geomechanics of hydraulic fracturing microseismicity part 1 shear hybrid and tensile events we investigate the geomechanical behavior of hydraulic fracturing induced microseismicity microseismic events are commonly used to discern stimulation patterns and hydraulic fracture evolution however techniques beyond fracture mapping are required to explain the mechanisms of microseismicity in this series we present an approach to combine seismological and geomechanical techniques to investigate how microseismicity relates to propagating hydrofractures as well as existing natural fractures and faults part 1 describes the first analysis step which is to characterize the microseismic events by their source parameters focal mechanisms and fault plane orientations these parameters are used to determine the mechanical conditions responsible for activation of discrete populations or subpopulations of microseismic events that then can be interpreted in their geological and operational context first we compare microseismic fault plane populations from a mississippian barnett shale texas data set that are determined using a traditional double couple model shear only with a tensile source model hybrid events which may be more suitable for hydraulic fracturing conditions second we employ a new method to distinguish fault planes from auxiliary planes using iterative stress inversion and critical stress instability selection criteria the result is an enhanced microseismic characterization that includes geomechanical parameters such as slip tendency and local activation stress state during the operation using this approach on the barnett shale data two microseismic fault sets are resolved an inclined northeast southwest set with dominant shear and a vertical north south set with more hybrid behavior the results are used in part 2 to further investigate the heterogeneity of the stimulations and to compare models for microseismic activation

geochronological evidence supporting antarctic deglaciation three million years ago the response of the antarctic ice sheets to increased global temperatures is an important unresolved issue in the assessment of future climate change in particular considerable controversy exists as to whether the east antarctic ice sheet suffered extensive deglaciation during the mid pliocene epoch 3 myr ago when temperatures were only slightly warmer than today although the ice sheet is widely assumed to have existed in something like its present form for the past 14 myr ref 1 marine diatoms eroded from the antarctic interior have been found in glacial till deposits high in the transantarctic mountains2 3 and have been bio stratigraphically dated at 3 myr before present this age has been disputed4 because it implies marine deposition in the antarctic interior and hence substantial deglaciation at a time when other evidence has been marshalled for the persistence of cold polar conditions4 here we report k ar and 40ar 39 ar ages for a volcanic ash bed in diatom bearing glaciomarine strata cored in ferrar fiord east antarctica by the ciros 2 drill hole5 which confirm the age of the diatoms at 3 myr and hence also confirm the mid pliocene deglaciation

cosmogenic 3he concentrations in ancient flood deposits from the coombs hills northern dry valleys east antarctica interpreting exposure ages and erosion rates abstract in situ produced cosmogenic 3 he analyses provide independent support for the model of a stable hyper arid polar climate persisting in east antarctica since the mid miocene and provide quantitative constraints on long term rates of erosion within the dry valleys in the coombs hills area a series of cobble size boulders form mega ripples with wavelengths of approximately 50 m their topographic position and association with features characteristic of scabland such as stripped corrugated bedrock surfaces indicate the boulders were deposited by subglacial floodwaters such outburst flooding could only have occurred during overriding of the northern dry valleys by a greatly expanded east antarctic ice sheet timing of the overriding episode has been previously assigned to 14 8 to 13 6 ma by correlation with volcanic ash deposits dated by 40 ar 39 ar in the asgard range of the dry valleys cosmogenic 3 he concentrations in clinopyroxene from ferrar dolerite boulders are consistent with 8 6 to 10 4 ma exposure calculated using scaling factors appropriate for antarctica and assuming zero erosion these are among the oldest surface exposure dates yet measured on earth but are not however consistent with the 40 ar 39 ar chronology used to define the age of the landscape due to unconstrained levels of erosion erosion rates of 0 03 0 06 m ma 1 are necessary to have produced the measured boulder exposure age if they were deposited at 14 8 ma these are less than half the steady state erosion rate derived from cosmogenic 3 he in the nearby bedrock surfaces 0 17 m ma 1 and testify to the extreme stability of the landscape

facies and cyclicity of the late permian bainmedart coal measures in the northern prince charles mountains macrobertson land antarctica the late permian bainmedart coal measures form part of the permo triassic amery group which crops out in the beaver lake area of the northern prince charles mountains macrobertson land antarctica the exposed strata are believed to have formed in graben or half graben sub basins on the western edge of the lambert graben a major failed rift system sedimentological analysis has revealed that these rocks formed in alluvial environments in which swiftly flowing rivers of low sinuosity represented by facies a1 and a2 flowed northward down the axis of the basin and were associated with waterlogged floodbasin and peat forming wetlands facies b1 b4 a third facies association comprising facies c1 c3 interpreted as the deposits of lake floor and delta environments is exclusively developed within a distinctive fine grained interval here named the dragon s teeth member the proportion of association b facies within the succession increases markedly above the level of the dragon s teeth member at about 300 m above the base of the formation flat low angle and undulatory bedding structures preserved within channel deposits are suggestive of sediment deposition in flow conditions which were often critical or supercritical presence of massive and chaotic intervals of sandstone further implies some deposition from high concentration aqueous flows alluvial channel bodies show evidence of incision into underlying substrates both during initiation and at later stages in channel belt construction the lack of interfingering between channel deposits and coals suggests that thick peats formed only in areas and at times of minimal clastic sediment supply analysis of well developed cyclicity within the coal measures suggests that the dominant control on sequence architecture was climatic related to precessional milankovitch fluctuations of c 19 kyr periodicity cycles began abruptly with the deposition of coarse grained material in high energy alluvial channels which contracted with time in response to changes in water supply rainfall upper parts of cycles are dominated by finer grained sediments and then coal indicative of progressively reduced coarse sediment input tectonic processes overprinted this pattern at least once during the period of sediment accumulation to form the dragon s teeth member

dating of sirius group tillites in the antarctic dry valleys with cosmogenic3he and21ne we measured in situ produced cosmogenic3he and21ne in boulder and bedrock surface samples in and near sirius group tillites from two localities in southern victoria land antarctica pyroxene quantitatively retains cosmogenic3he for millions of years the deposit at mt fleming has a minimum exposure age of 6 5 ma while 6 ma is a probable minimum age for the table mountain tillite these lower limits not taking into account erosion of the sampled surfaces are based on the samples with the highest concentrations of cosmogenic noble gases and currently accepted production rates since the plagioclase bearing mt fleming samples almost certainly lost part of their cosmogenic ne the minimum exposure age at this location is presumably even 50 higher than the stated value the concentrations of cosmogenic ne in our samples constrain uplift rates of the transantarctic mountains to 170 m ma these data contradict the hypothesis of a collapse of the east antarctic ice sheet in the pliocene coupled with high uplift rates and support the model of a stable ice sheet since the middle miocene

pleistocene deglaciation chronology of the amery oasis and radok lake northern prince charles mountains antarctica abstract the east antarctic ice sheet is the largest ice mass on earth with a capacity to raise global sea level by up to 65 m as the lambert glacier amery ice shelf drainage system is the largest to reach the coast of antarctica quantifying its evolution over the quaternary is a vital component in developing an understanding of the antarctic response to future climate change here we present a deglaciation chronology based on 10 be and 26 al in situ cosmogenic exposure ages of the northern prince charles mountains which flank the lambert glacier amery system and that records the progressive emergence of mcleod massif and radok lake basin from beneath the mac robertson land lobe of the east antarctic ice sheet the exposure ages monotonically decrease with both decreasing altitude and increasing proximity to the amery ice shelf at the antarctic coast exposure ages from the crests of mcleod massif near the edge the amery ice shelf and from fisher massif 75 km further inland each at 1200 m above sea level are 2 2 0 3 and 1 9 0 2 ma respectively suggesting their continuous exposure above the ice sheet at least since close to the plio pleistocene boundary an extensive plateau at 800 m altitude on mcleod massif above battye glacier records the massif s increased emergence above the ice sheet surface at about between 880 and 930 ka ago indicating 400 m of ice volume reduction in the mid pleistocene correcting these apparent ages for a reasonable choice in erosion rate would extend this event to 1 15 ma a period identified from prydz bay odp core 1167 when sedimentation composition alters and rates decrease 10 fold exposure ages from boulder mantled erosional surfaces above and beyond the northern end of radok lake at 220 m range from 28 to 121 ka independent of choice of model interpretation to explain this age spread the most recent major reoccupation of radok lake by battye glacier ice occurred during the last glacial cycle moraine ridges at the lower altitude of 70 125 m were deposited during the final withdrawal of battye glacier ice from the lake basin between 11 and 20 ka ago this new chronology indicates that the highest amery oasis peaks have not been overridden by the mac robertson land lobe of the east antarctic ice sheet for at least the past 2 ma since this time we document 3 major periods of regional reduction in ice sheet volume at 1 1 ma during the last glacial cycle 120 to 30 ka and through the last glacial maximum 20 to 10 ka that resulted in an overall 1000 m of ice lowering in the battye glacier radok lake region

plio pleistocene sedimentation in ferrar fiord antarctica a 166 m thick plio pleistocene sequence of glacial sediments has been cored in ferrar fiord in the southwestern corner of the ross sea antarctica the core has the following lithofacies massive diamictite 33 of the core interpreted as lodgement or waterlain till weakly stratified diamictite 25 waterlain till or proximal glaciomarine sediment well stratified diamictite 8 proximal glaciomarine or glaciolacustrine sediment sandstone 25 sand of aeolian or supraglacial origin mudstone 7 derived from subglacial debris and transported offshore in suspension and minor amounts of rhythmite and tuff the range of facies in this polar setting differs from those normally found in subpolar and temperate glacier fiord settings in the high proportion of aeolian derived sand and the low proportion of mudstone facies the core can be divided into two sequences based on composition and texture the sequence from 162 to 100 mbsf metres below the sea floor comprises alternations of diamictite dominated by basement lithologies and thin marine mudstone beds it is pliocene in age 4 9 2 0 ma and records several advances and retreats of ice through the transantarctic mountains and across the drill site from the west the sequence from 100 mbsf to the sea floor of pleistocene age consists of alternations of diamictite interpreted as lodgement and waterlain till and sandstone of aeolian origin deposited in a glaciolacustrine setting similar to ice covered lakes in the dry valleys today these sediments have a high volcanic component and hence are thought to have been derived by the grounding and advance of the ross ice shelf from the east past volcanic ross island this change in source is attributed to the rising transantarctic mountains increasingly containing east antarctic ice the pleistocene sequence above 100 mbsf clearly represents polar glacial sedimentation with alternations of till and glaciolacustrine sand mudstones from the pliocene sequence beneath include palynomorphs indicating times when the landscape was at least partially vegetated but contain no evidence of meltwater influence

the morphology structural evolution and significance of push moraines abstract push moraines glaciotectonic ice marginal moraines have a restricted distribution at modern glacier margins and consequently are of potential value in reconstructing pleistocene ice sheets providing data both on former glaciodynamics and on the palaeoenvironment of the glacial foreland to the wider earth science community push moraines are of interest as analogues for thin skin tectonics within orogenic belts this paper reviews the morphology structural geology formation and significance of push moraines the morphological and structural characteristics of small seasonal push moraines through to large multi crested examples produced by sustained glacier advances are reported before the primary controls on push moraine formation are examined these controls include the nature of the applied glacial stress field the presence and properties of decollement horizons and the shear strength and rheology of the glacial foreland a conceptual model of push moraine formation is introduced in which the range of observed morphological and structural forms are viewed within a matrix defined by the main variables which control their formation the absence of consensus over which of these variables is of greatest importance currently limits the significance of push moraines in palaeoglaciological research as a consequence this review emphasises the need for future research in order to realise the true potential of push moraine in the reconstruction of pleistocene environments

redefinition of the amery ice shelf east antarctica grounding zone 1 new evidence is presented which shows that the amery ice shelf east antarctica extends 240 km upstream of the previously reported position we combine a digital elevation model of the amery ice shelf created from ers 1 satellite radar altimetry with measured ice thicknesses and a simple density model in a hydrostatic buoyancy calculation to map the extent of the floating ice this reveals that the ice is floating as far south as 73 2 s the result is confirmed by static gps measurements collected during three consecutive field campaigns on the amery ice shelf where the vertical component of the gps shows a clear tidal signal at 72 98 s other evidence for the grounding zone position comes from an analysis of satellite imagery mass flux calculations and ice radar data the southward extension of the grounding line substantially alters the shape and dimensions of the ocean cavity beneath the ice shelf which has implications for modeling studies of sub ice shelf processes such as basal melting and freezing ocean circulation and tides the new grounding line position will also improve geophysical studies where the computation of ocean tidal loading corrections is important for postglacial rebound estimates and correction of satellite altimetry measurements within the region

preservation of miocene glacier ice in east antarctica antarctic climate during the pliocene has been the subject of considerable debate one view holds that during part of the pliocene east antarctica was largely free of glacier ice and that vegetation survived on the coastal mountains1a 4 an alternative viewpoint argues for the development of a stable polar ice sheet by the middle miocene which has persisted since then5a 10 here we report the discovery of buried glacier ice in beacon valley east antarctica which appears to have survived for at least 8 1 million years we have dated the ice by 40ar 39ar analysis of volcanic ash in the thin overlying glacial till which we argue has undergone little if any reworking isotope and crystal fabric analyses of the ice show that it was derived from an ice sheet we suggest that stable polar conditions must have persisted in this region for at least 8 1 million years for this ice to have avoided sublimation

errata neogene fjordal sedimentation on the western margin of the lambert graben east antarctica the lambert graben is occupied by the world s largest fjord system through which flows the lambert glacier the amery ice shelf and their tributaries along the western margin of the graben in the northern prince charles mountains remnants of uplifted miocene and pliocene strata of the glacigenic fjordal pagodroma group total more than 800 m in thickness these sediments provide evidence for a dynamic east antarctic ice sheet during the neogene period each of the four pagodroma group formations defined from this region rests unconformably on either proterozoic or permo triassic rocks the unconformity surfaces represent parts of the walls and floors of neogene fjords for these surfaces to have been eroded the ice must have been grounded out as far as the continental shelf in prydz bay the pagodroma group was deposited by wet based glaciers discharging into a fjordal setting and includes lithofacies that are quite different from those produced by modern antarctic ice masses the principal lithofacies are massive diamicts and soulder gravels deposited both close to a calving grounded glacier terminus and from icebergs the few stratified diamicts are the product of more distal iceberg sedimentation an ice transported gravel lithofacies includes rockfall debris derived from palaeofjord walls and mixed with subglacially derived diamicts some lithofacies contain evidence of subaquatic slumping and gravity flowage volumetrically minor lithofacies include laminites with some exposures exhibiting large ice rafted clasts the laminites represent less proximal mainly ice free fjordal sediments resulting either from tidal current sorting of suspended sediment originating from subaquatic glaciofluvial discharge or from turbidity currents derived from unstable subaquatically deposited glacigenic sediment the pagodroma group provides a record of multiple glaciation by dynamic sliding glaciers carrying large amounts of both basal and supraglacial debris the closest modern analogues in terms of the thermal and dynamic characteristics of the neogene lambert glacier appear to be the fast flowing tidewater glaciers of east greenland these glaciers originate from the interior ice sheet and discharge large volumes of icebergs the resulting lithofacies are predominantly diamicts

consistency of stress state locations and source mechanisms of events induced by hydraulic fracturing downhole monitoring we present results of processed microseismic events induced by hydraulic fracturing and detected using dual downhole monitoring arrays the results provide valuable insight into hydraulic fracturing for our study we detected and located microseismic events and determined their magnitudes source mechanisms and inverted stress field orientation event locations formed a distinct linear trend above the stimulated intervals source mechanisms were only computed for high quality events detected on a sufficient number of receivers all the detected source mechanisms were dip slip mechanisms with steep and nearly horizontal nodal planes the source mechanisms represented shear events and the non double couple components were very small such small non double couple components are consistent with a noise level in the data and velocity model uncertainties strikes of inverted mechanisms corresponding to the nearly vertical fault plane are within the error of measurements identical with the strike of the location trend ambient principal stress directions were inverted from the source mechanisms the least principal stress 3 was determined perpendicular to the strike of the trend of the locations indicating that the hydraulic fracture propagated in the direction of maximum horizontal stress our analysis indicated that the source mechanisms observed using downhole instruments are consistent with the source mechanisms observed in microseismic monitoring arrays in other locations furthermore the orientation of the inverted principal components of the ambient stress field is in agreement with the orientation of the known regional stress implying that microseismic events induced by hydraulic fracturing are controlled by the regional stress field

stability of source mechanisms inverted from p wave amplitude microseismic monitoring data acquired at the surface we study the stability of source mechanisms inverted from data acquired at surface and near surface monitoring arrays the study is focused on p wave data acquired on vertical components as this is the most common type of acquisition we apply ray modelling on three models a fully homogeneous isotropic model a laterally homogeneous isotropic model and a laterally homogeneous anisotropic model to simulate three commonly used models in inversion we use geometries of real arrays one consisting in surface receivers and one consisting in buried geophones at the nearsurface stability was tested for two of the frequently observed source mechanisms strike slip and dip slip and was evaluated by comparing the parameters of correct and inverted mechanisms we assume these double couple source mechanisms and use quantitatively the inversion allowing non double couple components to measure stability of the inversion to test the robustness we inverted synthetic amplitudes computed for a laterally homogeneous isotropic model and contaminated with noise using a fully homogeneous model in the inversion analogously amplitudes computed in a laterally homogeneous anisotropic model were inverted in all three models we show that a star like surface acquisition array provides very stable inversion up to a very high level of noise in data furthermore we reveal that strike slip inversion is more stable than dip slip inversion for the receiver geometries considered here we show that noise and an incorrect velocity model may result in narrow bands of source mechanisms in hudson s plots

the spatial variation of weathering and soil depth across a triassic sandstone outcrop in this study we used an archive of borehole logs from the british geological survey to collect information on the spatial structure of weathering that extends from the surface to competent bedrock across the triassic sherwood sandstone group outcrop 750 km2 in the east midlands uk the borehole logs were used to estimate the thickness of the soil n 280 and soil and saprolite ss the overburden of ice may have increased sub glacial pore water pressure with the fractures and faults acting as a drainage system for the removal of dissolved weathering products

cenozoic marine sedimentation and ice volume variation on the east antarctic craton recycled cretaceous and cenozoic marine microfossils have been recovered from samples of the pliocene sinus formation samples were collected from outcrops in the reedy beardmore and ferrar glacier areas of the transantarctic mountains between lat 77 and 86 s the glaciogene sediments contained diatoms foraminifera calcareous nannoplankton silicoflagellates radiolarians sponge spicules palynomorphs and ostracodes of late cretaceous paleocene eocene late oligocene late miocene and pliocene age this suggests the presence of open marine basins on the east antarctic craton during late mesozoic and cenozoic time the apparent absence of early oligocene and early through middle and earliest late miocene assemblages suggests either that marine regression exposed the basin floors or that ice filled the basins during these times the high elevation setting of sirius formation outcrops suggests one of two hypotheses for their origin 1 they are in situ pliocene glaciomarine deposits that were uplifted 1 750 2 500 m with the transantarctic mountains to their present elevation 2 the sirius formation deposits are a mixture of derived sediments stripped from sub ice intracratonic basins and subsequently redeposited by ice flowing up the inland slope of the transantarctic mountains we favor the second hypothesis with transport to sites sometime within the past 3 m y

ice distal upper miocene marine strata from inland antarctica abstract glacimarine strata of the battye glacier formation 130 m thick pagodroma group exposed in the amery oasis of east antarctica provide a record of late miocene palaeoenvironmental conditions in an ice distal setting the formation overlies the amery erosion surface 300 m to 270 m above sea level that formed during an advance of the lambert glacier into prydz bay odp site 739 at least 750 km further north than today two lithological members a grey and muddier lower member and a brown sand rich upper member reflect variation in proximity to the terminus of the lambert glacier ice distal glacimarine diatom bearing mud up to 12 biogenic silica and in situ articulated molluscs occur in the lower member the battye glacier formation is significant because of its inland location which indicates that ice distal marine conditions existed 250 km inland from the current amery ice shelf edge similar neogene strata are known on land only from the pliocene sorsdal formation in the vestfold hills near the antarctic coast three stratigraphic intervals of diatom bearing mud are recognized from glacially reworked clasts and from in situ strata informally referred to as the mcleod beds and bed a the diatom bearing mud also contains sponge spicules and minor silicoflagellates and ebridians marine diatom biostratigraphy constrains the age of the beds to between 10 7 and 9 0 ma late miocene abundant benthic diatoms suggest deposition within shallow euphotic waters the high abundance of intercalary valves of eucampia antarctica from an interval of the mcleod beds suggests that there was less winter sea ice than in prydz bay today it is unlikely that sea ice was perennial because the presence of thalassionema spp and stellarima stellaris roper hasle et sims suggests that summer sea surface temperatures were too warm 0 c and 3 c respectively the palaeoclimate at the time of deposition appears to have been analogous to that in modern fjords of east greenland e g kangerdlugssuaq fjord which is consistent with the depositional model proposed previously for the pagodroma group the three diatom bearing mud intervals were deposited in the amery oasis 250 km inland of the current amery ice shelf edge when the east antarctic ice sheet was reduced in size relative to today

microscale modeling of fluid flow geomechanics seismicity relationship between permeability and seismic source response in deformed rock joints studying rock joint deformation including both slippage and opening mechanisms provides an opportunity to investigate the connection between the permeability and seismic source mechanisms a microscale fluid flow geomechanics seismicity model was built to evaluate the transport response and failure mechanism of microcracks developed along a joint in berea sandstone samples during deformation the modeling method considers comprehensive grain cement interactions fluid flow behavior is obtained through a realistic network model of the pore space in the compacted assembly the geometric description of the complex pore structure is characterized to predict permeability of the rock sample as a function of rock deformation by using a dynamic pore network model as a result of microcracks development forces and displacements in grains involved in bond breakage are measured to determine seismic moment tensor shear and nonshear displacements are applied to the joint samples to investigate their effects on permeability evolution and failure mechanism of microcracks during joint deformation in addition the effect of joint roughness is analyzed by performing numerical compression tests we also investigate how confining pressure affects volumetric deformation leading to opening or closure of developed microcracks and permeability changes of samples with joints

shear wave group velocity surfaces in low symmetry anisotropic media abstractshear waves excited by natural sources constitute a significant part of useful energy recorded in downhole microseismic surveys in rocks such as fractured shales exhibiting symmetries lower than transverse isotropy ti the shear wavefronts are always multivalued in certain directions potentially complicating the data processing and analysis this paper discusses a basic tool the computation of the phase and group velocities of all waves propagating along a given ray that intends to facilitate the understanding of geometries of the shear wavefronts in homogeneous anisotropic media with this tool arbitrarily complex group velocity surfaces can be conveniently analyzed providing insights into possible challenges to be faced when processing shear waves in anisotropic velocity models that have symmetries lower than ti among those challenges are complicated multipathing and the presence of cones of directions known as internal refraction cones in which no fast shear waves propagate and t

a new moment tensor decomposition for seismic events in anisotropic media summary investigating the mechanisms of small seismic sources usually consists of three steps determining the moment tensor of the source decomposing the moment tensor into parameters that can be interpreted in terms of physical mechanisms and displaying those parameters this paper concerns the second and third steps two existing methods the riedesel jordan and hudson pearce rogers parameters and displays are reviewed compared and contrasted and advantages and disadvantages of the two methods are discussed one disadvantage is that neither method takes into consideration the effect of anisotropy on the interpretation in microseisms anisotropy can be important a new procedure based on the biaxial decomposition of the potency tensor is introduced which explicitly allows for anisotropy and interprets the moment tensor in terms of an isotropic pressure change and a displacement discontinuity on a fault it is shown that this interpretation is always possible for any moment tensor whatever the anisotropy to compare the pressure change with the displacement discontinuity it is useful to be able to determine the volume change from the pressure source in any medium this depends on the embedded bulk modulus which differs from the normal bulk modulus the embedded modulus in isotropic media is well known and the equivalent anisotropic result is derived in this paper interpreting a seismic source in terms of the volume change due to a pressure change and a displacement discontinuity on a fault allows a simple 3 d graphical glyph to be used to display the interpretation

minimum 10be exposure ages of early pliocene for the table mountain plateau and the sirius group at mount fleming dry valleys antarctica using accelerator mass spectrometry ams we have measured 10be and 26al in quartz from granites and sandstones from table mountain and mount fleming antarctica our data show that the plateau surface at table mountain had formed by early pliocene time at the latest granites fringing but within the sirius group at table mountain give a minimum exposure age of 2 6 ma for this deposit a sandstone clast on the ferrar dolerite surface just outside and below and thus postdating the sirius group has a minimum age of 2 9 ma two samples from the sirius group at mount fleming have 10be concentrations that have reached secular equilibrium this deposit is at least 4 8 m y old the sirius group at mount fleming cannot have been deposited after 3 0 2 5 ma as implied by biostratigraphic data our dates contradict the hypothesis that in the pliocene east antarctica was deglaciated and the climate was significantly warmer and wetter the preservation of these surfaces indicates a continuous cold desert in the dry valleys since the beginning of the pliocene the high 10be concentrations we have measured cannot be reconciled with uplift of the transantarctic mountains at a rate of 1 km m y during the past 3 m y

microseismicity derived fault planes and their relationship to focal mechanism stress inversion and geologic data general stress and faulting trends have been retrieved through the analysis of mining induced microseismic events m 0 at two sites related to an mn 2 6 rockburst and an excavation at depth a comparison of results obtained through principal component analysis pca of seismicity focal mechanism and stress inversion with in situ measurements of stress and structural mapping data show that under stable stress conditions the p b t and stress inversion axes are consistent with in situ measurements of stresses stress inversion and pca fault planes lie within 10 to 20 of the most significant mapped features at the sites and the pca technique provides a robust approach for the determination of fault planes

influence of a velocity model and source frequency on microseismic waveforms some implications for microseismic locations in this paper we examine the influence of a velocity model and microseismic source frequency on microseismic waveforms and event locations finite difference waveform synthetics are generated based on the cotton valley hydraulic fracture experiment where we vary the vertical heterogeneity of the velocity models as well as the microseismic source frequencies we find that differences between plausible velocity models lead to changes in arrival times of approximately 0 0035 seconds for p waves and 0 0085 seconds for s waves based on the average p and s wave velocities the difference in the p and s wave traveltimes is equivalent to approximately 20 m in location difference significant increases in the waveform coda develop with increasing model heterogeneity and increasing source frequency the presence of signal noise as well as other sources of error e g uncertainty in geophone location will likely lead to further increase in uncertainty in location error estimates thus we note that location error due to incorrect velocity models cannot be ignored

on the feasibility of inversion of single well microseismic data for full moment tensor the existing paradigm widely accepted in the microseismic community asserts the impossibility of unambiguous estimation of full seismic moment tensor from three component data recorded in a single straight borehole the statement of inversion nonuniqueness related to the lack of illumination of the off plane moment component in the zero solid angle ray apertures tacitly assumes the slowness vectors normal to the relevant wave fronts to be confined to the plane containing the ray trajectories although such arrangements of the rays and slownesses do take place for vertical wells drilled in horizontally layered isotropic and vti transversely isotropic with a vertical symmetry axis formations azimuthal anisotropy commonly expected for hydraulically fractured hydrocarbon bearing shales makes the slowness vectors deviate from a plane arrange themselves into nonzero solid angle apertures and yield theoretically unique inverse problems for seismic moment tensors this paper examines those problems for the anisotropy parameters characterizing fractured shales and siltstones in the bakken their strong azimuthal anisotropy entails not only formally unique but importantly for practical applications well posed inverse problems resulting in robust estimates of the complete moment tensors from single borehole data

cenozoic landscape evolution of the convoy range to mackay glacier area transantarctic mountains onshore to offshore synthesis on the basis of geomorphic mapping we reconstruct the landscape evolution of the convoy range to mackay glacier area of the rifted margin of the transantarctic mountains and compare the land record with that obtained from offshore marine sedimentary rocks in the ross sea three landform assemblages reflect 1 fluvial planation and dissection 2 local glaciation under temperate conditions and 3 overriding by the east antarctic ice sheet overall landscape evolution is typical of a passive continental margin contrasts in morphology between the convoy range and the adjacent dry valleys and royal society mountains reflect the varying location of the initial drainage divide in relationship to the rifted coast in a wider synthesis we draw the following conclusions for the 260 km long mcmurdo sector of the transantarctic mountains denudation since rifting at ca 55 ma has removed a wedge 4 7 km thick at the coast declining inland to 1 km most denudation occurred in the eocene from planation and incision of river valleys near the coast a subsequent pulse of denudation most rapid at 34 31 ma and declining until ca 17 ma coincided with further crustal extension and a change from cool temperate to polar climate during the same interval there was a progressive decrease in landscape modification by warm based glaciers and or rivers between 14 8 and 13 6 ma the maximum overriding antarctic ice sheet flowed northeastward across the mountains leaving meltwater features crossing high altitude saddles and areally scoured bedrock near the coast since 13 6 ma the landscape has seen little change under a hyperarid polar climate either by local glaciers or subaerially fragile middle miocene surficial deposits still survive there has been tectonic stability since the middle miocene

late cenozoic glacial history of the ross embayment antarctica abstract knowledge of the cenozoic terrestrial and marine glacial history of antarctica has been developed through studies of on land surface outcrops and subsurface drillcores and through examination of drillcores and piston cores obtained from a variety of offshore marine geological settings these field and laboratory endeavors have been a major target of the antarctic earth science community for more than thirty years the ross sea sedimentary basins including the byrd basin west antarctica wilkes and pensacola basins east antarctica and the transantarctic mountains provide significant data on the cenozoic glacial record a record that has been traced back to at least 38 ma close to the eocene oligocene boundary this paper reviews the late cenozoic history of the transantarctic mountains and flanking sedimentary basins with emphasis on the debate between the stabilist view of antarctic ice sheet history see clapperton and sugden 1990 and our favored multi glacial dynamic ice sheet model

four year comparison of water contents beneath a grass ley and a deciduous oak wood overlying triassic sandstone in lowland england summary differences in the seasonal water dynamics of a sand soil overlying triassic sandstone have been investigated to a depth of 9 m beneath both a grass ley and a pendunculate oak woodland within clipstone forest nottinghamshire england fortnightly measurements with a neutron probe over a four year period allowed a comparison of the soil rock water content to depths rarely reported in spring the rate of decrease of water content of the uppermost 2 m of soil was much greater under grass than oak woodland in contrast the rate of decrease under oak was greater after leafing out in may while the rate of rewetting in early autumn was lower for this land use until senescence and leaf fall in late autumn in the uppermost 2 m of soil a depth that includes all plant roots the soil moisture minima were between 47 and 58 mm lower under oak than grass in each year of monitoring as a result of both these drier conditions and the comparatively late leaf fall of this species penetration of the winter season wetting front to 2 m was delayed by between one and three months at the oak site relative to grass in years of near average rainfall rewetting at 9 m lags by 10 12 months compared to the surface giving an average penetration rate for the wetting front to this depth of 25 30 mm day 1 with little observable differences between the land uses preferential flow is evident under both sites affecting the profile to 3 m in all years and to at least 6 m following winters experiencing exceptional rainfall

full waveform based complete moment tensor inversion and source parameter estimation from downhole microseismic data for hydrofracture monitoring downhole microseismic monitoring is a valuable tool in understanding the efficacy of hydraulic fracturing inverting for the moment tensor has gained increasing popularity in recent years as a way to understand the fracturing process previous studies utilize only part of the information in the waveforms such as direct p and s wave amplitudes and make far field assumptions to determine the source mechanisms the method is hindered in downhole monitoring when only limited azimuthal coverage is available in this study we develop an approach to invert for complete moment tensor using full waveform data recorded at a vertical borehole we use the discrete wavenumber integration method to calculate full wavefields in the layered medium by using synthetic data we find that at the near field range a stable complete moment tensor can be retrieved by matching the waveforms without additional constraints at the far field range we discover that the off plane moment tensor component is poorly constrained

microseismic moment tensors a path to understanding frac growth microseismic monitoring is a valuable tool in understanding the efficacy of hydraulic fracture treatments determination of event locations and magnitudes leads to estimations of the geometry of the fracture zone and certain dynamics of the fracturing process with sufficient resolution the hypocenters may even reveal failure planes or other underlying structures controlling the distribution of events and of interest to petroleum engineers to test various hypotheses on fracture growth

cenozoic landscape evolution of an east antarctic oasis radok lake area northern prince charles mountains and its implications for the glacial and climatic history of antarctica abstract ice free areas antarctica reveal a multi million year history of landscape evolution but most attention up to now has focused on the transantarctic mountains the amery oasis in the northern prince charles mountains borders the lambert glacier amery ice shelf system that drains 1 million km2 of the east antarctic ice sheet and therefore provides a record of fluctuations of both local and regional ice since the ice sheet first formed in early oligocene time this glacial record has been deciphered by i geomorphological mapping from aerial photographs and on the ground ii documenting the relationship between thick well dated uplifted glaciomarine strata and the underlying palaeolandscape iii examining surficial sediment facies and iv surface exposure dating using 10be and 26al the se amery oasis records at least 10 million years of landscape evolution beginning with a pre late miocene phase of glacial erosion followed by deposition of glaciomarine strata of the battye glacier formation pagodroma group in late miocene time a wet based ice sheet next expanded over the se amery oasis following which deposition of the glaciomarine pliocene bardin bluffs formation pagodroma group took place both formations were uplifted by at least 500 and 200 m respectively their tops are characterised by geomorphological surfaces upon which intensive periglacial activity took place higher level bedrock areas were subjected to deep weathering and tor formation early pleistocene time was characterised by expansion of a cold based ice sheet across the whole area but it left little more than patches of sandy gravel and erratic blocks late pleistocene expansion of local ice the battye glacier saw deposition of moraine mound complexes on low ground around radok lake and ice dammed lake phenomena subglacial drainage of the lake escaped to the east exhuming the sediment filled gorges holocene landscape modification has been relatively superficial overall the landscape of the amery oasis evolved primarily under the influence of wet based probably polythermal glaciers in miocene and pliocene times whereas the quaternary period was characterised mainly by cold based glaciers that had comparatively little impact on the landscape

resedimentation of debris on an ice cored lateral moraine in the high arctic kongsvegen svalbard abstract in ice cored landform assemblages the process of resedimentation via sediment flow is important in determining the morphology and sedimentary facies distribution after the ice core has melted this paper documents the sediment flow processes associated with the resedimentation of an ice cored lateral moraine at kongsvegen svalbard decay of the ice cored lateral moraine is dominated by the development of a sediment flow fan which has an hour glass form in plan the fan comprises a broad source area on the crest of the lateral moraine separated from the fan surface composed of tessellated flow lobes by a narrow ice floored channel system the principle sedimentary facies associated with this fan include matrix supported diamictons laminated silts and fine sands the evolution of this fan and the likely end products after complete deglaciation are discussed and this paper contributes modern analogue data relevant to the interpretation of the pleistocene landform and sediment record

the structure and origin of prydz bay and macrobertson shelf east antarctica abstract a marine geophysical survey in early 1982 conducted by the australian bureau of mineral resources indicated that much of prydz bay is underlain by a sedimentary basin severe seismic multiples preclude an accurate estimate of total sediment thickness but interpretation of the seismic and magnetic data suggest that it is probably at least 5 km the trends of the southeast basin margin and of mild faulting and folding in the southwest indicate an overall nne trend roughly orthogonal to the continental margin in the south of prydz bay two series of seismic sequences are evident separated by a mildly erosional unconformity the lower series ranges from poorly to well stratified has minor folding and faulting and probably derives from continental and perhaps shallow marine pre breakup sediments the upper series is generally well stratified and prograded near the shelf edge it probably represents shallow marine post breakup sediments the seabed is distinctly unconformable with the underlying sediments implying both that much of the upper series sediments and some of the lower series sediments have been bulldozed off by advances of the amery ice shelf and that present sedimentation rates are very low possible thin moraines or tillites in the northeast part of the prydz bay are also attributed to these glacial advances the continental slope and rise sedimentary section ranges from at least 3 km thick off prydz bay to thin off the macrobertson shelf to the west reflecting the more prolific sediment source in prydz bay the deep water section includes several seismic sequences the most distinctive being interpreted as sheet volcanics and turbidite fans the deepest visible unconformity is locally strongly faulted and may separate the pre breakup and post breakup sediments indo antarctic breakup has been tentatively dated as early neocomian 130 ma and the e w orientation of the resultant antarctic coast invites interpretation of the lambert glacier prydz bay structure as a possible failed rift arm of a triple junction direct information on the age and nature of the sediments under prydz bay is lacking but permian continental sediments cropping out at beaver lake to the south may correspond to the lower pre breakup series this interpretation gains some support from analogies with fault bounded intracratonic basins in india which contain permian to triassic continental strata and which may have been juxtaposed prior to breakup the upper series probably consists of upper cretaceous and cainozoic sands and shales with moraines or tillites at the top of the section

a marine and terrestrial sirius group succession middle beardmore glacier queen alexandra range transantarctic mountains antarctica a succession of sirius group glacigene sediments which crop out along the western margins of the beardmore valley between cherry icefall and hewson glacier below the cloudmaker is designated as the stratotype of the cloudmaker formation this new formation overlies a multiply glaciated pavement dominion erosion surface cut into the precambrian goldie formation and is disconformably overlain by the meyer desert formation sirius group the cloudmaker formation comprises bedded and massive diamictons bedded sands and silts and laminated clays assemblages of foraminifera occur throughout the cloudmaker formation and indicate that these basal sirius group sediments were deposited in brackish glacial marine environments the general absence of diatoms suggest these marine waters were ice covered similar marine assemblages are also present in basal sirius group sediments at oliver bluffs dominion range recycled marine diatom assemblages in the sirius group at the latter locality indicate that the host sediments have an age of 3 8 ma pliocene the cloudmaker formation is placed in the pliocene although a latest miocene age for the basal sediments cannot be ruled out stratigraphie sedimentologic and paleontologic evidence suggests that beardmore valley was occupied by a fjord and tidewater glacier system that extended at least 165 km through the transantarctic mountains from the southwestern ross sea the stratigraphy of the cloudmaker formation consists of a succession of members separated by disconformities it is hypothesised that these strata were deposited by a dynamic valley glacier system that underwent a history of glacier advance and grounding alternating with glacier retreat and flotation over a marine water column a combination of fjord basin sediment filling and sea level oscillations may also have influenced the pattern of glacier ice advance and retreat within beardmore paleofjord the marine cloudmaker formation is overlain by the terrestrial diamicton dominated meyer desert formation at oliver bluffs the meyer desert formation diamictons are interbedded with fluvial and lacustrine sediments successions that contain in situ vascular plant fossils principally the southern beech nothofagus mosses and beetle remains a magellanic type flora and fauna occupied the coastal margins of the beardmore paleofjord the vertical transition from the basal marine cloudmaker formation to terrestrial meyer desert formation provides a sea level datum that can be used to assess the extent of post sirius group tectonic uplift uplift rates at the cloudmaker section 90 km inland from the transantarctic mountain front or rift shoulder margin in the queen alexandra mountain block are determined to be 429 or 350 m myr this assumes a total uplift of 1331 m for the uppermost marine sediments of the cloudmaker formation and maximum diatom based ages for the sirius group of 3 1 ma or 3 8 ma gross similarities in stratigraphy and interpreted paleoenvironments are apparent between the cloudmaker succession beardmore paleofjord and the upper miocene pliocene successions at the mouth of taylor paleofjord 800 km to the north contrasting present day elevational settings for these two widely separated marine successions indicates the post sirius rate of tectonic uplift for the transantarctic mountains has been significantly greater in the queen alexandra block

variations in the composition of the clay fraction of the cenozoic pagodroma group east antarctica implications for determining provenance abstract the cenozoic pagodroma group in the northern prince charles mountains east antarctica is a glaciomarine succession of fjordal character comprising four uplifted formations of different ages the composition of the the assemblage of the upper oligocene to lower miocene mount johnston formation is characterised by the dominance of illite and intermediate concentrations of chlorite similar to that assemblage is the clay mineral suite of the middle miocene fisher bench formation where illite and chlorite together account for 95 of the clay minerals the middle to upper miocene battye glacier formation is the only formation with significant and persistent smectite concentrations although illite is still dominant the kaolinite concentration is also high and is even higher than that of chlorite the clay fraction of the upper pliocene to lower pleistocene bardin bluffs formation is characterised by maximum kaolinite concentrations and relatively low illite and chlorite concentrations the bulk of the clay fraction in each formation can be explained by the physical weathering and erosion of a nearby source under glacial conditions in the case of mount johnston formation and fisher bench formation this source may be situated in the metavolcanic and gneissic rocks of fisher massif the sediments of the bardin bluffs formation indicate a local source within the amery oasis where proterozoic granitoid rocks and gneisses and permo triassic fluvial rocks of the amery group are exposed these results suggest a strong local imprint on the glacial sediments as northwards flowing ice eroded the bedrock in these areas the origin of the clay fraction of the battye glacier formation is a matter of debate the smectite and kaolinite content most easily can be explained by erosion of sources largely hidden beneath the ice upstream less likely these clay minerals reflect climatic conditions that were much warmer and wetter than today facilitating chemical weathering

cold glaciers erode and deposit evidence from allan hills antarctica here we report previously undescribed features of erosion and deposition by a cold polar glacier a recent study challenged the assumption that cold glaciers neither slide nor abrade their beds but no geological evidence was offered the features we describe include abrasion marks subglacial deposits glaciotectonically deformed substrate isolated blocks ice cored debris mounds and boulder trains all products of a recent cold ice advance and retreat mapping these features elsewhere in antarctica will document recent shifts in the east antarctic ice sheet margin providing new insight on regional mass balance changes

dense surface seismic data confirm non double couple source mechanisms induced by hydraulic fracturing we have determined source mechanisms for nine high quality microseismic events induced during hydraulic fracturing of the montney shale in canada seismic data were recorded using a dense regularly spaced grid of sensors at the surface the design and geometry of the survey are such that the recorded p wave amplitudes essentially map the upper focal hemisphere allowing the source mechanism to be interpreted directly from the data given the inherent difficulties of computing reliable moment tensors mts from high frequency microseismic data the surface amplitude and polarity maps provide important additional confirmation of the source mechanisms this is especially critical when interpreting non shear source processes which are notoriously susceptible to artifacts due to incomplete or inaccurate source modeling we have found that most of the nine events contain significant non double couple dc components as evident in the surface amplitude data and the resulting mt models furthermore we found that source models that are constrained to be purely shear do not explain the data for most events thus even though non dc components of mts can often be attributed to modeling artifacts we argue that they are required by the data in some cases and can be reliably computed and confidently interpreted under favorable conditions

estimation of groundwater recharge to chalk and sandstone aquifers using simple soil models abstract on the assumption that the water draining below the root zone is potentially available for groundwater recharge two current uk methods for estimating annual groundwater recharge have been compared with a new soil model using data from four sites under permanent grass in the uk two sites representative of the chalk aquifer at bridgest farm hampshire and fleam dyke cambridgeshire and two sites on the triassic sandstone at bicton college devon and bacon hall shropshire a four root layers model frlm the penman grindley model and the uk meteorological office rainfall and evaporation calculation system morecs were used the new soil model was run with potential evaporation as input both from the morecs and from the penman monteith equation the models were run for the chalk sites both with and without a bypass flow of 15 of rainfall bypass was not considered for the sandstone sites the performance of the models was tested against neutron probes measurements of soil moisture deficits in addition the annual groundwater recharge estimated from the models was compared with the published values obtained from the zero flux plane method generally the penman grindley model was more successful in predicting the time for soil to return to its field capacity than in predicting the magnitude of the soil moisture deficit the annual groundwater recharge was predicted with reasonable accuracy the morecs relatively tended to overestimate the soil moisture deficits and to delay the time at which the soil returns to its field capacity the consequences were underestimates of annual groundwater recharge owing either to the higher values of potential evaporation calculated from the morecs or tothe high available water capacity values associated with the soils under consideration the new soil model frlm predicts the soil moisture deficits successfully and hence is reliable in estimating the annual groundwater recharge the model is capable of doing this with potential evaporation input calculated either from the morecs or from the penman monteith equation the model also demonstrated that the inclusion of 15 of rainfall as bypass flow is viable for chalk sites

shear and tensile earthquakes caused by fluid injection 1 we apply rock mechanics concepts to the seismological observations in order to explain why during hydraulic injection some events display tensile and some shear deformation the presence of non shear components depends on the differential stress and the fracture orientation with respect to the 1 direction provided the slip vector is parallel to the traction we define four types of earthquakes according to the ratio of the shear and tensile components assuming a griffith failure envelope hybrid events containing both shear and tensile components can occur for fractures striking within 22 5 of 1 we argue that pure tensile fractures striking parallel to 1 are unlikely in the presence of natural fractures the low shear traction of tensile events also implies their small stress drops by applying the analysis to two different data sets soultz sous forets and cotton valley we show that different orientations of natural fractures and differential stress in the targeted formations made each region favorable for different non dc components in the injection induced seismicity

surface microseismic imaging in the presence of high velocity lithologic layers surface microseismic monitoring above regions containing high velocity units will be influenced by a reduction in the effective array aperture and contain significant seismic coda due to an increase in reflected and converted wave energy which can influence the capability of surface arrays to image microseismic events we have examined the imaging difficulties due to the reduction of the effective array aperture and increased coda within microseismic data caused by the presence of a fast anhydrite layer we have generated and used finite difference full waveform microseismic synthetics derived from 1d sonic log data taken from an unconventional shale reservoir in complex anhydrite geology two imaging techniques are used to locate the synthetic microseismic events we use a simplistic and easily reproducible standard diffraction imaging procedure and a more sophisticated technique moment tensor microseismic imaging mtmi we have confirmed that the presence of high velocity layers such as anhydrite reduce the overall aperture of a surface array which result in poor resolution of imaged events and reduction in the accuracy of event locations more importantly we have determined that the coda in the microseismic data can isolate itself from the direct arrival stacked into the final imaging result and it can be misinterpreted as separate events located directly below the true source location which is unavoidable given the ambiguity between event location and time comparison of the two imaging procedures found that even though the more sophisticated mtmi was able to better cope with the effects caused by high velocity layers it still demonstrated a significant reduction in resolution of imaged events a reduction in accuracy and evidence of multiple and converted energy still present in the final imaging result

effect of fracture roughness on seismic source and fluid transport responses to explain how fracture roughness affects seismic source and transport response of deformed fractured rock we developed a microscale fluid flow geomechanics seismicity model the modeling method considers comprehensive grains and cement interactions fluid flow behavior is obtained through realistic network models of the pore space in the compacted assembly in addition forces and displacements in the grains involved in the bond breakage are measured to determine seismic moment tensor the results of our work show that in addition to stress conditions in the target formation geological properties of preexisting fractures affect volumetric deformation of the seismic source as well the results of the model proves that roughness of fractures applied in a berea sample causes deviation of source mechanism of acoustic emission events toward opening tensile part and enhances the permeability of the sample significantly during its failure even under confining pressure

further testing of the bedding plane slip model for hydraulic fracture opening using moment tensor inversions abstractmoment tensors are calculated by using the p wave first motion peak amplitudes of 59 microseismic events with high signal to noise ratio these events are from a surface microseismic data set gathered during hydraulic fracture stimulation of the marcellus gas shale in washington county pennsylvania usa the majority of these 59 events have a horizontal nodal plane a few degrees characteristic of a dip slip horizontal slip moment tensor if the horizontal nodal plane is an auxiliary the vertical nodal plane has a pure dip slip motion which is inconsistent with the opening motion for vertical hydraulic fractures that enables proppant loading this points to slip on horizontal nodal planes with the auxiliary vertical nodal planes aligned with the local maximum horizontal stress orientation as indicated by drilling induced fractures in nearby vertical wells these 59 microseismic events are caused by slip on horizontal mechanical discontinuities such as bedding planes during the opening of ver

recharge of the upper chalk aquifer at a site in hampshire england 1 water balance and unsaturated flow abstract measurements of the annual cycle of changes in water content and potential in the 40 m thick unsaturated zone of upper chalk at a site in southern england are described measured evaporation continued at the penman potential rate until the soil moisture deficit reached 175 mm this suggested that a root constant of 200 mm would be more appropriate than the much lower values generally used the field capacity concept could not be reconciled with the timing of renewed water recharge and the reasons for this are discussed the mechanisms of water flow through the unsaturated zone of the chalk are examined and it is shown that at this upper chalk site matrix flow is the dominant recharge mechanism

the neogene east antarctic ice sheet a dynamic or stable feature abstract this paper is a review of the history and behaviour of the east antarctic ice sheet during the late neogene and is a response to the publication of sugden et al 1993a the case for a stable east antarctic ice sheet in geografiska annaler 75a 4 the antarctic ice sheet is a critical factor in the global climate and oceanographic system knowledge of its historical development is critical to understanding global palaeoceanographic and palaeoclimatic systems and their development the webb harwood hypothesis proposes that the ice sheet while being present in antarctica for more than 40 ma was until recently ca 2 5 ma a dynamic feature waxing and waning under a more temperate climatic and glaciologic regime the stabilistic hypothesis proposes that the current ice sheet has existed in its present cold and polar form for at least the last 14 ma the case for a stable east antarctic ice sheet is the clearest statement of the stabilistic argument to date the authors find support for their viewpoint by presenting evidence from several geologic data bases that does not support their own null meltdown hypothesisr which they deem to be equivalent to the webb harwood hypothesis thereby they conclude supporting the stabilistic hypothesis however their conclusions are weakened by failure to reject their null hypothesis conflict between the meltdown and webb harwood hypotheses infraction of geological laws and poor application of stratigraphic principles several issues are highlighted here as important for direction of future research and discussion concerning late cenozoic antarctic glacio climatic history

bias in magnitude for earthquakes with unknown focal mechanism this study investigates errors induced by the use of average double couple radiation coefficients for the computation of earthquake magnitude indeed when an earth quake focal mechanism cannot be anticipated before calculating its magnitude we show that the induced error depends on several factors such as event location moni toring network aperture type of seismic phase involved in the calculation p s waves and focal mechanism energy radiated at lower amplitude is less likely to be observed so applying an absolute lower bound on radiation equal to 0 1 we show that errors in magnitudem are expected to range within the 0 5 0 2 interval this indicates that errors have a stronger tendency towards under estimation than over estimation we also present simulations of the spatial distribution of such errors for two double couple mechanisms and one tensile opening which reveal strong spatial dependencies on i the radiation pattern and ii the coverage of the focal sphere by the monitoring network we show that the variability of errors significantly decreases with increasing network aperture we apply this procedure to a field dataset namely the monitor ing of hydraulic fracturing in the cotton valley formation of texas in this case if event focal mechanisms were not accounted for errors in magnitude would generally fall within the above mentioned interval except for a few events presenting a larger under estimation error would reachm 0 4 when the magnitude is computed using p waves only a clear spatial pattern of errors is also observed at the cotton valley project characterized by a west to east change in error polarity but presenting a non varying pattern in depth finally such errors in magnitude have an insignifi cant impact on frequency size distribution of events b value estimates based on such frequency size distributions are within the uncertainty domain of estimates based on corrected frequency size distributions

the matter of size on the moment magnitude of microseismic events abstractwe investigated the method of estimating seismic moment and moment magnitude for microseismic events we determined that the m0t defined by bowers and hudson is the proper scalar moment to be used in microseismic studies for characterizing the size of an event and calculating its moment magnitude for non double couple sources the proportional relationship between body wave amplitude and seismic moment in the brune model breaks down so under such situations the brune model is not an appropriate way to estimate the seismic moment and magnitude moreover the s wave alone is not sufficient for determining the total seismic moment instead the p wave must be analyzed an example barnett shale data set was studied and the results concluded that the magnitudes estimated with the brune model could be off by as much as 1 92 with an absolute average of 0 35 the moment magnitudes based on the scalar moment m0t also gave a significantly different event size distribution and b value estimation finall

high quality surface microseismic data illuminates fracture treatments a case study in the montney monitoring hydraulic fracture stimulations from the surface is a technique that in the past met with mixed success one reason for this experience is that the measurement has often been treated as if it were only a minor variant of the reflection surveys our industry is most familiar with while reflection seismic sources are designed to generate primarily p waves fracturing rocks emit both p and s waves with the much larger proportion of energy as s waves to capture the information content in the microseismic wavefield surveys must be designed to record and processing strategies designed to use the full vector wavefield energy emitted by the fracture process to record the full vector wavefield requires the use of appropriate sensors capable of recording low frequencies and three components

digital elevation models for the lambert glacier amery ice shelf system east antarctica from ers 1 satellite radar altimetry the lambert glacier amery ice shelf system is a major component of the east antarctic ice sheet this paper presents two digital elevation models dems that have been generated for the lambert amery system from validated european remote sensing satellite ers 1 radar altimeter waveform data the first dem covers the amery ice shelf only and was produced using kriging on a 1 km grid the second is a coarser 5 km dem of the entire lambert amcry system generated via simple averaging procedures the dems provide unprecedented surface elevation information for the lambert amery system and allow new insight into the glaciology of the region

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

fluvial sedimentology and revised stratigraphy of the triassic flagstone bench formation northern prince charles mountains east antarctica the flagstone bench formation ranges in age from earliest triassic to norian late triassic and is exposed in the beaver lake area of the northern prince charles mountains this sandstone dominated formation rests conformably on the bainmedart coal measures and represents the upper part of the permian triassic amery group it is divisible into three members the ritchie jetty and mckelvey members in ascending order nine sedimentary facies assignable to three facies associations major channel crevasse fan and flood basin deposits are recognized within the formation ritchie member sedimentation took place during a transition from consistently hygric to seasonally dry conditions and the unit comprises sandstone dominated sheet like channel deposits interspersed with few thin mottled haematite rich flood basin siltstones deposition took place under fluctuating discharge conditions chiefly within the channel tracts of axially northwesterly northeasterly flowing low sinuosity braided rivers the jetty member shows a gross upward fining profile dominated in the lower part by poorly sorted pebbly sandstones and in the upper part by ferruginous mudcracked siltstones mottled palaeosols calcrete and thin massive sandstone sheets this unit reflects deposition of easterly directed alluvial fans and extensive flood basin silt under a semi arid climatic regime the upper triassic sandstone dominated mckelvey member shows a return to axial drainage along the lambert graben with sedimentation occurring primarily within low sinuosity braided channel tracts under wetter climatic conditions

source analysis of a potential hydraulic fracturing induced earthquake near fox creek alberta an earthquake with a reported magnitude of 4 4 ml was detected on 13 june 2015 in western central alberta canada this event was the third felt earthquake this year near fox creek a shale gas exploration region our results from full moment tensor inversions of regional broadband data show a strong strike slip mechanism with near vertical fault plane solutions the decomposition of the moment tensor solution is overwhelmingly double couple while only a modest 20 contribution is attributed to compensated linear vector dipole the depth of this earthquake is 3 4 km near the base of the sedimentary layer and the moment magnitude m 3 9 of this event is considerably smaller than the initial reported ml value the hypocenter location depth and mechanism are favorable to a possible association between this earthquake and hydraulic fracturing operations within the duvernay shale

determination of moment tensor and location of microseismic events under conditions of highly correlated noise based on the maximum likelihood method we examine the problem of localization of a single microseismic event and determination of its seismic moment tensor in the presence of strongly correlated noise this is a typical problem occurring in monitoring of microseismic events from a daylight surface during producing or surface monitoring of hydraulic fracturing we propose a solution to this problem based on the method of maximum likelihood we discuss mathematical aspects of the problem some features and weak points of the proposed approach estimate the required computing resources and present the results of numerical experiments we show that the proposed approach is much more resistant to correlated noises than diffraction stacking methods and time reverse modeling

low apparent stress observed for mw 0 6 microearthquakes recorded during hydraulic fracturing stimulation in the carthage cotton valley gas field understanding the source characteristics of hydraulic fracturing induced microearthquakes is expected to provide better understanding of both the fracturing process and the influence of pre existing structures on the distribution of events however details of the source characteristics of microearthquakes remain largely unknown one controversial issue is whether the mechanism of such events differs from natural tectonic events that is whether significant reductions of effective stress and or volumetric change occur because of the stimulation herein to address this question we estimated the apparent stress of the 61 m w 0 6 microearthquakes observed during the hydraulic fracturing in the carthage cotton valley gas field we first obtained the apparent stress by estimating the radiated seismic energy from the duration of the relative moment rate function and then adjusted the values considering the possibility of seismic energy underestimation the initial value range of 0 001 0 02 mpa is consistent with other past studies of hydraulic fracturing induced microearthquakes although the adjustment increases the original value by a factor of 10 it is still within the lower bound of the range of constant apparent stress commonly observed for natural tectonic events furthermore relatively lower apparent stress was observed for the events striking subparallel to the maximum horizontal compressional stress axis this implies the mechanism of these events could be different from that of events optimally oriented for failure although the uncertainty of their measurements was expected to be large compared with other events because of their small magnitude online material table with information on microearthquakes observed during the hydraulic stimulation in the carthage cotton valley gas field

full waveform based microseismic source mechanism studies in the barnett shale linking microseismicity to reservoir geomechanics abstractseismic moment tensors mts of microearthquakes contain important information on the reservoir and fracturing mechanisms difficulties arise when attempting to retrieve complete mt with conventional amplitude inversion methods if only one well is available with the full waveform approach near field information and nondirect waves i e refracted reflected waves help stabilize the inversion and retrieve complete mt from the single well data set however for events which are at far field from the monitoring well a multiple well data set is required in this study we perform the inversion with a dual array data set from a hydrofracture stimulation in the barnett shale determining source mechanisms from the inverted mts requires the use of a source model which in this case is the tensile earthquake model the source information derived includes the fault plane solution slip direction vp vs ratio in the focal area and seismic moment the primary challenge of extracting source parameters fro

major neogene fluctuations of the east antarctic ice sheet stratigraphic evidence from the lambert glacier region stratigraphic and sedimentological data are presented from a region likely to directly record the evolution of the east antarctic ice sheet along the western margin of the lambert graben which now drains 1 106 km2 or one eighth of the total area of the east antarctic ice sheet extensive remnants of cenozoic glaciomarine fjordal sediment known as the pagodroma group are preserved as far as several hundred kilometers inland from the open coast the sediments resemble those produced by tidewater glaciers in the arctic rather than those of modern antarctica four separate formations of the pagodroma group spanning the interval from early miocene or older to pliocene or early pleistocene are preserved the oldest and highest crop out at nearly 1500 m above sea level each formation was deposited in close proximity to an ice margin grounded on the fjord bottom during major recessional phases of the lambert glacier underlying each formation is a glacially cut erosion surface each surface records a separate stage of fjord excavation when ice expanded onto the continental shelf in prydz bay evidence from offshore drilling in prydz bay and these data indicate fluctuations of the lambert glacier terminus in excess of 500 km in neogene time thereby reflecting large changes in the volume of the ice sheet depositional episodes were succeeded by phases of uplift totalling more than 1500 m

genesis of hummocky moraines by thrusting in glacier ice evidence from svalbard and britain irregular mounds of glacial debris commonly referred to as 9hummocky moraine9 until recently were linked to ice stagnation during rapid climatic amelioration however recent work in scotland has demonstrated that some hummocky moraine dating from the younger dryas event c 10 000 years bp was the product of deposition at active ice margins observations at modern high arctic glacier margins in svalbard 76 80 n indicate that some moraines of this type form under a dynamic glaciological regime mainly by thrusting in active polythermal ice undergoing strong longitudinal compression this situation is particularly common where there is a transition from warm based ice in the interior of a glacier to cold based ice at the margins or snout from their morphological similarity rectilinear slopes facing up glacier and irregular downglacier faces and apparent stacking of slabs of sediment of subglacial derivation it is concluded that some assemblages of british moraines are also the product of thrusting this process appears to be most dominant in polythermal glaciers rather than in temperate glaciers on this basis it is tentatively suggested that the younger dryas in britain was characterized by a climatic regime similar to that in svalbard today mean annual temperature 5 c 400 1000 mm precipitation and that the associated glaciers may have been of polythermal character

seismicity induced by hydraulic fracturing in shales a bedding plane slip model passive seismic monitoring of microseismic events induced in oil or gas reservoirs is known as microseismic monitoring microseismic monitoring is used to understand the process of hydraulic fracturing which is a reservoir stimulation technique we use a new geomechanical model with bedding plane slippage induced by hydraulic fractures within shale reservoirs to explain seismicity observed in a typical case study of hydraulic fracturing of a shale gas play in north america microseismic events propagating from the injection point are located at similar depths within the uncertainty of their locations and their source mechanisms are dominated by shear failure with both dip slip and strike slip senses of motion the prevailing dip slip mechanisms have one nearly vertical nodal plane perpendicular to the minimum horizontal stress axis while the other nodal plane is nearly horizontal such dip slip mechanisms can be explained by slippage along bedding planes activated by the aseismic opening of vertical hydraulic fractures the model explains the observed prevailing orientation of the shear planes of the microseismic events as well as the large difference between seismic and hydraulic energy

moment tensor migration imaging we develop and apply an imaging procedure for simultaneous location and characterization of seismic source properties called moment tensor migration imaging the procedure constructs images for moment tensor components using a weighted diffraction stack migration and combines ray theoretical green s functions with a reverse time moment tensor imaging methodology by applying an approximation we term the ray angles only approximation we form an expression for moment tensor migration imaging where the migration weights depend only on the take off and arrival angles for rays leaving receiver positions and incident upon the image points moment tensor migration imaging retains the benefits of diffraction stack procedures for source location and characterization namely speed flexibility and the potential for incorporating non linear stacking procedures whilst also providing the benefits of moment tensor imaging such as the inclusion of multiple phase and multiple component data the collapsing of the source radiation pattern estimation of the moment tensor we examine variations of the imaging procedure through a synthetic test we show that although the assumptions required for the imaging and ray angles only approximation may not be strictly valid for realistic survey geometries a simple weight adjustment can be used to obtain more accurate and stable results in these situations in our synthetic example we find that the use of a p wave only migration without this reweighting structure produces poor results whereby the resulting images show activity upon incorrect moment tensor components however many of these effects are mitigated by use of the reweighting scheme and the results are further improved through the introduction of non linear stacking operators such as semblance weighted stacks the highest quality moment tensor images for the synthetic test examined here are obtained through the use of both p wave and s wave wave fields this highlights the importance of multicomponent data and multiphase modelling when characterizing seismic sources we also find that the imaged moment tensor components vary proportionately when the input velocities are perturbed by a scale factor this suggests for the geometry investigated here derived source properties such as fault plane solutions and shear tensile components will not be influenced by bulk changes in seismic velocities finally we show the application to a real microseismic event observed using a surface array during hydraulic fracturing we find that the procedure collapses the seismic radiation pattern into an anomaly with a maximum at the hypocentre and our derived mechanism is consistent with the observed radiation pattern from the source

the reliability of microseismic moment tensor solutions surface versus borehole monitoring abstractsource mechanisms of microseismic events resolved as moment tensor solutions usually are obtained using either surface monitoring arrays which appear to obtain mechanisms with high shear components or borehole arrays which tend to constrain more variable mechanisms with higher tensile components however the corresponding reliability of the solutions remains unclear synthetic tests are therefore conducted to compare the reliability of moment tensor solutions from surface and two and three well borehole arrays based purely on geometry moment tensor inversion is carried out for synthetically generated amplitudes with added random noise and the bias and variance in the solutions are calculated for the surface array all inversions are able to constrain reliable results with negligible bias and low variance whereas borehole geometries with two wells produce reliable results only when including p and s wave amplitudes recorded on three components in the inversion as is usual surface a

late neogene sirius group strata in reedy valley antarctica a multiple resolution record of climate ice sheet and sea level events late neogene sirius group strata from tillite spur and quartz hills in the reedy glacier area antarctica demonstrate the variability in sirius group facies and contrasts sirius group strata deposited at high and low paleo elevation respectively the tillite spur and quartz hills formations pliocene are formally defined here the tillite spur formation type section crops out on the edge of the wisconsin plateau overlooking tillite spur it comprises 32 m of alternating coarse gray conglomerate and muddy olive brown diamictites the quartz hills formation type section crops out above the western margin of reedy glacier in a pre existing cirque towards the southern end of the quartz hills it comprises c 100 m of alternating massive diamictites and rhythmically interbedded sandstone and laminated mudstones which were deposited close to sea level and subsequently rapidly uplifted 500 m myr 1 to their present elevation at c 1500 m three orders of paleoclimatic variability are recorded in the sirius group strata from reedy valley 1 recycled marine microfloras in glacial diamictites indicate intervals of marine incursion into the antarctic cratonic interior co occurring with reductions in the east antarctic ice sheet 2 an advancing and retreating paleo reedy glacier deposited a glacial interglacial sequence alternating on a 10 100 kyr scale 3 centimeter and millimeter stratification in strata of the quartz hills formation record annual kyr scale variability

focal mechanism determination for microseismic events and its application to the left bank slope of the baihetan hydropower station in china determination of the focal mechanism of microseismic ms events occurring in rock engineering plays an important role in hazard evaluation and forecasting a complete moment tensor inversion strategy is proposed to analyse ms events recorded at the left bank slope of the baihetan hydropower station southwest of china a coordinate system rotation procedure is adopted to construct a reliable 1 d velocity model for the green s function calculation the layered velocities are accurately determined by inversion using the recorded blasts and geological survey results to reduce the influence of noise contamination only the waveforms in the frequency range of 60 150 hz are analysed before moment tensor inversion a relocation procedure using an eikonal solver is performed to accurately locate seismic sources a robust global optimization routine is applied to maximize the objective function thereby determining the focal mechanism the proposed method is tested using a hypothetical seismic source in the sensor network used for monitoring ms events in the rock slope the synthetic test shows that the method is robust and can provide accurate solutions when subject to location error noise contamination and velocity model disturbances the analysis results of the 12 ms events show that the moment tensors characterizing ms events present significant non double couple components and that the majority of the ms events have a strike orientation in accordance with that of the main staggered zones

focal mechanism determination of induced microearthquakes in an oil field using full waveforms from shallow and deep seismic networks a new relatively high frequency full waveform matching method was used to study the focal mechanisms of small local earthquakes induced in an oil field which are monitored by a sparse near surface network and a deep borehole network the determined source properties are helpful for understanding the local stress regime in this field during the waveform inversion we maximize both the phase and amplitude matching between the observed and modeled waveforms we also use the polarities of the first p wave arrivals and the average s p amplitude ratios to better constrain the matching an objective function is constructed to include all four criteria for different hypocenters and source types comprehensive synthetic tests showed that our method is robust enough to determine the focal mechanisms under the current array geometries even when there is considerable velocity inaccuracy the application to several tens of induced microseismic events showed satisfactory waveform matching between modeled and obs

inferring in situ stress changes by statistical analysis of microseismic event characteristics two commonly estimated fractal dimensions called b and d values represent statistical characteristics in the distribution of magnitude sizes b and spatial hypocenter locations d of microseismic events respectively we establish that the values of these two dimensions are related to specific stress regimes through the case study of a heavy oil field drained using cyclic steam stimulation we infer that the measured temporal variation in fractal dimension b is most likely due to significant changes in the local stress regime over a seven month period ranging from extensional faulting fractures opening via a strike slip regime to finally compressive faulting fractures closing the fracture dimension d indicates predominantly planar to spherical hypocenter spatial distributions in the first and last stages but changes to a more linear to planar spatial pattern in the intermediate strike slip regime when the vertical stress is anticipated to be in between the maximum and minimum horizontal stre