late pliocene and quaternary glaciations of new zealand abstract evidence of late pliocene glaciations is fragmentary the ross glaciation in northwest south island is correlated with the first marine faunal evidence of marked cooling in the wanganui basin in southern north island it is inferred to be in the 2 6 2 4 ma age range the porika glaciation in a separate area of northwest south island is younger judged by palynology and is correlated with a cooling 2 2 2 1 ma bp inferred from stratigraphic evidence of lowered sea level in the wanganui basin a gap of 1 5 ma in the record of glaciations is largely filled by wanganui basin marine sediments although an unconformity cuts out the record between ca 1 45 and 1 0 ma bp since then the many sedimentary cycles caused by sea level changes are presumed to be glacio eustatic in origin uplifted interglacial marine terraces back to marine oxygen isotope stage 17 and river terraces formed by cold climate aggradation are linked into the cyclic sequence through loess and tephra in their cover beds east of the south island cores from the dsdp site 594 in the southwest pacific record the earliest glaciation and higher in the core nine periods of south island glaciation in the last 0 7 ma onshore because of uplift and erosion only the last four glaciations assigned to oxygen isotope stages 10 8 6 and 4 2 are identified being named nemona waimaunga waimea and otira glaciations they are best known in north westland northwest south island where the relations of glacial outwash and interglacial shoreline deposits are displayed the late otira glaciation stage 2 is radiocarbon dated as beginning somewhat before 22 3 ka bp culminating ca 18 ka bp and ending at ca 14 ka bp when rapid deglaciation began a relatively small advance at ca 12 ka bp may have been followed by little change until after 8 6 ka bp recession was then followed by a period of advance from ca 5 ka bp until recent centuries and a subsequent recession that still continues

oblique slip on the puysegur subduction interface in the 2009 july mw 7 8 dusky sound earthquake from gps and insar observations implications for the tectonics of southwestern new zealand summary the mw 7 8 dusky sound earthquake of 2009 july 15 was the largest earthquake in new zealand in the past 80 yr and is the only major subduction interface earthquake in the new zealand historical record we have estimated the coseismic and early post seismic slip distribution in the earthquake by inversion of gps and differential interferometric synthetic aperture radar dinsar observations we show that slip during the earthquake was highly obliqueandessentiallyintheaustralia pacificrelativeplatemotiondirection failureoccurred onaca 80by50kmpatchofthesubductioninterfacewithmaximumslip5 6m inthisregion the offshore alpine fault carries up to 30 mm yr 1 of slip before terminating at resolution ridge near the southern end of the 2009 slip patch the southernmost part of the alpine fault trace lies near the up dip end of the 2009 slip patch and the fault probably exists only within the crust of the over riding plate in this region terminating at shallow depth where it meets the subduction interface there is no evidence for rupture of the alpine fault during the 2009 event however coulomb stress changes from the subduction earthquake have brought this section of the alpine fault closer to failure in contrast to many subduction zones undergoing oblique subduction where the slip in major earthquakes is partitioned into more or less pure thrustearthquakesonthesubductioninterfaceandstrike slipearthquakesinthebackarc thisis a case where the majority of the subduction interface slip is not partitioned with only a shallow convergence zone west of the strike slip alpine fault undergoing contraction approximately normal to subduction zone strike north of the 2009 earthquake region the alpine fault lies further east relative to the subduction interface and partitioning between strike slip on the alpine fault and trench normal thrusting on the subduction interface takes place in a more typical fashion our results provide the first clear demonstration of non partitioned oblique slip between the australian and pacific plates offshore of southern new zealand

river drainage patterns in the new zealand alps primarily controlled by plate tectonic strain the persistence of dendritic drainage patterns implies that rivers reorganize after a tectonic perturbation preserving no long term record of that tectonic event numerical simulations of the evolution of drainage patterns in the southern alps new zealand however reveal rivers that resist reorganization and thus preserve a record of plate tectonic strain over 10 million years

quartz fabrics in the alpine fault mylonites influence of pre existing preferred orientations on fabric development during progressive uplift strong quartz crystallographic preferred orientations cpos were developed during dislocation creep in the mylonite zone exposed in the hanging wall of the dextral reverse alpine fault zone new zealand the cpos have a consistent asymmetry indicating a high ratio of simple to pure shear strain with a shear sense of dextral up to the nw consistent with the mesoscopic shear sense indicators and with slip on the active fault there is a transition from y maxima and asymmetric single girdles in mylonites and ultramylonites within 300 m of the present fault trace to cross girdle fabrics in the protomylonites further from the fault the strong y maxima or single girdle cpos are ascribed to high ductile shear strains under amphibolite facies conditions while the cross girdle patterns found in the protomylonites are interpreted to represent deformation under lower temperature conditions however the observed fabric transition cannot logically be attributed to variations in temperature during the last increment of deformation the highly oriented y maximum fabrics formed at high temperature contain very few grains suitably oriented for basal slip so that the slip systems activated during subsequent shear at lower temperatures during exhumation were prism or rhomb further from the fault where shear strains under high temperature conditions were lower weaker fabrics developed under these conditions were modified at higher levels in the crust into crossed girdle patterns this interpretation implies that intense localisation of shear strain along the fault zone within the lower crust must have occurred in order for the high temperature fabrics to become sufficiently intense to be preserved this in turn implies that deep seated localised shear was taking place early during the evolution of the current oblique slip plate boundary fault the results of this study also indicate that the current model that operation of certain slip systems in quartz is mostly a function of temperature is incorrect future work should consider the effects of deformation history total strain and the presence of other mineral phases

a 2300 year paleoearthquake record of the southern alpine fault and fiordland subduction zone new zealand based on stacked turbidites turbidites from three sedimentary basins data and probably the a d 1826 fiordland earthquake and the well dated a d 1717 alpine fault earthquake the recurrence intervals are shorter than recently published recurrence data from the alpine fault on land reflecting mixed fault source earthquake records and potentially increased alpine fault segmentation offshore online material details of the laboratory methods and analytical techniques applied to sedimentrary cores photos of seafloor substrates and fan core oxcal codes and results and sediment transport analysis 1 embed inline graphic 1 gif

trends cycles and nonstationarities in isotope signals of phanerozoic seawater abstract the new set of 87 sr 86 sr 18 o and 13 c experimental data for phanerozoic seawater the bochum ottawa isotope dataset has been tested by wavelet discontinuity and sliding window correlation dimension analyses for cyclicities and nonstationarities in the isotope signal the tests indicate discontinuities in the strontium isotope signal at 500 340 288 210 65 and 28 ma while for the oxygen and carbon isotopes they are at 500 385 290 210 and 65 ma these discontinuities often coincident with major stage boundaries reflect mostly single likely tectonic events that do not affect the structure of the underlying system the two most pronounced nonstationarities in all isotope systematics are at 65 and 210 ma respectively that is at the k t and norian rhaetian transitions wavelet analysis for all three isotope systems yields a long term quasi periodicity at 94 125 ma best developed during the paleozoic with superimposed intermittent 48 57 and 29 35 ma oscillations all likely a reflection of plate reorganizations within the caledonian hercynian and alpine tectonic cycles

frictional strength rate dependence and healing in dfdp 1 borehole samples from the alpine fault new zealand abstract the alpine fault in southern new zealand is a major plate boundary fault zone that according to various lines of evidence may be nearing the end of its seismic cycle and approaching earthquake failure in order to better characterize this fault and obtain a better understanding of its seismic potential two pilot boreholes have been completed as part of a larger drilling project samples representative of the major lithologic subdivisions of the fault zone at shallow 100 m depths were recovered and investigated in laboratory friction experiments we show here that materials from within and very near the principal slip zone psz tend to exhibit velocity strengthening frictional behavior and restrengthen heal rapidly compared to samples of the wall rock recovered near the psz fluid saturation causes the psz to be noticeably weaker than the surrounding cataclasites 0 45 and eliminates the velocity weakening behavior in these cataclasites that is observed in dry tests our results indicate that the psz has the ability to regain its strength in a manner required for repeated rupture but its ability to nucleate a seismic event is limited by its velocity strengthening nature we suggest that seismogenic behavior at depth would require alteration of the psz material to become velocity weakening or that earthquake nucleation occurs either within the wall rock or at the interface between the wall rock and the psz coseismic ruptures which propagate to the surface have been inferred for previous earthquakes on the alpine fault and may be facilitated by the slightly weaker psz material and or high rates of healing in the psz which support fault locking and eventual stress drops

rapid creation and destruction of sedimentary basins on mature strike slip faults an example from the offshore alpine fault new zealand abstract seismic reflection profiles and multibeam bathymetric data are integrated to analyse the structure of the 25 km long strike slip dagg basin associated with the marine section of the alpine fault fiordland new zealand the basin is developing in almost 3000 m water depth at a releasing bend whilst contemporaneous transpression results in inversion of its southern end fiord derived glacio marine sediments flooded the basin during the last glaciation and provide a stratigraphic framework for structural analysis geometrical analysis enables an estimation of 450 1650 m of dextral displacement on the alpine fault at the releasing bend since the development of an unconformity estimated to have formed at between 30 and 110 ka this implies a dextral slip rate ranging from a possible minimum of 4 mm yr to the maximum of 35 mm yr constrained by the pacific australian plate motion rate despite total dextral displacement of 480 km on the alpine fault zone and a growth history spanning 15 20 myr this geomorphically well expressed and structurally complex strike slip basin developed and evolved rapidly during the late pleistocene and thus represents only the latest phase in the evolution of the alpine fault upward splaying structures within the fault zone exhibit a rapid spatial evolution in pleistocene strata which may reflect the interactions between high fault slip rate voluminous sedimentation supply inherited structural complexities in the basement rocks and deeper cover sequence and interactions between adjacent faults the present through going releasing bend at the northern end of the basin may have evolved from a more complex pull apart basin that developed between separate segments of the alpine fault the results from dagg basin illustrate the rates at which structural complexities and sedimentary basins can develop within highly active very mature through going continental wrench faults strike slip basins on the scale of 40 80 km 2 on such faults may be ephemeral features that can be developed and destroyed on a time scale of 10 5 10 6 years

cyclicity and paleoenvironmental dynamics rocknest platform northwest canada the superbly exposed rocknest formation northwest territories canada contains 140 to 160 shallowing upward cycles 1 to 15 m thick that contain distinctive marker beds and can be correlated for 200 km parallel to strike and 120 km perpendicular to strike cycles are grouped according to cycle base lithology which reflects paleogeographic position on the platform shale based cycles of the distal inner shelf pass westward into dolosiltite based cycles then into tufa based cycles of the shoal complex and then into grainstone based cycles of the outer shelf cycles are bounded by erosional surfaces that become less pronounced away from the shoal complex cycles formed in response to small asymmetric rapid rise slow fall eustatic oscillations in sea level 10 m during sea level rise rapid transgression and submergence of tidal flats occurred along the eastern margin of the shoal complex followed by eastward expansion of the shoal complex and slow progradation of tidal flats over lagoonal facies during sea level fall a glacio eustatic model for cyclicity accounts for the data favoring asymmetric eustatic sea level oscillations subaerial exposure and vadose diagenesis of platform during sea level falls arrested progradation and incomplete shoaling of many cycles and cycle periods of 20 000 to 100 000 yr 18 000 to 30 000 yr for rocknest inner shelf slopes ranged from 8 cm km average at high sea level stand to 2 cm km average at low sea level stand tidal flat progradation rates were 7 to 9 km 1 000 yr interaction of inner shelf slope sea level fall rate and sedimentation rate generates complete condensed or expanded cycle profiles one dimensional computer modeling reveals that sedimentation rates of shoal complex facies were 250 cm 1 000 yr that lag times in sedimentation following transgression may have ranged from zero on the shoal complex to 2 000 yr on the distal inner shelf and that subtidal sedimentation rates may have ranged from 80 cm 1 000 yr for the proximal inner shelf to 20 cm 1 000 yr for the distal inner shelf

high resolution seismic images of potentially seismogenic structures beneath the northwest canterbury plains new zealand 1 the transpressional boundary between the australian and pacific plates in the central south island of new zealand comprises the alpine fault and a broad region of distributed strain concentrated in the southern alps but encompassing regions further to the east including the northwest canterbury plains low to moderate levels of seismicity e g 2 m 5 events since 1974 and 2 m 4 0 in 2009 and holocene sediments offset or disrupted along rare exposed active fault segments are evidence for ongoing tectonism in the northwest plains the surface topography of which is remarkably flat and even because the geology underlying the late quaternary alluvial fan deposits that carpet most of the plains is not established the detailed tectonic evolution of this region and the potential for larger earthquakes is only poorly understood to address these issues we have processed and interpreted high resolution 2 5 m subsurface sampling interval seismic data acquired along lines strategically located relative to extensive rock exposures to the north west and southwest and rare exposures to the east geological information provided by these rock exposures offer important constraints on the interpretation of the seismic data the processed seismic reflection sections image a variably thick layer of generally undisturbed younger i e 59 ka quaternary sedimentary sequence that shows evidence of moderate faulting and folding during and subsequent to deposition these quaternary units are in unconformable contact with late cretaceous tertiary interbedded sedimentary and volcanic rocks that are highly faulted folded and tilted the lowest imaged unit is largely reflection free permian triassic basement rocks quaternary age deformation has affected all the rocks underlying the younger alluvial sediments and there is evidence for ongoing deformation eight primary and numerous secondary faults as well as a major anticlinal fold are revealed on the seismic sections folded sedimentary and volcanic units are observed in the hanging walls and footwalls of most faults five of the primary faults represent plausible extensions of mapped faults three of which are active the major anticlinal fold is the probable continuation of known active structure a magnitude 7 1 earthquake occurred on 4 september 2010 near the southeastern edge of our study area this predominantly right lateral strike slip event and numerous aftershocks ten with magnitudes 5 within one week of the main event highlight the primary message of our paper that the generally flat and topographically featureless canterbury plains is underlain by a network of active faults that have the potential to generate significant earthquakes

the structural evolution of active fault and fold systems in central otago new zealand evidence revealed by drainage patterns abstract central otago in new zealand is an area of active continental shortening in which a peneplain surface cut into schist has been deformed by folds which are developed above buried reverse faults we use the drainage patterns in this region to demonstrate various processes in fold and fault growth and interaction that would be difficult to identify by other means in particular we show 1 how simple asymmetric folds can develop into box folds 2 how apparently continuous ridges were formed by the coalescing of quite separate propagating fold and fault segments 3 evidence for the relative ages or relative uplift rates of adjacent structures and 4 evidence for the propagation direction of folds or faults as they grow the few quantitative estimates we obtain for fault propagation rates suggest an increase in length of 10 50 m per earthquake on faults about 20 km long these estimates are very uncertain but are similar in magnitude to an estimate made in nevada for a normal fault of similar size and are also similar to predicted estimates from theoretical growth models they raise the question of whether fault growth earthquake recurrence rates and climate change can interact to produce semi regular discrete features in an active landscape

structure and evolution of the seismically active ostler fault zone new zealand based on interpretations of multiple high resolution seismic reflection profiles abstract to improve our understanding of active faulting away from the main plate boundary on new zealand s south island we have acquired high resolution seismic data across the ostler fault zone twelve 1 2 km long lines perpendicular to fault strike and a 1 6 km long crossline were collected in a region of the mackenzie basin where surface mapping delineates significant complexity in the form of two non overlapping reverse fault strands separated by a transfer zone characterised by multiple smaller strands and increased folding interpretation of the resultant images includes a 45 55 west dipping principal fault and two 25 30 west dipping subsidiary faults one in the hanging wall and one in the footwall of the principal fault the geologically mapped complexities are shown to be caused by shallow variations in the structure of the principal fault which breaks the surface in the north and south but not within the transfer zone where it forms a triangle zone with associated backthrusting and minor faulting these complexities only extend to 300 m depth structures below this level are markedly simpler and much more 2d in nature with the principal fault strand extending over a much longer distance than the individual strands observed at the surface since longer faults are susceptible to larger earthquakes than shorter ones seismic hazard at the study site may be higher than previously thought multiple surface fault strands that give way to a single more major stand at relatively shallow depths may be a common feature of segmented fault systems the deepest layered reflections at our site are consistent with the presence of a late cretaceous tertiary basin underlying the present day mackenzie basin structural restoration of the seismic images back to the base of quaternary fluvioglacial terraces and back to the top of a late pliocene pleistocene fluviolacustrine unit indicate that compression was initiated prior to the late pliocene and that it has continued at a comparatively steady rate of about a millimetre per year to the present day the fluviolacustrine unit has experienced 440 800 m of along fault vertical offset and 870 1080 m of horizontal shortening since that time our study demonstrates that structural reconstructions based on high resolution seismic reflection data provide critical displacement information that can be used to estimate slip rates

stresses and strains in a twisted subduction zone fiordland new zealand summary in the fiordland region of the south island of new zealand the subducted australian plate steepens from south to north becoming near vertical below 75 km depth between doubtful and milford sounds this steepening is accompanied by a sharp change in strike of the subduction zone of about 17 here we investigate stress and strain in this twisted subduction zone using earthquakes recorded during a three month deployment of 24 portable digital seismographs we determine focal mechanisms of 115 earthquakes of ml 2 5 4 5 using both first motion polarity data and amplitudes of seismogram envelopes we also invert for the stress tensor orientation for regions within both the subducted and overlying plates using a method which invokes the coulomb failure criterion and considers all p wave first motions together regardless of whether or not they are sufficient to define single event focal mechanisms focal mechanisms and stress inversions for earthquakes in the overlying plate indicate normal faulting shallower than 16 km and thrust faulting at greater depths this stress and strain regime is related to the 17 change in strike of the subduction zone which leads to an arching up of the subducted plate at the bend such arching is consistent with the exposure of lower crustal granulite facies rocks near the bend earthquakes in the subducted plate show predominantly normal faulting relative to the plate arrival time inversions for 3 d seismic velocity structure indicate that a zone of high vp 8 5 km s 1 in the uppermost mantle of the overlying plate abuts the vertical portion of the subduction zone stresses and strains in the subducted plate are consistent with a model in which the sharp change in strike of the subduction zone is a consequence of the obliquely converging subducted plate having to bend around this zone the steep dip of the subducted plate to the north appears to be a natural consequence of the minimization of membrane stress in the plate arising from the sharp bend along strike this mechanism for steepening the plate is quite different to that of trench retreat usually used to explain steep subduction

tectonics climate and mountain topography 1 by regressing simple independent variables that describe climate and tectonic processes against measures of topography and relief of 69 mountain ranges worldwide we quantify the relative importance of these processes in shaping observed landscapes climate variables include latitude as a surrogate for mean annual temperature and insolation but most importantly for the likelihood of glaciation and mean annual precipitation to quantify tectonics we use shortening rates across each range as a measure of topography we use mean and maximum elevations and relief calculated over different length scales we show that the combination of climate negative correlation and tectonics positive correlation explain substantial fractions 25 but 50 of mean and maximum elevations of mountain ranges but that shortening rates account for smaller portions 25 of the variance in most measures of topography and relief i e with low correlations and large scatter relief is insensitive to mean annual precipitation but does depend on latitude especially for relief calculated over small 1 km length scales which we infer to reflect the importance of glacial erosion larger scale averaged over length scales of 10 km relief however correlates positively with tectonic shortening rate moreover the ratio between small scale and large scale relief as well as the relative relief the relief normalized by the mean elevation of the region varies most strongly with latitude strong positive correlation therefore the location of a mountain range on earth with its corresponding climatic conditions not just tectonic forcing appears to be a key factor in determining its shape and size in any case the combination of tectonics and climate as quantified here can account for approximately half of the variance in these measures of topography the failure of present day shortening rates to account for more than 25 of most measures of relief raises the question is active tectonics overrated in attempts to account for present day relief and exhumation rates of high terrain

significance of brittle deformation in the footwall of the alpine fault new zealand smithy creek fault zone abstract the smithy creek fault represents a rare exposure of a brittle fault zone within australian plate rocks that constitute the footwall of the alpine fault zone in westland new zealand outcrop mapping and paleostress analysis of the smithy creek fault were conducted to characterize deformation and mineralization in the footwall of the nearby alpine fault and the timing of these processes relative to the modern tectonic regime while unfavorably oriented the dextral oblique smithy creek thrust has kinematics compatible with slip in the current stress regime and offsets a basement unconformity beneath holocene glaciofluvial sediments a greater than 100 m wide damage zone and more than 8 m wide extensively fractured fault core are consistent with total displacement on the kilometer scale based on our observations we propose that an asymmetric damage zone containing quartz carbonate chlorite epidote veins is focused in the footwall damage zone asymmetry likely resulted from the fact that the hanging wall was mostly deformed at greater depth than the footwall rather than resulting from material contrasts across the fault plane kinematic inversions on mineralized fractures within the damage zone suggest veins formed in the current stress regime from fluids comparable to those now circulating in the footwall the smithy creek fault zone is therefore a rare exhumed example of the modern footwall hydrothermal system and of a structure actively accommodating footwall deformation near the alpine fault zone two significantly less mature subvertical faults having narrow 20 cm or less damage zones and similar orientations to nearby strike slip segments of the alpine fault crosscut the mineralized zone at smithy creek we envisage that hydrothermal mineralization strengthened the fault core causing it to widen as later slip was partitioned into the now weaker surrounding damage zone with progressive alteration formation of favorably oriented faults became preferable to reactivation of the existing structure

displacement since the pliocene along the southern section of the alpine fault new zealand relocation of a fiordland derived pliocene conglomerate halfway formation that is currently exposed 100 km northeast of its source area indicates that the average displacement rate on the alpine fault new zealand since the pliocene must have been 27 4 mm yr and probably 35 5 mm yr this represents at least three quarters of the currently predicted plate velocity and indicates that a high proportion of plate motion in the region has been partitioned along the alpine fault since the pliocene these results combined with the apparent absence of major displacement on the alpine fault for at least the past 250 yr indicate that a large earthquake may be due the provenance of the halfway formation also allows crude estimates of uplift since the pliocene of 200 800 m for the west coast cascade valley and 1 6 km for western fiordland

deriving fault slip histories to test for secular variation in slip with examples from the kunlun and awatere faults abstract although offset and age data from displaced landforms are essential for identifying earthquake clusters and thus testing whether faults slip at uniform or secularly varying rates it is not clear how the uncertainties in such measurements should be propagated so as to yield a robust fault slip history i e record of fault displacement over time here we develop a monte carlo approach for estimating the distribution of geologically reasonable fault slip histories that fit the offset and age data from a population of dated and displaced landforms the model assumes that the landforms share common faulting histories the offset and age constraints are correct and the fault has not reversed shear sense analysis of the model results yields both a precise average slip rate in the case where a linear fit is applied to the data and a best fit fault slip history in the case where the linear constraint is removed the method can be used to test for secular variation in slip because the uncertainty on this best fit history is quantified by applying the method to previously published morphochronologic data from faulted late quaternary terrace risers along the kunlun fault in china and the awatere fault in new zealand we have assessed the extent to which our modeled average slip rates match previously reported values and the data support previous interpretations of uniform slip rate the kunlun data set yields average slip rates of 8 7 3 6 2 1 mm yr and 5 1 1 6 1 2 mm yr 68 27 confidence for the central and eastern reaches of the fault respectively both of which match previously published slip rates our analysis further indicates that these fault reaches have both slipped uniformly over the latest quaternary in contrast analysis of data from the saxton river site along the awatere fault reveals a mid holocene deceleration in slip rate from 6 2 1 6 1 4 mm yr to 2 8 1 0 0 6 mm yr this result contradicts previous interpretations of uniform slip along the awatere fault the monte carlo method we present here for quantifying fault slip histories using the offset and age data from a population of faulted landforms provides an important tool for distinguishing temporally uniform from secularly varying fault slip

quaternary slip rate and geomorphology of the alpine fault implications for kinematics and seismic hazard in southwest new zealand glacial landforms at 12 localities in 9 river valleys are offset by the southern end of the onshore alpine fault offsets cluster at 435 1240 and 1850 m consistent with evidence for glacial retreat at 18 58 and 79 calendar ka the peak of an offset fluvial aggradation surface is correlated with the last glacial maximum at 22 ka displacement rates derived from features aged 18 22 58 and 79 cal ka are 24 2 2 2 23 2 4 9 21 4 2 6 and 23 5 2 7 mm yr respectively with uncertainties at the 95 confidence level the joint probability weighted mean and arithmetic mean of all observations pooled by rank are 23 1 1 5 23 2 1 4 and 23 1 1 7 mm yr respectively we conclude that the mean surface displacement rate for this section of the alpine fault is 23 1 mm yr with standard error in the range of 0 7 0 9 mm yr the reduction in estimated long term slip rate from 26 6 mm yr to 23 2 mm yr results in an increase in estimated hazard associated with faulting distributed across the rest of the plate boundary model dependent probabilities of alpine fault rupture within the next 50 yr are in the range 14 29 the 36 3 mm yr of total plate motion nuvel 1a is partitioned into 23 2 mm yr of alpine fault dextral strike slip 12 4 mm yr of horizontal motion by clockwise block rotations and oblique dextral reverse faulting up to 80 km southeast of the alpine fault and 5 3 mm yr of heave on reverse faults at the peripheries of the plate boundary

contemporary horizontal velocity and strain rate fields of the pacific australian plate boundary zone through new zealand we have inverted velocity solutions from nine geodetic networks distributed across new zealand to derive present day continuous horizontal velocity and strain rate fields at the earth s surface throughout the country the nine networks contain a total of 362 global positioning system gps stations that have been observed at least twice and at least a year apart between 1991 and 1998 the model velocity field is expanded as bicubic spline interpolation functions defined within a curvilinear grid that covers the country and extends into the assumed rigid australian and pacific plates to west and east the inversion jointly minimizes the magnitudes of fitted strain rates and the misfit to the observed velocity data the spline technique allows high spatial resolution of strain rate variations especially in regions with spatially dense gps data expansion of the model velocity field on the surface of a sphere allows arbitrarily large areas to be studied previously known aspects of new zealand plate boundary deformation are highlighted with improved resolution including back arc extension in the taupo volcanic zone rotation of the hikurangi forearc away from this zone in the north island and a band of high shear strain rate under the southern alps to the southeast of the alpine fault our results reveal several new features including a region of enhanced shear straining apparently associated with strike slip faults in the southern north island and a band of contractional straining subparallel and well east of the alpine fault that is similar to features found in numerical and sandbox models of continental collision

developing sub 5 m lidar dems for forested sections of the alpine and hope faults south island new zealand implications for structural interpretations abstract kilometre wide airborne light detection and ranging lidar surveys were collected along portions of the alpine and hope faults in new zealand to assess the potential for generating sub 5 m bare earth digital elevation models dems from ground return data in areas of dense rainforest bush cover as an aid to mapping these faults the 34 km long franz whataroa lidar survey was flown along the densely vegetated central most portion of the transpressive alpine fault six closely spaced flight lines 200 m apart yielded survey coverage with double overlap of swath collection which was considered necessary due to the low density of ground returns 0 16 m 2 or a point every 6 m2 under mature west coast podocarp broadleaf rainforest this average point spacing 2 5 m allowed for the generation of a robust high quality 3 m bare earth dem the dem confirmed the zigzagged form of the surface trace of the alpine fault in this area originally recognised by norris and cooper 1995 norris and cooper 1997 and highlights that the surface strike variations are more variant than previously mapped the 29 km long hurunui hope lidar survey was flown east of the main divide of the southern alps along the dextral slip hope fault where the terrain is characterised by lower rainfall and more open beech forest flight line spacings of 275 m were used to generate a dem from the ground return data the average ground return values under beech forest were 0 27 m 2 and yielded an estimated cell size suitable for a 2 m dem in both cases the lidar revealed unprecedented views of the surface geomorphology of these active faults lessons learned from our survey methodologies can be employed to plan cost effective high gain airborne surveys to yield bare earth dems underneath vegetated terrain and multi storeyed canopies from densely forested environments across new zealand and worldwide

crustal deformation and stress transfer during a propagating earthquake sequence the 2013 cook strait sequence central new zealand the 2013 cook strait earthquake sequence began on 18 july 2013 with two foreshocks of mw 5 7 and mw 5 8 and culminated in the mw 6 6 cook strait and lake grassmere events on 21 july and 16 august respectively located 50 km south of new zealand s capital wellington the earthquakes generated the most significant ground shaking in the wellington and marlborough regions in recent decades during the first event located under cook strait continuously recording gps instruments across central new zealand recorded up to 5 cm of horizontal displacement modeling suggests that the rupture was 25 km long with up to 90 cm of dextral strike slip the second event located 20 km to the southwest caused displacements of up to 25 cm at gps sites located around the clifford bay area in addition two interferograms from radarsat 2 and terrasar x showed up to 30 cm of line of sight displacement in the vicinity of lake grassmere modeling indicates predominantly dextral strike slip of up to 2 1 m coulomb stress changes induced by the earlier foreshocks suggest that the cook strait event was triggered by the preceding events and that the lake grassmere event was subsequently triggered by the cook strait earthquake

tectonic tremor and deep slow slip on the alpine fault 1 tectonic tremor is characterized by persistent low frequency seismic energy seen at major plate boundaries although predominantly associated with subduction zones tremor also occurs along the deep extension of the strike slip san andreas fault here we present the first observations of tectonic tremor along new zealand s alpine fault a major transform boundary that is late in its earthquake cycle we report tectonic tremor that occurred on the central section of the alpine fault on 12 days between march 2009 and october 2011 tremor hypocenters concentrate in the lower crust at the downdip projection of the alpine fault coincide with a zone of high p wave attenuation low qp and bright seismic reflections occur in the 25 45 km depth range below the seismogenic zone and may define the deep plate boundary structure extending through the lower crust and into the upper mantle we infer this tremor to represent slow slip on the deep extent of the alpine fault in a fluid rich region marked by high attenuation and reflectivity these observations provide the first indication of present day displacement on the lower crustal portion of the australia pacific transform plate boundary

advanced seismic imaging techniques characterize the alpine fault at whataroa new zealand the plate bounding alpine fault in new zealand is a 850 km long transpressive continental fault zone that is late in its earthquake cycle we have acquired and processed reflection seismic data to image the subsurface around the main drill site of the deep fault drilling project dfdp 2 the resulting velocity models and seismic images of the upper 5 km show complex subsurface structures around the alpine fault zone the most prominent feature is a strong reflector at depths of 1 5 2 2 km with an apparent dip of 48 to the southeast below the dfdp 2 borehole which we assume to be the main trace of the alpine fault above the main reflector parallel reflectors suggest the presence of a 600 m wide damage zone additionally subparallel reflectors are imaged that we interpret as secondary branches of the main fault zone conjugate faults imaged by the data show the complexity of the subsurface the derived p wave velocity model reveals a 300 600 m thick sedimentary layer with velocities of 2 3 km s above a schist basement with velocities of 4 5 5 5 km s a low velocity layer can be observed within the basement at 0 8 2 km depth a small scale low velocity anomaly appears at the top of the basement that can be correlated to the fault zone the results provide a reliable basis for a seismic characterization of the dfdp 2 drill site that can be used for further structural and geological investigations of the architecture of the alpine fault in this area

detailed images of the shallow alpine fault zone new zealand determined from narrow azimuth 3d seismic reflection data previous high resolution seismic reflection investigations of active faults have been based on 2d profiles unfortunately 2d data may be contaminated by out of the plane reflections and diffractions that may be difficult to identify and eliminate although full 3d seismic reflection methods allow out of the plane events to be recognized and provide superior resolution to 2d methods they are only rarely applied in environmental and engineering studies because of high costs a narrow azimuth 3d acquisition and processing strategy is introduced to produce a high resolution seismic reflection volume centered on the alpine fault zone new zealand the shallow 3d images reveal late quaternary deformation structures associated with this major transpressional plate boundary fault the relatively inexpensive narrow azimuth 3d acquisition pattern consisting of inline source and receiver lines was easily implemented in the field to provide 2 by 4 m cmp coverage over an approximately 500 by 200 m area the narrow

the alpine fault new zealand near milford sound and to the southwest from 70 km northeast of milford sound 44 14 s 168 55 e to the coast at milford sound 44 53 s 167 83 e the trace of the alpine fault is nowhere more than 1 2 km from the arc with a centre at 48 81 s 173 20 e and a radius of 628 km 5 65 latitude earthquake epicentres indicate that the arc defines the position of the fault just off fiordland s outer coast and then to near the north end of puysegur trench at 46 9 s 165 25 e along the fault vertically to a depth of 10 km the fiordland rocks are 0 6 mg m 3 denser than those to the northwest displaced post glacial topography at and near milford sound shows that the dip of the fault is southeast at 75 5 and that the faulting is pure dextral at a rate of at least 46 5 mm yr

pn anisotropy beneath the south island of new zealand and implications for distributed deformation in continental lithosphere pn travel times from regional earthquakes recorded both by stations on new zealand and by ocean bottom seismographs deployed offshore indicate anisotropy in the uppermost mantle beneath the region the largest anisotropy of 8 2 1 lies beneath the deforming part of the south island to just off its west coast a zone roughly 100 200 km wide the fastest propagation is aligned n60 e 3 essentially parallel to the largely strike slip relative plate motion since 20 ma also n60 e the magnitude of anisotropy decreases abruptly northwest and southeast of this zone and on the southeast side of the island the orientation of fastest propagation is between n32 w and n s the n60 e orientation of fast propagation is consistent with finite strain within the uppermost part of the mantle lithosphere if the measured 850 km of displacement of the pacific plate past the australia plate is spread over a region with a width of 100 200 km the agreement of this orientation of fast propagation with the orientation or relative plate motion suggests the possibility of but does not require some dynamic recrystallization in rock as cold as 500 800 c where peierls creep seems to be the likely deformation mechanism such a strain distribution matches deformation of a thin viscous sheet that obeys a constitutive relationship of the form e n where e is the average strain rate and is the operative deviatoric stress with an average value of n 3 10 presumably the nw se fast propagation in the region southeast of the island results from strain that precedes the cenozoic deformation that has shaped the island

ultrahigh resolution seismic reflection imaging of the alpine fault new zealand 1 high resolution seismic reflection surveys across active fault zones are capable of supplying key structural information required for assessments of seismic hazard and risk we have recorded a 360 m long ultrahigh resolution seismic reflection profile across the alpine fault in new zealand the alpine fault a continental transform that juxtaposes major tectonic plates is capable of generating large m 7 8 damaging earthquakes our seismic profile across a northern section of the fault targets fault zone structures in holocene to late pleistocene sediments and underlying triassic and paleozoic basement units from 3 5 to 150 m depth since ultrashallow seismic data are strongly influenced by near surface heterogeneity and source generated noise an innovative processing sequence and nonstandard processing parameters are required to produce detailed information on the complex alluvial glaciofluvial and glaciolacustrine sediments and shallow to steep dipping fault related features we present high quality images of structures and deformation within the fault zone that extend and complement interpretations based on shallow paleoseismic and ground penetrating radar studies our images demonstrate that the alpine fault dips 75 80 to the southeast through the quaternary sediments and there is evidence that it continues to dip steeply between the shallow basement units we interpret characteristic curved basement surfaces on either side of the alpine fault and deformation in the footwall as consequences of normal drag generated by the reverse slip components of displacement on the fault the fault dip and apparent 35 m vertical offset of the late pleistocene erosional basement surface across the alpine fault yield a provisional dip slip rate of 2 0 0 6 mm yr the more significant dextral slip rate cannot be determined from our seismic profile

orbital forcing of mid latitude southern hemisphere glaciation since 100 ka inferred from cosmogenic nuclide ages of moraine boulders from the cascade plateau southwest new zealand cosmogenic nuclide be 10 exposure dating of moraine boulders in the cascade valley southwest new zealand reveals three phases of glaciation with similar maximum magnitude since 100 ka in this area 8 10 lateral moraines were deposited during the last glacial maximum lgm at 22 19 ka and 15 lateral moraines and three end moraines were deposited during recession after the lgm also three exposure ages of 29 33 ka from pre lgm deposits may indicate increased weathering and erosion at the onset of the lgm in new zealand as has been suggested by other studies an exposure age of 57 8 2 7 ka from one of the highest moraines combined with previous studies of cave speleothems glacial features offset by the alpine fault the vostok dust record and sediment cores supports the inference that a significant glacial phase culminated at 66 58 ka a cluster of five exposure ages from older moraines reveals a glacial phase with at least three advance retreat cycles at 79 0 3 9 ka correlation between the ages of glacial periods and the timing of southern hemisphere summer insolation minima suggests that orbital forcing has played a first order role in regulating glacial extent in new zealand

the obliquely convergent plate boundary in the south island of new zealand implications for ancient collision zones abstract the alpine fault of new zealand forms the western boundary of a zone of distributed deformation formed by the oblique convergence of continental crust belonging to the pacific and australian plates structural and geodetic data from the alpine fault show that a large proportion of the total plate displacement is accommodated by rapid oblique slip on the fault the remaining displacement is distributed over a 200 km wide zone to the east the collision may be modelled as a two sided deforming orogen with the partitioning of deformation being controlled by erosional differences between the narrow high strain inboard and broad low strain outboard sides in ancient collision zones little evidence may remain of the nature and amount of displacement on the inboard side partitioning of deformation among pre existing structures complicates interpretation of the outboard zone radiometric ages may post date collision by several tens of millions of years and indicate slow isostatic uplift and unroofing collision ages if preserved may be recognized by high uplift rates calculated from muscovite biotite pairs

deriving a long paleoseismic record from a shallow water holocene basin next to the alpine fault new zealand a sedimentary sequence that was highly sensitive to fault rupture driven changes in water level and sediment supply has been used to extract a continuous record of 22 large earthquakes on the alpine fault the fastest slipping fault in new zealand at hokuri creek in south westland an 18 m thickness of holocene sediments accumulated against the alpine fault scarp from ca a d 800 to 6000 b c we used geomorphological mapping sedimentology and paleoenvironmental reconstruction to investigate the relationship between these sediments and alpine fault rupture we found that repeated fault rupture is the most convincing mechanism for explaining all the features of the alternating peat and silt sedimentary sequence climate has contributed to sedimentation but is unlikely to be the driver of these cyclical changes in sediment type and paleoenvironment other nontectonic causes for the sedimentary alternations do not produce the incremental increase in basin accommodation space necessary to maintain the shallow water environment for 6800 yr our detailed documentation of this near fault sedimentary basin sequence highlights the advantages of extracting paleoearthquake records from such sites the continuity of sedimentation abundance of dateable material and pristine preservation of older events

evidence for a rock avalanche origin for the hillocks moraine otago new zealand abstract a landform in otago new zealand previously interpreted as a glacial deposit has been investigated described and reinterpreted as a rock avalanche deposit the hillocks is a conspicuous cluster of small conical hills on the dart river floodplain the landform is protected under a local bylaw because of its identification as an outstanding example of a glacial kame deposit however the geological and geomorphological setting and the deposit morphology sedimentology and lithology suggest that it was formed by a large c 22 5 10 6 m 3 rock avalanche subsequent to glacial retreat and that the deposit temporarily dammed the dart river valley relative age dating evidence suggests that it is at least several hundred years old but younger than ca 7500 b p this work highlights the problem of paleoclimatic reconstructions using moraines as indicators of regional climate events despite similarities in form and in some cases sedimentology by applying an understanding of landslide initiation runout and depositional process we demonstrate that it is possible to distinguish the deposits produced by landslides from those produced by glacial deposition

late cenozoic exhumation model of new zealand impacts from tectonics and climate abstract late cenozoic convergence between the australian and pacific plates has led to extensive crustal deformation and exhumation in new zealand over the past five decades the convergence associated exhumation history of the palaeozoic mesozoic new zealand basement has been studied using various thermochronometric techniques here we compile 992 published ages and invert them to estimate the temporal and spatial variation in exhumation rates since 25 ma which we then interpret with a plate tectonic reconstruction model the results reveal widespread increases in the exhumation rates at 6 4 ma a time correlated with accelerations in the relative plate motion the absolute increases in exhumation rates are however not uniformly distributed over new zealand since the plio pleistocene the inferred models suggest variable response of exhumation to global cooling in the non glaciated eastern north island the hikurangi subduction margin the million year average exhumation rates have remained relatively low 5 km myr have been observed in the collision zone of the central southern alps of south island where both tectonic deformation and precipitation rates are highest in fiordland the puysegur subduction margin despite the weak crustal deformation the exhumation rates have been high 0 5 3 km myr which we suggest is due to intensified glacial erosion our findings highlight the determining role of tectonics in setting up the regional exhumation pattern but both strong tectonic deformation and efficient erosion are required to maintain rapid exhumation rates the influence of climate on mountain erosion can only be distinguished in regions under slow to mediate exhumation

potentially active faults in the rapidly eroding landscape adjacent to the alpine fault central southern alps new zealand 1 potentially active faults are exposed in the steep glaciated topography of the central southern alps new zealand immediately adjacent to the alpine fault plate boundary four major faults exposed along the flanks of three of the highest mountain ranges strike 10 23 km potentially 40 km nne oblique to the alpine fault dipping 57 12 nw in the opposite direction youngest discernable motions were reverse dip slip accommodating both margin perpendicular shortening and dextral margin parallel components of plate motion kinematic analysis yields a compression axis 295 10 9 trend or plunge equivalent to the contemporary shortening determined from seismological and geodetic studies suggesting the faults may be active although definitive evidence for recent movement or single event displacements is lacking there are 106 other potentially active faults mapped in central southern alps with strike lengths 4 73 km earthquake parameters were assigned from fault trace lengths and historical earthquake statistics indicating potential for mw 5 5 7 4 earthquakes at recurrence intervals of 1000 10 000 years such long recurrence intervals are consistent with the faults having little surface expression with rapid erosion of these seismically agitated mountains erasing any evidence of surface rupture during periods between earthquakes the central southern alps faults exemplify the difficulty in fully deciphering long term e g holocene or quaternary records of seismicity in tectonically active regions with rapidly evolving landscapes although there may be little evidence of surface ruptures remaining in the landscape the faults are still an important potential source of earthquakes and seismic hazard

crustal deformation during 1994 1998 due to oblique continental collision in the central southern alps new zealand and implications for seismic potential of the alpine fault the positions of 115 ground marks in a 150 100 km area of oblique continental collision in the central southern alps new zealand have been measured by global positioning system gps two to four times between 1994 and 1998 contemporary velocity and strain rate fields derived from these observations are largely invariant along the northeasterly strike of the mountains and alpine fault across strike more than 60 of the strain occurs within a band from 5 km nw to 20 km se of the alpine fault but significant strain continues at least a further 60 km se to near the edge of the southern alps foothills projections of the fault parallel and fault normal components of velocity onto an alpine faultnormal profile show that about 85 of the nuvel 1a model relative plate motion is observed within the gps network the surface displacements in the high strain rate region are well fit by a model in which stable slip or shearing is occurring at 50 70 of the relative plate rate in a region deeper than about 5 8 km on the down dip extension of the se dipping alpine fault material shallower than this is behaving elastically and thus storing elastic strain in the region of the alpine fault the longer wavelength displacements can be modeled either as distributed deformation beneath the southern alps or by localization of elastic strain around the upper end of a discrete nw dipping fault or shear zone that is slipping stably below about 30 km depth and would outcrop near the se boundary of the mountains if extrapolated to the surface strain determined from a small scale survey network crossing the alpine fault indicates no significant near surface aseismic fault slip on the central alpine fault over the past 25 years our results are consistent with independent geological evidence that the central section of the alpine fault is capable of producing large to great earthquakes

low frequency earthquakes reveal punctuated slow slip on the deep extent of the alpine fault new zealand we present the first evidence of low frequency earthquakes lfes associated with the deep extension of the transpressional alpine fault beneath the central southern alps of new zealand our database comprises a temporally continuous 36 month long catalog of 8760 lfes within 14 families to generate this catalog we first identify 14 primary template lfes within known periods of seismic tremor and use these templates to detect similar events in an iterative stacking and cross correlation routine the hypocentres of 12 of the 14 lfe families lie within 10 km of the inferred location of the alpine fault at depths of approximately 20 30 km in a zone of high p wave attenuation low p wave speeds and high seismic reflectivity the lfe catalog consists of persistent discrete events punctuated by swarm like bursts of activity associated with previously and newly identified tremor periods the magnitudes of the lfes range between ml 0 8 and ml 1 8 with an average of ml 0 5 we find that the frequency magnitude distribution of the lfe catalog both as a whole and within individual families is not consistent with a power law but that individual families frequency amplitude distributions approximate an exponential relationship suggestive of a characteristic length scale of failure we interpret this lfe activity to represent quasi continuous slip on the deep extent of the alpine fault with lfes highlighting asperities within an otherwise steadily creeping region of the fault

relationships between kinematic indicators and strain during syn deformational exhumation of an oblique slip transpressive plate boundary shear zone the alpine fault new zealand abstract in order to assess how different elements of plate boundary scale shear zone tectonite fabrics reflect the boundary kinematics and strain history we have examined a range of such structures within the active alpine fault mylonite zone new zealand in this oblique slip zone we find that quartz cpo fabric symmetry and individual mica grain lineations reflect incremental stretches but develop stable orientations parallel to the finite stretching direction s 1 this s 1 trends oblique to the plate motion vector because the shear zone experiences some extrusion toward the free surface conversely asymmetric structures such as shear bands and mica fish reflect simple shear dominated deformation late in the shear zone history parallel to the imposed relative plate motion vector finally linear fabrics are a poor record of the mylonitic deformation in this zone because 1 they are dominantly inherited and have been only partially re oriented during mylonitisation and 2 macroscopically they become less visible at higher strains due to fabric homogenisation generally these results indicate that particularly in heterogeneous polyphase shear zones a full understanding of the movement history can only be obtained by considering kinematic information from as many different sources as possible

continental transforms a view from the alpine fault abstract continental transform faults are dominantly highly localized strike slip shear zones hundreds of kilometers long that accumulate tens to hundreds of kilometers of displacement from work on the alpine fault we pose the questions what is the deep structure of a continental transform and how does the displacement become localized we review research on the alpine fault and propose a model in which the fault partitions at depth into a steep zone extending into the mantle with largely fault parallel motion and a flat ductile decollement in the lower crust the fault localizes around two thirds of the plate motion within a 100 km wide zone of distributed deformation a review of other active continental fault systems suggests that variation between them may reflect their tectonic origins the nature of the crust in which they develop the presence of a significant oblique component of motion and the displacement rate all however have evidence for the development of a single principal fault zone that carries 50 of the total displacement and extends as a localized zone of shear into the upper mantle we review mechanisms of strain weakening and suggest that localization of a principal fault may be initiated in the seismogenic crust and through a series of positive feedbacks eventually extend through the lower crust into the upper mantle

triple junction kinematics accounts for the 2016 mw 7 8 kaikoura earthquake rupture complexity the 2016 moment magnitude mw 7 8 kaikoura earthquake generated the most complex surface ruptures ever observed although likely linked with kinematic changes in central new zealand the driving mechanisms of such complexity remain unclear here we propose an interpretation accounting for the most puzzling aspects of the 2016 rupture we examine the partitioning of plate motion and coseismic slip during the 2016 event in and around kaikoura and the large scale fault kinematics volcanism seismicity and slab geometry in the broader tonga kermadec region we find that the plate motion partitioning near kaikoura is comparable to the coseismic partitioning between strike slip motion on the kekerengu fault and subperpendicular thrusting along the offshore west hikurangi megathrust together with measured slip rates and paleoseismological results along the hope kekerengu and wairarapa faults this observation suggests that the west hikurangi thrust and kekerengu faults bound the southernmost tip of the tonga kermadec sliver plate the narrow region around kaikoura where the 3 fastest slipping faults of new zealand meet thus hosts a fault fault trench fft triple junction which accounts for the particularly convoluted 2016 coseismic deformation that triple junction appears to have migrated southward since the birth of the sliver plate around 5 to 7 million years ago this likely drove southward stepping of strike slip shear within the marlborough fault system and propagation of volcanism in the north island hence on a multimillennial time scale the apparently distributed faulting across southern new zealand may reflect classic plate tectonic triple junction migration rather than diffuse deformation of the continental lithosphere

plate boundary deformation in south island new zealand is related to inherited lithospheric structure abstract the alpine fault is the main active structure in the oblique continental collision zone of south island new zealand it is continuous at the surface for 800 km and accommodates 70 of current plate motion a 460 km offset of basement rocks suggests it has accommodated 50 of plate displacement since 45 ma geophysical geological and contemporary kinematic data are successfully modeled by slip on a narrow alpine fault zone extending into the lower crust the data are consistent with plate boundary deformation occurring on either northwest or southeast dipping shear zones in the upper mantle or with widely distributed strain in the upper mantle we propose that the position of the alpine fault and any associated lithospheric discontinuity is controlled by an eocene passive margin that separated palaeozoic continental lithosphere of the challenger plateau from much younger oceanic lithosphere strike slip motion since 25 ma has translated the passive margin into the continental collision zone resulting in subduction of oceanic lithosphere beneath south island and progressive localisation of shear strain near the alpine fault the eocene rift boundary formed by exploiting cretaceous oceanic transform faults and an older discontinuity within the new zealand continent we propose that a precursor to the alpine fault could be as old as palaeozoic inherited structure has clearly controlled the first order deformation pattern through new zealand since at least 100 ma and demonstrates that ancient faults can play an important role in determining lithospheric scale patterns of deformation at continental plate boundaries

late quaternary slip rates and slip partitioning on the alpine fault new zealand abstract published geological data on late quaternary offsets on the alpine fault new zealand have been assembled into a common format and analysed with respect to uncertainties uncertainties arise mainly from measurement of offset features relating apparent offsets to actual fault slip and dating the offset features despite the considerable uncertainties the data form a coherent set consistent with a relatively constant rate of strike slip of 27 5 mm year between milford sound and hokitika this rate represents 70 75 of the fault parallel interplate motion north of the confluence with the hope fault the rate drops substantially dip slip rates on the other hand show considerable variation along strike rising to a maximum of more than 10 mm year in the central section and decreasing to zero at the southern end partitioning of c 25 of the interplate slip on to structures east of the alpine fault occurs in the central section consistent with predictions from critical wedge models the partitioning of all the fault normal component of displacement on to other structures in the south may be related in part to a doubling in width of the deforming wedge to the east most probably however the fault normal displacement is mainly accommodated by underthrusting of the australian plate offshore due to a change in the nature of the crust from continental to oceanic

thermochronological evidence of a low angle mid crustal detachment plane beneath the central south island new zealand oblique continental convergence and uplift in the southern alps new zealand is largely accommodated by dextral transpression on the alpine fault however towards the south of the orogen the alpine fault becomes increasingly strike slip despite evidence for high exhumation rates in the pacific plate here we present 41 new apatite and zircon fission track ages to investigate the role of the southern alpine fault in pacific plate exhumation since the miocene through development of a new maximum likelihood fission track age calculation method to overcome extremely low 0 1 ppm 238u concentrations in apatites we estimate the width of the fully reset apatite zone ages 5 ma southeast of the southern alpine fault which has been previously overestimated instead this zone is 30 km wide rather than 60 km we combine our exhumation profile with thermo kinematic modelling to impose constraints on fault kinematics and deformation history the surface cooling age pattern can be well reproduced by exhumation along a listric reverse fault which shallows to a low angle 6 10 mid crustal detachment beneath the southern lakes this structure is comparable to the listric central alpine fault geometry previously constrained by thermo kinematics models to the north of our study region we propose this detachment plane is continuous beneath a large region of central south island and may be acting to accommodate underthrusting of australian crust beneath the pacific plate this article is protected by copyright all rights reserved

visualization of active faults using geometric attributes of 3d gpr data an example from the alpine fault zone new zealand three dimensional ground penetrating radar gpr data are routinely acquired for diverse geologic hydrogeologic archeological and civil engineering purposes interpretations of these dataareinvariablybasedonsubjectiveanalysesofreflectionpatterns such analyses are heavily dependent on interpreter expertiseandexperience usingdataacquiredacrossgravelunitsoverlyingthealpinefaultzoneinnewzealand wedemonstratethe utilityofvariousgeometricattributesinreducingthesubjectivity of3dgprdataanalysis weuseacoherence basedtechniqueto compute the coherency azimuth and dip attributes and a graylevel co occurrence matrixglcmmethod to compute the texture basedenergy entropy homogeneity andcontrastattributes a selection of the gpr attribute volumes allows us to highlight key aspects of the fault zone and observe important features not apparent in the standard images this selection also provides information that improves our understanding of gravel deposition andtectonicstructuresatthestudysite anewdepositional structuralmodellargelybasedontheresultsofouranalysisofgprattributes includes four distinct gravel units deposited in three phases and a well defined fault trace this fault trace coincides with a zone of stratal disruption and shearing bound on one side by upward tilted to synclinally folded stratified gravels and on the other side by moderately dipping stratified alluvial fan gravelsthatcouldhavebeenaffectedbylateralfaultdrag whenused in tandem the coherence and texture based attribute volumes can significantly improve the efficiency and quality of 3d gpr interpretation especially for complex data collected across activefaultzones

a 6000 year long paleoseismologic record of earthquakes along the xorkoli section of the altyn tagh fault china abstract long records of paleoearthquakes are essential for understanding earthquake recurrence behavior of active faults and for evaluating regional seismic hazard however paleoseismic data on the altyn tagh fault atf one of the longest strike slip fault in asia are scarce we document a long paleoseismic record along the xorkoli section of the central atf eight and probably nine earthquakes are identified based on event evidence in the form of open fissures folds unconformities and upward fault terminations with modeled mean 95 confidence ages of a d 1598 1491 1741 yr event a a d 797 676 926 yr b b c 668 732 589 yr c b c 956 1206 715 yr d b c 1301 1369 1235 yr e b c 2105 2233 1987 yr f probable b c 2663 2731 2601 yr g b c 2818 2878 2742 yr h b c 3396 3522 3205 yr i the mean recurrence interval is 620 410 yr with a coefficient of variation cov of 0 67 indicating that earthquake recurrence is weakly periodic with individual intervals ranging from as short as 150 yr to as long as 1460 yr a global compilation of 35 strike slip paleoseismic sites yields a similar average cov of 0 69 synthesis of paleoseismic sites from the central atf indicates that not all earthquakes ruptured to the eastern end of the xorkoli section within the aksay restraining bend given that the 420 yr elapsed time since the most recent event well within a cov of mean interval a large surface rupturing earthquake could occur at any time along the central atf

a 2000 yr paleoearthquake record along the conway segment of the hope fault implications for patterns of earthquake occurrence in northern south island and southern north island new zealand paleoseismic trenches excavated at two sites reveal ages of late holocene earthquakes along the conway segment of the hope fault the fastest slipping fault within the marlborough fault system in northern south island new zealand at the green burn east gbe site a fault perpendicular trench exposed gravel colluvial wedges fissure fills and upward fault terminations associated with five paleo surface ruptures radiocarbon age constraints indicate that these five earthquakes occurred after 36 b c e with the four most recent surface ruptures occurring during a relatively brief period 550 yr between about 1290 c e and the beginning of the historical earthquake record about 1840 c e additional trenches at the green burn west gbw site 1 4 km west of gbe reveal four likely coseismically generated landslides that occurred at approximately the same times as the four most recent gbe paleoearthquakes independently overlapping with age ranges of events gb1 gb2 and gb3 from gbe combining age constraints from both trench sites indicates that the most recent event gb1 occurred between 1731 and 1840 c e the penultimate event gb2 occurred between 1657 and 1797 c e gb3 occurred between 1495 and 1611 c e gb4 occurred between 1290 and 1420 c e and gb5 occurred between 36 b c e and 1275 c e these new data facilitate comparisons with similar paleoearthquake records from other faults within the alpine hope jordan kekerengu needles wairarapa al hp jkn wr fault system of throughgoing fast slip rate 10 mm yr reverse dextral faults that accommodate a majority of pacific australia relative plate boundary motion these comparisons indicate that combinations of the faults of the al hp jkn wr system may commonly rupture within relatively brief 100 year long sequences but that full wall to wall rupture sequences involving all faults in the system are rare over the span of our paleoearthquake data rather the data suggest that the al hp jkn wr system may commonly rupture in subsequences that do not involve the entire system and potentially at least sometimes in isolated events

geomorphology denudation rates and stream channel profiles reveal patterns of mountain building adjacent to the san andreas fault in northern california usa relative horizontal motion along strike slip faults can build mountains when motion is oblique to the trend of the strike slip boundary the resulting contraction and uplift pose off fault seismic hazards which are often difficult to detect because of the poor vertical resolution of satellite geodesy and difficulty of locating offset datable landforms in active mountain ranges sparse geomorphic markers topographic analyses and measurement of denudation allow us to map spatiotemporal patterns of uplift along the northern san andreas fault between jenner and mendocino california emergent marine terraces found southwest of the san andreas fault record late pleistocene uplift rates between 0 20 and 0 45 mm yr 1 along much of the coast however on the northeast side of the san andreas fault a zone of rapid uplift 0 6 1 0 mm yr 1 exists adjacent to the san andreas fault but rates decay northeastward as the coast becomes more distant from the san andreas fault a newly dated 4 5 ma shallow marine deposit located at 500 m above sea level masl adjacent to the san andreas fault is warped down to just 150 masl 15 km northeast of the san andreas fault and it is exposed at just 60 110 masl to the west of the fault landscape denudation rates calculated from abundance of cosmogenic radionuclides in fluvial sediment northeast of and adjacent to the san andreas fault are 0 16 0 29 mm yr 1 but they are only 0 03 0 07 mm yr 1 west of the fault basin average channel steepness and the denudation rates can be used to infer the erosive properties of the underlying bedrock calibrated erosion rates can then be estimated across the entire landscape using the spatial distribution of channel steepness with these erosive properties the lower elevation areas of this landscape that show high channel steepness and hence calibrated erosion rate are distinct from higher elevation areas with systematically lower channel steepness and denudation rates these two areas do not appear to be coincident with lithologic contacts assuming that changes in rock uplift rates are manifest in channel steepness values as an upstream propagating kinematic wave that separates high and low channel steepness values the distance that this transition has migrated vertically provides an estimate of the timing of rock uplift rate increase this analysis suggests that rock uplift rates along the coast changed from 0 3 to 0 75 mm yr 1 between 450 and 350 ka this zone of recent relatively rapid crustal deformation along the plate boundary may be a result of the impingement of relatively strong crust underlying the gualala block into the thinner weaker oceanic crust left at the western margin of the north american plate by the westward migration of the subduction zone prior to establishment of the current transform plate boundary the warped pliocene marine deposits and the presence of a topographic ridge support the patterns indicated by the channel steepness analyses and further indicate that the zone of rapid uplift may herald elevated off fault seismic hazard if this uplift is created by periodic stick slip motion on contractional structures

combining strong motion insar and gps data to refine the fault geometry and source kinematics of the 2011 mw 6 2 christchurch earthquake new zealand the space time distribution of coseismic slip of the 2011 february 21 mw 6 2 christchurch earthquake new zealand is explored differently from all previous studies through a joint inversion of geodetic and strong motion data the geodetic data consist of both global position system gps from campaign and continuous stations and synthetic aperture radar sar interferograms from two ascending satellite tracks the strong motion data consist of 10 stations located in the canterbury plains these stations offering a good azimuthal coverage of the event the kinematic rupture model for the analysed event was obtained using the parametrization and non linear inversion scheme proposed by delouis et al in particular for any subfault we explore for the local source time function local slip history slip direction and rupture onset time the geometry of the fault plane used for the kinematic inversion is inferred from the analysis of the geodetic data to validate our results we perform a resolution study for both the single and complete data sets and an errors analysis of our final kinematic rupture model considering the complexity highlighted by superficial deformation data we adopted a fault model consisting of two partially overlapping segments with dimensions 15 11 and 7 7 km2 corresponding to different faulting types this two fault model instead of single fault model is needed to reconstruct the complex shape of the superficial deformation data the total seismic moment resulting from the joint inversion is 3 0 1025 dyne cm mw 6 2 with an average rupture velocity of 2 0 km s 1

new on fault evidence for a great earthquake in a d 1717 central alpine fault new zealand the dextral reverse alpine fault is the major onshore plate boundary structure between the australian and pacific plates in new zealand no previous study of the central portion of the 200 km long central segment has provided on fault evidence for the most recent event mre using lidar light detection and ranging data coupled with field mapping we recognized the main trace of the alpine fault north of gaunt creek south island as a north striking fault scarp we enhanced a natural exposure that revealed evidence for repeated late holocene thrust fault movement the north northwest striking fault zone is characterized by a distinct 5 50 cm thick clay fault gouge layer juxtaposing hanging wall bedrock mylonites and cataclasites over unconsolidated late holocene footwall colluvium the bedrock is cut by a strath terrace and overlain by mid holocene ca 5400 calibrated 14 c yr b p alluvial terrace which has been faulted repeatedly and is conformably overlain by undeformed late holocene colluvium and alluvium an unfaulted peat at the base of the scarp is buried by post mre alluvium and yields a calibrated 2 radiocarbon age of a d 1710 1930 which dates the mre as post 1709 our data are consistent with sparse on fault data and validate earlier off fault records that suggest an a d 1717 mre the 1717 event had a moment magnitude of m w 8 1 0 1 based on the 380 km long surface rupture because the fault has not ruptured for 300 yr it is likely approaching the end of its seismic cycle and poses a significant seismic hazard to new zealand

microstructures imply cataclasis and authigenic mineral formation control geomechanical properties of new zealand s alpine fault abstract the alpine fault is capable of generating large mw 8 earthquakes and is the main geohazard on south island nz and late in its 250 291 year seismic cycle to minimize its hazard potential it is indispensable to identify and understand the processes influencing the geomechanical behavior and strength evolution of the fault high resolution microstructural mineralogical and geochemical analyses of the alpine fault s core demonstrate wall rock fragmentation assisted by mineral dissolution and cementation resulting in the formation of a fine grained principal slip zone psz a complex network of anastomosing and mutually cross cutting calcite veins implies that faulting occurred during episodes of dilation slip and sealing fluid assisted dilatancy leads to a significant volume increase accommodated by vein formation in the fault core undeformed euhedral chlorite crystals and calcite veins that have cut footwall gravels demonstrate that these processes occurred very close to the earth s surface microstructural evidence indicates that cataclastic processes dominate the deformation and we suggest that powder lubrication and grain rolling particularly influenced by abundant nanoparticles play a key role in the fault core s velocity weakening behavior rather than frictional sliding this is further supported by the absence of smectite which is reasonable given recently measured geothermal gradients of more than 120 c km 1 and the impermeable nature of the psz which both limit the growth of this phase and restrict its stability to shallow depths our observations demonstrate that high temperature fluids can influence authigenic mineral formation and thus control the fault s geomechanical behavior and the cyclic evolution of its strength

microseismicity in southern south island new zealand implications for the mechanism of crustal deformation adjacent to a major continental transform shallow 25km diffuse crustal seismicity occurs in a zone up to 150km wide adjacent to the southern alpine fault new zealand as a consequence of distributed shear and thickening in the obliquely convergent australian pacific plate boundary zone it has recently been proposed that continental convergence here is accommodated by oblique slip on a low angle detachment that underlies the region and as such forms a previously unrecognized mode of oblique continental convergence we test this model using microseismicity presenting a new 15 month high resolution microearthquake catalog for the southern lakes and northern fiordland regions adjacent to the alpine fault we determine the spatial distribution moment release and style of microearthquakes and show seismicity in the continental lithosphere is predominantly shallower than 20km in a zone up to 150km wide but less frequent deeper microseismicity extending into the mantle at depths of up to 100km is also observed the geometry of the subducted oceanic australian plate is well imaged with a well defined benioff zone to depths of 150km in detail the depth of continental microseismicity shows considerable variation with no clear link with major active surface faults but rather represents diffuse cracking in response to the ambient stress release the moment release rate is 0 1 of that required to accommodate relative plate convergence and the azimuth of the principal horizontal axis of contraction accommodated by microseismicity is 120 15 20 clockwise of the horizontal axis of contractional strain rate observed geodetically thus short term microseismicity independent of knowledge of intermittent large magnitude earthquakes may not be a good guide to the rate and orientation of long term deformation but is an indicator of the instantaneous state of stress and potential distribution of finite deformation thus we show that both the horizontal and vertical spatial distribution of microseismicity can be explained in terms of a low angle detachment model

near surface clay authigenesis in exhumed fault rock of the alpine fault zone new zealand o h ar isotopic xrd and chemical analysis of illite and chlorite abstract exhumed fault rock of the central alpine fault zone south island new zealand shows extensive clay mineralization and it has been the focus of recent research that aims to describe the evolution and frictional behavior of the fault using quantitative x ray powder diffraction 40 ar 39 ar geochronology hydrogen isotope d geochemistry and electron microbeam analysis we constrain the thermal and fluid conditions of deformation that produced two predominant clay phases ubiquitous to the exposed fault damage zone illite and chlorite illite polytype analysis indicates that most end member illite and chlorite material formed in equilibrium with meteoric fluid d 55 to 75 but two locations preserve a metamorphic origin of chlorite d 36 to 45 chlorite chemical geothermometry constrains crystal growth to t 210 296 c isotopic analysis also constrains illite growth to t

seismic p wave velocity model from 3 d surface and borehole seismic data at the alpine fault dfdp 2 drill site whataroa new zealand

balancing the plate motion budget in the south island new zealand using gps geological and seismological data summary the landmass of new zealand exists as a consequence of transpressional collision between the australian and pacific plates providing an excellent opportunity to quantify the kinematics of deformation at this type of tectonic boundary we interpret gps geological and seismological data describing the active deformation in the south island new zealand by using an elastic rotating block approach that automatically balances the pacific australia relative plate motion budget the data in new zealand are fit to within uncertainty when inverted simultaneously for angular velocities of rotating tectonic blocks and the degree of coupling on faults bounding the blocks we find that most of the plate motion budget has been accounted for in previous geological studies although we suggest that the porter s pass amberley fault zone in north canterbury and a zone of faults in the foothills of the southern alps may have slip rates about twice that of the geological estimates up to 5 mm yr 1 of active deformation on faults distributed within the southern alps 100 km to the east of the alpine fault is possible the role of tectonic block rotations in partitioning plate boundary deformation is less pronounced in the south island compared to the north island vertical axis rotation rates of tectonic blocks in the south island are similar to that of the pacific plate suggesting that edge forces dominate the block kinematics there the southward migrating chatham rise exerts a major influence on the evolution of the new zealand plate boundary we discuss a model for the development of the marlborough fault system and hikurangi subduction zone in the context of this migration

national seismic hazard model for new zealand 2010 update a team of earthquake geologists seismologists and engineering seis mologists has collectively produced an update of the national probabilistic seismic hazard 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 hazard basis 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 with over 200 new onshore and offshore fault sources and utilizes new new zealand based and 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 the seismicity parameters probabilistic seismic hazard maps produced from the new nshm show a similar pattern of hazard to the earlier model at the national scale but there are some significant reductions and increases in hazard at the regional scale the national scale differences between the new and earlier nshm appear less than those seen between much earlier national models indicating that some degree of consis tency has been achieved in the national scale pattern of hazard estimates at least for return periods of 475 years and greater online material table of fault source parameters for the 2010 national seismic hazard model

how do lineations reflect the strain history of transpressive shear zones the example of the active alpine fault zone new zealand abstract lineations within mylonites exhumed in the hanging wall of new zealand s active alpine fault zone have a complicated relationship to contemporary plate kinematics the shear zone is triclinic and macroscopic object lineations are not usually parallel to the simple shear direction despite high total simple shear strains 150 this is mostly because the lineations are inherited from pre mylonitic fabrics and have not been rotated into parallelism with the mylonitic stretching direction which pitches c 44 in the fault plane furthermore some lineations have been variably rotated depending on whether they are present in shear bands or microlithons which accommodated bulk strains with different vorticities total strains required to obtain parallelism between the finite maximum principal stretching direction calculated from transpression models and these mylonitic lineations are pure shear stretch s 1 3 5 simple shear 11 7

the last glacial interglacial transition lgit in south westland new zealand paleoecological insight into mid latitude southern hemisphere climate change abstract high resolution pollen stratigraphy from three peat cores located within 20 km of lateglacial moraines in south westland new zealand provide detailed records of climate change during the last glacial interglacial transition lgit the pollen record shows the replacement of grassland by shrubland prior to ca 15 300 14 c yr bp 18 300 cal yr bp followed by the progressive development of broadleaf shrubland and scattered forest prior to ca 12 000 14 c yr bp 14 400 cal yr bp local vegetation changes around the time of the younger dryas chronozone 11 10 ka 14 c bp are evident but are not necessarily a result of regional climate cooling vegetation changes between ca 12 000 and 10 000 14 c yr bp 14 400 and 11 400 cal yr bp indicate a period of increased precipitation tall podocarp forest similar to that of the contemporary forest was well established by ca 10 000 14 c yr bp 11 400 cal yr bp a period of increased westerly circulation over southern new zealand is considered to be the most likely mechanism for causing the increased precipitation between ca 12 000 and 10 000 14 c yr bp 14 300 and 11 400 cal yr bp increased precipitation would also provide a mechanism for initiating lgit ice advance in the area data from these records show some support for global climate change models that propose inter hemispheric linkage but may be more supportive of a climate change model that incorporates an increased westerly circulation over southern new zealand during the lgit