evolution of faulting and plate boundary deformation in the southern taranaki basin new zealand abstract faulting and folding in the southern taranaki basin constrain the evolution of the new zealand plate boundary since 80 ma sedimentary rocks up to 8 km thick record multiple phases of deformation which have been examined using 2d and 3d seismic reflection data resulting in fault displacement time curves and basin wide isopach maps with temporal resolutions of 5 10 myr and 1 4 myr pre and post 23 ma respectively three main phases of tectonic activity have been recognised late cretaceous and palaeocene extension 80 55 ma mainly oligocene and younger contraction and plio pleistocene 3 7 0 ma extension most of the largest faults e g cape egmont fault accrued displacement during the late cretaceous and were reactivated one or more times during subsequent episodes of deformation the oldest phase of extension occurred during gondwana break up and was ubiquitous throughout the basin contraction along the eastern boundary of the basin associated with the onset of hikurangi margin subduction commenced as early as late eocene the zone of contraction widened and migrated westward during the miocene with reverse faults and folds in westernmost parts of the basin formed in the late miocene 7 5 ma initiation and episodic widening of this zone of contraction may have been partly triggered by changes in the rate of plate convergence contraction is now mainly confined to the northern south island and has been succeeded to the north by plio pleistocene extension the present day transition zone between extension in the north and contraction in the south is defined by a wnw trending line across the basin the extension contraction transition migrated southward during the late miocene and pliocene consistent with steepening of the subducting plate and associated southward movement of the southern termination of the hikurangi subduction system

stress strain paradox plate coupling and forearc seismicity at the cascadia and nankai subduction zones abstract in the continental forearcs of the cascadia and nankai subduction zones geodetic strain measurements indicate crustal contraction in the direction of plate convergence nearly margin normal but earthquake focal mechanisms and other stress indicators show maximum compression along strike margin parallel it is evident that the geodetic strain signals reflect the temporal fluctuations of elastic stress associated with subduction earthquake cycles not the absolute stresses the absolute margin normal stress is not only much less than the margin parallel stress but also no greater than the lithostatic value indicating a very weak subduction thrust fault weak subduction faults are also consistent with geothermal data which require very low frictional heating along the faults great subduction earthquakes occur at very low shear stresses and cause small perturbations to the forearc stress regime because these small elastic stress perturbations are relatively fast they give large strain rates that are detected by geodetic measurements the present nearly margin normal contraction in both places is due to the locking of the subduction fault and the consequent increase in elastic stress in the direction of plate convergence with the margin parallel compression being dominant the small increase in margin normal stress may change the forearc seismicity in cascadia from a mixture of thrust and strike slip types into mainly thrust before the next great subduction earthquake in nankai the change should be from strike slip to quiescence as observed in the nankai forearc prior to the 1944 1946 great subduction earthquakes

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

global crustal stress pattern based on the world stress map database release 2008 the world stress map wsm project is a global compilation of information on the contemporary crustal stress field from a wide range of stress indicators the wsm database release 2008 contains 21 750 stress data records that are quality ranked using an updated and refined quality ranking scheme almost 17 000 of these data records have a c quality and are considered to record the orientation of maximum horizontal compressional stress sh to within 25 as this is almost a triplication of data records compared with the first wsm database release in 1992 we reinvestigate the spatial wave length of the stress patterns with a statistical analysis on a global 0 5 grid the resulting smoothed global stress map displays both the mean sh orientation that follows from the maximum smoothing radius for which the standard deviation is b25 and a countour map that displays the wave length of the stress pattern this smoothed global map confirms that long wave length stress patterns n2000 km exist for example in north america and ne asia these have been used in earlier analyses to conclude that the global stress pattern is primarily controlled by plate boundary forces that are transmitted into the intraplate region however our analysis reveals that rather short wave length of the stress pattern b200 km are quite frequent too particularly in western europe alaska and the aleutians the southern rocky mountains basin and range province scandinavia caucasus most of the himalayas and indonesia this implies that local stress sources such as density contrasts and active fault systems in some areas have high impact in comparison to plate boundary forces and control the regional stress pattern

instability of a lithospheric step beneath western north island new zealand lithospheres of different thicknesses are often juxtaposed by movement on a continental transform boundary such a boundary with a step change in densities may trigger a gravitational instability as lateral pressure gradients are created where normal mantle lithosphere terminates against less dense asthenospheric mantle here we show for plausible values of the lithospheric viscosity a mechanism by which the thicker mantle lithosphere will drip off into the lower density asthenosphere as the mantle deforms it also progressively thickens and then thins the overlying crust creating a topographic wave that migrates in concert with the removal of mantle lithosphere within western north island new zealand geophysical data define a sharp lithospheric step across the taranaki ruapehu line and geological observations provide a history of uplift and subsidence that has propagated southward in the past 12 m y the rate of observed north to south migration of the wave 30 mm yr its wavelength 250 km and amplitude 1 km are compatible with it being caused by progressive removal of mantle lithosphere if the viscosity of the uppermost lithospheric mantle is 5 10 20 pa s providing one of the clearest examples yet of this fundamental geological process

smoothing and extrapolation of crustal stress orientation measurements the theory and mechanics of a statistical smoothing algorithm for estimating stress fields based on observed data are described incorporated into the algorithm are tunable parameters which allow the user to adjust the smoothness and fidelity of the fitted stress field in addition the user has the option of using robustness weights or to weight the predicted stress field by assigning quality ranks to each data point fitted stress fields can be displayed as either a gridded map axes of maximum or minimum horizontal stress are shown as short bars located at each point in an evenly spaced grid or as a stress trajectory map examples of predicted stress fields for southern california and western canada based on borehole elongation data are displayed as stress trajectory maps a predicted paleostress field for the spanish peaks intrusion complex in colorado based on vertical dike orientations is displayed as a gridded map the smoothing algorithm is not limited to the analysis of stress orientation data any data consisting of a set of undirected lines measured at discrete locations are appropriate for input possible candidates include strain data mineral or intersection lineations and lineaments

the moho in australia and new zealand abstract australia and new zealand share in part a history in the gondwana supercontinent australia has a long and complex tectonic history with the last major accretion in the early paleozoic whereas new zealand is still undergoing major plate boundary processes the australian continent is relatively well covered with both active and passive seismic techniques multiple sources of information are therefore available for building a model of moho depth results from on shore and off shore refraction experiments are supplemented by receiver functions from a large number of portable stations and the recently augmented set of permanent stations moho picks from more than 10 500 km of full crustal reflection profiles provide valuable additional constraints the composite data set provides good sampling of much of australia though coverage remains low in some remote desert areas the various datasets provide multiple estimates of the depth to moho in many regions and the consistency between the different techniques is high some of the thinnest crust lies beneath the archean craton in the pilbara and in the neighbourhood of the simpson desert thick crust is encountered beneath parts of the proterozoic in central australia and beneath the paleozoic lachlan fold belt in southeastern australia there are a number of zones of sharp contrast in depth to moho notably in the southern part of central australia despite most of the continental material around new zealand being submerged moho data for this region is mainly onshore concentrating on the australia pacific plate boundary two major wide angle reflection transects provide the bulk of the active source data with just a few traditional reflection profiles offshore the plate boundary provides an abundance of local earthquakes for tomographic imaging and this data is supplemented with receiver functions from both portable and permanent networks onshore the combined coverage is as dense as that of australia although it could be argued that a higher spatial resolution is required to capture the nature of the moho of tectonically active new zealand three regions of thickened crust can be identified one beneath the southern alps another beneath fiordland and below the wanganui basin between the north and south island thin crust is identified west of the volcanic arc with extensive underplating below the back arc region

shortening of an overriding plate and its implications for slip on a subduction thrust central hikurangi margin new zealand 1 at subduction plate boundaries strains accumulate within the overriding plate in response to motion of the down going plate to a first approximation margin normal interplate slip and shortening in the overriding plate sum to the total plate convergence therefore margin normal interplate slip can be estimated by measuring shortening in the overriding plate and total plate convergence here we quantify margin normal interplate slip by measuring shortening of the upper plate along a profile which extends up to 480 km across and approximately normal to the central hikurangi margin new zealand long term deformation is estimated for periods of millions of years using data from seismic reflection lines and cross sections while contemporary strain rates are derived from global positioning system gps geodetic velocities these data permit comparison of plate convergence rates determined by seafloor spreading data with the rates of contraction over short 7 years and long 2 5 and 5 myr periods of time on this part of the plate boundary total margin normal shortening in the overriding plate over the last 5 myr was 9 28 km and accounts for 6 19 of the total convergence 145 160 km at rates of 2 6 mm yr the remaining 80 or more of plate convergence has been accommodated by slip on the subduction thrust gps contraction along approximately the same profile indicates 14 16 mm yr of contemporary shortening across the terrestrial part of the upper plate which is approximately modeled by 80 interplate coupling on the subduction interface down to depths of 30 km the contrasting proportions of inferred interplate coupling for contemporary and geological data sets are consistent with stick slip behavior on the plate interface and with slip being principally achieved during intermittent large earthquakes the general shapes of short and long term shortening profiles are similar and suggest that the highest strains occur at or immediately east of the mohaka fault these strain profiles are consistent with a model where high strains in the upper plate are concentrated near the down dip end of the contemporary locked zone on the plate interface this model requires that the down dip end of the interseismic locked zone has on average been approximately stable over a period of at least 2 5 5 myr

mapping crustal stress and strain in southwest british columbia 1 this paper investigates the orientation and sources of stress in the forearc of the cascadia subduction zone in southwest british columbia using bayesian inversion results from focal mechanism data and comparing results with gps derived short term strain rates the subduction margin in this region includes a change in orientation from n s in washington state to nw se in british columbia over 1000 focal mechanisms from north american crustal earthquakes have been calculated to identify the dominant style of faulting and 600 were inverted to estimate the principal stress orientations and the stress ratio our results indicate the maximum horizontal compressive stress orientation changes with distance to the trench from approximately margin normal along the coast to approximately margin parallel 100 150 km inland from the coast comparing stress orientations with gps data we relate the margin normal stress direction to subduction related strain rates due to the locked interface between the north american and juan de fuca plates just west of vancouver island further from the margin the plates are coupled less strongly and the margin parallel maximum horizontal compressive stress in the north american plate relates to the northward push of the oregon block which is also observed in the horizontal shortening direction of the residual strain rates after the subduction component is removed

understanding tectonic stress in the oil patch the world stress map project knowledge of the present day tectonic stress is essential for numerous applications in petroleum exploration and production and in civil and mining engineering such as improving the stability of boreholes and tunnels and enhancing petroleum production through natural or induced fractures the world stress map wsm project is a collaborative project between academia industry and government that is building a comprehensive global database of present day stress information to better understand the state and sources of contemporary tectonic stress in the lithosphere figure 1

present day stress field of southeast asia article i nfo it is now well established that ridge push forces provide a major control on the plate scale stress field in most of the earth s tectonic plates however the sunda plate that comprises much of southeast asia is one of only two plates not bounded by a major spreading centre and thus provides an opportunity to evaluate other forces that control the intraplate stress field the cenozoic tectonic evolution of the sunda plate is usually considered to be controlled by escape tectonics associated with india eurasia collision however the sunda plate is bounded by a poorly understood and complex range of convergent and strike slip zones and little is known about the effect of these other plate boundaries on the intraplate stress field in the region we compile the first extensive stress dataset for southeast asia containing 275 a d quality 177 a c horizontal stress orientations consisting of 72 stress indicators from earthquakes located mostly on the periphery of the plate 202 stress indicators from breakouts and drilling induced fractures and one hydraulic fracture test within 14 provinces in the plate interior this data reveals that a variable stress pattern exists throughout southeast asia that is largely inconsistent with the sunda plate s approximately ese absolute motion direction the present day maximum horizontal stress in thailand vietnam and the malay basin is predominately north south consistent with the radiating stress patterns arising from the eastern himalayan syntaxis however the present day maximum horizontal stress is primarily oriented nw se in borneo a direction that may reflect plate boundary forces or topographic stresses exerted by the central borneo highlands furthermore the south and central sumatra basins exhibit a ne sw maximum horizontal stress direction that is perpendicular to the indo australian subduction front hence the plate scale stress field in southeast asia appears to be controlled by a combination of himalayan orogeny related deformation forces related to subduction primarily trench suction and collision and intraplate sources of stress such as topography and basin geometry

deep seismic expression of a foreland basin taranaki basin new zealand a deep seismic reflection profile shot across the south taranaki basin new zealand indicates up to 10 km of crustal thickening beneath the taranaki boundary fault at the eastern margin of the basin the seismic data also show a broad flexure of the entire crust the locus of the flexure producing load appearing to be in the vicinity of the taranaki boundary fault such crustal thickening and flexure suggest a compressional foreland basin style of late cenozoic development rather than the rift graben origin previously assumed this change in interpretation for the south taranaki basin has implications for evaluating the thermal history of the basin and its possibilities for hydrocarbon prospects the study therefore demonstrates the value of deep seismic exploration of a hydrocarbon bearing basin in its early stage of exploration

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

collisional model for rapid fore arc block rotations arc curvature and episodic back arc rifting in subduction settings 1 we review geophysical and geological data from 23 active and ancient plate boundaries to document a compelling spatial and temporal relationship between collision plate boundary curvature rapid tectonic rotations and the occurrence of back arc rifting our observations support a conceptual model where the change from subduction to collision causes rapid fore arc rotation when viewed in a reference frame relative to the bounding tectonic plates leading to marked plate boundary curvature our global compilation reveals that most active back arc rifts are associated with rapidly rotating fore arcs and nearby collisions thus we propose that collision and rapid fore arc rotations play a major role in the evolution and kinematics of back arc basins we conduct numerical modeling to better understand the physical processes behind these observed rapid tectonic rotations at convergent margins our results suggest that the presence of an indentor or choke point in the subduction system e g collision can generate rapid rotation of the fore arc about a nearby pole and lead to back arc rifting the rate of fore arc rotation and back arc rifting depends on the incoming indentor velocity and can be greatly enhanced by slab rollback and the presence of a low viscosity back arc where viscosity of the back arc is low fore arc rotation dominates where back arc viscosity is high the formation of strike slip faults and tectonic escape dominates our observational and model derived results illustrate that shallow crustal forces produced by the entry of buoyant features into subduction zones are a fundamental mechanism for the generation of fore arc block rotations plate boundary curvature back arc rift evolution and tectonic escape in subduction systems rollback of the subducting slab within the mantle will certainly enhance the processes we describe but it is not the only driving force

stress field of italy mean stress orientation at different depths and wave length of the stress pattern we have studied the stress pattern of italy using a dataset with 590 data records from the world stress map database release 2008 and 106 new data records to test the hypothesis the mean orientation of maximum horizontal stress sh is different at different depth sections for this we split the dataset into a shallow 0 6 km and a deep 6 40 km depth section for the data analysis we used a new statistical tool that calculates the mean sh orientation on a 0 2 grid the tool takes into account the distance to each grid point number and quality of the data records within the search radius and the radial distribution the result is a smoothed italian stress map that displays both the mean sh orientation and the wave length of the stress pattern the stress pattern does not vary in depth except for two areas sardinia and southern apulia therefore stress data from different depths can be used to estimate the mean sh orientation and the wave length of the stress pattern in italy furthermore the smoothed italian stress map reveals that most of italy has short wave length stress patterns 150 km this indicates that the stress field is not controlled by first order stress sources of plate tectonics i e the convergence of africa with respect to eurasia but that second order stress sources such as topography density strength contrasts and major faults systems are of great importance in four regions western part of the alps northern tuscany northern adriatic sea calabria and eastern part of sicily the wave length is 100 km high values of the circular variance of the mean sh orientation observed here are driven by third order local stress sources such as basins or local neotectonic structures

focal mechanisms of large earthquakes in the north island of new zealand slip partitioning at an oblique active margin we have used body wave modelling to determine the source parameters of 22 moderate to large earthquakes that have occurred along the hikurangi subduction margin and elsewhere in the north island of new zealand since 1964 we have also included events from the harvard cmt catalogue since 1977 as that catalogue contains smaller events than can be modelled with body waves we have found that shallow earthquakes occurring in the back arc taupo volcanic zone and its extension to the north show predominantly normal faulting with nodal planes parallel to the regional fabric and t axes indicating extension in a direction in agreement with geodetic measurements a normal faulting solution for the 1974 opunake earthquake is compatible with the mapping of active faults in the offshore taranaki region and the initiation depth of 17 km is close to the expected brittle ductile transition for that area earthquakes within the subducted plate at the southwestern end of the margin are dominated by down dip tension that is rotated towards the deepest part of the subducting plate further north the events in the upper part of the wadati benioff zone 200 km show pure down dip tension while this association is less obvious for the deeper events suggesting that the aseismic part of the subducting slab inferred from plate reconstructions has reached the 670 km discontinuity normal faulting earthquakes associated with plate bending below the region of interplate contact occur along the length of the margin while shallow normal faulting events also occur in the trench indicating that some slab pull propagates to that region we infer that large interplate earthquakes are not imminent because in other similar areas they are preceded by outer rise compressional events that have not been recorded in the region in historical times slip vectors of interplate thrust earthquakes indicate that the oblique plate motion across the margin is fully partitioned that is the plate interface accommodates very little transcurrent motion which is instead accommodated by faults in the overlying australian plate extensional geodetic strain has been measured across the margin in the northeast which has been regarded as unusual in view of the plate convergence we suggest that the topography at this part of the margin is too steep to be supported by the current horizontal forces due to friction on the plate interface this may have occurred due to a reduction in friction because of the subduction of seamounts and the subsequent entrapment of sediments this also being consistent with the idea of underplating at this part of the margin or due to the subduction of less buoyant crust other margins such as japan and mid america where there is known to be subduction of sediments also show extension in the forearc compressional strain observed across the margin in the southwest is more usual for a convergent margin but it does not show the partitioning we see in focal mechanisms these data might only agree after the long term compressional strain accumulation has been averaged over a complete seismic cycle large historical and palaeo earthquakes have occurred along the length of the margin associated with deformation in both the axial and the coastal ranges in addition along the length of the margin the rate of recent interplate thrust activity is low compared to margins that have a high proportion of aseismic slip these factors indicate that the entire length of this margin is capable of producing large earthquakes

stress and strain from earthquakes at the southern termination of the taupo volcanic zone new zealand abstract we use first motion polarity data from small earthquakes recorded by a recent dense seismograph deployment to determine 16 new focal mechanisms at the southern termination of the taupo volcanic zone tvz these crustal earthquakes are between 11 km and 41 km deep and have focal mechanisms which range from normal to strike slip we then combine these focal mechanism data with previously determined focal mechanisms to investigate earthquake strain directions a prominent feature of the combined data is the consistency of the t axes which indicates that subhorizontal nnw extensional strain predominates at all depths in the crust at the southern termination of the tvz we then use all currently available first motion data to invert for the stress tensor orientation first motion data from earthquakes throughout the crust show a consistent minimum principal stress 3 orientation which is subhorizontal and oriented nw the 3 azimuth that we observe 316 is perpendicular to the strike of recent aligned vents in the southern tvz very similar to the extension direction in the ruapehu segment of the tvz determined from structural data and consistent with the 3 direction determined from a stress inversion using crustal earthquakes in the central tvz north of lake taupo this suggests that the stresses driving the opening of the tvz continue to be active at its southern termination the stress and strain results combined with the earthquake distribution are consistent with a model where the tvz is only the present day surface expression of an extensive region of active mantle corner flow that is progressively eroding thicker crust to the south we also investigate the temporal evolution of stress around mt ruapehu the southernmost large andesitic volcano in the tvz given previous suggestions that this may change during the eruption cycle we find no major change in the stress tensor orientation at the time of the 1995 eruption using first motion data from earthquakes 15 20 km from the volcano

structural control of volcanism and caldera development in the transtensional taupo volcanic zone new zealand abstract the taupo volcanic zone tvz new zealand comprises several segments with variable components of extension and is characterised by longitudinal segmentation into a central zone dominated by rhyolitic calderas and extremities with only andesitic composite volcanoes modern

the australian stress map knowledge of the in situ stress field of the australian continent has increased greatly since compilation of the world stress map in 1992 principally by analysis of borehole breakouts and drilling induced tensile fractures in petroleum wells stress orientations are variable across the australian continent as a whole however within 15 of 16 individual stress provinces defined in the australian continent of one to a few hundred kilometres scale mean stress orientations are statistically significant the stress provinces and stress trajectory mapping reveal that there are systematic continental scale rotations of stress orientation within australia unlike many other continental areas stress orientations do not parallel the direction of absolute plate motion nonetheless the regional pattern of stress orientation is consistent with control by plate boundary forces if the complex nature of the convergent northeastern boundary of the indo australian plate and stress focusing by collisional segments of the boundary is recognized

dust deposition in the aral sea implications for changes in atmospheric circulation in central asia during the past 2000 years we investigated mineral aerosol dust deposition in the aral sea with intention to understand the variability of dust in central asia and its implications for atmospheric circulation change in the late holocene using an 11 12 m sediment core of the lake we calculated bulk sediment fluxes at high time resolution and analyzed grain size distributions of detrital sediments a refined age depth model was established by combined methods of radiocarbon dating and archeological evidence besides a principal component analysis pca of grain size fractions and elements fe ti k ca sr was used to assess the potential processes controlling detrital inputs the results suggest that two processes are mainly relevant for the clastic input as the medium silt fractions and ti fe and k are positively correlated with component 1 c1 and the fine size fractions 6 mm are positively correlated with component 2 c2 taking the results of the pca geological backgrounds clastic input processes into account we propose that the medium silt fractions and in particular the grain size fraction ratio 6e32 mm 2e6 mm can serve as indicators of the variability of airborne dust in the aral sea region on the contrary the fine size fractions appear to be contributed mainly by the sheetwash processes the bulk sediment deposition fluxes were extremely high during the little ice age lia ad 1400e1780 which may be related to the increased dust deposition as indicated by the variations of grain size ratio and ti the history of dust deposition in central asia can be divided into five distinct periods with a remarkably low deposition during ad 1e350 a moderately high value from ad 350e720 a return to relatively low level between ad 720 and ad 1400 including the medieval warm period mwp ad 755e1070 an exceptionally high deposition from ad 1400 to 1940s and an abnormally low value since 1940s the temporal variations in the dust deposition are consistent with the changes in the siberian high sh and mean atmospheric temperature of the northern hemisphere during the past 2000 years with low high annual temperature anomalies corresponding to high low dust supplies in the aral sea sediments respectively the variations in the fine size fraction also show a broadly similarity to a lacustrine d

crustal seismicity in taranaki new zealand using accurate hypocentres from a dense network a large dense network of three component broad band seismographs was used to determine accurate hypocentres for earthquakes in taranaki new zealand they allow us to characterize seismicity around mt taranaki a large dormant andesite cone volcano and to map precisely two major lineations of crustal seismicity a minimum 1 d velocity model was used to locate 389 local earthquakes using the probabilistic non linear earthquake location program nonlinloc there are few earthquakes beneath mt taranaki itself and all are relatively small and shallow 10 km deep the shallow seismogenic zone can be explained by the crust being unusually hot thus causing the base of the brittle ductile transition to be shallower than normal beneath mt taranaki this is supported by a high heat flow anomaly in this area the absence of any volcanic earthquakes beneath mt taranaki suggests that active volcanic processes are currently unlikely and the shallow brittle ductile transition depth means that precursory volcano tectonic seismicity from any future magmatic intrusion is unlikely to occur below 10 km depth the permanent seismic network can locate earthquakes in taranaki reasonably accurately and can reproduce most of the details seen by the temporary seismograph deployment provided that only the best hypocentres are considered however beneath mt taranaki which is the most important area for volcano monitoring hypocentres determined by the permanent network are too deep by 4 12 km the active cape egmont fault zone cefz west of mt taranaki is the most seismically active area with earthquakes in the upper crust to about 22 km depth spatial and temporal clustering earthquakes with similar waveforms and an absence of obvious main shocks imply that earthquake swarms make up a significant proportion of the seismicity in this area earthquakes in eastern taranaki occur primarily along the taranaki ruapehu line trl thought to be a major boundary across which the crustal thickness changes by about 10 km these earthquakes are less clustered have a b value typical of tectonic earthquakes and occur in the lower crust to a depth of 35 km with the upper crust almost aseismic the abrupt cessation of seismicity at 35 km depth is consistent with this boundary marking the moho with no earthquakes in the mantle the concentration of earthquakes in the lower crust requires it to be drier and more mafic than the wet quartzo feldspathic composition often used to model crustal rheology there is no change in maximum earthquake depth across the currently accepted location of the trl but there is a 10 km decrease in maximum earthquake depth some 25 km to the north of the currently accepted location this suggests that the true position of the trl is 25 km north of the hitherto accepted position

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

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

geochemistry geothermics and relationship to active tectonics of gujarat and rajasthan thermal discharges india abstract most thermal spring discharges of rajasthan and gujarat in northwestern india have been sampled and analysed for major and trace elements in both the liquid and associated gas phase and for 18 o 16 o d h in water 3 he 4 he and 13 c 12 c in co 2 in gas isotopic ratios most thermal springs in rajasthan are tightly associated to the several regional ne sw strike slip faults bordering ne sw ridges formed by archaean rocks at the contact with quaternary alluvial and aeolian sedimentary deposits of the rajasthan desert their ca hco 3 immature character and isotopic composition reveals 1 meteoric origin 2 relatively shallow circulation inside the crystalline archaean formations 3 very fast rise along faults and 4 deep storage temperatures of the same order of magnitude as discharging temperatures 50 90 c thermal spring discharges in gujarat are spread over a larger area than in rajasthan and are associated both with the nnw sse fault systems bordering the cambay basin and the ene wsw strike slip fault systems in the saurashtra province west of the cambay basin chemical and isotopic compositions of springs in both areas suggest a meteoric origin of deep thermal waters they mix with fresh or fossil seawater entering the thermal paths of the spring systems through both the fault systems bordering the cambay basin as well as faults and fractures occurring inside the permeable deccan basalt trap in the saurashtra province the associated gas phase at all sampled sites shows similar features 1 it is dominated by the presence of atmospheric components n 2 and ar 2 it has high crustal 4 he enrichment 3 it shows crustal 3 he 4 he signature 4 it has low co 2 concentration and 5 the only analysed sample for 13 c 12 c isotopic ratio in co 2 suggests that co 2 has a strong isotopically light organic imprint all these features and chemical geothermometer estimates of spring waters suggest that any active deep hydrothermal system at the base of the cambay basin about 2000 3000 m has low to medium enthalpy characteristics with maximum deep temperature in the storage zone of about 150 c in a regional overview both thermal emergences of rajasthan and gujarat could be controlled by the counter clockwise rotation of india

oblique back arc rifting of taupo volcanic zone new zealand taupo volcanic zone tvz is a back arc rift innorth island new zealand its geometry andkinematics are investigated using shaded reliefimages field examination of faults and offset streamchannels the results show that tvz trends nne is 250 km long by hikurangi margin in the north island of new zealand 20 km wide and consists of fivesegments extension is principally manifest as steeplydipping 60 90 normal faults parallel to tvz these in the last 300 kyr have experienced acomponent of dextral shear tvz is therefore anoblique back arc rift the dextral shear is 37 of thetotal displacement which for previously estimatedspreadingrates 7mm yr correspondsto 2 6mm yr thisvalueissimilartopreviousestimatesofthedextralshear from the back arc to the forearc domains in thenorthisland distributeddextralshearacrosstvzthussuggests that strain partitioning across the plateboundary at latitudes of tvz is less significant thanpreviously thought

long term slip rates and fault interactions under low contractional strain wanganui basin new zealand the newly mapped kapiti manawatu fault system kmfs in southern north island new zealand accommodated 3 5 km of basement throw over the last 3 myr along strike throw profiles are generated using seven stratigraphic markers interpreted from seismic reflection profiles acquired 3 km apart the profiles are symmetrical about their point of maximum displacement and cumulative profiles suggest that the reverse fault system behaves coherently the kmfs originates from the reactivation of extensional structures with fault lengths remaining constant over time contractional deformation started at circa 1750 400 ka maximum dip slip rates along individual faults are 1 77 0 53 and 0 74 0 22 mm yr 1 for the 0 120 and 120 1350 ka periods respectively the maximum cumulative throw rates across the kmfs are 4 9 1 5 and 1 5 0 5 mm yr 1 for the same periods long term strain rates across the kmfs are 2 5 times smaller than strain rates in the forearc basin of the hikurangi subduction margin located less than 100 km to the east the faults of the kmfs may extend to depth and link with the subducted pacific plate

heterogeneity of structure and stress in the rotokawa geothermal field new zealand geometric characterization of a geothermal reservoir s structures and their relation to stress field orientation is vital for resource development subsurface structure and stress field orientations of the rotokawa geothermal field new zealand have been studied for the first time using observations obtained from analysis of three acoustic borehole televiewer logs while an overall ne sw fracture strike exists heterogeneity in fracture dip orientation is evident dominant dip direction changes from well to well due to proximity to variously oriented graben bounding faults fracture orientation heterogeneity also occurs within individual wells where fractures clusters within certain depth intervals have antithetic dip directions to the well s dominant fracture dip direction these patterns are consistent with expected antithetic faulting in extensional environments a general shmax orientation of ne sw is determined from induced features on borehole walls however numerous localized azimuthal variations from this trend are evident constituting stress field orientation heterogeneity these variations are attributed to slip on fracture planes evidenced by changes in the azimuth of drilling induced tensile fractures either side of a natural fracture correlation of observed fracture properties and patterns to well permeability indicators reveal that fractures play a role in fluid flow in the rotokawa geothermal reservoir permeable zones commonly contain wide aperture fractures and high fracture densities which have a dominant ne sw strike orientation and nw dip direction studies of this kind which show strong interdependency of structure and stress field properties are essential to understand fluid flow in geothermal reservoirs where structural permeability dominates

origin and evolution of intracratonic thermal fluids from central western peninsular india abstract the chemical and isotopic composition of several thermal springs and associated gas phases in a large sector of central western peninsular india has been investigated such springs have meteoric isotopic signature and emerge after very well developed convective circulation at depth along important tectonic structures such as the son narmada tapti rift zone and the west coast fault chemical components in both gas and liquid phases and geothermometric estimations suggest that such springs are not related to the presence of any active hydrothermal systems at shallow depth in any of the studied areas the hottest convective water emerges at tattapani at near boiling point for water at atmospheric pressure 90 c in association with an n2 rich gas phase of clear meteoric signature since such fluids do not carry any corrosive components they could be conveniently exploited for industrial purposes such as drying processes from a tectonic point of view the presence of thermal emergences scattered in a wide area along geologically well defined structures which also generate frequent moderate earthquakes suggests that such structures are active although the isotopic composition of thermal springs points to a meteoric origin their feeding aquifers are not topographically driven as in most active alpine orogenic belts the relative high quantity of total helium in the associated gas phase suggests also that they are really deep old long circulating waters we propose for such waters the term intracratonic thermal waters since the isotopic signature of he in the gas phase does not show any release of primordial 3he in any of the areas of spring emergence based on the quite low 3he 4he ratio in the gas phase we suggest also that in spite of its morphological shape the narmada son tapti rift zone cutting the indian subcontinent in two is more related to paleo suture rather than to a mid continental rift system

seasonal variations in the isotopes of oxygen and hydrogen in geothermal waters from bakreswar and tantloi eastern india implications for groundwater characterization abstract 18o and d values of non thermal and thermal waters from the bakreswar and tantloi geothermal areas indicate a meteoric origin for the thermal springs both non thermal and thermal waters undergo seasonal isotopic variations being enriched in 18o and d in the winter relative to the rainy season for non thermal waters this is due to a higher rate of evaporation in winter as a consequence of depleting atmospheric humidity the effect is more pronounced for surface waters than groundwaters the degree of variation is in general very low for thermal waters the difference in issuing temperature as well as small variations in the stable isotopic composition and tritium content of the springs are suggestive of very low to moderate dilution of thermal waters by nearby shallow groundwater agnikund the hottest spring 71 c is least diluted 10 by local non thermal waters and hence is the best representative of deep seated thermal water the presence of very low amounts of tritium 0 6 0 5 to 1 9 0 5 tu in thermal waters indicates their long subsurface circulation time 50 years similar 18 o and d values for bakreswar and tantloi spring waters point to their origin from the same meteoric water and therefore they are genetically related recharge of the springs is likely to take place somewhere in the vicinity of gondwana basins occurring along the central part of the chotanagpur plateau

ridge forces absolute plate motions and the intraplate stress field torque poles are calculated for a variety of possible forces acting on the plates including ridge push slab pull and collisional resistance these torque poles are then compared to the directions of absolute plate motions there is a strong correlation between ridge torque poles and the azimuth of absolute plate motions for the north american south american pacific cocos and eurasian plates simple slab pull torques correlate well with absolute motion azimuths for the pacific nazca and cocos plates and moderately well with the absolute motion azimuth of the indoaustralian plate collisional resistance torque poles correlate with the absolute motion azimuth of the eurasian plate only the correlations are presented as further evidence that the absolute reference frame for plate motion is determined by the surface plates themselves torque poles for various forces are also compared with several long wavelength features of the global intraplate stress field that also tend to be aligned with absolute motion directions in general ridge torque directions agree well with the orientations of maximum horizontal stresses for stable north america western europe and south america and provide an alternative explanation for the alignment in terms of ridge push forces rather than basal drag collisional resistance forces can also explain the alignment of stresses in western europe for the indoaustralian plate the torque pole for collisional resistance forces is consistent with the general pattern of stresses in at least the western half of the plate but is not a good predictor of the entire data set for the plate other processes in addition to collisional resistance must be important for the indo australian plate ridge push forces may account for a significant portion of the long wavelength features of the intraplate stress field especially away from continental collisions such a conclusion is consistent with negative buoyancy of the slab being an important component of the driving mechanism as previously suggested slab forces may be largely balanced within the subducted slab itself and thus have limited effect on deformation of the surface plates

hot springs and the geothermal energy potential of jammu kashmir state n w himalaya india abstract india has an estimated geothermal power potential of 10 600 mwe but this potential is entirely undeveloped at present the geothermal atlas of india prepared by the geological survey of india gsi in 1991 describes some 340 hot spring sites and identifies more than 300 sites with geothermal potential in at least seven key geothermal provinces throughout india there are more than 20 hot spring sites in jammu kashmir state mainly in the chenab valley in the lesser central himalaya the kashmir valley and in the high himalaya region of ladakh at least three localities in the ladakh region chamuthang and puga in the indus valley and panamik in the nubra valley are considered to have geothermal power generation potential of between 3 and 20 mwe the puga hot spring area located at the junction of the indian and tibetan plates along the indus suture zone has the greatest potential for the near term development of geothermal energy in the indian subcontinent the area exhibits vigorous geothermal activity in the form of hot springs mud pools sulphur and borax deposits covering an area of c 15 km 2 the discharges are concentrated in an east west elongated area of some 4 km 2 near the mouth of the puga valley the puga geothermal field is bounded by faults and its reservoir rocks consist of granite gneiss and schist there is both direct and indirect evidence to support the existence of an active magmatic system at a depth of 5 7 km geophysical surveys have delineated a conspicuous low resistivity zone below the puga field systematic and comprehensive evaluation of the geothermal potential of the puga area began in 1973 thirty four wells have been drilled in the puga geothermal field to date at least 17 of which have resulted in mixed steam and water blow outs the discharges from some of the wells have temperatures of more than 120 c thermal studies indicate temperatures of more than 220 c at a depth of about 2 5 km below the puga valley corresponding to the main reservoir level chemical thermometry also suggests a reservoir temperature of 250 c while reservoir modelling studies suggest temperatures of up to 160 c at a depth of 450 m the high concentration of lithium rubidium and cesium in the geothermal water has been interpreted as indicating a magmatic source and young granitic intrusions and shallow crustal melting processes have been postulated as the most likely heat source for the puga geothermal field it is estimated that more than 5000 mwh of geothermal energy is available at puga which could be used for heating for greenhouse cultivation and eventually to generate electricity studies have indicated that there is a 90 probability that the puga field could sustain a 20 mwe power plant if the puga geothermal field could be developed it is very likely that it could be followed by the development of the chamuthang and panamik fields jammu kashmir state suffers from an acute shortage of power particularly in the mountainous region of ladakh the development of geothermal potential would provide for baseload needs especially in the winter months when the region s hydro power stations are frequently either shut down or working at significantly reduced efficiency because of freezing of the indus river however any development would need to be undertaken with great care to avoid damaging ladakh s vulnerable high altitude desert environment and its unique plant and animal life

subduction platform subsidence and foreland thrust loading the late tertiary development of taranaki basin new zealand borehole seismic and gravity data are used to investigate deformation of continental lithosphere at a miocene collisional zone deformation is manifested in the three following principal forms a long wavelength 500 km platform subsidence ascribed to mantle convection flexural deformation on a scale of 100 200 km due to crustal thrusting at the eastern boundary of the taranaki basin and a ductile thickening evident on the deep seismic section of taranaki basin that occurs on a scale of 10 km evidence for flexural deformation principally comes from the deep seismic section that shows a 150 km wavelength bending of the moho down toward the major zone of thrusting within the taranaki fault zone paleowater depths however provide evidence for an initial early miocene regional subsidence that is too long in wavelength to be explained by flexure induced from thrust sheet loading instead we propose that this broad platform subsidence was driven by loading from a deep source probably subduction induced flow in the mantle by 22 19 ma 1 2 km of water existed over most of the area now occupied by south taranaki basin by 19 17 ma the water depth in the zone east of the taranaki basin the taranaki fault zone had been replaced by rock due to submarine thrusting and crustal thickening this build up of submarine topography in the taranaki fault zone constitutes part of the load 25 8 mpa that created and maintains south taranaki basin gravity data place further constraints on loading at the thrust front and point to an additional intracrustal loading equivalent to 15 7 mpa over a 50 km wide zone this intracrustal load is explained as being due to thick skinned thrusting bringing denser lower crustal rocks nearer to the surface in the thrust zone the complete load on the taranaki foreland is therefore in three parts the submarine topographic load the intracrustal load and the loading of infilling sediments

andersonian wrench faulting in a regional stress field during the 2010 2011 canterbury new zealand earthquake sequence the initial mw7 1 darfield earthquake sequence was centred west of christchurch city in the south island of new zealand but aftershocks including a highly destructive mw6 3 event eventually extended eastwards across the city to the coast the mainshock gave rise to right lateral strike slip of up to 5 m along the segmented rupture trace of a subvertical fault trending 085 58 across the canterbury plains for c 30 km in agreement with teleseismic focal mechan isms near field data however suggest that the mainshock was composite initiating with reverse slip north of the surface rupture stress determinations for the central south island show maximum compressive stress s1 to be horizontal and oriented 115 58 the principal dextral rupture there fore lies at c 3 08 to regional s1 the classic andersonian orientation for a low displacement wrench fault an aftershock lineament trending c 1458 possibly represents a conjugate left lateral strike slip structure this stress field is also consistent with predominantly reverse slip reactivation of nne ne faults along the southern alps range front the main strike slip fault appears to have a low cumulative displacement and may represent either a fairly newly formed fault in the regional stress field or an existing subvertical fault that happens to be optimally oriented for frictional reactivation

audiomagnetotelluric studies to trace the hydrological system of thermal fluid flow of bakreswar hot spring eastern india a case history an audiomagnetotelluric amt study has been carried out in the bakreswar hot spring bhs area of eastern india to locate the geothermal source in the vicinity of bhs phase tensor analysis of the amt data shows that the region is broadly 2d rapid relaxation inversion rri for both transverse electric te and transverse magnetic tm modes has been carried out to obtain resistivity images of the subsurface amt results show that the north south fault close to bakreswar is a shallow feature not deeper than 300 m and thus cannot act as a heat source the subsurface formation below the fault zone is highly resistive up to a great depth indicating the absence of a heat source and geothermal reservoir in the vicinity of the bhs amt results indicate that the location of the geothermal reservoir is deep and lies beyond the profiles of measurement in the northwestern side of the bakreswar hot spring

present day dynamics of the aegean region a model analysis of the horizontal pattern of stress and deformation in order to gain quantitative insight into the forces that control the present day stress field and pattern of horizontal motions in the aegean region we adopt a forward model approach mechanisms that have been proposed to explain the present day tectonics are represented to first approximation in terms of the expected force distributions on the basis of a thin elastic shell representation of the aegean lithosphere we then calculate the stress field and displacements associated with these force sets and compare the results with observations of the state of stress based on geological studies of fault kinematics strain as expressed by earthquake focal mechanisms and horizontal motions measured by means of satellite geodesy the two most commonly cited mechanisms suggested to control the aegean tectonics 1 the push exerted by the westward moving anatolian block and 2 forces associated with the hellenic subduction zone are first analyzed separately it is found that the westward anatolian push alone does not explain the observed prevalence of tensional stress this is also expressed in a mismatch between the displacements computed to result from the westward push and the observed horizontal velocities regarding the forces on the aegean overriding margin we find that a model with outward pulling forces of uniform magnitude acting normal to the arc from the sw peloponnese to rhodes yields a stress field that matches the observed pattern of tension to a large extent this distribution of forces is consistent with the notion of gravitational spreading of the aegean lithosphere the pattern of seismic strain of the overriding margin may evidence the occurrence of a small additional resistive force although the prevalence of tension thus appears due mainly to the subduction related forces other aspects of the stress field and also the pattern of horizontal motions indicate that these forces act in combination with westward push our model results allow us to address the relation between the forces experienced by the upper plate and the kinematics of subduction not just in terms of a vertical cross section but also by taking into account the along arc dimension

geochemical evaluation of thermal springs in odisha india the indian state of odisha has a number of thermal springs these thermal springs are located at eight places attri tarabalo deulajhari magarmuhan bankhol badaberena taptapani and boden and belong to mahanadi geothermal province which is an archean pre cambrian geothermal province the thermal water discharging from these springs shows moderately acidic to moderately alkaline character ph 5 05 8 93 and the temperature ranges from 28 boden to 58 c tarabalo total dissolved solids tds also shows a wide variation between 16 9 bankhol and 595 mg l deulajhari a wide variation in the chemical characteristics of the thermal waters has been observed as they are located in different geological settings based on water chemistry all the thermal springs can broadly be grouped into three water types na cl ca hco3 and na hco3 the thermal spring water from attri tarabalo and deulajhari belongs to na cl water type which is due to the circulation through granitic rocks higher concentrations of cl and f in these thermal waters further suggest limited mixing and longer residence time as compared to the other areas where ca hco3 and na hco3 water types were found anion variation diagram clearly indicates that the thermal waters from attri tarabalo and deulajhari are fast ascending and fall in the mature water field thus their chemical signatures can be used to determine the reservoir temperature however in other areas water chemistry is shaped by near surface groundwater mixing processes and thus the chemical geothermometers may not be applicable to determine the reservoir temperature no appreciable temporal variations have been observed in the water chemistry of the thermal waters

subsurface fracture analysis and determination of in situ stress direction using fmi logs an example from the santonian carbonates ilam formation in the abadan plain iran abstract the relationship between the present day stress field and natural fractures can have significant implications for subsurface fluid flow in particular fractures that are aligned in orientations favourable for reactivation by either shear or tensile failure in the in situ stress field often exhibit higher hydraulic conductivities the ilam formation of southwestern iran is an important hydrocarbon reservoir containing numerous natural fractures however little is known about the state of stress in this region or any of iran s petroleum provinces we conducted analysis of the present day maximum horizontal stress orientation and the density orientation and hydraulic conductivity of natural fractures in the ilam carbonates using high resolution formation micro imager resistivity logs in two wells a total of 51 breakouts with an overall length of 215 m were observed in the two wells indicating a maximum horizontal stress orientation of 68 n 7 6 in well a and 58 n 6 3 in well b furthermore the wellbore derived stress orientations determined herein are consistent with those inferred from nearby earthquake focal mechanism solutions indicating that stresses in the sedimentary cover are linked to the resistance forces generated by arabia eurasia collision furthermore the correlation between stress orientations estimated from earthquake focal mechanism solutions and breakouts indicates that focal mechanism solution data which is often considered to be unreliable for stress field analysis near transform margins may provide reliable information on the stress orientation near continental collision zones the image log data also reveals three sets of open and presumably hydraulically conductive fractures with strikes of i 160 170 n ii 110 140 n and iii 070 080 n fracture set iii is consistent with being formed and open in the present day stress field however fracture sets i and ii strike at a high angle to the present day maximum horizontal stress and are interpreted herein to be the result of either pre or syn folding related forces the observation that different sets of open fractures in the field can be either sensitive or insensitive to the present day stress is critical for improving hydrocarbon recovery

motion and rigidity of the pacific plate and implications for plate boundary deformation 1 using up to 11 years of data from a global network of global positioning system gps stations including 12 stations well distributed across the pacific plate we derive present day euler vectors for the pacific plate more precisely than has previously been possible from space geodetic data after rejecting on statistical grounds the velocity of one station on each of the pacific and north american plates we find that the quality of fit of the horizontal velocities of 11 pacific plate pa stations to the best fitting pa euler vector is similar to the fit of 11 australian plate au velocities to the au euler vector and 20 better than the fit of nine north american plate na velocities to the na euler vector the velocities of stations on the pacific and australian plates each fit a rigid plate model with an rms residual of 0 4 mm yr while the north american velocities fit a rigid plate model with an rms velocity of 0 6 mm yr our best fitting pa au relative euler vector is located 170 km southeast of the nuvel 1a pole but is not significantly different at the 95 confidence level it is also close 70 km in position and 3 in rate to a pole derived from transform faults identified from satellite altimetry suggesting that the vector has not changed significantly over the past 3 myr our relative euler vector is also consistent with all known geological and geodetic evidence concerning the au pa plate boundary through new zealand the gps sites offshore of southern california are presently moving 4 5 1 mm yr relative to predicted pacific velocity with their residual velocities in approximately the opposite direction to pa na relative motion likewise the easternmost sites in south island new zealand are moving 3 1 mm yr relative to predicted pacific velocity with the residuals in approximately the opposite direction to pa au relative motion these velocity residuals are in the same sense as predicted by elastic strain accumulation on known plate boundary faults but are of a significantly higher magnitude in both southern california and new zealand implying that the plate boundary zones in both regions are wider than previously believed index terms 1206 geodesy and gravity crustal movements interplate 8155 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8158 tectonophysics evolution of the earth plate motions present and recent 3040 8159 tectonophysics evolution of the earth rheology crust and lithosphere keywords pacific plate motion plate rigidity plate boundary deformation

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

statistical trends in the intraplate stress field the world stress map wsm database contains thousands of intraplate stress indicators with the potential to provide important constraint for arguments about the relationship between tectonic stresses and both the kinematics and dynamics of plate motion previous studies which relied almost exclusively on visual inspection of the data established the existence of broad regions of uniform maximum horizontal compressive stress orientation shmax and stress regimes on a regional scale in the present study we present a statistical analysis of the wsm stress indicators with the aim of quantifying trends in both the shmax orientations and stress regimes the analysis was carried out within 5 5 bins which provide a resolution of several hundred kilometers only the 4537 high quality wsm indicators with rating of a to c were used in the analysis we present results for two types of analysis on the information contained within the bins first we evaluate the spatial distribution of the average stress regime normal strike slip or thrust second we apply the rayleigh test a standard statistical method in the analysis of directional data to the distribution of shmax orientations to test the null hypothesis that the orientations are random an important aspect of our study is the quantification of the conclusions drawn from visual inspection of the world stress map our results indicate that broad regions of uniform shmax orientations exist in most continental regions at high confidence levels 90 and 95 and are less robust in the slowest moving continental plates we also quantify the predominance of strike slip and compressional stress regimes in continental regions importantly our analysis provides information about trends in the shmax orientations in regions where large amounts of scatter in the directional data prevented conclusions being drawn from visual inspection of the data for example in western north america and continental australia furthermore we find a strong correlation between average shmax orientations and both the ridge push torque and the absolute plate velocity azimuths our observation that a greater number of shmax orientations correlate with the ridge push torque directions is further evidence that the intraplate stress field is strongly influenced by the ridge push force

contemporary tectonic stress pattern of the taranaki basin new zealand the present day stress state is a key parameter in numerous geoscientific research fields including geodynamics seismic hazard assessment and geomechanics of georeservoirs the taranaki basin of new zealand is located on the australian plate and forms the western boundary of tectonic deformation due to pacific plate subduction along the hikurangi margin this paper presents the first comprehensive wellbore derived basin scale in situ stress analysis in new zealand we analyze borehole image and oriented caliper data from 129 petroleum wells in the taranaki basin to interpret the shape of boreholes and determine the orientation of maximum horizontal stress s hmax we combine these data 151 s hmax data records with 40 stress data records derived from individual earthquake focal mechanism solutions 6 from stress inversions of focal mechanisms and 1 data record using the average of several focal mechanism solutions the resulting data set has 198 data records for the taranaki basin and suggests a regional s hmax orientation of n068 degrees e 22 degrees which is in agreement with nw se extension suggested by geological data furthermore this ene wsw average s hmax orientation is subparallel to the subduction trench and strike of the subducting slab n50 degrees e beneath the central western north island hence we suggest that the slab geometry and the associated forces due to slab rollback are the key control of crustal stress in the taranaki basin in addition we find stress perturbations with depth in the vicinity of faults in some of the studied wells which highlight the impact of local stress sources on the present day stress rotation

groundwater helium an indicator of active tectonic regions along narmada river central india abstract results of a survey of dissolved helium fluoride and electrical conductivity in groundwater from across the main stem of the narmada river between bharuch in the west and amarkantak in the east are reported this survey was undertaken to identify active tectonic regions based on locations of high helium concentrations interpreted as indicative of upward migration of deep fluids existence of deep fluids in this region has been hypothesised earlier based on various geophysical studies in the narmada rift basin a major tectonic feature in central india samples with high helium concentration are clustered in two broad regions with known intersecting faults indicating the possibility of plumes with high helium concentration being injected into shallower groundwater in these regions facilitated by these faults and fractures locations of groundwater samples having excess fluoride remarkably correspond to these two clusters of excess helium this suggests a possible commonality between the causal factor of excess helium and higher fluoride in groundwater which needs to be further investigated

topography boundary forces and the indo australian intraplate stress field the relative contribution of topographic e g ridge push continental margins and elevated continental crust and plate boundary e g subduction and collisional forces to the intraplate stress field in the indo australian plate iap is evaluated through a finite element analysis two important aspects of the iap intraplate stress field are highlighted in the present study 1 if substantial focusing of the ridge push torque occurs along the collisional boundaries i e himalaya new guinea and new zealand many of the first order features of the observed stress field can be explained without appealing to either subduction or basal drag forces and 2 it is possible to fit the observed shmax maximum horizontal stress orientation and stress regime information with a set of boundary conditions that results in low tectonic stress magnitudes e g tens of megapascals averaged over the thickness of the lithosphere throughout the plate this study therefore presents a plausible alternative to previous studies of the iap intraplate stress field which predicted very large tectonic stress magnitudes hundreds of megapascals in some parts of the plate in addition topographic forces due to continental margins and elevated continental material were found to play an important role in the predicted stress fields of continental india and australia and the inclusion of these forces in the modeling produced a significant improvement in the fit of the predicted intraplate stresses to the available observed stress information in these continental regions a central focus of this study is the relative importance of the boundary conditions used to represent forces acting along the northern plate margin we note that a wide range of boundary conditions can be configured to match the large portion of the observed intraplate stress field and this nonuniqueness continues to make modeling the iap stress field problematic while our study is an important step forward in understanding the sources of the iap intraplate stress field a more complete understanding awaits a better understanding of the relative magnitude of the boundary forces acting along the northern plate margin

a revised crustal stress orientation database for canada abstract the canadian database on contemporary crustal stress has not been revised systematically in the past two decades here we present the results of our new compilation that contains 514 new data records for the orientation data of maximum compressive horizontal stress and 188 data records that were re assessed in total the canadian stress database has now 1667 data records which is an increase of about 45 from these data a new canadian stress map as well as one for the province of alberta is presented to analyse the stress pattern we use the quasi median on the circle as a smoothing algorithm that generates a smoothed stress map of the maximum compressive horizontal stress orientation on a regular grid the newly introduced quasi interquartile range on the circle estimates the spreading of the data and is used as a measure for the wave length of the stress pattern the result of the hybrid wavelength analysis confirms that long spatial wavelength stress patterns 1000 km exist in large areas in canada the observed stress pattern is transmitted through the intra plate regions the results reveal that shorter spatial wave length variation of the maximum compressive horizontal stress orientation of less than 200 km prevails particularly in south eastern and western canada regional stress sources such as density contrasts active fault systems crustal structures etc might have a significant impact in these regions in contrast to these variations the observed stress pattern in the alberta basin is very homogeneous and mainly controlled by plate boundary forces and body forces the influence of curvature of the rocky mountains salient in southern alberta is minimal the present day horizontal stress orientations determined herein have important implications for the production of hydrocarbons and geothermal energy in the alberta basin

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor

the influence of basement structure on the evolution of the taranaki basin new zealand the taranaki basin situated offshore western new zealand is one of several large sedimentary basins formed during the late cretaceous in response to break up of the palaeo pacific margin of gondwana a review of published structural stratigraphic and geochronological data indicates that ne to nne striking basement faults generated during palaeozoic to mesozoic terrane accretion along the gondwana margin have strongly influenced the development of the basin the main basin bounding faults the cape egmont fault zone and the taranaki fault correspond to the boundaries of a narrow belt of plutonic rocks known as the median tectonic zone geological data from onshore south island suggests that right lateral movement occurred along the boundaries of the median tectonic zone during the early cretaceous from the late cretaceous to early tertiary ne to nne striking normal faults within the taranaki basin controlled deposition in a series of en echelon half grabens and sub basins many of the normal faults were later reactivated during a phase of compressional deformation associated with the development of the australian pacific plate boundary through new zealand reverse movement on the taranaki fault began in the early miocene and deformation propagated westward reaching the cape egmont fault zone in the late miocene to early pliocene

on the relationships between slab dip back arc stress upper plate absolute motion and crustal nature in subduction zones 1 statistical analysis of modern oceanic subduction zone parameters such as the age of a downgoing plate or the absolute plate motions is performed in order to investigate which parameter controls the dip of a slab and conversely what the influence of slab geometry is on upper plate behavior for that purpose parameters have been determined from global databases along 159 transects from all subduction zones that are not perturbed by nearby collision or ridge plateau seamount subduction on the basis of tomographic images slabs that penetrate through or lie on the 670 km discontinuity are also identified the results of the statistical analysis are as follows 1 back arc stress correlates with slab dip i e back arc spreading is observed for deep dips deeper than 125 km larger than 50 whereas back arc shortening occurs only for deep dips less than 30 2 slab dip correlates with absolute motion of the overriding plate the correlation is even better when the slab lies on or even more penetrates through the 670 km discontinuity 3 slabs dip more steeply by about 20 on average beneath oceanic overriding plates than beneath continental ones 4 slabs dip more steeply on average by about 10 near edges 5 slab dip does not correlate with the magnitude of slab pull the age of subducting lithosphere at the trench the thermal regime of the subducting lithosphere the convergence rate or the subduction polarity east versus west the present study provides evidence that the upper plate absolute motion plays an important role on slab dip as well as on upper plate strain retreating overriding plates are often oceanic ones and thus may partially explain the steeper slab dips beneath oceanic upper plates one can infer that low slab dips correlate well with compression in continental advancing upper plates whereas steep dips are often associated with extension in oceanic retreating upper plates excess weight of old slabs is often counterbalanced by other forces probably asthenospheric in origin such as lateral mantle flow near slab edges or anchor forces to determine slab dip

a bayesian approach to estimating tectonic stress from seismological data summary earthquakes are conspicuous manifestations of tectonic stress but the non linear relationships between the stresses acting on a fault plane its frictional slip and the ensuing seismic radiation are such that a single earthquake by itself provides little information about the ambient state of stress moreover observational uncertainties and inherent ambiguities in the nodal planes of earthquake focal mechanisms preclude straightforward inferences about stress being drawn on the basis of individual focal mechanism observations however by assuming that each earthquake in a small volume of the crust represents a single uniform state of stress the combined constraints imposed on that stress by a suite of focal mechanism observations can be estimated here we outline a probabilistic bayesian technique for estimating tectonic stress directions from primary seismological observations the bayesian formulation combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationship between the stresses acting on a fault and the resultant seismological observation we show our bayesian formulation to be equivalent to a well known analytical solution for a single errorless focal mechanism observation the new approach has the distinct advantage however of including 1 multiple earthquakes 2 fault plane ambiguities 3 observational errors and 4 any prior knowledge of the stress field our approach while computationally demanding in some cases is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters such as seismic anisotropy and geodetic strain rate observations and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations

temporal stability of deformation rates comparison of geological and geodetic observations hikurangi subduction margin new zealand abstract we examine how well contemporary horizontal velocity fields from global positioning system gps geodetic measurements describe long term deformation rates million year rates of extension shortening strike slip and vertical axis rotations are compared with modelling of gps velocities from the last 10 15 years in the hikurangi subduction margin new zealand within measurement uncertainties of mainly 50 the rates of deformation and vertical axis rotations for each time interval are usually indistinguishable the comparable deformation rates are consistent with the notion of near constant rates since 1 5 ma during this time oblique relative plate motion was partitioned with the majority 85 of margin normal motion accommodated on the plate interface and most 60 margin parallel motion by strike slip faulting and vertical axis rotations in the upper plate prior to 1 5 ma gps velocities cannot be reliably used to describe deformation and rotations of the hikurangi margin because at this time the taupo rift commenced opening the boundary between raukumara and wairoa rotational domains was abandoned and the rates of upper plate shortening increased the broad compatibility of gps and geological deformation and rotation rates since 1 5 ma suggests that the build up of contemporary elastic strains in the north island measured by gps is largely uniform for much of the duration of each seismic cycle the good agreement between the gps and geological deformation rates in the north island is consistent with the view that contemporary elastic strains will mainly be converted to permanent dip slip on the subduction thrust and to displacement on upper plate faults during future large magnitude earthquakes

overpressures in the taranaki basin distribution causes and implications for exploration analysis of subsurface pressure data from taranaki basin using direct e g repeat formation tester and indirect measurements drilling parameters and wireline log data such as sonic and resistivity indicates the presence of three pressure zones a near hydrostatic regime zone a that extends across the entire basin and to varying depths an underlying overpressured regime zone b with pressures approximately 1100 psi 7 584 mpa above hydrostatic that extends throughout the manaia graben and north along the eastern basin margin at depths of 1900 to 4100 m 6234 13 451 ft and a third regime zone c with approximately 2100 psi 14 479 mpa overpressure that directly underlies zone a and zone b in different parts of the basin although well penetrations are limited the primary cause of overpressure is interpreted to be disequilibrium compaction preserved in upper eocene and oligocene marine shales in parts of the basin hydrocarbon generation and in particular cracking to gas at high maturities is interpreted to contribute to overpressures the overpressures drain laterally and vertically into permeable units intervening transition zones seals comprise lithologic boundaries diagenetic zones and fault planes oligocene carbonates although commonly thin provide an effective barrier to vertical hydraulic communication over much of the basin the manaia graben is a partially closed system with overpressures retained by a complex combination of a top shale seal overlying a regional sequence boundary lithologic barriers within fault compartments fault planes and subcropping sequences episodic fault breach enables vertical transfer of fluids from zone b to zone a in a dynamic fault valve process to date all oil reserves have been found in zone a a large proportion of gas condensate reserves are within zone b and no commercial reserves have been established within zone c the spatial definition of these zones and the appropriate pressure regime is important for well design drilling safety determining hydrocarbon column heights and gas expansion factors and for exploration migration analysis regional analysis of pressure regimes can identify subsurface barriers and seals faults in particular are key elements in fluid migration and the focusing of liquids at abrupt pressure transitions the strength of fault planes and diagenetic zones is the likely control on dynamic fluid release zone c has been very lightly explored and may represent a potential for large dry gas accumulations the zone may be sealed by a diagenetic zone crosscutting lithologic boundaries conventional mapping horizons

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

remarks on the relationship between the tectonic regime the rake of the slip vectors the dip of the nodal planes and the plunges of the p b and t axes of earthquake focal mechanisms abstract we use a triangular representation of the plunges of p b and t axes to compare the different ways tectonic regime is inferred from earthquake focal mechanisms in recent works we argue that p b and t axes provide a reasonable estimate of principal stress directions when faulting is close to andersonian conditions and that this can be estimated from the location on a triangular diagram we analyze the geometrical relationship between the plunges of p b and t axes on one hand and the rake of slip and dip of nodal planes on the other hand we show that the rake and dip level curves correspond to trajectories of the vertical direction along great and small circles with respect to the frame of the p b and t axes this shows that dip slip faulting is compatible with vertical p or t axes but does not require it and instead requires horizontal b axes it also shows that strike slip faulting does not require vertical b axes but p and t axes with equal plunges this also reveals that focal mechanisms where p b and t axes all have moderate plunge correspond to two very different types of nodal planes a steeply dipping one with oblique slip and a moderately dipping one with strike slip seismically active and moderately dipping strike slip faults are to be found among these events

the stress pattern of iceland moritz ziegler mojtaba rajabi oliver heidbach gylfi pall hersir kristjan agustsson sigurveig arnadottir arno zang