uncertainties in the relative positions of the australia antarctica lord howe and pacific plates since the late cretaceous we determined parameters that describe finite rotations and their uncertainty regions for relative plate motion at the spreading centers between the pacific and antarctica plates between australia and antarctica and between the lord howe rise and australia we combined these to yield a range of possible finite rotations describing the relative positions of the pacific australia antarctica and lord howe plates since the late cretaceous if the pacific australia plate boundary has had its present trend since anomaly 18 time reconstructions show 330 110 km of motion of the pacific plate relative to the lord howe rise since anomaly 5 time 9 8 m y 420 110 km since anomaly 6 time 19 5 m y 770 330 km since anomaly 13 time 35 6 m y and 820 260 km since anomaly 18 time 43 0 m y we examined two cases for times prior to anomaly 18 assuming a late cretaceous age of australia antarctica separation if a plate boundary existed between the lord howe rise and pacific plates since the late cretaceous with no plate boundary in antarctica reconstructions with the lord howe rise fixed predict 610 200 km of westward motion of the pacific plate between the times of anomalies 31 and 22 followed by 260 100 km of northward motion between the times of anomalies 22 and 18 if the lord howe rise was fixed to the pacific plate until the eocene but a plate boundary existed between east and west antarctica reconstructions show very little motion across this boundary between the times of anomalies 31 and 22 followed by convergence between the times of anomalies 22 and 18 this second case also brings 70 80 m y paleomagnetic poles from the pacific and east antarctica plates into better agreement than the first case but large uncertainties in the reconstructions do not allow the first case to be conclusively eliminated

numerical models of lithospheric deformation forming the southern alps of new zealand compression of the entire continental lithosphere is considered using two dimensional numerical models in order to study the influence of the lithospheric mantle on the geometry of continental collision in its initial stages the models are based on the central section of new zealand southern alps where continental collision has occurred along the alpine fault since about 7 ma they incorporate brittle elastic ductile rheology heat transfer surface processes and fault localisation the models are compared to the surface relief the gps convergence velocity the measured electrical conductivity and the geometry of the crustal root imaged from seismic velocity measurements the crustal deformation is characterized by localized uplift at the plate boundary alpine fault and by two secondary zones of faulting one is located about 60 to 80 km east of the alpine fault at the start of upper crust bending or tilting and the other is located about 100 to 130 km east of the alpine fault as a result from shear strain propagating to the surface through the ductile lower crust the observed asymmetric shape of the crustal root is best reproduced for a mantle lithosphere strength of the order of 200 mpa and an intermediate rate of strain softening a lower strength of the mantle lithosphere can produce symmetric thickening but provides an amplitude of the crustal root too small when compared to observations the observed 20 km offset between the maximum in surface relief and the crustal root was not satisfactorily reproduced this offset is most likely due to the three dimensionality of oblique collision in new zealand southern alps

lithospheric structure across oblique continental collision in new zealand from wide angle p wave modeling 1 oblique convergence between the australian and pacific plates in south island new zealand has resulted in crustal thickening and distributed deformation within both plates we measure this thickening and image the deformation with seismic wide angle data along a 600 km long transect that spans the plate boundary p wave arrival times from 34 000 rays are used to construct a two dimensional model for seismic velocity with depth crustal velocities average 6 1 and 6 2 0 23 km s for the australian and pacific sides of the boundary respectively upper mantle velocities average 8 1 0 25 km s distributed deformation is indicated by the following observations a reduction in upper crustal and midcrustal velocities by 4 west of the plate boundary ascribed to flexural bending stresses a velocity reduction of 8 immediately east of the alpine fault linked to high pore fluid pressures 17 km of crustal thickening to form a 44 1 4 km deep crustal root that is offset 10 20 km se of the highest mountains a velocity reversal below the midcrust in the eastern part of the crustal root caused either by heating or an artifact from seismic anisotropy strong thickening of a 7 0 0 4 km s fast lower crust within the crustal root and a low velocity zone in the australian upper mantle due to sampling the slow orientation of upper mantle anisotropy

estimation of rock physics properties from seismic attributes part 2 applications abstractthe estimation of quantitative rock physics properties is of great importance for reservoir characterization and monitoring in co2 storage or enhanced oil recovery as an example we have combined the high resolution results of full waveform inversion fwi methods with rock physics inversion because we consider a generic and dynamic rock physics model our method is applicable to most kinds of rocks for a wide range of frequencies the first step allows determination of viscoelastic effective properties i e quantitative seismic attributes whereas the rock physics inversion estimates rock physics properties porosity solid frame moduli fluid phase properties or saturation this two step workflow is applied to time lapse synthetic and field cases the sensitivity tests that we had previously carried out showed that it can be crucial to use multiparameter inputs to accurately recover fluid saturations and fluid properties however due to the limited data availability and difficulties in get

anisotropy of schists contribution of crustal anisotropy to active source seismic experiments and shear wave splitting observations we have made sets of five independent compressional and shear wave velocity measurements which with density allow us to completely characterize the transverse isotropy of samples from five metamorphic belts the haast schist terrane south island new zealand poultney slate chugach phyllite coldfoot schist and pelona schist united states these velocity measurements include compressional wave velocities for propagation parallel perpendicular and at 45 to the symmetry axis shear wave velocity for propagation and particle motion perpendicular to the symmetry axis and shear wave velocity for propagation parallel to the symmetry axis velocity measurements were made up to pressures of 1 gpa 35 km depth where microcracks are closed and anisotropy is due to preferred mineral orientation our samples exhibit compressional wave anisotropy of 9 20 as well as significant shear wave splitting metamorphic terranes that are anisotropic to ultrasonic waves may also be anisotropic at the scale of active and passive seismic experiments our data suggest that a significant thickness 10 20 km of appropriately oriented steeply dipping foliation schist in the crust could contribute as much as 45 of observed shear wave splitting our data set can also be used to model the effects of crustal anisotropy for active source seismic experiments in order to determine if the anisotropy of the terrane is significant and needs to be taken into account during processing and modeling of the data

the enigma of the arthur s pass new zealand earthquake 1 reconciling a variety of data for an unusual earthquake sequence the 1994 arthur s pass earthquake mw6 7 is the largest in a recent sequence of earthquakes in the central south island new zealand no surface rupture was observed the aftershock distribution was complex and routine methods of obtaining the faulting orientation of this earthquake proved contradictory we use a range of data and techniques to obtain our preferred solution which has a centroid depth of 5 km m0 1 3 1019 n m and a strike dip and rake of 221 47 112 respectively discrepancies between this solution and the harvard centroid moment tensor together with the global positioning system gps observations and unusual aftershock distribution suggest that the rupture may not have occurred on a planar fault a second strike slip subevent on a more northerly striking plane is suggested by these data but neither the body wave modeling nor regional broadband recordings show any complexity or late subevents we relocate the aftershocks using both one dimensional and three dimensional velocity inversions the depth range of the aftershocks 1 10 km agrees well with the preferred mainshock centroid depth the aftershocks near the hypocenter suggest a structure dipping toward the nw which we interpret to be the mainshock fault plane this structure and the harper fault 15 km to the south appear to have acted as boundaries to the extensive aftershock zone trending nnw sse most of the ml 5 aftershocks including the two largest ml6 1 and ml5 7 clustered near the harper fault and have strike slip mechanisms consistent with motion on this fault and its conjugates forward modeling of the gps data suggests that a reverse slip mainshock combined with strike slip aftershock faulting in the south is able to match the observed displacements the occurrence of this earthquake sequence implies that the level of seismic hazard in the central south island is greater than previous estimates

material balance in alpine orogeny recent geophysical data are combined with older information for an updated picture of alpine kinematics using semiquantitative considerations of material balance in the alps a conventional pile of thin peel nappes is disrupted by a central longitudinal system of steep faults and steeply limbed folds both affecting disharmoniously the entire edifice of otherwise flat lying nappes it is particularly from late tertiary phases of deformation that structures of the second type the insubric system with the insubric line and the belt of late alpine windows acquired prominence for the present aspect of the alps these late structures formed as a dextrally transpressive intracontinental branch of the africa europa plate boundary mostly between areas of extension early motions in the late cretaceous to the late eocene were probably responsible for at least half of the 300 km dextral displacement required for the palinspastic restoration of the inner west carpathians and the dinarides during oligocene extension the late alpine batholiths intruded in a belt roughly along the insubric line while deep crustal and lithospheric roots were destroyed in the latest oligocene to middle miocene the adriatic plate moved dextrally to the west along the insubric transfer fault from its frontal insubric indenter a lower crust upper mantle flake probably first obducted in the cretaceous was detached and wedged into the penninic nappes of the western alps bird s head of the ivrea body both the northern and the southern transfer faults of the insubric indenter were disrupted and inactivated by late miocene to later events the giudicarie and neo north apennine events instead of the inactivated insubric fault the windows belt of en echelon folds assumed the role of dextral transpression all of these successive zones of motion are entangled in the ligurian knot largely hidden under the sea or young sediments a large part of the pre alpine crust and practically the whole mantle were subducted only in some cases were high pressure rocks of shallow continental origin re obducted the lithospheric root of the neo alps is largely contained in a vertical slab under the alps but some parts seem to have been removed and others disharmonically displaced with respect to the surface structures

anatomy structural evolution and slip rate of a plate boundary thrust the alpine fault at gaunt creek westland new zealand minimum slip rates calculated for plate vector parallel slickenside trends in cataclasite on the sole of the alpine fault at gaunt creek westland new zealand range from 18 to 24 mm yr between half and two thirds of the total relative motion between the pacific and australian plates is being accommodated by movement on a single structure the alpine fault during the past 14 ka the leading edge of the alpine fault has changed from a moderately southeast dipping oblique reverse fault to a shallowly dipping thrust the hanging wall pacific plate is composed of a gradational sequence from basal gouge through pseudotachylite bearing cataclasite to progressively more coherent schist derived mylonite which has been faulted against subhorizontally bedded fluvio glacial gravel in the footwall australian plate during uplift the hanging wall sequence has been internally sheared and imbricated producing duplex structures and retrogressively veined and altered by pervasive hydrothermal fluid flow erosion of the exhumed fault zone produced angular cataclasite and mylonite derived talus fan breccias building a west dipping apron beneath the fault scarp wood fragments from near the base off the talus breccias have been 14 c dated at 12 650 90 yr b p progressive tectonic shortening resulted in 180 m of overthrusting of a schist derived nappe across an irregular talus fan surface composed of its own erosional debris the structural history of the alpine fault at gaunt creek illustrates the importance of the interaction between fault induced topography and erosion and the control these processes exert on the continued tectonic geometric and geomorphic evolution of the fault zone

lithospheric deformation during the early stages of continental collision numerical experiments and comparison with south island new zealand 1 the nature of lithospheric deformation during continental plate collision still remains unresolved while it has often been proposed that the mantle lithosphere is accommodated by distributed thickening of a viscous root an alternate hypothesis suggests that significant portions of convergent mantle lithosphere essentially undergo underthrusting or subduction to further consider this issue we model the thermochemical evolution of the lithosphere mantle system using arbitrary lagrangian eulerian finite element techniques we incorporate a mix of viscous thermally activated power law creep and plastic frictional coulomb with strain softening rheologies in the numerical experiments to treat disparate composition in the crust and mantle a range of rheological and mechanical parameters is explored to determine controls on the style of lithospheric deformation the models suggest that during the initial stages of plate collision the mantle lithosphere is characterized by plate like behavior and underthrusting subduction of the upper region in conjunction with distributed thickening and rayleigh taylor type viscous instability of the lower portion depending on the material rheology temperature regime and imposed convergence velocity the deforming mantle lithosphere demonstrates various combinations of these end member behavioral modes the modeling results are interpreted in the context of observed lithospheric deformation across south island new zealand a combined style of underthrusting and distributed thickening is consistent with the observed crustal structure in the young collisional orogen as well as seismic imaging of the geometry of the underlying lithosphere

some thermal and mechanical consequences of rapid uplift an example from the southern alps new zealand abstract the thermal evolution of continental crust during active collision is modeled through numerical solutions of the two dimensional heat conduction equation for a rapidly moving medium the boundary conditions used in the modeling are derived from geological and geophysical observations from the active collision zone in the south island of new zealand the problem domain over which the solutions are obtained consists of a 40 km horizontal by 25 km vertical spatial plane with a vertical discontinuity at 10 km from the western boundary to the east of this discontinuity vertical uplift rates of up to 10 mm a occur over a timespan of up to 4 ma temperature distributions are calculated at 10 ka intervals over the 4 ma duration a two dimensional high temperature region is established upon initiation of uplift of the eastern block due to the advective component carrying heat upwards more rapidly than it can be dissipated laterally from the problem domain temperatures within the upper 5 km are greater than 400 c after 2 25 ma with geothermal gradients of up to 200 c km attained within the upper 3 km at times greater than 2 5 ma the vertical temperature distribution changes little while the anomalously high temperatures spread laterally into the stationary crust using rheological equations to describe the brittle behaviour of a water saturated upper crust and the ductile behaviour of a quartz dominated lower crust together with the thermal distribution of the conduction models the mechanical evolution of a collision zone is investigated in addition to high crustal temperatures and associated high heat flow rapid uplift produces a weakening of the crust by raising of the depth of transition from brittle to ductile behaviour within the zone of most rapid uplift the brittle ductile transition rises from 13 km to less than 5 km after 1 5 ma of uplift further uplift reduces the brittle layer to 3 km thickness and causes lateral spreading of the low strength zone the reductions in crustal strength caused by the thermal weakening produce a high strain zone within the region of maximum uplift which is incapable of sustaining large differential stresses this causes horizontal and vertical stress transfer and results in shallow seismicity increases in the adjacent crust as well as in intermediate depth seismicity within the high strength upper mantle because the thermal and mechanical anomalies discussed are a function of rapid uplift all regions of active continental collision may be expected to exhibit similar behaviour some mechanical and thermal characteristics of the himalayan collision zone are briefly examined in light of the numerical modeling

the effect of crustal anisotropy on reflector depth and velocity determination from wide angle seismic data a synthetic example based on south island new zealand when deriving velocity models by forward modelling or inverting travel time arrivals from seismic refraction data a heterogeneous but isotropic earth is usually assumed in regions where the earth is not isotropic at the scale at which it is being sampled the assumption of isotropy can lead to significant errors in the velocities determined for the crust and the depths calculated to reflecting boundaries laboratory velocity measurements on rocks collected from the haast schist terrane of south island new zealand show significant up to 20 compressional p wave velocity anisotropy field data collected parallel and perpendicular to the foliation of the haast schist exhibit as much as 11 p wave velocity anisotropy we demonstrate using finite difference full wavefield modelling the types of errors and problems that might be encountered if isotropic methods are used to create velocity models from data collected in anisotropic regions these reflector depth errors could be as much as 10 15 for a 10 km thick layer with significant 20 p wave velocity anisotropy the implications for south island new zealand where the problem is compounded by extreme orientations of highly anisotropic rocks foliation which varies from horizontal to near vertical are considered finally we discuss how the presence of a significant subsurface anisotropic body might manifest itself in wide angle reflection refraction and passive seismic datasets and suggest ways in which such datasets may be used to determine the presence and extent of such anisotropic bodies d 2002 elsevier science b v all rights reserved

intermediate depth earthquakes in a region of continental convergence south island new zealand it is rare to find earthquakes with depths greater than 30 km in continent continent collision zones because the mantle lithosphere is usually too hot to enable brittle failure however a handful of small intermediate depth earthquakes 30 97 km have been recorded in the continental collision region in central south island new zealand the earthquakes are not associated with subduction but all lie within or on the margins of thickened crust or uppermost mantle seismic high velocity anomalies the largest of the earthquakes has m l 4 0 corresponding to a rupture radius of between 100 and 800 m providing bounds on the upper limit to the rupture length over which brittle failure is taking place in the deep brittle plastic transition zone the earthquake sources may be controlled by large shear strain gradients associated with viscous deformation processes in addition to depressed geotherms

preliminary results from a geophysical study across a modern continent continent collisional plate boundary the southern alps new zealand abstract the southern alps of south island new zealand is a young transpressive continental orogen exhibiting high uplift rates and rapid transcurrent movement a joint us nz geophysical study of this orogen was carried out in late 1995 and early 1996 to derive a three dimensional model of the deformation the measurements undertaken include active source and passive seismology magnetotelluric and electrical studies and petrophysics preliminary models for the active source seismic measurements across south island confirm in general terms a thickened crust under the southern alps a high velocity lower crustal layer and a major crustal discontinuity associated with the alpine fault the anisotropy in physical properties of the rocks of the plate boundary zone is clearly demonstrated in the preliminary results of laboratory seismic velocity measurements shear wave splitting and resistivity the mid crust under the southern alps coincides with a major electrical conductivity high which possibly corresponds to fluid in the crust the top lies at about 15 km close to the base of shallow seismicity east of the alpine fault offshore the marine reflection data have consistently imaged a reflective lower crust adjacent to south island these data are showing complex structure particularly off western and southeastern south island the complexity in structure high quality data and consistency in results from several techniques indicates that the south island experiment will contribute significantly to our knowledge of transpressive plate boundaries in particular and the continental lithosphere in general

fission track analysis of the late cenozoic vertical kinematics of continental pacific crust south island new zealand during the late cenozoic the pacific plate has been converging obliquely with the australia plate in south island new zealand a result of this convergence has been the growth of a major mountain range the southern alps at the leading edge of the pacific plate the results of fission track analysis of 140 samples from 13 transects across the alps reported here establish the late cenozoic vertical kinematics amount age and rate of rock uplift of the pacific crust underlying the alps the late cenozoic rock uplift of the pacific crust is asymmetrical with respect to the alpine fault being a maximum 19 km immediately east of the central part of the fault with lesser values at the eastern 3 km northern 10 km and southern 8 km extremities of the alps the age of the start of rock uplift varies spatially across the southern alps the earliest indications from fission track analysis being at 8 ma at the southern end of the alps decreasing to 5 ma at the northern end and 3 ma along the southeastern margin this age variation reflects the longer time over which the southern parts of the alps have been in collision the rate of propagation of rock uplift southeastward into the pacific plate has been 30 mm yr nearly 4 times the late cenozoic average rate of convergence normal to the plate boundary late cenozoic mean rock uplift rates range from a maximum of 2 8 mm yr at the alpine fault to a minimum of 1 0 mm yr in the east and have been sustained for periods of 3 8 m y accompanying denudation has exhumed amphibolite grade rocks immediately east of the alpine fault the rock uplift has been controlled by oblique slip displacement on the alpine fault a continental crustal section at least 19 km thick has been uplifted on the alpine fault comparison of the late cenozoic mean rock uplift rates with uplift rates derived from reset zircon data 2 10 mm yr near the alpine fault shows that uplift has accelerated over time but only significantly since 1 3 0 3 ma the amount of mesozoic uplift ranged from minimal amounts north of arthur s pass to 3 km near mount cook to 10 km in the south at lake wanaka

statistical rock physics combining rock physics information theory and geostatistics to reduce uncertainty in seismic reservoir characterization any physical theory is a kind of guesswork there are good guesses and bad guesses the language of probability allows us to speak quantitatively about some situation which may be highly variable but which does have some consistent average behavior our most precise description of nature must be in terms of probabilities richard feynman this paper presents snapshots of current and emerging trends in applied statistical rock physics for reservoir characterization by integrating fundamental concepts and models of rock physics statistical pattern recognition and information theory with seismic inversion and geostatistics we can quantify and reduce uncertainties in reservoir management rock physics allows us to link seismic response and reservoir properties and to extend the available data to generate training data for the classification system seismic imaging brings indirect but nevertheless spatially exhaustive lateral and vertical information about reservoir properties that are not available from pinpoint well data classification and estimation methods based on computational statistical techniques such as nonparametric bayesian classification bootstrap and neural networks help quantitatively measure interpretation uncertainty and the mis classification risk at each spatial location geostatistical stochastic simulations add spatial correlation and small scale variability which is hard to identify from seismic only because of the limits of resolution combining deterministic physical models with statistical techniques leads to new methods for interpretation and estimation of reservoir rock properties from seismic data these formulations identify the most likely interpretation the uncertainty of the interpretation and guide quantitative decision analysis subsurface heterogeneity delineation is a key factor in reliable reservoir characterization these heterogeneities occur at various scales and can include variations in lithology pore fluids clay content porosity pressure and temperature some methods used in seismic reservoir characterization are purely statistical others are deterministic based on physical models theoretical laboratory each group of techniques can have some

fluid generation and pathways beneath an active compressional orogen the new zealand southern alps inferred from magnetotelluric data 1 forty one wideband magnetotelluric mt soundings were collected in a 150 km long transect across the southern alps of the central south island of new zealand an active compressional orogen decomposed mt impedance tensors vertical magnetic field relations and reconnaissance soundings at two locations off line imply an approximately two dimensional geometry here with average regional geoelectric strike of n40 e similar to surface geologic trends two independent two dimensional inversion algorithms were applied to the mt data and both imply a concave upward u shaped middle to lower crustal conductive zone beneath the west central portion of the island the average conductivity of this zone in the strike direction appears to be much higher than that required across strike and may represent anisotropy or along strike conductive strands narrower than the transverse magnetic cross strike mode mt data can resolve the deep crustal conductor under the southern alps is interpreted to represent mainly a volume of fluids arising from prograde metamorphism within a thickening crust fluid interconnection and electrical conduction are promoted by shear deformation the conductor rises northwestward toward the trace of the alpine fault but attains a near vertical configuration at a depth of 10 km and reaches close to the surface 5 10 km inland of the fault trace itself the transition to vertical orientation at this depth is interpreted to occur as fluids ascend across the brittle ductile transition in uplifting schist and approach the surface through induced hydrofractures the high grade schist becomes resistive after depletion of fluids and continues to extrude toward the alpine fault shallow extensions of the deep high conductivity are coincident with modern hydrothermal veining and gold mineralization interpreted to be of deep crustal provenance to the southeast high conductivity also reaches the surface coincident with a major back thrust fault zone of the doubly vergent southern alps orogen which also exhibits evidence for expulsion of high temperature fluids the higher conductivity inferred along strike possible anisotropy could reflect more efficient fluid interconnection in this higher strain direction as well as possible contributions by sheared fluid deposited graphite conductivity of the uppermost mantle of the south island is low consistent with advection of cold mantle lithosphere into the underlying asthenosphere as suggested by p wave delay studies

origin of the torlesse terrane and coeval rocks south island new zealand the carboniferous to lower cretaceous torlesse terrane and haast schist derivatives constitute the major part of the complexly deformed facies of the eastern province of new zealand strata consist mainly of quartzofeldspathic graywacke and mudstone intercalated with minor but widely distributed conglomerate and volcanics with associated chert and limestone clastic rocks were deposited largely by sediment gravity flow mechanisms in a deep marine environment also present are a few highly fossiliferous shallow marine and terrestrial deposits of limited areal extent which rest unconformably on or in fault contact with torlesse flysch several periods of deformation are recognized and melange is present on both local and regional scales metamorphism ranges from zeolite to greenschist facies the bulk of the rocks fall into five areally extensive and mutually exclusive fossil zones of the following ages permian atomodesma middle triassic early late triassic torlessia late triassic monotis and late jurassic early cretaceous contacts between major fossil zones are mainly tectonic petrographic analysis permits subdivision of torlesse sandstones into five major petrofacies that correspond in age to the five major fossil zones the sandstone petrofacies mainly arkosic together with the composition of conglomerate clasts mainly indurated torlesse rocks indicate that the source terrane was a continental volcano plutonic arc probably part of gondwanaland coupled with autocannibalistic reworking of older uplifted torlesse rocks in contrast to the quartzofeldspathic nature of the torlesse coeval sedimentary rocks of the eastern province are volcanogenic they are thought to represent related forearc basin maitai murihiku terranes and trench complex caples terrane deposits derived from a volcanic island arc brook street terrane three petrofacies are established for maitai murihiku and caples sandstones the petrofacies indicate a common evolving immature to submature volcanic island arc source for these terranes a reconstruction of new zealand s eastern and western provinces is proposed in permian and triassic times the torlesse was deposited in trench slope or borderland basins along a trench transform margin fronting a continental volcano plutonic arc source western province gondwanaland deposition was spasmodic but voluminous and was accompanied by concurrent deformation and accretion resulting in parallel belts of torlesse rock younging outward from the gondwanaland margin at the same time the brook street terrane volcanic arc and associated terranes were forming to the west of the torlesse site separated from gondwanaland by a marginal sea in latest triassic or early jurassic times the torlesse was rafted into the volcanic arc system via transform faulting approximately parallel to the gondwana margin the collision event resulted in tectonic thickening of torlesse and caples rocks at the plate interface and metamorphism to haast schist the source was then dominated by older partly metamorphosed torlesse terrane newly uplifted along the collision front closing of the marginal sea behind the brook street terrane in late jurassic early cretaceous times resulted in juxtapositioning with the western province gondwanaland along the median tectonic line

three dimensional lithospheric structure below the new zealand southern alps uppermost mantle seismic structure below the southern alps in south island new zealand is investigated by teleseismic p wave travel time residual inversion the three dimensional tomographic images show a near vertical high velocity 2 4 structure in the uppermost mantle that directly underlies thickened crust along the nnessw axis of the southern alps the center of the high velocity anomaly lies to the east of the alpine fault which bounds pacific and australian plate rocks the oblique collision of these plates resulted in the uplift of the southern alps during the past 5 7 m y also a high velocity anomaly 3 5 corresponding to the hikurangi subduction zone lies to the northeast of the southern alps anomaly and low velocity anomalies 3 underlying parts of northwestern and southern south island may be signatures of late tertiary extension and volcanism the data consist of teleseismic arrival times from the new zealand national seismograph network and arrival times recorded during the 1995 1996 southern alps passive seismic experiment crustal heterogeneity was accounted for by back projecting the rays through an independently obtained three dimensional crustal velocity and moho depth model the southern alps uppermost mantle velocity anomalies are most simply explained by lithospheric thickening below the center of convergence accompanied by thinning and asthenospheric upwelling adjacent to the region of convergence

a geodynamic framework for interpreting crustal scale seismic reflectivity patterns in compressional orogens summary 2 d plane strain finite element models are used to calculate crustal deformation patterns within model compressional orogens and the results are compared with natural examples the fundamental driving mechanism for model deformation is provided by asymmetric detachment and underthrusting of mantle lithosphere with deformation being rooted at the stress singularity where the mantle detaches deformation steps up into the overlying crust and spreads laterally according to the rhcological properties assumed for the crust the crust is modelled using plastic frictional and viscous rheologies and incorporates the effects of compositional layering and variable geothermal gradients overall deformation is determined by balancing the internal strength of the crust against the sum of applied boundary stresses plus the gravitational stress induced by mass redistribution within the deforming orogen the amount of convergence in the models is limited to 150 km or less and so the results are not strictly comparable with larger orogens involving greater convergence nevertheless larger orogens seem to evolve through stages that may be understood in terms of the models provided that consideration is confined to smaller scale components that are limited in time and space the continuum deformation calculated by the finite element models is qualitatively converted to equivalent pattcrns of discrete faults and shear zones by associating these discrete features with the areas of highest cumulative strain using the results of sandbox experiments as guides significant styles of deformation include 1 coupling between step up shears and subhorizontal detachments at one or more levels 2 localization of upper crustal deformation by subduction of the lower crust and 3 pinning of deformation by surface denudation a partial catalogue of such model styles is presented in which the strength of basal coupling between crust and mantle the number of rhcological layers within the crust the thickness of subducted lower crust and the extent of surface denudation are varied systematically compressional orogens with a wide range of ages are characterized by crustal scale seismic reflectivity similar to patterns of fault shear zones represented in this catalogue of styles this similarity suggests that crustalscale seismic reflection data can be used to constrain the dynamic processes involved in compressional orogcnesis

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

thermochronological analysis of the dynamics of the southern alps new zealand the isotopic ages of material exposed close to the alpine fault in the southern alps new zealand vary in a consistent fashion along the orogen for the k ar system muscovite and biotite ages display two distinct spatial trends that meet in the area of fox glacier where a strong relationship is observed between k ar age and altitude excess argon is present in samples between mount kinnaird and haast pass in the southwest of the southern alps giving unrealistically old inconsistent k ar ages across this region incorporation of excess argon appears to be highly variable however and minimization of its influence on dynamical interpretations of thermochronology is possible through considering only the youngest age from a given area such treatment indicates that excess argon contamination does not play an important role in the systematic k ar age variation identified along the southern alps the observed age distribution is consistent with estimates of the modern rapid uplift and exhumation of the southern alps beginning ca 5 ma k ar mica ages older than this south of the copland valley indicate that substantial late cenozoic exhumation occurred along the southern alps prior to the development of the modern tectonic regime but at rates lower than at present total exhumation during the current phase of tectonism in the southern alps decreases from the whataroa river southward north of fox glacier the southern alps have attained a dynamical steady state such that the observed distribution of exhumation will not change significantly with further deformation and denudation under current conditions

focal mechanisms of large earthquakes in the south island of new zealand implications for the accommodation of pacific australia plate motion b the plate motion model nuvel 1 predicts oblique convergence between the pacific and australian plates in the south island of new zealand we used p and sh body waveform analysis to constrain the focal mechanisms of the 15 largest earthquakes ms 5 8 that have occurred in this region since 1964 in order to see how the plate motion is accommodated at the southern end of the alpine fault convergence is achieved by oblique slip movement along a concentrated zone of deformation in the southern offshore region one event may be related to thrusting of the australian plate beneath the pacific plate and another strike slip event probably demonstrates movement on an active strike slip fault system parallel to but offset from the southern limit of the alpine fault this geometry provides a possible mechanism for the rapid uplift of the fiordland region deformation in the northern south island is more distributed in the south west marlborough region partitioning occurs between strike slip faulting in the se and reverse faulting farther nw in the buller region we suggest that the partitioning developed as a consequence of an increasing component of shortening that was accommodated by slip on reactivated pre existing normal faults in the buller region shortening in the buller region may have deflected the ne end of the alpine fault towards the nw forming the prominent bend the marlborough fault system with its youngest and most active faults to the se probably developed in an attempt to maintain a through going strike slip structure as each of the strike slip faults was transported towards the north west partitioning of the opposite polarity with reverse faulting se of the strike slip faulting occurs in north east marlborough the boundary between the two different styles of partitioning in ne and sw marlborough appears to coincide with a change in the nature of the downgoing slab and a change in strike of faults of the marlborough fault system a normal faulting earthquake on the northern edge of the chatham rise probably results from a complex interaction of the buoyant continental crust in that region with the subduction zone and the overlying marlborough fault system

on steady states in mountain belts the dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state this concept is often invoked but the nature of the steady state is commonly not specified we identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical model results and natural examples these types are 1 flux steady state 2 topographic steady state 3 thermal steady state and 4 exhumational steady state they refer to the erosional flux the topography the subsurface temperature field and the spatial pattern of cooling ages respectively models suggest that the topography will reach a steady mean form at the scale of an orogenic belt but perfect topographic steady state is unlikely to be achieved at shorter length scales thermal steady state is a precondition for exhumational steady state and in the case of temperature dependent deformation topographic steady state exhumational steady state is characterized by reset age zones spatially nested according to closure temperature as illustrated in natural systems from new zealand the cascadia accretionary margin and taiwan

large offset seismic surveying using ocean bottom seismographs and air guns instrumentation and field technique repeatable closely spaced signal sources from large capacity air guns and detection and recording of signals using highly flexible microprocessor controlled digital ocean bottom seismographs allow us to acquire high quality large offset marine seismic refraction and reflection data the acquired data are readily adaptable to various processing techniques originally developed for seismic reflection data there are several requirements and problems specific to the technique for example bubbly signals from one or two large capacity air guns are often preferable to bubble suppressed signals from tuned arrays in identifying weak arrivals at large offset distances recorded water wave signals at near ranges provide precise locations of detectors relative to shots

strain distribution across the australian pacific plate boundary in the central south island new zealand from 1992 gps and earlier terrestrial observations as part of a geodetic experiment aimed at understanding the deformation associated with the australian pacific plate boundary in the south island of new zealand in 1992 we reoccupied using global positioning system gps techniques a first order triangulation and trilateration network established in 1978 between christchurch on the east coast and hokitika on the west the network crosses the south island a few tens of kilometers southwest of the region where the plate boundary changes from a single throughgoing oblique slip fault the alpine fault to a series of subparallel strike slip faults the marlborough faults the gps data have been analyzed as daily network solutions with about 12 stations in each solution rms repeatabilities for stations with multiple occupations are 4 mm 8 mm and 15 mm in the north east and vertical components respectively the observed strain across the network is consistent with the entire nuvel ia pacific australia plate velocity being accommodated on land across this part of the south island shear strain rates derived from the gps and terrestrial data show that the highest strain rate 0 4 rad yr occurs in the region of the southern alps and alpine fault this rate is about two thirds of the rate predicted from the nuvel ia plate velocity model assuming that all the plate boundary deformation occurs across this region implying that about two thirds of the plate motion is accommodated in the vicinity of the alpine fault significant shear strain rates greater than 0 2 rad yr are also observed farther east particularly in the region of the porters pass amberley fault zone demonstrating that this zone accommodates a significant part of the plate boundary deformation using dislocation modeling we show that the variation in fault parallel shear strain rates across the alpine fault is reasonably consistent with a nonoptimized dislocation model involving a 50 dipping fault that is presently locked to a depth of 12 km one explanation for this observation is that the upper 12 km of the crust in this area is storing most of the right lateral shear component of the relative plate motion as elastic energy that will be released in a future major earthquake the variation in the other component of shear strain which may be interpreted as fault normal relative contraction is not explained by a simple dislocation model implying that the normal component of plate motion is taken up in other ways

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

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

contrast in crustal structure across the clipperton transform fault from travel time tomography a three dimensional 3 d seismic refraction study of the clipperton transform fault northern east pacific rise reveals anomalously low compressional velocities from the seafloor to the moho we attribute this low velocity anomaly to intensive brittle deformation caused by transpression across this active strike slip plate boundary the seismic velocity structure south of the clipperton transform appears unaffected by these tectonic forces but to the north seismic velocities are reduced over 10 km outside the zone of sheared seafloor this contrast in seismic velocity structure corresponds well with the differences in mid ocean ridge morphology across the clipperton transform we conclude that the amount of fracturing of the upper crust which largely controls seismic velocity variations is strongly dependent on the shallow temperature structure at the ridge axis intermittent supply of magma to the shallow crust north of the clipperton transform allows seawater to penetrate deeper and the cooler crust is brittle to a greater depth than south of the transform where a steady state magma lens is known to exist the crustal thickness averages 5 7 km only slightly thinner than normal for oceanic crust and variations in moho depth in excess of 0 3 km are not required by our data the absence of large crustal thickness variations and the general similarity in seismic structure imply that a steady state magma lens is not required to form normal east pacific rise type crust perhaps a significant portion of the lower crust is accreted in situ from a patchwork of short lived gabbro sills or from ductile flow from a basal magma chamber as has been postulated in some recent ophiolite studies

teleseismic p wave delays and modes of shortening the mantle lithosphere beneath south island new zealand a high speed zone in the mantle directly beneath the southern alps of new zealand is required by the recorded pattern of teleseismic p waves two parallel lines of 80 seismographs spaced at 2 km intervals recorded three earthquakes from the western pacific with epicentral distances of 52 53 and 78 azimuthal bearings were all within 15 degrees of the mean trends of the seismograph lines differences between measured delays and those predicted from the crustal structure reach 0 8 s along one line and 1 0 s along the other with the rays for the earliest arriving signals passing the depth of 120 km beneath the center of the island assuming these early arrivals are due to structure within the mantle shallower than 200 km they imply that the core of the high speed zone lies beneath the thickest crust which has been shortened by 100 km of convergence during the past 6 7 myr although the shape and position of the high speed body cannot be fixed uniquely a roughly symmetric body centered about a depth of 120 km 80 100 km wide with a depth extent of 100 km and with a maximum speed advance of 7 satisfies the observations the pattern of residuals does not fit with those predicted by simple models of intracontinental subduction in which crust and mantle lithosphere are detached and one slab of mantle lithosphere underthrusts the other rather the residuals favor thickening of mantle lithosphere by a more homogenous straining of it as if mantle lithosphere beneath continental crust behaved as a continuum an excess mass in the mantle is also required by the observed gravity anomalies once allowance is made for the seismically determined crustal thickness this high density mantle anomaly provides sufficient force per unit length to maintain the crustal root which is approximately twice as thick as that necessary to support the topography

subduction of continental crust in the western alps as a result of recent deep reflection and refraction seismology the crustal structure of the western alps is now quite well defined however this raises the question of what is present below the moho such as a crustal eclogitic root this study attempts to estimate the volume of this eclogitic root on the basis of palinspastic reconstructions even with a minimum estimate of the crustal material involved in the subduction processes which took place during the alpine orogeny a significant eclogitized crustal root must be present down to depths of around 100 km below the po plain a maximum estimate suggests that a large part of this root could now be recycled in the asthenosphere

double sided onshore offshore seismic imaging of a plate boundary super gathers across south island new zealand abstract onshore offshore seismic refraction profiling allows for the determination of crustal and mantle structures in the transition between continental and oceanic environments islands and narrow landmasses have the unique geometry of allowing for double sided onshore offshore experiments that favor the construction of composite super gathers using the acquisition of onshore offshore and ocean bottom seismometer receiver gathers land explosion shot gathers and near vertical incidence multichannel seismic mcs profiling a number of sites at plate boundaries are amenable to the application of double sided onshore offshore imaging including the indo australian pacific transform boundary on south island new zealand by comparing the ratio of island width to mantle refraction pn maximum crossover distance using nondimensional distances we provide an indicator of raypath coverage for crustal illumination islands or narrow land masses whose widths are less than twice their maximum crossover distance are candidates for double sided onshore offshore experiments the sight south island geophysical investigation experiment in new zealand is located where the width of south island is sufficiently narrow with respect to its crustal thickness that a double sided onshore offshore experiment allows for complete crustal imaging of the associated plate boundary

the mid cenozoic challenger rift system of western new zealand and its implications for the age of alpine fault inception analysis of the structure and sedimentary geology of western new zealand has identified a middle eocene to early miocene continental rift system 1 200 km long and 100 200 km wide named here the challenger rift system four phases of rift development occurred 1 infra rift subsidence 2 active axial trough subsidence 3 expanded rift subsidence involving collapse of the rift shoulders and 4 incipient sea floor spreading the spatial and temporal distribution of these phases identifies a north island and a south island rift segment and shows that rifting propagated toward the center of the rift from both ends the northern segment shows a simple pattern of rifting that is comparable with vink9s model of rift propagation the southern segment with locked zones and rift nucleation segments is comparable to courtillot9s model of rift propagation the sea floor spreading history of the southwest pacific shows that the northern rift segment probably linked with a sea floor spreading center in the norfolk basin and the southern segment linked with the southeast indian ridge this is corroborated by the good correlation between the ages of sea floor magnetic anomaly lineations that are aligned with the rift and the biostratigraphic ages of rifting the probable continuity of the rift system in its early development precludes pre miocene transcurrent displacement on the alpine fault an early miocene 23 m y b p age of alpine fault inception is indicated by the age and pattern of rift disruption attributed to compression that originated at the australia pacific plate boundary the modern australia and pacific plates were not discrete entities therefore until the early miocene

assessment of crustal velocity models using seismic refraction and reflection tomography two tomographic methods for assessing velocity models obtained from wide angle seismic traveltime data are presented through four case studies the modelling inversion of wide angle traveltimes usually involves some aspects that are quite subjective for example 1 identifying and including later phases that are often difficult to pick within the seismic coda 2 assigning specific layers to arrivals 3 incorporating pre conceived structure not specifically required by the data and 4 selecting a model parametrization these steps are applied to maximize model constraint and minimize model non uniqueness however these steps may cause the overall approach to appear ad hoc and thereby diminish the credibility of the final model the effect of these subjective choices can largely be addressed by estimating the minimum model structure required by the least subjective portion of the wide angle data set the first arrival times for data sets with moho reflections the tomographic velocity model can be used to invert the pmp times for a minimum structure moho in this way crustal velocity and moho models can be obtained that require the least amount of subjective input and the model structure that is required by the wide angle data with a high degree of certainty can be differentiated from structure that is merely consistent with the data the tomographic models are not intended to supersede the preferred models since the latter model is typically better resolved and more interpretable this form of tomographic assessment is intended to lend credibility to model features common to the tomographic and preferred models four case studies are presented in which a preferred model was derived using one or more of the subjective steps described above this was followed by conventional first arrival and reflection traveltime tomography using a finely gridded model parametrization to derive smooth minimum structure models the case studies are from the se canadian cordillera across the rocky mountain trench central india across the narmada son lineament the iberia margin across the galicia bank and the central chilean margin across the valparaiso basin and a subducting seamount these case studies span the range of modern wide angle experiments and data sets in terms of shot receiver spacing marine and land acquisition lateral heterogeneity of the study area and availability of wide angle reflections and coincident near vertical reflection data the results are surprising given the amount of structure in the smooth tomographically derived models that is consistent with the more subjectively derived models the results show that exploiting the complementary nature of the subjective and tomographic approaches is an effective strategy for the analysis of wide angle traveltime data

inverse rock physics modeling for reservoir quality prediction abstractseismic reservoir characterization requires a transform of seismically derived properties such as p and s wave velocities acoustic impedances elastic impedances or other seismic attributes into parameters describing lithology and reservoir conditions a large number of different rock physics models have been developed to obtain this link their relevance is however constrained by the type of lithology porosity range textural complexity saturation conditions and the dynamics of the pore fluid because the number of rock physics parameters is often higher than the number of seismic parameters this is known to be an underdetermined problem with nonunique solutions we have studied the framework of inverse rock physics modeling which aims at direct quantitative prediction of lithology and reservoir quality from seismic parameters but where nonuniqueness and data error propagation are also handled the procedure is based on a numerical reformulation of rock physics models so that the seismi

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

upper mantle anisotropy in the new zealand region shear wave splitting parameters of fast polarization direction and delay time t are determined using data from the southern alps passive seismic experiment sapse on the south island of new zealand and in the surrounding region our results clearly show that are subparallel to trends of the alpine and marlborough faults and to the pacific australian plate boundary the t values range from 0 6 2 2 s with an average value of 1 6 s the largest values are from the central south island the main source of the observed shear wave splitting is an anisotropic region between 40 400 km the width of the zone is approximately 200 km we attribute the coincidence of surface structural trends with the measured and the large t values to significant shear deformation in a 200 km thick zone along the plate boundary extending from the surface to deep within the upper mantle

rock physics modeling of unconsolidated sands accounting for nonuniform contacts and heterogeneous stress fields in the effective media approximation with applications to hydrocarbon exploration by treating contact stiffness as a variable one can extend the effective medium approximation used to obtain elastic stiffness of a random pack of spherical grains more specifically we suggest calibrating effective media approximation based on contact mechanics by incorporating nonuniform contact models the simple extension of the theory provides a better fit for many laboratory and field experiments and can provide insight into the micromechanical bonds associated with unconsolidated sediments this approach is motivated by repeated observations of shear wave measurements in unconsolidated sands where observed shear wave velocities are lower than predicted by the hertz mindlin contact theory we present the calibration process for well log data from a north sea well penetrating a shallow gas discovery and a deepwater well in the gulf of mexico finally we demonstrate the benefit of using this model for amplitude variation with angle ava analysis of shallow sand targets in exploration and reservoir studies

seismic inversion for reservoir properties combining statistical rock physics and geostatistics a review there are various approaches for quantitative estimation of reservoir properties from seismic inversion a general bayesian formulation for the inverse problem can be implemented in two different work flows in the sequential approach first seismic data are inverted deterministically or stochastically into elastic properties then rock physics models transform those elastic properties to the reservoir property of interest the joint or simultaneous work flow accounts for the elastic parameters and the reservoir properties often in a bayesian formulation guaranteeing consistency between the elastic and reservoir properties rock physics plays the important role of linking elastic parameters such as impedances and velocities to reservoir properties of interest such as lithologies porosity and pore fluids geostatistical methods help add constraints of spatial correlation conditioning to different kinds of data and incorporating subseismic scales of heterogeneities

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

western fiordland orthogneiss early cretaceous arc magmatism and granulite facies metamorphism new zealand u pb isotopic analyses of zircons from a distinctive suite of previously undated granulite facies metaplutonic rocks here termed the western fiordland orthogneiss wfo in fiordland southwest new zealand indicate synkinematic magmatic emplacement between 120 and 130 ma ago these rocks were previously interpreted as possibly being of precambrian age initial pb and sr ratios are consistent with arc subduction related magmagenesis with little or no involvement of ancient continental crust subsequent high pressure 12 kb metamorphism of the wfo may reflect a major collision event involving crustal thickening by overthrusting of a 15 km thick sequence metamorphism ceased 116 ma ago based on206pb 238u ages of zircon from a retrogressed granulite u pb isotopic analysis of apatite along with previously published rb sr mineral ages indicate that final uplift and cooling to 300 400 c was largely completed by 90 ma the average uplift rate during this period is inferred to have been in excess of 1 mm yr unmetamorphosed gabbronorites of the darran complex in eastern fiordland inferred by some investigators to be the granulite protolith yield concordant u pb zircon ages of 137 1 ma u pb ages of apatite and previously published k ar mineral ages indicate that these rocks experienced a rapid and simple cooling history lasting only a few million years the high grade wfo and unmetamorphosed darran complex are now separated by a profound structural break however the ages and similarities in initial pb and sr isotopic ratios suggest that both suites are products of the same early cretaceous cycle of subduction related magmatism the timing of early cretaceous magmatism and metamorphism collision and resultant crustal thickening and subsequent great uplift and erosion in fiordland has important implications for terrane accretion and the evolution of relative plate motions along the new zealand segment of the gondwana margin

the tectonic evolution of the southern alps new zealand insights from fully thermally coupled dynamical modelling summary we present here the results of numerical models of the southern alps in which the thermal and dynamical developments of the orogen are fully coupled to one another this interlinkage allows the use of a wide range of thermal and physical features of the orogen as constraints on the applicability of our models in particular the thermal aspect of this method enables the prediction of the distribution of thermochronological ages at the surface of the model perturbation of the geothermal structure due to rapid uplift and exhumation causes an intrinsic weakening and concentration of strain along the equivalent of the alpine fault zone in these models this thermal weakening of the crust also produces a zone of high strain antithetic to the alpine fault in the upper crust that is comparable to the main divide fault zone within the southern alps the introduction of orographic rainfall and erosional processes into the model leads to the development of high asymmetric topography comparable to that of the southern alps this topographic profile results from the capture of available precipitation by the windward side of the orogen and the resultant rain shadow on the leeward side due to the time required to accumulate suycient topography for this rain capture evect to become significant the establishment of this high asymmetric topography lags the initiation of surface uplift by several million years comparison of the observed thermal history of the southern alps with that seen in models based on divering hypotheses of the tectonic evolution of the south island shows that the present tectonic regime of the orogen most probably developed in a single rapid reorganization of plate motions at approximately 5 ma with relative stability of the tectonic regime since that time the variation in isotopic ages along the southern alps is consistent with that expected from variation in accumulated uplift and exhumation along the orogen arising from the obliquity of convergence of the australian and pacific plates

continental crust under compression a seismic refraction study of south island geophysical transect i south island new zealand 1 the 1996 south island geophysical transect sight active source seismic survey was designed to show the style of lithospheric thickening due to late cenozoic oblique convergence across the australian pacific plate boundary in new zealand as part of this study two seismic refraction lines were shot across central south island and offshore extensions of the continental crust in the tasman sea and pacific ocean we present the data and a 603 km long seismic velocity profile of the crust and uppermost mantle along one of these seismic transects a tomographic inversion of 62 563 travel times from crustal and upper mantle refractions and wide angle reflections resulted in a model with a two layer crust upper crustal velocities were between 5 9 and 6 3 km s and lower crustal velocities were between 6 5 and 7 0 km s continental compression has locally reduced the seismic velocities in the pacific plate crust by 0 2 0 3 km s a possible effect of high strain and fluids in the crust the thickening of the crust from 28 km at the east coast of south island to 37 km beneath the southern alps can account for about 25 of the 80 110 km shortening of pacific plate crust while the rest must be accounted for by rapid erosion of mesozoic sedimentary rocks on the west side of the orogen in our model the lower crust forms a continuous 2 6 km thick layer beneath central south island the asymmetric topography of the southern alps is reflected in the crustal root which has a steeper flank at the west coast this observation is consistent with westward underthrusting of pacific lower lithosphere beneath south island that has been suggested in earlier studies

sub crustal earthquakes within the australia pacific plate boundary zone beneath the southern alps new zealand abstract sub crustal earthquakes have been observed sporadically for 40 years in the central south island of new zealand we report on 20 events recorded between december 2008 and february 2012 near the alpine fault in the continental collision zone between the australian and pacific plates a subset of 18 events at depths of 47 74 km occurs south of mt cook and together with recently reported tremor locations indicates along strike variations in deformation behaviour along the plate boundary the sub crustal earthquakes south of mt cook increase in depth frequency and size southwards towards the puysegur subduction zone focal mechanisms could be determined for 14 earthquakes and exhibit predominantly strike slip and reverse faulting solutions stress inversion analysis of the focal mechanisms yields a stress field favouring oblique reverse faulting we interpret the geographic and vertical distributions of these sub crustal events in relation to a previously proposed tectonic model of a remnant passive margin that formed south of new zealand in the eocene and was overridden when dextral strike slip motion initiated on the alpine fault we infer that sub crustal earthquakes occur along the leading edge of this structure which is attached to the continental australian crust

subcrustal earthquakes in the central south island new zealand and the root of the southern alps the pukaki microearthquake network has revealed significant earthquake activity deeper than 15 km in the central south island new zealand extending to a depth of 73 km beneath the crest of the southern alps events deeper than 25 km define a planar seismic zone that has a strike of 41 and dips northwest at 19 gravity models suggest that earthquakes in this zone are occurring in a seismogenic uppermost mantle underlying an aseismic lower crustal root to the southern alps the 17 difference in strike of the dipping seismic zone and the alpine fault provides an explanation for the pattern of uplift and crustal thickening seen in the central south island

rippled scour depressions on the inner continental shelf off central california abstract side scan sonar records taken during the recent coastal ocean dynamics experiment code show elongate shore normal rippled depressions of low relief on the inner continental shelf off central california between bodega bay and point arena these features extend up to 2 km from the coast into water depths of up to 65 m the proposed mechanism for their generation is storm generated bottom currents associated with coastal downwelling during the late fall and winter which scour the surficial fine sand sediment and expose the coarser sand substrate in the depressions the zones of most intense erosion and the irregular spacing of the features may be controlled by submerged rock ledges and other prominent coastal features the large straight crested ripples within the depressions heights to 40 cm wavelengths to 1 7 m are probably formed by large amplitude long period surface waves generated by winter storms

age and origin of the new zealand orocline in relation to alpine fault movement the alpine fault and the recurved arc structures orocline in the late palaeozoic mesozoic rangitata orogen are two of the first order structures of the new zealand subcontinent a commonly held view is that the orocline originated as a gigantic drag fold with alpine fault movement in view of the post oligocene age of the alpine fault however this concept involving a single recurved arc cannot reconcile the two published sets of palaeomagnetic data on tectonic rotations within the rangitata orogen and its cover rocks these data indicate at least 62 of dextral rotation during each of the mesozoic rangitata orogeny and the late cenozoic kaikoura orogeny a new model presented here postulates that there are actually two dextral recurved arcs a western arc which lies mainly outside the australia pacific plate boundary zone has a multiple origin having formed chiefly during the late triassic phase of the rangitata orogeny by the subduction accretion of the exotic rakaia terrane an eastern arc coincides with the area of the present plate boundary zone it formed as a mega brittle ductile shear zone with the late cenozoic development of the modern australia pacific plate boundary which includes the alpine fault this solves the problem of the nature and location north of the alpine fault of the relative plate movement evident as 480 km of displacement on the alpine fault a major implication of this model for plate tectonic reconstruc tions of the sw pacific is that only approximately 500 km of dextral displacement has occurred through new zealand during the late cretaceous cenozoic compared with the commonly adopted figure of 1000 km

the continental collision zone south island new zealand comparison of geodynamical models and observations the south island zone of oblique continent continent convergence occurs along a 400 km long section of the modern australia pacific plate boundary zone across which about 50 km of shortening has been accommodated since about 10 ma the orogen comprises a central mountain range southern alps flanked on both sides by what are interpreted to be foreland basins two essential features that characterize the orogen are 1 the degree of denudation that accompanied deformation and 2 a fundamental structural asymmetry the architectural asymmetry of the orogen can be explained by plane strain finite element models of continental convergence incorporating mantle subduction comparison of model and orogen polarity implies that pacific plate mantle subducts the models predict two crustal scale dipping shear zones that form above the point where the pacific mantle subducts the localized one more distant from the incoming plate retro step up shear zone corresponds to the alpine fault whereas its conjugate pro step up shear zone corresponds to the distributed strain and thrusting along the eastern margin of the mountain belt parameters that modify the model boundary conditions top surface degree of denudation basal zone subduction load crust mantle velocity discontinuity subduction of lower crust mantle retreat and distributed decrease in mantle velocity and the internal strength of the crust two layer crust with moderate coupling temperature distribution strain weakening are varied in a series of numerical model calculations that establish the combination of material properties and boundary conditions that lead to different cross sectional architectures of the modeled collision zone in turn these are compared with observations about the south island orogen the calculations show how the style and extent of deformation across the whole orogen depend on the rheological properties of the crustal layer and on the balance between its internal strength and the combined effects of the boundary and gravitational stresses north to south along strike differences in the width and two dimensional architecture of the orogen simulated in the experiments by varying the model parameters can be explained by a combination of southward increases in preconvergent crustal thickness geothermal gradient convergence and potentially subduction retreat with the added possibility of a southward decrease in the component of lower crustal subduction

provenance of permian triassic and ordovician metagraywacke terranes in new zealand evidence from 40ar 39ar dating of detrital micas single crystal 40 ar 39 ar ages of detrital micas from greenland group ordovician low grade metagraywackes of the west coast south island new zealand indicate a source area having muscovite age patterns of 490 515 ma the detrital muscovite ages are characteristic of granitoid and gneiss terranes of the ross adelaide fold belt of antarctica therefore the source area for the greenland group sedimentary rocks was the immediately adjacent pacific margin of gondwana similar age determinations for rakaia terrane permian triassic torlesse supergroup metagraywackes of the wellington and canterbury regions of new zealand indicate that their source area included rocks having prominent muscovite cooling ages populations of 210 290 ma 80 and 410 460 ma 15 the torlesse detrital muscovite age data thus suggest that the source area of the metagraywackes was not within the lachlan fold belt of southeast australia and analogues in antarctica nor in the adjacent ross adelaide fold belt rather the rakaia terrane of the torlesse metagraywackes is a true suspect terrane derived from a source area within the hunter bowen fold belt of northeast australia and the immediately adjacent older orogens of eastern queensland

three dimensional critical wedges tectonics and topography in oblique collisional orogens in orogens deforming in oblique compression both the long wavelength mean topography of averaged slopes and the higher frequency topography first harmonic of valleys and ridges are related to the mechanics of deformation in three dimensions and cannot be adequately modeled in two dimensions a method of analysis of the principal stresses failure planes and topography is presented for three dimensional critical wedges in a critical coulomb orogen which is at failure throughout the components of the stress tensor are interrelated through the failure condition defined in terms of the principal stresses variation of any of the cartesian components must be accommodated by adjustment of one or more of the other components so that the orogen remains at failure this coupling of cartesian components to maintain the wedge at failure permits exploration of the behavior of a three dimensional critical orogen in which shear stresses arise outside of the plane of convergence internal adjustment of shear stresses to externally imposed stress conditions results in the formation of characteristic orogen shapes for an oblique collision zone such as the southern alps of new zealand the resultant mountain belt is one of an obliquely deforming outboard fold thrust belt with subdued relief rising abruptly into a steep backslope to the main divide which falls steeply to the indentor forming the inboard slope the outboard topographic slope is reduced in relation to that of the two dimensional orogen the rigid indentor has a fixed strike and therefore imposes a failure orientation adjacent to the indentor that differs from that of the ideal three dimensional critical wedge solution this produces several different slip orientations and minor partitioning of strain near the indentor first harmonic topography of valleys and ridges arises due to nonlinear heterogeneous behavior of both erosional and mechanical processes and is characterized by uplift controlled ridges in the outboard and incision controlled valleys in the inboard

are crustal thickness variations in old mountain belts like the appalachians a consequence of lithospheric delamination comparison of moho geometry and reflection character of active collision zones like the alps with those of fossil collision zones like the appalachians lends support for the view that lithospheric delamination is both a common and fundamentally important component of collisional orogeny in particular the relative crustal thinning commonly observed beneath the internides of old collisional orogens is an expected consequence of delamination neither precollisional crustal thickness variations nor an unrelated postcollision extensional event is required to produce this feature acceptance of the delamination hypothesis in turn fundamentally alters one s view of the tectonic evolution of old collisional orogens in the case of the appalachians delamination has direct implications for the interpretation of alleghanian granites the direction of subduction leading to final closure between laurentia and gondwana and the thermal state of the lithosphere at the onset of atlantic rifting a corollary of the delamination hypothesis is that lateral reflectivity variations cannot be used to define paleogeographic terranes in the deep crust of old orogens conversely the observation that delamination leaves a distinctive geophysical imprint on the crust itself provides an important additional clue for deciphering the tectonic evolution of such regions

thermal modeling of the southern alps new zealand finite element modeling of the thermal regime across the southern alps of new zealand has been carried out along two profiles situated near the franz josef and haast valleys the modeling involves viscous deformation beneath the southern alps including both uplift and erosion and crustal lithospheric thickening as a result of crustal shortening extending to 20 mm y of a 25 km thick crust published uplift rates and crustal thickness variations along the two profiles are used to constrain the modeled advection of crustal material and results are compared with the recent heat flow determinations 190 50 mw m2 in the franz josef valley and 90 25 mw m2 in the haast valley comparisons of the model with published k ar and fission track ages show that the observed heat flow in the franz josef valley is consistent with observed zircon fission track ages of around 1 ma if the present day uplift rate is close to 10 mm y major thermal differences between the franz josef and haast profiles appear to be due to different uplift and erosion rates there is weak evidence that frictional heating close to the alpine fault zone is not significant the modeling provides explanations for the distribution of seismicity beneath the southern alps and predicts a low surface heat flow over the eastern foothills due to the dominant thermal effect of crustal thickening beneath this region predicted temperatures at mid crustal depth beneath the zone of maximum uplift rate are 50 100 c cooler than those indicated in previously published models which implies that thermal weakening of the crust may not be the main factor causing the aseismicity of the central southern alps the results of the modeling demonstrate that the different types of reset age data in the region within 25 km of the alpine fault are critical for constraining models of the deformation and the thermal regime beneath the southern alps

source parameters of large historical 1918 1962 earthquakes south island new zealand we have studied 18 earthquakes of m w 5 5 within the north island new zealand region to determine fault parameters for earthquake hazards and regional tectonic studies since most large m w 6 5 earthquakes in the north island occurred prior to 1961 these events provide important information to supplement studies of more recent seismicity our results indicate that no large plate interface earthquakes have occurred in the central and southern north island for the past 80 years although six strike slip earthquakes of m w 6 8 occurred within the australian upper plate during an extremely active 25 year period that began in 1917 only the m w 7 2 strike slip events were associated with surface faulting indicating the difficulties that may arise in attempting to identify active faults within this region two earthquakes m w 6 9 7 1 off the northeastern north island in 1947 appear to have occurred along the plate interface and were associated with local tsunamis having runup heights of up to 10 m two m w 6 8 events also occurred within the pacific lower plate highlighting the hazards related to intraslab events slip vectors for the earthquakes studied suggest that the majority of transcurrent motion along the plate margin is accommodated within the australian plate similar to the results obtained from studies of more recent smaller earthquakes pure thrusting occurs along the plate interface and t axes of intraslab events indicate downdip tension in the pacific plate

exposed cross sections through the continental crust implications for crustal structure petrology and evolution abstract the continental crust is exposed in cross section at numerous sites on the earth s surface these exposures which appear to have formed by obduction along great faults during continental collision may be recognized by exposures of deep crustal rocks exhibiting asymmetric patterns of metamorphic grade and age across the faults and by distinctive bouguer anomaly patterns reflecting dipping basement structure and an anomalously deep mantle from an examination of five complexes which meet these criteria it is concluded that the most prominent layering in the crust is not compositional but metamorphic the lower crust consists of granulite facies rocks of mafic to intermediate composition while the intermediate and shallow levels consist predominantly of amphibolite facies gneisses and greenschist facies supracrustal rocks respectively post metamorphic granitic intrusions are common at intermediate to shallow levels position of discontinuities in refraction velocity where present commonly correspond to changes in composition or metamorphic grade with depth the continental crust is characterized by lateral and vertical heterogeneities of varying scale which are the apparent cause of the complex seismic reflections recorded by cocorp field observations coupled with geochemical data indicate a complex evolution of the lower crust which can include anatexis multiple deformation polymetamorphism and reworking of older crustal material the complexity of the crust is thus the result of continuous evolution by recycling and metamorphism through time in a variety of tectonic environments

from collision to collapse phases of lithospheric evolution as monitored by seismic records abstract deep seismic reflection profiles in europe and elsewhere cover a range of different tectonic units specifically in western and central europe they cross structures relating to the alpine variscan and caledonian orogens with considerable crustal shortening delamination and interfingering the variscan mountain belts in france and germany show collapsed structures from various collision events between 300 and 350 ma ago still further north in middle england and the southwest baltic sea traces of the caledonian collision around 400 ma and associated collapse structures are visible here the terrain east avalonia cadomia docked to the colliding continents of baltica and laurentia in a complex pattern with closing oceans and compressional boundaries which can still be seen in today s seismic sections in britain and the sw baltic sea all the processes of crustal shortening interfingering and delamination were certainly active during the compressional stages of these earlier orogens and have left their marks which are still recognizable in today s seismic image of the crust crustal roots and high elevations have disappeared in the extensional collapse phase thermal events have intruded underplated or otherwise modified the stretched lower crust in the variscan internides massif granite production started and the lower crust assumed an especially strong and thick sheared laminated structure with a plane moho the various tectonic stages are illuminated by a gross analysis of reflectivity patterns we postulate that the fate of these patterns from their origin to their death is imbedded in thermally and rheologically varying creep processes which always accompany the brittle and ductile deformation in the earth s crust

tomographic inversion of local earthquake data from the hengill grensdalur central volcano complex iceland parameters is generally low however a quantitative analysis of resolution provides an unambiguous assessment of well resolved volumes within the better resolved regions of the model the averaging volumes are 1 2 km and 2 4 km in vertical and horizontal extent respectively results of tomographic inversion image three distinct bodies of anomalously high velocity two of these extend from near the surface to a depth of about 3 km these high velocity volumes are located directly beneath the surface expressions of the extinct grensdalur volcano and the extinct husmuli basalt shield the third high velocity structure occurs in the depth range of 3 4 km but does not extend to the surface these three high velocity bodies are interpreted to be solidified magmatic intrusions relatively low velocities underlay limited portions of the trace of the present accretionary axis and a low velocity body is imaged in the roots of the active hengill volcano the volume of lower velocities located beneath the surface expression of the hengill volcano is interpreted to be a region of partial melt

pore pressure and oceanic crustal seismic structure summary marine refraction studies during the past decade have found considerable lateral variability in the seismic properties of the upper basaltic regions of the oceanic crust in many localities compressional and shear wave velocities are quite low at the top of the basalt section and velocities increase rapidly with depth it is concluded that pore pressure may be at least in part responsible for the low upper crustal velocities and contribute significantly to the lateral variability this is supported by compressional and shear wave velocity measurements as functions of confining pressure and pore pressure for basalt from the juan de fuca ridge and dolerite from the samail ophiolite oman within the oceanic crust regions of overpressure and underpressure will possess anomalous velocities the magnitude of which will depend upon the porosity and the deviation of the pore pressure from hydrostatic the influence of pore pressure on velocities is expected to diminish with depth and is unlikely to be significant at lower crustal depths where porosity is extremely low of significance poisson s ratio is shown to be dependent on pore pressure as well as confining pressure at constant confining pressure poisson s ratio increases with increasing pore pressure thus overpressured regions within the upper oceanic crust are likely to have relatively high poisson s ratios as well as low compressional and shear wave velocities

dynamics of pacific plate crust in the south island new zealand zone of oblique continent continent convergence here we analyze topographic and fission track data to quantify the response of the surface of the pacific plate in south island new zealand to late cenozoic oblique continental convergence across the alpine fault over the central 350 km length of the southern alps mountain chain we derive and map the rates of mean surface uplift the rates of working associated with mean surface uplift during the late cenozoic mountain building the amounts and rates of denudation and consequent isostatic rebound and the tectonic component of rock uplift the rate of mean surface uplift ranges from 0 3 mm yr over most of the area east of the main divide the highest rates of mean surface uplift occur to the southeast of the regions of highest mean elevation and relief the rate of working against gravity during uplift of the mean surface ranges from 2 5 mw m 2 in the southwest to 10 mw m 2in the central eastern parts of the alps areas of lower mean elevation uplifted most recently have received rates of energy input similar to that of areas of higher mean elevation where uplift started earlier the amount of denudation is large compared with the mean surface uplift and ranges from 18 km adjacent to the alpine fault to 2 km along the southeast margin of the southern alps the rate of denudation ranges from 2 5 to 0 5 mm yr with increasing distance from the alpine fault across the alps to the southeast the amount of isostatic uplift ranges from a maximum of 14 km adjacent to the alpine fault to 2 km along the southeast margin of the alps the tectonic component of uplift varies from 4 km along the alpine fault to 1 km along the eastern margin of the alps

waveform inversion of seismic refraction data and applications to young pacific crust summary we present a method for constraining the velocity depth structure in the earth using seismic refraction waveform data we test the method with synthetic data from known models and apply it to a set of data collected in 1982 june from the east pacific rise at 13 n from the magma expedition in this iterative process wkbj seismograms are computed for a starting model the difference between these and the observed seismograms is used to update the model subject to physical constraints an important first step in the inverse scheme is the linearization of the wkbj seismogram equation allowing us to compute differential seismograms partial derivatives of the synthetic seismogram with respect to specific model parameters this linearization provides the means for estimating required model perturbations based on the misfit in the seismograms the choice of a suitable numerical strategy for computing an updated model is a crucial second step in formulating a working algorithm because the data contain noise synthetic seismograms can only fit the data to this noise level in this case infinitely many models fit the data to this tolerance and some of these estimates are non physical involving negative layer thicknesses a successful strategy must choose from among these possibilities a well defined physically reasonable new model in a commonly used approach to solving non linear problems the perturbation to the starting model is minimized while improving the fit to the data after several iterations the final model which possesses no special properties still tends to resemble the starting model when used with the magma data this technique essentially does not perturb the model at all a method we find much more satisfactory involves solving for the new model directly while applying physically important constraints as constraints we require the velocity gradient remain below a fixed value and penalize the roughness of the new model we thus solve for the smoothest model fitting the data to the specified misfit

deep seismic profile across a proterozoic collision zone surprises at depth collisions between continents generate the world s most striking mountains the deep structure of these collision zones inferred from seismic reflection profiles1 3 can be equally dramatic if less well understood improved knowledge of the structure of ancient collisional belts now known to have developed through plate tectonic processes4 5 can provide important new insights into the mechanisms of crustal growth although many such belts have been partly destroyed by severe post collisional deformation6 7 or magmatism8 some have been preserved in the stable interiors of continents9 one example is the early proterozoic trans hudson orogen9 10 in western canada here we present seismic reflection images across the entire orogen which reveal a broadly symmetric structure with reflections linked to island arc rocks dipping beneath both bounding archaean cratons the observed reflection geometries imply a doubling of crustal thickness during the collision along crust penetrating faults the presence of a significant amount of archaean crust at depth the extent of which could not have been determined from surface mapping suggests the need for caution in inferring crustal growth rate from the surface area of juvenile crust11 12

spatial constrained inverse rock physics modelling predicting reservoir parameters such as porosity lithology and saturations from geophysical parameters is a problem with non unique solutions the variance in solutions can be extensive especially for saturation and lithology however the reservoir parameters will typically vary smoothly within certain zones in vertical and horizontal directions in this work we integrate spatial correlations in the predicted parameters to constrain the range of predicted solutions from a particular type of inverse rock physics modelling method our analysis is based on well log data from the glitne field where vertical correlations with depth are expected it was found that the reservoir parameters with the shortest depth correlation lithology and saturation provided the strongest constraint to the set of solutions in addition due to the interdependence between the reservoir parameters constraining the predictions by the spatial correlation of one parameter also reduced the number of predictions of the other two parameters moreover the use of additional constraints such as measured log data at specific depth locations can further narrow the range of solutions

the kinematics of the plate boundary zone through new zealand a comparison of short and long term deformations summary surveys of shear strain rates derived from repeated triangulation cover about one quarter of the area of the plate boundary zone through new zealand and are well distributed within it using a method developed by haines relating shear strains to the total strain and velocity fields the dilatational and rotational strain rates and the velocities within the deformed zone are derived the plate boundary zone is shown to be two dimensional for the most part in that gradients of the velocity along the length of the zone are small or zero the shear strain rates are not uniform however they reach a maximum along a central axis and decrease gradually to zero toward the sides nor are the two independent components of strain one involving shortening or extension perpendicular and the other shear parallel to the zone equally developed everywhere there is a clear geographic separation with shortening developed over the subduction thrust and shear developed behind in a zone of wrench faulting time variations in the strain field in part of the region above the subduction interface are related to changes in the degree of coupling across the interface a velocity field is computed the relative velocity of the two plates from this data agree very well with that derived from seafloor spreading data these strain and velocity fields derived from geodetic studies give the short term kinematics of the plate boundary zone the long term kinematics of the zone are estimated from 1 uplift and subsidence data which are related to changes in crustal thickness and hence to dilatational strain and 2 variation in the declination of primary magnetization in rocks of known age related to the rotational strain the rate of rotational strain has increased in time from about 2 to 3 myr 1 10 myr ago to about 9 myr 1 today the increase can be understood as a secondary effect of a developing compressional component increasing the coupling between the plates so that more of the motion parallel to the zone is accommodated by distributed shear and less by aseismic slip the rates of strain averaged over the last 1 myr or so and at a scale length of a few tens of kilometres are closely similar in distribution and magnitude to the strain rates derived from short term kinematics while therefore at scale lengths of a few hundred metres or so faulting is very important and the deformation is discontinuous with unstrained blocks faulted with large but uncertain slip against adjacent blocks the deformation at these longer scale lengths is continuous and regular the two consequences of this study are that 1 strain from geodetic data can be directly related to the average long term deformation and therefore can be an important tool in the study of deformation in regions of current tectonic activity and 2 at scale lengths of a few tens of kilometres the deformation of a region can be described as the deformation of a continuum and we can ignore the effects of faulting

isotopic ages from the nelson region of south island new zealand crustal structure and definition of the median tectonic zone abstract plutonic rocks in the rotoroa complex and drumduan terrane of south island new zealand yield zircon u pb dates of 156 and 142 ma respectively that are interpreted as crystallization ages hornblende and biotite 40 ar 39 ar dates of 140 130 ma from the rotoroa represent either emplacement ages cooling ages or a metamorphic resetting event these two units crop out between the brook street terrane and the separation point batholith and lack any clear affinity with tectonostratigraphic terranes of the new zealand western or eastern provinces the rotoroa complex and drumduan terrane are interpreted as part of a series of dismembered mesozoic volcanic plutonic arc complexes that are sandwiched between terranes of the western and eastern provinces occupying a structural position here referred to as the median tectonic zone mtz correlative units in fiordland on the opposite side of the alpine fault include the mackay intrusives darran complex largs terrane lochburn formation and the halfway peak gabbro farther south on stewart island the anglern complex and paterson group are part of the same structural belt the mtz is an extension of the original concept of the median tectonic line put forth by landis and coombs 1967 dismemberment and juxtaposition of arc magmatic assemblages in the mtz with western and eastern province terranes is related to large scale transcurrent faulting in the early cretaceous its essential features as a regional tectonostratigraphic terrane were established by 117 ma as indicated by stitching of the rotoroa complex to the takaka terrane western province by the separation point batholith 117 114 ma the echinus granite yields a 310 ma u pb zircon crystallization age that suggests the granite and associated gneisses are part of the western province which may constrain the position of the western margin of the mtz near nelson city

metamorphism and uplift of alpine schist in the franz josef fox glacier area of the southern alps new zealand geothermometry and geobarometry of 10 garnet oligoclase zone schists in the franz josef fox glacier area southern alps new zealand give temperatures ranging from 415 to 625 c and pressures from 5 2 to 9 2 kbar indicating a t p array of about 50 c kbar and inferred peak temperature conditions over a c 15 km thick section at depths between c 20 and 34 km the present day distribution of the schist samples implies that only about one third of the original crustal section is now exposed the garnet oligoclase zone schists represent the deeper part of a metamorphosed and deformed accretionary complex that was associated with late palaeozoic early mesozoic subduction along the gondwana continental margin partial uplift c 0 2 m ma and erosion of the complex during jurassic cretaceous times rangitata uplift was synchronous with d2 deformation and recrystallization as recorded by the p t array cenozoic kaikoura uplift and exhumation of the schist since c 30 ma to form the southern alps was associated with oblique slip movement on the alpine fault the present day position and steep eastward dip of isograds and d2 structures suggest considerable clockwise rotation during uplift associated with ductile attenuation and tectonic thinning by over two thirds of the original schist sequence largely due to simple shear along schistosity planes as the schist generally shows only incipient greenschist facies retrograde recrystallization an apparently complete although contracted prograde mineral sequence has been preserved by rapid uplift 5 km ma of hot rock and the effects of limited shear heating near the alpine fault

global earth structure inference and assessment summary a suite of compressional and shear phase arrival times p s pp pcp ss scs pkpab pkpbc pkpdf sksac and two sets of differential times ss s410s ss s660s are used to infer lateral variations in p and s velocity structure in the entire earth crust mantle and core volumetric heterogeneity is parametrized by 22 depth layers each of which is subdivided into a grid of cells in addition to volumetric hetero geneity we determine topography on the major internal velocity discontinuities station corrections event relocation parameters and inner core anisotropy a total of 96 300 unknowns the model parameters are estimated using an iterative lanczos algorithm to obtain a partial singular value decomposition a total of 5000 lanczos values and vectors are used to construct model parameter estimates as well as measures of model parameter resolution and covariance the lanczos resolution estimates provide lower bounds on conventional svd based measures throughout most of the mantle we find that regions beneath the continents particularly in the northern hemisphere are well resolved with the exception of africa velocity variations are moderately well resolved in that portion of the outer core lying beneath the continents velocity heterogeneity is poorly resolved in the inner core where cell dimensions are small and deviations in velocity heterogeneity trade off with variations in anisotropy variations in the uppermost mantle 2 3 per cent are correlated with surface tectonics while at greater depths high velocity variations coincide with regions of past and present subduction the high velocity anomalies extend into the lower mantle although with a reduced amplitude 0 5 1 0 per cent until the lowest mantle 2 5 per cent at the base of the outer core a large scale pattern of heterogeneity 0 8 per cent is observed slower at the poles in the inner core we infer a peak anisotropy of 2 3 per cent which varies laterally and with depth however the magnitude and distribution of the anisotropy trades off strongly with velocity heterogeneity

low seismic wave speeds and enhanced fluid pressure beneath the southern alps of new zealand a region of low seismic wave speed is detected beneath the central southern alps of new zealand on the basis of traveltime delays for both wide angle reflections and p waves from teleseismic events respective ray paths for these p waves are mutually perpendicular ruling out anisotropy as a cause of the delays the low speed region measures about 25 km by 40 km has a speed reduction of 6 10 and is largely above the downward projection of the alpine fault the most likely cause of the low speed zone is high fluid pressure due to excess water being released by prograde and strain induced metamorphism into the lower crust because enhanced fluid pressure reduces the work required for deformation the existence of the central southern alps low speed zone implies that this part of the australian pacific plate boundary is relatively weak

the transition from subduction to continental collision crustal structure in the north canterbury region new zealand summary the north canterbury region marks the transition from pacific plate subduction to continental collision in the south island of new zealand details of the seismicity structure and tectonics of this region have been revealed by an 11 week microearthquake survey using 24 portable digital seismographs arrival time data from a well recorded subset of microearthquakes have been combined with those from three explosions at the corners of the microearthquake network in a simultaneous inversion for both hypocentres and velocity structure the velocity structure is consistent with the crust in north canterbury being an extension of the converging chatham rise the crust is about 27 km thick and consists of an 11 km thick seismic upper crust and 7 km thick seismic lower crust with the middle part of the crust being relatively aseismic seismic velocities are consistent with the upper and middle crust being composed of greywacke and schist respectively while several lines of evidence suggest that the lower crust is the lower part of the old oceanic crust on which the overlying rocks were originally deposited the distribution of relocated earthquakes deeper than 15 km indicates that the seismic lower crust changes dip markedly near 43 s to the south west it is subhorizontal while to the north east it dips north west at about lo fault plane solutions for these earthquakes also change near 43 s for events to the south p axes trend approximately normal to the plate boundary reflecting continental collision while for events to the north t axes are aligned down the dip of the subducted plate reflecting slab pull while lithospheric subduction is continuous across the transition it is not clear whether the lower crust near 43 s is flexed or

three dimensional lateral crustal thickening in continental oblique collision an example from the southern alps new zealand summary crustal thickening in an oblique continental collision such as in the south island of new zealand necessarily involves deformation processes in three dimensions 3 d we have investigated the role played by the strength of the lower crust using simplified 3 d mechanical models these models show that crustal thickening occurs away from the area of maximum compression along an axis inclined to the plate boundary about 10 20 to the plate boundary in the case of the south island and perpendicular to the convergence direction furthermore the specific geometry of the relatively old and strong australian lithosphere versus the pacific lithosphere also controls the location of crustal thickening these conditions could explain the observed mismatch between the locations of maximum elevation and minimum gravity in south island new zealand as a consequence of decoupled deformation owing to low viscosity lower crust 1 i ntr o duction two dimensional modelling approaches for continental oblique collision implicitly assume that convergence occurs perpendicular to the plate boundary and that deformation is identical in sections perpendicular to the plate boundary however crustal and lithospheric thickening under oblique collision necessarily involve three dimensions the extra degree of freedom allows a component of lateral movement to occur the lithospheric deformation leading to the formation of the southern alps of south island new zealand demand a 3 d modelling approach here continental oblique convergence has been accommodated since about 6 ma and the topography and gravity data indicate that surface deformation and thickening at depth are geometrically offset we study the lithospheric scale deformation of the region using simple mechanical models based on the collision of two lithospheric blocks one being mechanically weaker than the other the weakest block will deform in one of two ways it can thicken vertically producing a crustal root and mountain ranges or it can spread laterally in the horizontal direction towards regions of lower compression this lateral flow away from the area of maximum compression is favoured if the weakest block is unable mechanically to support the weight of thickened material the question that we pose is if the convergence is oblique will the direction of flow remain oriented parallel to the margins of the lithospheric blocks that represent the plate boundary

porosity from seismic data a geostatistical approach using a geostatistical technique called cokriging the areal distribution of porosity is estimated first in a numerically simulated reservoir model then in an oil bearing channel sand of alberta canada the cokriging method consistently integrates 3 d reflection seismic data with well measurements of the porosity and provides error qualified linear mean square estimates of this parameter in contrast to traditional seismically assisted porosity mapping techniques that treat the data as spatially independent observations the geostatistical approach uses spatial autocorrelation and crosscorrelation functions to model the lateral variations of the reservoir properties in the simulated model the experimental root mean square porosity error with cokriging is 50 percent smaller than the error in predictions relying on a least squares regression of porosity on seismically derived transit time in the reservoir interval in the alberta reservoir a cross validation study at the wells demonstrates that the co

a focused look at the alpine fault new zealand seismicity focal mechanisms and stress observations the alpine fault is the pacific australian plate boundary in the south island of new zealand this study analyzes 195 earthquakes recorded during the 6 month duration of the southern alps passive seismic experiment sapse in 1995 1996 and two mr 5 0 earthquakes and aftershocks in 1997 which occurred close to the central part of the alpine fault precise earthquake locations are derived by simultaneous inversion for hypocenter parameters a one dimensional velocity model and station corrections together with focal mechanisms calculated using a first motion and amplitude ratio method these results provide a picture of the seismotectonics in the central south island over a 6 month period moment tensor inversions of three earthquakes provide an independent means of comparison to the focal mechanisms derived using the amplitude first motion method to validate our observations over time we compare the sapse seismicity with the seismicity recorded by the new zealand national seismic network nznsn and a local network at lake pukaki east of the southern alps 6 months versus 8 years our study indicates that the alpine fault releases elastic strain seismically from the surface down to 10 12 km depth between milford sound in the south and the hope fault in the north the seismicity rate of the alpine fault is low but comparable to locked sections of the san andreas fault with large earthquakes expected seismicity decreases north of bruce bay at the alpine fault and within a triangular region along the alpine fault located between the hope and porters pass fault zones we interpret this as the result of deformation distributed on the alpine fault and the hope and porters pass fault zones the base of the seismogenic zone is fairly uniform at 12 km 2km over large parts of the south island the high alps region has a shallower base of the seismogenic zone indicating localized elevated temperatures east of the alpine fault most of the study region deforms under a uniform stress field with a maximum principal horizontal shortening direction of 110o 120 o similar to geodetic observations and plate motions this confirms that the region is not undergoing strain partitioning the earthquake data show that the deformation away from the alpine fault is distributed on mainly nne trending thrust faults and strike slip transfer faults with a maximum seismogenic depth of 12km

deep structure of the alps what do we really know abstract in the last five decades the deep structure of the alps has been probed by every geophysical method applicable and the resulting amount of data is unmatched for any other orogen in this study an attempt is made to review the data and the proposed structural models with the aim of separating the certain from the probable and from the speculative information this can be achieved by first reviewing the theoretical resolving power and ambiguity of the applied interpretation methods and then analysing the proposed models the methods reviewed are inversion of surface wave data teleseismic and local earthquake seismic tomography near vertical reflection seismology wide angle reflection and refraction seismology and gravity modelling all information about the moho rated as certain is combined to give a moho map of the alpine area the information rated as certain and probable and additional qualitative arguments are used to discuss a crustal model of the western and central alps represented by two cross sections major structural elements in this crustal model are a thick overthrust penninic nappe system wedging at mid to lower crustal levels a discontinuous moho and strong variations along the strike of the orogen whereas the structures of the european upper crust and of the penninic nappe system are well constrained only few and isolated lower crustal structural elements are rated as certain finally the shape of the lower lithosphere in the alps is discussed by review and comparison of the results from surface wave teleseismic travel time residual and tomographic studies qualitative arguments suggest the existence of a lithospheric root or slab beneath the alps probable tomographic information suggests a south vergent european lithospheric slab beneath the southern alps and the po plain despite the considerable number of studies aimed at resolving the deepest part of alpine orogeny the available quantitative information on the sub moho structure cannot be rated as certain

three dimensional numerical experiments of strain partitioning at oblique plate boundaries implications for contrasting tectonic styles in the southern coast ranges california and central south island new zealand a three dimensional numerical model is used to investigate the nature and distribution of crustal scale deformation and strain partitioning across obliquely convergent transpressive plate boundaries a uniform elastic plastic crustal layer obeying murrell s extension to three dimensions of the griffith failure criterion was deformed under basal kinematic boundary conditions that correspond to the oblique convergence between two mantle lithospheres one of which detaches and subducts beneath the other the results show deformation concentrated in relatively narrow shear zones the character planar versus curved and dip of these shear zones or crustal scale faults depend on the relative amount of convergence versus transcurrent motion imposed across the plate boundary in models dominated by transcurrent boundary conditions two separate sets of coexisting structures develop 1 a pair of planar relatively shallow dipping thrust zones arranged in a v structure that accommodate convergent motion and 2 a set of curved near vertical strike slip zones arranged in a flower structure that accommodates the transcurrent motion in models dominated by convergence both contractional and transcurrent deformations are accommodated by oblique slip across a single pair of structures that have the same geometry as the thrust shear zones there is a gradational behavior between these end member partitioned and nonpartitioned modes for intermediate boundary conditions in all cases the dip of the shear zones predicted by the numerical model is in good agreement with the dip of ideal faults predicted by mohr s incipient faulting hypothesis the two basic modes are interpreted to underlie the contrasting tectonic styles of the southern coast ranges california and central south island new zealand factors other than obliquity of convergence which play a role in strain partitioning are discussed