predicting the elastic response of organic rich shale using nanoscale measurements and homogenisation methods determination of the mechanical response of shales through experimental procedures is a practical challenge due to their heterogeneity and the practical difficulties of retrieving good quality core samples here we investigate the possibility of using multiscale homogenisation techniques to predict the macroscopic mechanical response of shales based on quantitative mineralogical descriptions we use the novel peakforce quantitative nanomechanical mapping technique to generate high resolution mechanical images of shales allowing the response of porous clay organic matter and mineral inclusions to be measured at the nanoscale these observations support some of the assumptions previously made in the use of homogenisation methods to estimate the elastic properties of shale and also earlier estimates of the mechanical properties of organic matter we evaluate the applicability of homogenisation techniques against measured elastic responses of organic rich shales partly from published data and also from new indentation tests carried out in this work comparison of experimental values of the elastic constants of shale samples with those predicted by homogenisation methods showed that almost all predictions were within the standard deviation of experimental data this suggests that the homogenisation approach is a useful way of estimating the elastic and mechanical properties of shales in situations where conventional rock mechanics test data cannot be measured

spatial and temporal isotopic domains of contrasting igneous suites in western and northern sulawesi indonesia abstract palaeocene to pliocene magmatism in nw sulawesi shows a progression from an older series with calc alkaline tholeiitic signatures 51 17 ma to a younger series of mafic intermediate high k magmas 14 5 ma and felsic k rich calc alkaline cak magmas 9 2 ma the isotopic and geochemical compositions of the older series samples indicate that the more westerly samples have been generated in a continental arc setting and the more easterly samples in an oceanic arc this distinction defines the boundary between the western and northern sulawesi tectonic terranes the younger series high k magmas have unusual isotopic compositions with variable but low 143nd 144nd high 87sr 86sr values and high 208pb 204pb for their 206pb 204pb ratios compared to subduction related magmas the diversity of the isotopic compositions points towards a source with a long and heterogeneous geochemical evolution most likely located within the australian subcontinental lithospheric mantle the younger series felsic cak magmatism has a more homogeneous isotopic and geochemical signature and reflects melting of continental crust of australian origin this geochemical progression in time is very similar to that seen in central sulawesi chem geol 156 1999a 67 and is best explained by normal subduction of an oceanic plate followed by melting of an underthrust sliver of australian continent the size of this microcontinent can be estimated from the areal extent of low nd isotope magmas in western sulawesi ranging from approximately 4 s to 1 n underthrusting must have happened prior to 14 ma indicating that this event cannot be equated to the collision between sulawesi and the sula platform which occurred at 5 ma while subduction beneath western sulawesi ceased prior to the onset of potassic magmatism in this region it continued beneath northern sulawesi producing predominantly calc alkaline suites

tectonic history of sumba island indonesia since the late cretaceous and its rapid escape into the forearc in the miocene abstract the island of sumba lies within the sunda banda forearc and contains volcanic plutonic and volcaniclastic rocks that record a history of arc volcanism extending from late cretaceous 80 ma or earlier to oligocene 31 ma time during the late cretaceous sumba formed part of a great indonesian volcanic arc system near southeastern eurasia between late cretaceous and early miocene time sumba remained part of that arc system which ceased to be volcanically active by 31 ma during the late miocene 18 ma sumba as part of the relict arc system was situated near the present site of alor and wetar at 16 ma sumba was torn from the relict arc and began to move at a velocity of 50 mm yr in a west south westerly direction volcanism along the modern banda arc soon followed by 7 ma sumba finally came to rest after having moved 450 km into the forearc we interpret the rapid motion of sumba into the forearc as a discrete block to have been a response to the collision between australia and indonesia in the area of timor the savu basin possibly originated as an arc crestal rift which then opened behind sumba as the latter moved westward over the past 16 my more than 3 km of sediment have been deposited in the savu basin by erosion from the surrounding islands sumba stopped moving to the west south west at 7 ma after reaching approximately its present location since then the island has ceased to be a discrete tectonic fragment and has behaved as an integral part of the forearc during the past 7 my compressional tectonics within the forearc has led to elevation of the rocks exposed on sumba by as much as 4 km

predicting porosity from acoustic velocities in siliciclastics a new look two principally different mechanisms of porosity reduction induced elastic stiffening of siliciclastic rocks are recognized which in the domain of grain supported siliciclastics with less than 15 volume clay result in two linear trends with different slopes in the acoustic velocity porosity plane transition between the two mechanisms occurs at about 30 porosity and roughly coincides with the transition from 1 early diagenesis characterized by mechanical compaction and initial intergranular bonding to 2 advanced chemical diagenesis caused by pressure solution and cementation peculiarities of velocity stress relations in each of these diagenetic domains suggest that while the stress factor is important in loose sandstones it has practically very little effect on the frame moduli of consolidated less than about 30 porosity sandstones at stress magnitudes beyond the closure stress of microcracks introduced by natural or coring related processes appropriate grain contact and effective medium

evidence for a submerged and displaced continental borderland north banda sea indonesia the banda sea is separated into two oceanic fragments the south and north banda basins by a large intervening region of ridges and basins called the banda ridges the north and south banda basins appear to be trapped pieces of pre tertiary oceanic crust whereas the banda ridges are a submerged and displaced continental borderland structurally very similar to the southern california offshore borderland analysis of dredged rocks from the banda ridges suggests an origin from western irian jaya

fractal analysis of tidal channels in the bahia blanca estuary argentina the fractal dimension d was estimated for nine tidal channels depicted in thematic mapper tm landsat 5 imagery to derive information about the degree of geomorphological control on a tidal channel network characteristic of the bahia blanca estuary argentina two methods box counting and contiguity were used to estimate fractal dimensions for each tidal channel all channels produced d values close to 1 meaning that they are self affine fractal features however these fractal dimensions do not represent the meandering pattern complexity characteristic of the tidal channels analysed although both methods allowed for estimation of d the contiguity method showed that three of the channels actually are not fractal but have sinusoidal characteristics a condition that was not detected by the former method

controlled laboratory experiments to assess the geomechanical influence of subsurface injection and depletion processes on 4d seismic responses laboratory experiments are performed with soft synthetic reservoir sandstone cemented under stress and with synthetic overburden caprock material consisting of compacted clay kaolinite in brine the rock like materials are loaded mechanically under stress paths representative of stress changes occurring in the subsurface as a result of injection increasing pore pressure or depletion followed by injection into a storage reservoir static stress strain behaviour and multidirectional p and s wave velocities are monitored during the tests the tests with sandstone are performed on dry material and simple poroelastic modelling is performed to relate these data to the behaviour of fluid water co2 saturated samples under the same stress paths the focus is on identifying 4d seismic attributes that may be used in the field to interpret monitoring measurements this could help diagnose stress changes in the overburden signalling the risk of co2 leakage from a reservoir if the compressive or tensile strength limit of the overburden is reached and of course to help quantify amounts of co2 stored

predicting horizontal velocities from well data the imperial college borehole test site consists of four boreholes with depths lying between 260 and 280m the boreholes intersect several cyclical sequences of sandstones mudstones and limestones the formations are highly laminated and ultrasonic measurements on preserved core have shown that the mudstones are intrinsically anisotropic little or no anisotropy is associated with the sandstones and limestones a scheme is proposed to predict synthetic vertical and horizontal p and s wave logs combining an isotropic effective medium theories the gassmann equation and backus averaging the scheme extends previous sand shale models to transversely isotropic rock formations the model assumes that the anisotropy is due to layering and due to the preferred horizontal orientation of the clay minerals pores and cracks within the mudstones the pores and cracks within the sandstones and limestones are randomly orientated after fitting the model to the ultrasonic data to obtain the unknown parameters the model successfully predicts the sonic log and the direct arrival times from a cross hole survey

mapping stress and structurally controlled crustal shear velocity anisotropy in california we present shear velocity anisotropy data from crustal earthquakes in california and demonstrate that it is often possible to discriminate structural anisotropy polarization of the shear waves along the fabric of major active faults from stress induced anisotropy polarization parallel to the maximum horizontal compressive stress stress directions from seismic stations located near but not on the san andreas fault indicate that the maximum horizontal compressive stress is at a high angle to the strike of the fault in contrast seismic stations located directly on one of the major faults indicate that shear deformation has significantly altered the elastic properties of the crust inducing shear wave polarizations parallel to the fault plane

stratigraphy and tectonic setting of the cretaceous and paleogene volcanic sedimentary successions in northwest sulawesi indonesia implications for the cenozoic evolution of western and northern sulawesi abstract new field and laboratory data from nw sulawesi indonesia integrated with existing information provide a tectonostratigraphic framework for the cretaceous and paleogene of this region the study area straddles two distinct provinces referred to as western and northern sulawesi western sulawesi forms the rifted continental margin of eastern sundaland it consists of a metamorphic basement partly of australian origin overlain by late cretaceous turbidites that were deposited in a fore arc setting latimojong formation these are in turn covered by volcanic sedimentary successions that were deposited during the early middle eocene to earliest miocene they represent a transgressive cycle from syn rift siliciclastics through nummulitic limestone and associated shelf sediments to deeper marine mudstones and turbidites budungbudung and tinombo formations during the same period northern sulawesi developed as an oceanic island arc characterized by bimodal volcanism papayato volcanics founded on back arc oceanic crust the cretaceous and paleogene volcanic and sedimentary suites show lithological and geochemical characteristics that reflect the contrasting tectonic setting of the two provinces the tectonic relationship between the two domains is not clear they probably formed a more or less continuous belt throughout the cenozoic but were definitely connected not later than the early miocene strong deformation in the paleogene formations in the northern part of nw sulawesi and their unconformable relationship with the overlying formations may be the result of the collision of the north arm of sulawesi with a continental fragment of australian derivation during the early miocene or it may be related to the formation of a metamorphic core complex in a mid miocene extensional tectonic setting a second major tectonic event which commenced in the pliocene and is still ongoing affected the entire region

temporal association of arc continent collision progressive magma contamination in arc volcanism and formation of gold rich massive sulphide deposits on wetar island banda arc whole rock 87sr 86sr and 18o analyses of volcanic rocks and 3he 4he analyses of sulphides and sulphates from mineralized rocks on wetar indonesia indicate a variable contribution of assimilated crustal material or sediment sourced from the subducted australian craton to the south these new data support the idea of progressive source contamination with precisely dated events showing that wetar island hosts the most extreme examples of crustal assimilation in the region the increased continental contamination occurs during the pliocene zanclian to piacenzian during distinct magmatic events between 5 and 4 ma and at 2 4 ma when 87sr 86sr ratios in unaltered lavas with whole rock 18o values between 5 7 and 9 6 increase from 0 707484 to extreme radiogenic values of 0 711656 the earlier of these magmatic events is important in the generation of the hydrothermal systems responsible for the mineralization recorded on wetar samples from this yield radiogenic 3he 4he ratios between 0 5 and 1 4 r ra similar to the data from volcanic rocks on nearby romang the later magmatic event coincides with the arrival of the australian continental margin at the subduction zone along the banda arc progressive incorporation of continental sourced components into the source region below the wetar island edifice coincides with the formation of gold rich volcanogenic massive sulphide deposits hosted within the contaminated volcanic pile

anisotropy of experimentally compressed kaolinite illite quartz mixtures the anisotropy of physical properties is a well known characteristic of many clay bearing rocks this anisotropy has important implications for elastic properties of rocks and must be considered in seismic modeling preferred orientation of clay minerals is an important factor causing anisotropy in clay bearing rocks such as shales and mudstones that are the main cap rocksofoilreservoirs thepreferredorientationofclaysdepends mostly on the amount of clays and the degree of compaction to studytheeffectoftheseparameters wepreparedseveralsamples compressingattwoeffectiveverticalstressesamixtureofclays illite and kaolinite and quartz silt with different clay quartz ratios the preferred orientation of the phases was quantified with rietveld analysis on synchrotron hard x ray images pole figures for kaolinite and illite display a preferred orientation of clay platelets perpendicular to the compaction direction increasing in strength with clay content and compaction pressure quartz particles have a random orientation distribution aggregate elastic properties can be estimated by averaging the singlecrystal properties over the orientation distribution obtained from the diffraction data analysis calculated p wave velocity anisotropy ranges from 0 pure quartz sample to 44 pure clay sample highly compacted but calculated velocities are much higher than measured velocities this is attributed to uncertainties about single crystal elastic properties and oriented micropores and limited grain contacts that are not accounted for in themodel inthiswork wepresentaneffectivemethodtoobtain quantitative data helping to evaluate the role of clay percentage and compaction pressure on the anisotropy of elastic properties ofclay bearingrocks

cross borehole tomography in anisotropic media anisotropy has significant effect on traveltime cross borehole tomography even relatively weak anisotropy cannot be ignored if accurate velocity estimates are desired since isotropic traveltime tomography treats anisotropy as inhomogeneity traveltime data in our examples were synthetically generated by a ray tracing code for anisotropic media and the computed quasi p wave traveltimes were subsequently inverted using the dual tomography technique carrion 1991 the results of the tomographic inversion show typical artifacts due to the anisotropy and that accurate imaging is impossible without taking the anisotropy into account

petrologic isotopic and radiometric age constraints on the origin and tectonic history of the malino metamorphic complex nw sulawesi indonesia the malino metamorphic complex mmc is located at the western end of the north arm of sulawesi it consists of mica schists and gneisses derived from proximal turbidite and granitoid protoliths with intercalations of greenschist amphibolite marble and quartzite forming an e w elongated dome like structure bounded on all sides by faults the age of the mmc is constrained between devonian and early carboniferous this paleozoic age the presence of archean and proterozoic inherited zircons and the isotopic signature of the mica schists and gneisses indicate that the terrane was derived from the new guinea australian margin of gondwana similarities with basement rocks in the bird s head suggests a common origin greenschists forming a discontinuous selvage metamorphic carapace around the complex were derived from adjacent autochthonous paleogene formations the rocks of the mmc show a barrovian type progression from greenschist through epidote amphibolite to amphibolite facies p t estimations suggest a depth of burial of up to 27 30 km k ar and 40ar 39ar cooling ages of 23 11 ma and a 7 ma age for unconformably overlying volcanic rocks indicate that the complex was exhumed during the miocene two tectonic scenarios are considered 1 the continental fragment docked with sulawesi during the mesozoic and was exhumed as a metamorphic core complex during the miocene 2 it was subducted beneath the north arm during the late oligocene and then rapidly returned back to the surface

effective medium modeling of gas hydrate filled fractures using the sonic log in the krishna godavari basin offshore eastern india 1 indian national gas hydrate program expedition 01 has established that clay rich marine sediment from the krishna godavari kg basin in the eastern indian margin hosts one of the richest gas hydrate deposits in the world resistivity at bit images and pressure cores reveal that the gas hydrate morphology in clay rich sediment varies from complex vein structures grain displacing to invisible pore filling existing rock physics models which relate acoustic data to in situ gas hydrate concentrations generally assume isotropic pore filling gas hydrate which yields misleading concentration estimates for fractured fine grained sediments the anisotropic kg basin sediment presents additional complications here we apply differential effective medium theory to incorporate grain displacing morphologies by which gas hydrate is included as vertical ellipsoids with aspect ratios ranging from those of thin veins up to those of nodules in an elastic anisotropic background we have estimated gas hydrate concentrations from sonic velocities at hole 10d in the kg basin considering three basic gas hydrate morphologies i pore filling ii grain displacing and iii a combination of grain displacing and pore filling average gas hydrate saturations for these three cases are 35 42 27 30 and 33 41 of the total porosity respectively in the depth range 60 140 m below seafloor mbsf saturation is highest at 67 mbsf for any morphology but the values differ between morphologies for the pore filling morphology the maximum gas hydrate saturation of 56 is 18 22 higher than the grain displacing morphology and 2 9 higher than the combined morphology estimates differ by 6 of the sediment volume with rotations of gas hydrate veins from vertical to horizontal

neogene basin history and paleomagnetism of a rifted and inverted forearc region on and offshore sumba eastern indonesia the island of sumba is located in the arc trench gap at the junction of the sunda and banda arcs to elucidate its enigmatic forearc position stratigraphic and paleomagnetic data were collected along three transects in central and east sumba sumba represents the emerged part of a terrane of se asian origin results of stratigraphic and paleomagnetic investigations on central and east sumba are presented and discussed in order to identify patterns of horizontal and vertical crustal movements a synthetic seismogram of the onshore record enables correlation with the offshore neogene e of sumba in order to interpret the data in a regional context the neogene basin history of sumba started when overall subsidence took place around the transition from early to middle miocene on east sumba above a basal condensed interval up to 600 m of middle late miocene volcaniclastic submarine fan deposits occur the sediments reflect island arc volcanism and are interpreted as parts of a prograding submarine fan system on a north dipping paleoslope fed by a volcanic source to the south of sumba biostratigraphic data indicate a high volcanic supply during the middle miocene and early middle tortonian a waning supply during the late tortonian and renewed supply during the messinian these patterns probably reflect variation in volcanic activity during the messinian calcilutites and foraminiferal chalks became dominant and deposition of these pelagic sediments continued into the early pliocene using the pattern of magnetic polarity changes in a selected interval the position of the mioceneepliocene boundary is better constrained seismic studies in the offshore area e of sumba van der werff 1995a b indicate the presence of an extensive tract of n prograding turbidites on sumba ridge savu basin the proposed correlation with the onshore record suggests lateral continuity from the island into the offshore area where the volcaniclastic submarine fan system presumably had its largest development subsidence proceeded so fast i m ka on east sumba that before the beginning of the late miocene sediments were deposited below the ccd this pattern suggests that the sumba region underwent strong crustal attenuation due to rifting as this was coupled with the arrival of volcaniclastics we envisage intra arc rifting coupled with the growth of a short lived volcanic arc further south its initiation at the transition of middle late miocene suggests interaction with the then approaching banda arc subduction system the paleomagnetic data indicate that during this process sumba was at a paleolatitude of 12 south and underwent a counter clockw ise rotation of 5 the reappearance of planktonic foraminiferal assemblages during the latest miocene and their present elevation above sea level suggest an average rate of post miocene uplift of 0 7 mm a emergence of sumba probably did not take place before 3 ma this inverted motion of the sumba terrane is probably coupled with the change to the present tectonic situation in which volcanic activity was resumed in the present inner arc after a non volcanic interval during the spreading stage 1 1997 elsevier science ltd

joint elastic electrical effective medium models of reservoir sandstones improvements in the joint inversion of seismic and marine controlled source electromagnetic data sets will require better constrained models of the joint elastic electrical properties of reservoir rocks various effective medium models were compared to a novel laboratory data set of elastic velocity and electrical resistivity obtained on 67 reservoir sandstone samples saturated with 35 g l brine at a differential pressure of 8 mpa with mixed results hence we developed a new three phase effective medium model for sandstones with pore filling clay minerals based on the combined self consistent approximation and differential effective medium model we found that using a critical porosity of 0 5 and an aspect ratio of 1 for all three components the proposed model gave accurate model predictions of the observed magnitudes of p wave velocity and electrical resistivity and of the divergent trends of clean and clay rich sandstones at higher porosities using only a few well constrained input parameters the new model offers a practical way to predict in situ porosity and clay content in brine saturated sandstones from co located p wave velocity and electrical resistivity data sets

occurrence and spatial distribution of metals in intertidal sediments of a temperate estuarine system bahia blanca argentina intertidal sediments of the inner and middle zone from the bahia blanca estuary were sampled for geochemical and environmental assessment of metals cd cu pb zn mn ni cr and fe results indicate that both the organic matter content and the sediment grain size plays an important role in controlling the differential concentrations of the metals found in sediments from both zones for most of the elements except mn sediment metal concentrations were greater in the middle zone although the concentrations did not exceed the maximums for quality of marine sediments in this sense anthropogenic impact i e sewage drain appears to be a key factor in the distribution of metals within the estuarine system comparing the levels obtained with quality levels lel and sel except cu that showed levels slightly above the lel the rest of the concentrations of metals were lower to those levels the low metal concentrations obtained within this highly impacted estuarine system suggest that the great volume of water that flooding the extensive flats in each tidal cycle has much importance although the potential risks of metals to the estuarine environment were low taking into account the toxicity of some of these metals continuity of monitoring is highly recommended

microfracturing and microporosity in shales shales are ubiquitous rocks in sedimentary basins where their low permeability makes them efficient seals for conventional oil and gas reservoirs and underground waste storage repositories waste waters co2 nuclear fuels moreover when they contain organic matter they form source rocks for hydrocarbons that may escape towards a more porous reservoir during burial a process referred to as primary migration and when the hydrocarbons cannot escape these rocks can be exploited as oil or shale gas reservoirs while the presence of fractures at the outcrop scale has been described the existence of fractures at smaller scales their link with microporosity the mechanisms that created them their persistence over geological times and their effect on the petrophysical properties of shales represent scientific challenges for which drillings in various sedimentary basins over the past decades may hold timely key data here we review and synthetize the current knowledge on how microfractures and micropores in shales can be imaged and characterized and how they control their anisotropic mechanical properties and permeability one question is whether such microfractures when observed in outcrops or in drilled core samples extracted from boreholes are related to decompaction and do not exist at depth another question is whether veins observed in shales represent microfractures that were open long enough to have acted as flow paths across the formation the mechanisms of microfracture development are described some have an internal origin fracturing by maturation of organic matter dehydration of clays while others are caused by external factors tectonic loading importantly the amount of microfracturing in shales is shown to depend strongly on the content in 1 organic matter and 2 strong minerals the nucleation of microfractures depends on the existence of mechanical heterogeneities down to the nanometer scale their propagation and linkage to create a percolating network will depend on the presence of heterogeneities at the meso to macro scales such percolating microfracture networks could control both the long term sealing capabilities of cap rocks and the further propagation of hydraulic fracturing cracks finally possible areas of research for describing the mechanism of microfracture formation in greater detail and how this impacts the transport and mechanical properties of shales are also discussed

deep scour holes at tidal channel junctions bahia blanca estuary argentina abstract deep scour holes are common features at the junction of tidal channels in the bahia blanca estuary argentina where both channels have similar morphodynamic characteristics in order to study their possible origin and evolution pattern the two largest known holes in the estuary were investigated these holes are located in the tres brazas channel and la lista channel respectively and have depths of 12 27 m 2 17 m relative relief with respect to the channels bottoms their borders have a steep scour side 3 5 at the mouth of each confluent channel and a gentle side 1 5 corresponding to a depositional zone at the opposite downstream side geomorphologic characteristics the nature of the tidal circulation associated to the tres brazas channel and estimates of the net sediment transport suggest that the evolution of the holes is related to flood dominance acting on the steep side inner face and ebb dominance over the gentle outer side holes migrate headward in a pattern opposite to similar holes formed in fluvial reaches

tidal circulation pattern on a tidal flat minas basin canada abstract although tidal flats have been studied extensively from the geomorphologic sedimentologic and stratigraphic standpoints there is little information related to the actual water circulation over them and its consequences on sediment transport and the corresponding changes in the geomorphology and sediment distribution the circulation induced by tidal forcing over a macrotidal flat in the minas basin bay of fundy canada is addressed while the geomorphologic and wind influences on the currents are also assessed tidal currents are reversible although the main axis orientation depends on the local morphology since a linear ridge runs along the main axis of the flat differences among sites are evidently associated with their position in relation to the ridge and also to the length of the inundation time forcing for the observed minor rotation to the right may originate in the surface water slope developed by the differential water filling of the area since wind was mostly calm and rarely exceeded 10 m s the observed circulation was the result of the interaction of the tidal wave and the general morphology of the intertidal flat

preferred orientation of phyllosilicates effects of composition and stress on resedimented mudstone microfabrics abstract development of a preferred orientation of clay minerals is investigated in response to changes in vertical effective stress and composition in resedimented material boston blue clay boston blue clay bbc an illitic glacio marine clay composed of 57 clay sized particles

the effect of clay distribution on the elastic properties of sandstones the shape and location of clay within sandstones have a large impact on the p wave and s wave velocities of the rock they also have a large effect on reservoir properties and the interpretation of those properties from seismic data and well logs numerical models of different distributions of clay structural laminar and dispersed clay can lead to an understanding of these effects clay which is located between quartz grains structural clay will reduce the p wave and s wave velocities of the rock if the clay particles become aligned or form layers the velocities perpendicular to the alignment will be reduced further s wave velocities decrease more rapidly than p wave velocities with increasing clay content and therefore poisson s ratios will increase as the velocities decrease these effects are more pronounced for compacted sandstones small amounts of clay that are located in the pore space will have little effect on the p wave velocity due to the competing influence of the density effect and pore fluid stiffening the s wave velocity will decrease due to the density effect and thus the poisson s ratio will increase when there is sufficient clay to bridge the gaps between the quartz grains p wave and s wave velocities rise rapidly and the poisson s ratios decrease these effects are more pronounced for under compacted sandstones these general results are only slightly modified when the intrinsic anisotropy of the clay material is taken into account numerical models indicate that there is a strong nearly linear relationship between p wave and s wave velocity which is almost independent of clay distribution s wave velocities can be predicted reasonably accurately from p wave velocities based on empirical relationships however this does not provide any connection between the elastic and petrophysical properties of the rocks numerical modelling offers this connection but requires the inclusion of clay distribution and anisotropy to provide a model that is consistent with both the elastic and petrophysical properties if clay distribution is ignored predicting porosities from p wave or s wave data for example can result in large errors estimation of the clay distribution from p wave and s wave velocities requires good estimates of the porosity and clay volume and verification from petrographic analyses of core or cuttings for a real data example numerical models of the elastic properties suggest the predominance of dispersed clay in a fluvial sand from matching p wave and s wave velocity well log data using log based estimates of the clay volume and porosity this is consistent with an interpretation of other log data

a refraction seismic field study to determine the anisotropic parameters of shales shales are known to be transversely isotropic ti which can lead to incorrect subsurface imaging if isotropic behavior is assumed by knowing the anisotropic parameters of the shales it is possible to correct for the anisotropic effects in seismic data thereby obtaining a more correct subsurface image two p wave refraction seismic field studies were undertaken in areas of steeply dipping marine shales of the wapiabi formation to determine the anisotropic parameters of these shales in situ the first survey was located in jumpingpound creek alberta canada and the other location was west of longview alberta canada seismic lines were laid out parallel perpendicular and 45 to the local strike directions at both locations the compressional headwave velocities along strike were determined to be faster than the velocities perpendicular to strike analysis of the jumpingpound creek data location yielded anisotropic parameters of e 0 14 0 05 and 0 00 0 08 whereas at longview the anisotr

measured anisotropy in pierre shale the five elastic coefficients which characterize a transversely isotropic medium have been measured for the pierre shale the first arrival times deduced from two closely spaced vertical seismic profiles provide values of magnitude and direction of the phase velocity at a given depth for different locations of the sources from these velocities we can estimate the five elastic coefficients by assuming that the p and sv wave velocities have only a small dependence on the angle of propagation on the other hand it is shown that the accuracy in the difference between the directions of propagation and particle motion is not sufficient to determine the anisotropy this work was industrially sponsored through the integrated geophysics project

the elastic anisotrophy of shales shales constitute about 75 of the clastic fill sedimentary basins and have a decisive effect on fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure the elastic stiffnesses of a shale with partially oriented clay particles is expressed in terms of the coefficients w sub lmn in an expansion of the clay particle orientation distribution function in generalized legendre functions application is made to the determination of the anellipticity of shales for transverse isotrophy the anellipticity quantifies the deviation of the p wave slowness curve from an ellipse and is shown to depend on a single coefficient w sub 400 in the expansion of the clay particle orientation distribution function if w sub 400 is small the anellipticity may be neglected as is apparently the case for a near surface late tertiary shale studied by winterstein and paulson strongly aligned clay particles result in a positive value of w sub 400 and a positive anellipticity in agreement with the majority of the field measurements however less well ordered shales could have a significantly positive second moment w sub 200 but only a small positive or even negative value of w sub 400 for such shales the anellipticity would be small or negative despite amore preferred alignment of clay particles in the bedding plane numerical examples of clay particle orientation distribution functions leading to zero or negative anellipticity are given less

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

a comparison of laboratory and field measurements of p wave anisotropy1 p wave velocity anisotropy determined from a cross hole survey at the imperial college borehole test site compares favorably with that measured in the laboratory on core from the holes the holes penetrate a layered sequence of sandstones shales and carbonates of the namurian upper limestone group the laboratory measurements of the vertical and horizontal velocities of core samples indicate that the shales exhibit p wave anisotropies of over 20 but that the sandstones and limestones are only slightly anisotropic these discrete measurements have been used in combination with wireline data to produce a log of p wave anisotropy including the anisotropic information vastly improves the match between observed and synthetic traveltimes from the cross hole data set this implies that there is little frequency dependence of intrinsic p wave anisotropy inversion of the cross hole traveltimes highlights the need for good angular coverage in order to resolve the anisotropy parameters the observed p wave anisotropy of the field data is due to the combined effect of sedimentary layering and the intrinsic anisotropy of the rocks the intrinsic anisotropy is found to be the dominant factor

mesozoic cenozoic rift drift sequence of asian fragments from gondwanaland abstract the university of cambridge atlas map plotting computer program has been used to plot a reconstruction of the dispersal of continental blocks from eastern gondwanaland from the late jurassic 160 ma until the late miocene 10 ma the geological basis for the reconstruction rests on the concept of south tibet burma western thailand malaya and sumatra having been part of the eastern gondwana continent during the late palaeozoic and early mesozoic the reconstruction is also based on the view that these asian continental blocks were rifted from eastern gondwanaland in the late jurassic this rifting episode gave rise to the continental margin of central new guinea and northern australia it was associated with the sea floor spreading anomalies preserved in the floor of the northeastern indian ocean the model considers the indication of crustal uplift in the middle jurassic followed by profound subsidence in the cretaceous and palaeogene exposed in the islands of the outer banda arc from seram to timor and the similar jurassic cretaceous facies in eastern sulawesi implies that these areas formed part of this rifted northern margin of australia in the jurassic subsequent tectonic collision and associated major strike slip movements have deformed and disrupted these rock sequences during the cainozoic the date of the rifting that removed south tibet burma western thailand and malaya from gondwanaland is controversial the indications in favour of the rifting episode having occurred in the jurassic rather than in the permo triassic are stratigraphie structural observations on the northwestern australian shelf in the banda arc and in central new guinea the identification of the continental blocks removed by this rifting is based partly on stratigraphie correlation with the banda arc and new guinea and partly on indications that the age of collision of tibet burma western thailand and malaya with asia was a late cretaceous event and not triassic jurassic as is generally held there are very few reliable land based palaeomagnetic measurements to constrain the movements of these dispersed continental fragments from gondwanaland the computer generated map reconstructions put forward here fit the available indian ocean sea floor spreading data although they are not unique solutions much of the critical ocean floor data associated with the rifting and dispersal of these continental fragments has been destroyed in the tectonic collision processes that occurred at the asian continental margin

elastic wave velocities and attenuation in an underground granitic repository for nuclear waste the behavior of a quartz monzonite rock mass subjected to a thermal load from emplaced canisters with electric heaters simulating high level nuclear waste was monitored by a cross hole seismic technique in a drift 340 m below the surface in the stripa mine facility in sweden traveltimes and amplitudes of 20 to 60 khz ultrasonic compressional p and shear s waves were measured over the experiment duration of 750 days on 2 to 4 m paths between four diamond drilled boreholes around a heater the signals were transmitted between the boreholes in six different directions and at different depths path averaged p and s wave velocities were obtained from the times of flight of pulses of acoustic waves between separate p and s wave piezoelectric transmitter and receiver crystals the attenuation q super 1 was obtained by a spectral ratio technique when the heater was turned on the p and s wave velocities increased to 4 and 10 percent respectively and stabilized at the elevated values the p wave velocities along a particular profile were found to increase linearly with the mean temperatures in the profiles sampled these mean temperatures increased 25 degrees to 55 degrees c during the course of the experiment when the heater was turned off after 398 days of heating the velocities decreased with temperature and finally reached levels in most cases below those observed prior to heating the rock the highest thermal stress close to the heater was estimated at 55 mpa q sub alpha values increased throughout the heating interval reaching changes of up to 60 percent shortly after turning off the heater the q values reveal no direct correlation with temperature or the closely associated thermal stress although these phenomena clearly are driving the variation in q there is strong evidence relating attenuation properties to fracture closure and pore pressure changes associated with draining of the rock mass

the palu metamorphic complex nw sulawesi indonesia origin and evolution of a young metamorphic terrane with links to gondwana and sundaland abstract the palu metamorphic complex pmc is exposed in a late cenozoic orogenic belt in nw sulawesi indonesia it is a composite terrane comprising a gneiss unit of gondwana origin a schist unit composed of meta sediments deposited along the se sundaland margin in the late cretaceous and early tertiary and one or more slivers of amphibolite with oceanic crust characteristics the gneiss unit forms part of the west sulawesi block underlying the northern and central sections of the western sulawesi province the presence of late triassic granitoids and recycled proterozoic zircons in this unit combined with its isotopic signature suggests that the west sulawesi block has its origin in the new guinea margin from which it rifted in the late mesozoic it docked with sundaland sometime during the late cretaceous u th pb dating results for monazite suggest that another continental fragment may have collided with the sundaland margin in the earliest miocene high pressure hp and ultrahigh pressure uhp rocks granulite peridotite eclogite are found as tectonic slices within the pmc mostly along the palu koro fault zone a major strike slip fault that cuts the complex mineralogical and textural features suggest that some of these rocks resided at depths of 60 120 km during a part of their histories thermochronological data u th pb zircon and 40ar 39ar from the metamorphic rocks indicate a latest miocene to mid pliocene metamorphic event which was accompanied by widespread granitoid magmatism and took place in an extensional tectonic setting it caused recrystallization of and new overgrowths on pre existing zircon crystals and produced andalusite cordierite sillimanite staurolite assemblages in pelitic protoliths indicating ht lp buchan type metamorphism the pmc was exhumed as a core complex at moderate rates c 0 7 1 0 mm yr accompanied by rapid cooling in the plio pleistocene some of the uhp rocks were transported to the surface at significantly higher rates 16 mm yr the results of our study do not support recent plate tectonic reconstructions that propose a nw australia margin origin for the west sulawesi block e g hall et al 2009

ultrasonic velocities in cretaceous shales from the williston basin compressional and shear wave velocities were measured in the laboratory from 1 bar to 4 kbar confining pressure for wet undrained samples of cretaceous shales from depths of 3200 and 5000 ft in the williston basin north dakota these shales behave as transversely isotropic elastic media the plane of circular symmetry coinciding with the bedding plane for compressional waves the velocity is higher for propagation in the bedding plane than at right angles to it and the anisotropy is greater for the 5000 ft shale for shear waves the sh wave perpendicular to bedding and the sv wave parallel to bedding propagate with the same speed which is about 25 percent lower than that for the sh wave parallel to bedding in general compressional and shear velocities are higher for the indurated 5000 ft shale than for the friable 3200 ft shale all velocities increase with in increasing confining pressure to 4 kbar the 3200 ft shale exhibits velocity hysteresis as a function of pressure whereas this effect is a

geomorphologic and sediment transport characteristics of the middle reach of the bahia blanca estuary argentina the geomorphologic and sediment transport characteristics of the middle reach of the bahia blanca estuary argentina are presented a large intertidal sedimentary structure divides the curved funnel shaped reach into the main channel which includes the waterway and the vieja channel the right margin of the study area is bordered by a low marsh tidal flat complex sedimentological and low penetration seismic data show that the area is formed mostly by relict sediments of pleistocene and pliocene ages present day deposits are very thin and are concentrated on the left platform between the navigation route and the intertidal structure comparison of detailed bathymetric surveys separated by 6 75 years resulted in a net erosion for all the area of 2 4 106 m3 assuming that the volume of sediments dredged from the navigation channel 510 000 m3 in 6 years was originated on the erosional sectors of the study area approximately 250 000 m3 yr are still exported from the reach net accumulation up to 2 m is concentrated on the left margin while erosional zones up to 4 5 m are located on the right margin of the main channel and the middle portion of vieja channel sediment transport calculations from 15 current meter stations distributed in the area indicate a net bed load transport of sand sized material directed towards the mouth of the estuary the results suggest that dynamically the middle reach of the bahia blanca estuary does not behave as a meander as was expected from its general shape although a preliminary estimation may indicate that the dredged sediment may proceed from the right margin the general circulation of the estuary indicates that all reaches interchange sediments with their adjacent sectors sediments deposited in the middle reach are coming from the erosional processes acting in the inner reach and on the flanks of tidal flat channels

t matrix approach to shale acoustics summary the t matrix approach of quantum scattering theory is used here to place many long wavelength equivalent medium approximations for porous composites polycrystals and cracked media on a common footing and to indicate their limitations but also to derive some new results based on two point statistics in this way we have obtained an insight into the difficult problem of elastic inclusions at finite concentrations which is of foremost relevance when estimating the effective material parameters of porous cracked shales involving stacks of more or less horizontally aligned clay platelets mixed together with more rounded silt minerals and with fluid filling the spaces a rather involved perturbative analysis of the effects of interactions between or structural correlations among the various inclusions minerals and cavities making up a real shale of hexagonal symmetry was performed in an attempt to obtain a better match between theoretical predictions based on a combination of coherent and optical potential approximations and experimental results recovered from ultrasonic wave speeds for the effective elastic stiffness tensor for the particular data set considered in this study the t matrix approach was able to match the data better than the approach of hornby et al but the match was not completely satisfactory further progress in theoretical shale modelling may come from a better knowledge of the elastic properties of pure clay minerals a more detailed knowledge of the microstructure of shales the incorporation of constraints obtained from comparisons between theoretical predictions and experimental results as well as a continuing development of the t matrix approach numerical results also for the effect of bedding parallel microcracks on the elasticity of such a real shale have value in illustrating the importance of taking into account the effects of spatial distribution when trying to deal with non dilute mixtures of highly contrasting material properties

a new velocity model for clay sand mixtu res1 none of the standard porosity velocity models e g the time average equation raymer s equations is satisfactory for interpreting well logging data over a broad depth range clays in the section are the usual source of the difficulty through the bias and scatter that they introduce into the relationship between porosity and p wave transit time because clays are composed of fine sheet like particles they normally form pores with much smaller aspect ratios than those associated with sand grains this difference in pore geometry provides the key to obtaining more consistent resistivity and sonic log interpretations a velocity model for clay sand mixtures has been developed in terms of the kuster and toksoz effective medium and gassmann theories in this model the total pore space is assumed to consist of two parts 1 pores associated with sand grains and 2 pores associated with clays including bound water the essential feature of the model is the assumption that the geometry of pores associated with sand grains is significantly different from that associated with clays because of this porosity in shales affects elastic compliance differently from porosity in sand stones the predictive power of the model is demonstrated by the agreement between its predictions and laboratory measurements and by its ability to predict sonic logs from other logs over large depth intervals where formations vary from unconsolidated to consolidated sandstones and shales

effects of sand shale anisotropy on amplitude variation with angle ava modelling the sawan gas field pakistan as a key case study for south asia s sedimentary basins amplitude variation with angle ava is a technique widely used in the characterisation of hydrocarbon reservoirs and assumes the earth s crust to be an isotropic medium yet anisotropy is ubiquitous in stratigraphic sequences and has first order effects on seismic ava responses when investigating subsurface prospects this work analyses the effects of anisotropic strata on ava responses using the lower goru formation middle indus basin pakistan as a case study in the study area shale intervals are interbedded with reservoir sands of the sawan gas field shales in this field form laminae or are dispersed within reservoir sands making the lower goru formation an example of a vertically transversely isotropic vti medium in this work we calculate the effective saturated mechanical properties of the lower goru formation based on rock physics templates the backus 1962 average typically designed for layered media combined with the empirical relations of brown and korringa 1975 and wood 1955 the input data used in our rock physics modelling is based on detailed petrophysical analyses of well data using the saturated effective mechanical properties of the lower goru formation we generate angle dependent reflection coefficient curves and seismic ava responses based on exact and approximate solutions for both isotropic and anisotropic reservoir scenarios our results suggest that the effects of lithological anisotropy are more pronounced in places with thick shale beds within reservoir sands conversely angle dependent reflection curves and seismic ava responses based on isotropic or anisotropic cases give similar solutions in the presence of thin shale beds as a corollary of this work we present a bayesian inversion method for the estimation of porosity in vti media

geochemical and tectonic relationships in the east indonesian arc continent collision region implications for the subduction of the australian passive margin abstract van bergen m j vroon p z and hoogewerff j a 1993 geochemical and tectonic relationships in the east indonesian arc continent collision region implications for the subduction of the australian passive margin in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 97 116 variations in the isotopic signatures of volcanics along the east sunda banda arc reflect changes in the nature and amount of sedimentary material supplied by the northeast indian ocean floor and the adjacent australian passive continental margin which form the two major domains of the indian ocean plate that approach the arc system a compilation of isotopic data for 200 500 km long arc sectors shows that the trend in magmatic signatures follows distinct subduction collision stages reached by the corresponding oceanic and continental margin sections entering the trench system maximum amounts of magma source contamination are inferred for volcanics near an extinct sector north of timor where the australian continent started to collide with the arc first pb nd isotopic source mixing models point to contamination by sediments with variations in composition similar to observed along arc changes in sediments entering the trench the results indicate an increasing contribution of subducted continental material in the direction of the collision region mass balance calculations considering the magmatic output and minimum input of subducted continental material required to generate the composition of the volcanic arc in the collision region are difficult to reconcile with subduction of ocean floor sediments alone thicknesses of sediments presently covering oceanic crust near the margin are close to calculated thicknesses of the sediments fluxed into the trench and magmatically returned to the arc crust but cannot account for the additional volumes of material accreted on the overriding plate in the same period of time it is inferred that leading portions of the australian continental margin have reached magma generation zones in the easternmost sunda arc and western banda arc which implies subduction to depths greater than 100 km

prediction of elastic wave velocities in sandstones using structural models elastic wave propagation in fluid saturated sandstones depends upon two sets of rock features 1 the volume fractions and elastic constants of the rock constituents quartz clay water etc and 2 microstructural geometry grain contacts pore aspect ratios while the former data are usually obtainable the latter are relatively inaccessible we present a new method for determining microstructural data using idealized but physically representative models of sandstone the key to the method is the simulation of certain depositional and diagenetic processes in a manner that completely specifies the geometry of the resulting models hence the geometric features of the grain space and void space required for various theories of elastic propagation can be calculated directly from the models we find good agreement between predictions and measurements of compressional and shear wave velocities in both clean and clay bearing saturated sandstones in contrast with previous efforts at predicting velocitie

modulus decomposition of compressional and shear velocities in sand bodies the advent of borehole shear slowness measurements in sonically slow formations has lead to breakthroughs in the subsurface profiling of geological bodies in sand bodies compressional and shear velocities depend predictably on porosity mineralogy grain contacts and fluid saturation an interpretation is best performed by decomposing the velocities into moduli that are intrinsic measures of the rock frame and pore fluid compressibilities careful experiments on pure materials i e pure quartz sandstones demonstrate two simplifying constitutive relationships first the bulk and shear frame moduli are simple functions of the porosity a comparison of the measured shear frame modulus to the prediction for the pure material distinguishes sand from shale second the ratio of the bulk and shear frame moduli is a constant 0 9 independent of the porosity the measured velocities are directly inverted to yield the bulk modulus of the pore fluid the fluid saturation effects are so dramatic at high porosit

stress and structure induced anisotropy in southern california from two decades of shear wave splitting measurements we measure shear wave splitting sws parameters i e fast direction and delay time using 330 000 local earthquakes recorded by more than 400 stations of the southern california seismic network 1995 2014 the resulting 232 000 sws measurements 90 000 high quality ones provide a uniform and comprehensive database of local sws measurements in southern california the fast directions at many stations are consistent with regional maximum compressional stress hmax however several regions show clear deviations from the hmax directions these include linear sections along the san andreas fault and the santa ynez fault geological blocks nw to the los angeles basin regions around the san jacinto fault the peninsular ranges near san diego and the coso volcanic field these complex patterns show that regional stresses and active faults cannot adequately explain the upper crustal anisotropy in southern california other types of local structures such as local rock types or tectonic features also play significant roles

the tectonic emplacement of sumba in the sunda banda arc paleomagnetic and geochemical evidence from the early miocene jawila volcanics the island of sumba is a continental fragment in the fore arc region near the transition between the sunda arc and banda arc in southeastern indonesia paleomagnetic and geochemical evidence from the early miocene volcanics of the jawila formation in western sumba constrain the final drift stage and tectonic emplacement of the island the lavas range from predominantly andesites to dacites and display textural evidence for a weak metamorphism rock magnetic and mineral chemical data point to pseudo single to multi domain titanojmagnetite fe ti o with grain sizes up to 10 pm as the main carrier of remanence the jawila formation reveals a chrm direction with declination 4 6 inclination 19 2 c 9 9 and a paleolatitude of 9 9 s which corroborates earlier results chamalaun and sunata 1982 taking paleomagnetic evidence from other formations on the island into account we conclude that the sumba fragment has occupied approximately its present position since the miocene the talc alkaline affinity and trace element signatures of the lavas point to an origin in an arc environment this occurrence of subduction related volcanic activity in the early miocene on sumba implies that a volcanic arc existed south of the present day east sunda arc or that the island was located within the latter arc between sumbawa and eastern flores and still had a minor southward drift to cover

rock physics modeling of a dispersed clay sandstone and dispersed quartz shale sequence abstract the elastic and petrophysical properties of the fluvial rocks of the miocene in the western basin of the gulf of thailand display typical signatures of dispersed clay sandstones and dispersed quartz shales that is the relationships between various properties exhibit two strong trends associated with a grain supported domain and a matrix supported domain the minimum porosity and maximum p velocity occur at the transition between these domains at a clay volume of approximately 40 50 this means that the hardest rocks occur at this transition a simple rock physics model has been developed that quantifies the elastic properties over a large depth range but does not explicitly account for the dispersed nature of the clay and quartz it employs a single aspect ratio at each depth within an inclusion based modeling scheme the required aspect ratio at each depth can be estimated from the depth the porosity and the clay volume of the rock

melange versus forearc contributions to sedimentation and uplift during rapid denudation of a young banda forearc continent collisional belt abstract new sedimentary geochemistry and petrographic analyses provide the most extensive sedimentary documentation yet of the rapid denudation of the young timor orogen the data from three basins including two widely separated well dated sections of the synorogenic megasequence of timor leste and a re dated dsdp 262 constrain the source and timing of detrital sediment flux during forearc continent collision along the timor sector of the banda arc the exhumed synorogenic piggy back basins formed above a melange unit that developed at the expense of a weak stratigraphic horizon in the mesozoic stratigraphy and was exhumed to the sea floor in latest messinian time following an interval of deep marine chalky marl sedimentation an increasingly muddy sediment flux indicates that the island of timor became emergent and shed sediment by 4 5 ma comparison of exhumed sections with similar patterns in the dsdp262 chemistry suggests that the sediment source was probably located some 50 60 km distant from the basin which is consistent with the aileu region of timor leste that shows an appropriate exhumation history all sedimentation between 4 5 and 3 2 ma was probably derived from a low relief rapidly eroding and mudstone dominated landscape with geochemical affinities to the triassic mudstone derived synorogenic melange the melange unit overlies and surrounds the banda terrane and was presumably structurally emplaced by propagation of a decollement through the triassic rocks during the collision after 3 2 ma sedimentation was dominated by hard rock lithologies of the banda terrane consisting of forearc cover and basement the latter including elements of metamafic rocks and metapelites this phase of sedimentation was accompanied by rapid uplift which may have been partly driven by a transient imbalance between rock uplift and denudation as resistant lithologies emerged from below melange like mudstone previous work has suggested that the timing of collision in timor leste and west timor was substantially different our reevaluation of dsdp 262 facies migration history in the context of the re dating presented here favours a relatively synchronous onset of uplift in both halves of the island but with different partitioning of strain between the foreland and hinterland in each half of the island

the role of texture cracks and fractures in highly anisotropic shales organic shales generally have low permeability unless fractures are present however how gas oil and water flows into these fractures remains enigmatic the alignment of clay minerals and the alignment of fractures and cracks are effective means to produce seismic anisotropy thus the detection and characterization of this anisotropy can be used to infer details about lithology rock fabric and fracture and crack properties within the subsurface we present a study characterizing anisotropy using s wave splitting from microseismic sources in a highly anisotropic shale we observe very strong anisotropy up to 30 with predominantly vti vertical transverse isotropy symmetry but with evidence of an hti horizontal transverse isotropy overprint due to a ne striking vertical fracture set parallel to the maximum horizontal compressive stress we observe clear evidence of a shear wave triplication due to anisotropy which to our knowledge is one of only a very few observations of such triplications in field scale data we use modal proportions of minerals derived from x ray fluorescence data combined with realistic textures to estimate the contribution of intrinsic anisotropy as well as possible contributions of horizontally aligned cracks we find that aligned clays can explain much of the observed anisotropy and that any cracks contributing to the vertical transverse isotropy vti must have a low ratio of normal to tangential compliance zn zt typical of isolated cracks with low hydraulic connectivity subhorizontal cracks have also been observed in the reservoir and we propose that their reactivation during hydraulic fracturing may be an important mechanism to facilitate gas flow

comparison between analytical and 3d finite element solutions for borehole stresses in anisotropic elastic rock we present a rigorous validation of the analytical amadei solution for the stress concentration around an arbitrarily orientated borehole in general anisotropic elastic media first we revisit the theoretical framework of the amadei solution and present analytical insights that show that the solution does indeed contain all special cases of symmetry contrary to previous understanding provided that the reduced strain coefficients b11 and b55 are not equal it is shown from theoretical considerations and published experimental data that the b11 and b55 are not equal for realistic rocks second we develop a 3d finite element elastic model within a hybrid analytical numerical workflow that circumvents the need to rebuild and remesh the model for every borehole and material orientation third we show that the borehole stresses computed from the numerical model and the analytical solution match almost perfectly for different borehole orientations vertical deviated and horizontal and for several cases involving isotropic transverse isotropic and orthorhombic symmetries it is concluded that the analytical amadei solution is valid with no restriction on the borehole orientation or the symmetry of the elastic anisotropy

physical characteristics of the bahia blanca estuary argentina abstract based on temperature salinity and current velocity and direction data the physical characteristics of the bahia blanca estuary are described data were gathered in vertical profiles made in longitudinal as well as in hourly surveys freshwater runoff averages 2 m3 s 1 however peak floods may reach 10 50 m3 s 1 the temperature distribution is quite homogeneous in the estuary based on the salinity distribution the estuary can be divided into two sectors an inner one showing partially mixed characteristics with a strong tendency to become sectionally homogeneous during runoff conditions similar to the historical averages and an outer sector which is sectionally homogeneous salinity values in the inner sector may be larger than those observed in the inner continental shelf this is initiated by the restricted circulation in the inner estuary and added to by the tidal washing of back estuary salt flats and by evaporation processes analysis of the residual circulation shows a marked difference in the direction of mass transport in the deeper regions of the sections northern flank the flow reverses with depth being headward near the bottom however net transport is landward in the shallower parts

upper triassic carbonate deposits of seram indonesia palaeogeographic and geodynamic implications abstract the upper triassic limestones of central and western and seram were deposited on an extensive carbonate platform already identified in various localities all around the banda sea sinta ridge central east sulawesi buru misool and the wombat plateau off nw australia the triassic deposits are found in the parautochthonous as well as in the allochthonous series of seram the facies of the two series are of gondwanian australian type in the parautochthonous and of laurussian asian type in the allochthonous the asinepe limestone manusela formation on which this study is based has been considered as part of the allochthonous series the triassic reefal lithotypes can be divided into four main facies as follows 1 the boundstone facies forming the buildup cores 2 the oncolitic grainstone rudstone facies indicating high energy conditions 3 foraminiferal packstone grainstone facies characteristic of moderate to high energy conditions and 4 the foraminiferal megalodont mudstone facies inferred to have accumulated in a quiet lagoonal environment forming the buildup cores of about 4 m long 2 m high they are separated by depressions filled with reef detrital sands the asinepe limestone was deposited during the late triassic carnian norian to rhaetian this range is corroborated by foraminiferal and palynological data and the coral framebuilders give evidence for a norian rhaetian age there is a some consensus that seram and the island of buru located west of seram belong to the same tectonic block seram buru block according to geochemical and geodynamic interpretations the seram buru block is derived from irian jaya or from papua new guinea the palynological results are consistent with reconstructions that place the seram buru block in a palaeogeographic zone distinct from that of sulawesi and therefore from the kolonodale block for these reasons it is here proposed that during the upper triassic the seram buru block and the kolonodale block were two separated entities the former located in a more tropical position than the latter in addition the seram palynological association shows a composite microflora of the warm onslow and the cold ipswich types suggesting that the seram microcontinent moved progressively to the north and crossed the boundary between the temperate and the warm subequatorial belts at one point in the late triassic early jurassic

crustal seismic anisotropy beneath shillong plateau assam valley in north east india shear wave splitting analysis using local earthquakes abstract we present crustal anisotropy estimates constrained by shear wave splitting sws analysis using local earthquakes in the shillong plateau and assam valley area north east india ne india region splitting parameters are determined using an automated cross correlation cc method we located 330 earthquakes recorded by 17 broadband seismic stations during 2001 2014 in the study area out of these 330 events seismograms of 163 events are selected for the sws analysis relatively small average delay times 0 039 0 084 s indicate existence of moderate crack density in the crust below the study area it is found that fast polarization directions vary from station to station depending on the regional stress system as well as geological conditions the spatial pattern of crustal anisotropy in the area is controlled mostly by tectonic movement of the indian plate towards ne presence of several e w and n s trending active faults in the area also play an important role on the observed pattern of crustal anisotropy

linking preferred orientations to elastic anisotropy in muderong shale australia the significance of shales for unconventional hydrocarbon reservoirs nuclear waste repositories and geologic carbon storage has opened new research frontiers in geophysics among many of its unique physical properties elastic anisotropy had long been investigated by experimental and computational approaches here we calculated elastic properties of cretaceous muderong shale from australia with a self consistent averaging method based on microstructural information the volume fraction and crystallographic preferred orientation distributions of constituent minerals were based on synchrotron x ray diffraction experiments aspect ratios of minerals and pores determined from scanning electron microscopy were introduced in the self consistent averaging our analysis suggested that phyllosilicates i e illite mica illite smectite kaolinite and chlorite were dominant with 70 vol the shape of clay platelets displayed an average aspect ratio of 0 05 these platelets were aligned parallel to the bedding plane with a high degree of preferred orientation the estimated porosity at ambient pressure was 17 vol and was divided into equiaxial pores and flat pores with an average aspect ratio of 0 01 our model gave results that compared satisfactorily with values derived from ultrasonic velocity measurements confirming the validity and reliability of our approximations and averaging approach

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

origin of geochemical variability by arc continent collision in the biru area southern sulawesi indonesia analyses of igneous rocks from the eocene calc alkaline and miocene geochemistry can be modelled by varying contributions potassic volcanic arc in southwest sulawesi indicate that magmas from the mantle wedge fluid from the subducted slab became more heterogeneous in their trace element and pb sr nd and the presence or absence of a subducted sedimentary isotopic signature following the collision of the buton microcontinent component white patchett 1984 gill williams with the arc at 15 ma isotopic ratios become more continental 1990 woodhead johnson 1993 kepezhinskas et al 4 my after the collisional event sr sr 0 7085 nd 1997 peate et al 1997 alves et al 1999 hoogewerff nd 0 5125 pb pb 19 2 pb pb 15 73 1999 pearce et al 1999 eiler et al 2000 despite pb pb 39 4 as the overriding plate consists of young agreement on the importance of these components there sundaland crust whereas the subducted sediment is likely to is still some dispute about the importance of an ocean have been shed from a compositionally distinct microcontinent of island basalt oib component in the wedge stolz et al australian derivation we can be certain that the continental isotopic 1990 edwards et al 1991 and the implied role of signature reflects subduction of continental material rather than residual rutile ryerson watson 1987 foley et al crustal contamination the isotopic compositions of the magmas 2000 if an arc is built upon continental crust or can be explained by the melting of a mixed mantle wedge consisting overlain by a thick layer of sediment there is a potential of fluid fluxed and sediment modified morb mantle in this model contribution from the upper plate via assimilation the maximum amount of sediment added to the mantle source is fractional crystallization afc processes which can 10 sometimes be difficult to distinguish from the signature of subducted sediment davidson 1987 thirlwall et al 1996 gasparon varne 1998 the only unambiguous way to distinguish between subducted sediment and

oxygen isotope systematics of the banda arc low delta o 18 despite involvement of subducted continental material in magma genesis abstract this study reports new laser fluorination oxygen isotope data for 60 volcanic rocks and 15 sediments distributed over the whole length of the banda arc eastern indonesia the melt oxygen isotope values 18omelt were calculated from phenocryst 18o data using theoretical and empirical mineral melt fractionation factors the 18omelt of individual volcanic centers within the arc varies between 5 57 and 6 54 except for serua 18omelt 6 13 7 48 and ambon 18omelt 8 12 8 38 these 18omelt values are up to 2 lower than new and previously published oxygen isotope data obtained on whole rock powders by conventional methods we attribute this discrepancy to post emplacement low temperature alteration and or to a systematic deviation of the bulk analysis sediment 18owr calculated from the 18o carbonate and silica fractions both measured conventionally range between 12 9 and 24 2 the low 18omelt values excluding serua and ambon overlap with the mantle range and are in agreement with simple two component source mixing models that predict 1 5 addition of subducted continental material to a depleted morb type source in the sub arc mantle this percentage is consistent with previous models based on sr nd pb th he hf isotope data however correlations between incompatible trace element ratios and oxygen isotope systematics requires involvement of partial melts derived from subducted continental material as the major slab component rather than bulk addition the contribution of hydrous fluids from both subducted altered oceanic crust and continental material is probably of minor importance magma mantle wedge interaction models could account for the observed low 18o signatures but predicted effects are difficult to distinguish from models without mantle wedge interaction assimilation of arc crust material is thought to be important for the high 18omelt values of serua and ambon afc modelling suggests up to 20 and 80 assimilation at serua and ambon respectively inclusions of meta sedimentary material and whole rock sr nd isotopes point to assimilation processes at nila but this probably had little effect on the 18o of phenocrysts which record original source values according to radiogenic isotope data magma sources in the banda arc are the most heavily influenced by fluxes of subducted continental material among currently active oceanic island arcs hence the results of this study suggest that high 18o 6 5 in arc lavas are difficult to reconcile with addition of subducted components to magma sources but must reflect assimilation of arc crustal material

a physical model for shear wave velocity prediction the clay sand mixture model of xu and white is shown to simulate observed relationships between s wave velocity or transit time porosity and clay content in general neither s wave velocity nor s wave transit time is a linear function of porosity and clay content for practical purposes clay content is approximated by shale volume in well log applications in principle the model can predict s wave velocity from lithology and any pair of p wave velocity porosity and shale volume although the predictions should be the same if all measurements are error free comparison of predictions with laboratory and logging measurements show that predictions using p wave velocity are the most reliable the robust relationship between s and p wave velocities is due to the fact that both are similarly affected by porosity clay content and lithology moreover errors in the measured p wave velocity are normally smaller than those in porosity and shale volume both of which are subject to errors introduced by imperfect models and imperfect parameters when estimated from logs because the model evaluates the bulk and shear moduli of the dry rock frame by a combination of kuster and toksoz theory and differential effective medium theory using pore aspect ratios to characterize the compliances of the sand and clay components the relationship between p and s wave velocities is explicit and consistent consequently the model sidesteps problems and assumptions that arise from the lack of knowledge of these moduli when applying gassmann s theory to this relationship making it a very flexible tool for investigating how the v p v s relationship is affected by lithology porosity clay content and water saturation numerical results from the model are confirmed by laboratory and logging data and demonstrate for example how the presence of gas has a more pronounced effect on p wave velocity in shaly sands than in less compliant cleaner sandstones

velocity anisotropy in shale determined from crosshole seismic and vertical seismic profile data crosshole and vertical seismic profile vst data made possible accurate characterization of the elastic properties including noticeable velocity anisotropy of a near surface late tertiary shale formation shear wave splitting was obvious in both crosshole and vsp data in crosshole data two orthologonally polarrized shear s waves arrived 19 ms in the uppermost 246 ft 75 m vertically traveling s waves of the vsp separated about 10 ms in the uppermost 300 ft 90 m but remained at nearly constant separation below that level a transversely isotropic model which incorporates a rapid increase in s wave velocities with depth but slow increase in p wave velocities closely fits the data over most of the measured interval elastic constants of the transvesely isotropic model show spherical p and s2 wave velocity surfaces but an ellipsoidal s1 wave surface with a ratio of major to minor axes of 1 15 the magnitude of this s wave anisotropy is consistent with and lends credence to s wave anisotropy magn

velocity anisotropy and attenuation of shale in under and overpressured conditions the seismic velocity and attenuation of fully saturated shales were measured for the first time under overpressured conditions using the ultrasonic reflection technique shale cores from naturally overpressured horizons in the north sea were tested in the laboratory at confining and pore pressures relevant to in situ conditions a single frequency tone burst pulse wave was used to determine the seismic wave velocities and quality factors of the shale samples with errors less than 0 3 and 0 1 db cm respectively at a frequency of 0 75 mhz sample length changes with varying confining and pore pressure were measured and the pore pressure equilibration time was monitored for each sample the anisotropy of the seismic attributes vp vs qp and qs was determined over a range of differential pressures from 5 to 60 mpa with respect to the predominant foliation the ultrasonic velocity data followed a transversely isotropic pattern depending on the direction of wave propagation with respect to the laminations the poisson s ratio was found to rise by 5 as the shale material progressed from a normally pressured to an overpressured state the quality factor q characteristics were interpreted in terms of pore geometry and connectivity as well as the directional permeability of the transversely isotropic shale material the results were converted to bulk and shear loss modulus defects and a positive bulk loss was observed for waves propagating perpendicular to the lamination plane even above differential pressures of 20 mpa this indicates different levels of biot flow and squirt flow attenuation mechanisms acting within the shale structure depending on the wave propagation and vibration directions

texture and anisotropy analysis of qusaiba shales scanning and transmission electron microscopy synchrotron x ray diffraction microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried qusaiba shales from the rub alkhali basin saudi arabia kaolinite illite smectite illite mica and chlorite show strong preferred orientation with 001 pole figure maxima perpendicular to the bedding plane ranging from 2 4 6 8 multiples of a random distribution m r d quartz feldspars and pyrite crystals have a random orientation distribution elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution assuming a nonporous material the average calculated bulk p wave velocities are 6 2 km s maximum and 5 5 km s minimum resulting in a p wave anisotropy of 12 the calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample in the ultrasonic experiment which measures the effects of the shale matrix as well as the effects of porosity velocities are smaller p wave maximum 5 3 km s and minimum 4 1 km s the difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample which have not been taken into account in the matrix averaging

effective medium theory and multiple linear regression based velocity estimation in syn rift clastic sequence of the krishna godavari basin india abstract an inclusion model based on the kuster toksoz effective medium theory along with gassmann theory is tested to forward model velocities for fluid saturated rocks a simulated annealing algorithm along with the inclusion model effectively inverts measured compressional velocity vp to achieve an effective pore aspect ratio at each depth in a depth variant manner continuously along with depth early cretaceous syn rift clastic sediments at two different depth intervals from two wells well a 2160 2274 m and well b 5222 5303 m in the krishna godavari basin india are used for this study shear velocity vs estimated using modelled pore aspect ratio offers a high correlation coefficient 0 95 for both the wells with measured data the modelled pore aspect ratio distribution suggests the decrease in pore aspect ratio for the deeper interval mainly due to increased effective vertical stress the pore aspect ratio analysis in relation to total porosity and volume of clay reveals that the clay volume has insignificant influence in shaping the pore geometry in the studied intervals an approach based on multiple linear regression method effectively predicts velocity as a linear function of total porosity the volume of clay and the modelled pore space aspect ratio of the rock we achieved a significant match between measured and predicted velocities the correlation coefficients between measured and modelled velocities are considerably high approximately 0 85 and 0 8 for vp and vs respectively this process indicates the possible influence of pore geometry along with total porosity and volume of clay on velocity

rifting of the northern margin of the australian continent and the origin of some microcontinents in eastern indonesia abstract continental australia is bounded on the east south and west sides by passive margins and the geological histories of these are well documented falvey and mutter 1981 the northern margin of the australian continent is now an active collision margin its previous history as a passive margin has rarely been examined this paper shows how the late palaeozoic to mesozoic sequence which forms the northern margin of the australian continent in the island of new guinea is readily related to the tectonic stages of a rift drift sequence rifting start of breakup began at about 230 m y ago at the permian triassic boundary the onset of seafloor spreading is marked by a post breakup unconformity and ranges in age along the northern margin of the continent from 185 m y in papua new guinea to 170 m y in irian jaya from there the age of the post breakup unconformity continues to young in a southwesterly direction along the western margin of the australian continent reflecting the opening of the indian ocean off western australia the timing of the onset of spreading in central papua new guinea is consistent with the timing of the initiation of spreading in the proto pacific ocean proposed by nur and ben avraham 1977 by the end of the jurassic the northern margin of the australian continent faced a seaway which linked the proto indian and proto pacific oceans this newly formed ocean was separated from the pre existing oceans of the neo tethys and panthalassa by a screen of continents or microcontinents the identity of this screen is discussed and it is suggested that part of it is preserved in the microcontinents of eastern indonesia

mesozoic and late tertiary submarine fan sequences and their tectonic significance sumba indonesia abstract the indonesian island of sumba occupies a critical zone which separates a normal subduction complex java trench system from a continent island arc collision zone banda arc sumba is considered by some authors to be a microcontinental fragment although in this context its pre fragmentation origin is uncertain detailed studies of the stratigraphy of sumba however throw light on the origin and subsequent geological history of the island and surrounding areas on available evidence the oldest outcropping rocks are of cretaceous age and locally contain a tropical tethyan marine fauna they comprise dark coloured sometimes carbonaceous and often volcanogenic mudstones sandstones gravels and diamictites pervasively intruded by andesitic and dacitic dykes and locally intruded by granodiorite plutons these sediments are siliclastic and appear to have had a continental provenance the cretaceous rocks in many areas compromise part of a major submarine fan complex which at least in south central sumba prograded towards the southwest and south shallow marine and non marine paleogene sediments and volcanic agglomerates lie unconformably above the uplifted tilted and eroded cretaceous strata these are overlain in turn by the widely outcropping miocene sumba formation an oceanic sequence with island arc affinities accessible outcrops of the sumba formation comprise platform carbonates with abundant reef developments in west sumba and a major submarine fan pelagic chalk complex in east sumba the fan complex which extends beneath the southern savu sea north of sumba is dominated by large scale slumps olistostromes and thin and thick bedded turbidites turbidite sands and gravels invariably are volcaniclastic containing components derived from a typical inner volcanic arc complex paleocurrent indicators are difficult to find in the sumba formation thus it is uncertain at this stage whether the volcaniclastic turbidites were derived from the present volcanic arc or from an undetermined source which may since have subsided the portion of the fan complex which underlies east sumba however has undergone vertical uplift since its emplacement of between one and several kilometres uplift is actively in progress at present possibly due to underthrusting by northward moving australian continental crust in this context the island of sumba comprises an uplifted north tilted and subaerially exposed part of the forearc basin of the indonesian arc this uplift can be related to initial stages of continental collision

joint elastic electrical properties of reservoir sandstones and their relationships with petrophysical parameters we measured in the laboratory ultrasonic compressional and shear wave velocity and attenuation 0 7 1 0 mhz and low frequency 2 hz electrical resistivity on 63 sandstone samples with a wide range of petrophysical properties to study the influence of reservoir porosity permeability and clay content on the joint elastic electrical properties of reservoir sandstones p and s wave velocities were found to be linearly correlated with apparent electrical formation factor on a semi logarithmic scale for both clean and clay rich sandstones p and s wave attenuations showed a bell shaped correlation partial for s waves with apparent electrical formation factor the joint elastic electrical properties provide a way to discriminate between sandstones with similar porosities but with different clay contents the laboratory results can be used to estimate sandstone reservoir permeability from seismic velocity and apparent formation factor obtained from co located seismic and controlled source electromagnetic surveys

orogeny in arc continent collision the banda arc and western new guinea eastern indonesia contains a modern continent island arc collision that demonstrates how a complex juxtaposition of continental and oceanic elements can occur in an orogenic belt shallow earthquakes show that strike slip faulting transports large crustal blocks into out of and along the collision zone while crustal shortening and thickening occur by steep angle thrust faulting near the strike slip faulting whereas strike slip faulting is paramount in positioning australian continental rocks so as to enclose the oceanic and island arc rocks of eastern indonesia its role may be overshadowed by the contemporaneous thrusting and may confuse geologic interpretations of the resulting orogenic belt

a sand wave field in the entrance to bahia blanca estuary argentina abstract sand waves in the mouth of the bahia bllanca estuary show differences in wavelength crestlength and crest shape characteristics between two sectors of the field these differences may be explained by assuming that the residual ebboriented currents are stronger in the southern sector crest bifurcations on the centerline are suggestive of intermediate energy conditions and the development of secondary flows oblique to the main current direction the large lee slopes and the presence of megaripple fans are indicative of flow separation a condition seldom mentioned for subtidal sand waves boundaries of the sand wave field may be controlled by the thickness of the surficial sand layer rapid reduction of the water depth as produced by a large marginal shoal and variations in grain size an average migration rate of 33 m yr 1 was calculated from repeated bathymetric surveys assuming that sand waves preserve shape and size the established net sediment flux over the crests is 0 025 cm3 cm 1 s 1 current measurements made during four individual tidal cycles yielded a net bedload sediment transport of 0 048 cm3 cm 1 s 1

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

the sumba enigma is sumba a diapiric fore arc nappe in process of formation abstract the anomalous updomed morphological expression of sumba island its enigmatic lack of strong neogene deformation and the northward morphological indentation of southern sumbawa and flores require explanation the stratigraphy of sumba may be correlated with the cretaceous to miocene part of the timor allochthon the sedimentary and eruptive rock succession in sumba shows remarkable similarities with the allochthonous palelo wiluba and cablac deposits of timor in both islands the cretaceous parts of these sequences are regarded as characteristic of fore arc deposits built on thin continental crust the timor nappe is interpreted as a 5 km thick tectonic flake of the banda fore arc thrust onto the australian continental margin in the mid pliocene collision the postulated sumba nappe has not yet been thrust onto the australian margin which in the sumba region has not yet converged as close to the arc as in the timor area the postulated sumba nappe is interpreted as a diapiric elongated dome of the sunda fore arc that is being squeezed by the converging margin of australia against the volcanic islands of sumbawa and flores the absence of indications on the seismic reflection profiles for the presence of the thrust fault of the sumba nappe may perhaps be explained by the thrusts being nearly horizontal within flat lying strata the savu thrust is correlated with the probably older pre late pliocene wetar suture as a major southward dipping lithospheric rupture east of 124 e this suture does not seem to have moved much since the mid pliocene collision that emplaced the nappes on timor however microearthquake data suggest some activity is continuing

spatial variations of shear wave anisotropy near the san jacinto fault zone in southern california we examine crustal anisotropy at several scales along and across the san jacinto fault zone sjfz by systematically measuring shear wave splitting sws parameters the analyzed data are recorded by 86 stations during 2012 2014 including five linear dense arrays crossing the sjfz at different locations and other autonomous stations within 15 km from the main fault trace shear phase arrivals and sws parameters fast directions and delay times are obtained with automated methods the measurement quality is then assessed using multiple criteria resulting in 23 000 high quality measurements we find clear contrast of fast directions between the sw and ne sides of the sjfz stations on the sw side have fast directions consistent overall with the maximum horizontal compression direction shmax while stations on the ne side show mixed patterns likely reflecting lithological topographic variations combined with fault zone damage the fast directions in the anza gap section with relatively simple fault geometry agree with the inferred shmax and the delay times at an array within that section are smaller than those observed at other across fault arrays these indications of less pronounced damage zone in the anza section compared to other segments of the sjfz are correlated generally with geometrical properties of the surface traces significant variations of fast directions on several across fault arrays with station spacing on the orders of a few tens of meters suggest that shallow fault structures and near surface layers play an important role in controlling the sws parameters

late cenozoic tectonic development of the southeast asian continental margin in the banda sea area abstract the late cenozoic tectonic development of the southeast asian continental margin around the banda sea is complicated by interaction with external geological elements southeast asian internal elements are the banda volcanic arc and previous older arcs external elements are the australian continental crust and the indian and pacific oceanic crusts these external elements are now trapped behind the banda volcanic arc three main geological events are responsible for the present configuration of the banda sea and adjacent areas 1 1 collision between the banda volcanic arc and australian continental crust 2 2 emplacement of the banda sea oceanic crust and 3 3 emplacement of microcontinents now present in and around the banda sea the geology of timor is fundamental to tectonic interpretations of the collision between the banda volcanic arc and australia differences exist in the tectonic interpretation of timor and include either overthrusting upthrusting or melange formation the present paper follows geological data contained in geological maps published by the geological survey of indonesia in which overthrust structures are clearly shown paleomagnetic and paleontologic data indicate that the overthrust units were from southern paleolatitudes depth and magnetic lineation data support the interpretation that the banda sea is underlain by old oceanic crust similar orientation of magnetic lineations in the banda sea and the argo abyssal plain suggests that they have the same origin geological data from northern banda microcontinents dredged samples from the banda lucipara ridges and comprehensive geological development of the northern banda arc support the interpretation that the microcontinents were translated left laterally westward from irian jaya

origin of marginal basins of the nw pacific and their plate tectonic reconstructions abstract geometry of basins can indicate their tectonic origin whether they are small or large the basins of bohai gulf south china sea east china sea japan sea andaman sea okhotsk sea and bering sea have typical geometry of dextral pull apart the java makassar celebes and sulu seas basins together with grabens in borneo also comprise a local dextral transform margin type basin system similar to the central and southern parts of the shanxi basin in geometry the overall configuration of the philippine sea resembles a typical sinistral transpressional pop up structure these marginal basins except the philippine sea basin generally have similar or compatible rift history in the cenozoic but there do be some differences in the rifting history between major basins or their sub basins due to local differences in tectonic settings rifting kinematics of each of these marginal basins can be explained by dextral pull apart or transtension these marginal basins except the philippine sea basin constitute a gigantic linked dextral pull apart basin system formation of the gigantic linked dextral pull apart basin system in the nw pacific is due to nne to ene ward motion of east eurasia this mainly was a response to the indo asia collision which started about 50 ma ago the displacement of east eurasia can be estimated using three aspects 1 the magnitude of pull apart of the dextral pull apart basin system 2 paleomagnetic data from eastern eurasia and the region around the arctic and 3 the shortening deficits in the large tibetan plateau all the three aspects indicate that there was a large amount 1000 to 1200 km of northward motion of the south china block and compatible movements of other blocks in eastern eurasia during the rifting period of the basin system such a large amount of motion of the eastern eurasia region contradicts any traditional rigid plate tectonic reconstruction but agrees with the more recent concepts of non rigidity of both continental and oceanic lithosphere over geological times based on these three estimates the method developed for restoration of diffuse deformation of the eurasian plate and the region around the arctic and the related kinematics of the marginal basins we present plate tectonic reconstructions of these marginal basins in global plate tectonic settings at the four key times 50 35 15 and 5 ma the plate tectonic reconstructions show that the first order rift stage and post rift stage of the marginal basins are correlated with the first order slow uplift stage and the rapid uplift stage of the tibetan plateau respectively the proto philippine sea basin was trapped as a sinistral transpressional pop up structure at a position that was 20 south of its present position at about 50 ma ago or earlier while the japan arc migrated eastward during the rifting period of the japan sea basin the shikoku basin opened and the parece vela basin widened

the stress sensitivity of shaley sandstones the link between the stress sensitivity of shaley sandstones and their porosity and clay content is investigated this is achieved by firstly fitting a compliance based stress sensitivity law to laboratory measurements of ultrasonic velocity taken from four sets of reservoir sandstones extracted from a variety of depositional settings correlations are then sought between the independent parameters of this law and the porosity or clay fraction of the rocks which are then subsequently interpreted in terms of framework or pore space related microstructural clay models the general conclusion drawn from the results is that both of the parameters defining the stress sensitivity law the asymptotic modulus and the stress dependent excess compliance clearly vary with porosity however only the asymptotic modulus shows a convincing trend with clay and there is little observed variation of the stress dependent compliance with clay there is therefore a resultant variation of stress sensitivity with clay but it is controlled only by the asymptotic modulus the analysis also concludes that all four data sets fall into a framework related category of clay model

lattice preferred orientation and seismic anisotropy in sedimentary rocks summary although it is well known that sedimentary rocks can be seismically anisotropic there have been few detailed investigations of the underlying cause of such anisotropy here we investigate anisotropy due to the preferred orientation of minerals or lattice preferred orientation lpo in a suite of sedimentary rocks seismic properties are predicted by averaging single crystal elastic constants of minerals according to their crystal orientation and modal volume fraction in the rock aggregate both electron backscattered diffraction ebsd and x ray texture goniometry xtg are tested as quantitative techniques for measuring the lpo of sedimentary rocks although ebsd has promise for future lpo measurements in polymineralic sedimentary rocks problems currently remain in measuring low symmetry phases e g feldspars and very small clay or mica particles however the lpo of very fine grained phyllosilicates can be measured using xtg and the lpo of low symmetry minerals can be measured using manual ebsd pattern analysis here we use such a hybrid approach to estimate lpo in a suite of sedimentary samples the seismic properties calculated from lpo data show anisotropy values for p waves ranging from 1 5 per cent in sandstones to over 3 5 per cent in a siltstone to 12 per cent in a shale the effect of thin multilayering on long wavelength propagation in a siltstone is predicted by applying backus type averaging the layering does not enhance the anisotropy because of the small differences in density and in elasticity between the two layer types the lpo of phyllosilicates and to a lesser extent dolomite and siderite seem to contribute significantly to the seismic anisotropy of phyllosilicate rich rocks siltstones and shales the weak lpo of quartz in sandstones causes a few per cent anisotropy cumulatively our results suggest that field observations of seismic anisotropy have the potential to be used as an indicator of rock lithology

prediction of sonic velocities in shale from porosity and clay fraction obtained from logs a north sea well case study abstractprediction of sonic velocities in shales from well logs is important for seismic to log ties if the sonic log is absent for a shaly section for pore pressure anomaly detection and for data quality control an anisotropic differential effective medium dem was used to simulate elastic properties of shales from elastic properties and volume fractions of silt and wet clay a hypothetical composite material that includes all clay minerals and water anisotropic elastic coefficients of the wet clay were assumed as a first order approximation to be linearly dependent on wet clay porosity wcp here by wcp we mean a ratio of a pore volume occupied by water to a total volume of the wet clay effects of silt inclusions on elastic coefficients of shales were taken into account by using the anisotropic differential effective medium model silt inclusions were modeled as spherical quartz particles simulated elastic coefficients of shales were used to calculate compressional and shear velocities and th

the evolution of sumba island indonesia revisited in the light of new data on the geochronology and geochemistry of the magmatic rocks abstract the island of sumba presently located in the southern row of islands of the eastern nusa tenggara province of eastern indonesia has a unique position being part of the sunda banda magmatic arc and subduction system it represents a continental crustal fragment located at the boundary between the sunda oceanic subduction system and the australian arc continent collision system separating the savu basin from the lombok basin new data on magmatic rocks collected from sumba are presented in this paper including bulk rock major and trace element chemistry petrography and whole rock and mineral 40k 40ar ages three distinct calc alkaline magmatic episodes have been recorded during cretaceous paleogene all of them characterized by similar rock assemblages i e pyroclastic rocks basaltic andesitic lava flows and granodioritic intrusions they are i the santonian campanian episode 86 77 ma represented by volcanic and plutonic rock exposures in the masu complex in eastern sumba ii the maastrichtian thanetian episode 71 56 ma represented by the volcanic and plutonic units of sendikari bay tengairi bay and the tanadaro complex in central sumba and iii the lutetian rupelian episode 42 31 ma of which the products are exposed at lamboya and jawila in the western part of sumba no neogene magmatic activity has been recorded

pore filling material and its effect on velocity in rocks a new method estimates the dependence of p and s velocities in rocks on elastic properties of the pore filling material by going beyond gassmann s relations and accounting for pore filling materials with nonzero shear stiffness the resulting estimates are in good agreement with experimental data and gassmann s relations for values of velocity in water saturated rocks predicted from velocity measured on dry rocks the method successfully predicts the temperature dependence of velocity 1 in frozen rocks at the ice water phase transition and 2 in rocks saturated with heavy hydrocarbon undergoing solid liquid phase transition

effective anisotropic velocity model from surface monitoring of microseismic events we develop a methodology to obtain a consistent velocity model from calibration shots or microseismicity observed on a buried array using a layered 1d isotropic model derived from checkshots as an initial velocity model we invert p wave arrival times to obtain effective anisotropic parameters with a vertical axis of symmetry vti the nonlinear inversion uses iteration between linearized inversion for anisotropic parameters and origin times or depths which is specific to microseismic monitoring we apply this technique to multiple microseismic events from several treatments within a buried array the joint inversion of selected events shows a largely reduced rms error indicating that we can obtain robust estimates of anisotropic parameters however we do not show improved source locations for joint inversion of multiple microseismic events we obtained thomsen anisotropic parameters of 0 15 and of 0 05 which are consistent with values observed in active seismic surveys these values allow us to locate microseismic events from multiple hydraulic fracture treatments separated across thousands of metres with a single velocity model as a result we invert the effective anisotropy for the buried array region and are able to provide a more consistent microseismicity mapping for past and future hydraulic fracture stimulations

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in

paleomagnetic evidence for the paleoposition of sumba island indonesia abstract jurassic paleomagnetic directions have been obtained for the sedimentary rocks in sumba the mean direction is 59 2 in declination and 44 2 in inclination the reliability of the direction is ascertained through thermal demagnetization and the presence of normal and reversed polarities comparison with the permian paleomagnetic direction of timor indicates that sumba was subjected to a clockwise rotation through 79 4 relative to timor since the jurassic when sumba is restored by a counter clockwise rotation the sumba pole is gradually approaching the jurassic pole of australia as well as the timor permian pole this implies that at least until the jurassic sumba and timor were situated at the australian continental margin and that sumba rotated clockwise during or after the jurassic