thermal state of the taranaki basin new zealand the taranaki basin is an active margin basin that has been significantly affected by miocene subduction tectonics along the pacific australian plate boundary we have analyzed its present day thermal state using 354 bottom hole temperatures bhts from 115 wells distributed throughout the basin the measured temperatures were corrected using an exact solution to bullard s equation rather than the horner approximation thereby allowing for recovery dependence on well diameter and correction for some bhts at early time after circulation had ceased thermal conductivity measurements were completed on 256 samples from eight wells and matrix conductivities were determined for six end member lithologies by inversion formation conductivities are based on the conductivity and relative proportion of each end member component corrected bhts in situ thermal conductivity and estimates of sediment heat production were combined to compute the present day steady state heat flow the average heat flow is 60 mw m 2 but important geographic variations are present heat flow on the western platform is remarkably consistent at 53 60 mw m 2 attesting to its relative stability since the late cretaceous heat flow in the southern part of the basin is 65 70 mw m 2 due to as much as 3 km of late miocene erosion on the southern onshore and to the south of the peninsula heat flow is 50 3 mw m 2 possibly due to the heat sink effects of crustal thickening heat flow is highest at 74 mw m 2 on the northern peninsula adjacent to the taranaki volcanic zone suggesting a causal relationship between quaternary volcanism and high heat flow

strain partitioning in the transition area between oblique subduction and continental collision hikurangi margin new zealand spatial differences in late quaternary structural style and deformation rates indicate a complex pattern of strain partitioning within the transition area from oblique subduction beneath southern north island to oblique continental collision in northern south island new zealand the late quaternary structure of the offshore southern hikurangi margin is determined here using seismic reflection profiles mr1 side scan sonar swath images em12dual multibeam swath bathymetry and backscatter images and sediment core and dredge samples where oblique 50 subduction of the oceanic hikurangi plateau is occurring beneath southern wairarapa region the steep dissected upper margin consists of a wedge of rocks that are being deformed by strike slip and reverse faults beneath the lower margin an accretionary wedge of quaternary age has developed rapidly by frontal accretion of a thick succession of turbidites on the pacific plate estimates of late quaternary geological strain rates have been made on two margin perpendicular transects across southern north island and the offshore margin to budget the predicted nuvel 1a plate motion more than 33 55 of the total plate motion is expressed in the offshore part of the upper plate above the subduction detachment in the central hikurangi margin between 40 s and 41 s this offshore deformation could potentially include margin parallel fault slip of up to 14 15 mm yr across the upper plate strain is partitioned into zones of folding and thrust faulting and possibly more than one zone of strike slip faulting but the partitioning may be incomplete with oblique slip thrusting an important component of the deformation the wide distribution of deformation within the upper plate partially reflects strong coupling between the subducting oceanic plateau and the leading edge of the overriding plate this coupling increases toward the southwest where the continental part of the subduction zone beneath marlborough may now be inactive or very strongly coupled toward the southwest the transpressive deformation style of the upper wairarapa margin continues into the upper marlborough margin and onshore into the strike slip marlborough fault system of northern south island in contrast the accretionary wedge narrows to the southwest and terminates in southeastern cook strait approximately above the transition from subducted oceanic crust to subducted continental crust of the pacific plate farther southwest beneath the lower marlborough margin low strain folding and thrust faulting is occurring but the style of deformation is not typical of the accretionary wedge this shortening results either from a small amount of subduction slip beneath marlborough and or from contractional strain partitioned to the southeast of the continental transpression zone whereas the initial onset of continental collision occurs in marlborough the surface expression of deformation of the pacific plate occurs south of 42 30 s normal faulting of the northwestern margin of the continental chatham rise possibly reflects flexural extension of the pacific plate crust at the southern end of the subduction zone whereas folding and thrust faulting of the north canterbury coastal region results from nw se contraction of the delaminated upper crust entering the southern alps collision zone

neotectonic deformation in central eurasia a geodynamic model approach funding was granted by the spanish government through the project mite cgl2014 59516 p and alpimed piecsic 201530e082

paleostress adjacent to the alpine fault broader implications from fault analysis near nelson south island new zealand stress tensor determinations from probable mio pliocene age minor faults along the edge of the richmond block northwest of the alpine fault system of south island show pervasive thrusting rather than strike slip motion as proposed in some analyses this study with results almost identical to that of nicol and wise 1992 on the other side of the alpine marlborough fault system shows that the present pattern of regional compression at high angles to the alpine fault has persisted through much of the neogene over a width of about 150 km normal to the alpine fault zone one explanation might be san andreas type models invoking strike slip motion concentrated in fault zones by highly lubricating gouge coupled with strain partitioning to allow compression in adjacent regions to act at high angles to strike such models are difficult to apply to the new zealand example which now must include deformed forelands on either side of the zone but which shows little or no strike slip motion instead a model is proposed for a crustal scale flower structure to accommodate the along strike convergence of opposite dipping subducting plates a regional surface slab comprising marlborough and its adjacent forelands is undergoing compression normal to the strike of the system while semidetached deeper plate motion accommodates most of the fundamental converging oblique strike slip displacements

plate coupling in the northern south island and southernmost north island new zealand as illuminated by earthquake focal mechanisms subduction of the pacific plate in the northern south island and southernmost north island of new zealand is transitional insofar as the crustal thickness of the pacific plate increases significantly along strike in the northern south island focal mechanisms of 145 events shallower than 100 km in this region have been determined using both first motion polarity data and amplitudes of seismogram envelopes the stress regime in the subducted plate appears to be dominated by slab pull t axes in both the upper and lower planes of the dipping seismic zone generally parallel the local dip of the zone and the average azimuth of these t axes is rotated some 25 clockwise out of the direction of dip of the subducted plate this can be related to the asymmetrical shape of the subducted slab in contrast the stress regime in the overlying plate appears to be dominated by subhorizontal compression low angle thrust events near the plate interface in cook strait and the southernmost north island concentrate in two areas which may mark the updip and downdip edges of a locked region identified from global positioning system gps observations an absence of low angle thrust events near the plate interface in the northern south island and the tendency of p axes of events in the subducted plate to become more horizontal suggest that plate coupling there is stronger than in the southernmost north island differential coupling at the plate interface provides a viable mechanism for producing the large tectonic rotations seen in the northern south island

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

crustal structure and neotectonics of the puysegur oblique subduction zone new zealand abstract eocene oligocene rifting followed by miocene quaternary strike slip and obliquely convergent tectonics are responsible for crustal thinning in the solander basin and subsequent development of the puysegur oblique subduction zone southwest new zealand highly oblique convergence at a rate of 35 mm yr is being partitioned between oblique subduction at the puysegur trench thrusting within the trench slope strike slip faulting on the puysegur bank and minor shortening within the solander basin subduction is young and a volcanic arc is not yet well developed we present seismic reflection data recorded across the puysegur subduction zone and solander basin three strike slip fault zones are recognised on the basis of seismic and bathymetric data in the puysegur bank region north of the profile some displacement on the eastern fault is transferred eastward to the hauroko fault but most strike slip motion is inferred to be west of fiordland south of the profile strike slip faults merge with faults of the puysegur ridge active thrusting dominates the trench slope where a thick sedimentary section is evident and bottom simulating reflectors are common the relatively steep average slope angle of 6 suggests the sediments are moderately well cemented possibly similar to sediments found in the solander basin the small amount of sediment found on the subducting plate is consistent with little or no accretion at the margin patches of reflectivity we interpret as sediment at the top of the subducted plate suggest that the slab has a moderate dip of 10 20 to 20 km depth in the solander basin seismic reflection data clearly image the sedimentary section and show well developed crustal and upper mantle reflections to depths of 30 35 km 12 13 s twt on the basis of lower crustal reflectivity and gravity modelling the base of the crust beneath the adjacent stewart island shelf is at 30 km 9 s twt and rises to a depth of 20 km 8 s twt beneath the solander basin prominent dipping reflections which we interpret as an active fault can be traced to 30 km depth 12 s twt where they merge into a zone of strong reflectivity in the upper mantle

measurement and analysis of depression storage on a hillslope a precise photogrammetric technique was used to determine the microtopography of seven 2 6 m 1 2 m experimental units located on a hillslope surface elevations were determined with an accuracy of better than 1 mm from which contours at 2mm intervals were interpolated these contour plots were then manually interpreted to define depressions and associated storage volumes analysis of the results highlighted the complex variability of depression storage over the hillslope for example there being little relation between depression storage volumes and unit slope this study also highlights the sampling problem for the measurement of depression storage on natural surfaces which appears not to have been formally recognized previously and also emphasizes the practical difficulty of achieving depression storage estimates with coefficients of variation less than ten per cent to 50 per cent much of this variability being due to problems of interpretation rather than measurement of the surface

micro drilling id tims u pb dating of single monazites a new method to unravel complex poly metamorphic evolutions application to the uht granulites of andriamena north central madagascar in terranes subject to complex metamorphic evolution zircon and monazite u pb system can record successive growth and or resetting episodes conven tional isotope dilution thermal ionisation mass spec trometry id tims dating of fractions or single grains from conventionally separated zircon and monazite populations may produce inaccurate ages a new tech nique combining textural analysis and id tims dating on single monazite crystals is proposed this method is applied directly on thin sections with three successive steps comprising 1 a characterisation of textural rela tionships using electron microprobe analyses and ima ges 2 extraction by micro drilling of selected monazites and 3 u pb dating of each extracted grain by id tims the potential for this in situ dating technique are tested on ultra high temperature uht granulites from north central madagascar four dis tinct events on a single thin section were distinguished the uht metamorphism was dated at 2 5 ga while two retrogression events were dated at 790 and 500 ma finally a single crystal shielded in quartz seems to preserve a pre metamorphic age around 2 7 ga

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

variation of the present day stress field within the north german basin insights from thin shell fe modeling based on residual gps velocities abstract we present a finite element based dynamic modeling study of the recent stress conditions within the north german basin which is part of the central european basin system based on geological geophysical and geomorphological data after compilation and evaluation of existing data thin shell modeling is applied to understand the recent structural evolution of the central european basin system cebs and its transition towards the baltic shield in contrast to previous modeling approaches we include a complex pattern of major faults from the alpine front to the sorgenfrei tornquist zone stz and gps measured residual velocities to define the boundary conditions of the model major deviations of the stresses occur along strong contrasts in the lithospheric structure and influence the stress pattern significantly high intraplate compression is a responsible large scale reactivation of the faults associated with the pre existing basin framework in northern central europe with an important record on vertical motions the modeled slip subsidence rates of the faults in the north german basin are in the order of 0 01 and 0 2 mm year 1 which are in accordance with field observations because no fault exhibits large quaternary displacement rates in the study area

estimating ages of late quaternary stream terraces from analysis of weathering rinds and soils rates of growth of rock weathering rinds and rates of changes of soil morphologic and chemical properties that are calibrated at sites of known ages produce powerful tools for estimating ages of geomorphic surfaces particularly when materials datable by conventional methods are not widespread sequences of latest quaternary stream terraces from the south island of new zealand are ideally suited for application of these calibrated age techniques because climate and source materials for terrace deposits are internally consistent within two regions west land and marlborough modal and mean thicknesses of weathering rinds formed in surface cobbles of torlesse graywacke provide age estimates for latest pleistocene and holocene stream terraces in marlborough with uncertainties estimated at 5 to 40 modal rind thickness of subsurface cobbles provides age estimates for latest quaternary westland sites with uncertainties of 10 to more than 50 few dated soils are available to constrain rates of soil development in westland and marlborough furthermore soils were sampled from only one pedon on each surface morphologic data however provide least squares age estimates for westland sites with uncertainties typically greater than 100 and the calibration data can further bracket likely soil ages to less than 50 uncertainty the regression data from marlborough are less reliable but profile index ratios help bracket ages to at least 50 distributions of oxalate extractable fe and ai and total major element concentrations allow age estimates for westland and marlborough soils with uncertainties estimated at 15 to 50 despite these uncertainties the three techniques combine to provide age estimates with the high resolution needed to examine details of fault slip rates or stream downcutting the calibration data and weathering rates used herein are applicable only to the new zealand region studied although similar calibrated age techniques should provide high resolution dating in many other regions such techniques are particularly useful when multiple approaches are available to provide independent cross checks

computer simulations of california tectonics confirm very low strength of major faults recent improvements in the technique of modeling fault networks with thin plate finite elements yield full convergence of the solutions without any compromise in the representation of the frictional rheology of the upper crust or the transition to dislocation creep in the lower crust we apply these techniques to model the california region incorporating all faults with estimated slip rate over 1 mm yr as well as variations in elevation heat flow and crustal thickness velocity boundary conditions on the model sides are based on the nuvel 1 plate model and an approximation of deformation in the great basin the frictional and dislocation creep rheologic constants of the crust are calibrated to reproduce the observed variations in the maximum depth of seismicity which occurs at model temperatures of 350 410 c this leaves two free parameters the time averaged coefficient of friction on faults and the apparent activation energy for creep in the lower crust these parameters are systematically varied in three sets of 10 81 and 64 experiments respectively the predictions of each model are tested against three published data sets a set of 79 geologic limits on average slip rate on faults a set of 221 principal stress directions and a set of 841 secular rates of geodetic baselines both trilateration and vlbi very long baseline interferometry the patterns of model scores indicate that the time averaged friction coefficient of major faults is only 0 17 0 25 or only 20 30 of the value 0 85 that is assumed for the friction in the intervening blocks the laser trilateration data taken alone would indicate a preference for a high stress model but this model is one with very little fault slip and seismicity which can be rejected on other grounds in the final three parameter set of 64 models we test whether the anomalous weakness of faults is uniform or proportional to net slip with slip dependent weakening there is a general reduction in prediction errors which supports the hypothesis the geologic data and geodetic data agree in implying that fault weakness that is friction of 0 17 is general with an additional 30 slip dependent weakening of the san andreas to friction of 0 12 or 14 of normal the stress data however are fit best if all weakness is slip dependent effectively only the san andreas is weak thus the hypothesis that all weakening is slip dependent should not be rejected the best models predict all available data with rms root mean square mismatch of as little as 3 mm yr 6 of the relative plate velocity so their predictions may be useful for seismic hazard estimation at least along faults where no data are available this study extends the finding of very low friction from subduction zones where it was previously documented to a dominantly strike slip system in which underthrusting of wet sediment is not widespread return of previously subducted water from the mantle and its chemical or physical binding in fine grained gouge are possible explanations for the very low friction

present day stress field modelling of southern italy constrained by stress and gps data abstract the present day tectonic setting of the italian peninsula is very complex and involves competing geodynamic processes in this context southern peninsular italy is characterised by extension along the apenninic belt and in the tyrrhenian margin and by transpression in the apulia gargano region the extension is well defined by means of geological seismological and contemporary stress data for the latter only few data are available in the apulia gargano region leaving the state of stress in that area unresolved here we develop a finite element model of the southern italian region in order to predict the contemporary stress field our model predictions are constrained by model independent observations of the orientation of maximum horizontal stress s hmax the tectonic regime and the horizontal velocities derived from gps observations we performed a blind test with 31 newly acquired s h max orientations in the southern apennines these new data come from the analysis of orehole breakouts performed in 46 deep oil exploration wells ranging in depth from 1300 to 5500 m the model results agree with the stress data that define a prevailing nw se s h max orientation along the apenninic belt and foredeep and thus are capable to predict the stress field where no stress information is available we first analyse how much model predictions based on older data deviate from present day stress data and then recalibrate the models based on our new stress data giving insight into the resolution of both models and data in the studied region which is affected by low deformation rates we find that geodetic data alone cannot resolve such low levels of deformation due to the high relative measurement errors we conclude that both gps and stress data are required to constrain model results

abrupt strike slip fault to subduction transition the alpine fault puysegur trench connection new zealand swath bathymetry and other geophysical data collected over the fiordland margin southwest of new zealand are used to investigate the mechanism of transform subduction transition between the alpine fault and the puysegur trench two segments of the pacific australian plate boundary in this region the cenozoic southeast tasman basin which obliquely underthrusts fiordland at the puysegur trench is separated from the cretaceous tasman basin by the resolution ridge system a major lithospheric discontinuity of the downgoing plate interpretation of seafloor morphology shows that the alpine fault extends offshore along the fiordland coast and splits into west and east branches the west branch cuts obliquely across the margin and connects sharply to the puysegur subduction front at the northeastern tip of the resolution ridge system earthquake and seismic reflection data indicate that the west branch is genetically controlled by downgoing plate structures associated with the resolution ridge system hence the west branch is interpreted as the surface trace of the plate boundary segment extending between the alpine fault and the puysegur trench we conclude that the development of the strike slip segment of the plate boundary and its sharp transition to the puysegur subduction are controlled by inherited structures of the australian plate furthermore according to geophysical data presented here a tearing of the downgoing plate can be interpreted beneath the west branch a review of geophysical data along the region of the alpine fault hikurangi trough northeast new zealand shows a progressive transform subduction transition that is accommodated by motion partitioning between the subduction interface and strike slip faults this transition is accounted for by an interplate coupling that progressively increases toward the alpine fault in relation with a gradual thickening of the downgoing crust the comparison between the fiordland and the hikurangi strike slip subduction transitions show that presence of inherited downgoing plate crustal faults properly oriented with respect to the plate motion facilitates a sharp strike slip subduction transition

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

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

the motion of crustal blocks driven by flow of the lower lithosphere and implications for slip rates of continental strike slip faults geodetic measurements in actively deforming areas of the continents reveal the pattern of deformation in the lithosphere if the dominant forces acting on crustal blocks are tractions at their bases then the long term motion of each block will be given by the average velocity of the underlying lithosphere slip rates between blocks estimated in this way from recent geodetic measurements across fault zones in the south island of new zealand and southern california are in good agreement with slip rates estimated geologically

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

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

formation and suppression of strike slip fault systems strike slip faults are a defining feature of plate tectonics yet many aspects of their development and evolution remain unresolved for intact materials and or regions a standard sequence of shear development is predicted from physical models and field studies commencing with the formation of riedel shears and culminating with the development of a throughgoing fault however for materials and or regions that contain crustal heterogeneities normal and or thrust faults joints etc that predate shear deformation kinematic evolution of strike slip faulting is poorly constrained we present a new plane stress finite strain physical analog model developed to investigate primary deformation zone evolution in simple shear pure strike slip fault systems in which faults or joints are present before shear initiation experimental results suggest that preexisting mechanical discontinuities faults and or joints have a marked effect on the geometry of such systems causing deflection lateral distribution and suppression of shears a lower limit is placed on shear offset necessary to produce a throughgoing fault in systems containing preexisting structures fault zone development observed in these experiments provides new insight for kinematic interpretation of structural data from strike slip fault zones on earth venus and other terrestrial bodies

terrestrial and gps measurements of deformation across the taupo back arc and hikurangi forearc regions in new zealand geodetic measurements of deformation across the taupo back arc and hikurangi forearc regions of new zealand are derived from global positioning system gps measurements made in 1990 and 1991 and triangulation observations made in the 1920s 1950s and 1970s the gps horizontal coordinate differences have precisions of 5 6 mm and the triangulation observations have precisions of 0 7 1 2 arc sec these different kinds of observation allow simultaneous estimation of strain parameters and single epoch coordinates for a total of 184 stations at 68 of which gps observations were made under the assumption that no shift of the scale or orientation of the gps reference frame is embodied in the data from 13 gps stations within the taupo volcanic zone tvz common to the 1990 and 1991 surveys the rotational dilatational and shear components of the deformation rate tensor within the tvz can be estimated for that 1 year interval the principal extension rate from 1990 to 1991 is 0 21 0 09 10 6 yr 68 confidence at an azimuth of 124 13 corresponding to 8 4 mm yr extension over 40 km neither the orthogonal principal extension rate 0 02 0 03 10 6 yr nor the rotation rate 0 06 0 04 rad yr is significant the dilatation rate of 0 23 0 09 10 6 yr is therefore produced by uniaxial extension the data from 75 stations distributed from behind the back arc region and well into the forearc region which were surveyed in at least two of the triangulation or gps epochs between the 1920s and 1991 allow the spatial variation of the shear components of the deformation rate tensor to be estimated the maximum engineering shear rates lie in the range 0 1 0 2 10 6 yr within the tvz and maintain these values with similar orientations in the forearc region to the east the western and southern margins of active extension are reasonably well determined by changes in orientation and magnitude of the shear component these results provide confirmation of the previously less well determined deformation field and in comparison with subduction models indicate that the surface deformation is reflecting variation from north to south of coupling of the subduction plate interface and that both trench suction and gravitational collapse probably contribute to the extension in the forearc region

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

determining rheology from deformation data the case of central italy 1 the study of geodynamics relies on an understanding of the strength of the lithosphere however our knowledge of kilometer scale rheology has generally been obtained from centimeter sized laboratory samples or from microstructural studies of naturally deformed rocks in this study we present a method that allows rheological examination at a larger scale utilizing forward numerical modeling we simulated lithospheric deformation as a function of heat flow and rheological parameters and computed several testable predictions including horizontal velocities stress directions and the tectonic regime to select the best solutions we compared the model predictions with experimental data we applied this method in italy and found that the rheology shows significant variations at small distances the strength ranged from 0 6 0 2 tn m within the apennines belt to 21 6 tn m in the external adriatic thrust these strength values correspond to an aseismic mantle in the upper plate and to a strong mantle within the adriatic lithosphere with respect to the internal thrust we found that strike slip or transpressive but not compressive earthquakes can occur along the deeper portion of the thrust the differences in the lithospheric strength are greater than our estimated uncertainties and occur across the adriatic subduction margin using the proposed method the lithospheric strength can be also determined when information at depth is scarce but sufficient surface data are available

petrogenesis of tourmaline granites and topaz granites the contribution of experimental data abstract fluorine and boron are generally only minor components of granitic rocks but may be found highly concentrated in certain tourmaline granites and topaz granites up to 1 wt b2o3 and 3 2 wt f respectively studies of various examples of these granite types which occur as small bodies emplaced at shallow levels p lithostatic textural and petrographic data indicate that the tourmaline and topaz granite magmas crystallized at low to moderate temperatures below 700 c and that a fluid phase may have been present during the crystallization interval both granites varieties are peraluminous co up to 5 characterized by the presence of white micas lithium micas or muscovite aluminium silicates and other al rich minerals garnet cordierite boron and fluorine are hosted by tourmaline schorl rich member of the schorl dravite series topaz and mica respectively these granites have low ca fe mg and ti contents each the crystallization of tourmaline granite and topaz granite magmas is discussed using experimental data derived from studies of granitic systems with added boron and fluorine both elements act as a flux enabling boron and fluorine enriched melts to persist to temperatures as low as 650 c at 1 kbar in addition the effect of increasing fluorine content displaces the minimum in q ab or at ph2o 1 kbar toward the albite apex plots of fluorine rich topaz granites coincide with this trend suggesting that the role of fluorine in magmatic processes may have affected the rock composition as well as crystallization temperatures boron rich granites plot near the low ph2o minima in qz ab or suggesting that boron has less of an influence on minimum melt compositions the low temperatures of crystallization permits phases such as muscovite or andalusite topaz and two alkali feldspars to crystallize directly from f and b enriched melts at low pressures in addition the limited available experimental data are used to compare the effects of fluorine and boron on major and trace element distribution during melt vapour interaction

large tectonic rotations since the early miocene in a convergent plate boundary zone south island new zealand abstract a palaeomagnetic study in part of the new zealand plate boundary zone provides new constraints on the temporal and spatial distribution of neogene and quaternary tectonic rotations thermal demagnetization of samples from cretaceous basaltic dykes palaeocene oligocene micritic limestone and miocene and pliocene siltstones in the marlborough region south island have defined stable high temperature magnetic components which are interpreted as the primary magnetization declination anomalies after tectonic corrections are interpreted as rigid body rotations about a vertical axis of sample sites relative to the pacific plate all palaeomagnetic data from marlborough cluster into three main groups a 60 100 clockwise rotation affected palaeocene to middle miocene sedimentary sequences across marlborough between 18 ma and 8 ma coeval with a phase of low angle thrusting the absence of this rotation in a late cretaceous dyke swarm defines the present western limit of the early rotating zone a regional 20 clockwise rotation occurred in the last 4 ma during the development of the marlborough fault system in a zone of dextral transpression although locally clockwise rotations 40 may have occurred near some of the major dextral strike slip faults however a negligible rotation is observed in the same period in the region to the southeast of the major kekerengu dextral strike slip fault which appears to have acted as a hinge zone accommodating relative rotation by dextral strike slip on an arcuate fault bending and internal deformation the observed tectonic rotations record the overall clockwise rotation of the trend of the southern end of the hikurangi margin from w to nw in the early miocene to ne today determined independently from the long term relative plate motion data for the pacific and australian plates

the kinematics of northern south island new zealand determined from geologic strain rates relative motions within the distributed plate boundary zone of northern south island new zealand are determined through an inversion of geologic strain rate estimates the quaternary fault slip rate estimates define the shear strain rates and rock uplift rates provide information on the horizontal divergence rates an erosion rate to rock uplift rate ratio along with a crustal compensation factor is estimated in order to convert rock uplift rates to horizontal divergence rates because of the uncertainty in erosion rates horizontal divergence rates are given a large standard error of the three horizontal strain rate components obtained from these data completely define the horizontal velocity gradient tensor strain rate distributions are matched with spline polynomial functions which can be constrained to behave rigidly within specified regions such as the pacific or australian plates inversion of the strain rate distribution assuming uniform erosion rates across the northern south island yields a velocity field that has small differences in both magnitude 10 larger and direction with the nuvel 1a plate motion model between pacific and australian plates a revised strain rate data set obtained from a variable erosion model in which erosion rates are a linear function of the log of the average annual rainfall magnitudes yields a velocity field with expected directions that are indistinguishable from the nuvel 1a plate motion model between pacific and australian plates but velocity magnitudes are still 10 15 higher than the plate motion model therefore the average values of slip rate on strike slip faults in marlborough required by the nuvel 1a plate motion model are typically close to the low end of the published range of slip values for those structures the major strike slip structures within the marlborough region are accommodating 80 100 of the total plate motion between australia and pacific plates on northern south island as much as 20 of the relative motion could be accommodated by shear generated by folding or thrust faulting with a single orientation between the major structures the magnitude of plate motion contributed by the major faults indicates that the distributed geodetic shear strains measured across northern south island and discussed by bibby 1981 and walcott 1984 are not a form of irrecoverable strain but rather a feature of the strain field that will eventually be released primarily as concentrated slip on the strike slip structures within the region strain modeling indicates that the earthquake moment release over the last 150 years within the northwest nelson province which is west of the marlborough region is at least half an order of magnitude higher than the long term rate of moment release overall the northwest nelson region is playing only a minor role in taking up the long term plate motion

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

finite element modeling of neotectonics in new zealand 1 thin shell finite element methods that incorporate faults realistic rheology laterally varying heat flow and topography and plate velocity boundary conditions have been used to model the neotectonics of new zealand we find that new zealand s faults have effective friction of 0 17 comparable to that found in other pacific rim regions the long term average slip rate of the alpine fault varies along strike generally increasing northeastward until slip is partitioned among the strands of the marlborough system the average slip rate 30 mm yr when combined with published geodetic results and historical seismicity strongly suggests a high probability of future large earthquakes tectonic deformation of north island is controlled by a balance between differential topographic pressure and traction from the hikurangi subduction thrust the hikurangi forearc is an independent plate sliver moving relative to the pacific and australian plates there is a complicated zone of slip partitioning in the transition from the alpine fault to the puysegur trench an offshore thrust fault the southern segment of which may correspond to the waipounamou fault system parallels to the se coast of south island and needs to be included in seismic hazard estimates

origin of small scale segmentation and transpressional thrusting along the alpine fault new zealand the alpine fault is the major structural feature of the australian pacific plate boundary in the south island of new zealand geologic evidence suggests that half to three quarters of the plate boundary displacement is accommodated by movement on the fault detailed investigation of the central section of the alpine fault has revealed that it consists of oblique thrust sections striking 020 050 that are linked by subvertical right lateral faults striking between 065 and 090 the segmentation is on a scale of 1 10 km similarly oriented right lateral faults are abundant southeast of the alpine fault and are consistent with stresses induced in an elastic layer by an oblique slip ductile fault zone below propagation of the fault to the surface is predicted to result in an en echelon arrangement of strike slip and thrust segments it is suggested that the spatial distribution of segments is affected by the existence of deeply incised valleys in the hanging wall that disturb the stress field to depths of 1 4 km the segmentation is near surface and does not appear to act as a barrier to the propagation of large earthquakes

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

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

bending within the axial tectonic belt of new zealand in the last 9 myr from paleomagnetic data abstract tongaporutuan stage late miocene 11 6 myr sedimentary rocks at two localities within the axial tectonic belt of new zealand have a direction of magnetisation in which the declination is 020 11 and 030 8 d 95 the directions of magnetisation in rocks of similar age outside the belt have a declination like that of the earth s present axial dipole 360 the clockwise deviation of the declination is inferred to indicate bending of the rocks within the zone of deformation between the pacific and indian plates due to the oblique convergence of these plates

kinematic modelling of neotectonics in the persia tibet burma orogen summary we apply a new kinematic modelling technique program neokinema to estimate neotectonic flow in the persia tibet burma orogen the models fit geodetic benchmark velocities geological fault slip rates and stress directions seismic moment tensor orientations using a weightedleast squares method models predict long term velocities anelastic strain rates and preferred fault slip rates averaged over timescales of 10 4 10 6 yr while we find a few regions of low anelastic strain rate the mean continuum strain rate in the preferred model is 2 2 10 16 s 1 0 7 per cent ma 1 so the india eurasia collision should not be modelled as an interaction between rigid microplates for most faults preferred fault slip rates agree with geological slip rates within their uncertainty bounds this suggests that deformation imaged by geodesy over tens of years is consistent with deformation over 10 4 10 6 yr given appropriate elastic corrections we also calculate maps of long term average seismicity rate based on model fault slip rates and anelastic strain rates in the continuum using the seismicity parameters of most comparable type of plate boundary the pattern is generally in agreement with actual m 5 67 earthquakes in the cmt catalogue 1977 2002 except that the himalayan front high zagros and altyn tagh zones have been quieter than predicted the spatial integral of our forecast over the orogen is 371 m 5 67 earthquakes 25 75 yr versus 238 which actually occurred if this discrepancy has high significance it means that some step s in our forecast method are faulty such as the assumption of equal coupled seismogenic thickness in all continental convergent boundaries if it is only an artefact of stochastic time dependence then this may have occurred in the orogen in the external calibration region or in both independent evidence suggests that large earthquakes with many aftershocks will occur along the himalayan front in the future possibly reducing this discrepancy

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

late quaternary strike slip on the eastern part of the awatere fault south island new zealand new zealand straddles the obliquely convergent boundary between the pacific and australian plates in central south island plate motion is accommodated by oblique collision of continental crust along the alpine fault in the southern alps and in north island by subduction of oceanic crust beneath the continental hikurangi margin between these two zones oblique convergence is accommodated across the 150 km wide marlborough fault system which is transitional between the two different styles of margins dextral slip in the marlborough fault system is partitioned among four principal faults of which the awatere fault is one our data on the eastern part of the awatere fault provide insight into styles of surface faulting and active deformation in continental transpression zones we 1 document the segmentation and kinematics of oblique slip on the fault including a discrepency between long term and short term accumulation of vertical motion 2 describe an along strike gradient in the degree of slip partitioning of oblique plate motion 3 measure late quaternary strike slip rates of 6 8 mm yr at several sites along the fault rates that decrease eastward to

on depressional storages the effect of dem spatial resolution depression storage can be a significant storage element on a watershed surface accounting for the retention of much water over the past decade many models were developed to derive landscape features however relatively little is known about the impact of changing the spatial and or temporal resolutions on subsequent features in this paper the surface topography was measured with the aid of a laser scanner with millimeter resolution emphasis was laid on quantifying the effect of changing spatial resolution upon geometric properties of depressional storages digital mapping allowed the visualization of the location and topology of potential water surfaces and the manner in which water might move from one depression to another from the pond analysis and associated spatial mapping it became clear that most geometric characteristics relating to size and spatial location of depression storage including area volume and depth are scale dependent the relationship between the contributing area of each depression and the surface area of the same depression at each pour depth was established and the organization inherent in such relationship was explored furthermore it was found that these geometric objects may best be described by resorting to fractal geometry a popular tool for quantifying variability across scales

a three plate kinematic model for lau basin opening 1 we present revised compilations of bathymetry magnetization acoustic imagery and seismicity data for the lau basin and surrounds we interpret these data to more precisely locate the plate boundaries in the region and to derive a three plate kinematic model for the opening of the lau basin during the brunhes chron our tectonic model includes the niuafo ou microplate which is separated from the australian plate along the peggy ridge lau extensional transform zone central lau spreading center and from the tongan plate along the newly discovered fonualei rift and spreading center our model shows that australia tonga plate motion between 15 5 s and 19 s is partitioned across the microplate and it resolves the former apparent conflict between geodetic versus seafloor spreading velocities regionally this implies that the angular rate of opening of the lau basin has been faster than that of the havre trough to the south and that the rapid current rates of pacific subduction at the tonga trench 240 mm yr at 16 s have been sustained for at least 0 78 m y

effect of depression storage capacity on overland flow generation for rough horizontal surfaces water transfer distance and scaling overland flow triggering on rough surfaces was investigated using an understanding oriented model the model was based on conditioned walker technique and developed to simulate and analyse the evolution of puddle connection on numerically generated rough surfaces the percolation theory gave a theoretical framework to formalize model outputs and to study overland flow scaling overland flow triggering appeared consistent with a percolation process a scale change exponent was suggested new insights based on the concept of transfer distance of water were emphasized transfer distance enabled us to analyse the water redistribution inside a field and helped to define rainfall efficiency when infiltration occurred copyright 2002 john wiley sons ltd

computer simulations of alaskan neotectonics ongoing deformation and fault slip neotectonics in the alaskan bering sea region were modeled with thin plate finite element methods by computing anelastic strain rate stress and velocity fields which represent time averages over several seismic cycles models included variable crust and lithosphere thickness heat flow and elevation and incorporated all faults known or thought to be active three sets of experiments totaling 46 models were computed with systematic variations of shear traction on the megathrust fault friction within north america internal friction of lithospheric blocks and mantle creep strength model quality was scored by comparing predictions to geologic data on fault slip rates the most compressive horizontal principal stress direction and geodimeter and very long baseline interferometry vlbi baseline rates best results were obtained with a driving traction of only 10 15 mpa on the aleutian megathrust and fault friction of only 0 17 within north america this is clearly a low stress model the fanning of away from the syntaxis was reproduced but does not imply high deviatoric stress magnitudes within the north american plate the aleutian forearc west of kodiak island moves westward along strike at rates which increase to 65 mm yr 1 in the komandorsky region however no crust is presently escaping westward from the alaskan syntaxis instead it is shortened and stacked by thrusting principally in the vicinity of the chugach and wrangell mountains because stresses in this model are low and are delicately balanced against topography it is likely that the present regime represents a transient response to plio pleistocene glacial mass redistribution and differs from typical tectonic flow in the tertiary

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

local regional and plate scale sources for the stress field in the adriatic and periadriatic region abstract the stress field at a specific location is the sum of regional stress controlled by plate scale tectonic processes with local sources here we evaluate and discuss the different sources from geodynamic to local scale and the controlling factors including the jurassic paleogeography of the adriatic passive margin of present day stress in the adriatic sea and periadriatic regions of italy using two kinds of numerical models 3d mantle scale viscoelastic models and 2 5d lithosphere scale thin shell models the subcrustal stress field of the slabs in the dinarides hellenic and apennines calabrian subduction zones are characterized by downdip extension and compression respectively this difference is explained by the velocity of the adriatic slab with respect to the upper mantle in the hotspot reference frame the slab in the calabrian subduction zone is encroached and down pushed whereas the slab in the hellenic subduction zone is sustained by the mantle flow at the plate scale the upper crustal stress field at the apennines front is governed by the different nature of the lithosphere probably oceanic in the ionian sea and continental elsewhere which in turn determines first order rotations of the stress axes second order rotations of the stress axes depend on the jurassic paleogeography and consequent differential advancement of the thrust fronts with recesses and salient occurring in correspondence with jurassic structural highs and lows respectively the eastward relative motion of the mantle with respect of the lithosphere enhances the onset of nw se oriented compression within the adriatic plate consistent with observations finally 2 5d thin shell models demonstrate that present day stress does not simply follow the long wavelength pattern 500 1000 km due to plate tectonics and mantle interaction but is greatly affected by the presence of second and third order sources like crustal structure faults and topography most importantly these factors give an observable effect in data

the strength of faults in the crust in the western united states abstract the strength of secondary faults within plate boundary zones and of master faults like the san andreas has been controversial for decades we use a global finite element code with a variable resolution grid and global plate driving forces to determine whether the effective friction on the san andreas fault is high 0 6 1 intermediate 0 3 0 5 or low 0 2 whether a single value of can be used for all mapped faults within california and whether weakening of the ductile lower crust associated with faulting is important we compare our model results with existing data on fault slip rates gps velocities stress field and earthquake depth distribution the comparison indicates that all faults are weak 0 2 and that additional weakening of major faults is important all viable solutions also indicate that weakening of the lower crust below major faults is necessary the strongest faults in the region have in the range 0 2 0 05 the san andreas fault is a very weak fault among weak faults with

evolution of product phase assemblages during thermal decomposition of muscovite under strong disequilibrium conditions we investigated the thermal decomposition of muscovite in natural granite powders heated to 1175 c for durations from 5 min to 68 h at 1 bar paying special attention to the early stages of decomposition this study shows that muscovite is completely transformed after 5 min muscovite pseudomorphs consist of glass mullite and al rich oxides for short durations 5 and 40 min the al rich phase was identified by xrd electron diffraction and tem microanalysis as al 2 o 3 containing 4 8 wt feo total fe probably a few weight percents of mgo and possibly up to 10 wt sio 2 faint superstructure spots and diffuse streaks observed in electron diffraction patterns suggest vacancy or trace elements ordering in the al 2 o 3 defect spinel structure al 2 o 3 displays an unexpected acicular morphology elongated along three directions at 120 in the basal 001 musc planes and parallel to lateral faces of the former muscovite mullite forms rods elongated in the basal 001 musc planes along a direction at 90 from one set of al 2 o 3 needles the al 2 o 3 structure appears to be a metastable phase that is replaced by corundum for longer durations

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

temporal variations in latest quaternary slip across the australian pacific plate boundary northeastern south island new zealand rates of latest quaternary slip from stream terraces and moraines displaced by faults of the alpine shear system in ne south island new zealand vary in space and time detailed histories of fault slip are obtained from combining displacement data with estimates of the age of the surface from weathering characteristics precision in surface ages is 5 20 using rock weathering rinds and 15 50 using soil properties the oldest surfaces examined are 15 20 ka and have right lateral fault offsets up to 400 600 m the main faults of the in the ne south island the wairau awatere clarence hope kekerengu and porters pass faults have average latest quaternary right lateral slip rates of 3 10 5 10 7 10 25 40 5 7 and 3 4 mm yr respectively every fault has undergone a substantial decrease in lateral slip rate in the last 3 5 kyr summed across the plate boundary the average latest quaternary slip rates are comparable to long term rates of horizontal slip across the australian pacific plate boundary around 40 mm yr parallel to the boundary and rates of geodetic strain and seismic moment release over the last 50 100 years approximately the same however sums of lateral fault slip rates over the interval from 15 to 5 ka exceed the plate motions whereas late holocene lateral fault slip rates are less than half the long term average the best explanation of these variations is slip across the plate boundary is episodic varying over perhaps 5 kyr intervals this implies that 15 20 kyr is the time interval necessary to average out shorter 5 kyr episodic variations in plate boundary motions

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

rapid plate motion variations through geological time observations serving geodynamic interpretation past and current plate motions are increasingly well mapped from high temporal resolution paleomagnetic and geodetic studies revealing rapid variations that occur on short timescales relative to the time it takes for the large scale structure associated with mantle buoyancy to evolve the rates of change of plate velocities hold key information on the geodynamic tectonic and earth s surface processes that may have caused them rapid plate motion changes thus provide us with a unique opportunity to quantify the forcing associated with these processes important mechanisms capable of inducing such rapid changes include evolving plate boundary forces for example those associated with slab sinking or orogeny along convergent margins as well as temporal variations in pressure driven flow within the asthenosphere that link plate velocity variations explicitly to changes in dynamic topography here we focus on a findings from recent kinematic observations and b the quantitative framework that allows t

styles of crustal deformation in compressional orogens caused by subduction of the underlying lithosphere abstract crustal scale deformation is calculated for models in which the driving mechanism corresponds to the asymmetric detachment and underthrusting of the underlying mantle lithosphere the plane strain finite element model results provide indications of the styles of deformation to be expected in small compressional orogens in particular these styles occur where shortening of the mantle lithosphere is achieved by the nearly rigid convergence between lithospheric mantles and the subduction of one mantle beneath the other the crust is modelled using coulomb plastic frictional and thermally activated power law viscous rheologies and the effects of compositional layering and variable geothermal gradients are included results are presented for a range of models in which the strength of the coupling between the model crust and its basal boundary surface denudation partial and total subduction of the crust and compositional layering are examined the results show the development of inclined step up shear zones which are a consequence of conjugate thrusting in regions of coulomb controlled rheology these zones link to sub horizontal shear zones which occur where composition and temperature render the crust viscously weak the model strain fields are interpreted in terms of deformation on discrete planes and the seismic reflectivity fabric that may be associated with this discrete deformation finally we ask whether similar seismic reflectivity fabric can be recognized in observations from small compressional orogens

prehistoric dates of the most recent alpine fault earthquakes new zealand we use four methods to investigate the earthquake history over the past 600 yr of the central alpine fault new zealand trenches across the active fault trace at five locations identify two ruptures on the fault in the past 450 yr three other indirect indicators episodes of landsliding and aggradation dated either via 14 c or from forest establishment on the resulting surfaces and tree ring growth anomalies provide further evidence for these two earthquakes and a greater resolution in estimates of their timing and extent the most recent earthquake occurred in a d 1717 and the rupture extended over a section of fault between milford and the haupiri river a distance of 375 km about 1630 another earthquake occurred on the fault and this extended between at least the paringa and ahaura rivers 250 km regional episodes of landsliding and forest establishment provide evidence for a third earthquake at about 1460 over the same section of fault the pattern of earthquake recurrence is not regular but averages 200 yr and varies from 100 yr to at least 280 yr which is the lapsed time since the most recent rupture

evidence from gps measurements for contemporary interplate coupling on the southern hikurangi subduction thrust and for partitioning of strain in the upper plate the spatial extent and strength of contemporary coupling between the pacific and australian plates on the hikurangi subduction interface beneath the wellington region of new zealand are not well known consequently the potential for the plate interface to produce great thrust earthquakes or to load the major wellington and wairarapa faults in the overlying plate is also unknown to address these issues a gps network across the southern north island has been partially or wholly surveyed six times between 1992 and 1999 and yields well determined relative velocities between 82 points the relative velocity of the east coast with respect to the west coast across the 80 km width of the southern end of the north island is 14 mm yr 1 at an azimuth of 258 this is about one third of and closely parallel to the nuvel 1a relative velocity of the pacific with respect to the australian plate 39 4 mm yr 1 at 261 strain rate solutions indicate partitioning of contemporary strain with a 35 change in principal axis orientations across the network using elastic dislocation theory an inversion of the observed point velocities and their full variance covariance matrix determines the variation with depth of contemporary coupling at the subduction interface if uniform coupling is assumed then 100 coupling occurs from very shallow depths down to 29 1 km however if variable coupling is assumed it reaches 100 at depths between 16 and 24 km at greater depths there is a transition zone at least 20 km wide down to a depth of at least 40 km over which contemporary coupling diminishes to zero these depth ranges correlate moderately well with low angle thrust focal mechanisms recently obtained by other workers and indicate that the downdip width of the interface over which a great thrust earthquake could occur exceeds 100 km elastic dislocation models also explain the observed partitioning of strain with coulomb stress calculations indicating that the wairarapa fault is being loaded at seismogenic depths

subduction and back arc activity at the hikurangi convergent margin new zealand the hikurangi margin is a region of oblique subduction with northwest dipping intermediate depth seismicity extending southwest from the kermadec system to about 42 s the current episode of subduction is at least 16 20 ma old the plate convergence rate varies along the margin from about 60 mm a at the south end of the kermadec trench to about 45 mm a at 42 s the age of the pacific lithosphere adjacent to the hikurangi trench is not known

stress change and effective friction coefficient along the sumatra andaman sagaing fault system after the 26 december 2004 m w 9 2 and the 28 march 2005 m w 8 7 earthquakes the 2004 aceh and 2005 nias events are the two greatest earthquakes of the past 40 years with a total rupture of 1700 km long and a coseismic slip reaching up to 25 m these two earthquakes have caused large stress perturbations which significantly altered seismic activity in the sumatra andaman region using both detailed mapping of failure planes and various slip distributions we calculate this stress change along the sumatra andaman sagaing fault system from central sumatra to southern myanmar the static coulomb stress change delta cff and the observed seismic activity are in very good agreement with a coulomb index similar to 20 greater than the one obtained for random events compared to previous studies this high coulomb index confirms two important issues on the use of static stress change criterion unsuited to study near field aftershocks and only relevant for aftershocks analysis on large and mature faults at a time scale of several months the calculated delta cff distribution suggests that the 2004 and 2005 earthquakes inhibit failure on the north andaman rift and on the sagaing fault while failure is encouraged along the transform andaman zone the central andaman rift the west andaman fault the sumatra fault system and the offshore thrust faults west of sumatra island the maximum value of similar to 15 20 bar 1 5 2 mpa for delta cff is reached in the northern part of the sumatra fault system this high value together with the lack of major earthquake in the last 170 years result in a high seismic hazard for this region our results are also consistent with temporal evolution of both earthquakes location and focal mechanism prior to and after the events in particular we explain the occurrence and the mechanism of seismic swarms observed in the central andaman rift and along the west andaman fault finally our calculations reveal that the seismicity in the andaman rift zone can only be explained if mu 0 5 this result leads to two end member models one with a constant and high fault friction and one with spatial variations for which friction may depend on either the nature of the lithosphere oceanic versus continental or the fault type

seismic anisotropy beneath the lower half of the north island new zealand teleseismic scs and sks events recorded on nine broadband seismograph stations have been used to investigate seismic anisotropy beneath the lower half of the north island new zealand this area lies above the hikurangi subduction zone and the array provides ray paths which sample the mantle both above and below the slab shear wave splitting measurements give similar fast polarizations and delay times at each station the average sks fast polarization is approximately ne sw subparallel to the strike of subduction and the major geological features with an average sks delay time of 1 6 0 1 s this lack of variation in splitting parameters suggests that similar fast polarizations are found in both the mantle wedge and the subslab mantle the anisotropy in the lithospheric portion of the mantle wedge is most likely caused by the preferred orientation of olivine due to the shear deformation associated with oblique convergence any anisotropy in the slab is probably due to fossil mineral alignment anisotropy in the asthenosphere is most likely caused by the preferred orientation of olivine due to asthenospheric flow the similar ne sw fast polarizations found in the asthenosphere both above and below the slab suggest that the mantle flow is in a trench parallel direction in both regions

sequential kinetics of a muscovite out reaction a natural example a natural example of sequential kinetics for the muscovite dehydration reaction in highly deformed mylonitic gneisses is analyzed studied textures consist of deformed pegmatitic muscovite crystals surrounded by fibrolitic sillimanite tightly intergrown with biotite and with potassium feldspar in the pressure shadows potassium feldspar andalusite biotite and quartz appearing in the crystal core constitute the products of muscovite breakdown produced by topotactic replacement of muscovite within a single crystal non isochemical decomposition of muscovite is proposed in which diffusion of k outward from the crystal took place along the muscovite interlayer and shear planes parallel to 001 the chemical potential gradient calculated for k capable of producing the texture observed within the pegmatitic crystals results not only from the overstepping of the muscovite out reaction but also from the difference in free energy between andalusite and sillimanite under p t conditions where andalusite is stable the overall reaction within the andalusite stability field consists of the transformation 1 ms 1 qtz 1 and 1 kfs 1 h 2 o and of the indirect replacement 0 25 sil 0 25 and andalusite nucleation and growth took place completely inside muscovite whereas most of the potassium feldspar was produced outside preferentially at pressure shadows after out ward intracrystalline diffusion of k super and fibrolitic sillimanite dissolution in the matrix the rate limiting step of this reaction process was initially the migration rate of the muscovite andalusite and muscovite potassium feldspar interfaces however it was followed by a diffusion controlled step the change in the relative rates of the reaction mechanisms was due to the coarsening of the reaction products the low amount of energy and time required for non reconstructive transformations periodic bond chains of the tetrahedral sheet of muscovite are inherited by potassium feldspar and those of the octahedral sheet by andalusite the magnitude of the heat flow associated with a possible contact metamorphic episode and the slow diffusion of k within the crystal intracrystalline diffusion took place through a double monolayer of absorbed molecules of water approximately 10 aa localized at microcleavages produced by basal slip in the interlayer level instead of a proper lattice diffusion process the derived rate law at constant p and t considering the cases of 2 kbar and 605 degrees c and 3 kbar and 639 degrees c for the diffusion controlled process gives a time span of about 10 000 years for the growth of these metamorphic textures which seems to be a reasonable estimate for a contact metamorphic event

neotectonics and long term seismicity in europe and the mediterranean region we present a neotectonic model of ongoing lithosphere deformation and a corresponding estimate of long term shallow seismicity across the africa eurasia plate boundary including the eastern atlantic mediterranean region and continental europe gps and stress data are absent or inadequate for the part of the study area covered by water thus we opt for a dynamic model based on the stress equilibrium equation this approach allows us to estimate the long term behavior of the lithosphere given certain assumptions about its structure and physics for both land and sea areas we first update the existing plate model by adding five quasirigid plates the ionian sea adria northern greece central greece and marmara to constrain the deformation pattern of the study area we use the most recent data sets to estimate the lithospheric structure the models are evaluated in comparison with updated data sets of geodetic velocities and the most compressive horizontal principal stress azimuths we find that the side and basal strengths drive the present day motion of the adria and aegean sea plates whereas lithostatic pressure plays a key role in driving anatolia these findings provide new insights into the neotectonics of the greater mediterranean region finally the preferred model is used to estimate long term shallow seismicity which we retrospectively test against historical seismicity as an alternative to reliance on incomplete geologic data or historical seismic catalogs these neotectonic models help to forecast long term seismicity although requiring additional tuning before seismicity rates are used for seismic hazard purposes

estimation of current plate motions in papua new guinea from global positioning system observations plate tectonic motions have been estimated in papua new guinea from a 20 station network of global positioning system sites that has been observed over five campaigns from 1990 to 1996 the present velocities of the sites are consistent with geological models in which the south bismarck woodlark and solomon sea plates form the principal tectonic elements between the pacific and australian plates in this region active spreading is observed on the woodlark basin spreading centre but at a rate that is about half the rate determined from magnetic reversals the other major motions observed are subduction on the new britain trench seafloor spreading across the bismarck sea seismic lineation convergence across the ramu markham fault and left lateral strike slip across the papuan peninsula these motions are consistent with a 8 2 myr 1 clockwise rotation of the south bismarck plate about a pole in the huon gulf and a rotation of the woodlark plate away from the australian plate second order deformation may also be occurring in particular manus island and northern new ireland may be moving northward relative to the pacific plate at 5 8 mm yr 1 significant at the 95 but not at the 99 confidence level which may suggest the existence of a north bismarck plate

hope fault jordan thrust and uplift of the seaward kaikoura range new zealand in the northern south island of new zealand displacement at the pacific indian plate boundary is accommodated by the east north east striking right lateral strike slip marlborough fault system the southernmost marlborough fault is the hope fault the late pleistocene holocene horizontal slip rate on this fault is 20 25 mm yr about half of the rate of pacific australian plate motion near the eastern end of the hope fault most displacement is transferred to the north northeast striking jordan thrust but the average dip slip rate at the surface trace of this thrust is less than 4 mm yr we propose that most slip takes place on a blind thrust expressed at the surface by the fault propagation folding of the seaward kaikoura range and that the rate of uplift of this range is as high as that of the southern alps 6 to 10 mm yr the major restraining bend of the alpine fault has the same average slip rate as the wairau fault 4 6 mm yr even though the alpine fault is an east dipping reverse separation fault at the restraining bend this low slip rate results in uplift of the spenser mountains east of the bend at a rate lower than that of the southern alps and seaward kaikoura range

using microstructures and titaniq thermobarometry of quartz sheared around garnet porphyroclasts to evaluate microstructural evolution and constrain an alpine fault zone geotherm abstract interpretations of deformation processes within ductile shear zones are often based on the characterisation of microstructures preserved in exhumed rocks however exhumed microstructures provide only a snapshot of the closing stages of deformation and we need ways of understanding how microstructures change through time and at what rate this occurs to address this problem we study optical microstructures and electron backscatter diffraction ebsd data from samples of quartz layers deflected around garnet porphyroclasts which generate local stress and strain rate perturbations during mylonitic deformation in the alpine fault zone of new zealand during shearing around rigid garnet porphyroclasts quartz undergoes grain size reduction in response to locally increased stresses while c axes reveal increasing components of rhomb and prism slip reflecting a local increase in shear strain and strain rate titaniq thermobarometry and quartz microstructures suggest a rather narrow range of recorded quartz deformation temperatures around 450 500 c which we propose reflects the cessation of grain boundary migration driven deformation given that temperatures well above the brittle ductile transition for quartz 350 c are preserved we anticipate that rapid cooling and exhumation must have occurred from the 500 c isotherm ultimately we propose a modified geotherm for the central alpine fault zone hanging wall which raises the 500 c isotherm to 11 km depth near the brittle ductile transition our updated alpine fault zone geotherm implies a hotter and weaker middle to lower crust than previously proposed

two sided orogen collision and erosion from the sandbox to the southern alps new zealand in continental collision zones the indentor is of approximately the same vertical dimension as the material being deformed thereby allowing material to move over the indentor and out of the deforming orogen this simple constraint on the height of the indentor differs from that imposed by the bulldozer model of wedge deformation and results in the formation of an orogen with two opposite dipping topographic slopes these two wedges are mechanically coupled and the mechanics are strongly influenced by the erosion conditions imposed on the wedge where the growing mountains perturb prevailing moisture laden winds the erosion pattern is highly asymmetric erosional work being concentrated at the toe of the steep wedge facing the indentor the inboard wedge concentration of erosional energy results in concentration of mechanical energy in the same region and produces the distinctive geological and geophysical patterns associated with continental collision these include rapid uplift and exposure of deep crustal assemblages adjacent to the indentor accompanied by high crustal heat flow and anomalously low seismicity the outcrop pattern along the inboard wedge evolves from that of a crustal cross section currently exposed in the southern alps to one dominated by repetitive nappe structures consisting predominantly of lower crustal units as in the western alps of europe the other wedge the outboard wedge undergoes relatively little erosion is broad with a more gentle surface slope and maintains an outcrop pattern consisting of upper crustal material

fault slip rates for the active external dinarides thrust and fold belt 1 we present estimates of slip rates for active faults in the external dinarides this thrust and fold belt formed in the adria eurasia collision zone by the progressive formation of ne dipping thrusts in the footwalls of older structures we calculated the long term horizontal velocity field slip rates and related uncertainties for active faults using a thin shell finite element method we incorporated active faults with different effective fault frictions rheological properties appropriate geodynamic boundary conditions laterally varying heat flow and topography the results were obtained by comparing the modeled maximum compressive horizontal stress orientations with the world stress map database the calculated horizontal velocities decrease from the southeastern external dinarides to the northwestern parts of the thrust and fold belt this spatial pattern is also evident in the long term slip rates of active faults the highest slip rate was obtained for the montenegro active fault while the lowest rates were obtained for active faults in northwestern slovenia low slip rates influenced by local active diapirism are also characteristic for active faults in the offshore central external dinarides these findings are contradictory to the concept of adria as an internally rigid aseismic lithospheric block because the faults located in its interior release a part of the regional compressive stress we merged the modeling results and available slip rate estimates to obtain a composite solution for slip rates

the last 25 ma of rotational deformation in part of the new zealand plate boundary zone abstract the marlborough fault system is a zone of dextral transpression in continental crust and marks the southern end of the hikurangi subduction system between the obliquely convergent australian and pacific plates detailed mapping over an area of 100 km2 has revealed a complex history of deformation during the last 25 ma the development of a thrust belt in the miocene referred to as d1 deformation was synchronous with the deposition of a thick submarine fan complex the beginning of d1 deformation may mark the initiation of the subduction zone in this part of the plate boundary zone subsequently in the plio pleistocene the region formed a zone of dextral shear marked by major strike slip faults and zones of distributed deformation referred to as d2 deformation crustal blocks less than 5 km across may have rotated ca 60 clockwise about vertical axes relative to the pacific plate in the last 4 ma the pattern of deformation during the last 10 ka to 100 years is consistent with the long term d2 deformation and suggests that large crustal blocks resting on the subducted pacific plate have rotated clockwise about vertical axes relative to the pacific plate accommodated by dextral shear further to the sw in the marlborough fault system the overall effect of the deformation has been the rotation of the edge of the southern part of the hikurangi margin from a w to nw trend in the early miocene to a ne trend today

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

the velocity field along the san andreas fault in central and southern california the velocity field within a 100 km broad zone centered on the san andreas fault between the mexican border and san francisco bay has been inferred from repeated surveys of trilateration networks in the 1973 1989 interval the velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the san andreas fault in the transverse ranges of southern california across strike profiles of the fault parallel component of velocity exhibit the expected sigmoidal shape whereas across strike profiles of the fault normal component of velocity are flat and featureless no significant convergence upon the fault is observed even along the big bend sector of the fault simple dislocation models can explain most of the features of the observed velocity field but those explanations are not unique about 35 mm yr of relative plate motion is accounted for within the span of the trilateration networks geologic studies indicate that the secular slip rate on the san andreas fault is about 35 mm yr the agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes the relative motion observed across the san andreas fault 35 mm yr plus that observed across the eastern california shear zone 8 mm yr accounts for most 43 mm yr of the observed north america pacific relative plate motion 47 mm yr