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

subducted sediments upper plate deformation and dewatering at new zealand s southern hikurangi subduction margin abstract the southern end of new zealand s hikurangi subduction margin accommodates highly oblique convergence between the pacific and australian plates we carry out two dimensional 2d seismic reflection tomography and pre stack depth migrations on two seismic lines to gain insight into the nature of subducted sediments and upper plate faulting and dewatering at the toe of the wedge we also investigate the ne to sw evolution of emergent upper plate thrust faulting using 47 seismic lines spanning an along strike distance of 270 km the upper sequence of sediments that ultimately gets subducted the mes sequence has an anomalously low seismic velocity character at the southwestern end of the margin 150 km east of kaik ura the mes sequence has experienced greater compaction for an equivalent effective vertical stress than it has some 200 km further to the northeast this difference is likely attributable to greater horizontal compression in the southwest caused by impingement of the chatham rise on the deformation front relationships between velocity and effective vertical stress suggest that the mes sequence is well drained in the vicinity of frontal thrusts corroborated by evidence for upper plate dewatering along those thrusts effective drainage of the mes sequence likely promotes interplate coupling on the southern hikurangi margin the decollement is generally hosted near a seismic reflector known as reflector 7 east of kaik ura however reflector 7 becomes accreted indicating that subduction slip at the southwestern end of the margin is no longer hosted at or above this reflector instead the decollement steps down to a deeper stratigraphic level further inboard further to the sw approximately in line with the lower kaik ura canyon the offshore manifestation of subduction driven compression ceases

the tectonic history of drake passage and its possible impacts on global climate this study provides an integrated review of plate tectonic models of the evolution of the antarctica patagonia connection compared to geological records collected on land in patagonia and tierra del fuego and offshore along the northern edge of the scotia sea a temporal framework for the sedimentary and tectonic events of the north scotia ridge and tierra del fuego is constructed with additional data compiled from entire patagonia and the austral basin this review provides robust correlations of seaways and tectonic events along the scotia and south america plates and indicates that the opening of the drake passage was not steady state since ca 30 ma rather the regions forming the present day northern limit of this gateway experienced important paleogeographic changes from deep marine basins to shallow ridges and emerged regions during the late oligocene and early middle miocene time our compilation of geological data shows that emergence along the north scotia ridge and tierra del fuego was achieved at 23 22 ma and has been followed by elimination of the patagoniano sea in patagonia starting at 22 23 ma and achieved at 20 ma this transition towards more continental sedimentation in southern south america is correlated with more shallow marine conditions in the austral basin this succession of events had a strong influence on the general geometry of the drake passage corresponding to a constriction of its northern limit starting in the window 29 22 ma and achieved at 21 ma this period of active deformation in southern south america also corresponds to a period of the global climate having two anomalies well known from the isotopic records the late oligocene warming around 26 ma and the mid miocene climatic optimum which ended between 15 and 14 ma the possible effects of the post oligocene tectonic evolution of the drake passage region on general oceanic circulation are discussed causes for the synchronicity between tectonic events and these global warming events are examined

geometry of the hikurangi subduction thrust and upper plate north island new zealand 1 we use 2800 line km of seismic reflection data to map the offshore character and geometry of the hikurangi subduction thrust and outer forearc wedge to depths of 15 km for 200 km along strike south of hawke bay the subduction thrust is relatively smooth dips less than 8 and the wedge is characterized by accretion of young sediment and topographic slopes of less than 3 in hawke bay and north for 200 km a kink in the subduction thrust is apparent with a downdip increase in dip to angles greater than 8 at depths of 10 15 km there is a corresponding steepening of the topographic slope to greater than 3 outboard of the kink and the wedge is characterized by lithified sedimentary rock and slope failure the kink in the subduction thrust is a locus of inherent weakness in the subducting slab we suggest its occurrence relates to a northward increase in subduction rate that controls initial slab dehydration and fluid release rates and hence intraslab deformation patterns the subduction thrust geometry in combination with a northward increase in subducting plate roughness and decrease in the amount of sediment accreted causes the observed spatial change in character of the subduction thrust and forearc wedge

thermal evolution of the new zealand hikurangi subduction margin impact on natural gas generation and methane hydrate formation a model study abstract we present an integrated 2d model of thermal and microbial generation of methane migration into the gas hydrate stability zone hsz and formation of methane hydrates the model reconstructs the shallow 0 20 km thermal structure of the subduction interface between the australian plate and the subducting pacific plate and the trench basin pegasus basin modelled temperatures of less than 110 c within pegasus basin constrain the generation of oil and gas whilst a cool thermal regime is predicted to limit thermogenic generation of gas to a burial depth of 10 km it extends the interval where prolific microbial gas generation occurs the modelled rate of microbial generation of methane increases beneath the hsz and peaks at 1600 m below seafloor diffusive upward migration of microbially generated methane is interpreted to lead to widespread methane hydrate formation and the presence of a semi continuous bottom simulating reflector bsr predicted average hydrate saturation within the hsz is 0 9 for a modelled sedimentary organic matter content of 0 5 and 1 6 for 1 organic matter in fine grained pegasus basin sediments considerably higher concentrations of methane hydrate of up to 20 70 are predicted to occur where gas migration is focussed within the frontal anticline and proto thrust zone southeast of the modern accretionary wedge and in channel and basin floor sandstones related to the hikurangi channel the hikurangi channel sedimentary system transported coarse clastic sediments eroded from the rising southern alps along the eastern margin of the pegasus basin since the miocene it provides carrier beds specifically for transport of thermogenic gas generated close to the subduction interface a buried mesozoic accretionary wedge originating from subduction of the pacific plate beneath gondwana further focusses the migration of gas focussed migration of thermogenic gas leads to the highest predicted hydrate concentrations in potential channel sand reservoirs

geological controls on focused fluid flow through the gas hydrate stability zone on the southern hikurangi margin of new zealand evidenced from multi channel seismic data highly concentrated gas hydrate deposits are likely to be associated with geological features that promote increased fluid flux through the gas hydrate stability zone ghsz we conduct conventional seismic processing techniques and full waveform inversion methods on a multi channel seismic line that was acquired over a 125 km transect of the southern hikurangi margin off the eastern coast of new zealand s north island initial processing employed with an emphasis on preservation of true amplitude information was used to identify three sites where structures and stratal fabrics likely encourage focused fluid flow into and through the ghsz at two of the sites western porangahau trough and eastern porangahau ridge sub vertical blanking zones occur in regions of intensely deformed sedimentary layering it is interpreted that increased fluid flow occurs in these regions and that fluids may dissipate upwards and away from the deformed zone along layers that trend towards the seafloor at eastern porangahau ridge we also observe a coherent bottom simulating reflection bsr that increases markedly in intensity with proximity to the centre of the anticlinal ridge 1d full waveform inversions conducted at eight points along the bsr reveal much more pronounced low velocity zones near the centre of the ridge indicating a local increase in the flux of gas charged fluids into the anticline at another anticline western porangahau ridge a dipping high amplitude feature extends from the bsr upwards towards the seafloor within the regional ghsz 1d full waveform inversions at this site reveal that the dipping feature is characterised by a high velocity zone overlying a low velocity zone which we interpret as gas hydrates overlying free gas these results support a previous interpretation that this high amplitude feature represents a local up warping of the base of hydrate stability in response to advective heat flow from upward migrating fluids these three sites provide examples of geological frameworks that encourage prolific localised fluid flow into the hydrate system where it is likely that gas charged fluids are converting to highly concentrated hydrate deposits

continental extension of the pacific plate at the southern termination of the hikurangi subduction zone the north mernoo fault zone offshore new zealand a complex transition from subduction at the hikurangi margin to transpressive continental collision across the southern alps occurs in the ne south island region of new zealand offshore the southern limit of oceanic subduction is constrained by the chatham rise a submerged continental plateau on the pacific plate which is presumably too buoyant for normal subduction in the nw corner of the rise is the north mernoo fault zone nmfz a 100 by 300 km region of basement involved active normal faulting of late miocene circa 8 6 ma to recent age the nmfz evolved contemporaneously with the rotation and development of the adjacent plate boundary zone growth faulting is characteristic within the sedimentary cover which is generally less than 2 km thick but the distribution of faulting has varied temporally the amount of mid pliocene recent extension is estimated to be not more than a few percent the nmfz consists of an array of overlapping south dipping normal faults which are typically 2 5 km apart and which trend roughly e w at a high angle to the plate boundary zone late quaternary surface traces are widely distributed on the mid to upper continental slope but many surface scarps are poorly preserved due to extensive erosion of the seafloor the western end of the fault zone crosses submarine canyons at the southern end of the hikurangi trough and almost abuts two fold and thrust fault systems on the ne south island continental margin although few data constrain the kinematics of extension a single mw 6 1 earth quake at the western end of the nmfz suggests planar rotating faults with a component of left lateral oblique slip two possible models of regional extension are considered 1 lateral buckling of the upper crust in which faulted slivers of crust are peeled off as the chatham rise slides past the transpressive marlborough fault system toward the southern alps and 2 flexure of the edge of continental pacific plate as the chatham rise is bent downward into the southern end of the hikurangi subduction zone improved seismological data and deep crustal seismic reflection profiles may help to constrain the kinematics of deformation

asymmetry and anisotropy of microwave backscatter at low incidence angles this paper presents the first results from a study of upwind downwind asymmetry uda and upwind crosswind anisotropy uca of the ku band radar backscatter at low incidence angles 0 to 18 from satellite observations incidence angle wind speed and sea state dependence were a particular focus data were obtained from the ku band hh polarized precipitation radar data in the tropical rainfall mapping mission colocated with measurements from buoys it is shown that there is a statistically significant directional signal in the uda and uca data when the radar incidence angle is greater than 5 in particular a higher radar backscatter was observed from the downwind as opposed to the upwind look direction this is contrary to scatterometer measurements at moderate incidence angles as a whole the main trends for these negative asymmetries increase the absolute magnitudes with increasing wind speed this uda is explained by the use of non gaussian statistics of the sea surface slope by contrast there is a change in behavior of the uca of microwave backscatter at a critical wind speed of about 6 to 8 m s the magnitude of uca apparently decreases with increasing wind speed below this wind speed range and then it increases for higher wind speeds sensitivities to both incidence angle and sea state are also analyzed

time dependent modeling of slow slip events and associated seismicity and tremor at the hikurangi subduction zone new zealand we present a time dependent slip model of 12 slow slip events sses occurring in the hikurangi margin of new zealand during 2010 and 2011 this model is obtained by inverting daily gps solutions from geonet s continuous gps network on the north island and northern south island we compare the properties of these sses to observations in japan cascadia and mexico and find that hikurangi sses have comparatively large amounts of slip up to 27 cm high slip rates up to 1 4 cm d and a large range of depths 10 40 km durations 7 270 days and sizes mw 5 9 6 9 we further investigate the relationship between the cape turnagain sse and an associated seismic swarm and find that observations are consistent with stress triggering outside the slowly slipping region however other explanations cannot be ruled out we also compare slip during the long term manawatu sse with the tremor epicenters found by ide 2012 and note that tremor locations are offset in the downdip direction relative to the slipping region similar to observations in the bungo channel of japan and guerrero mexico

fluid accumulation along the costa rica subduction thrust and development of the seismogenic zone in 2011 we acquired an 11 55 km 3 d seismic reflection volume across the costa rica margin nw of the osa peninsula to accurately image the subduction thrust in 3 d to examine fault zone properties and to infer the hydrogeology that controls fluid accumulation along the thrust following processing to remove water column multiples noise and acquisition artifacts we constructed a 3 d seismic velocity model for kirchhoff prestack depth migration imaging images of the plate boundary thrust show high reflection amplitudes underneath the middle to lower slope that we attribute to fluid rich poorly drained portions of the subduction thrust at 5 km subseafloor beneath the upper slope the plate interface abruptly becomes weakly reflective which we interpret as a transition to a well drained subduction thrust mineral dehydration during diagenesis may also diminish at 5 km subseafloor to reduce fluid production and contribute to the downdip change from high to low amplitude there is also a layered fabric and systems of both thrust and normal faults within the overriding plate that form a plumbing system faults commonly have fault plane reflections and are presumably fluid charged the faults and layered fabric form three compartmentalized hydrogeologic zones 1 a shallow ne dipping zone beneath the slope 2 a steeply sw dipping zone beneath the shelf slope break and 3 a ne dipping zone beneath the shelf the more direct pathway in the middle zone drains the subduction thrust more efficiently and contributes to reduced fluid pressure elevates effective stress and creates greater potential for unstable coseismic slip

polynostratigraphy and palaeoenvironments across the oligocene miocene boundary within the centinela formation southwestern argentina abstract palynological analysis of the centinela formation exposed in the foothills of the patagonian andes has revealed the presence of pollen dinoflagellate cysts and chlorococcalean and prasinophycean algae these groups are here reported from the centinela formation for the first time sporomorph and dinoflagellate cyst assemblages suggest a late oligocene and early miocene age these results coincide with a 87 sr 86 sr age close to the age of the oligocene miocene boundary obtained from the lower part of the section palynological information from the centinela formation permits correlation with upper oligocene and lower miocene units cropping out along the atlantic patagonian coast assemblages from the lower part of the section suggest that the beds were deposited under marine near shore palaeoenvironmental conditions with a strong continental influence in the middle part of the section high dinoflagellate cyst ratios coincide with a maximum flooding surface recorded in the centinela formation towards the top of the centinela formation the sporomorph assemblages reflect the development of vegetation adapted to coastal environments which agrees with the sparse occurrence of marine palynomorphs a new dinoflagellate species hystrichostrogylon sulcatum is proposed this species appears to range across the oligocene miocene boundary and is particularly abundant in the lowest miocene

tomographic evidence for hydrated oceanic crust of the pacific slab beneath northeastern japan implications for water transportation in subduction zones 1 we estimate detailed seismic velocity structure around the pacific slab beneath northeastern japan by double difference tomography a remarkable low velocity zone with a thickness of 10 km which corresponds to much hydrated oceanic crust is imaged coherently along the arc at the uppermost part of the slab the zone gradually disappears at depths of 70 90 km suggesting the occurrence of intensive dehydration reactions there the concentration of intraslab earthquakes at these depths supports dehydration embrittlement hypothesis as a mechanism for generating intraslab earthquakes a low velocity zone imaged immediately above the slab at depths 70 km probably reflects a hydrous layer that absorbs water expelled from the slab and carries it to deeper depths along the slab our observations suggest that an along arc variation in arc volcanism might be related to that in the development of the hydrous layer above the slab

elevated fluid pressure and extreme mechanical weakness of a plate boundary thrust nankai trough subduction zone pore fluid pressure is a key parameter governing both the shear strength of faults and the conditions for seismic and tsunamigenic slip on subduction zone megathrusts however quantitative constraints on this parameter based on in situ data in these or any faults have proven elusive using seismic interval velocities derived from a three dimensional seismic reflection survey we compute porosity fluid pressure and effective stress at the plate interface in the nankai trough subduction zone offshore southwestern japan to 20 km down the fault dip using well constrained locally calibrated empirical relationships between velocity porosity and effective stress we show that the fault and immediately subjacent footwall are nearly undrained implying that the subduction megathrust slips under a shear stress of

mapping sea surface oil slicks using radarsat 2 quad polarization sar image 1 polarimetric sar decomposition parameters average alpha angle and entropy h are estimated for oil slick contaminated sea surfaces and slick free conditions using a radarsat 2 quad polarization sar image the values of h and within oil slick areas are significantly higher than those of the ambient sea surface indicating the dominance of bragg scattering for the slick free ocean and non bragg scattering for the oil slick area in land classification the conformity coefficient is often used to discriminate surface scattering with double bounce or volume scattering based on this rationale we also develop a method using as a logical scalar descriptor to map oil slicks under low to moderate wind conditions the proposed method is assessed using a radarsat 2 quad polarization sar image of oil slicks in the gulf of mexico analysis shows that when is positive the sea surface is slick free whereas is negative for oil slick areas this method provides a simple and effective mapping technique for oil slick detection

a magneto and chemostratigraphically calibrated dinoflagellate cyst zonation of the early palaeogene south pacific ocean abstract investigation of the early palaeogene palaeoecological and palaeoclimatological evolution of the polar regions is hindered by the absence of calcite microfossils in sedimentary archives which are conventionally the main dating tool to overcome this problem we have generated large datasets of organic dinoflagellate cyst dinocyst assemblages from southern ocean shelf sediments over the past decade and we here calibrate these to the geomagnetic polarity time scale gpts using magnetostratigraphy and stable isotope stratigraphy this now for the first time allows a high resolution southern pacific ocean dinocyst zonation for the late palaeocene to late eocene 58 36 million years ago ma we compile published dinocyst chronologies from ocean drilling program odp hole 1171d on the south tasman rise hole 1172a d on the east tasman plateau and integrated ocean drilling program iodp hole u1356a on the wilkes land margin correlation to dinocyst zonations from new zealand lead to revisions of the magnetostratigraphic age model at holes 1171d and 1172a d stable carbon and oxygen isotope records reveal the stratigraphic location of the palaeocene eocene thermal maximum 56 ma and the middle eocene climatic optimum 40 ma respectively the resulting zonation consists of thirteen dinocyst zones calibrated to the geomagnetic polarity time scale gpts of vandenberghe et al 2012 which can likely be applied to the entire southern ocean finally we apply the revised stratigraphy to all published tex86 data a biomarker based proxy for sea surface temperature sst from odp site 1172 to assess long term climate evolution this shows that southwest pacific sst trends mimic the global compilation of benthic foraminiferal oxygen isotopes even better than previously appreciated

velocity determination for pore pressure prediction overpressured formations exhibit several of the following properties when compared with a normally pressured section at the same depth dutta 2002 1 higher porosities 2 lower bulk densities 3 lower effective stresses 4 higher temperatures 5 lower interval velocities and 6 higher poisson s ratios

splay fault branching from the hikurangi subduction shear zone implications for slow slip and fluid flow gns science s mbie funded contracts grant number co5x1204 and c05x0908 gas hydrates resources marsden fund project grant number gns0902

climatic and ecologic changes during miocene surface uplift in the southern patagonian andes abstract the up to 4 km high southern patagonian andes form a pronounced topographic barrier to atmospheric circulation in the southern hemisphere westerlies and cause one of the most drastic orographic rain shadows on earth geologic data imply that this climatic pattern has been established or significantly enhanced during miocene surface uplift of this andean segment we report evidence for important climatic and ecologic changes in the eastern foreland of the patagonian andes that appear to be the result of this uplift to provide constraints on miocene plant ecosystems and precipitation in the eastern leeward foreland of the patagonian andes we determined carbon and oxygen isotope values of pedogenic carbonate nodules from a 500 m thick section of the continental santa cruz formation the age of these deposits was constrained by ar ar dating of intercalated tuffs which range from 22 to 14 ma at 16 5 ma the 13 c values increase by 3 the 18 o values decrease by 2 and the scatter in the oxygen isotope data increases significantly we interpret these changes as the consequence of 1 km surface uplift in this andean segment from the 18 o values and increased aridity to its east from the 13 c values and the increased scatter in the 18 o values sediments overlying the santa cruz formation are very limited in extent and volume and dominated by coarse conglomerates related to pleistocene and older glaciations it thus seems that by 14 ma deposition in the eastern foreland of the southern patagonian andes had essentially ceased as the result of rain shadow formation

subduction evolution and mantle dynamics at a continental margin central north island new zealand 1 central north island new zealand provides an unusually complete geological and geophysical record of the onset and evolution of subduction at a continental margin whereas most subduction zones are innately two dimensional north island of new zealand displays a distinct three dimensional character in the back arc regions specifically we observe mariana type subduction in the back arc areas of central north island in the sense of back arc extension high heat flow prolific volcanism geothermal activity and active doming and exhumation of the solid surface evidence for emplacement of a significant percent of new lithosphere beneath the central north island comes from heat flux of 25 mw km of strike of volcanic zone and thinned crust underlain by rocks with a seismic wave speed consistent with underplated new crust seismic attenuation qp 1 is high 240 and rhyolitic and andesitic volcanism are widespread almost complete removal of mantle lithosphere is inferred here in pliocene times on the basis of the rock uplift history and upper mantle seismic velocities as low as 7 4 0 1 km s in contrast southwestern north island exhibits chilean type back arc activity in the sense of compressive tectonics reverse faulting low heat flow thickened lithosphere and strong coupling between the subducted and overriding plates this rapid switch from mariana type to chilean type subduction occurs despite the age of the subducted plate being constant under north island moreover stratigraphic evidence shows that processes that define the extensional back arc area the central volcanic region are advancing southward into the compressional system wanganui basin at about 10 mm yr we link the progression from one system to another to a gradual and viscous removal of thickened mantle lithosphere in the back arc regions thickening occurred during the miocene within the taranaki fault zone the process of thickening and convective removal is time and temperature dependent and has left an imprint in both the geological record and geophysical properties of central north island which we document and describe

correlated transient fluid pulsing and seismic tremor in the costa rica subduction zone continuous measurements of fluid flow were made over a six month period across the nicoya peninsula costa rica pacific convergent margin utilizing osmotically driven fluid flow meters designed to quantify both inflow and outflow rates on the order of 10 5 to 3 cm d significant transience in flow was observed through the surface of the forearc three periods of correlated flow signals were seen on the subduction forearc among three instruments located in the out of sequence thrust oost zone over along margin strike distances of 30 km amplitudes of ground velocity recorded on collocated ocean bottom seismometers obs increase during the three correlated flow events the seismic signal has frequency characteristics that resemble volcanic and non volcanic tremor we hypothesize that repeated plate boundary slow slip events potentially originating at the up dip limit of the seismogenic zone generate the observed signals within the toe of the forearc we propose a model in which the poro elastic stress strain field around a series of creep dislocations simultaneously forces flow through fracture networks in the forearc and oceanic basement rocks and induces diffuse flow through the shallow sediments the former generates the seismic tremor like noise recorded by the obss and the latter generates the flow transients recorded by the fluid flow meters we suggest that high sensitivity fluid flow meters can be utilized to detect transient tectonic strain events in offshore environments where traditional geodetic techniques lack resolution or are not possible d 2005 elsevier b v all rights reserved

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

evolution of fluid expulsion and concentrated hydrate zones across the southern hikurangi subduction margin new zealand an analysis from depth migrated seismic data identification of methane sources controlling hydrate distribution and concentrations in continental margins remains a major challenge in gas hydrate research lack of deep fluid samples and high quality regional scale seismic reflection data may lead to underestimation of the significance of fluid escape from subducting and compacting sediments in the global inventory of methane reaching the hydrate zone the water column and the atmosphere the distribution of concentrated hydrate zones in relation to focused fluid flow across the southern hikurangi subduction margin was investigated using high quality long offset 10 km streamer pre stack depth migrated multichannel seismic data analysis of low p wave velocity zones bright reverse polarity reflections and dim amplitude anomalies reveals pathways for gas escape and zones of gas accumulation the study shows the structural and stratigraphic settings of three main areas of concentrated hydrates 1 the opouawe bank dominated by focused periodic fluid input along thrust faults sustaining dynamic hydrate concentrations and gas chimneys development 2 the frontal anticline with a basal set of protothrusts controlling permeability for fluids from deeply buried and subducted sediments sustaining hydrate concentrations at the crest of the anticline and 3 the hikurangi channel with buried sand dominated channels hosting significant amounts of gas beneath the base of the hydrate zone in sand dominated channels gas injection into the hydrate zone favors highly concentrated hydrate accumulations the evolution of fluid expulsion controlling hydrate formation offshore southern hikurangi is described in stages during which different methane sources in situ buried and thermogenic have been dominant

focussed fluid flow on the hikurangi margin new zealand evidence from possible local upwarping of the base of gas hydrate stability the southern hikurangi subduction margin is characterized by significant accretion with predicted high rates of fluid expulsion bottom simulating reflections bsrs are widespread on this margin predominantly occurring beneath thrust ridges we present seismic data across the porangahau ridge on the outer accretionary wedge the data show high amplitude reflections above the regional bsr level based on polarity and reflection strength we interpret these reflections as being caused by free gas we propose that the presence of gas above the regional level of bsrs indicates local upwarping of the base of gas hydrate stability caused by advective heatflow from upward migrating fluids although we cannot entirely rule out alternative processes simplified modelling of the increase of the thermal gradient associated with fluid flow suggests that funnelling of upward migrating fluids beneath low permeability slope basins into the porangahau ridge would not lead to the pronounced thermal anomaly inferred from upwarping of the base of gas hydrate stability focussing of fluid flow is predicted to take place deep in the accretionary wedge and or the underthrust sediments above the high amplitude reflections sediment reflectivity is low a lack of lateral continuity of reflections suggests that reflectivity is lost because of a destruction of sediment layering from deformation rather than gas hydrate related amplitude blanking structural permeability from fracturing of sediments during deformation may facilitate fluid expulsion on the ridge a gap in the bsr in the southern part of the study area may be caused by a loss of gas during fluid expulsion we speculate that gaps in otherwise continuous bsrs that are observed beneath some thrusts on the hikurangi margin may be characteristic of other locations experiencing focussed fluid expulsion

oil slick observation at low incidence angles in ku band on the 20 april 2010 the oil platform deep water horizon in the gulf of mexico suffered an explosion during the final phases of drilling an exploratory well as a result an oil film covered the sea surface area of several thousand square kilometers in the present paper the data of the ku band precipitation radar which operates at low incidence angles were used to explore the oil spill event the two scale model of the scattering surface was used to describe radar backscatter from the sea surface the algorithm for retrieval of normalized radar cross section at nadir and the total slope variance of large scale waves compared to the wavelength of electromagnetic wave 22 mm was developed for the precipitation radar swath it is shown that measurements at low incidence angles can be used for oil spill detection this is the first time that the dependence of mean square slope of large scale waves on wind speed has been obtained for oil slicks from ku band data and compared to mean square slope obtained by cox and munk from optical data

a numerical study of the southwestern atlantic shelf circulation stratified ocean response to local and offshore forcing 1 this article discusses the results of a suite of numerical simulations of the oceanic circulation in the southwestern atlantic shelf region that are aimed to characterize its mean circulation and seasonal variability and to determine the dynamical mechanisms controlling them our experiments indicate that south of 40s the mean circulation is dominated by a general northeastward flow in the southern portion of the shelf which is controlled by the discharges from the magellan straits tidal mixing wind forcing and the offshore influence of the malvinas current farther north the region from 40 st o 33s presents the highest seasonal variability with intrusions of cold sub antarctic waters

hydrogeology and mechanics of subduction zone forearcs fluid flow and pore pressure at subduction zones fluid flow pore pressure and tectonic processes are tightly interconnected excess pore pressure is driven by tectonic loading and fluids released by mineral dehydration and it has profound effects on fault and earthquake mechanics through its control on effective stress the egress of these overpressured fluids which is in part governed by the presence of permeable fault zones is a primary mechanism of volatile and solute transport to the oceans recent field measurements new constraints gained from laboratory studies and numerical modeling efforts have led to a greatly improved understanding of these coupled processes here we summarize the current state of knowledge of fluid flow and pore pressure in subduction forearcs and focus on recent advances that have quantified permeability architecture fluxes the nature and timing of transience and pressure distribution thus providing new insights into the connections between fluid metamorphic mechanical and fault slip proc

diverse slow slip behavior at the hikurangi subduction margin new zealand 1 the installation of a continuous gps cgps network in new zealand since 2002 has enabled the discovery of 15 slow slip events at the hikurangi subduction margin our analysis and interpretation of the cgps data reveal a marked diversity in characteristics of slow slip events sses in the north island with durations varying from 6 days to 1 5 years equivalent moment release between mw 6 3 7 2 and recurrence intervals of repeating sses on the order of 2 years to more than 5 years the duration and magnitude characteristics of hikurangi sses appear to be related to the depth where they occur the deepest longest duration and largest sses occur at the southern hikurangi margin near the downdip limit of deep down to 40 km depth strong interseismic coupling the shallowest shortest duration smallest and most frequent sses occur at the northern and central hikurangi margin near the downdip limit of unusually shallow 10 15 km depth interseismic coupling the direction of slip on the interface in the hikurangi sses is consistent with slip partitioning at the hikurangi subduction margin we also show that moment accumulation rates on the interface for the time periods between sses are 40 higher than for the period of more than a decade averaging through the sses indicating that sses compose a major portion of the overall moment release budget of the hikurangi subduction interface

fluid budgets along the northern hikurangi subduction margin new zealand the effect of a subducting seamount on fluid pressure we estimate fluid sources around a subducted seamount along the northern hikurangi subduction margin of new zealand using thermomechanical numerical modelling informed by wedge structure and porosities from multichannel seismic data calculated fluid sources are input into an independent fluid flow model to explore the key controls on overpressure generation to depths of 12 km in the thermomechanical models sediment transport through and beneath the wedge is calculated assuming a pressure sensitive frictional rheology the change in porosity pressure and temperature with calculated rock advection is used to compute fluid release from compaction and dehydration our calculations yield more precise information about source locations in time and space than previous averaged estimates for the hikurangi margin the volume of fluid release in the wedge is smaller than previously estimated from margin averaged calculations 14 m3 yr 1 m 1 and is exceeded by fluid release from underlying subducting sediment 16 m3 yr 1 m 1 clay dehydration contributes only a small quantity of fluid by volume 2 m3 yr 1 m 1 from subducted sediment but the integrated effect is still significant landward of the seamount fluid source terms are used to estimate fluid pressures around a subducting seamount in the fluid flow models using subducted sediment permeability derived from porosity and testing two end members for decollement permeability models in which the decollement acts as a fluid conduit predict only moderate fluid overpressure in the wedge and subducting sediment however if the subduction interface becomes impermeable with depth significant fluid overpressure develops in subducting sediment landward of the seamount the location of predicted fluid overpressure and associated dehydration reactions is consistent with the idea that short duration shallow slow slip events sses landward of the seamount are caused by anomalous fluid pressures alternatively it may result from frictional effects of changing clay content along the subduction interface

nonlinear variations of the physical properties along the southern ecuador subduction channel results from depth migrated seismic data abstract we use two high quality pre stack depth migrated multichannel seismic profiles acquired to quantify physical properties variations of underthrust sediments along the first 30 km of subduction off the erosional southern ecuadorian margin seismic data show three zones along the subduction channel referred to as zones i ii and iii characterized by distinct velocity and velocity derived physical properties which are in agreement with values estimated from experimental results of deformation in granular media these three zones result from transformational changes of underthrust sediments governed by fundamentally different physical processes that control their mechanical behavior at increasing confining pressures based on our observations and its comparison with experimental results we argue that the transformations undergone by underthrust sediments as they dip into the subduction zone are the following within zone i progressively increasing velocity and decreasing velocity derived porosity indicates continuous sediment compaction which must be accompanied by effective fluid drainage along the decollement and or across the accretionary wedge the underthrust material is here unconsolidated from a mechanical point of view laboratory experiments indicate that the dominant processes at this range of pressures are grain rolling particle rotation and frictional slip at grain contacts within zone ii velocity and porosity remains constant for 16 km sis 72 and 12 km sis 18 this suggests undrained conditions resulting in growing fluid overpressure at the subduction channel grain deformation is similar to zone i within zone iii velocity increases and porosity falls rapidly indicating sediment compaction and subsequent release of over pressured fluids where grain deformation is likely to be elastic this might be the dominant process until the grains attain their crushing strength resulting in granular cataclasis and eventually in the collapse of the system we suggest that over pressured fluid release may induce hydrofracturation and it is likely to increase inter plate coupling down from zone iii

the application of sea wave slope distribution empirical dependences in estimation of interaction between microwave radiation and rough sea surface the use of hydrological surface wind and sea wave slope dependences for the calculation of microwave characteristics of the ldquoocean atmosphererdquo system by kirchhoff method is discussed here as an important example we review results of our experiment on bistatic sensing of the sea surface in this experiment the sun is a powerful natural source of microwave radiation noise for the sea surface sensing for the receiving of solar radiation in the region of quasi specular scattering three two polarization radiometers 0 8 2 25 and 6 0 cm are used the results of joint hydrological and radiometric experiments wind speed from 0 to 15 m s are reported as a result the improved quantitative model for microwave 3 50 ghz band radiometric calculations in remote sensing of the ldquoocean atmosphererdquo system is presented

a two way nested simulation of the oceanic circulation in the southwestern atlantic this article presents the results of a high resolution 1 12 two way nested simulation of the oceanic circulation in the southwestern atlantic region a comparison between the model results and extant observations indicates that the nested model has skill in reproducing the best known aspects of the regional circulation e g the volume transport of the acc the latitudinal position of the bmc the shelf break upwelling of patagonia and the zapiola anticyclone sensitivity experiments indicate that the bottom stress parameterization significantly impacts the mean location of the brazil malvinas confluence and the transport of the zapiola anticyclone the transport of the brazil current strengthens during the austral summer and weakens during the austral winter these variations are driven by the wind stress curl over the southwestern atlantic the variations of the transport of the malvinas current are out of phase with those of the brazil current most of the seasonal variability of this current is concentrated in the offshore portion of the jet the inshore portion has a weak seasonality that modulates the magnitude of the patagonian shelf break upwelling using passive tracers we show that most of the entrainment of deep waters into the shelf occurs in the southernmost portion of the patagonian shelf and along the inshore boundary of the brazil current shelf waters are preferentially detrained near the brazil malvinas confluence consistent with previous studies our simulation also shows that south of 42 s the malvinas current is composed of two jets which merge near 42 s to form a single jet farther north

velocity porosity relationships for water saturated siliciclastic sediments seeking a global empirical relationship between compressional wave velocity and porosity for siliciclastic sediments we have brought together an extensive suite of both new and published log and core based data we undertook a detailed statistical analysis of ocean drilling program data from amazon fan to examine variables affecting compressional velocity in shallow unconsolidated sediments we identify three dominant variables porosity shale fraction and consolidation history and present two empirically determined boundary curves one for normally consolidated sediments and a second for highly consolidated environments e g accretionary prisms these two empirical relationships predict the compressional velocity of siliciclastic sedimentary rocks with water filled pores as a function of porosity and clay content for the full range of observed porosities velocities of siliciclastic sedimentary rocks decrease rapidly with both increasing porosity and increasing clay content at fractional porosities higher than about 0 4 fluid dominates the elastic properties and velocity exhibits a subtle dependence on porosity remarkably the amazon fan data show that clay content has no direct influence on velocity at high porosities both clay content and sorting do indirectly affect velocity through their control of porosity burial affects velocity not only by compaction related porosity decrease but also by pressure induced increase of intergrain coupling because of the sensitivity of velocity to consolidation history particularly at intermediate fractional porosities of about 0 30 0 40 no single velocity porosity relationship can apply to all high porosity sediments the two proposed relationships fit the majority of published and new data they are applicable however only for normally pressured in situ conditions and water filled pores

velocity porosity relationships in smectite rich sediments shikoku basin japan 1 at the nankai trough japan smectite rich sediments of the shikoku basin are both underthrust beneath and frontally accreted to the outer accretionary wedge to understand the changes that occur in the physical properties of sediments as they are underthrust or incorporated into the accretionary wedge it is necessary to characterize those physical properties outboard of the deformation front one key relationship to constrain is between the compressional wave velocity vp and porosity in order to estimate pore fluid pressure and determine the strength of fault rocks at depth here we investigate how the type of clay minerals and proportions of the different clays may affect the velocity porosity relationship with particular emphasis on the abundance of hydrous smectitic clays using data from iodp sites c0011 and c0012 in the shikoku basin we demonstrate that when the core based porosity is corrected for the abundance of smectite the resultant velocity porosity relationship does not fit previously established transforms therefore we propose a new empirical relationship for the smectite rich sediments of the shikoku basin and caution against the indiscriminate use of global and or pre existing models in smectite rich formations

breaking a subduction termination from top to bottom the large 2016 kaikōura earthquake new zealand abstract subduction systems globally terminate allowing plate motion to be transferred from the oceanic megathrust onto continental and or oceanic transform faults the mechanism of this kinematic transition over earthquake timescales is however poorly understood due to a lack of relevant data here we study the 2016 mw 7 8 kaik ura earthquake in new zealand the first large instrumentally recorded earthquake across a subduction termination to investigate this transfer mechanism in detail we find that the kaik ura earthquake unlike standard subduction earthquakes globally involved a predominance 80 of coseismic slip on upper plate faults and minor triggered slip on the underlying oceanic subduction thrust in the months following the earthquake the subduction thrust accommodated most of the earthquake s afterslip down dip of its co seismic rupture zone this top down strain release mechanism is in accord with local geological geodetic and historical seismicity data which suggest that the bulk of plate convergence 75 is accommodated in the upper plate we suggest therefore that this alternative strain release mechanism which is distinct from standard plate boundary earthquakes is characteristic of subduction terminations and results in the majority of seismic tsunami hazard being on steep near surface faults

simultaneous long term and short term slow slip events at the hikurangi subduction margin new zealand implications for processes that control slow slip event occurrence duration and migration 1 we document a sequence of simultaneous short term and long term slow slip events sses at the hikurangi subduction zone during the 2010 2011 period the sequence of short term events each 2 3 weeks in duration ruptured much of the shallow plate interface 15 km at central and northern hikurangi over a 6 month period was accompanied by microseismicity and involved patchy irregular migration of sse slip we suggest that the patchy migration of the short term sse is due to large scale 100 3500 km heterogeneities on the plate interface related to seamount subduction and sediment subduction and or underplating this is in contrast to a 2010 2011 long term sse at the central hikurangi margin which evolved steadily over 1 5 years and ruptured much of the plate interface between 20 and 70 km depth we suggest that the occurrence of long term versus short term sses at hikurangi is related to differences in effective normal stresses and relative heterogeneity of the subduction interface the long term sse sequence began 1 year before the short term sequence coulomb stress change models suggest that the long term sse may have triggered initiation of the subsequent short term sse sequence initiation of the short term sequence occurred in a region just updip of or within an interseismically locked portion of the plate interface and may be located within the updip transition from seismic to aseismic behavior alternatively it could be characteristic of a region undergoing partial interseismic coupling this is in contrast to sses observed elsewhere in the world that typically occur within the downdip transition from seismic to aseismic behavior

hydrologic detection and finite element modeling of a slow slip event in the costa rica prism toe 1 we investigate transient fluid flux through the seafloor recorded near the costa rica trench during the 2000 costa rica seismogenic zone experiment using a 2 d fully coupled poroelastic finite element model we demonstrate that the observed hydrologic anomalies are consistent with a model of propagating slow slip at the subduction interface between the frontal prism and downgoing plate there are two sources of volumetric strain that drive fluid flux at the seafloor in response to fault slip at depth 1 compression and dilation in the vicinity of the tips of a slipping patch and 2 extension and compression due to flexure of the seafloor the superposition of these two effects results in distinctive spatial and temporal patterns of fluid flow through the seafloor in a forward modeling approach time series from shear ruptures with a range of fault length to depth ratios in a heterogeneous crust are generated and compared with flow rate observations assuming a constant propagation rate and an elliptical profile for the distribution of slip along the decollement the set of model predictions enables us to infer the probable rupture location extent propagation velocity and duration from a single flow rate time series the best fit model suggests that the slow slip event initiated within the toe at a depth of less than 4 km and propagated bilaterally at an average rate of 0 5 km d 1 this interpretation implies that stress in the shallow subduction zone is relieved episodically furthermore the costa rica data suggest that episodic slow slip events may initiate in the prism toe without being triggered by a seismic event further downdip

tectonic and geological framework for gas hydrates and cold seeps on the hikurangi subduction margin new zealand the imbricated frontal wedge of the central hikurangi subduction margin is characteristic of wide ca 150 km poorly drained and over pressured low taper not vert similar 4 thrust systems associated with a relatively smooth subducting plate a thick trench sedimentary sequence not vert similar 3 4 km weak basal decollement and moderate convergence rate not vert similar 40 mm yr new seismic reflection and multibeam bathymetric data are used to interpret the regional tectonic structures and to establish the geological framework for gas hydrates and fluid seeps we discuss the stratigraphy of the subducting and accreting sequences characterize stratigraphically the location of the interplate decollement and describe the deformation of the upper plate thrust wedge together with its cover sequence of miocene to recent shelf and slope basin sediments we identify approximately the contact between an inner foundation of deforming late cretaceous and paleogene rocks in which widespread out of sequence thrusting occurs and a 65 70 km wide outer wedge of late cenozoic accreted turbidites although part of a seamount ridge is presently subducting beneath the deformation front at the widest part of the margin the morphology of the accretionary wedge indicates that frontal accretion there has been largely uninhibited for at least 1 2 myr this differs from the offshore hawkes bay sector of the margin to the north where a substantial seamount with up to 3 km of relief has been subducted beneath the lower margin resulting in uplift and complex deformation of the lower slope and a narrow 10 20 km active frontal wedge five areas with multiple fluid seep sites referred to informally as wairarapa uruti ridge omakere ridge rock garden and builders pencil typically lie in 700 1200 m water depth on the crests of thrust faulted anticlinal ridges along the mid slope uruti ridge sites also lie in close proximity to the eastern end of a major strike slip fault rock garden sites lie directly above a subducting seamount structural permeability is inferred to be important at all levels of the thrust system there is a clear relationship between the seeps and major seaward vergent thrust faults near the outer edge of the deforming cretaceous and paleogene inner foundation rocks this indicates that thrust faults are primary fluid conduits and that poor permeability of the cretaceous and paleogene inner foundation focuses fluid flow to its outer edge the sources of fluids expelling at active seep sites along the middle slope may include the inner parts of the thrust wedge and subducting sediments below the decollement within anticlinal ridges beneath the active seep sites there is a conspicuous break in the bottom simulating reflector bsr and commonly a seismically resolvable shallow fault network through which fluids and gas percolate to the seafloor no active fluid venting has yet been recognized over the frontal accretionary wedge but the presence of a widespread bsr an extensive protothrust zone 200 km by 20 km in the hikurangi trough and two unconfirmed sites of possible previous fluid expulsion suggest that the frontal wedge could be actively dewatering there are presently no constraints on the relative fluid flux between the frontal wedge and the active mid slope fluid seeps article outline

variations in temperature gradients identify active faults in the oregon accretionary prism abstract a multi channel seismic survey mcs yields high resolution images of geologic structures within the oregon accretionary prism in addition to revealing the internal geometry of the prism a prominent bottom simulating reflector bsr provides indirect estimates of temperature gradients the bsr marks the phase transition within the pore space of the sediments of small amounts of solid gas hydrate above the reflector to free gas below although the absolute value of temperature gradients depends on assumptions of gas hydrate stability conditions velocity functions and seafloor temperature relative differences reflecting regional trends and local anomalies are unaffected by the assumptions involved in calculation of temperature gradient from the position of the bsr broad scale landward decreases in temperature gradient reflect the increasing depth to the oceanic crust across the accretionary prism correlation of anomalously high temperature gradients with two out of sequence thrusts indicates that these structures are currently acting as conduits for warm fluids

relationships between ku band radar backscatter and integrated wind and wave parameters at low incidence angles by using ten years of collocated precipitation radar and buoy data the relationships between ku band normalized radar cross section and integrated wind and wave parameters e g significant wave height wave period wave steepness and wave age at low incidence angles are analyzed for different sea states using correlation and dependence analysis the results show that the relationships are significantly different for different sea states second the potential for inverting these parameters directly from a single is investigated the results reveal that the retrieval of wind speed above 10 m u10 is most suitable for a nonpure swell sea and that the performance of significant wave height hs retrieval decreases with the ratio of swell to wind waves for wave period and wavelength a feasible inversion can only be performed for a wind wave dominated sea wave steepness a is strongly correlated with in all sea states and can even be higher than that for u10 in pure swell seas it is suggested from the present data set that real wave age may be retrieved from a swell dominated sea and therefore has a low value cutoff furthermore the extent to which u10 retrieval depends on sea state is examined by calculating the correlation coefficient between residuals and various standard wave parameters and then by determining the partial correlation coefficient between and each wave parameter controlled by u10 both results indicate that wind direction is better taken into account above 13 5 moreover an auxiliary parameter related to wave slope such as wave steepness would help to improve retrieval performance significant wave height data are of secondary use but an implementation with real wave age information might not significantly improve wind speed retrieval to improve the performance of hs and wave period retrieval auxiliary information such as wind speed wave steepness or wave age is needed finally multivariable empirical models are proposed

inherited structural control from repeated cretaceous to recent extension in the north mernoo fault zone western chatham rise new zealand abstract the active north mernoo fault zone nmfz is the youngest of three discrete phases of basement involved extensional faulting to deform the northwestern corner of the continental chatham rise since the cretaceous the first two phases inferred to be of late cretaceous and eocene age respectively were both part of widespread extensional systems that developed over most of the chatham rise region the third phase the late miocene to recent nmfz developed on the northwestern corner of the rise as a consequence of the interaction between the chatham rise plateau and the southern end of the hikurangi subduction zone a study of seismic reflection data from the northwestern chatham rise has revealed 1 1 the detailed structure that relates to each phase of normal faulting 2 2 the patterns of fault reactivation during successive episodes of extension 3 3 the significant structural control that older deformational fabrics have had on the development of the nmfz during the late cretaceous phase of extension two major fault bounded half grabens together with other smaller basins developed beneath the upper continental slope these e w trending s dipping faults are inferred to have accommodated about 2 7 km of horizontal extension across a 30 km wide region the early cenozoic extensional system reactivated some cretaceous half graben structures but mainly formed new faults with similar geometry in crust north of the cretaceous structures the early cenozoic faults are inferred to have accommodated about 1 4 km of horizontal extension across a 60 km wide region the late cenozoic nmfz also reactivated some of the cretaceous normal faults and almost all of the major early cenozoic normal faults in this region in addition many new extensional structures developed and produced an e w to wnw ese trending southward dipping domino style array of faults up to 100 km in width although the density of faults in the nmfz is greater than that of the two previous extensional systems to include this region the total horizontal extension since late early pliocene times is estimated to be no more than 3 km the common reactivation of old normal faults during the late cenozoic development of the nmfz indicates a significant level of structural inheritance from the previous episodes of extension to effect the region furthermore the parallelism between the newly developed faults and the older two extensional systems suggests that the normal faults could be reactivating structures in the torlesse terrane basement which in turn relate to an early mesozoic phase 100 ma of accretionary tectonics the kinematics of active extension within the nmfz is therefore likely to be influenced by the pre existing structural discontinuities that resulted from a history of poly phase deformation

the kinematics of a transition from subduction to strike slip an example from the central new zealand plate boundary 1 we develop a kinematic model for the transition from subduction beneath the north island new zealand to strike slip in the south island constrained by gps velocities and active fault slip data to interpret these data we use an approach that inverts the kinematic data for poles of rotation of tectonic blocks and the degree of interseismic coupling on faults in the region convergence related to the hikurangi subduction margin becomes very low offshore of the northern south island indicating that in this region the majority of the relative plate motion has been transferred onto faults within the upper plate as suggested by previous studies this result has implications for understanding the likely extent of subduction interface earthquake rupture in central new zealand easterly trending strike slip faults such as the boo boo fault are the key features that facilitate the transfer of strike slip motion from the northern south island faults further north into the southern north island and onto the hikurangi subduction thrust our results also indicate that the transition from rapid forearc rotation adjacent to the hikurangi subduction margin to a strike slip dominated plate boundary with negligible vertical axis rotation in the south island occurs via a crustal scale hinge or kink in the upper plate compatible with paleomagnetic and structural geological data despite the ongoing tectonic evolution of the central new zealand region our study highlights a remarkable consistency between data sets spanning decades gps thousands of years active faulting data and millions of years paleomagnetic data and bedrock structure

integrated stratigraphy and paleontology of the lower miocene monte leon formation southeastern patagonia argentina unraveling paleoenvironmental changes and factors controlling sedimentation abstract marine sedimentary rocks of the lower miocene monte leon formation of southeastern patagonia austral basin argentina are important geological archives for better understanding regional tectonics paleoenvironments oceanography and climate in this paper we describe assemblages of invertebrates palynomorphs foraminifera ostracods and calcareous nannofossils in a stratigraphical and sedimentological framework which suggest deposition during a transgressive regressive cycle from base to top the lowermost outcropping deposits of the punta entrada member represent an inner shelf environment formed during a transgressive phase the zone of maximum flooding is marked by a high diversity of protoperidiniaceans heterotrophic and offshore dinoflagellate cysts an increase in the percentage and size of planktonic foraminifera and a decrease in shallow water benthic foraminifera regressive deposits in the upper part of the punta entrada member exhibit a progradational stratal stacking pattern and are characterized by an upward decrease in bioturbation and in the content of marine invertebrates the dinoflagellate cyst assemblages point toward shallower and more restricted marine conditions than in underlying deposits the cycle ends with the monte observacion member which contains an impoverished and mostly reworked fauna of invertebrates the presence of monospecific reefs of crassostrea orbignyi the decrease in dinoflagellate cysts and calcareous microfossils diversity and the increase of continental palynomorphs suggest progressively shallower conditions and increasing influence of freshwater discharge although eustatic controls could have contributed to the sedimentary evolution of the monte leon formation the upward regressive trend is interpreted as the result of tectonism linked to the andean orogeny which led to the uplift exhumation and erosion of the highlands in the west this is supported by the abundance of pyroclastic material together with reworked specimens of upper cretaceous forams and upper cretaceous and middle eocene dinoflagellate cysts in the upper part of the punta entrada member and in the monte observacion member