of the previously identified parameters apply to theentire fault, and so embodied in the previous approach isthe assumption that the average coseismic displacement D(derived as the average across the entire fault plane) isequivalent to the surface coseismic displacement. Whilesurface coseismic D is often observed to be less than themodeled subsurface D in well-instrumented earthquakes(e.g., Wells and Coppersmith, 1994), we do not need tomake any subsurface-to-surface conversions for the NSHM.This is because T is calculated from D and the slip rate(equation 4) and both of these parameters are applicableto the entire fault plane rather than just the surface trace.Such conversions would instead be relevant in the caseof D being applied to fault displacement hazard analyses,in which surface coseismic D is the parameter of fundamen-tal importance.

Fault Source Domains. In this section we provide an over-view of fault sources grouped according to the seismotec-tonic domains or regions they occupy in New Zealand(Figs. 2a; 3), and as such, these domains bear a close resem-blance to the seismotectonic zonation scheme used for thedistributed seismicity model (Fig. 4). Further details on theindividual faults can be found in the references cited inⒺ Table S1 (see supplement). Figure 2b also shows sites(typically trenches) where paleoearthquake informationhas been collected. Domains 1 to 12 in Figures 2a and 3are numbered sequentially in later parts of the text, alongwith the Hikurangi and Fiordland subduction interfaces (do-mains 13 and 14). Fault numbers (e.g., 321) refer to the num-bers in Ⓔ Table S1 (see supplement) and Figure 3.

1. Extensional Western North Island Faults: The westernNorth Island faults domain, located west of the active back-arc Havre trough–Taupo rift (Figs. 2a; 3a,b), consists of twosets of faults: (1) north-northwest-striking faults in the northnear Auckland, which formed early in the evolution of theback-arc rift, and (2) northeast-striking faults south of Tar-anaki (westernmost land in Fig. 3a), which appear to formthe southern extension of the active back-arc rift and mayextend well to the east of where they are currently mapped

(Fig. 3a,b; Giba et al., 2010). No faults in this domain haveruptured in the historical period (post-1840 A.D.).

Slip rates are constrained for many faults (e.g., Pillans,1990; Nodder, 1993; Townsend et al., 2010), but wherepaleoseismic data are absent, rates were inferred from:(1) geomorphic expression, (2) rates on contiguous along-strike segments of the same fault, or (3) long-term (pre-Quaternary) rates.

The main differences between the new fault source mod-el and the Stirling et al. (2002) model are the lengthening of anumber of the fault sources, especially the extension offshoreof faults in the southeast of the domain (National Instituteof Water and Atmospheric Research [NIWA], unpub-lished data).

The fault source model is likely to be incomplete in thisdomain due to the difficulties in identifying active faults inthe soft, easily erodible Plio-Pleistocene sediments that un-derlie a significant portion of the domain (Edbrooke, 2005;Townsend et al., 2008).

2. Extensional Havre Trough–Taupo Rift: This domainrepresents the continental arc and back-arc of the Hikurangisubduction margin, which widens northward as it transitionsfrom the Taupo rift to the southern Havre trough (Wright,1993; Wysoczanski et al., 2010). There has been one majorhistorical surface rupturing earthquake on land and poten-tially one offshore. On land, the 1987 Mw 6.5 Edgecumbeearthquake ruptured the Edgecumbe fault (174), and severalother nearby faults (Beanland et al., 1989; Beanland et al.,1990). The 1992 Mw 6.3 Bay of Plenty earthquake poten-tially ruptured a fault in the offshore Whakatane Graben(Webb and Anderson, 1998).

Slip rates are well constrained for a number of on-landfaults (e.g., Berryman et al., 1998; Villamor and Berryman,2001, 2006a; Villamor et al., 2007; Canora-Catalan et al.,2008; McClymont et al., 2009). However, where paleoseis-mic data are absent, on-land slip rates were inferred: (1) fromfaults along-strike, (2) as a proportion of the total extensionrate along transects across the rift, and (3) from geomorphicexpression. Offshore, rates are well constrained beneath thecontinental shelf, from displacement of postglacial (<20 ka)markers on a dense grid of seismic-reflection profiles (Tayloret al., 2004; Bull et al., 2006; Lamarche et al., 2006). Inwater depths greater than 150 m, slip rates were estimatedon the basis of geomorphic expression and inferred propor-tion of the regional extension rate derived from kinematicmodeling byWallace et al. (2004) (NIWA, unpublished data).

The most significant change from that of the ear-lier NSHM is the addition of ∼135 new faults in the offshoreBay of Plenty. This is the result of a significant amount ofnew mapping and reinterpretation of existing data (Lamarcheet al., 2006; Bull et al., 2006; NIWA unpublished data). Aswell as the additional faults, some faults in the 2002 modelhave been replaced with multiple, predominantly northeast-striking faults (e.g., Mayor Island 1, 2, 3, and 4 in the 2002model; Fig. 1). On land, many of the fault traces have been


Figure 4. (a) Crustal seismicity of New Zealand. The map shows the distribution ofM ≥ 4 earthquakes for the period 1964 to mid-2009,for depths of 0–30 km (black circles) and for depths greater than 30 km (gray squares). The boundaries of zones defined for the newregionalization are also shown. These are largely delineated from the Domains in Figure 2, along with additional considerations regardingcrustal seismicity patterns (black circles); (b) parameters associated with the regionalization scheme. The gray shades indicate zones ofsimilar slip type that are combined to provide more statistically stable seismicity parameters. The combinations of zones are distinguishedby the gray scales, and parameters TE (slip type), B (b-value of the Gutenberg–Richter relationship) and Mcutoff (maximum magnitude oftruncation for the Gutenberg–Richter relationship) are listed on the left of the map. See the text for further explanation; and (c) contour mapshowing the N-values (number of events ≥ 4 for the period 1964–2009) per 0:1° × 0:1° cell for 0–30 km depth.


mapped in more detail and a number of new faults added,reflecting the large amount of new work on Taupo rift faults(Nairn et al., 2005; Villamor and Berryman, 2006a,b;Tronicke et al., 2006; Nicol et al., 2006; Villamor et al.,2007; Berryman et al., 2008; Canora-Catalan et al., 2008;Mouslopoulou et al., 2008; McClymont et al., 2008, 2009;Nicol et al., 2009; Begg and Mouslopoulou, 2010; Nicolet al., 2010; Villamor et al., 2011). The slip rates for manyfaults have also been refined, the largest change being theRangipo fault (255, 256, 264, 268), which has reduced from∼3 to ∼0:2 mm=yr (Villamor et al., 2007).

The fault source model is likely to be incomplete in theareas of the Taupo and Okataina calderas. Thick vegetationcover, thick volcanic deposits, and the presence of manylakes are likely to have obscured some active faults andproduced the obvious gaps in fault sources in Figure 3b,c.

3. Contractional Kapiti–Manawatu Faults: The Kapiti–Manawatu faults domain is located west of the southernNorth Island axial ranges (Figs. 2a; 3a,b) and consists of re-verse faults uplifting the eastern side of the Wanganui basin(Fig. 3b). Many have associated hanging wall anticlines andfootwall synclines (Lamarche et al., 2005), and the onshorefaults are inferred to be blind reverse faults beneath anticlines(Melhuish et al., 1996; Jackson et al., 1998). No faults in thisdomain have ruptured the ground surface in the historicalperiod.

Slip rates are well constrained for only a few faults (e.g.,Pillans, 1990; Nodder et al., 2007) and in the absence ofpaleoseismic data were inferred for on-land faults by conver-sion of fold differential uplift rates to dip-slip rates. The off-shore rates north of Kapiti Island (Fig. 3b) were determinedfrom displacement of a postglacial surface (∼10:8 ka) andseafloor scarps assuming an inferred relict seafloor age of6.5 ka. Rates south of Kapiti Island were inferred from con-sideration of bathymetric expression and regional geologicaland GPS data.

The largest differences between this model and that ofthe earlier NSHM are the addition of seven offshore faults,which replace the earlier Wairau offshore fault source inter-pretation (Lamarche et al., 2005; Nodder et al., 2007; NIWAunpublished data). Onshore the fault distribution has beenrevised slightly, with many faults lengthened to includeadjoining structures in order to calculate displacements thatmatch observed field displacements.

4. North Island Dextral Fault Belt: The North Islanddextral fault belt or system (Beanland and Haines, 1998;Mouslopoulou et al., 2007, 2008, 2009) is centered uponthe North Island axial ranges (Figs. 2a; 3a,b,c), and is a seriesof range-parallel strike-slip faults that accommodate much ofthe margin-parallel plate motion (Cashman et al., 1992; VanDissen and Berryman, 1996; Beanland and Haines, 1998;Mouslopoulou et al., 2007; Nicol and Wallace, 2007). Atleast two historical ground-surface rupturing earthquakeshave occurred in this domain: the 1855 Mw 8.2 Wairarapa

earthquake, which occurred on the Wairarapa (345) and Al-fredton (321) faults (Grapes and Downes, 1997; Schermeret al., 2004; Rodgers and Little, 2006), and the 1934Mw 7.4 Pahiatua earthquake, which occurred on the Waipu-kaka and Saunders Road faults (326) (Schermer et al., 2004).

Slip rates have been constrained for many faults (e.g.,Marden and Neall, 1990; Van Dissen and Berryman, 1996;Begg and Van Dissen, 1998; Heron et al., 1998; Langridge,Berryman, and Van Dissen, 2005; Mouslopoulou et al.,2007; Little et al., 2009; Carne et al., 2011). Where paleo-seismic data were absent, however, slip rates were assignedfrom (1) rates on faults along-strike where possible, particu-larly in the central to northern area, (2) relative geomorphicexpression, and (3) inferred regional slip-rate budget (e.g.,taking into account the decreasing margin-parallel compo-nent to the north). Offshore data in the Bay of Plenty onlyconstrain the dip-slip component of the displacement rate(NIWA, unpublished data).

The main difference between the new model and that ofthe earlier NSHM is the inferred continuity of faults along-strike, especially in the central to northern area, and their ex-tension offshore into the Bay of Plenty (Fig. 3a,c) in the north(Lamarche et al., 2006: NIWA, unpublished data) and CookStrait (Fig. 3b) in the south (Pondard and Barnes, 2010).

5. Hikurangi Subduction Margin Forearc: This domain,located east of the North Island axial ranges (Figs. 2a; 3a,b,c), is the partly uplifted forearc (onshore–offshore) and ac-cretionary wedge (offshore) portion of the Hikurangi subduc-tion margin (Lewis and Pettinga, 1993; Barnes et al., 2010;Paquet et al., 2011). Only structures interpreted to be rootedin sufficiently strong rocks of the upper plate are included,and so thrust faults from the Late Cenozoic frontal accretion-ary wedge are not included in this domain. The only fault tohave ruptured in the historical period is the onshore–offshoreNapier fault (242), which ruptured in the Mw 7.8 1931Napier earthquake (Hull, 1990; Kelsey et al., 1998).

Slip rates are well constrained for only a few faults (e.g.,Kelsey et al., 1998; Barnes, Nicol, and Harrison, 2002; Lan-gridge, Van Dissen, et al., 2005; Litchfield et al., 2007; Ber-ryman et al., 2009; Mountjoy and Barnes, 2011), but wherepaleoseismic data are absent were inferred by several meth-ods. The majority of the Raukumara Peninsula (Fig. 3a)normal faults were assigned low (<1 mm=yr) slip rates inaccordance with the Repongaere fault (217, Berryman et al.,2009). Slip rates for many of the faults beneath the conti-nental shelf were constrained by postglacial (<20 ka)seismic-reflection markers. The rates for the remainder of theoffshore faults were inferred either from comparable struc-tures along strike where possible, or by consideration of geo-morphic and structural expression, available stratigraphicconstraints, and assumed total convergence rates (taking ac-count of the increasing convergence rate to the north; Barnesand Mercier de Lepinay, 1997; Barnes et al., 1998; Lewiset al., 2004; Wallace et al., 2004; Barnes et al., 2010; Mount-joy and Barnes, 2011).


The largest change from the Stirling et al. (2002) modelis the addition of about 30 offshore fault sources. This ismainly the result of new data acquisition and interpretationsof active faulting (e.g., Barnes, Nicol, and Harrison, 2002,Barnes, Lamarche, et al., 2010; Barnes and Nicol, 2004; Ped-ley et al., 2010; Paquet et al., 2011; Mountjoy and Barnes,2011). Most of the faults in the 2002 model did not have slip-rate estimates, and revisions have been made here to the fewthat previously did. The interpreted sense of displacement ofsome faults in the northwest of the Raukumara Peninsula haschanged from normal to reverse as a result of correlation withseismically imaged offshore faults (NIWA, unpublisheddata). A few faults in the 2002 model have been removedbecause they are no longer considered to be active (e.g., theAorangi Anticline fault), are antithetic to other faults (e.g.,the Kidnappers faults), or the calculated Mmax is <6:0(and these earthquakes are accommodated in the distributedseismicity model) (e.g., some Raukumara Peninsula normalfaults).

Some active faults may be as yet unmapped in the cen-tral to southern part of the domain. This is attributed to com-plex Tertiary structure and presence of easily erodiblesediments in the area.

6. Extensional North Mernoo Fault Zone, ChathamRise: The entirely submarine North Mernoo fault zone is anarray of active continental extensional faults on the north-western (Mernoo) slope of the Chatham Rise (Figs. 2a;3d) (Barnes, 1994a, b). These reactivated faults lie adjacentto the southern tip of the Hikurangi subduction zone and mayhave formed by either lateral buckling of the crust (Andersonet al., 1993) or flexural extension (Barnes, 1994a). The onlyhistorical large magnitude earthquake in this domain is the1965 Mw 6.1 Chatham Rise earthquake, which ruptured anormal fault in thewestern part of the region (Anderson et al.,1993).

Slip rates are not constrained for individual faults, butlow rates are assigned on the basis of an analysis of asuccession of Pliocene-Quaternary unconformities, whichdemonstrated that extensional strain is unlikely to exceeda few percent (Barnes, 1994a).

These fault sources replace the two previously modeledin 2002 (faults 35 and 36 in the 2002 model), and have com-paratively reduced slip rates.

7. Strike-Slip Marlborough Fault System: The Marlbor-ough fault system domain lies east of the northern part of theAlpine fault (387; Fig. 3d), in the transition zone from theHikurangi subduction margin in the north to the South Islandcontinental collision zone in the south (Fig. 2a). These faultsoccur above the southern portion of the Hikurangi subduc-tion interface, which at depths of <30 km plays a minor rolein accommodating plate motions, relative to the Marlbor-ough faults (Reyners et al., 1997; Reyners, 1998; Wallaceet al., 2012 ). Three faults have ruptured during the historicalperiod: (1) the Hope River segment of the Hope fault (409)

during the Mw 7–7.3 1888 North Canterbury (Amuri) earth-quake (McKay, 1888; Cowan, 1991); (2) the eastern segmentof the Awatere fault (357), during the Mw ∼ 7:5 1848 Marl-borough earthquake (Grapes et al., 1998; Mason and Little,2006); and (3) the Poulter fault (422), during the Mw 7.01929 Arthur’s Pass earthquake (Berryman and Villa-mor, 2004).

Slip rates are well constrained on land from displacedgeomorphology (e.g., Freund, 1971; Knuepfer, 1992; Woodet al., 1994; Benson et al., 2001; Nicol and Van Dissen,2002; Langridge et al., 2003; Langridge and Berryman,2005; Mason et al., 2006; Zachariasen et al., 2006; Van Dis-sen and Nicol, 2009). Where paleoseismic data are absent,slip rates were inferred where possible from along-strike con-tinuity of geomorphic expression. Offshore, only the BooBoo fault (383, 384) has a dextral rate inferred directly fromdisplaced submarine geomorphology (NIWA, unpublisheddata). The remaining submarine dextral faults have rates as-signed largely by extrapolation from contiguous onshoretraces, and consideration of the regional relative plate motionbudget (e.g., Stirling et al., 2008; Robinson et al., 2011).

The largest change to the Stirling et al. (2002) model isthe extension of the faults offshore into Cook Strait and east-ern Marlborough (e.g., Barnes and Audru, 1999a, b; Barnesand Pondard, 2010; Pondard and Barnes, 2010). One keyfinding of these recent studies is confirmation that faultsdo not directly link across Cook Strait with the North Islanddextral fault belt, that strike-slip faulting extends into thesouthern Hikurangi margin, and that the offshore extent ofthe Wairau fault is limited to about 40 km in Cook Strait(cf. previous Wairau offshore source). Several scenariosare accounted for in the new model for possible combina-tions of earthquake ruptures involving the Awatere, Vernon,and Cloudy faults, and the Jordan, Kekerengu, Needles, andChancet faults. Onshore, a small number of faults have beenadded, and some previous slip rates have been revised fromthe 2002 model.

8. Contractional Northwestern South Island Faults: Thenorthwestern South Island faults domain, located north andwest of the central and northern Alpine fault, forms the wes-tern side of the South Island continental collision zone(Fig. 2a). Many are former normal faults, now reactivatedas range-bounding reverse faults (Bishop and Buchanan,1995; Ghisetti and Sibson, 2006). There have been two largemagnitude earthquakes in the historical period: (1) theMw 7.2 1968 Inangahua earthquake ruptured a blind faultbetween two surface fault traces, while secondary rupturesoccurred on the Lyell (381) and Inangahua (386) faults (An-derson et al., 1994), and; (2) the White Creek fault (352)ruptured in the Mw 7.8 1929 Buller earthquake (Henderson,1937; Berryman, 1980).

Slip rates are poorly constrained for these faults, in partbecause of the heavily forested, mountainous terrain. Gentlefolding and minor faulting of river terraces, and other geo-morphic expressions, however, indicate the slip rates are


likely to be less than 1 mm=yr (Berryman, 1980; Suggate,1987, 1989; Fraser et al., 2006), so low slip rates are inferredfor all of the faults.

The main change from the earlier NSHM is the extensionof faults along strike in order to match the calculated coseis-mic displacements with observed field displacements. Therehave also been some minor revisions of slip rates.

9. Contractional North Canterbury Faults: The NorthCanterbury faults domain lies in the southern part of the tran-sition zone from the Hikurangi subduction margin to theSouth Island continental collision zone (Figs. 2a; 3d). Forthis study, the Marlborough slope thrust faults are includedin this domain, rather than domain 5, because they appear tobe associated with predominantly continental deformationrather than active subduction (Barnes et al., 1998; Wallaceet al., 2009, Wallace et al., 2012). No faults in this domainhave ruptured the ground surface in the historical period.

Slip rates are generally poorly constrained (cf. Howardet al., 2005), and where paleoseismic data are absent, sliprates were largely inferred from their geomorphic expressionand presence of Pleistocene growth sequences. The slip ratesbeneath the north Canterbury continental shelf were esti-mated from folding rates derived from Late Pleistocene un-conformities (Barnes, 1996).

The largest change to the Stirling et al. (2002) model isthe addition of several offshore faults, particularly east ofMarlborough (e.g., Stirling et al., 2008). On land, manyfaults have been reinterpreted, a few combined, and severalnew faults are added in the southwest corner along the Can-terbury foothills (GNS Science, unpublished data). The com-plex source model for the Mw 6.7, 1994 Avoca earthquakewas treated as a fault source in the Stirling et al. (2002) mod-el, but it has been removed from the present model. The exactgeometry of the source is ambiguous and is best accountedfor in the revised distributed seismicity model.

10. Contractional Southern South Island Faults: Thesouthern South Island faults domain, located east of thecentral and southern Alpine fault, forms the southeastern sideof the South Island continental collision zone (Fig. 2a). Manyof the reverse faults bound ranges and basins and form twopredominant sets, trending northeast and northwest, whichprobably reflect reactivation of basement normal faults (Nor-ris and Turnbull, 1993; Ghisetti et al., 2007). There has beenone historical surface rupturing earthquake in this domain.The Mw 7.1, 4 September 2010 Darfield, Canterbury, earth-quake ruptured the Canterbury Plains in the northeastern cor-ner of the domain (Quigley et al., 2010; Beavan, Samsonov,Denys, et al., 2010).

Slip rates are well constrained for only a few faults (e.g.,Beanland et al., 1986; Van Dissen et al., 1993; Litchfield andNorris, 2000; Pace et al., 2005; Amos et al., 2007; Barrellet al., 2009). Where paleoseismic data are absent, slip rateswere inferred from a combination of geomorphic expressionand long-term uplift rates (Bennett et al., 2005, 2006) and are

within the bounds of ∼2 mm=yr total horizontal contractionacross the region (Norris, 2004; Wallace et al., 2007).

There have been two main changes from the faultsmodeled by Stirling et al. (2002): (1) the lengthening of anumber of faults along-strike to match the calculated displa-cements with field observations, and (2) the addition offaults, particularly in the east and offshore southwest Fiord-land, as a result of new mapping (e.g., Pettinga et al., 2001;Barnes et al., 2005; Sutherland, Berryman, and Norris,2006). The most noteworthy recent addition is the Greendalefault, the newly identified source of theMw 7.1, 4 September2010 Darfield earthquake (Quigley et al., 2010). The earth-quake also involved rupture of blind faults at the western andcentral sections of the fault (Beavan, Samsonov, Motagh,et al., 2010), not shown in our simple representation ofthe Greendale source (Fig. 3d). A few previous faults havealso been removed (faults 6, 7, 19, 20, 31, 32, 36 of the 2002model), because they are no longer considered active. Sliprates for many faults have been refined, the largest changebeing the reduction of slip rate on the Cape Balleny fault(536, fault 21 in the 2002 model) from 25 to 5 mm=yr(Lamarche and Lebrun, 2000; Lebrun et al., 2003), becauseit is no longer considered to be associated with the southernAlpine fault system (Sutherland, Berryman, and Norris,2006; Sutherland, Barnes, and Uruski, 2006).

It is likely that additional, as yet unrecognized faultsoccur in the rapidly uplifting and eroding Southern Alps,where markers for mapping and measuring active deforma-tion are not well preserved (e.g., Cox and Barrell, 2007).There are also possibly other, as yet unidentified, faultsources of low slip rate hidden beneath the thick sedimentsof the Canterbury Plains (northeast corner of the domain),which obscured the Greendale fault prior to the 4 September2010 Darfield earthquake.

11. Alpine Fault: The Alpine fault, bounding the westernside of the Southern Alps and Fiordland (Figs. 2a; 3d,e), isby far the longest fault in the South Island (Berryman et al.,1992; Norris and Cooper, 2001; Barnes et al., 2005; Suther-land, Berryman, and Norris, 2006; Sutherland et al., 2007),and is described as a separate domain. In this model theAlpine fault is divided into three segments, the Resolution(504), central (432), and northern (387) segments, but theWairau fault (376, domain 7) is also a contiguous segmentto the northeast (e.g., Berryman et al., 1992; Barnes and Pon-dard, 2010). The Alpine fault has not ruptured in the histor-ical period.

Slip rates are well constrained, and decrease northwardfrom 31 mm=yr off central Fiordland (Barnes, 2009), to23 mm=yr in southern Westland (Sutherland, Berryman, andNorris, 2006), and to 14 mm=yr at the southern end of thenorthern segment (Langridge et al., 2010).

Changes to the Alpine fault source modeled by theearlier NSHM include revised structure, segmentation, andslip rate of the southern, offshore portion of the fault, slight


revisions to onshore slip rates, and the removal of overlap-ping sources north of the Hope fault.

12. Western Fiordland Margin and Caswell High: Thewestern Fiordland Margin and Caswell High domain islocated entirely offshore, west of Fiordland (Figs. 2a; 3e),and includes two main groups: (1) westward-verging thrustfaults that accommodate northwest-southeast crustal shorten-ing (Delteil et al., 1996; Lebrun et al., 2000; Wood et al.,2000; Barnes, Davy, et al., 2002), and (2) normal faults alongthe southeast edge of the Caswell High (Fig. 3e), which areforming as a result of flexure of the Australian Plate beyondthe convergent deformation (Malservisi et al., 2003). Whilethere have been several recent large thrust earthquakes nearthe Alpine fault in this region (see section 14, Fiordland sub-duction interface, and Van Dissen et al., 1994; Reyners andWebb, 2002; Reyners et al., 2003; Robinson et al., 2003; Fryet al., 2010; Beavan, Samsonov, Denys, et al., 2010), it is notcertain if any ruptured the seafloor in the Fiordland basin.

Individual fault slip rates are not well constrained.Fiordland and Milford basin thrust slip rates are inferredfrom displacement of late Pleistocene seismic stratigraphyand regional shortening estimates (Barnes, Davy, et al.,2002). Slip rates of the Caswell High normal faults are de-rived from an extension rate determined on a mid-Pliocene(∼3 Ma) seismic marker.

This model represents a substantial revision of the ear-lier NSHM in this region. Together with the Fiordland sub-duction zone (518, 508), these faults replace five oblique-slipreverse faults (faults 288 to 292 in the 2002 model).

13. Hikurangi Subduction Interface: One of the most im-portant changes to the earlier NSHM is the treatment of theHikurangi subduction interface or megathrust, located on theeastern side of the North Island (Fig. 3). When the earlierNSHM was developed, less was known about the earthquakepotential of the Hikurangi subduction interface, and the para-meter values assigned to it were uncertain. Since that time,significant progress has been made in our understanding ofthe seismogenic potential and tectonics of the megathrust(see review in Wallace et al., 2009). In particular, geodeticobservations of contemporary interseismic coupling on themegathrust and the occurrence of slow slip events at thedowndip termination of coupling beneath the North Islandsuggest that the interface may produce earthquakes as largeas Mw 9. A range of earthquake sizes may be produced bythe interface, given that the southern portion is stronglycoupled, and the northern portion currently shows aseismiccreep (Wallace et al., 2009).

To encompass the variety of opinion on the seismogenicpotential of the subduction thrust, an expert panel (encom-passed by the coauthor list) was convened to develop andweight a series of potential earthquake sources for the Hikur-angi subduction interface. Based on the overall characteris-tics of the subduction margin, historical seismicity, anddistribution of interseismic coupling and slow slip events

(Wallace et al., 2009), the margin was divided into three dif-ferent source lengths, each length with two coincidentsources defining end-member dimensions for the interface:(1) southern Hikurangi margin (Wellington sources, 328 and342), (2) central Hikurangi margin (Hawke’s Bay sources,253 and 254), and (3) northern Hikurangi margin (Rauku-mara sources, 143 and 144). The sources are shown onFigure 3 (as lines with teeth) and the parameters listed inⒺ Table S1 (see supplement). The underpinning geodetic,geological, and seismological data used to develop thesesources are provided in Wallace et al. (2009). A furthersource based on a combination of the three larger sources(Wellington, Hawke’s Bay, and Raukumara) is also definedin the model (source 328b).

The southern Hikurangi source model is ∼220 km long(extending along-strike from Cook Strait to Cape Turnagain)and∼60–140 km wide with a downdip rupture depth of 25 to30 km and an updip rupture depth of 5–15 km. There washealthy debate within the expert panel regarding the likelyupdip limit of the interface sources. The 15-km depth limitassumes that seismogenic rupture will not continue updipbeneath the Cretaceous Pahau Terrane (Reyners andEberhart-Phillips, 2009), while the shallower updip limit as-sumes that significant seismogenic rupture can propagateupdip until the unconsolidated, active portion of the ac-cretionary wedge is reached (e.g., Wallace et al., 2009). Sin-gle-event displacements (D) derived with an equation ofD asa function of subduction source length (McCaffrey, 2008) forthe southern Hikurangi sources are in the range of 3–8 m,while Ds of 9–22 m are defined for the combined source.Long-term slip rates are taken to be 25� 5 mm=yr andinterseismic coupling coefficients on the interface are 0:7�0:2 (Wallace et al., 2004, 2009). For the wider rupture model(combining 5 km updip depth and 30 km downdip depth),application of equations 5 and 6 give Mw 8:4, and withthe following equations:

T � M0=M0rate; (7)

and

M0rate � μLW�SR�; (8)

(in which M0rate is the seismic moment rate, and SR is theseismic slip rate; Brune, 1968; Wesnousky, 1986) a recur-rence interval T of 1000 years is calculated. The narrowerrupture model (from 15 km to 25 km depth) producesMw 8.1 events and T of 550 years. Finally, the source com-bining all three of the larger sources has an Mw 9.0 and T of7050 years. All the previous estimates of T incorporate cou-pling coefficients estimated from the GPS modeling (Wallaceet al., 2009). Also, because the three coincident rupture mod-els are intended to be used simultaneously in the NSHM, theM0rate is assigned to each model according to a Gutenberg–Richter-based weighting scheme. This balances the seismicmoment rate when used together in the fault source model


and results in the lowest magnitude (Mw 8.1) having theshortest T, and the Mw 9.0 having the longest T.

The methodology described for the southern Hikurangisegment is also repeated for the northern and central Hikur-angi segments, with the throughgoingMw 9.0 source (see theprevious discussion in Fault Sources) applied to these twoparts of the subduction zone as well. These segments areeach 200 km long and 68–101 km wide. In these cases, theupdip limit of the subduction earthquake rupture is 5 km andthe downdip limit varies from 15–20 km. The values of Dare in the range of 3–7 m based on McCaffrey (2008).Convergence rates on the central Hikurangi margin segmentare 44� 7 mm=yr and coupling coefficients are probablylow (0.1–0.3; Wallace et al., 2004, 2009), yielding an aver-age T for events with Mw 8.1–8.3 of 1100–1400 years.Convergence rates at the northern Hikurangi margin are54� 6 mm=yr and coupling coefficients are also low(0.1–0.3; Wallace et al., 2004). Thus, Mw 8.1–8.3 earth-quakes are calculated with T of 900–1150 years. The lackof historical or paleoseismic data constraining the recurrencebehavior of Hikurangi subduction interface earthquakesmakes the calibration of our Hikurangi source model difficultat the present time.

Finally, the Kermedec trench is the continuation of theHikurangi subduction zone to the northeast of New Zealand,and undoubtedly has considerable seismic potential. How-ever, we assume that the contribution to on-land hazard inNew Zealand from Kermedec trench earthquakes will beminor compared with the much closer Hikurangi subductionzone sources.

14. Fiordland Subduction Interface: The Fiordlandsubduction zone is located at the southwestern corner ofthe South Island and has been the source of numerous largeearthquakes in the historical period. The most recent largeevents are theMw 7.2, 10 August 2003 Secretary Island earth-quake and theMw 7.6–7.8, 15 July 2009 Dusky Sound earth-quake (Reyners et al., 2003; Fry et al., 2010; Beavan,Samsonov, Motagh et al., 2010). Our characterization ofthe Fiordland subduction interface sources is based on threefactors: (1) the extent of ruptures modeled for the 2003 and2009 earthquakes (Fig. 3e, based on fig. 1 in Fry et al.,2010); (2) a source linking the 2003 and 2009 ruptures,and (3) a 550-km long source linking the 2009 source withthe Puysegur subduction interface. The methodology forestimation of Mw and T for the four sources is essentiallythe same as for the Hikurangi sources, using the orthogonalcomponent of plate motion minus the dip-slip component ofall upper-plate faults intersected along a roughly east–westtransect at the source latitudes. The resulting slip rate is5–10 mm=yr (preferred over 8 mm=yr) at the latitude of the2003 source, and 10–22 mm=yr (preferred over 16 mm=yr) atthe latitude of the 2009 source. Application of equations 7 and8, the relationship of McCaffrey (2008), and a Gutenberg–Richter-based weighting scheme to balance slip rateacross the overlapping sources produces Mw 7.1 and T of

200–350 years for the 2003 source, Mw 7.8 and T of 350–700 years for the 2009 source, Mw 7.9 and T of 778–1550 years for the 2003� 2009 source, and Mw 8.6 and Tof 10,850–21,700 years for the Puysegur �2009 source.We acknowledge that the long recurrence interval assignedto the Puysegur source is only based on slip rate balancingat the latitude of Fiordland. Shorter recurrence intervalsmay apply well to the south of New Zealand where the sub-duction zone is the only active element of the plate boundary.

Distributed Earthquake Sources

In addition to defining the locations, magnitudes, andfrequencies of large (Mw 7–7.9) to great (Mw ≥ 8) earth-quakes on the crustal faults and subduction zones, we alsoallow for the occurrence of moderate-to-large earthquakes(Mw 5 up to the maximum magnitude assumed for theregion) to occur on unmapped or unknown faults (e.g., theMw 7.1, 4 September 2010 Darfield earthquake). We refer tothis as the distributed seismicity source model. While ouroverall approach is similar to that used in the earlier NSHM,the input data and several important steps in the methodologyhave been revised. The regionalization (zonation) schemeused in the earlier NSHM has been substantially updated torepresent the current understanding of the distribution ofseismicity (Fig. 4a) and tectonics (Figs. 1–3) in the country(Fig. 4b). The b-value of the Gutenberg–Richter distributionis calculated on a regional basis (as for the earlier NSHM), butusing the maximum-likelihood method of Aki (1965) andearthquake data from 1964 to early July 2009 (the earlierNSHM used data to the end of 1997). The method used inthe older model was that of Weichert (1980), which allowsfor combining multiple time periods with varying complete-ness levels. However, we now conclude that the larger un-certainties in the magnitudes, locations, and depths of theolder data do not justify use of the older data. To ensureestimates of the b-value are based on a sufficient numberof earthquakes, the 16 crustal zones are combined into 5zones of similar slip type (Fig 4b). This allows for larger datasamples than if the zones are used individually as done in theearlier NSHM. Specifically, the b-value estimates are nowmade on subcatalogs of between 658 and 1363 events.Subcrustal zones are also defined to encompass the dippingslabs of the Hikurangi and Fiordland subduction zones, andnormal-faulting mechanisms are assigned to these zones. Thea-values are calculated on a 0:1° × 0:1° grid, at five depthlevels (10, 30, 50, 70, and 90 km), and b-values are assignedto the grid cells according to the b-value of the zone. In ourcalculations we assume that the one ML magnitude scaleused extensively in the New Zealand catalog is equivalent toMw. While a New Zealand-based regression equation forML −Mw conversion is under development and thereforeunavailable at the present time, our methodology for obtain-ing distributed seismicity parameters from the cumulativetotal of M ≥ 4 events since 1964 minimizes the impact ofML −Mw differences in the PSH model. The impact of these


differences on the hazard calculations would be negligible,based on many past observations of how changes to sourcemodels in high seismicity regions translate to only very smallchanges in hazard estimates.

In the earlier NSHM, the gridded a-value was smoothedusing a 50-km Gaussian smoothing kernel. To optimize thesmoothing in the updated model, we compare smoothed seis-micity models with three different smoothing kernels: (1) a50-km Gaussian kernel; (2) a Stock and Smith (2002) adap-tive Gaussian kernel; and (3) a density-based adaptive kernelbased onWerner et al. (2012). The models are retrospectivelytested using a learning period of 1840.0–1998.0 and a testingperiod of 1998.0–1999.0. Using the information gain perearthquake (Harte and Vere-Jones, 2005) to evaluate themodel forecasts, which is based on the likelihood of eachobserved earthquake and the total number of events forecastby the model, the 50-km Gaussian kernel model is signifi-cantly better for the period tested. We therefore use a 50-kmGaussian to smooth the a-value in the updated model.Additionally, we smooth the b-values across zone bordersusing the same kernel in the same way as applied in the ear-lier NSHM.

The maximum magnitude, Mcutoff , assigned to theGutenberg–Richter magnitude–frequency distribution ofeach zone, and hence, each grid cell within each zone, isrevised. The revision is in consideration of the changes tothe fault source model, and our conclusions regarding incom-pleteness of the fault model. In the new model we apply auniform Mcutoff of 7.2 for all zones, except the Taupo volca-nic zone (TVZ, light gray zone in Fig. 4b), which is assignedan Mcutoff of 6.5. A map showing the spatial distribution ofN-values (number of events ≥ M4 for the period 1964–2009.5) per 0:1° × 0:1° grid cell is shown in Figure 4c.

An acknowledged problem with the current dataset isthe presence of restricted or assigned depths in the GeoNetearthquake catalog for New Zealand (see Data and Re-sources). More than 75% of the events we use have assigneddepths of 0, 5, 12, or 33 km. The misfit of this assigned depthto the true depth for each event is not well understood, de-spite significant past attempts to address the issue (McGinty,2001). In the updated version of the model, we assign theseearthquakes equally to the 10-km and 30-km depth layers.

Lastly, we model the seismicity rates up to Mcutoff foreach grid cell without altering the source dimension for thelarger magnitudes. Although some hazard modeling meth-odologies assign fictitious faults to each grid cell by way ofMw − L scaling relationships, experience has generallyshown these adjustments to have undetectable influence onhazard in high seismicity regions.

Magnitude–Frequency Distributions

The magnitude–frequency distributions derived from thesource models are shown in Figure 5. We show the cumulativeannual rate of events (number of events per year ≥ M, in logscale) as a function of magnitude, for the fault and distributed

seismicity models and the combined model. We also showfor comparison the combined source model. For the faultsources, the individual event rates and magnitudes are basedon the mean or preferred values given in Ⓔ Table S1 (seesupplement); the distributed seismicity rates are based on thecalculated a-values and b-values for all grid cells and depthlayers (Fig. 4b,c).

The magnitude–frequency distribution for the faultsource model shows a typical monotonic fall-off in cumula-tive frequency as a function of magnitude. The stepped shapeof the curve at Mw greater than about 7.8 is due to the lim-ited number of earthquakes of that magnitude range. Atmagnitudes less than about Mw 6 the slope of the fault dis-tribution is subhorizontal, due to there being relatively fewfault-derived earthquakes at that magnitude range. In con-trast, the distributed seismicity curve shows a sloping lineartrend from Mw 5 to Mw 7.2. This is a direct consequence ofthe distributed seismicity events being calculated accordingto the Gutenberg–Richter relationship. The combined curveshows a generally linear slope throughout the magnituderange of the graph, which is a typical observation globally(e.g., Wesnousky et al., 1982; Stirling et al., 1996). The maindivergences from linearity are in the range of Mw 7.2–8.0,where the distribution shows downward steps in rates atabout Mw 7.2, and at about Mw 8.0 where the rates show astep to the right on the graph. This is in contrast with thecombined curve from the earlier NSHM, which shows anslight upward bulge in rates relative to the new model atabout Mw 7.3 and lower rates at Mw greater than 8.0. Theshape of the combined distribution for the new model is con-trolled by: (1) the Mcutoff for most of the distributed seismi-city model being set to Mw 7.2, therefore contributingsignificantly to the combined distribution at Mw less than7.2; (2) the new modeling of crustal faults producing a slightdecrease in rates of Mw 7.2–7.5; and (3) the new Hikurangi

Figure 5. Magnitude–frequency distributions for the faultmodel, distributed seismicity model, combined model, and the com-bined model of the earlier NSHM. See the text for further explana-tion (Magnitude–Frequency Distributions).


subduction interface model producing an increase in rates forMw 8.0–9.0. The increase in maximum magnitude toMw 9.0on the interface is clearly evident in Figure 5.

Ground-Motion Prediction Equations

The ground-motion prediction equations (GMPEs) usedin the NSHM for peak ground accelerations (PGAs) and 5%damped acceleration response spectra in New Zealand crus-tal and subduction zone earthquakes are those developed byMcVerry et al. (2006). This is currently the only suite ofGMPEs available for New Zealand, and we have restrictedour analysis to this suite because the suitability of foreignGMPEs for New Zealand conditions is presently unknown(e.g., Next Generation Attenuation models, or NGAs). Inparticular, concern surrounds application of the NGA sitecondition metric (VS30) to New Zealand conditions, with re-solution of this issue being the topic of considerable researchat the present time. Site classes are instead more descriptiveand geologically based (e.g., site class A, hard rock; B, rock;C, shallow or stiff soil; D, deep or soft soil; McVerry et al.,2006). Equations are given for both the larger of tworandomly oriented othogonal horizontal components of mea-sured ground motion and the geometric mean of the compo-nents, and take account of the different tectonic types ofearthquakes in New Zealand. The equations also modelthe faster attenuation of high-frequency earthquake groundmotions in the TVZv (domain 2) than elsewhere. Both thecrustal and subduction zone attenuation expressions havebeen obtained by modifying overseas models for each ofthese tectonic environments to better match New Zealanddata and to cover site classes that relate directly to those usedfor seismic design in New Zealand codes.

The McVerry et al. (2006) model uses all available datafrom the New Zealand strong-motion earthquake accelero-graph network up to the end of 1995 that satisfy variousselection criteria, supplemented by selected data from digitalseismographs. A more up-to-date New Zealand model usingpost-1995 data is not available at the present time. The seis-mographs provide additional records from rock sites, andinformation on motions involving propagation paths throughthe volcanic region, classes of data that are sparse in recordsproduced by the accelerograph network. The New Zealandstrong-motion dataset (prior to September 2010) lacks re-cords in the near-source region, with only one record froma distance of less than 10 km from the source and at magni-tudes greater thanMw 7.2. The New Zealand data used in theregression analyses range in source distance from 6 to400 km (the selected cutoff, in which the distance is the clo-sest distance to the fault rupture plane) and in Mw from 5.08to 7.23 for PGA, with the maximum magnitude reducing toMw 7.09 for response spectra data. The required near-sourceconstraint is obtained by supplementing the New Zealanddataset with overseas peak ground acceleration data (but notresponse spectra) recorded at distances less than 10 km fromthe source. Further near-source constraints are obtained from

the overseas attenuation models, in terms of relationshipsthat are maintained between various coefficients that controlthe estimated motions at short distances. Other coefficientsare fitted from regression analyses to better match theNew Zealand data.

The need for different treatment of crustal and subduc-tion zone earthquakes is most apparent when the effects ofsource mechanism are taken into account. For crustal earth-quakes, reverse mechanism events produce the strongestmotions, followed by strike-slip and normal events. For sub-duction zone events, the reverse mechanism interface eventshave the lowest motions, at least in the period range up toabout 1 s, while the slab events, usually with normal mecha-nisms, are generally strongest (McVerry et al., 2006).

The McVerry et al. (2006) GMPEs have been used in theearlier NSHM (i.e., the GMPE was used prior to eventual pub-lication) and in hundreds of hazard studies in New Zealand.In particular, they have been used in the derivation of theelastic site spectra in the new Loadings Standard for NewZealand, NZS1170.5:2004 (Standards New Zealand, 2004).Only one change has been implemented in the McVerry et al.(2006) GMPE since being applied to the earlier NSHM, andthat is a correction to the site class term. Specifically, thenonlinear site effect term has been been changed (McVerryet al., 2006).

Hazard Analysis

Methodology

We use the locations, sizes, tectonic type or crustalmechanism, and recurrence rates of earthquakes defined inour source model to estimate the PSH for a grid of sites witha spacing of 0.1 degrees in latitude and longitude. We use thestandard methodology of PSHA (Cornell, 1968) to constructPSH maps. For a given site, we: (1) calculate the annualfrequencies of exceedance for a suite of ground motionlevels (i.e., develop a hazard curve) from the magnitude, re-currence rate, earthquake type, and source-to-site distance ofearthquakes predicted from the source model; and (2) esti-mate the maximum acceleration level that is expected tobe exceeded for a range of return periods. For each site, step(1) is repeated for all sources in the source model, and step(2) is calculated by summing the results of step (1) to give theannual frequencies of exceedance for a suite of accelerationlevels and spectral periods at the site due to all sources. Thehazard calculations are made with the same FORTRAN codeused to develop the 2002 NSHM. This is our standard codefor PSHA in New Zealand and was the focus of considerablein-house QA around the time of the 2002 NSHM.

We generally assume a Poisson model of earthquakeoccurrence for the earthquake sources, in that earthquakeprobabilities are based on the average time-independent rateof earthquake occurrence on each fault. The three exceptionsto Poissonian modeling are the time-dependent probabilitiesassigned to the Wellington (Wellington–Hutt Valley), Wair-


arapa, and southern Ohariu fault sources as a result of the“It’s Our Fault” research (Rhoades et al., 2010). New paleo-seismic information on the activity of these faults accumu-lated over the last several years has resulted in revisedestimates for some, or all, of the following: (1) the timingof the most recent rupture and several previous ruptures;(2) the size of single-event displacements; and (3) the Holo-cene dextral slip rate. The conditional probability of ruptureof these faults has been evaluated in light of this new infor-mation, using a renewal process framework and four recur-rence-time distributions (exponential, log-normal, Weibull,and inverse Gaussian). Conditional probabilities for the next100 years used in the new NSHM are: Wellington fault (Well-ington–Hutt Valley segment), 11%; southern Wairarapafault, 1.3%–7.7%; and Ohariu fault, 3.9%–5.1% (Rhoadeset al., 2010).

Our calculation of ground motions follows the standardpractice of modern PSHA and accounts for the uncertainty inestimates of ground motion from the McVerry et al. (2006)GMPE in the calculation of PSH (up to 3 standard deviationsbelow and above the median). Only Mw 5.25 and greater areincluded in the hazard analysis, consistent with the recom-mended usage of the McVerry et al. (2006) GMPE. In anycase, inclusion of earthquakes in the range ofMw 5.0 to 5.25does not have a perceptible impact on hazard in high-seismcity New Zealand.

Because the McVerry et al. (2006) GMPE has separateexpressions for crustal earthquakes of different slip type (i.e.,strike-slip, normal and reverse, and slip types intermediatebetween these extremes), and for subduction interface, shal-low subduction slab and deep slab earthquakes, we estimateaccelerations applicable to the slip type and tectonic envir-onment of each earthquake source. Each fault source isassigned a particular slip type, and the attenuation expressionfor that slip type is used for the fault in the hazard calcula-tions. In the case of the dipping subduction interface sourceswe use the interface attenuation expression. For the distrib-uted seismicity (point) sources, the slip type assigned to thepoint source is the slip type of the enclosing seismotectoniczone (Fig. 4b). For the deep zones we simply use the shallowand deep slab expressions of the model, based on the obser-vation that essentially all of the deep seismicity in the coun-try is attributed to the dipping Hikurangi and Fiordland slabs.Application of the volcanic path attenuation expression forthe Taupo volcanic zone (TVZ), which strongly reducesaccelerations with distance, is limited to faults and pointsources located in the TVZ (normal-volcanic zone in Fig. 4b).We apply this to the whole path length for earthquakes in thiszone, rather than just the part of the path contained within theTVZ zone.

Hazard Maps and Spectra

Hazard estimates are shown for the new NSHM in mapform (Fig. 6a–f), and we also compare these maps withmaps from the earlier NSHM, for the case of the 475-year

PGA hazard (Fig. 6g). Response spectra for the new NSHMand earlier NSHM are also shown for the main centersof Auckland, Wellington, Christchurch, and Dunedin(Fig. 7a–d). All hazard maps and spectra are based on classC (shallow soil) site conditions (see McVerry et al., 2006 fordefinition of site classes). For each of the maps shown, wecalculate the hazard with the McVerry et al. (2006) GMPEand with the GMPE uncertainty set to three standard devia-tions. Maps for PGA and spectral acceleration (0.5- and 1-speriods) for 475-year and 2500-year return periods (approxi-mately 10% and 2% probability of exceedance in 50 years)are shown, with acceleration measured in units of g.

The 475-year PGA map shows a pattern of hazard that ishighest from the southwestern South Island to the easternNorth Island (the northeast-trending zone of PGA ≥ 0:5g).Hazard in this northeast-trending zone reflects the greatestconcentration of active fault sources and seismicity in themodel. In particular, the Fiordland (southwestern-most SouthIsland), Alpine fault (western-central South Island), andHope fault (northern-central South Island) sources are mostresponsible for this zone of high hazard in the South Island.The crustal and Hikurangi subduction zone sources show astrong influence on hazard in the eastern North Island.Comparison of Figure 6a with the equivalent map from theearlier NSHM (Stirling et al., 2002; Fig. 6g) shows that thebiggest change in hazard is in the southeast of the NorthIsland. The new Hikurangi subduction interface model(see Fault sources) has obvious impact on the hazard in thisarea, and highlights the importance of the new subductioninterface modeling. The new subduction interface modelingmore than counteracts the 50% reduction in the Wellingtonfault (Wellington–Hutt Valley source) hazard from thePoissonian-based estimates used in the earlier NSHM.

Otherwise, the pattern of hazard is similar at a nationalscale, with hazard decreasing away from the axis of the coun-try toward the far north and south. Similar patterns of hazardare reflected by the 475-year spectral acceleration maps(Fig. 6b,c ), and the 2500-year maps (Fig. 6e,f).

The graphs of site-specific response spectra for class C(shallow soil) sites show hazard for 150-, 475-, 1000-, and2500-year return periods, and the spectra are compared withthe corresponding spectra from the earlier NSHM (Fig. 7a–d).For Auckland, the spectra have reduced significantly fromthe earlier NSHM, reflecting the influence of the newly dis-tributed seismicity model on the hazard estimates. The in-creased b-value in the new model (about 1.1 for the newmodel versus less than 1 for the earlier NSHM) is the primaryreason for the reduced spectral accelerations in Auckland.For Wellington, the only significant change to the spectrafrom the earlier NSHM is a slight increase in hazard at spec-tral periods of 0.4 s and greater. This increase in longer per-iod hazard is due to the changes to the Hikurangi subductioninterface sources. For Christchurch, hazard has increased forperiods less than about 0.6 s, reflecting the decreased b-valuein the new NSHM (less than 1 in the new NSHM and close to1.2 in the older NSHM). Lastly, spectra for the city of


Figure 6. Seismic hazard maps for 475- and 2500-year return periods (10% and 2% probability of exceedance in 50 years) for class C(shallow soil) site conditions: (a) peak ground acceleration (PGA) for 500-year return period; (b) spectral acceleration (SA) 0.5 s for 475-yearreturn period; (c) SA 1 s for 475-year return period; (d) PGA for 2500-year return period; (e) SA 0.5 s for 2500-year return period; (f) SA 1 sfor 2500-year return period; and (g) PGA for 475-year return period from the earlier NSHM for comparison. (Continued)




Figure 7. Response spectra for the cities of: (a) Auckland, (b) Wellington, (c) Christchurch, and (d) Dunedin. Spectra for 150, 475, 1000,and 2500 years for class C (shallow soil) site conditions are shown in each case, along with the earlier NSHM spectra for comparison.


Dunedin generally show a slight increase in hazard for thenew NSHM. This reflects a slightly decreased b-value in thenew NSHM (less than 1 in the new NSHM and greater than 1in the earlier NSHM).

Deaggregation

Deaggregation graphs show the contributions to thehazard estimates according to magnitude and source-to-sitedistance; the graphs are typically used to develop design orscenario earthquakes for specific sites. We show deaggrega-tion graphs for Auckland, Wellington, Christchurch, andDunedin in Figure 8. Each graph shows the contributionsto the 475-year PGA, along with an additional graph showingthe 475-year 1-s spectral acceleration (SA) for Wellington.

The Auckland deaggregation plot (Fig. 8a) shows the475-year PGA to be dominantly controlled by the distributedseismicity sources at Mw 5–6.8 and distances of less than70 km. The minor contributions from the Wairoa north fault(Mw 6.7 at 22 km; 4% contribution) and Kerepehi offshorefault (Mw 7.2 at 38 km; 2% contribution) can also be seen onthe graph.

Wellington’s 475-year PGA hazard is dominantly con-trolled by fault sources. Peaks representing the Wellingtonfault (Wellington–Hutt Valley) (Fig. 8b; Mw 7.5 at less than1 km; 20% contribution), Ohariu south fault (Mw 7.6 at 5 km;20% contribution), and Wairarapa faults (Mw 8.1 at 17 km;13% contribution) are most obvious on the plot. The

475-year SA 1-s graph for Wellington is also provided inFigure 8c to show the contribution to hazard from two of thesouthernmost Hikurangi subduction interface sources(Mw 8.1, 8.4, and 9.0 at 23 km; combined contribution ofabout 20%). The great earthquakes produced by thesesources contribute most significantly to long-period motions.

The 475-year PGA hazard for the city of Christchurch(Fig. 8d) is dominated by the distributed seismicity model(Mw 5–6.8 at distances of less than 50 km). Fault sourcesat the margin of and beneath the Canterbury Plains alsocontribute to the hazard. Specifically, the Springbank andPegasus 1 sources (453 and 449, respectively; Mw 7.0 at 27and 22 km, respectively; 7% combined contribution), Ashleyfault (451; Mw 7.2 at 30 km; 5% contribution), and PortersPass–Grey fault sources (446 and 447;Mw 7.5 at 44 km; 4%contribution) dominate the hazard at the city. None of thepeaks on Figure 8d are due to the Greendale fault (450),source of theMw 7.1, 4 September 2010 Darfield earthquake.The preliminary recurrence interval assigned to that faultsource (minimum 16,000 years) is considerably longer thanthe recurrence intervals for the previously cited fault sources.

The hazard for Dunedin is dominated by earthquakesproduced by the distributed seismicity model. The main faultsources contributing to the model are the Akatore fault(Fig. 8e; Mw 7.4 at 13 km; contribution 14%), Taieri Riverfault (Mw 7.1 at 47 km; contribution 6%), and Waipiata fault(Mw 7.4 at 60 km; contribution 3%).

Figure 8. Deaggregation graphs for the cities of (a) Auckland, (b) and (c) Wellington, (d) Christchurch, and (e) Dunedin. In all casesexcept for (c) the deaggregation is for 475 year PGA, for class C (shallow soil) site conditions. In the case of (c), the deaggregation is for475 year 1 s SA to show the contribution of Hikurangi subduction interface sources at longer spectral periods.


Discussion

The new NSHM has involved a national-scale update ofthe fault source and distributed source models, both in termsof data and methods. The overall pattern of hazard remainssimilar to that of the earlier NSHM, without the large differ-ences seen between earlier NSHMs (compare Smith andBerryman, 1986 with Stirling et al., 1998 and 2002). At thenational-scale the pattern of hazard therefore seems to haveachieved some degree of consistency, but with notable dif-ferences at the regional scale. Notable increases in hazard areapparent in the eastern North Island due to the influence ofthe Hikurangi subduction zone modeling and associated off-shore upper plate fault sources; decreases are apparent inAuckland due to the influence of the new distributed seismicitymodel. Numerous combinations of decreases and increases inhazard are apparent in many other parts of the country. Thecontinued use of the McVerry et al. (2006) GMPE means thatnone of the differences in hazard are due to changes to thechoice of GMPE, except for the minor change to the site classterm (see Ground-Motion Prediction Equations).

The Mw 7.1, 4 September 2010 Darfield, Canterbury,earthquake occurred on a fault source not recognized priorto the earthquake (Quigley et al., 2010). The Greendale faultsource has now been included in the fault source model (seeⒺ Table S1 in the supplement; source 450b). However, be-fore this inclusion the earthquake was to some extent alreadyaccounted for in the NSHM. The maximum magnitudeassumed in the distributed seismicity model for the area ofthe earthquake is 7.2 (i.e., larger than the Darfield event;Fig. 4b), and the combined annual rate of Darfield-sizeevents from the subset of distributed seismicity grid cellslocated in the immediate vicinity of the earthquake (Fig. 9)is around 1=11; 000. This is of similar order to the uncertainfield-based rate estimates for the Greendale fault (1=16; 000;see Ⓔ Table S1 in the supplement; Quigley et al., 2010).Lastly, the deaggregation for Christchurch (Fig. 8c) showsthat Mw 7–7.5 fault and distributed source-derived earth-quakes at distances less than 40 km are important contribu-tors to the hazard. Therefore, earthquakes similar to theDarfield event feature prominently in the NSHM, and in facthave already been identified as important scenario earth-quakes for Christchurch in studies commissioned by theterritorial authority Environment Canterbury (Stirling et al.,2001, 2008). Similarly, the size and location of the Mw 6.2,22 February 2011 Christchurch aftershock were also consis-tent with the distributed seismicity model for that area.However, the ground motions produced by the earthquakewere considerably stronger in the near field (within 10 km)than the motions expected for an earthquake of that size inthe McVerry et al. (2006) GMPE.

A significant issue limiting the applicability of theNSHM to short return periods (certainly those less than the475-year return period) is the availability of non-Poissonian(time-dependent) earthquake probabilities. Non-Poisonnianprobabilities only exist for the major Wellington region faults

at the present time (Rhoades et al., 2010). As is the generalcase for PSH models, the NSHM is not developed to provideestimates of short return period hazard. This is because of thefollowing three reasons: (1) a lack of time-dependent earth-quake probabilities for virtually all of the earthquake sources.Obtaining time-dependent probabilities involves a consider-able effort of data evaluation and processing, and is thereforelimited to faults that have been intensely studied, such as theWellington region faults for the “It’s Our Fault” project(Rhoades et al., 2010); (2) a lack of statistical seismology-based time-dependent earthquake probabilities (e.g., after-shock probabilities), which is a topic of intense research atthe present time (e.g., Gerstenberger et al., 2007), and (3) theinability to incorporate fault interaction physics and associatedprobabilities into the NSHM with high confidence (e.g.,Robinson and Benites, 2001). Items (2) and (3) are topicsof active research, testing, and evaluation, but are not yet readyfor implementation directly in the NSHM at the present time.

Figure 9. Simplified trace of the Greendale fault and thedistributed seismicity grid cells in the immediate vicinity. The ac-companying magnitude–frequency distribution shows the com-bined earthquake rates for these cells (cumulative number ofevents ≥ M), and the 1=16; 000 year maximum-rate estimate forthe Greendale fault from field data.


Data quality and quantity with respect to the sourcemodel have been greatly improved in the new NSHM, withthe inclusion of over 200 fault sources and 11 years of seis-micity data. The largest contribution to the fault source mod-el has been the inclusion of offshore fault data, mainly in theoffshore regions of domains 2, 3, 5, 6, 7, 9, and 12. Never-theless, prominent gaps in the offshore coverage of faultsources remain in some offshore areas of domains 1, 2 (farnortheast), 8, and 10. Future improvement to the onshorecomponent of the fault source model will benefit from stu-dies that are able to identify active faults in areas of highlyerodible geological formations (e.g., domains 1 and 5), areasof high sedimentation (e.g., domains 2 and 10), and areas ofthickly forested mountainous terrain (e.g., domain 8).

A major advance in the NSHM has been the use of geo-detic data and models to develop a much-improved sourcemodel for the Hikurangi subduction interface. However, weacknowledge that this model is a simplified approximation ofthe understanding of how plate motion is accommodated atthe subduction interface. The Hikurangi subduction interfacemodel will undoubtedly be improved in future. Futuregeodetically orientated enhancements to the NSHM will alsoarise from the inclusion of geodetic data in the calculation ofdistributed seismicity rates, which are at present based solelyon the earthquake catalog.

A future update of the McVerry et al. (2006) GMPE isjustified by the lack of inclusion of any strong-motion datapost-1995 in the GMPE. In particular, inclusion of the strong-motion data from the Mw 7.1, 4 September 2010 Darfield,Canterbury, earthquake and devastatingMw 6.2, 22 February2010 Christchurch aftershock will constitute significantmodifications to the database used for development of a newGMPE in New Zealand. Near-field ground motions (less thanabout 10 km distance) were unusually strong for theChristchurch earthquake, relative to what was expected foran earthquake of that size. Furthermore, relocation of theearthquake catalog with the new nationwide 3D-seismicvelocity model (Eberhart-Phillips, 2010) is needed in orderto redefine the depths assigned to restricted events (see Dis-tributed Earthquake Sources section).

Finally,we emphasize that themaps and spectra are basedonmean or preferred parameters for all of the sources and havenot included an analysis of the influence of parameter uncer-tainties on the hazard. Only the aleatory uncertainty in theMcVerry et al. (2006) GMPE has been incorporated into thehazard analysis, as was the case for the earlier NSHM. Futureworkwill be to quantify the site-specific uncertainty in hazardfor the NSHM and enhance the model to include tools forquantifiying short-term earthquake hazard (e.g., Gerstenber-ger et al., 2005; Rhoades and Evison, 2005). In particular,focussed work on the aftershock sequence of the Mw 7.1,4 September 2010 Darfield, Canterbury, earthquake, includ-ing the devastating Mw 6.2, 22 February 2010 Christchurchaftershock, is being given highest priority in this regard.Occurrence of this major earthquake sequence in an area of(formerly) low seismicity rates (northeastern area of domain

10), absence of known faults, and in the case of the Darfieldearthquake, featureless topography highlights the need forbetter detection of low slip-rate faults that are buried beneaththick sediments. The Canterbury earthquakes have clearlyshown that these low slip-rate faults can rupture with majorconsequences. Finally, an even more challenging task is toprovide reliable short-term earthquake hazard estimates priorto the initiation of a major earthquake sequence.

Conclusions

We have produced an update of the NSHM for NewZealand, the first national-scale update since the NSHM ofStirling et al. (2002). The model incorporates a fault sourcemodel that has been updated with over 200 new onshore andoffshore fault sources and utilizes new New Zealand-basedand international scaling relationships for the parameteriza-tion of the faults. The distributed seismicity model has alsobeen updated to include post-1997 seismicity data, a newseismicity regionalization, and improved methodology forcalculation of the seismicity parameters. Probabilistic seis-mic hazard maps produced from the new model show asimilar pattern of hazard to the older maps at the nationalscale, but some significant reductions and increases in hazardat the regional scale. The national-scale differences betweenthe new NSHM and earlier NSHM appear less than those seenbetween earlier NSHMs, showing that some degree of con-sistency in the national-scale pattern of hazard estimates hasbeen achieved, at least for return periods of 475 years andgreater. While the new NSHM is by no means the final wordon seismic hazard in New Zealand, it represents a consider-able advance in terms of data quality, quantity, methodology,and evolution of a large multidisciplinary, multi-institutionalapproach to PSH modeling in this country (New Zealand).

Data and Resources

Seismicity data are available on the GeoNet website(www.geonet.org.nz; last accessed March 2012), and thefault source and distributed seismicity models are availablein electronic form from Mark Stirling for use in research. Allmaps and graphs are also available in electronic form fromMark Stirling. Data on the active faulting in the Wairarapaand Wellington regions are available from http://www.gw.govt.nz/assets/council-publications/The_1855_Wairarapa_Earthquake_Symposium_Proceedings_Volume_Web_Version.pdf. Data on the all-day field trip to the Wairarapafault and 1855 rupture sites are avialable from http://www.gw.govt.nz/assets/council-publications/1855%20Field%20Trip%20guide.pdf (last accessed July 2010).

Acknowledgments

We wish to thank GeoNet (www.geonet.org.nz) for providing seismi-city catalog data used in the distributed seismicity model, and numerouspeople in GNS Science and NIWAwho assisted with preparation of the ac-tive fault database used as input to the fault source model. Contributions to


http://www.geonet.org.nz




http://www.gw.govt.nz/assets/council-publications/The_1855_Wairarapa_Earthquake_Symposium_Proceedings_Volume_Web_Version.pdf




http://www.gw.govt.nz/assets/council-publications/1855%20Field%20Trip%20guide.pdf







various expert panel meetings and additional information came from UrsulaCochran, Roberto Basilli, and William Fry. The Foundation for ResearchScience and Technology is thanked for financial support, and the manuscriptbenefited from reviews by Mark Hemphill-Haley, an anonymous reviewer,Annemarie Christophersen, and John Beavan.

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http://dx.doi.org/10.1029/175GM12

http://dx.doi.org/10.1029/175GM12

http://dx.doi.org/10.1029/2003JB002412

http://dx.doi.org/10.1080/00288306.2010.526547

http://dx.doi.org/10.1080/00288306.2010.526547

http://dx.doi.org/10.1029/2011JB008640

http://dx.doi.org/10.1029/2004JB003241

http://dx.doi.org/10.1029/2004JB003241



http://dx.doi.org/10.1029/2009GC002610

http://dx.doi.org/10.1785/0120090340

Zachariasen, J., K. Berryman, R. Langridge, C. Prentice, M. Rymer,M. Stirling, and P. Villamor (2006). Timing of late Holocenesurface rupture of the Wairau fault, Marlborough, New Zealand,New Zeal. J. Geol. Geophys. 49, 159–174.

GNS ScienceP.O. Box 30368Lower Hutt, New Zealand

(M.S., G.M., M.G., N.L., R.V., K.B., M.R., D.R., W.S., A.N., K.C.)

National Institute of Water and Atmospheric ResearchPrivate Bag 14901Wellington, New Zealand

(P.B., L.W., P.V., R.L., G.L., S.N.)

Department of Civil and Natural Resources EngineeringUniversity of CanterburyP.O. Box 4800Christchurch, New Zealand

(B.B.)

Department of Geological SciencesUniversity of CanterburyP.O. Box 4800Christchurch, New Zealand

(J.P.)

Victoria University of WellingtonP.O. Box 600Wellington, New Zealand

(K.J.)

Manuscript received 2 June 2011


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