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

depositional facies of a mud shoreface in suriname south america a mud analogue to sandy shallow marine deposits abstract immense volumes of argillaceous muds are being deposited along the world s longest continuous mud coastline which faces the open equatorial atlantic not only are these muds deposited in an environment normally associated with sand deposits but just as in sandstones sedimentary structures within these muds record the dynamic processes that deposited them this study investigates a 100 km long portion of the suriname coast utilizing cores bathymetric surveys and field observations from nearshore and innershelf environments using terminology borrowed from sand coastlines the innershelf nearshore of suriname is divided into transition zone shoreface foreshore and backshore the transition zone consists of a mix of offshore sands and shoreface muds shoreface and foreshore are subdivided into bank and interbank zones these zones are transitory because mud banks which make up the bank zones migrate westwardly mud banks are up to 5 m high 50 to 60 km long 10 to 20 km wide and oriented at oblique angles to the coastline these banks generally consist of fluid muds which are so fluid that they interact with surface waves causing them to be altered and damped banks are attached to the shoreline and commonly produce progradation of the coastline substrate within the interbank zone is more consolidat d than within the mud banks because of lack of wave dampening wave energies are relatively high within the interbank zone producing erosion of the shoreface and shoreline sand beaches are generally formed within the erosional interbank shoreline the vertical sedimentary sequence within the shoreface muds is a record of bank migration and other sedimentary processes present wave and current energies are recorded by scour and fill features discontinuity features micro cross laminations lenticular laminations and parallel to subparallel laminations laminations appear to be created by boundary layer shearing within fluid muds which are above wave base and made mobile by wave generated shore parallel currents large scale evidence for migration of the mud banks is westward dipping acoustical reflectors within the banks these reflectors which are over a kilometer apart mark the boundaries of annual migration events biogenic structures are generally absent within the fluid bank muds but are present within the more consolid ted interbank zone and associated with discontinuity features which are buried interbank surfaces migration and vertical stacking of mud banks are recorded by vertical sequences of massive and laminated muds which were deposited by mud banks and discontinuity features which were formed by interbank zones the coastal deposits of suriname are a mud analogue to nearshore and innershelf sand deposits transition zones of both mud and sand systems reflect a transition from offshore to shoreface processes and sediments both mud and sand shoreface foreshore systems reflect sediment input and wave current and tidal processes that act on them mud banks of suriname resemble linear sand ridges on the continental shelf of the eastern u s a in shape oblique orientation to the coastline and orientation with respect to dominant direction of transport processes the sequence of massive and laminated muds with discontinuity features resembles laminated to burrowed sequences found in ancient and recent nearshore and shallow marine sands

imaging subduction from the trench to 300 km depth beneath the central north island new zealand with vp and vp vs summary recent dense deployments of portable digital seismographs have provided excellent control on earthquakes beneath the central north island of new zealand here we use a subset of the best recorded earthquakes in an inversion for the 3 d vp and vp vs structure the data set includes 39 123 p observations and 18 331 s observations from 1239 earthquakes and nine explosions the subducted plate is imaged as a high vp low vp vs feature vp within the mantle of the subducted slab is almost always 8 5 km s 1 which requires the ca 120 myr slab to be unusually cold the low vp vs within the subducted plate closely parallels the lower plane of the dipping seismic zone it most likely indicates fluid resulting from dehydration of serpentine in the slab mantle and the earthquakes themselves are likely to be promoted by dehydration embrittlement we identify a region with vp 8 0 km s 1 directly above the dipping seismic zone can be interpreted as sinking entrained with the motion of the subducted slab and forming a viscous blanket that insulates the slab from the high temperature mantle wedge material in the overlying low vp region can be interpreted as rising within a return flow within the wedge the volcanic front appears to be controlled by where this dipping low vp region meets the base of the crust the thickness of the backarc crust also shows significant variation along strike in the central taupo volcanic zone tvz the crust is ca 35 km thick while southwest of mt ruapehu the crust thickens by ca 10 km there is no significant low vp zone in the mantle wedge in this southwestern region suggesting that this thicker crust has choked off mantle return flow the seismic tomography results when combined with constraints on mantle flow from previous shear wave splitting results provide a plausible model for both the distribution of volcanism in the central north island and the exceptional magmatic productivity of the central tvz

the role of event beds in the preservation of organic carbon in fine grained sediments analyses of the sedimentological processes operating during deposition of the whitby mudstone formation toarcian lower jurassic preserved in northeast england abstract geologists have recently observed that source rocks commonly contain a wide variety of microfabrics including diminutive ripples and burrows the existence of these fabrics challenges the assumption that persistent bottom water anoxia and low energy conditions are necessary prerequisites for enhanced organic carbon preservation in these units in order to enhance our understanding of the depositional and diagenetic processes responsible for organic carbon preservation in these strata the lower jurassic whitby mudstone formation which contains mudstones with up to 14 2 total organic carbon has been investigated using optical electron optical and geochemical methods four thinly bedded mudstone lithofacies were identified a silt bearing clay rich mudstones b clay rich mudstones c clay calcareous nannoplankton and organic carbon bearing mudstones and d cement rich mudstones internally individual beds are typically sharp based and normally graded they are either laminated partially bioturbated or homogenized where depositional fabrics are preserved pellets silt lags ripple lamination shell pavements wave enhanced sediment gravity flows of fluid mud and organo minerallic aggregates have been observed the presence of up to 14 2 toc in units that are sharp based and normally graded suggests that mass flows possibly generated by storms likely influenced sedimentation during deposition of these mudstones the abundant organo minerallic fabrics in these units indicates that at least some of the organic carbon was delivered to the seafloor as marine snow aggregates that likely formed in the water column following phytoplankton blooms homogenization of bed tops indicates that between sediment delivery episodes an infauna was able to colonize the seafloor implying that the bottom waters were at least partly oxygenated during these intervals these fabrics suggest that during deposition of the whitby mudstone formation organic carbon was being preferentially preserved below regions of high primary organic production the close association between sharp based graded beds and organo minerallic aggregates indicates that large volumes of organic carbon were delivered episodically to the seafloor and that conditions at the sediment water interface were episodically dynamic here organic carbon is likely to have been preferentially preserved because the frequency of depositional events was sufficiently high to minimize both oxidant diffusion into the sediment and organic carbon mineralization while bottom water anoxia may have developed during the phytoplankton blooms it was unlikely to have been persistent because the microfabrics present indicate that there was sufficient time and oxygen available for an infauna to disrupt the sediment between deposition events

genesis and depositional model of subaqueous sediment gravity flow deposits in a lacustrine rift basin as exemplified by the eocene shahejie formation in the jiyang depression eastern china abstract subaqueous sediment gravity flow ssgf deposits have recently been recognized as a major reservoir plays in lacustrine basins research on their genesis and depositional models are crucial to understand gravity flow evolution and the distribution of their deposits this study analysed ssgf deposits in the third member of the shahejie formation in the jiyang depression eastern china based on 3 d seismic data well log data and core observations the types and origins of ssgf the distribution patterns and depositional models of ssgf deposits have been investigated the dominant types of ssgf include muddy debris flows sandy debris flows high density turbidity currents surge like low density turbidity currents and quasi steady low density turbidity currents which are mainly caused by river floods and sediment failures the overall distribution of ssgf deposits is controlled by the sediment supplies basin structure and sequence stratigraphic framework paleotopography flood energy triggering mechanism and the slope angle of the delta front are also important ssgf deposits associated with river floods can be further subdivided into elongated and fan shaped deposits elongated sandstones are composed predominantly of bedload dominated and suspension load dominated hyperpycnal flow deposits the fan shaped sandstones can be subdivided into an inner fan a middle fan and an outer fan inner fan deposits are dominated by gully filling debrites middle fan deposits are composed predominantly of channel fill deposits while outer fan deposits consist of thin bedded and laterally extensive lobe intervals ssgf deposits triggered by sediment failures can be further subdivided according to their proximity to slumping proximal intermediate and distal parts the proximal deposits are composed predominantly of slide and slump deposits the intermediate deposits are dominated by sandy debrite tongues while the distal deposits are composed predominantly of thin bedded surge like low density turbidites this study offers some insight into the types origin of gravity flow as well as the distribution of their deposits in a lacustrine rift basin

models of the upper mantle beneath the central north island new zealand from speeds and anisotropy of subhorizontal p waves pn 1 the central north island of new zealand shows significant variations in pn wave speeds over small distances ranging from 8 5 0 2 km s to 7 4 0 1 km s over a distance of 150 km a combination of national network seismometers local volcanic seismic monitoring networks and temporary deployments are used to collect arrival times from local events during the period of 1990 2006 the data set consists of approximately 11 200 pn observations from 3000 local earthquakes at 91 seismograph sites we have created a method that allows us to model the predominant wavelength features of p wave speeds in the uppermost mantle as well as estimating values of mantle anisotropy and irregularities in the crust beneath stations using least squares collocation the resulting model shows distinct variations in uppermost mantle pn velocities velocities of less than 7 5 km s are found beneath the back arc extension region of the central volcanic region and under the taranaki volcanic region indicating the presence of water and partial melt the region to the east shows extremely high velocities of 8 3 8 5 km s where the p waves are traveling within the subducting pacific slab slightly lower than normal mantle velocities of 7 8 8 1 km s are found in the western north island suggesting a soft mantle pn anisotropy estimates throughout the north island show predominately trench parallel fast directions ceasing to nulls in the west anisotropy measurements indicate the strain history of the mantle null anisotropy measurements suggest an undisturbed mantle suggesting that mantle beneath the western north island is young

roughness at the base of the seismogenic zone contributing factors the cutout depth of microseismic activity in continental fault zones appears to correspond to the onset of greenschist metamorphic conditions at about 300 c it can generally be modeled as the transition from frictional to quasi plastic behavior in quartzofeldspathic crust shear resistance increases with depth through the frictional regime to peak at the transition beneath which it falls off exponentially with increasing temperature larger earthquake ruptures ml 5 5 nucleate around this transition depth where the highest concentrations of strain energy may accumulate varying depth and amplitude of the peak shear resistance along strike induce fluctuations in strain energy concentration at the base of the seismogenic zone factors affecting the depth of the transition include crustal composition geometry and mode of faulting fluid pressure levels in the frictional regime and water content in the quasi plastic regime quasi plastic strain rate and geothermal gradient evaluation of their relative importance is complicated because several are interdependent however compositional change may cause abrupt irregularities in seismogenic depth and peak shear resistance while regional variations in heat flow look to be particularly effective in creating long wavelength heterogeneities in strain energy concentration affecting faulting style

transition from storm wave dominated outer shelf to gullied upper slope the mid pliocene orinoco shelf margin south trinidad shelf edge deltas are a key depositional environment for accreting sediment onto shelf margin clinoforms the moruga formation part of the palaeo orinoco shelf margin sedimentary prism of south east trinidad provides new insight into the incremental growth of a pliocene storm wave dominated shelf margin relatively little is known about the mechanisms of sand bypass from the shelf break area of margins and in particular from storm wave dominated margins which are generally characterized by drifting of sand along strike until meeting a canyon or channel the studied st hilaire siltstone and trinity hills sandstone succession is 260 m thick and demonstrates a continuous transition from gullied with turbidites uppermost slope upward to storm wave dominated delta front on the outermost shelf the basal upper slope deposits are dominantly mass transport deposited blocks as well as associated turbidites and debrites with common soft sediment deformed strata the overlying uppermost slope succession exhibits a spectacular set of gullies which are separated by abundant slump scar unconformities tops of rotational slides then filled with debris flow conglomerates and sandy turbidite beds with interbedded mudstones the top of the study succession on the outer shelf area contains repeated upward coarsening sandstone rich parasequences 2 to 15 m thick with abundant hummocky and swaley cross stratification clear evidence of storm swell and storm wave dominated conditions the observations suggest reconstruction of the unstable shelf margin as follows i the aggradational storm wave dominated shelf edge delta front became unstable and collapsed down the slope ii the excavated scars of the shelf margin became gullied but gradually healed aggraded by repeated infilling by debris flows and turbidites and then new gullying and further infilling and iii renewed storm wave dominated delta front prograded out across the healed outer shelf re establishing the newly stabilized shelf margin the moruga formation study along with only a few others in the literature confirms the sediment bypass ability of storm wave dominated reaches of shelf edges despite river dominated deltas being by far the most efficient shelf edge regime for sediment bypass at the shelf break this article is protected by copyright all rights reserved

episodic river flooding events revealed by palynological assemblages in jurassic deposits of the brent group north sea spore and pollen sporomorph assemblages from middle jurassic marine deposits of the brent group in the northern north sea are investigated to assess temporal and spatial variations in vegetation and depositional processes four wells were sampled for palynology from the penguins cluster and the don north east fields through the rannoch formation shoreface succession hyperpycnite deposits occur throughout but are concentrated within the lower part of the section these are expressed by sand prone beds displaying waxing and waning current motifs normally graded muddy beds and structureless mudstones hyperpycnal hypopycnal deposits resulting from episodic river flooding represent important sedimentary features as they may be preserved below fair weather wave base in more offshore settings and potentially be the only record of the former presence of a nearby river mouth the hyperpycnites typically contain abundant botryoccocus spp amorphous organic matter aom and hinterland sporomorph taxa with relatively few marine components compared to associated marine shoreface facies variations in palynofacies assemblages and botryococcus spp abundances indicate frequent river mouth avulsion ordination of samples using non metric multidimensional scaling nmds indicates that shoreface samples of the sampled wells are relatively distinct but hyperpycnite samples are highly similar regardless of their sampled well this suggests that depositional processes and spore pollen sources i e catchment zones were similar among hyperpycnite events across different wells abundant bisaccate pollen botryococcus spp and aom within interpreted hyperpycnites suggest sediment mixing along the fluvial drainage path during flooding events the terrestrial signature of hyperpycnite sporomorph assemblages demonstrates that underflows remained coherent as they descended the shoreface profile with little turbulent mixing with ambient marine waters sporomorph assemblages display few large changes through time suggesting vegetation on the adjacent coastal plain was relatively static through the studied interval

on modeling boundary layer and gravity driven fluid mud transport 1 a model for fine sediment transport processes in the fluvial and coastal environment is proposed based on a simplified two phase formulation this simplified approach for fine sediment transport is essentially single phased however it retains several critical mechanisms originated from the complete two phase formulation by incorporating closures of carrier fluid turbulence and turbulent suspension and rheology of the sediment the model is first tested with laboratory measurements of flow velocity and concentration for fine sand transport driven by steady currents next particle diameter and density are prescribed in the model according to fractal dimensions of typical flocs for fluid mud observed on the continental shelf the model is able to predict the dynamics of tidal driven lutocline behavior observed on the amazon shelf and wave supported gravity driven fluid mud transport measured at the po prodelta model results also indicate strong interplay between flow turbulence and fluid mud concentration suggesting that the mechanism of sediment induced stratification on damping the carrier fluid turbulence is crucial in determining the fluid mud behavior results are encouraging for incorporation in the future of more comprehensive descriptions on floc dynamics mud bed consolidation and various mud rheology closures

palaeoenvironments palaeogeography and physiography of a large shallow muddy ramp late cenomanian turonian kaskapau formation western canada foreland basin the kaskapau formation spans late cenomanian to middle turonian time and was deposited on a low gradient shallow storm dominated muddy ramp dense well log control coupled with exposure on both proximal and distal margins of the basin allows mapping of sedimentary facies over about 35 000 km2 the studied portion of the kaskapau formation is a mudstone dominated wedge that thins from 700 m in the proximal foredeep to 50 m near the forebulge about 300 km distant regional flooding surfaces permit mapping of 28 allomembers each of which represent an average of ca 125 kyr more than 200 km from shore calcareous silty claystone predominates whereas 100 to 200 km offshore mudstone and siltstone predominate from about 30 to 100 km offshore centimetre bedded very fine sandstone and mudstone record along shelf sse directed storm generated geostrophic flows five to thirty kilometres from shore decimetre bedded hummocky cross stratified fine sandstone and mudstone record strongly oscillatory wave dominated flows whereas some gutter casts indicate shore oblique apparently mostly unidirectional geostrophic flows nearshore facies are dominated by swaley cross stratified or intensely bioturbated clean fine sandstone interpreted as recording respectively areas strongly and weakly affected by discharge from distributary mouths shoreface sandstones grade locally into river mouth conglomerates and sandstones including conglomerate channel fills up to 15 m thick locally brackish lagoonal shelly mudstones are present on the extreme western margin of the basin there is no evidence for clinoform stratification which indicates that the kaskapau sea floor had extremely low relief lacked a shelf slope break and was probably nowhere more than a few tens of metres deep the absence of clinoforms probably indicates a long term balance between rates of accommodation and sediment supply mud is interpreted to have been transported 250 km offshore in a sea bed nepheloid layer repeatedly re suspended by storms fine grained sediment accumulated up to a mud accommodation envelope perhaps only 20 to 40 m deep continuous re working of the sea floor by storms ensured that excess sediment was redistributed away from areas that had filled to the accommodation envelope being deposited in areas of higher accommodation further down the transport path the facies distributions and stratal geometry of the kaskapau shelf strongly suggest that sedimentary facies especially grain size were related to distance from shore not to water depth as a result the 100 to 300 m depth interpreted from calcareous claystone facies for the more central parts of the interior seaway might be a significant overestimate

a depositional model for organic rich duvernay formation mudstones abstract the upper devonian duvernay formation of western canada is an organic rich shale formation now targeted as a hydrocarbon reservoir we present a detailed sedimentological analysis of the duvernay formation in order to better understand organic rich mudstone depositional processes and conditions and to characterize the vertical and lateral heterogeneity of mudstone lithofacies that affect petrophysical and geomechanical rock properties organic rich mudstone facies of the duvernay formation were deposited in a dynamic depositional environment by a variety of sediment transport mechanisms including suspension settling turbidity currents and bottom water currents in variably oxygenated bottom waters suspension settling dominated in distal relatively deep areas of the basin but evidence for weak turbidity currents and bottom water currents was observed in the form of graded beds and thin grain supported siltstone laminae organic enrichment primarily occurred in distal areas as a result of bottom water anoxia and low depositional rates of inorganic sediment in deep water locations near platform margins alternating silty sandy contourite beds and organic rich mudstone beds are present the former interpreted to have been deposited and reworked by bottom water currents flowing parallel to slope in shallower more oxygenated settings mudstone lithologies vary from calcareous to argillaceous these sediments were deposited from suspension settling turbidity currents and bottom water currents although primary sedimentary structures are often obscured by extensive bioturbation locally organic enrichment in dysoxic rather than anoxic bottom waters was driven by a slightly increased sedimentation rate and possibly also by aggregation of sedimentary particles in the water column due to interaction between organic matter and clay minerals large variations observed in sediment composition from siliceous to calcareous to argillaceous reflect multiple biogenic carbonate and clastic sediment sources sediment composition is influenced by basin morphology circulation patterns sea level variation and proximity to sediment sources

parasequence types in shelfal mudstone strata quantitative observations of lithofacies and stacking patterns and conceptual link to modern depositional regimes mudstone strata have a vast variety of physical biogenic and chemical attributes at the lamina to bed scale approximately millimeters to decimeters thick our observations of more than 7 km of paleozoic to cenozoic mudstones revealed ordered patterns in this variety i e recurrent associations of lithofacies bedding style sedimentary structures and stratal architecture at bedset to parasequence scales approximately decimeters to meters thick we quantified characteristics of each association and their stacking patterns in vertical succession and linked them to sets of depositional processes most shelf mudstone strata appear to have accumulated in one of three facies association successions fass that can be related to depositional regimes through characteristic modes of sediment transport and accumulation as well as variations in benthic energy and oxygen levels we interpret these three fass as records of mud accumulation on different portions of continental shelves that were dominated by storm waves river floods or tidal currents each fas records a distinct parasequence type this approach can help fully integrate insights from oceanographic studies into more robust interpretations of the rock record and rock property maps

compositional controls on early diagenetic pathways in fine grained sedimentary rocks implications for predicting unconventional reservoir attributes of mudstones diagenesis significantly impacts mudstone lithofacies processes operating to control diagenetic pathways in mudstones are poorly known compared to analogous processes occurring in other sedimentary rocks selected organic carbon rich mudstones from the kimmeridge clay and monterey formations have been investigated to determine how varying starting compositions influence diagenesis the sampled kimmeridge clay formation mudstones are organized into thin homogenous beds composed mainly of siliciclastic detritus with some constituents derived from water column production e g coccoliths s depleted type ii kerogen as much as 52 6 total organic carbon toc and others from diagenesis e g pyrite carbonate and kaolinite the sampled monterey formation mudstones are organized into thin beds that exhibit pelleted wavy lamination and are predominantly composed of production derived components including diatoms coccoliths and foraminifera in addition to type iis kerogen as much as 16 5 toc and apatite and silica cements during early burial of the studied kimmeridge clay formation mudstones the availability of detrital fe iii and reactive clay minerals caused carbonate and silicate buffering reactions to operate effectively and the pore waters to be fe ii rich these conditions led to pyrite iron poor carbonates and kaolinite cements precipitating preserved organic carbon being s depleted and sweet hydrocarbons being generated in contrast during the diagenesis of the sampled monterey formation mudstones sulfide oxidation coupled with opal dissolution and the reduced availability of both fe iii and reactive siliciclastic detritus meant that the pore waters were poorly buffered and locally acidic these conditions resulted in local carbonate dissolution apatite and silica cements precipitation natural kerogen sulfurization and sour hydrocarbons generation differences in mud composition at deposition significantly influence subsequent diagenesis these differences impact their source rock attributes and mechanical properties

ichnology and sedimentology of a mud dominated deltaic coast upper cretaceous alderson member lea park fm western canada abstract current depositional models largely promote the perception that all open coastal distal sea proximal land gradients are reflected by upward coarsening grain size trends and that shoreline deposits are represented by prominent sand bodies although commonly the case significant departures from this model may occur when the availability of coarser sediment calibers sand sized and larger is limited this is especially true where alongshore sediment transport influenced depositional systems are associated with rivers that supply abundant suspended sediments underestimating the role of grain size segregation may lead to misinterpretations of energy levels and water depths especially in some shale dominated sedimentary units the upper cretaceous alderson member lea park fm is an up to 180 m thick gas charged shale unit that we interpret as an ancient analogue for modern offshore and mud dominated deltaic coasts sedimentological and ichnological data collected from 27 cores indicate that much of the sediment volume of the alderson member was deposited in relatively shallow water under the influence of tidal and wave processes in a deltaic coastal setting characteristic features reflecting these depositional affinities include 1 increased proportions of terrestrially derived organic matter 2 indications of thixotropic to soupy substrates e g fluid mud coupled with rapid depositional rates 3 an impoverished ichnological signal planolites dominated suites 4 micro laminated shale 5 shale on shale erosional contacts 6 scour and fill structures and 7 intervals of low angle cross stratification the interpretation of relatively shallow water settings is also supported by recurring root bearing horizons glossifungites ichnofacies demarcated transgressive surfaces of erosion and conglomeratic surfaces at particular stratigraphic levels the deposits are interpreted to include offshore subaqueous deltas muddy shoreface and or tidal flat and aggradational muddy coastal plain chenier plain sub environments the results of this study improve our knowledge of ichnological and sedimentological characteristics of shallow marine shale units and are potentially useful for recognition of similar nearshore mud prone deposits elsewhere

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

contrasting modes of shelf sediment dispersal off a high yield river waiapu river new zealand abstract recent studies of continental margins suggest that small high yield rivers are capable of generating shelf sediment gravity flows an idea that fundamentally alters our understanding of material flux from the continents to the ocean discharge measurements indicate that the waiapu river north island new zealand reaches hyperpycnal concentrations 36 kg m 2 on a yearly basis this study contrasts shelf edge basins with a broad trough along the shelf edge off the waiapu river testing whether there is evidence that shelf sediment gravity flows propagate to topographic lows observations and measurements through geochemical and sedimentological analyses of sediment cores em1002 swath bathymetry and chirp sub bottom profiles suggest differing transport modalities on the outer shelf in general a southern trough shaped region exhibits high terrigenous inputs and non steady state 210pb profiles whereas the northern basins contain steady state 210pb profiles and increased marine influence sediment gravity flows dominate accumulation in the southern region whereas within the northern portion surface plume sedimentation is indicated overall this study suggests that sediment gravity flows could be bypassing the northern basins perhaps a result of oceanographic influences and bathymetric steering as they seek a more direct route across the shelf

distinguishing between stress induced and structural anisotropy at mount ruapehu volcano new zealand 1 we have created a benchmark of spatial variations in shear wave anisotropy around mount ruapehu new zealand against which to measure future temporal changes anisotropy in the crust is often assumed to be caused by stress aligned microcracks and the polarization of the fast quasi shear wave is thus interpreted to indicate the direction of maximum horizontal stress but can also be due to aligned minerals or macroscopic fractures changes in seismic anisotropy have been observed following a major eruption in 1995 96 and were attributed to changes in stress from the depressurization of the magmatic system three component broadband seismometers have been deployed to complement the permanent stations that surround ruapehu creating a combined network of 34 three component seismometers this denser observational network improves the resolution with which spatial variations in seismic anisotropy can be examined using an automated shear wave splitting analysis we examine local earthquakes in 2008 we observe a strong azimuthal dependence of and so introduce a spatial averaging technique and two dimensional tomography of recorded delay times the anisotropy can be divided into regions in which agrees with stress estimations from focal mechanism inversions suggesting stress induced anisotropy and those in which is aligned with structural features such as faults suggesting structural anisotropy the pattern of anisotropy that is inferred to be stress related cannot be modeled adequately using coulomb modeling with a dike like inflation source we suggest that the stress induced anisotropy is affected by loading of the volcano and a lithospheric discontinuity

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

three dimensional tomographic imaging of the taranaki volcanoes new zealand 3 d models of the p wave velocity vp the ratio of p to s wave velocity vp vs and the p wave quality factor qp are determined for the crust in taranaki new zealand using local tomography and data from a dense network average spacing 5 km of 68 three component broad band seismographs vp and vp vs models were determined by jointly inverting p traveltimes and s p traveltime intervals and a qp model by inverting t t qp observations derived from modelling the velocity amplitude spectrum of p wave arrivals an approximately 5 km diameter region of high vp and low vp vs beneath the taranaki volcanoes extends from the surface to a depth of about 10 km and images the roots of the volcanoes formed by successive magmatic intrusions at mt taranaki this will probably be the path through which future magma intrusions will reach the surface we are unable to image any magma storage within the upper 16 km of the crust as the volumes involved are probably smaller than the 5 km resolution of our models the volcanoes sit in the taranaki basin a large sedimentary basin characterized by low vp c 4 km s 1 and high vp vs 1 9 attributed to unconsolidated water saturated sediments and these are underlain by basement rocks with vp 5 km s 1 and vp vs 1 7 there is a c 20 per cent contrast in vp across the taranaki fault at the eastern boundary of the taranaki basin and a small shallow high vp vs 2 0 anomaly above the seismically active cape egmont fault zone west of the taranaki volcanoes although the qp model is of significantly lower resolution than the vp and vp vs models it shows a low qp anomaly c 100 between 4 and 10 km depth that corresponds to the deepest onshore part of the taranaki basin

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

clinoforms paleobathymetry and mud dispersal across the western canada cretaceous foreland basin evidence from the cenomanian dunvegan formation and contiguous strata large scale muddy clinoform stratification is rare in cretaceous marine strata of the western canada foreland basin most offshore mudstone units show near parallel to gently diverging stratification that reflects differential basin subsidence the early to middle cenomanian dunvegan formation of broadly deltaic character is unusual in that it comprises a spectacular set of clinothems these clinothems have been mapped over a 950 km dip transect and downlap from nw to se onto a phosphatic condensed section termed the fsu marker our regional mapping shows that the fsu marker is of basin wide extent and marks the abrupt cessation of deposition for up to about 2 my in the south in the northwest the dunvegan formation forms a prominent wedge over 300 m thick interpreted to fill a high accommodation area muddy clinothems in this high accommodation area are relatively tall 80 m 115 m decompacted and extend about 80 km from the delta front to a zero edge at the downlap surface wave rippled and hummocky cross stratified fine sandstones of the upper delta front record the effects of storms and extend about 30 m 42 m decompacted below contemporaneous beach facies suggesting that effective wave base for sand transport was at about 40 m water depth mud was transported in deeper water presumably by storm driven flows towards the se the dunvegan formation gradually changes from a wedge to a tabular shape interpreted to indicate deposition in a low accommodation area in the transition from high to low accommodation areas clinothems become progressively less tall 50 to about 20 m 70 to about 29 m decompacted but longer 150 to 250 km the most down dip clinothems are essentially tabular and 400 km in extent in the high accommodation area offshore mud dispersal is inferred to have been limited by episodic geostrophic flows and possibly by permanent along shelf flows that swept mud probably suspended flocculated and pelleted into a shore parallel prism producing relatively short steep clinothems muddy clinothems downlap onto sandy condensed facies of the fsu marker the latter interpreted to have been deposited in shallow water prior to dunvegan deposition but which subsided below wave base in response to loading by the advancing deltaic clinothems in the southern low accommodation area tabular dunvegan mudstones suggest that the sea floor was able to aggrade to effective wave base i e about 40 m or less at which point wave resuspension of mud became frequent resulting in efficient off and along shore dispersal of mud by geostrophic currents the initiation of clinothem deposition is interpreted to coincide a with a phase of accelerated flexural subsidence in the northwest related to renewed tectonic loading and b possibly with the onset of large scale anticlockwise marine circulation at the inception of the greenhorn seaway in the early cenomanian together these tectonic and oceanographic events formed an effective sediment trap along the western margin of the seaway only after the western sediment trap had filled in late dunvegan time was mud again dispersed widely across the basin by storm processes in water less than about 40 m deep

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

fault slip accumulation in an active rift over thousands to millions of years and the importance of paleoearthquake sampling abstract the catastrophic earthquakes that recently september 4th 2010 and february 22nd 2011 hit christchurch new zealand show that active faults capable of generating large magnitude earthquakes can be hidden beneath the earth s surface in this article we combine near surface paleoseismic data with deep 1 ma timescales in the taranaki rift new zealand our analysis shows that the integration of different timescale datasets provides a basis for identifying active faults not observed at the ground surface estimating maximum fault rupture lengths inferring maximum short term displacement rates and improving earthquake hazard assessment we find that fault displacement rates become increasingly irregular both faster and slower on shorter timescales leading to incomplete sampling of the active fault population surface traces have been recognised for

probabilistic earthquake location in complex three dimensional velocity models application to switzerland 1 we present a new approach to determine precise and reliable hypocenter locations in the tectonically complex region of switzerland a three dimensional 3 d p wave velocity model to be used for earthquake relocation is obtained by simultaneously inverting arrival times of local earthquakes for hypocenter locations and 3 d p wave velocity structure a 3 d p wave velocity model derived from controlled source seismology css is used as an initial reference model the final 3 d model thus combines all available information from both css and local earthquake data the probabilistic nonlinear formulation of the earthquake location problem includes a complete description of location uncertainties and can be used with any kind of velocity model in particular the combination of nonlinear global search algorithms such as the oct tree importance sampling with probabilistic earthquake location provides a fast and reliable tool for earthquake location the comparison of hypocenter locations obtained routinely by the swiss seismological service sed to those relocated in the new 3 d velocity model using a probabilistic approach reveals no systematic shifts but does exhibit large individual shifts in some epicenter locations and focal depths we can attribute these large shifts in part to large uncertainties in the hypocenter location events with a low number of observations 8 and no observation within the critical focal depth distance typically show large location uncertainties improved hypocentral locations particularly for mine blasts and earthquakes whose routine hypocenter locations had been questionable confirm that improved velocity model and probabilistic earthquake location yield more precise and reliable hypocenter locations and associated location uncertainties for switzerland

fundamental and higher mode rayleigh wave characteristics of ambient seismic noise in new zealand 1 in order to use ambient seismic noise for mapping earth s structure it is important to understand the spatiotemporal characteristics of the noise field this study uses data collected during four austral winter months of 2002 to investigate new zealand s ambient seismic noise field in the double ocean wave frequency range 0 1 0 3 hz it is shown via beamforming analysis that there are two distinct dispersive waves in the data these waves can be separated their estimated phase velocities 2 5 2 and 4 3 km s in the frequency range 0 14 0 25 hz match well with fundamental and higher mode rayleigh dispersion curves studies of double wave frequency microseisms elsewhere generally show the rayleigh noise fields to be dominated by fundamental mode waves the reason why higher mode signals are observed here may reflect a combination of long ocean wave periods large waveheights the direct deep water approach to narrow continental margins and the proximity of the seismograph array to the source regions citation brooks l a j townend p gerstoft s bannister and l carter 2009 fundamental and higher mode rayleigh wave characteristics of ambient seismic noise in new zealand geophys res lett 36 l23303 doi 10 1029 2009gl040434

evaluation of the relative roles of global versus local sedimentary controls on middle to late pleistocene formation of continental margin strata canterbury basin new zealand determining the relative influence of eustasy versus local sedimentary processes on strata formation is a fundamental challenge in the study of continental margin stratigraphy in this paper the relative contribution of these factors on continental margin evolution during the middle to late pleistocene is evaluated using samples from integrated ocean drilling program expedition 317 core logging biostratigraphy and quantitative x ray diffraction mineralogy are used to delineate continental shelf sedimentary systems major lithological unconformities bound stratigraphic sequences that contain recurring compositional patterns and that resemble other examples of middle to upper pleistocene sequences however a preliminary chronology suggests that sequence boundary formation cannot be linked one to one with eustatic cycles and therefore these sequences can contain multiple ca 100 ka eustatic cycles smaller amplitude higher frequency transitions in sediment composition are interpreted as stratigraphic sequences driven by more rapid perturbations in the interplay of accommodation and sediment supply their stratigraphy is variable in time and across the shelf suggesting a strong influence of local sedimentary forcing in their formation changes in sediment composition after the middle pleistocene transition indicate that sediment transfer from onshore sources in the glaciated southern alps to the middle shelf occurred over a single 100 ka glacio eustatic cycle with an additional 100 ka lag before the mineralogical signal was preserved on the outer shelf this phenomenon is coincident with rapid shelf progradation in this basin suggesting a causal relation between across shelf sediment transport and margin progradation this is one of very few studies that provide insights at the core scale into the processes driving continental margin evolution during the middle to late pleistocene this work shows that compositional changes in mud dominated successions can lead to a sequence stratigraphic interpretation and the identification of high frequency sequences which may not be possible using a conventional stratigraphic approach

sedimentology and microfacies of a mud rich slope succession in the carboniferous bowland basin nw england uk a paucity of studies on mud rich basin slope successions has resulted in a significant gap in our sedimentological understanding in these settings here macro and micro scale analysis of mudstone composition texture and organic matter was undertaken on a continuous core through a mud dominated slope succession from the marl hill area in the carboniferous bowland basin six lithofacies all dominated by turbidites and debrites combine into three basin slope facies associations sediment starved slope slope dominated by low density turbidites and slope dominated by debrites variation in slope sedimentation was a function of relative sea level change with the sediment starved slope occurring during maximum flooding of the contemporaneous shelf and the transition towards a slope dominated by turbidites and then debrites occurring during normal or forced shoreline progradation towards the shelf margin the sediment starved slope succession is dominated by type ii kerogen whereas the slope dominated by low density turbidites is dominated by type iii kerogen this study suggests that mud dominated lower slope settings are largely active depositional sites with consistent evidence for sediment traction additionally the composition and texture of basin slope mudstones as well as organic content vary predictably as a function of shelf processes linked to relative sea level change

sedimentary processes and depositional environments of a continuous marine succession across the lower middle pleistocene boundary kokumoto formation kazusa group central japan abstract the chiba composite section of the kokumoto formation in central japan is a remarkable thick marine succession and is a candidate for formal recognition as the global boundary stratotype section and point gssp for the base of the middle pleistocene stage although there have been numerous studies of the kokumoto formation the sedimentology of the formation particularly in the chiba composite section has been unclear we use field observations and laboratory analyses to elucidate the sedimentary processes and depositional environments of the formation the chiba composite section includes the matuyama brunhes paleomagnetic reversal which is the primary guide for the lower middle pleistocene boundary along with multiple tephra deposits that provide isochronous correlational tie points one bed byk e also known as ontake byakubi tephra immediately underlies the paleomagnetic reversal and hence provides a useful widespread marker for the boundary the predominant silty beds of the chiba composite section are intensely bioturbated and lack evidence of episodic deposition such as slumps or muddy turbidites however minor sandy beds intercalated within the silty section particularly in its lower part are either 1 fining upward sequences with faint planar or ripple laminations and an erosional base or 2 sequences containing abundant mud clasts in a poorly sorted sand matrix with a sharp base and an irregular top surface the silty beds are interpreted to be hemipelagite formed by deposition of fine grained suspended material under stable and calm bottom water conditions the sandy deposits are interpreted to be sediment gravity flow deposits i e turbidites and debrites these sedimentary processes and the trace fossil assemblage indicate that the chiba composite section was formed in a continental slope environment the depositional environments of the chiba composite section together with tephrostratigraphy make it suitable for high resolution studies on the paleoenvironment paleoclimate and paleoceanography of the northwest pacific ocean across the lower middle pleistocene boundary it is therefore a suitable candidate to become the gssp for the middle pleistocene

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

revisiting late paleocene lower wilcox deltas gulf of mexico river dominated or mixed process deltas abstract spatial and temporal changes in physical depositional processes of shallow marine deltas affect facies distributions which are critical for reconstructing paleogeography and predicting reservoir heterogeneities the updated interpretation of the classical ancient river dominated lower wilcox delta in the gulf of mexico suggests more significant process variations than previously suggested the dominance of the storm wave process is indicated by wave ripple laminae and combined flow ripple laminae in the fair weather intervals and hummocky swaley cross stratification and low angle laminae in the storm beds however the relatively simple alternation of fair weather beds and storm beds is complicated by the presence of 1 normal and inversely graded siltstone to very fine grained sandstone beds suggesting hyperpycnites generated during the river flooding season 2 mud dominated heterolithics with delicate mud rhythmites suggesting tidal modulation between the storm events the storm wave generated succession with preservation of both river flood and tidal signals during fair weather condition represents regressive shoreline to shelf outbuilding the wave dominated delta or shoreface deposits are commonly truncated by fluvial dominated tide influenced distributary channels then overlain by tidal heterolithics and gradually open shelf deposits suggesting the development of small estuaries during transgressive phases of the wilcox shoreline the interpreted mixed process delta is linked to the last growth stage of the lower wilcox group prior to inundation of the texas shelf by thick marine mudstones its depositional setting was characterized by the widest lower wilcox shelf 50 km and a weakening sediment supply resulting in a stronger wave and tide influence relative to a weak fluvial influence this work thus provides a well constrained example of the complex interplay of fluvial wave and tidal currents in a process stratigraphy where decreasing river flux and relative sea level rise allowed wave reworking to become the dominant theme even though the same system has been previously interpreted as a classic river dominated delta many existing interpretations of ancient deltas thought to have mainly been controlled by a single process may need to be revisited and revised to take into account the natural spatial and temporal variability inherent to the shallow marine realm

sedimentologic character of ancient muddy subaqueous deltaic clinoforms down cliff clay member bridport sand formation wessex basin u k abstract muddy subaqueous clinoforms are a common feature of many modern deltas particularly those developed in basins with strong waves tides or oceanographic currents ancient examples have only rarely been reported implying that they are under recognized herein the sedimentological characteristics of muddy subaqueous deltaic clinoforms from the lower jurassic down cliff clay member of the bridport sand formation wessex basin uk are described and interpreted as a reference to re evaluate other ancient shallow marine mudstone successions deposits below the down cliff clay clinoforms consist of erosionally based bioclastic sandy limestone beds intercalated with upward thickening fossiliferous claystones and siltstones facies association a which record upward increasing water depth under conditions of minor input of clastic sediment and reworking by storm waves these deposits are downlapped by foreset to toeset deposits of the subaqueous deltaic clinoforms which comprise claystones and siltstones that contain calcareous nodules and are variably bioturbated by a low diversity trace fossil assemblages dominated by chondrites facies association b these foreset to toeset deposits record slow deposition undecompacted sediment accumulation rate of c 4 4 m myr from suspension fall out and distal sediment gravity flows under conditions of intermittent and or poor oxygenation of bottom waters clinoform foreset deposits dip paleoseaward at 2 and consist of siltstones and sandy siltstones that are moderately to completely bioturbated by a high diversity trace fossil assemblage facies association c thin

a major step in the continental moho and its geodynamic consequences the taranaki ruapehu line new zealand summary receiver function analysis reveals a 7 km step like change in crustal thickness across the taranaki ruapehu line tr line of north island new zealand the tr line runs east west between the active andesite volcanoes of mt taranaki and ruapehu and marks the southernmost extent of subduction zone volcanism in new zealand north of the tr line receiver functions show a strong and sharp p to s ps conversion at 25 1 5 km depth which is interpreted as a shallow moho at the tr line the moho ps conversion deepens across a step to 32 km depth and weakens further south the moho deepens to 35 km most of the 7 km step change in crustal thickness occurs over a lateral distance of 8 km yet there is little surface or topographic manifestation of the line given fresnel zone considerations the dip of the moho offset could vary between 90 and 45 gravity seismic attenuation and electrical data all show that the tr line is not only a step in crustal thickness but also a profound lithospheric boundary as mantle properties such as attenuation qp 1 implied density and electrical resistivity change abruptly across the line an east west oriented cluster of earthquakes with hypocentral depths of 20 40 km is centred on the moho step we propose that the moho step the earthquakes and the rapid change in mantle properties across the tr boundary are causally related processes that could be responsible for the phenomena described here include the rapid removal of mantle lithosphere and lower crust to the north of the tr line

three dimensional attenuation structure of the hikurangi subduction zone in the central north island new zealand summary we use waveform data from 2708 earthquakes recorded by dense seismograph deployments in the central north island of new zealand to image the 3 d attenuation structure of the hikurangi subduction zone down to ca 300 km depth attenuation images are obtained by determining the quality factor of p waves qp using a t inversion with a previously determined 3 d seismic velocity model we have included limited frequency dependence for qp with qp being frequency independent above 10 hz and having a frequency dependence of f 10 0 5 below 10 hz the qp images provide further constraint on the large scale features associated with subduction and magmatism beneath the central north island and serve to refine interpretations of crust and upper mantle structure from vp and vp vs the subducted plate is the most prominent feature in the qp images its high qp 900 1200 is consistent with the ca 120 myr old slab being relatively cold qp is better at resolving the slab than vp the coincidence of a strong gradient in qp with the upper plane of the dipping seismic zone indicates that even below 75 km depth the upper envelope of seismicity provides a good estimate of the location of the plate interface the mantle wedge is generally imaged as a relatively low qp 400 feature below 50 km depth however there are significant changes evident in the wedge along the strike of the subduction zone the most pronounced low qp in the mantle wedge occurs from ca 50 to 85 km depth beneath the productive rhyolite dominated central segment of the taupo volcanic zone suggesting a close link between volcanism and low qp in the shallow mantle wedge there is a strong correlation between low qp l owvp and high vp vs in this part of the mantle wedge suggesting that high temperature is the controlling influence on qp there within 30 km of the surface of the slab there is a large change in qp but only a modest change in vp our results are consistent with a fluid rich viscous blanket being entrained with the motion of the subducted slab down to ca 140 km depth where hydrous melting of mantle peridotite initiates trenchward of the volcanic front a strong horizontal gradient to higher qp is imaged in the mantle wedge we interpret this as a stagnant mantle nose not involved in the corner flow of the adjacent mantle the distribution of qp within both the slab and the overlying plate provides support for dehydration embrittlement being important in promoting seismicity in the mantle of the slab where qp is high at shallow depth in the forearc it is usually underlain by low qp near the plate interface this suggests that competent terranes in the forearc may act as aquicludes increasing fluid content in the rocks below and hence might control the distribution of coupling at the plate interface

subcrustal earthquakes in the central south island new zealand and the root of the southern alps the pukaki microearthquake network has revealed significant earthquake activity deeper than 15 km in the central south island new zealand extending to a depth of 73 km beneath the crest of the southern alps events deeper than 25 km define a planar seismic zone that has a strike of 41 and dips northwest at 19 gravity models suggest that earthquakes in this zone are occurring in a seismogenic uppermost mantle underlying an aseismic lower crustal root to the southern alps the 17 difference in strike of the dipping seismic zone and the alpine fault provides an explanation for the pattern of uplift and crustal thickening seen in the central south island

bedload transport of mud across a wide storm influenced ramp cenomanian turonian kaskapau formation western canada foreland basin abstract mudstone dominated shallow marine rocks of the kaskapau formation were deposited on a low gradient ramp that spanned the foredeep of the western canada foreland basin during the late cenomanian to middle turonian organic clay rich and silt rich mudstone accumulated on the flank of the forebulge 200 km from the western shoreline within this mudstone a large proportion of the clay minerals are organized into silt and very fine sand size aggregate grains these aggregates were produced both in the water column as marine snow and phytodetritus and also through reworking of previously deposited cohesive mud to form intraclasts the latter along with siliceous silt grains form wave and combined flow ripples graded beds scour fills and ripple tail lamination where sand size sediment comprising detrital siliceous calcareous bioclastic or phosphatic grains is present it is molded into combined flow ripples hcs gutter casts and lags thus all sediment grades indicate storm wave and current reworking of the sea floor at a distance of 200 km offshore the common occurrence of clay minerals in the form of aggregate grains organized into combined flow ripples and parallel lamination implies advective transport of clay minerals as bedload driven by combined flows across a very low gradient ramp on the distal part of this ramp latest cenomanian rocks include thin tongues of sw prograding quartz rich sandstone that was derived from an emergent forebulge this source was drowned during the early turonian eustatic rise when the sediment abruptly changed to organic rich mudstone dominated by clay mineral aggregates this compositional change was mainly a response to a sudden increase in distance to detrital sources in the west rather than a dramatic increase in water depth throughout much of early to middle turonian time the sea floor in the forebulge region lay above effective storm wave base for silt estimated at 70 m at sea level lowstands wave winnowing and erosion of the sea floor concentrated bioclastic lags at the top of siltier upward sequences lags are interpreted to correspond to falling stage lowstand and early transgressive systems tract deposits on the western margin of the basin previous studies may have substantially overestimated water depth for organic and clay rich calcareous mudstones in the western interior seaway

evaluating along strike variation using thin bedded facies analysis upper cretaceous ferron notom delta utah thin bedded delta front and prodelta facies of the upper cretaceous ferron notom delta complex near hanksville in southern utah usa show significant along strike facies variability primary initiation processes that form these thin beds include surge type turbidity currents hyperpycnal flows and storm surges the relative proportion of sedimentary structures generated by each of these depositional processes events has been calculated from a series of measured sedimentological sections within a single parasequence ps6 1 which is exposed continuously along depositional strike for each measured section sedimentological data including grain size lithology bedding thickness sedimentary structures and ichnological suites have been documented parasequence 6 1 shows a strong along strike variation with a wave dominated environment in the north passing abruptly into a fluvial dominated area then to an environment with varying degrees of fluvial and wave influence southward and back to a wave dominated environment further to the south east the lateral facies variations integrated with palaeocurrent data indicate that parasequence 6 1 is deposited as a storm dominated symmetrical delta with a large river dominated bayhead system linked to an updip fluvial feeder valley this article indicates that it is practical to quantify the relative importance of depositional processes and determine the along strike variation within an ancient delta system using thin bedded facies analysis the wide range of vertical stratification and grading sequences present in these event beds also allows construction of conceptual models of deposition from turbidity currents i e surge type turbidity currents and hyperpycnal flows and storm surges and shows that there are significant interactions and linkages of these often paired processes

dryland continental mudstones deciphering environmental changes in problematic mudstones from the upper triassic carnian to norian mercia mudstone group south west britain

stratigraphic completeness and resolution in an ancient mudrock succession funded by nerc fellowship grant number ne i02089x 1 santander student project scholarship grant

metastability mechanical strength and the support of mountain belts exhumed high pressure rocks from the caledonian root zone in norway provide analogues for processes occurring today under southern tibet allowing large scale geophysical observations from gravity and earthquakes to be linked with the mechanical properties of metastable rocks under high mountains metastability is essential for the survival of thick mountain roots and hence of high mountains and is in turn controlled by water if water is absent dry granulite formed from earlier melting episodes is both stable and strong and likely to survive in the eclogite stability field of deep root zones for hundreds of million years but if hydrous fluid is introduced the transformation of granulite to eclogite is relatively rapid and accompanied by a dramatic loss of strength in norway this transformation was initiated by water infiltration along fractures formed by earthquakes the same process as marked by deep earthquakes may be occurring today beneath southern tibet

surface seismic and electrical methods to detect fluids related to faulting in the absence of drilling surface based geophysical methods are necessary to observe fault zones and fault zone physical properties at seismogenic depths these in situ physical properties can then be used to infer the presence and distribution of fluids along faults although such observations are by nature indirect and become less exact with greater depth multiple observations of a range of such geophysical properties as compressional and shear seismic velocity vp and vs vp v5 ratio related to poisson s ratio resistivity and attenuation in and adjacent to fault zones offer the greatest hope of making inferences of the fault zone geometry fluids in the fault zone and fluid reservoirs in the surrounding crust for simple geometries fault zone guided waves can provide information on fault zone width and velocities for faults of the order of 200 m wide to address the question of whether a narrow fault zone can be imaged well enough at depths of seismic rupture to infer the presence of anomalously high fluid rock ratios we present synthetic seismic tomography and magnetotelluric examples for an ideal case of a narrow fault zone with a simple geometry large changes in material properties and numerous earthquakes within the fault zone a synthetic 0 5 km wide fault zone with 20 velocity reduction is well imaged using local earthquake tomography when sequential velocity inversions are done the true fault width is found even to 9 km depth although the calculated amplitude of the velocity reduction is lower than the actual amplitude vp vs is as well determined as vp magnetotelluric imaging of a synthetic fault zone shows that a conductive fault zone can be well imaged within the upper 10 km further a narrow 1 km very low resistivity 3 ohm m fault core can be imaged within a broad 5 km low resistivity 10 ohm m fault zone illustrating that regions of a fault containing large quantities of interconnected fluids within a broader conductive fault zone should be detectable thus variations in fluid content and fluid pressure can be inferred from electrical and seismic methods but there will always be uncertainty in these inferences due to the trade off with other factors such as intrinsic variations in porosity mineralogy and pore geometry the best approach is combined modeling of varied seismic and electrical data

detached mud prism origin of highstand systems tracts from mid pleistocene sequences wanganui basin new zealand marine siltstone successions 1 20 m thick form the upper part of sequences in the mid pleistocene castlecliff section 0 98 0 35 ma the siltstones were deposited within a broad shelf embayment at and about glacioeustatic highstands and are interpreted as highstand systems tracts hst shell rich to relatively shell poor contacts at the base of castlecliff hst are interpreted as downlap surfaces which mark the quenching of transgressive in situ biogenic accumulation backlap shellbed nonetheless the basal parts of castlecliff hst successions are enriched in fossil content in the context of the highstand successions as a whole and represent downlap shellbeds castlecliff hst are truncated above by sequence bounding ravinement surfaces such that complete sandier upward successions and subaerial exposure surfaces associated with sequence boundaries sensu stricto are never preserved modern highstand sedimentation in the taranaki bight offshore from castlecliff is characterized by a mid shelf mud depocentre and a coastal shore connected sand prism both of which are encroaching upon intervening shell rich relict and palimpsest transgressive deposits the mud depocentre is up to 9 m thick and deposition is influenced by a gyre caused by bathymetric steering of storm driven currents along the embayed coastline modern highstand deposition in the taranaki bight in which the mud depocentre is in part detached from the contemporary shore connected sand prism is regarded as an analogue for the deposition of the preserved lower parts of castlecliff hst the inferred architecture of castlecliff hst therefore need not refer to the shore connected progradational geometry predicted by traditional sequence models the model proposed herein may have application to other shelf palaeo embayments in which mid shelf focusing of fine grained sediment has resulted from coastal steering of currents

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

the use of 7be to identify event and seasonal sedimentation near the po river delta adriatic sea in october 2000 a major flood event of the po river occurred the resulting seabed deposit was initially sampled in december 2000 and most sites were reoccupied on subsequent cruises over a 3 yr period using the maximum penetration depth of the short lived radioisotope 7be half life 53 3 d the flood deposit was found to be up to 15 cm thick individual depocenters of thick strata were located immediately adjacent to the distributaries at the river mouth in relatively shallow water 30 m these flood deposit thicknesses are minimum estimates because the depth of 234th half life 24 1 d exceeds that of 7be in physically stratified flood sediment indicating that the first sediment deposited during the flood event likely originated from the river channel 30 55 of the estimated sediment load delivered to the shelf during the flood event can be accounted for using 7be penetration depths seasonal deposition also can be quantified using 7be after removing the effects of biological mixing seasonal deposition rates are a maximum of 6 cm yr 1 near the pila distributary decreasing to 2 cm yr 1 in the southern portions of the dispersal system

gravity driven sediment transport on the continental shelf implications for equilibrium profiles near river mouths an analytical model is developed for equilibrium bathymetric profiles off river mouths associated with the shoreward convex upward portion of subaqueous deltas and clinoforms the model builds on recent field results demonstrating that gravity driven flux of suspended mud is important on shelves provided that wave induced suspension of sediment supports the requisite turbid hyperpycnal layer because the maximum sediment load is determined by the critical richardson number the results are independent of the properties of the suspended mud or the bed the model assumes the equilibrium state to represent a balance between the supply of sediment by a river at the coast and the downslope bypassing of sediment to deep water within wave supported turbid near bed layers progressive seaward increases in bed slope across the convex shelf profile allow the attenuation of wave agitation with depth to be compensated for by a downslope increase in the contribution of gravity the model is consistent with shelf profiles off the mouths of the eel california ganges brahmaputra bangladesh waiapu new zealand po italy and rhone france rivers the equilibrium profile is predicted to be a function of wave climate and riverine sediment supply only with deeper and broader profiles associated with decreasing sediment supply increasing wave height and or increasing wave period

sedimentary evidence for enhanced hydrological cycling in response to rapid carbon release during the early toarcian oceanic anoxic event abstract a pronounced excursion in the carbon isotope composition of biospheric carbon and coeval seawater warming during the early toarcian 183 ma has been linked to the large scale transfer of 12c enriched carbon to the oceans and atmosphere a european bias in the distribution of available data means that the precise pattern tempo and global expression of this carbon cycle perturbation and the associated environmental responses remain uncertain here we present a new cm scale terrestrial dominated carbon isotope record through an expanded lower toarcian section from japan that displays a negative excursion pattern similar to marine and terrestrial carbon isotope records documented from europe these new data suggest that 12c enriched carbon was added to the biosphere in at least one rapid millennial scale pulse sedimentological analysis indicates a close association between the carbon isotope excursion and high energy sediment transport and enhanced fluvial discharge together these data support the hypothesis that a sudden strengthening of the global hydrological cycle occurred in direct and immediate response to rapid carbon release and atmospheric warming

toarcian black shales in the dutch central graben record of energetic variable depositional conditions during an oceanic anoxic event the wrong figure was printed in place of figure 4 in the february 2012 issue of jsr p 114 please

shear wave reflectivity anisotropies poisson s ratios and densities of a southern appalachian paleozoic sedimentary sequence abstract the physical properties of a sequence of paleozoic sedimentary rocks have been examined in detail with an emphasis on laboratory measurements of density shear wave velocity shear wave splitting and vp vs ratios seismic properties of 147 cores from 49 rock samples collected from the thorn hill sedimentary sequence of eastern tennessee are examined in terms of implications for future seismic studies in the southern appalachians the shear wave velocities of these rocks are strongly influenced by the relatively high shear wave velocity of quartz shear wave velocity anisotropy is present in most of the lithologic groups it is highest in the shales while being almost insignificant in the dolostones the related phenomenon of shear wave splitting occurs to some degree in all of the lithologies studied and at high pressures originates from mineral orientation splitting due to preferred mineral orientation is most prominent in the shales but also is significant in some of the carbonates compressional to shear velocity vp vs ratios of approximately 1 82 dolostones and 1 95 limestones effectively characterize the carbonates while other lithologies display wider ranges of vp vs primarily due to the influence of accessory minerals such as quartz densities of the sample suite range from 2 34 g cm3 shale to 2 86 g cm3 dolostone using average data for each lithologic group to calculate normal incidence reflection coefficients significant differences in the shear and compressional reflectivity of hypothetical interfaces are found normal incidence shear and compressional wave synthetic seismograms approximating the subsurface reflectivity of the entire thorn hill section indicate that three zones of high amplitude reflections would be seen on reflection records obtained over this 3327 m thick sequence overall the shear and compressional synthetics are similar in appearance differences are seen at some interfaces in the mississippian devonian interval which are more reflective to shear waves and in the ordovician martinsburg formation which appears more reflective to compressional waves

prograding muddy shelves in the paleogene wilcox deltas south texas gulf coast abstract core facies analysis integrated with subsurface well log correlations and seismic horizon mapping document two thick mudstone dominated deltaic successions in the wilcox group along the south texas gulf coast meters to tens of meter thick upper slope to outer shelf mudstones form units that lie at the base of upward coarsening successions which are interpreted as fluvial or storm wave dominated shelf deltas the muddy character of the deposits is observed in cores and inferred from well logs whereas the larger depositional architecture is interpreted from well log correlations and seismic data physical sedimentary structures described from a lower wilcox core reflect deposition on a mud dominated prodelta controlled by hyperpycnal processes normally and inversely graded beds are present indicating sustained flows that waxed and waned upward coarsening facies successions contain current ripples organic matter and siderite cemented bands low trace fossil abundance and low diversity which suggest deposition in a fluvial prodelta to shelf environment centimeter thick interbeds of normal and inversely graded mudstones siltstones and very fine grained sandstones with low intensities of bioturbation reflect the high physical and chemical stresses of hyperpycnal environments heterolithic stratification with lenticular wavy and flaser bedding indicates some tidal influence on the other hand cores of the middle wilcox reflect deposition on a muddy wave storm dominated shelf bioturbation intensities tend to be high with unstressed fully marine ichnological suites pervasively bioturbated sandy mudstones and muddy sandstones with cruziana ichnofacies wavy parallel and low angle lamination and structureless sandstones with ophiomorpha record deposition in a wave influenced prodelta to shelf environment hyperpycnal flows associated with river floods might have transported mud across the shelf to the outer shelf where prevailing wave and storm conditions facilitated suspension and transport of mud beyond the shelf edge previous studies have shown that wilcox delta sandstones are largely trapped on the shelf by contemporaneous growth faults however this paper illustrates that at times the wilcox shelf margin prograded through mud accretion

the role of fluids in lower crustal earthquakes near continental rifts earthquakes in the lower continental crust of the earth are rare as the lower crust is thought to be too hot to allow brittle failure so it is surprising that they occasionally occur where continental crust is rifting apart a study of three dimensional crustal structure and seismicity in the taupo volcanic zone an active continental rift in new zealand has now provided insight into how these earthquakes arise the crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones seismic velocities within the band are consistent with the presence of fluids and the linking of upper and lower crust seismicity to crustal structure point to a common explanation for all of the seismicity probably the weakening of faults on the periphery of an otherwise dry crust by hot fluids a report on three dimensional tomographic imaging of seismic velocities and attenuation in the taupo volcanic zone an active continental rift where earthquakes are known to occur in the lower crust finds that crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones the occurrence of earthquakes in the lower crust near continental rifts has long been puzzling as the lower crust is generally thought to be too hot for brittle failure to occur1 2 such anomalous events have usually been explained in terms of the lower crust being cooler than normal3 4 but if the lower crust is indeed cold enough to produce earthquakes then the uppermost mantle beneath it should also be cold enough2 and yet uppermost mantle earthquakes are not observed5 numerous lower crustal earthquakes occur near the southwestern termination of the taupo volcanic zone tvz an active continental rift in new zealand6 here we present three dimensional tomographic imaging of seismic velocities and seismic attenuation in this region using data from a dense seismograph deployment7 we find that crustal earthquakes accurately relocated with our three dimensional seismic velocity model form a continuous band along the rift deepening from mostly less than 10 km in the central tvz to depths of 30 40 km in the lower crust 30 km southwest of the termination of the volcanic zone these earthquakes often occur in swarms suggesting fluid movement in critically loaded fault zones8 seismic velocities within the band are also consistent with the presence of fluids and the deepening seismicity parallels the boundary between high seismic attenuation interpreted as partial melt within the central tvz and low seismic attenuation in the crust to the southwest this linking of upper and lower crustal seismicity and crustal structure allows us to propose a common explanation for all the seismicity involving the weakening of faults on the periphery of an otherwise dry mafic crust by hot fluids including those exsolved from underlying melt such fluids may generally be an important driver of lower crustal seismicity near continental rifts

isolated deep earthquakes beneath the north island of new zealand seismicity shallows towards the south along the tonga kermadec hikurangi margin deep and intermediate seismicity being absent altogether in the south island of new zealand beneath the taranaki region of the north island the maximum depth of the main seismicity is 250 km but very rare events occur directly below at 600 km these could be associated with a detached slab or a vertical aseismic continuation of the subducted pacific plate six small events that occurred in the 1990s were recorded extensively by digital instruments of the new zealand national network nznn and temporary deployments we relocate these events by a joint hypocentre determination jhd method and find their focal mechanisms using first motions and relative amplitudes of p and s arrivals the earthquakes relocate to a remarkably uniform depth of 603 3 kmrelative error 10 km absolute error in a line 30 km long orientated 40 ne roughly parallel to the strike of the intermediate depth seismicity the only consistent component of the focal mechanisms is the tension axis all lie close to horizontal and tend to align with the line of hypocentres we interpret this deep seismic zone as a detached sliver of plate lying horizontally with the same orientation as the main subducted plate above volume change caused by a phase change controlled by the pressure at 600 km and temperature in the sliver produces a pattern of strain that places the sliver under tension along its length

wave enhanced sediment gravity flows and mud dispersal across continental shelves reappraising sediment transport processes operating in ancient mudstone successions recent studies of marine shelf sediment dispersal show that wave enhanced sediment gravity flows are widespread phenomena and can transport large volumes of fluid mud rapidly across low gradient shelves flow evolution is controlled by sediment supply seabed gradient and spatial distribution of wave energy at the seabed using existing flow models we predict that such flows in mud dominated sediments will develop a three part microstratigraphy produced by changing flow conditions beginning with wave induced turbulent resuspension then development of a wave enhanced sediment gravity flow prior to lutocline collapse and suspension settling petrographic examination of modern flow deposits collected from the eel shelf reveals that resultant beds possess a microstratigraphy consistent with our hypothesis a silt rich basal subunit with curved ripple laminae abruptly overlain by a subunit composed of continuous intercalated silt clay laminae and an upper clay rich drape analyses of beds from ancient mud rich outer shelf and basinal successions cleveland ironstone jurassic uk and mowry shale cretaceous united states show that they too contain beds with this three part organization suggesting that such flows were active in these ancient settings too recognition of these microstructures in these ancient mud dominated successions demonstrates that sediment in these settings was commonly reworked and transported advectively downslope by high energy events contrasting with previous interpretations of these units that deposition was dominated by quiescent suspension settling identification of these recognition criteria now allows the products of this newly recognized sediment dispersal mechanism to be identified in other shale dominated successions

3d crustal structure from local earthquake tomography around the gulf of arta ionian region nw greece during summer of 1995 local seismicity was recorded in the area around the gulf of arta in northwestern greece by a dense temporary seismic network of the 441 local events observed at 37 stations 232 well locatable events with a total of 2776 p phase readings were selected applying the criteria of a minimum of 6 p observations and an azimuthal gap less than 180 this data set is used to compute a minimum 1d velocity model for the region several tests are conducted to estimate model stability and hypocenter uncertainties leading to the conclusion that relative hypocenter location accuracy is about 500 m in latitude and longitude and 1 km in depth the minimum 1d velocity model serves as initial model in the non linear inversion for three dimensional p velocity crustal structure by iteratively solving the coupled hypocenter velocity problem in a least squares sense careful analysis of the resolution capability of our data set outlines the well resolved features for interpretation the resulting 3d velocity model shows generally higher average crustal velocities in the east and the well resolved area of the eastern gulf of arta exhibits a homogeneous velocity around 6 km s for the whole upper crust a pronounced north south trending zone of low velocities in the upper 5 10 km is observed in the area of the katouna fault zone kfz at greater depths below 10 km the kfz is underlain by high velocity material e w profiles suggest a horst graben structure associated with the kfz