bounds on the width of mantle lithosphere flow derived from surface geodetic measurements application to the central southern alps new zealand summary we show that the strain rate pattern measured at the surface of an oblique collision zone the new zealand southern alps can be used to impose bounds on the width of present day deformation in underlying mantle lithosphere geological and geophysical evidence supporting localized shearing along the downdip extension of the alpine fault is used to constrain the upper slipping patch using finite element models we investigate the effect of different boundary conditions in the lower lithosphere on the predicted interseismic velocity profile at the surface for a homogeneous elastic rheology distributed lower lithosphere shear over widths greater than about 100 km causes the fit with interseismic velocities derived from global positioning system gps measurements to significantly degrade in comparison either localized shear along a slipping patch or distributed shear over a width less than 100 km can fit the data the strike parallel velocity component is most diagnostic between the differing models finite element models incorporating variations in elastic strength and non linear viscous creep in the crust and mantle lithosphere while indicating that some decoupling can occur between crust and mantle lithosphere also support the conclusion that mantle lithosphere cannot be deforming over a width greater than about 100 km in contrast shear wave splitting studies have been interpreted to show a wide 200 400 km deforming zone beneath the southern alps the discrepancy highlights the different timescales measured by gps geodesy compared to estimates of finite strain that has accumulated over millions of years

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

links between long term and short term rheology of the lithosphere insights from strike slip fault modelling the classical interseismic mechanical models of the lithosphere assume that the earth s lithosphere is a horizontally layered medium recent more sophisticated models include lateral variations of physical parameters and are shown to be as effective and sometimes more at reproducing the geodetic data during the seismic cycle than the stratified models these new models have in common to require a finite width low viscosity zone underneath the fault zone proposed explanations for the formation of these localised low viscosity zones include grain size reduction shear heating and localised presence of fluids all these mechanisms are valid in order to locally weaken an initially strong lower crust however they are not efficient to localise strain across strike slip faults in post orogenic settings when the lower crust is already weak a previous numerical modelling study showed that metamorphic core complexes are exhumed underneath transtensional step over in post orogenic setting here we designed a parametric study of the impact of the initial thickness of the weak crust and the width of the step over on the intensity of strain localisation we find that the smaller the width of the step over and the thicker the lower crustal low viscosity channel is the most intense is the localisation in a second round of experiments we do not impose the step over kinematic and find that transtensional bound ary conditions are sufficient to trigger long lasting weakening of the crust through the exhumation of lower crustal material using viscoelastic models intended to mimic the interseismic behaviour of a strike slip fault we find that the modified geometry of the brittle ductile transition is sufficient to explain the interseismic strain localisation across a strike slip fault zone we conclude that a long time after an earthquake has occurred the interseismic geodetic signal is more prone to reflect the rheology of the crust than postseismic relaxation

crust mantle mechanical coupling in eastern mediterranean and eastern turkey present day crust mantle coupling in the eastern mediterranean and eastern turkey is studied using the global positioning system gps and seismic anisotropy data the general trend of the shear wave fast splitting directions in ne turkey and lesser caucaus align well with the geodetic velocities in an absolute plate motion frame of reference pointing to an effective coupling in this part of the region of weak surface deformation farther south underneath the bitlis suture however there are significant pn delays with e w anisotropy axes indicating significant lateral escape meanwhile the gps reveals very little surface deformation this mismatch possibly suggests a decoupling along the suture in the aegean the shear wave anisotropy and the pn anisotropy directions agree with the extensional component of the right lateral shear strains except under the crete basin and other parts of the southern aegean sea this extensional direction matches perfectly also with the southward pulling force vectors across the hellenic trench however the maximum right lateral shear directions obtained from the gps data in the aegean do not match either of these anisotropies seismic anisotropy from rayleigh waves sampled at 15 s corresponding to the lower crust match the maximum right lateral maximum shear directions from the gps indicating decoupling between the crust and the mantle this decoupling most likely results from the lateral variations of the gravitational potential energies and the slab pull forces

seismic anisotropy and mantle creep in young orogens summary seismic anisotropy provides evidence for the physical state and tectonic evolution of the lithosphere we discuss the origin of anisotropy at various depths and relate it to tectonic stress geotherms and rheology the anisotropy of the uppermost mantle is controlled by the orthorhombic mineral olivine and may result from ductile deformation dynamic recrystallization or annealing anisotropy beneath young orogens has been measured for the seismic phase pn that propagates in the uppermost mantle this anisotropy is interpreted as being caused by deformation during the most recent thermotectonic event and thus provides information on the process of mountain building whereas tectonic stress and many structural features in the upper crust are usually orientated perpendicular to the structural axis of mountain belts pn anisotropy is aligned parallel to the structural axis we interpret this to indicate mountainparallel ductile i e creeping deformation in the uppermost mantle that is a consequence of mountain perpendicular compressive stresses the preferred orientation of the fast axes of some anisotropic minerals such as olivine is known to be in the creep direction a consequence of the anisotropy of strength and viscosity of orientated minerals in order to explain the anisotropy of the mantle beneath young orogens we extend the concept of crustal escape or extrusion tectonics to the uppermost mantle we present rheological model calculations to support this hypothesis mountain perpendicular horizontal stress determined in the upper crust and mountain parallel seismic anisotropy in the uppermost mantle require a zone of ductile decoupling in the middle or lower crust of young mountain belts examples for stress and mountain parallel pn anisotropy are given for tibet the alpine chains and young mountain ranges in the americas finally we suggest a simple model for initiating mountain parallel creep

quantitative experiments on phreatomagmatic explosions abstract an experimental set up for controlled generation of thermal explosions fuel coolant interactions has been built by an interdisciplinary research group of volcanologists physicists and engineering scientists the tee haus thermal explosion experiment during the last 3 years more than 500 experimental runs were performed aim of the project was not to build a mini volcano but to produce igniteable mixtures of water and hot melt on a small scale in order to investigate basic physical aspects such small scale mixtures however most probably also occur during phreatomagmatic events in nature mixtures of water and magma on a large scale may be modelled by combination of small elements earlier experimental studies of thermal explosions were carried out with the use of metal melts nearly exclusively therefore a carbonate melt approx 0 3 kg of 1 1 mass ratio na2co3 k2co3 was used for initial experimental series because of easy handling and more magma similarity by injection of water into this melt explosive mixtures were produced and ignited self triggering explosive interactions occurred in a wide melt temperature range 720 to 1040 c at melt temperatures exceeding 1000 c co2 increasingly degassed presence of non condensible gas bubbles in the melt strongly reduced the explosivity the intensity of explosions only slightly increased with higher melt temperatures but strongly increased with higher water injection velocities because of more intensive mixing a minimum injection velocity was found to be approx 0 7 m s 1 experiments with silicate melts derived from diverse remelted volcanic rocks were carried out with a slightly modified set up explosions were ignited by an additional trigger a shock wave of approx 8 j in volcanic systems shock waves of this magnitude are abundant volcanic tremor etc strong explosions with silicate melts were produced at melt temperatures between 1350 and 1750 c the produced explosions exerted repulsion forces of up to 24 000 n with a typical pulse duration of 1 ms carbonate melt resp 1 5 ms silicate melts the ejection velocity was found to be in a range between 200 and 400 m s 1 explosion energy values up to 500 j were calculated the maximum explosion pressure was calculated to be in the range between 10 and 100 mpa only part of the melt so called interactive melt reacts explosively with injected water most of the melt is passively ejected by and after the thermal explosion different fragmentation processes result in specific grain size and grain shape populations that can be distinguished from each other particles resulting from the fine fragmentation process that precedes and causes the thermal explosion are characterized by angular to subrounded shapes and grain sizes ranging from 20 m to 180 m the amount of interactive melt is proportional to the intensity of the explosion the maximum amount of water vapourized at the explosive interaction so called interactive water was estimated thus the water melt mass ratio for explosive interactions could be calculated the values range between 1 25 and 1 35 carbonate melt resp between 1 6 and 1 25 silicate melts

width of mantle deformation across a continental transform evidence from upper mantle pn seismic anisotropy measurements seismic anisotropy v p of at least 6 5 2 5 in the upper mantle pn phase is reported 200 km east of the alpine fault in south island new zealand when these new data are combined with a previous pn study and published sks splitting results two distinct domains of mantle deformation are inferred within south island in southern south island the deforming zone in the mantle lithosphere is as wide as 335 km whereas in mid south island the deforming zone narrows to 200 km both regions display wider zones of seismic anisotropy than found at other continental transforms of the world the width and orientation of mantle anisotropy in southern south island are consistent with a model of simple shear in a zone that has undergone 800 200 km of right lateral shear displacement a value close to that predicted by geological reconstructions hence displacement can be accommodated by distributed shear without faulting being required in the mantle

constraints on the lithospheric structure beneath the north pyrenean fault from teleseismic observations the pyrenean range is bordered to the north by the north pyrenean fault which represents the boundary between the european and the iberian plates reflection profiles have shown that the moho is vertically offset by 15 km at the latitude of the fault in order to determine the structure beneath the crust we have recorded teleseismic events on seismic stations deployed on both sides of the fault large p wave traveltime residual variations are observed over a very short distance the residuals given by the rays coming from the south are close to those predicted from the known moho offset southern stations are 0 5 s later they rule out a stacking of the iberian and european crusts underneath the north pyrenean zone as postulated in some models in contrast rays coming from the north give residual variations opposite to those expected from the known crustal structure southern stations are as much as 0 9 s earlier the simplest model fitting the data introduces an abrupt change in lithospheric thickness about 30 km north of the north pyrenean fault i e the southern lithosphere is about 60 70 km thicker than the northern lithosphere the p wave residual variations as a function of incidence angle suggest the existence of an anisotropy a low velocity vertical axis is in the vicinity of the fault this simple structure can be explained by the collision of a thick iberian plate with a thinned aquitaine plate margin a collision involving the imbrication of the crusts and a small decoupling of the lithosphere at the base of the iberian moho

central and eastern anatolian crustal deformation rate and velocity fields derived from gps and earthquake data abstract we present a new strain rate and associated kinematic model for the eastern and central parts of turkey in the east a quasi n s compressional tectonic regime dominates the deformation field and is partitioned through the two major structural elements of the region which are the conjugate dextral strike slip north anatolian fault zone nafz and the sinistral strike slip east anatolian fault zone eafz the observed surface deformation is similar to that inferred by anisotropy studies which sampled the region of the mantle closer to the crust i e the lithospheric mantle and the moho and is dependent on the presence or absence of a lithospheric mantle and of the level of coupling between it and the overlaying crust the areas of the central and eastern parts of turkey which are deforming at elevated rates are situated above areas with strong gradients in crustal thickness this seems to indicate that these transition zones situated between thinner and thicker crusts promote more deformation at the surface the regions that reveal elevated strain rate values are 1 the elazig bingol segment of the eafz 2 the region around the karliova triple junction including the yedisu segment and the varto fault 3 the section of the nafz that extends from the erzincan province up to the nafz ezinepazari fault junction and 4 sections of the tuz golu fault zone other regions like the adana basin a significant part of the central anatolian fault zone cafz the aksaray and the ankara provinces are deforming at smaller but still considerable rates and therefore should be considered as areas well capable of producing damaging earthquakes between m 6 and 7 this study also reveals that the central part of turkey is moving at a faster rate towards the west than the eastern part turkey and that the wedge region between the nafz and the eafz accounts for the majority of the counter clockwise rotation between the eastern and the central parts of turkey this change in movement rate and direction could be the cause of the extensional deformation and respective crustal thinning with the resulting upwelling of warmer upper mantle observed in tomographic studies for the region between the iskenderun bay and the cafz the partitioning of deformation into an extensional regime could be the cause of the relatively low levels of strain rate in the south west part of the eafz and the northern part of the dead sea fault zone finally using this new compilation of gps data for the central eastern part of turkey we obtained a new anatolia eurasia rotation pole situated at 2 01 w and 31 94 n with a rotation rate of 1 053 0 015 ma

tectonic evolution of the northern african margin in tunisia from paleostress data and sedimentary record abstract a reconstruction of the tectonic evolution of the northern african margin in tunisia since the late permian combining paleostress tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns the extension lasting from the late permian to the middle triassic is contemporaneous of the rifting related to the break up of pangea during liassic times regional extensional tectonics originated the dislocation of the initial continental platform in northern tunisia the evolution of the liassic ne sw rifting led during dogger times to the north african passive continental margin whereas in southern tunisia a n s extension associated with e w trending subsiding basins lasted from the jurassic until the early cretaceous after an upper aptian early albian transpressional event ne sw to ene wsw trending extensions prevailed during late cretaceous in relationship with the general tectonic evolution of the northeastern african plate the inversions started in the late maastrichtian paleocene in northern tunisia probably as a consequence of the africa eurasia convergence two major nw se trending compressions occurred in the late eocene and in the middle late miocene alternating with extensional periods in the eocene oligocene early middle miocene and pliocene the latter compressional event led to the complete inversion of the basins of the northwestern african plate originating the maghrebide chain such a study supported by a high density of paleostress data and including complementary structural and stratigraphic approaches provides a reliable way of determining the regional tectonic evolution

crust mantle structure of the central north island new zealand based on seismological observations abstract two geophysical features characterise the anomalous crust mantle structure beneath central north island of new zealand the apparent thinning of the felsic crust by a factor of at least 50 and upper mantle p wave velocities pn phase about 10 less than normal 7 3 7 4 km s pn velocities increase slowly to a maximum of 7 8 km s at a depth of about 80 100 km above a depth of 15 km seismic p wave velocities vp are 6 km s or less representing what is likely to be a mix of the original greywacke crust that has been stretched along with an unknown volume of intruded igneous rocks that are in various stages of cooling defining the moho is problematic in this dynamic region below a depth of 15 km there is a continuous increase in vp such that velocities 7 km s are reached at a depth as shallow as 20 km on a east west line and 7 4 km s on a north south line we interpret these wave speeds as a transition zone into low pn velocities rather than high lower crustal values of vp pn wave speeds as low as 7 4 km s are detected by tomographic methods to depths of at least 65 km and laterally over an area of at least 10 000 km2 a 1 4 partial melt in the mantle wedge beneath the central north island is estimated based on qp seismic anisotropy low values of pn and amplitudes of deep reflections these upper mantle features are more indicative of asthenosphere than lithosphere and coupled with the geological evidence for rapid uplift here at 5 ma are consistent with convective removal of the mantle lithosphere from western and central north island in late miocene times

a comparison of gps solutions for strain and sks fast directions implications for modes of shear in the mantle of a plate boundary zone abstract the strain rate and vertical velocity fields for new zealand are computed using gps data from geonet nz collected during the past decade two domains for shear in the mantle are inferred by comparing the principal shortening direction with the fast direction of shear wave splitting beneath the central southern part of the south island the strains are low and its unclear if irrotational strain is taking place or if the splitting here is dominated by anisotropy in the asthenosphere in contrast data for the central and northern south island suggest simple shear is dominant and distributed over a zone 200 km wide an analysis of the major strike slip faults confirms that the strike of the major south island fault systems makes a 60 15 angle with the shortening direction a map of the vertical component of geonet gps velocities shows regions of surface uplift 5 mm y in both the central south and north islands while the pattern of uplift in central south island is consistent with known geology the rate of uplift in the central north island is an order of magnitude higher than the geological rate estimated on a my time scale

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

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

on the last explosions of carbonatite pipe g3b gross brukkaros namibia pipe g3b is part of the upper cretaceous carbonatitic gross brukkaros volcanic field in southern namibia the pipe represents the root zone of a diatreme and is located 2800 m west of the rim of gross brukkaros a downsag caldera the pipe is exposed approximately 550 m below the original upper cretaceous land surface it cuts down into its own feeder dyke 0 3 m thick the pipe coalesced from two small pipes and in plan view is 19 m long and 12 m wide it consists of fragmented cambrian nama quartzites and shales of the fish river subgroup despite intensive brecciation the stratigraphic sequence of the country rocks is almost preserved in the pipe in addition the feeder dyke became fragmented too and can be traced in a 2 to 3 m wide zone full of carbonatite blocks along the southern margin of the pipe the void space of the breccia is 30 50 in volume finally after the disruption of country rocks and feeder dyke a little carbonatite magma intruded some of the void space the breccia of pipe g3b is considered to represent a root zone at the transition from the feeder dyke into a diatreme above formation of the breccia required a shock wave thought to have been associated with a last explosion of the diatreme immediately above the present level of exposure the explosion can be shown to have been phreatomagmatic in origin

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

depth variable crustal anisotropy patterns of crustal weakness and destructive earthquakes in canterbury new zealand abstract low strain rate areas of the earth are often host to long recurrence but damaging earthquake cycles in many cases these events occur on reactivated and previously unrecognized faults noise based imaging of seismic anisotropy is capable of revealing the seismic fabric of inherited structures as well as the preferred orientation of pervasive cracking in the upper crust both features with a potential relationship to failure on faults causing catastrophic earthquakes by understanding the orientation of seismic weaknesses seismic hazard in areas of low strain rate can be better understood the geometric relation of crustal anisotropy and the 3 d crustal stress tensor has the potential to qualitatively inform us of the location and or orientation of large crustal earthquakes in regions with little previously recorded seismicity but known tectonic loading directions in this study noise cross correlation techniques were used to measure surface wave dispersion these measurements were inverted to solve for azimuthal anisotropy of fundamental mode rayleigh waves in the canterbury region of the south island of new zealand the results of passive imaging show a distinct difference in magnitude and azimuth of surface wave anisotropy at different depths within the crust across the region we suggest that the approximately east west fast axis orientation at upper crustal depths reflects the cretaceous faulting of the impacting chatham rise and the approximately northeast southwest fast axis orientation at lower crustal depths reflects the present plate boundary strain direction the upper crust fast axis parallels the surface rupturing greendale fault which gave rise to the ongoing destructive canterbury earthquake sequence we suggest that the upper crust azimuthal anisotropy measured using ambient noise is capable of revealing dominant patterns of crustal weaknesses in regions like canterbury which are prone to low recurrence but highly damaging earthquakes

boundary layer mantle flow under the dead sea transform fault inferred from seismic anisotropy lithospheric scale transform faults play an important role in the dynamics of global plate motion near surface deformation fields for such faults are relatively well documented by satellite geodesy strain measurements and earthquake source studies and deeper crustal structure has been imaged by seismic profiling relatively little is known however about deformation taking place in the subcrustal lithosphere that is the width and depth of the region associated with the deformation the transition between deformed and undeformed lithosphere and the interaction between lithospheric and asthenospheric mantle flow at the plate boundary here we present evidence for a narrow approximately 20 km wide subcrustal anisotropic zone of fault parallel mineral alignment beneath the dead sea transform obtained from an inversion of shear wave splitting observations along a dense receiver profile the geometry of this zone and the contrast between distinct anisotropic domains suggest subhorizontal mantle flow within a vertical boundary layer that extends through the entire lithosphere and accommodates the transform motion between the african and arabian plates within this relatively narrow zone

pn anisotropy beneath the south island of new zealand and implications for distributed deformation in continental lithosphere pn travel times from regional earthquakes recorded both by stations on new zealand and by ocean bottom seismographs deployed offshore indicate anisotropy in the uppermost mantle beneath the region the largest anisotropy of 8 2 1 lies beneath the deforming part of the south island to just off its west coast a zone roughly 100 200 km wide the fastest propagation is aligned n60 e 3 essentially parallel to the largely strike slip relative plate motion since 20 ma also n60 e the magnitude of anisotropy decreases abruptly northwest and southeast of this zone and on the southeast side of the island the orientation of fastest propagation is between n32 w and n s the n60 e orientation of fast propagation is consistent with finite strain within the uppermost part of the mantle lithosphere if the measured 850 km of displacement of the pacific plate past the australia plate is spread over a region with a width of 100 200 km the agreement of this orientation of fast propagation with the orientation or relative plate motion suggests the possibility of but does not require some dynamic recrystallization in rock as cold as 500 800 c where peierls creep seems to be the likely deformation mechanism such a strain distribution matches deformation of a thin viscous sheet that obeys a constitutive relationship of the form e n where e is the average strain rate and is the operative deviatoric stress with an average value of n 3 10 presumably the nw se fast propagation in the region southeast of the island results from strain that precedes the cenozoic deformation that has shaped the island

on the origin of orogens in order to understand how orogens work a quantitative approach demonstrating proof of concept is essential our goal is to reconcile the diverse array of tectonic features observed in natural orogens in the context of working numerical models that are consistent with both the underlying physics and first order geological constraints we present a simple conceptual temperature magnitude t m framework for orogenesis in terms of the progression from small cold to large hot orogens and we use forward numerical models to test hypotheses corresponding to specific stages along the t m spectrum small cold orogens are analyzed using crustal scale singularity s point models in which suborogenic mantle lithosphere is kinematically subducted beneath crust that deforms by critical wedge mechanics the transition from oceanic subduction to continental collision and the subsequent evolution of large hot orogens has been investigated using both crustal and upper mantle scale models the latter including dynamic subduction of suborogenic mantle lithosphere large hot orogens with thick crust are characterized by elevated plateaus with a strong superstructure underlain by hot weak lower crustal infrastructure beneath plateaus tectonic processes are dominated by ductile flow of weak crust in response to differential pressure while plateau flanks form external thrust sense wedges we discuss four topical issues in orogenic tectonics including the response of the suborogenic mantle lithosphere to convergence the interaction of climate and tectonics the current debate concerning wedge versus channel flow models to explain the himalayan tibetan system and the interpretation of metamorphic architecture in terms of orogenic processes we conclude that collisional orogenesis is driven largely by subduction and accretion of material at convergent margins accompanied by shortening thickening and heating of deformed crust

earthquake cycle simulations with rate and state friction and power law viscoelasticity abstract we simulate earthquake cycles with rate and state fault friction and off fault power law viscoelasticity for the classic 2d antiplane shear problem of a vertical strike slip plate boundary fault we investigate the interaction between fault slip and bulk viscous flow with experimentally based flow laws for quartz diorite and olivine for the crust and mantle respectively simulations using three linear geotherms dt dz 20 25 and 30 k km produce different deformation styles at depth ranging from significant interseismic fault creep to purely bulk viscous flow however they have almost identical earthquake recurrence interval nucleation depth and down dip coseismic slip limit despite these similarities variations in the predicted surface deformation might permit discrimination of the deformation mechanism using geodetic observations additionally in the 25 and 30 k km simulations the crust drags the mantle the 20 k km simulation also predicts this except within 10 km of the fault where the reverse occurs however basal tractions play a minor role in the overall force balance of the lithosphere at least for the flow laws used in our study therefore the depth integrated stress on the fault is balanced primarily by shear stress on vertical fault parallel planes because strain rates are higher directly below the fault than far from it stresses are also higher thus the upper crust far from the fault bears a substantial part of the tectonic load resulting in unrealistically high stresses in the real earth this might lead to distributed plastic deformation or formation of subparallel faults alternatively fault pore pressures in excess of hydrostatic and or weakening mechanisms such as grain size reduction and thermo mechanical coupling could lower the strength of the ductile fault root in the lower crust and concomitantly off fault upper crustal stresses

lithospheric shear zones as constant stress experiments below the seismogenic zone plate boundaries are defi ned by lithospheric ductile shear zones these localize strain and are the main reason that convective motions in the earth s interior are expressed at the surface as plate tectonics we argue here that lithospheric shear zones operate at approximately constant stress equal to the yield strength of the surrounding rocks this places constraints on the bulk strength of the lithosphere and allows us to calculate the cumulative width of the shear zones as a function of depth the concept applies most clearly to strike slip shear zones but is also applicable to thrust and normal sense shear zones although these evolve with time due to temperature changes associated with burial or exhumation if shear zones operate at constant stress this affects their microstructural evolution and hence their rheology decreases in grain size due to dynamic recrystallization may cause a switch in the dominant deformation mechanism to grain size sensitive creep leading to weakening and strain localization a common argument based on a constant strain rate approach has been that such transitions will be inhibited by grain growth in a constant stress shear zone however dynamic recrystallization continues to maintain the low grain size even after the switch has occurred grain growth is inhibited under these conditions and hence the switch is permanent as long as the boundary conditions remain the same grain size reduction in shear zones is therefore a critical factor in maintaining plate tectonic processes

on the relation between seismic anisotropy and finite strain because seismic anisotropy in the upper mantle is due primarily to lattice preferred orientation lpo of olivine crystals induced by deformation observations of anisotropy can provide constraints on mantle deformation and flow in this paper we use a previously published theory for deformation induced lpo ribe and yu 1991 to quantify the relation between seismic anisotropy and deformation for two model compositions a pure olivine dunite aggregate and a harzburgite comprising 70 olivine and 30 enstatite analytical and numerical solutions of the governing equations show that the predicted lpo and hence also the seismic anisotropy depends only on the finite strain and not on the deformation path by which that strain is produced the magnitude of the anisotropy depends only on the ratios c1 c2 and c2 c3 where c1 c2 c3 are the lengths of the principle axes of the finite strain ellipsoid and the directions of maximum and minimum compressional wave velocity vp coincide with the axes c1 and c3 respectively we calculate the percent anisotropies for compresional and shear waves propagating along the three principle axes of the finite strain ellipsoid as functions of the axial ratios c1 c2 and c2 c3 for our two model compositions however inferences of the magnitude of finite strain obtained using these results are likely to be minimum estimates because our theory neglects the effects of dynamic recrystallization finally we present as a byproduct of this study a new direct method for calculating the finite strain produced by an arbitiary deformation history

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

felsic fire fountaining beneath archean seas pyroclastic deposits of the 2730 ma hunter mine group quebec canada abstract the lapilli tuff breccias ltb 1 and ltb 2 of the archean hunter mine group in the south central part of the abitibi greenstone belt are inferred to be the product of subaqueous lava fountaining intercalated sub wave base iron formations interstratified turbiditic tuffs the absence of wave induced sedimentary structures and the stratigraphic position of lapilli tuff breccias beneath basaltic komatiites support this contention a complete eruptive sequence shows a tripartite division into a massive breccia b stratified lapilli tuff and c turbiditic tuff lapilli tuff division the massive breccia division is characterized by clusters of isolated and compressed irregular shaped clasts inferred to be deposited directly from the hot magmatic lava fountain abundant vesicular pyroclasts with a vesicle content of up to 60 exhibit locally coalescing vesicles indicating bubble nucleation prior to eruption the prevalence of irregular to amoeboid clast shapes suggests transport from the vent in a steamy rich high density current to the site under a self generated steam cupola ubiquitous subequant lapilli size pyroclasts of the stratified lapilli tuff division suggest that significant ingress of water into the fountain changed the prevalent fragmentation process from magmatic to hydrovolcanic the turbiditic tuff lapilli tuff division composed of pumice lithic fragments and vitric ash is envisaged to have formed by gravitational collapse of a subaqueous turbulent eruptive plume this type of eruptive mechanism constituted a minor but important process of volcanic construction on the ocean floor during the archean and possibly during incipient arc and backarc formation in modern day settings

where is the real transform boundary in california 1 the zone of highest geodetically defined strain rate in california does not everywhere coincide with the surface trace of the san andreas fault saf to determine whether this reflects the pattern of long term permanent deformation we analyzed the velocity field on swaths across the transform located so as to avoid intersections among the major fault strands slip rates and flexural parameters for each fault were determined by finding the best fit to the velocity profile using a simple arctan model representing the interseismic strain accumulation our slip rates compare well with current geologic estimates which suggests that the present day velocity field is representative of long term motions we find that the transform is a zone of high strain rate up to 80 km wide that is straighter than the saf and has an overall trend closer to the relative plate motion vector than the saf most sections of the saf take up less than half of the total slip rate and slip is transferred from one part of the system to another in a way that suggests that the saf should not be considered as a unique locator of the plate boundary up to half of the total displacement takes place on faults outside the high strain rate zone distributed over several hundred kilometers on either side our findings substantiate previous suggestions that the transform has the characteristics of a macroscopic ductile shear zone cutting the continental lithosphere around which stress and strain rate decrease on a length scale controlled by the length of the transform

phreatomagmatism and its relevance abstract phreatomagmatic explosive volcanism results from the interaction of magma with external water groundwater or surface water close to or at the earth s surface magma of any composition acid to ultrabasic may be involved in this type of explosive activity at present the relevance of phreatomagmatism is realized increasingly because it takes place in many diverse environments and affects not only small monogenetic volcanoes but also large volcanoes at some volcanoes as for example at lake taupo new zealand a volume of several tens of km 3 of magma may have been mixed with several km 3 of external water phreatomagmatism has thus become an important aspect in volcanic hazard assessments other fields involving the interaction of water with a melt are the study of nuclear and other industrial safety hazards of magma mixing of diamond carrying volcanism and of hydrothermal ore deposits as well as geothermal and groundwater reservoirs experiments on the dynamics of magma water interactions provide increasing insight into the principles and hazards of phreatomagmatic explosions this type of research will become a new field in experimental petrology

continental transforms a view from the alpine fault abstract continental transform faults are dominantly highly localized strike slip shear zones hundreds of kilometers long that accumulate tens to hundreds of kilometers of displacement from work on the alpine fault we pose the questions what is the deep structure of a continental transform and how does the displacement become localized we review research on the alpine fault and propose a model in which the fault partitions at depth into a steep zone extending into the mantle with largely fault parallel motion and a flat ductile decollement in the lower crust the fault localizes around two thirds of the plate motion within a 100 km wide zone of distributed deformation a review of other active continental fault systems suggests that variation between them may reflect their tectonic origins the nature of the crust in which they develop the presence of a significant oblique component of motion and the displacement rate all however have evidence for the development of a single principal fault zone that carries 50 of the total displacement and extends as a localized zone of shear into the upper mantle we review mechanisms of strain weakening and suggest that localization of a principal fault may be initiated in the seismogenic crust and through a series of positive feedbacks eventually extend through the lower crust into the upper mantle

electrical resistivity tomography ert applied to karst carbonate aquifers case study from amdoun northwestern tunisia the amdoun region is characterized by a high degree of karstification due to the climate impact 1500 mm year 1 and the development of fracture network survey using electrical resistivity tomography ert is deployed to provide a cost effective characterization of the subsurface karst environments a total of seven ert profiles with lengths of 315 m were evaluated at the beja governorate nw tunisia the area represents a small syncline of boudabbous limestone rocks lower eocene which is covered by a thin layer of clay in this study an ert survey was conducted to examine the spatial distribution and shape of underground cavities in the karst area in jebel sabah anticline and ain sallem zahret medien syncline in this study geological hydro geological and electrical resistivity tomography ert methods were applied to determine the geometry of the perched aquifer in the amdoun region nw tunisia the area is characterized by fractured and karstic limestone aquifer of late cretaceous abiod fm and lower eocene boudabbous fm the aquifers have a karstic functioning and drain aquifers of economical interest despite some wells exploiting them seven resistivity profiles were conducted along the survey area at three sites the orientation extension and the degree of inclination of those profiles are shown in the location map the correct resistivity data were interpreted using earth imager 2d software the results of the interpreted geo electrical sections showed that the resistivity of the carbonate aquifer varied between 2 5 to over 5794 m the thickness of the perched aquifer ranged from 15 to 50 m while its depth from the surface lies between 10 and 60 m the ert not only provided precise near surface information but was also very useful for establishing the 3d geometry and the position of several potential cavities and karts the results show the presence of small to large isolated cavities at various depths the low resistivity of cavities in the boudabbous formation has been explained by the groundwater saturation the ert technique could be effectively used for 3d detection of underground limestone cavities

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

active thrusting and folding in the qilian shan and decoupling between upper crust and mantle in northeastern tibet fieldwork south of the city of gaotai gansu province china shows that active shortening of surface sediments in the foothills of the yumu shan a large fore mountain of the qilian shan at the northeastern edge of tibet involves both overthrusting and flexural slip folding north of this mountain we found and mapped a prominent north facing thrust scarp that offsets a holocene fan sloping gently 3 4 to the north part of this scarp appears to be related to the m 7 5 180 a d earthquake that may have led to the demise of the han dynasty city of luo tuo chen in the hexi corridor a set of 10 100 150 m long profiles measured across this scarp 3 2 m high on the average can be made to fit the diffusion degraded morphology of a surface break related to the 180 a d event using a value of about 3 3 m 2 10 3 yr for the mass diffusivity of fanglomerates in this part of gansu province smaller mountain facing scarps on a terrace capped foothill result from bedding slip concurrent with active folding of underlying steeply northdipping plioquaternary sandstone and conglomerate beds holocene uplift rates along the yumu shan which is only one of the qilian shan ranges are estimated to be between 0 4 and 1 9 mm yr which implies that much of the mountain formed in the quaternary the periclinal structure of the plioquaternary envelope under which the paleozoic core of the yumu shan plunges towards the west suggests that the whole 3200 m high mountain is a basement ramp anticline mountains striking parallel to the yumu shan with similar structure and comparable or greater sizes north and south of the hexi corridor probably also correspond to recent crustal ramp anticlines this implies that the wide mountainous upper crustal wedge making the northeastern edge of the tibet qinghai plateau is detached from the underlying lower crust and upper mantle

use of chloride mass balance and environmental isotopes for evaluation of groundwater recharge in the alluvial aquifer wadi tharad western saudi arabia groundwater recharge estimation has become a priority issue for humid and arid regions especially in regions like saudi arabia where the precipitation varies over space and time as a result of topography and seasonality wadi tharad is a typical arid area in western saudi arabia within its drainage area of 400 km 2 the groundwater system shows a graded hydrochemical zonation from the hydrocarbonate in the upper reach to the chloride zone in the lower reach the saturation index si varies depending on the concentrations of carbonate minerals the mean for calcite and dolomite is about in equilibrium e g zero value as halite and gypsum indices are negative it is undersaturated isotopic compositions of h and o in the groundwater show that the groundwater recharge resources are mainly from meteoric water the chloride mass balance method was refined to estimate the amount of recharge which is probably 11 of the effective annual rainfall these results can be used to improve the accuracy of future groundwater management and development schemes

the electrical resistivity tomography method in the detection of shallow mining cavities a case study on the victoria cave cartagena se spain former mining areas which have been under intensive mining activity raise some geotechnical concerns the main concerns that can arise are for example foundation problems on buildings placed on these mining areas and the damage to roads resulting in potholes these are due to the collapse of the mining cavities from natural alteration processes during the course of time in order to check its reliability the electrical resistivity tomography ert method was tried out on a selected area of la sierra minera where the location and orientation of the main caves are well known this technique was chosen because the climate of the study area is semi arid and the cave space is occupied by air so the electrical resistivity contrast between the cave itself and the host rock could be expected to be high the geophysical results have shown a close correlation with the position of known caves but further have highlighted the position of new cavities previously unknown before employing the ert method the discovery has been corroborated by speleologists inspection of the area the ert method has therefore proved to be very effective and suitable in providing sufficient subsurface information on shallow cavities

deep structure of lithospheric fault zones 1 we calculate the cumulative width w of ductile shear zones accommodating plate motion in continental lithosphere based on the assumptions that 1 the flow stress is controlled by the yield strength of intact rock at any given depth 2 the yield strength profile through the crust can be constrained from observations in exhumed shear zones and 3 strain localization is primarily caused by grainsize reduction leading to a switch to grainsize sensitive creep we use a mid crustal stress temperature profile measured in the whipple mountains california and calculate stress profiles at depth from published flow laws for feldspar and olivine we conclude thatwfor a plate boundary shear zone accommodating 50 mm yr displacement comparable to the san andreas transform may reach 180 km in the quartz rich mid crust depending on water fugacity and thermal gradient it narrows to a few meters in feldspathic lower crust and in the uppermost mantle and then widens rapidly with depth in the lower lithosphere we explore the effects of differences in crustal thickness and composition thermal gradient and water activity

s wave splitting in the offshore south island new zealand insights into plate boundary deformation local and regional s wave splitting in the offshore south island of the new zealand plate boundary zone provides constraints on the spatial and depth extent of the anisotropic structure with an enhanced resolution relative to land based and sks studies the combined analysis of offshore and land measurements using splitting tomography suggests plate boundary shear dominates in the central and northern south island the width of this shear zone in the central south island is about 200 km but is complicated by stress controlled anisotropy at shallow levels in northern south island a broader 200 km zone of plate boundary parallel anisotropy is associated with the transitional faulting between the alpine fault and hikurangi subduction and the hikurangi subduction zone itself these results suggest s phases of deep events 90 km in the central south island are sensitive to plate boundary derived ne sw aligned anisotropic media in the upper lithosphere supporting a thin viscous sheet deformation model

relationship between crustal finite strain and seismic anisotropy in the mantle pacific australia plate boundary zone south island new zealand summary the relationship between crust and mantle deformation in plate boundary zones is an outstanding problem in geodynamics new zealand provides a rare opportunity to examine the way strike slip faults relate to deep seated zones of lower crustal and mantle flow a conspicuous bend deflects elongated terranes such as the dun mountain ophiolite through 70 in the continental crust which we interpret as being the result of distributed dextral shear between the pacific and australian plates in the cenozoic we utilized variations in the strike of two different geological markers ophiolite terrane and fold belts towards the alpine fault to calculate finite strains in three crustal domains the deflection is best matched by a transpressional rather than a simple shear deformation these transpressional models predict maximum horizontal finite strain azimuths 10 that trend anticlockwise 30 to 10 from the alpine fault these azimuths match published fast polarization azimuths of sks and local 2 1 and strains es 1 9 without being reoriented towards the shear plane by recrystallization in agreement with our modelling of mantle flow the large sks shear wave splitting delays 2 s on the south island suggest that the direction of maximum finite stretch in the mantle is more likely horizontal than vertical this inference is consistent with the 3 d strain calculated from deflected markers in the crust

on the formation of deep seated subterranean peperite like magma sediment mixtures abstract in addition to large amounts of fragmented country rocks maar diatreme volcanoes commonly eject juvenile lapilli and cauliflower bombs containing many dispersed xenoliths and or xenocrysts derived from the country rocks surrounding the diatremes formation of these lapilli and bombs is attributed to thermohydraulic explosions in the root zones of the diatremes and their consequences the thermohydraulic explosions release shock waves which are capable of intensely fragmenting the surrounding country rocks vaporisation of water superheated during thermohydraulic explosions and its expansion to lower pressure causes ejection of major parts of the fragmented country rocks surviving sections of fragmented country rocks may collapse or slide into the partially evacuated root zone and thus form a mass flow deposit subsequent to each explosion when prior to a new explosion magma rises from the underlying feeder dyke into the root zone it intrudes this clastic debris inflates it and may mingle with the debris to form a peperite subsequent explosions can fragment and eject fragments of this peperite in the form of juvenile ash grains juvenile lapilli and bombs containing xenoliths or xenocrysts from the country rock debris lack of further explosions but continued rise and intrusion of magma will cause emplacement of such inflated peperite masses as plugs

linear model describing three components of flow in karst aquifers using 18o data the stable isotope of oxygen 18o is used as a naturally occurring ground water tracer time series data for 18o are analyzed to model the distinct responses and relative proportions of the conduit intermediate and diffuse flow components in karst aquifers this analysis also describes mathematically the dynamics of the transient fluid interchange between conduits and diffusive networks conduit and intermediate flow are described by linear systems methods whereas diffuse flow is described by mass balance methods an automated optimization process estimates parameters of lognormal pearson type iii and gamma distributions which are used as transfer functions in linear systems analysis diffuse flow and mixing parameters also are estimated by these optimization methods results indicate the relative proximity of a well to a main conduit flowpath and can help to predict the movement and residence times of potential contaminants the three component linear model is applied to five wells which respond to changes in the isotopic composition of point recharge water from a sinking stream in the madison aquifer in the black hills of south dakota flow velocities as much as 540 m d and system memories of as much as 71 years are estimated by this method also the mean median and standard deviation of traveltimes time to peak response and the relative fraction of flow for each of the three components are determined for these wells this analysis infers that flow may branch apart and rejoin as a result of an anastomotic or channeled karst network

teleseismic shear wave splitting and lithospheric anisotropy beneath and across the altyn tagh fault sixteen 3 component 5 sec stations along a profile crossing the altyn tagh fault atf at 90 e were used to measure shear wave splitting beneath tibet s northern edge splitting delay times t of 0 3 to 1 3 sec show a marked increase in a narrow zone centered on the fault implying anisotropy in the lithospheric mantle fast polarization directions fpd swing counterclockwise from a mean azimuth of 110 e in the qaidam basin south of the fault to a mean azimuth of 60 e in the altyn mountains this swing occurs in less than 40 km both the t increase and fpd swing are consistent with ductile sinistral shear along the 40 km wide low p wave velocity anomaly 6 8 imaged to a depth of 140 km beneath the fault by teleseismic tomography this confirms that the atf guides the northeastwards extrusion of the tibet qaidam s lithosphere relative to the tarim s

using stable isotope analysis δd δ18o to characterise the regional hydrology of the sierra de gador south east spain water stress is rapidly increasing in many mediterranean coastal zones mainly due to expansion in agriculture and tourism in this paper we focus on the sierra de gador campo de dalias aquifer system southeastern spain in order to assess the capability of water stable isotope analysis deltad delta 18 o to refine the understanding on recharge of this karstic aquifer system different types of surface and groundwater were sampled along an altitudinal gradient from the recharge zone in the mountains to the coastal plain surface water is restricted to local runoff collected in closed reservoirs runoff amounts collected in three of these reservoirs were monitored together with the precipitation in their catchments meteorological maps were used to detect the origin of the precipitation generating the majority of the runoff the results were compared to literature data on local and regional precipitation the use of oxygen and hydrogen isotopic composition has proved to be a useful tool to explain the origin of groundwater in a mediterranean karstic system such studies are however not numerous and are often limited to local scale recharge for fast reacting systems this paper focuses on the delta 18 o deltad relationships of local precipitation to explain the isotopic variability of a large karstic aquifer system the isotopic compositions of groundwater sampled along an altitudinal gradient from the recharge zone to the coastal plain are well displayed in a deltad delta 18 o diagram on a mixing line connecting a pole of mediterranean waters to a pole of atlantic waters the atlantic signature predominates in the shallow groundwater of natural springs reflecting the rainfall which produced the local runoff sampled the mediterranean signature is mainly restricted to deep groundwater from boreholes in the coastal plain the existence of a degree of spatial separation of groundwater types demonstrates that groundwater flow in a complex karstic system is not always continuous the mediterranean signature of deep groundwater could be due to past extreme rainfall events during which connectivity between recharge and reservoir exists while at the same time the atlantic signature of recent winter rains dominates in shallow groundwater the assumption that an equilibrium in isotopic composition is established within a continuous aquifer and that therefore a slope lower than 8 in a deltad delta 18 o diagram indicates evaporation is not necessarily valid c 2002 elsevier science b v all rights reserved

interaction experiments between water and hot melts in entrapment and stratification configurations abstract if water and hot melt come into contact either a vapor film is generated or and an explosive interaction takes place which of the two possibilities or both take place depends on several conditions the temperatures of the melt and water have important influences on the interaction behavior explosive interactions steam explosion occur only if the melt temperature is well above the boiling point of water but when the melt temperature is very high steam explosions are difficult to trigger by changing melt temperature and fixing the other conditions an optimal temperature range was often found for explosive interactions called temperature window the width and absolute values of the temperature window depend on the material properties of the melt the temperature of the water the ambient pressure the relative penetration velocity of the liquids the violence of disturbances and the configuration of the experiment in entrapment configuration experiments water is pressed into a crucible filled with hot melt in order to entrap the water by the melt the advantage of the entrapment configuration for volcanic simulation experiments is the easy handling of a variation of the water to melt mass ratio and furthermore the large variety of penetration possibilities of water into the melt therefore it is very likely to get a steam explosion with the entrapment configuration if a melt water combination is explosive at all a stratification configuration is formed when liquid magma is located on the sea bottom in experiments with the stratification configuration water is flooded cautiously over a crucible filled with hot melt so that after flooding a water layer separated by a vapor film is overlying the hot melt in stratification configurations a sequence of steam explosions can occur which may lead to an escalation and under appropriate circumstances to a thermal detonation

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

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

does interseismic strain localization near strike slip faults result from boundary conditions or rheological structure summary geodetic observations across most of the major strike slip faults show an interseismic strain rate which presents a sharp localization of elastic shear strain in the fault vicinity 20 60km the screw dislocation model of savage burford is commonly used to fit these geodetic data and to retrieve the far field velocity and the locking depth this model is very popular because of its inherent simplicity to derive fault slip rates and mostly because it predicts locking depths which are of the same order of magnitude as the base of the seismogenic zone 5 20km a first issue with the screw dislocation model is that localization is paradoxically introduced by imposing a step function in the velocity field at a depth where the crust is otherwise recognized to behave following a viscous rheology a second issue with this model is that it is not consistent with the rheological model of the crust that is valid for both postseismic 1 10yr interseismic several thousand years and long term geodynamic several thousand to several million years timescales here we use numerical models to study how alternative and more geologically realistic boundary conditions and rheological structures can lead to the localization of elastic strain at the earth s surface during the interseismic period we find that simple elastic models resembling the savage burford model but driven by far field plate velocity are inefficient at localizing strain unless this driving velocity is transmitted by a rigid indentor we also find that models including a weak viscous heterogeneity beneath the fault zone are able to produce appropriate localization of the deformation near the fault this alternative class of model is shown to be pertinent in regards to the boundary conditions and geological observations along exhumed ductile strike slip shear zone

ambient noise rayleigh wave tomography of new zealand summary we present the first new zealand wide study of surface wave dispersion using ambient noise observed at 42 broad band stations in the national seismic network geonet and the global seismic network gsn year long vertical component time series recorded between 2005 april 1 and 2006 march 31 have been correlated with one another to yield estimated fundamental mode rayleigh wave green s functions we filter these green s functions to compute rayleigh wave group dispersion curves at periods of 5 50 s using a phase matched filter frequency time analysis technique the uncertainties of the measurements are estimated based on the temporal variation of the dispersion curves revealed by 12 overlapping 3 month stacks after selecting the highest quality dispersion curve measurements we compute group velocity maps from 7 to 25 s period these maps and 1 d shear wave velocity models at four selected locations exhibit clear correlations with major geological structures including the taranaki and canterbury basins the hikurangi accretionary prism and previously reported basement terrane boundaries

crustal and upper mantle anisotropy related to fossilized transpression fabric along the denali fault northern canadian cordillera we analyze crustal and upper mantle structure near the denali fault northern canadian cordillera using 11 broadband seismic stations receiver functions at five stations within 5 30 km of the fault trace display a strong p to s conversion within the midcrust 10 25 km depth that systematically varies with back azimuth stacking and velocity inversion along complementary northwest southeast and northeast southwest back azimuth ranges yield a strong anisotropy 10 in the midcrust with complex crustal anisotropic behavior at least two layers close to the denali and duke river faults junction anisotropy occurs in a low velocity zone with the fast axis parallel to the denali fault trend three additional stations close to the denali fault 15 30 km as well as two stations further away 100 km show no significant crustal anisotropy shear wave sks splitting analysis indicates similar upper mantle anisotropy with a fast axis parallel to the trend of the denali fault for all stations except for station why located 125 km away we relate this crustal and upper mantle anisotropy to fossilized structural and mineral fabrics due to eocene transpression on the denali fault these results suggest the main transpression phase 400 km displacement was accommodated in a shear zone at least 50 60 km less than 125 km wide in the midcrust and upper mantle lack of clear anisotropy in the lowermost crust may relate to complex deformation within a detachment layer orogenic float model online material table of sks splitting information and figures of receiver function analysis

the mechanics of continental transforms an alternative approach with applications to the san andreas system and the tectonics of california article i nfo displacement on intracontinental transforms is commonly distributed over a zone several hundred km wide and may incorporate large regions of transtensional and transpressional strain but no consensus exists on what controls the distribution and style of this deformation we model the transform boundary as a weak shear zone of finite length that exerts shear stress on the deformable continental lithosphere on either side strain rate decreases away from the shear zone on a scale related to its length force balance in this system requires lateral gradients in shear strain rate to be balanced by longitudinal gradients in stretching rates which create zones of lithospheric thickening and thinning distributed anti symmetrically about the shear zone simple analytical estimates two dimensional 2d spectral models and 2d 3d numerical models are employed to study the spatial scales and magnitudes of the zones of uplift and subsidence using reasonable parameter values the models yield geologically relevant rates strain rate components inferred from the gps determined 2 d velocity field and analysis of seismicity using kostrov s method taken together with the geological data on the distribution of active faults uplift and subsidence suggest that the distribution and rates of active deformation in california are consistent with our predictions this validates the assumptions of the continuum approach and provides a tool for predicting and explaining the tectonics of california and of other intracontinental transform systems