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

relocation and assessment of seismicity in the iran region summary more than 2000 instrumentally recorded earthquakes occurring in the iran region during the period 1918 2004 have been relocated and reassessed with special attention to focal depth using an advanced technique for 1 d earthquake location a careful review of starting depths association of teleseismic depth phases and the effects of reading errors on these phases are made and when necessary waveforms have been examined to better constrain ehb focal depths uncertainties in ehb epicentres are on the order of 10 15 km in the iran region owing to the earth s lateral heterogeneity and uneven station distribution uncertainties of reviewed ehb focal depth estimates are on the order of 10 km as compared to about 4 km for long period p and sh body waveform inversions nevertheless these ehb depth estimates are sufficiently accurate to resolve robust differences in focal depth distribution throughout the iran region and within their errors show patterns that are in agreement with the smaller number of earthquakes whose depths have been confirmed by body wave modelling or local seismic networks the importance of this result is that future earthquakes with apparently anomalous depths can easily be identified and checked if necessary most earthquakes in the iranian continental lithosphere occur in the upper crust with the crustal shortening produced by continental collision accommodated entirely by thickening and distributed deformation in the zagros mountains nearly all earthquakes are confined to the upper crust depths 20 km and there is no evidence for a seismically active subducted slab dipping ne beneath central iran by contrast in southeastern iran where the arabian seafloor is being subducted beneath the makran coast low level earthquake activity occurs in the upper crust as well as to depths of at least 150 km within a northward dipping subducting slab near the oman line a region transitional between the zagros and the makran seismicity extends to depths of up to 30 45 km in the crust consistent with low angle thrusting of arabian basement beneath central iran in north central iran along the alborz mountain belt seismic activity occurs primarily in the upper crust but with some infrequent events in the lower crust particularly in the western part of the belt the talesh where the south caspian basin underthrusts nw iran earthquakes that occur in a band across the central caspian following the apscheron balkhan sill between azerbaijan and turkmenistan have depths in the range 30 100 km deepening northwards these are thought to be connected with either incipient or remnant northeast subduction of the south caspian basin basement beneath the east west trending apscheron balkhan sill curiously in this region of genuine mantle seismicity there is no evidence for earthquakes shallower than 30 km

comparison of magnitude estimates for new zealand earthquakes moment magnitude local magnitude and teleseismic body wave magnitude new zealand is one of the more seismically active countries in the world with more than 15 000 earthquakes located each year routine moment tensor analysis of regional seismic data for earthquakes with moment magnitude m w 3 5 4 0 has recently been implemented in new zealand nearly 330 regional moment tensor rmt solutions have been calculated for earthquakes in the new zealand region dating back to late 2003 this complements local magnitude m l the primary magnitude calculated by geonet in new zealand the rmt catalog along with 155 global centroid moment tensor global cmt catalog solutions is used to compare m w with m l for new zealand earthquakes in addition to m w and m l there are more than 330 teleseismic body wave magnitude m b values available from the united states geological survey and international seismological center catalogs for events that also have an m w these are used to examine the relationship between m w m l and m b for new zealand earthquakes there is a clear distinction in the relationship of m l to m w for shallow focus 33 km depth and deep focus 33 km depth earthquakes shallow focus earthquakes show m l to be fairly consistent with m w particularly for events with m w 4 5 and with graphic 1 deep focus earthquakes have m l consistently larger than m w more than a full magnitude unit for some events with graphic 2 m w and m b are in fairly good agreement regardless of the depth whereas m b estimates are consistently smaller than m l for deep events this suggests that m l is overestimated for deep focus events and that the large m ls are not the result of physical properties of the source 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif

itrf2008 plate motion model 1 the itrf2008 velocity field is demonstrated to be of higher quality and more precise than past itrf solutions we estimated an absolute tectonic plate motion model made up of 14 major plates using velocities of 206 sites of high geodetic quality far from plate boundaries deformation zones and glacial isostatic adjustment gia regions derived from and consistent with itrf2008 the precision of the estimated model is evaluated to be at the level of 0 3 mm a wrms no gia corrections were applied to site velocities prior to estimating plate rotation poles as our selected sites are outside the fennoscandia regions where the gia models we tested are performing reasonably well and far from gia areas where the models would degrade the fit antarctica and north america our selected velocity field has small origin rate bias components following the three axis x y z respectively 0 41 0 54 0 22 0 64 and 0 41 0 60 95 per cent confidence limits comparing our model to nnr nuvel 1a and the newly available nnr morvel56 we found better agreement with nnr morvel56 than with nnr nuvel 1a for all plates except for australia where we observe an average residual rotation rate of 4 mm a using our selection of sites we found large global x rotation rates between the two models 0 016 ma and between our model and nnr morvel56 of 0 023 ma equivalent to 2 5 mm a at the earth surface

three dimensional lithospheric deformation and gravity anomalies associated with oblique continental collision in south island new zealand summary isostatic considerations exhibit differences between the northern central and southern parts of the pacific australian plate collision in south island new zealand in the northern part mean elevations are moderate and the gravity low is small the central part contains the highest elevations and gravity and elevations correspond to each other relatively well and in the southern part the gravity low is strongest whereas the mean elevations are moderate again these differences indicate changes in the character of the isostatic compensation and are explained by increased thickening and widening of the crustal root from north to south and also by the long wavelength gravity response to a mantle density anomaly that increases towards the south a simple 3 d gravity model is derived that includes the detailed crustal structures from the south island geophysical transect sight experiment as well as a high density anomaly in the mantle inferred from teleseismic data the model indicates that cold and therefore dense upper mantle material penetrates the asthenosphere to a greater extent in the south similar to the behaviour of an apparently highly ductile lower crust as plate reconstruction suggests more lithospheric shortening in the north our model corresponds to lithospheric material escaping laterally to the south almost perpendicular to the compression caused by lithospheric shortening of the mantle therefore in addition to the prevailing mantle shear in new zealand there may also be a component of extrusional mantle creep beneath the southern alps orogen which could have caused some of the observed large seismic anisotropy in this region we may have also found evidence for submerged eocene miocene oceanic lithosphere beneath the southeastern part of south island that has been unaccounted for after plate reconstruction

temporal variations in coda duration of local earthquakes in the wellington region new zealand temporal variations of coda duration relative to event magnitude for local earthquakes near wellington have been investigated the region is one of plate convergence and subduction the data consist of routinely made observations for events from 1978 through 1985 1552 events magnitude 1 6 to 5 2 depth 0 5 to 90 0 km the observed average over time correspondence between duration as measured from the origin time and magnitude is reasonably well predicted by the single backscattering theory of coda formation for events of magnitude 4 or less for larger events the observed durations are longer than predicted this theory predicts that a temporal increase in scattering attenuation will reduce the coda duration relative to magnitude thus any temporal changes in the duration magnitude relation can be interpreted in terms of changes inq however it is necessary to consider spatial biases since the observed durations are relatively long for shallow events and for events of all depths at stations situated in the south eastern half of the region usually believed part of the accretionary border for both these situations other evidence would suggest that the scattering coefficient would be relatively high lowq these observations may be due to a relatively high component of surface wave scattering and the importance of multiple scattering in the later part of the coda in regions of lowq as suggested by finite element studies of coda formation despite the lack of any significant earthquakes during the 1978 1985 period there is nevertheless a significant temporal change in duration observed in the wellington region a change from relatively long to relatively short codas occurred in mid 1981 this change correlates well with changes in the rate of activity b value radon emission and ground tilt as derived from lake levels it is not yet clear how all these parameters are related physically but an episode of aseismic slip or creep along the plate interface below the region may have been the cause

sedimentary and structural evolution of the northwest arabian red sea margin abstract an investigation of the northwestern margin of the arabian peninsula midyan region provides new insights into the two stage development of the red sea graben system the early red sea suez stage and the later red sea aqaba stage the early stage is characterized by the passive subsidence of a continental graben since the early oligocene after a period of enhanced subsidence of the basin in the early miocene this stage ended at the langhian serra valian boundary 14 ma the later stage was initiated by a release of stresses by strike slip movement along the newly formed aqaba levant transform creation of the new plate boundary was accompanied by stagnation of extension in the gulf of suez branch of the early rift stage strike slip motion on the aqaba levant structure is younger than 14 ma and is recorded by the post langhian compressional structures in the area of the midyan peninsula which developed by transpression along the curved path of a left lateral strike slip fault

new c 270 kyr strike slip and uplift rates for the southern alpine fault and implications for the new zealand plate boundary abstract along 100 km of the alpine fault major valleys and glacial deposits can be matched across an 8000 m dextral offset we use paleontologic and stratigraphic age constraints to date c 270 ka marine sediments uplifted to 600 m elevation and overlying c 270 ka glacial deposits related to the 8000 m dextral offset these constraints yield a fault proximal australian plate uplift rate of 2 6 0 5 0 4 mm yr and an alpine fault dextral slip rate of 29 6 2 5 4 5 mm yr our rates resolve an apparent along strike drop in strike slip rate and instead support a relatively constant along strike dextral slip rate of 28 mm yr 80 of current australian pacific plate boundary motion we argue that the rate of dextral slip on the southern alpine fault has been relatively constant over the last 3 5 myr and that ductile fault processes may rate limit the fault from accommodating a progressively higher percentage of plate boundary motion through time i e the fault reached maturity long ago the spatiotemporally constant strike slip rate of the southern alpine fault and a previously published paleoseismic record of near regular earthquake recurrence both characterize the alpine fault as a mature plate boundary fault zone that behaves in a constant way with behavior predictable over timescales of thousands and hundreds of thousands of years

inherent anisotropic stiffness of weathered geomaterial and its influence on ground deformations around deep excavations the shear modulus g0 at very small strain 0 001 or less is an important parameter for predicting ground movements of many geotechnical structures recent advances in laboratory testing enable th

the nature of the plate interface and driving force of interseismic deformation in the new zealand plate boundary zone revealed by the continuous gps velocity field 1 new zealand straddles the boundary between the australian and pacific plates cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation with displacements on individual faults up to hundreds of kilometers however over periods of several years gps measurements show a remarkably smooth pattern of velocities we show here using a new method of back slip analysis that almost the entire plate boundary continuous gps velocity field can be predicted within measurement error from a simple model of elastic distortion due to deep slip on a single plate interface megathrust in the hikurangi and putsegur subduction zones or fault through continental lithosphere beneath the southern alps at the relative plate motion rates this suggests that the main driving force of plate boundary deformation is slip on the deeper moving part of the plate interface without buried creep in localized shear zones beneath individual surface faults the depth at which this deep slip terminates locking point line determines the width of deformation along the hikurangi margin there is also clockwise rotation of 150 km long segment of the fore arc wairoa domain at 4 5 1 ma relative to the australian plate about a pole in western north island model residuals in the velocity field are mainly a result of incomplete averaging of the cycle of slow slip events on the plate interface downdip of the locking point

surface rupture during the 2010 mw 7 1 darfield canterbury earthquake implications for fault rupture dynamics and seismic hazard analysis the september 2010 m w 7 1 darfield canterbury earthquake in new zealand is one of the best recorded earthquakes of this magnitude the earthquake occurred on a previously unidentified fault system and generated a 29 5 0 5 km long surface rupture across a low relief agricultural landscape high accuracy measurements of coseismic displacements were obtained at over 100 localities along the greendale fault maximum net displacement d max 5 3 0 5 m and average net displacement d avg 2 5 0 1 m are anomalously large for an earthquake of this m w d max surface rupture length srl and d avg srl ratios are among the largest ever recorded for a continental strike slip earthquake geologically derived estimates of moment magnitude m w g are less than the seismologically derived m w derived using widely employed srl m w scaling regressions m w g is greater than m w using d max and d avg m w regressions the geologically derived static stress drop of 13 9 3 7 mpa provides a context with which to compare this earthquake rupture to interplate and intraplate ruptures of similar m w this data set provides fundamental information on fault rupture processes relevant to seismic hazard modeling in this region and analogous settings globally

shear stresses on megathrusts implications for mountain building behind subduction zones 1 shear stresses on a subduction megathrust play an important role in determining the forces available for mountain building adjacent to a subduction zone in this study the temperatures and shear stresses on megathrusts in 11 subduction zones around the pacific rim hikurangi tonga izu ogasawara western nankai northeastern japan aleutians western alaska cascadia northern chile southern chile and se asia northern sumatra have been determined the main constraint is that vertical normal stresses beneath the highlands behind the subduction zone are nearly equal to horizontal normal stresses in the plane of a trench or arc normal section for a typical brittle and ductile megathrust rheology frictional shear stress gz for depth z and ductile shear stress a exp b rt at temperature t where a b are rheological parameters treated as constants rheological constants common to all the megathrusts crust mantle b are determined by simultaneously solving for the force balance in the overlying wedge and megathrust thermal structure using a simplex minimization algorithm taking account of the induced mantle corner flow at depth 65 15 km 2 and constant radiogenic heating 0 65 0 3 w m 3 2 throughout the crust the a constants are solved individually for each subduction zone assuming that the maximum depth of interplate slip earthquakes marks the brittle ductile transition the best fit solution shows two groupings of megathrusts with most subduction zones having a low mean shear stress in the range 7 15 mpa crust 0 032 0 006 mantle 0 019 0 004 and unable to support elevations 2 5 km for a typical frictional sliding coefficient 0 5 the low effective coefficients of friction suggest high pore fluid pressures at 95 lithostatic pressure tonga and northern chile require higher shear stresses with crust 0 095 0 024 mantle 0 026 0 007 suggesting slightly lower pore fluid pressures at 81 lithostatic ductile shear in the crust is poorly resolved but in the mantle appears to show a strong power law dependency with b 36 18 kj mol 1 amantle values are sensitive to the precise value of b but are in the range 1 20 kpa the power law exponent n for mantle flow is poorly constrained but is likely to be large n 4 the brittle ductile transition in the crust occurs at temperatures in the range 370 c 512 c usually close to the base of the crust and in the mantle at much lower temperatures 180 c 300 c possibly reflecting a marked change in pore fluid pressure or quasi ductile and subfrictional properties in subduction zones where the subducted slab is older than 50 ma a significant proportion of the integrated shear force on the megathrust is taken up where it cuts the mantle and temperatures are 300 c in much younger subduction zones the stress transmission is confined mainly to the crust the shear stresses particularly in the crust may be kept low by some sort of lubricant such as abundant water rich trench fill which lowers the frictional sliding coefficient or effective viscosity and or raises pore fluid pressure the unusual high stress subduction zone in northern chile lacks significant trench fill and may be poorly lubricated with a mean shear stress 37 mpa required to support elevations 4 km in the high andes however where the crust is thin in sediment starved and poorly lubricated subduction zones such as tonga the mean shear stress will still be low sediment may lubricate megathrusts accommodating underthrusting of continental crust such as in the himalayas or eastern central andes which have a low mean shear stress 15 mpa

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

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

three dimensional imaging of impact of a large igneous province with a subduction zone abstract how the thickened crust of a large igneous province on an incoming oceanic plate is accommodated at a subduction zone remains an open question new zealand is one of the few places to study this as at ca 105 ma the ca 35 km thick hikurangi plateau impacted the gondwana subduction zone in what is now the south island here we report on results from a forty station portable seismograph array in the southern south island designed to delineate the leading edge of the subducted plateau three dimensional images of vp and vp vs reveal the southwestern part of the plateau was a relatively narrow salient and the first part to be subducted the plateau then rotated clockwise about this salient until the southern edge of the plateau was parallel to subduction strike and subduction ceased at ca 100 ma our results suggest that the global scale plate reorganization event at 105 100 ma was due to a cessation of subduction caused by the hikurangi plateau choking the gondwana subduction zone rather than the subduction of mid ocean ridges as previously proposed the choking of gondwana subduction by the plateau also led to a concentration of slab pull in the adjacent subducted oceanic crust explaining the episode of basin opening and intraplate magmatism there that occurred at the same time our study underlines the havoc caused by impact of a large igneous province with a subduction zone

a common source rock for egyptian and saudi hydrocarbons in the red sea the northern red sea area hosts a classic triple junction of the red sea gulf of aqaba and gulf of suez rifted basins the sedimentary succession here can be divided into prerift pre miocene and synrift miocene and post miocene megasequences the prerift section has been penetrated in only a few wells drilled on the western egyptian side of the red sea whereas the synrift section is known on both the egyptian and the saudi sides of the red sea although the synrift units on both sides of the water are similar in facies thicknesses and depositional environments they have different stratigraphic nomenclatures the northern red sea consists of elongated troughs separated by elongated structural highs both of which trend northwest southeast gulf of suez trend these highs are dissected by cross elements trending northeast southwest gulf of aqaba trend and east northeast west southwest and are looked upon as strike slip faults dislocating these highs identified rich source rocks are present in the upper senonian carbonates the sudr and duwi formations on the western side of the sea the early miocene rudeis formation burqan group and the middle miocene kareem and belayim formations maqna group the pre miocene and the early miocene source rocks host oil prone kerogen whereas the middle and late miocene source rocks contain oil and gas prone kerogen all of these source rocks are sufficiently mature copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received january 18 1996 revised manuscript received october 11 1996 final acceptance march 21 1997 2faculty of science uae university p o box 17551 al ain united arab emirates we are especially grateful to the egyptian general petroleum corporation for supplying the materials and the necessary data on which the present work is based and the permission to publish it we also thank c g st c kendall and a e m nairn who read the early draft of this paper and offered valuable comments thanks to aapg reviewers d waples r j murris w maze and an anonymous reviewer for their constructive comments which we have used to improve our paper we acknowledge g cole bhp petroleum for granting permission to use some of his previous work

frictional properties and 3 d stress analysis of the southern alpine fault new zealand abstract new zealand s alpine fault af ruptures quasi periodically in large magnitude earthquakes paleoseismological evidence suggests that about half of all recognized af earthquakes terminated at the boundary between the central and south westland sections of the fault there fault geometry and the polarity of uplift change the south westland af exhibits oblique normal fault motion on a structure oriented 052 82 se that for at least 35 km along strike contains saponite rich principal slip zone gouges new hydrothermal friction experiments reveal that the saponite fault gouge is frictionally weak exhibiting friction coefficients between 0 12 and 0 16 for a range of temperatures t 25 210 c and effective normal stresses n 31 2 93 6 mpa the saponite gouge is rate strengthening in all velocity steps performed at velocities between 0 01 and 3 0 m s behavior conducive to aseismic creep a three dimensional stress analysis shows that the south westland af is favorably oriented with respect to the regional stress field for slip within the frictionally weak saponite fault gouge geometrically the fault is severely misoriented for slip in any fault forming materials with friction coefficients exceeding 0 5 the combination of weak gouges prone to aseismic creep strong asperities and low resolved shear stress may impede earthquake rupture propagation along the south westland alpine fault

low temperature thermochronology and thermokinematic modeling of deformation exhumation and development of topography in the central southern alps new zealand 1 apatite and zircon u th he and fission track ages were obtained from ridge transects across the central southern alps new zealand interpretation of local profiles is difficult because relationships between ages and topography or local faults are complex and the data contain large uncertainties with poor reproducibility between sample duplicates data do form regional patterns however consistent with theoretical systematics and corroborating previous observations young neogene ages occur immediately southeast of the alpine fault the main plate boundary structure on which rocks are exhumed partially reset ages occur in the central southern alps and older mesozoic ages occur further toward the southeast zircon apparent ages are older than apatite apparent ages for the equivalent method three dimensional thermokinematic modeling of plate convergence incorporates advection of the upper pacific plate along a low angle detachment then up an alpine fault ramp adopting a generally accepted tectonic scenario for the southern alps the modeling incorporates heat flow evolving topography and the detailed kinetics of different thermochronometric systems and explains both complex local variations and regional patterns inclusion of the effects of radiation damage on he diffusion in detrital apatite is shown to have dramatic effects on results geometric and velocity parameters are tuned to fit model ages to observed data best fit is achieved at 9 mm a 1 plate convergence with pacific plate delamination on a gentle 10 se dipping detachment and more rapid uplift on a 45 60 dipping alpine fault ramp from 15 km depth thermokinematic modeling suggests dip slip motion on reverse faults within the southern alps should be highest 22 km from the alpine fault and much lower toward the southeast

undrained anisotropy of k0 consolidated silt direct measurements of the initial shear strength and yielding anisotropy of a dense k0 consolidated silt are described and interpreted within a bounding surface framework the experiments were performed using the imperial college large hollow cylinder apparatus in which samples were sheared undrained with a range of orientations of the major principal stress 1 following initial k0 consolidation the interpretation is aided by data from oedometer and triaxial stress path tests strongly anisotropic stiffness yielding undrained strength and mobilized angle of shearing resistance characteristics are revealed the effects of drained and undrained stress changes applied to the samples after k0 consolidation are also described key words anisotropy hollow cylinder k0 consolidation silt bounding surface

a plate boundary earthquake record from a wetland adjacent to the alpine fault in new zealand refines hazard estimates abstract discovery and investigation of millennial scale geological records of past large earthquakes improve understanding of earthquake frequency recurrence behaviour and likelihood of future rupture of major active faults here we present a 2000 year long seven event earthquake record from john o groats wetland adjacent to the alpine fault in new zealand one of the most active strike slip faults in the world we linked this record with the 7000 year long 22 event earthquake record from hokuri creek 20 km along strike to the north to refine estimates of earthquake frequency and recurrence behaviour for the south westland section of the plate boundary fault eight cores from john o groats wetland revealed a sequence that alternated between organic dominated and clastic dominated sediment packages transitions from a thick organic unit to a thick clastic unit that were sharp involved a significant change in depositional environment and were basin wide were interpreted as evidence of past surface rupturing earthquakes radiocarbon dates of short lived organic fractions either side of these transitions were modelled to provide estimates for earthquake ages of the seven events recognised at the john o groats site three post date the most recent event at hokuri creek two match events at hokuri creek and two events at john o groats occurred in a long interval during which the hokuri creek site may not have been recording earthquakes clearly the preferred john o groats hokuri creek earthquake record consists of 27 events since 6000 bc for which we calculate a mean recurrence interval of 291 23 years shorter than previously estimated for the south westland section of the fault and shorter than the current interseismic period the revised 50 year conditional probability of a surface rupturing earthquake on this fault section is 29 the coefficient of variation is estimated at 0 41 we suggest the low recurrence variability is likely to be a feature of other strike slip plate boundary faults similar to the alpine fault

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

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

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

a bayesian approach to determining and parametrizing earthquake focal mechanisms summary we develop a new probabilistic bayesian method for estimating the distribution of focal mechanism parameters based on seismic wave polarity data we investigate the use of generalized matrix fisher distributions for parametrizing focal mechanism uncertainties the advantages of our approach are that it 1 models the data generation process and incorporates observational errors particularly those arising from imperfectly known earthquake locations 2 allows exploration of the entire parameter space 3 leads to natural point estimates of focal mechanism parameters 4 allows the inclusion of a priori information about the focal mechanism parameters and 5 allows the resulting posterior pdf to be well approximated by generalized matrix fisher distributions we present here the results of our method in two situations we first consider the case in which the seismic velocity of the region of interest described by a velocity model is presumed to be precisely known with application to seismic data from the raukumara peninsula new zealand we then consider the case in which the velocity model is imperfectly known with application to data from the kawerau region new zealand we find that our estimated focal mechanism solutions are for the most part consistent with all available polarity data and correspond closely to solutions obtained using established methods further the generalized matrix fisher distributions we examine provide a good fit to our bayesian posterior pdf of the focal mechanism parameters finally we demonstrate how informative prior distributions on focal mechanism parameters can be incorporated into our model

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

geochemical and petrographic characterization of campanian lower maastrichtian calcareous petroleum source rocks of hasbayya south lebanon abstract santonian paleocene marls and fine grained carbonates have been sampled in hasbayya locality south lebanon in order to evaluate their organic matter om content petroleum source rock potential and assess their depositional environment methods included total organic carbon toc total inorganic carbon tic total sulphur ts rock eval pyrolysis organic and inorganic petrography x ray fluorescence xrf gas chromatography mass spectrometry gc ms and curie point pyrolysis gas chromatography mass spectrometry cp py gc ms toc rock eval and vitrinite reflectance vrr results reveal excellent immature petroleum source rocks within the campanian lower maastrichtian interval with toc up to 11 6 wt hydrogen index hi up to 872 mg gtoc tmax up to 433 c and vrr average of 0 36 biomarker ratios and maceral analysis suggest a marine depositional environment with a dominance of algal as well as submicroscopic om original sediment composition and redox sensitive geochemical parameters suggest deposition of the om rich intervals under an oxygen minimum zone omz that was emplaced and controlled by primary productivity and nutrient supply pyrolysate composition shows an important content of organic sulphur compounds thiophenes increasing with toc and thus indicating the presence of type ii and type iis kerogen in the analysed sample set which is consistent with the presence of immature solid bitumen in the hasbayya region the data produced in this study coupled with regional correlations allow us to construct a conceptual depositional model for the upper cretaceous om rich rocks of the eastern mediterranean suggesting deposition under a productivity belt localized along the inner and outer shelf leading to a decrease in source rock quality and a shift in kerogen type toward the deeper parts of the levant basin

major earthquakes occur regularly on an isolated plate boundary fault the scarcity of long geological records of major earthquakes on different types of faults makes testing hypotheses of regular versus random or clustered earthquake recurrence behavior difficult we provide a fault proximal major earthquake record spanning 8000 years on the strike slip alpine fault in new zealand cyclic stratigraphy at hokuri creek suggests that the fault ruptured to the surface 24 times and event ages yield a 0 33 coefficient of variation in recurrence interval we associate this near regular earthquake recurrence with a geometrically simple strike slip fault with high slip rate accommodating a high proportion of plate boundary motion that works in isolation from other faults we propose that it is valid to apply time dependent earthquake recurrence models for seismic hazard estimation to similar faults worldwide

oblique plate convergence and interseismic strain accumulation 1 a simple half space elastic model is used to investigate interseismic strain accumulation above a subduction zone associated with oblique plate convergence the horizontal surface velocity field near the leading edge of the upper plate is found to rotate as distance from the trench increases above the locked portion of the plate interface surface velocity is more oblique than the plate convergence vector farther back toward the interior of the upper plate the surface velocity is less oblique than the plate convergence vector surface velocity fields emphasize the strike slip component of plate convergence near the locked zone and emphasize the dip slip component farther back this interseismic strain partitioning is purely elastic interseismic straining will be reversed during the eventual rupture of the locked zone

cross correlation based detection and characterisation of microseismicity adjacent to the locked late interseismic alpine fault south westland new zealand abstract the alpine fault is inferred on paleoseismological grounds to produce magnitude 8 earthquakes approximately every 330 yrs and to have last ruptured almost 300 yrs ago in 1717 ad despite approximately 90 of its typical interseismic period having elapsed since the last major earthquake the alpine fault exhibits little present day microseismicity and no geodetic evidence for shallow creep determining the mechanical state of the fault ahead of a future earthquake is a key objective of several studies including the deep fault drilling project dfdp here we use a network of borehole seismometers installed in conjunction with dfdp to detect and characterise low magnitude seismicity adjacent to the central section of the alpine fault we employ matched filter detection techniques automated cross correlation phase picking and singular value decomposition derived magnitude estimation to construct a high precision catalogue of 283 earthquakes within 5 km of the fault trace in an otherwise seismically quiet zone the newly recognised seismicity occurs in non repeating spatially and temporally limited sequences similar to sequences previously documented using standard methods but at significantly lower magnitudes of m l 1 8 these earthquakes are not clustered on a single distinctive structure and we infer that they are distributed throughout a highly fractured zone surrounding the alpine fault focal mechanisms computed for 13 earthquakes using manual polarity picks exhibit predominantly strike slip faulting consistent with focal mechanisms observed further from the fault we conclude that the alpine fault is locked and accumulating strain throughout the seismogenic zone at this location

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

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

wave velocity and stiffness measurements of the crag and lower london tertiaries at sizewell this paper describes an investigation into the body wave velocity and stiffness characteristics of the foundation soils at the site formerly considered for sizewell c nuclear power station results from both in situ and laboratory tests are presented in situ measurements comprised shear and compression wave velocities using cross hole and down hole techniques including the velocity of horizontally propagating horizontally polarized shear waves laboratory tests included torsional shear tests on hollow cylindrical samples triaxial compression and extension tests with local measurements of strain and resonant column tests sample quality and the effects of destructuring are evaluated the anisotropy of the wave velocity and of the stiffness characteristics is highlighted l article decrit des recherches sur la vitesse de propagation des ondes de volume et les caracteristiques de rigidite des sols d assise de l emplacement propose de la centrale nucleaire sizewell c il presente les resultats des essais

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

the magnitude frequency distribution of earthquakes recorded with deep seismometers at cajon pass southern california abstract the cumulative b value the slope of the gutenberg richter relationship between earthquake occurrence rate and magnitude is commonly found to be constant 1 network catalogues however reveal a decrease at small magnitudes b value is not just an artifact of catalogue incompleteness but that small earthquakes are really not as numerous as a constant b value extrapolated from larger events would predict in the cajon pass area southern california the b value of seismicity recorded by the local network scsn appears to decrease below about m l 1 6 in order to investigate whether this decrease is real or simply represents the network detection threshold we use seismicity recorded by the deep 1 5 and 2 5 km seismometers deployed in the cajon pass scientific drillhole between april 1992 and october 1994 the maximum amplitudes recorded downhole are compared to scsn magnitudes for events recorded by the network to determine the relationship between amplitude and m l as a function of hypocentral distance from the borehole magnitudes are then calculated for 1300 earthquakes which occurred within 40 km of the borehole magnitude frequency curves are calculated for those events within 18 km of the borehole and a constant b value is observed to m l 0 5

petroleum geochemistry of the midyan and jaizan basins of the red sea saudi arabia abstract during the 1960s petroleum exploration activities in the offshore red sea areas of saudi arabia tested gas and condensate reservoired in the miocene sands immediately below the mansiyah evaporites in the offshore midyan basin recent onshore exploration activity in the red sea has resulted in the discovery of accumulations of oil gas and condensate in the lower miocene maqna group in the midyan and jaizan basins as a result of this exploration success an effort to understand the origin of these hydrocarbons was initiated the two basins were assessed geochemically by addressing 1 the potential source rocks 2 the extent of the hydrocarbon kitchens and 3 characterization of the hydrocarbons the potential source rocks for the reservoired hydrocarbons are 1 the organic rich oil prone shales of the predominantly evaporitic mansiyah formation 2 the variable quality shales and carbonates of the magna group and 3 the moderately organic rich shales of the burqan and tayran groups the reservoired hydrocarbons were characterized by carbon isotopes gas chromatography mass spectrometry and gas chromatography and compared with the potential source rocks the results showed an acceptable match to the maqna and burqan organic rich units detailed burial history thermal modelling projects were undertaken to assess the hydrocarbon kitchens of both basins results for the midyan basin indicated that over large areas tayran and burqan sediments are oil to gas mature and may be sources for the gas and or condensate accumulations whereas the limited area of mature maqna sediments may be responsible for sourcing the black oil accumulations in the jaizan basin the maqna and burqan sediments range from high oil maturity to thermally spent due to high geothermal conditions and excessive burial the burial of the source rocks increases fairly rapidly from east to west in the jaizan basin

stress field and kinematics for diffuse microseismicity in a zone of continental transpression south island new zealand we analyze shallow 0 20 km microseismicity adjacent to the alpine fault in new zealand where there is oblique convergence of the australian and pacific plates focal mechanisms for 155 earthquakes june 2012 october 2013 are inverted to determine the orientation of the stress field this yields a principal horizontal axis of compression shmax 114 10 which cannot be explained in terms of the sum of stress from tectonic loading due to plate convergence indicated by gps observations and gravitational stresses the azimuth of slip vectors for individual focal mechanisms cluster perpendicular and parallel to the plate convergence vector these faults however strike at 45 to shmax from the stress inversion suggesting a very low coefficient of friction the earthquake slip directions may be kinematically controlled accommodating the plate convergence on a limited set of fractures similar to the segmentation for neotectonic faulting along the alpine fault which is partitioned into strike slip and thrust segments at a 1 10 km scale we suggest two possible controls on our calculated shmax azimuths firstly there may be a slight clockwise bias in the estimates of shmax from earthquakes slip may be occurring on a more limited range of fractures than assumed by the stress inversion method although this effect is likely to be relatively small 5 more importantly the components of the stress field may be relieved at different time scales during big earthquakes resulting in a residual stress field that varies significantly 15 on timescales of several large earthquakes

structural influence on hydrocarbon entrapment in the northwestern red sea egypt the northwestern part of the egyptian red sea has attracted the attention of many geologists because it lies at the triple junction of the main rifts between the red sea the gulf of aqaba and gulf of suez the geometry of the fault system in this area of the basin clearly indicates an extensional setting the area has a southwestward regional dip and it has experienced more extension than the rest of the gulf of suez six tectonic stages different in their stress history sedimentary fill and depositional setting are recognized for the northwestern red sea 1 cambrian to early cretaceous stage 2 late cretaceous to oligocene stage 3 early miocene stage 4 early to middle miocene stage 5 middle to late miocene stage and 6 post miocene stage magnetic gravity seismic surface and subsurface data from the northwestern red sea delineate several elongate structural highs separated by elongate troughs both highs and troughs have the same northwest southeast direction as the clysmic trend some of the highs are dissected by cross elements that trend northeast southwest and east northeast west southwest and laterally offset these highs the tectonic framework of the northwestern sector of the red sea had a significant influence on hydrocarbon generation migration and accumulation the evidence for this influence includes the following 1 the troughs form the main source kitchens where the precambrian basement rocks are present at depths exceeding 4877 m e g gemsa trough 2 the magnitude of throw on the clysmic fault is critical in the entrapment mechanisms 3 the cross elements play a major role in the hydrocarbon migration and accumulation because they truncate the extension of most of the oil fields and form their bounding faults and 4 all the discovered oil fields in the study area are structural and or combination traps and show good matches to the magnetic anomalies

the stiffness of natural london clay an investigation of natural london clay is reported involving advanced triaxial hollow cylinder apparatus hca and dynamic testing techniques significant anisotropy was revealed at all scales of deformation and the framework of cross anisotropic elasticity was found to apply broadly to the initial elastic behaviour the stiffness parameters obtained by independent techniques generally exhibited good agreement with the greatest deviation being seen in the poisson s ratios which fell far from the values usually assumed in conventional foundation analysis probing tests established the limits to the elastic domain over a range of depths showing that these scaled in proportion to the mean effective stress level as did those of a second kinematic surface that surrounded the elastic domain once engaged this second surface signified a new pattern of strain increment directions faster elastic plastic stiffness decay with strain and also a greater dependence of behaviour on recent stress history howev

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

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

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

seismic and geodetic constraints on plate boundary deformation across the northern macquarie ridge and southern south island of new zealand summary in the southern new zealand region the boundary between the australian and pacific plates changes from oblique continental convergence in the central south island of new zealand to interoceanic transcurrent motion along the macquarie ridge source parameters of recent post 1964 upper crustal events mw 5 3 in the region 43 53 s 155 175 e are determined using p and sh waveform analysis in order to investigate the nature of strain accommodated seismically throughout the region repeated occupation of three geodetic networks across the southern south island provides estimates of contemporary crustal strain seismicity over the last 35 years shows uneven spatial and temporal distribution with clusters of events occurring in regions along the plate boundary that exhibit structural variation focal mechanisms of individual earthquakes vary widely but are consistent with the accommodation of long term estimates of the relative plate motion across the southern south island geodetically measured principal contraction directions are consistent with p axis orientations the mode of accommodation of the relative plate motion varies throughout the region influenced by the change in crustal composition on either side of the plate boundary the underlying structure as a relic of previous relative motions and the variation of obliquity of the relative motion with respect to these structures

microseismicity and stress in the vicinity of the alpine fault central southern alps new zealand 1 we investigate present day microseismicity associated with the central alpine fault and the zone of active deformation and uplift in the central southern alps using 14 months of data robust hypocenter locations have been obtained for 1800 earthquakes of magnitudes between 0 3 and 4 2 we derived a magnitude scale with a frequency dependent attenuation factor f 0f where 0 1 89 0 02 10 3 s km that enables magnitudes to be calculated consistently for earthquakes of different sizes and frequency contents the maximum depth of the seismicity varies systematically with distance from the alpine fault from 10 2 km near the fault to 8 2 km within 20 km and 15 2 km further southeast this distribution correlates with lateral variations in crustal resistivity earthquake hypocenters are concentrated in areas of strong resistivity gradients and restricted to depths of resistivities 100 m rocks at greater depth are too hot too fluid saturated or too weak to produce detectable earthquakes focal mechanism solutions computed for 211 earthquakes ml 0 44 exhibit predominantly strike slip mechanisms we obtain a maximum horizontal compressive stress direction of 115 10 from focal mechanism inversion this azimuth is consistent with findings from elsewhere in the central and northern south island and indicates a uniform crustal stress field despite pronounced variations in crustal structure and topographic relief our stress estimates suggest that the alpine fault with a mean strike of 055 is poorly oriented in an andersonian sense but that individual thrust and strike slip segments of the fault s surface trace have close to optimal orientations

petroleum and source rock characterization based on c7 star plot results examples from egypt the main types of egyptian oils condensates have been reviewed and characterized by light end hydrocarbon c7 based geochemical star plots the technique relies on high resolution gas chromatography of the c7 compounds and compositional differences are evaluated by using crossplots and multivariate polar plots c7 results of oils condensates are presented for the three main hydrocarbon provinces in egypt the gulf of suez the western desert and the nile delta and nearby mediterranean for the gulf of suez there are two main oil types which were derived from 1 cretaceous eocene carbonate rich and 2 miocene siliciclastic rich source rocks for the western desert there are three distinct oil types two of these oil types probably originated from middle jurassic carbonaceous marine shale rich source rocks whereas the third oil was produced from upper cretaceous argillaceous limestones for the nile delta there are two types of oil the majority of the oils condensates from this region are derived from tertiary shale rich source rocks but some may have a cretaceous jurassic source the given examples show that the c7 based star plot is very effective as a discriminating tool and that the c7 results are supportive and supplementary to other more standard geochemical oil condensate correlation methods the c7 data give reliable results over a wide range of thermal maturities but some compounds may be sensitive to evaporative fractionation water washing and biodegradation special attention is given to what extent the c7 data provide reliable information on source rock typing for the egyptian petroleums it appears that marine carbonate rich type ii derived oils have very different c7 compound concentrations than terrestrial clastic type iii ii derived oils for any oil condensate source correlation study be it on an exploratory regional or production field scale the light end c7 data may provide extremely useful geochemical information

hydrocarbon source rock generative potential of the sudanese red sea basin abstract to date the sudanese red sea like the red sea as a whole represents a grossly under explored basin recently the basin has seen increased exploration interest with more than 15 wells being drilled some of which have been petroleum discoveries gas and condensate with oil shows a similar exploration trend has been seen in the saudi eriteria and egyptian sectors of the red sea the red sea rift marks the break up of the afro arabian plate in eocene oligocene time the tectonostratigraphic evolution can be subdivided into three major phases pre rift syn rift and post rift phase generally terrestrials and marginal to deep marine sediments were deposited with both good reservoir quality and potential source rocks being present the pre salt rudeis kareem shales are expected to be good petroleum source rocks for the basin moreover shales of base zeit post salt are considered the main source of the known accumulated hydrocarbon gas and condensate in the shallow targets with the condensate charge also expected from intra evaporites shales and pre salt sources along the salt windows the measured amount of toc hi and hydrocarbon generation from pyrolysis of kerogen of the examined samples indicate source rock generative potential of these intervals the toc contents for base zeit and interbeded shales of dungnab formations range from 0 60 to 5 40 wt while the hydrogen index hi values are in the range of 50 600mg hc gtoc suggesting dominantly type iii ii kerogen the high toc 1 5 and hi 300 values of base zeit and dungnab formations are limited to some intervals within these formations consequently the base zeit source rocks are considered very good for condensate and gas generation in comparison to their equivalents burqan and maqna group sources hi 350 600 mg hc gtoc on the saudi red sea sector rudeis kareem shales could perhaps possess good quality type ii kerogen the red sea s high pressure and temperature regimes have a significant impact on hydrocarbon maturation generation and the quality of the preserved accumlations presently the zeit source varies in maturity across the basin and within the oil window in the suakin and bashayer areas and at gas window elsewhere to the east towards offshore on the other hand the pre salt rudies kareem formations are currently in the late oil to wet gas zone and probably out of gas phase distally offshore however the salt tectonics makes for challenging exploration the salt movement is considered recent as it is only the recent sediments that appear to be controlled by salt movement

continent scale strike slip on a low angle fault beneath new zealand s southern alps implications for crustal thickening in oblique collision zones new zealand s southern alps lie adjacent to the continent scale dextral strike slip alpine fault on the boundary between the pacific and australian plates we show with a simple 2 d model of crustal balancing that the observed crustal root and erosion expressed as equivalent crustal shortening is up to twice that predicted by the orthogonal plate convergence since 11 ma and even since 23 ma when the alpine fault formed we consider two explanations for this involving a strong component of motion along the length of the plate boundary zone geophysical data indicate that the alpine fault has a listric geometry flattening at mid crustal levels and has accommodated sideways underthrusting of australian plate crust beneath pacific plate crust the geometry of the crustal root together with plate reconstructions requires the underthrust crust to be the hyperextended part of an asymmetric rift system which formed over 500 km farther south during the eocene the narrow remnant part today forms the western margin of the campbell plateau at 10 ma the hyperextended margin underwent shallow subduction in the puysegur subduction zone and then was dragged over 300 km along the length of the southern alps beneath a low angle 20 section of the alpine fault we speculate that prior to 10 ma more distributed lower crustal shortening and thickening occurred beneath the southern alps accommodating southward extrusion of continental crust in the northern part of the plate boundary zone providing a mechanism for clockwise rotation of the hikurangi margin

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

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

viscous plastic finite element models of fault bend folds abstract in finite element models of fault bend folds viscous and plastic material properties are used to simulate pressure solution creep and cataclasis respectively plastic deformation occurs primarily above ramp hinges however a band of high plastic strain is created in the lower hanging wall as material moves over the ramp hinges viscous deformation dominates above the ramp and flats where plastic deformation is negligible hanging wall material undergoes layer parallel shortening on the lower flat and lower part of the ramp layerparallel extension on the upper part of the ramp and upper flat and layer parallel shortening farther along the upper flat the stress invariant j 2 is highest above the ramp hinges and below the ramp whereas stress invariant j 1 is highest above and below the ramp the high j 1 below the ramp suppresses plastic deformation so that footwall deformation is predominantly viscous in multilayer models strain is concentrated in the weak layers especially on the limbs of the hanging wall anticline in models with bedding parallel slip surfaces in the hanging wall the strain on fold limbs is accommodated by interlayer slip and layers between slip surfaces develop individual neutral surfaces the models indicate that the relative and absolute amounts of deformation in fault bend folds resulting from pressure solution creep and cataclasis vary as a function of structural position and history

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

slow slip and frictional transition at low temperature at the hikurangi subduction zone temperature changes with depth do not appear to be a primary control for either slow slip or fault locking processes at the hikurangi margin north island new zealand both slow slip events and the geodetically observed transition from fault locking to free slip at depth occur at temperatures as low as 100 c shallow portions of faults exhibit brittle stick slip behaviour that gives way to more stable sliding with increasing depth limiting the depths to which earthquake inducing slip can occur the increase of temperature with depth is often assumed to transform friction in the fault from velocity weakening unstable to velocity strengthening stable and to change conditions from brittle to ductile1 2 3 4 5 a temperature of 350 c has been suggested to mark the base of the frictionally unstable portion of the fault which becomes free slipping at depth where temperatures rise above 450 c refs 2 4 6 here we show that both slow slip events and the geodetically observed transition from fault locking to free slip at the hikurangi subduction zone east of the north island new zealand occur at temperatures as low as 100 c suggesting that temperature is not a primary control on either slow slip or fault locking processes at the hikurangi margin although globally shallow slow slip events are rare five out of seven events observed so far at the hikurangi margin are less than 15 km deep

distribution of present day vertical deformation across the southern alps new zealand from 10 years of gps data 1 we use ten years of gps data from nine continuous and six semi continuous gps stations in a transect across the southern alps to measure rates of relative vertical movement with typical 1 uncertainties of 0 3 0 5 mm yr the estimated vertical rates define a fairly smooth profile across the range with the highest rates of 5 mm yr found near the crest of the mountains and 20 30 km southeast of the alpine fault the distribution of vertical rates supports models based on horizontal velocities from gps surveys in which interseismic coupling on the alpine fault decreases from 100 near the surface to zero by 13 18 km depth

biostratigraphy and depositional setting of maastrichtian eocene oil shales from jordan abstract large distance correlation of sedimentary organic rich facies units in jordan has been established by means of calcareous nannofossil biostratigraphy based on a biostratigraphic framework a better understanding of the deposition and distribution of maastrichtian to eocene oil shales is obtained a total of 812 samples representing 29 wells located across jordan were studied for calcareous nannofossil biostratigraphy the results reveal major regional changes in paleogeography leading to a change in oil shales distribution in time the tectonic settings have been determined for four different oil shale sequences of maastrichtian paleocene early eocene and middle eocene age large variations in thickness over short distances indicate syndepositional subsidence control in several fault bound sedimentary sub basins during the early maastrichtian transgression a thick oil shale dominated succession was accumulated in the south of jordan this transgression continued into the paleocene as represented by a thick sequence of oil shales in nannofossil zone np 3 in the late paleocene the gradual progradation of the oil shale facies from south to north coincided with an uplift of the sirhan sub basin in east jordan accordingly the oil shale distribution varies locally and shows a scattered geographic distribution in the late paleocene an up to 60 m thick succession of early eocene oil shales was found in central jordan localized restricted conditions which prevailed during the ypresian lutetian transition nannofossil zone np 14 were caused by the subsidence of the azraq hamza and sirhan sub basins these movements resulted in thick oil shale accumulation in the southeastern and central parts of jordan a gradual relative sea level fall during the bartonian resulted in a prograding and thinning of the oil shale facies from west to east in central jordan

recent advances in petroleum geochemistry applied to hydrocarbon exploration this paper presents a critical review of recent advances in the study of generation maturation and migration of petroleum the different source potentials for generating hydrocarbons depend on the type of kerogen in addition to the classic types i ii and iii a residual oxidized organic matter is also observed which has no potential for hydrocarbon generation coal is widely considered as a potential source for gas but some coals may generate sizeable amounts of oil as well the development of routine analytical tools particularly pyrolysis makes possible the preparation of geochemical logs that are the basis for screening samples and for interpreting other analyses among optical techniques the major subjects of discussion concern the nature of amorphous organ c matter which may encompass different chemical types of kerogen and the applicability of vitrinite reflectance techniques to type i and ii kerogens following important advances in identification of biological markers in sediments and crude oils these markers are used for oil source rock correlation and proposed for reconstruction of depositional environment and subsequent thermal evolution migration of hydrocarbons is now better understood and the importance of a hydrocarbon phase migration is widely recognized overpressuring of pore fluids is mainly responsible for expulsion of petroleum geologic models of basin evolution subsidence compaction thermal history and geochemical models hydrocarbon generation and migration become progressively available their integration int a comprehensive model should be one of the major developments in future petroleum exploration

model calculations of regional network locations for earthquakes in subduction zones algorithms for locating earthquakes recorded by local networks commonly assume a flat layered velocity structure even in island arc regions where the presence of a dipping lithospheric slab introduces large lateral velocity variations moreover because seismic stations occur along the narrow island arc the resulting linear network geometry degrades earthquake location to model this situation we trace rays in a spherical earth from hypothetical earthquakes through appropriate velocity models to networks of various geometries to isolate the effect of the slab most of the velocity models consist simply of a planar dipping constant velocity region embedded in a sphere with a constant lower seismic velocity we then use the calculated p and s travel times to relocate the hypothetical earthquakes with a flat layered velocity structure we perform calculations of this kind in a variety of models varying the dip of the slab the velocity contrast between the slab and the mantle the station geometry and the distance between the earthquakes and the slab mantle boundary we also perform calculations in more realistic models with geometry closely resembling two seismic networks in alaska these model calculations emphasize the great care that seismologists should exercise when interpreting local network locations in island arc regions in the present study all the relocations incorporate p and s arrivals at all stations and include no random or picking errors nevertheless the relocated hypocenters differ from the actual model hypocenters by up to 100 km or more and produce significant distortions in the wadati benioff zone the most prominent spurious feature is a clear increase in the apparent dip of the wadati benioff zone beneath a certain depth furthermore the relocation reduces the width or apparent thickness of the wadati benioff zone e g they produce an apparent thickness of 5 km or smaller for a zone of earthquakes with an actual thickness of 20 km however if different combinations of stations report different events it is possible to determine an apparent thickness which exceeds the actual thickness for local networks near subduction zones it is useful to estimate the mislocation and rms residual expected for each event recorded and located this can be accomplished by performing model calculations in a simple model with a constant velocity dipping slab embedded in a half space for such a simple model there exists only one ray path from each earthquake within the slab to each station and the travel time for this path can be calculated as a part of the routine network location process a relocation using the routine network location algorithm and these calculated travel times provides an indication of the expected mislocation and rms residual for the actual recorded event

continental tectonics in the aftermath of plate tectonics the success of plate tectonics required an acceptance of continental drift and thus a reinterpretation of the large scale geological history of most of the earth but the basic tenet of plate tectonics rigid body movements of large plates of lithosphere fails to apply to continental interiors where buoyant continental crust can detach from the underlying mantle to form mountain ranges and broad zones of diffuse tectonic activity

initiation and reactivation of faults during movement over a thrust fault ramp numerical mechanical models abstract with numerical continuum models we investigate the effects of fault geometry fault friction material properties and anisotropy on the initiation and reactivation of faults in the hanging wall of a thrust fault ramp the models use an elastic plastic frictional dilatant cohesion softening material in which deformation may localize as shear bands with a sharp lower fault bend backthrust shear bands propagate up from the concentration of differential stress at the fault bend with a rounded lower fault bend bedding parallel shear bands develop above the fault bend in the center of the layer where differential stress is highest friction on the ramp enhances the development of backthrusts and causes them to initiate at shallower dips increased overburden decreases the amount of localization within shear bands and the spacing between them shear bands that develop at the lower fault bend are weaker than the surrounding material and are thus potential sites of reactivation during subsequent deformation because of this potential reactivation the style of deformation at the upper fault bend depends on the deformation that accumulates at the lower fault bend at the upper fault bend backthrusts are reactivated as extension faults and are crosscut by more steeply dipping extension faults bedding parallel shear bands are reactivated at the upper fault bend with top to the hinterland sense of shear low angle extension faults are listric into the reactivated bedding parallel shear bands producing hinterland verging extensional duplexes above the upper flat

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

relation between surface velocity field and shear wave splitting in the south island of new zealand 1 the relative motion between the pacific and australian plates across the central south island of new zealand as measured by repeated gps measurements is distributed over a region more than 80 km wide the surface distribution of velocity is fit almost equally well by a model in which deformation of the lower lithosphere is concentrated into very narrow slip zones below one or two major faults and by a model in which the lower lithosphere deforms in a broad shear zone observations of the splitting of sks waves permit distinction between the two models on the basis of the finite strain they predict deformation in the deep lithosphere that was limited to narrow shear zones would not produce measurable splitting hence any splitting observed should not correlate with surface tectonics however the distribution of fast propagation directions revealed by observations of shear wave splitting do reflect surface tectonics in particular the orientations of fast propagation directions are consistent with the finite strain calculated by assuming that the distribution of velocity at depth within the lithosphere resembles the distribution of velocity measured at the surface by gps the observed distribution of splitting can be reproduced with an rms misfit of 15 provided that the velocity field is integrated over at least the time interval since significant convergence across the southern alps began at about 6 5 ma

is it all in the crust new observations suggest that earthquakes on land are only skin deep confined to the earth s outermost layer of crust this has prompted a rethink of what gives the tectonic plates their strength

viscoelastic coupling model for the earthquake cycle driven from below in a linear system the earthquake cycle can be represented as the sum of a solution which reproduces the earthquake cycle itself viscoelastic coupling model and a solution that provides the driving force we consider two cases one in which the earthquake cycle is driven by stresses transmitted along the schizosphere and a second in which the cycle is driven from below by stresses transmitted along the upper mantle i e the schizosphere and upper mantle respectively act as stress guides in the lithosphere in both cases the driving stress is attributed to steady motion of the stress guide and the upper crust is assumed to be elastic the surface deformation that accumulates during the interseismic interval depends solely upon the earthquake cycle solution viscoelastic coupling model not upon the driving source solution thus geodetic observations of interseismic deformation are insensitive to the source of the driving forces in a linear system in particular the suggestion of bourne et al 1998 that the deformation that accumulates across a transform fault system in the interseismic interval is a replica of the deformation that accumulates in the upper mantle during the same interval does not appear to be correct for linear systems

crust and mantle thickening beneath the southern portion of the southern alps new zealand summary an 8 54 0 20 km s 1pn speed is estimated on a line oriented ca n5 e from the alpine fault beneath the southern alps of south island based on a refraction experiment that uses the fiordland earthquake of august 2003 as a source this high pn speed results from both strong anisotropy in the mantle lid of 7 13 per cent and a high pn speed average of 8 3 0 3 km s 1 a maximum crustal thickness of 48 4 km is calculated for the southern south island near the town of wanaka this represents a crustal root of about 18 km compared to measured crustal thicknesses at the east and west coasts of the south island the average topography in the southern southern alps is of the order of 1000 m which is less than half that predicted by airy isostasy for an 18 km crustal root as recently proposed for the central south island 120 km to the north we propose that thickened cold and therefore more dense mantle lithosphere exists beneath southern south island and that this excess of mass is an effective load that pulls down the overlying crust the load is similar to that beneath the central southern alps despite the predicted convergence across the alpine fault there being nearly twice that at wanaka gravity modelling of crustal structure along a profile through wanaka suggests that this mass excess has a minimum density contrast of 35 5 kg m 3 between thickened mantle and asthenosphere assuming an across moho density contrast of 300 kg m 3 we speculate that the reason for the enhanced thickening beneath wanaka is that the subducted australian plate at the southwestern corner of the south island acts like a backstop onto which pacific mantle collides at 26 mm yr 1 ca 3 4 the full plate speed

focusing of relative plate motion at a continental transform fault cenozoic dextral displacement 700 km on new zealand s alpine fault reversing 225 km of late cretaceous sinistral motion the widely accepted 450 km cenozoic dextral strike slip displacement on new zealand s alpine fault is large for continental strike slip faults but it is still less than 60 of the cenozoic relative plate motion between the australian and pacific plates through zealandia with the remaining motion assumed to be taken up by rotation and displacement on other faults in a zone up to 300 km wide we show here that the 450 km total displacement across the alpine fault is an artifact of assumptions about the geometry of new zealand s basement terranes in the eocene and the actual cenozoic dextral displacement across the active trace is greater than 665 km with more than 700 km and 94 of the relative plate motion in the last 25 ma at an average rate in excess of 28 mm yr it reverses more than 225 km and 300 km of sinistral shear through zealandia in the late cretaceous when zealandia lay on the margin of gondwana providing a direct constraint on the kinematics of extension between east and west antarctica at this time