effects of fault slip distribution on the geometry and kinematics of the southern junggar fold and thrust belt northern tian shan abstract at the foreland edge of fold and thrust belts ftbs tectonic shortening could either be accommodated by thick skinned faulting and or structural wedges developed near range fronts or be transferred along detachment layers further into basins forming thin skinned structures although the geometry and kinematics of each structure have been well investigated studies that characterize slip distribution along a specific fault as well as the effects of variations in magnitude of fault displacement on the development of fault related folds are still lacking in this study we present a case study of the southern junggar thrust sjt a seismically active fault developed in the southern junggar ftb northern tian shan with an overall vergence to the north the results of structural interpretations of seismic reflection profiles combined with the age constraints provided by previous magnetostratigraphic studies demonstrate that 1 the kinematics of the sjt vary along strike from purely structural wedging to classical fault bend folding besides these end member models intermediate cases exist between them in which fault slip is partitioned by two stage structural deformation i e fault bend folding subsequent to structural wedging at the range front as a result part of the displacement is transferred northward forming the tugulu anticline 2 along strike variations in displacement along the tugulu fault frontal fault of the sjt also affect the geometry and kinematics of the tugulu anticline varying from detachment folding trishear fault propagation folding with a pure shear fault bend folding back limb and classical trishear fault propagation folding to fault bend folding with increasing displacement 3 the sjt has an average quaternary slip rate of 3 9 0 4 mm yr serving as a principal structure accommodating tectonic shortening in the southern junggar ftb the results of this study are helpful for seismic hazard assessments of the study area which may also shed light on structural evolution of fault related folds in other ftbs

fault interactions in the sea of marmara pull apart north anatolian fault earthquake clustering and propagating earthquake sequences summary knowledge on large earthquakes m 7 0 geology and fault kinematics is used to analyse conditions that favour isolated seismicity clustered earthquakes or propagating sequences along the north anatolian fault naf and the sea of marmara pull apart the overall naf marmara fault system is one of the most appropriate on earth to document fault interactions because reliable information covers almost completely two seismic cycles the past 500 yr coulomb stress analysis is used to characterize loading evolution in well identified fault segments including secular loading from below and lateral loading imposed by the occurrence of previous earthquakes earthquakes along the naf tend to occur where previous events have increased the stress but significant isolated events in the sea of marmara region 1894 1912 have occurred suggesting the secular loading has been the determining factor present day loading appears to be particularly high along the 70 km long segment located in the central marmara sea southwest of istanbul for the 18th century m 7 0 earthquake clusters we construct scenarios consistent with the tectonic and historical data we find that scenarios consistent with slip deficit and secular loading distributions from below clearly involve a sequence that propagates westward through the sea of marmara despite the structural complexity however the inference of a propagating sequence implies that each event has occurred in a segment previously stressed by lateral coulomb stress interactions the most likely scenarios for the propagating sequence are also consistent with coulomb stress interactions between faults with significant normal slip across the cinarcik basin propagating earthquake sequences do not occur every seismic cycle along the naf the loading has to be in a particular state of stress close to failure and uniform all along the fault segments to experience propagating earthquake sequences non uniform stress relief during the 18th century sequence explains the occurrence of isolated events in marmara in 1894 and 1912 as a consequence the wellknown 20th century sequence along the naf has not propagated as a sequence across the sea of marmara the most linear part of the naf across northern turkey behaves as a single fault segment accumulating stress during hundreds of years and rupturing entirely during very short periods the marmara pull apart fault system behaves as a major geometric complexity stopping or delaying the progression of earthquake clustering and propagating sequences fault zones interact with each other at a very large scale

geochemical characterization correlation and optical dating of tephra in alluvial sequences of central western argentina the synthesis of paleoclimatic archives provided by loess and alluvial sequences of central argentina has been hindered by the lack of a cohesive lithostratigraphic framework extending across the chaco pampean plains and catchments of the rios desaguadero colorado and negro this condition originates in part from the dearth of absolute chronological controls the occurrence of discrete tephra layers across this region may provide an opportunity to address this deficiency if a tephrochronological framework can be established the potential of such a project is assessed within the context of a pilot study constrained within alluvial sequences of central western argentina proximal to potential source vents in the southern volcanic zone the intersite discrimination and correlation of tephra layers on a geochemical basis is examined with indirect chronological control for the eruption of each generated by optical dating alluvial sediments on either side of each of five tephra units at a type site were dated using the optically stimulated luminescence of fine silt sized quartz thus providing an age control on each tephra ca 24 000 30 000 32 000 39 000 and 48 000 yr the geochemical composition of each tephra was derived using these data tephra layers at other sites in the study area were geochemically analyzed and in instances of statistical concordance in major oxide structure correlated to the type site and therefore ascribed ages this methodology identified a further sixth volcanic event between ca 24 000 and 30 000 yr not registered by type site tephras the extension of this initial tephrochronological framework beyond the alluvial sequences of central western argentina is encouraged by the occurrence of geochemically distinct tephra verified and dated in this study

overpressure generation and evolution in a compressional tectonic setting the southern margin of junggar basin northwestern china overpressure is widespread in the southern margin of the junggar basin northwestern china pressure measurements in drillstem tests and repeated formation tests and estimates from wire line logs indicate contrasting overpressure values between permeable sandstones and adjacent low permeability mudrocks in addition excess pressure differs among anticlines with similar depth lithologies and geologic age indicating significant lateral changes of overpressure major factors controlling overpressure generation and distribution include rapid sediment deposition pressure compartmentalization by thick mudrocks tectonic stress faulting and folding clay transformation and hydrocarbon generation are believed to be insignificant in overpressure generation in the southern junggar basin numerical modeling of pressure generation and evolution suggests that faulting and stratal tilting associated with folding are the most significant factors in the overpressure generation of a permeable sandstone the extremely high overpressure pressure coefficient up to 2 43 may have been caused by hydraulic adjustment within permeable sandstones associated with structural deformation caused by post miocene intense tectonic activities

role of overpressures and in situ stresses in fault controlled hydrocarbon migration a case study abstract two wells no 1 and no 2 separated by 2 km and situated in the upper prospective zone of a tertiary basin in south east asiat cross the same mio pleistocene shaly sandy series from 1500 m downwards these series are subject to significant overpressures related to an active margin comparison of well data in terms of sonic compaction profiles anomalous pressures and temperatures has provided evidence of both a positive pressure and a temperature anomaly below a vertical depth of 1800 m in well 2 this anomaly is closely associated with the presence of liquid hydrocarbons in the 1900 2000 m reservoir interval the confirmed deep source of these fluids and the amounts that have migrated during a short time interval can be explained only by the transitory dynamics of active transfers along faults and fractures the episodic nature of this movement is the result of hydromechanical mechanisms in which the interactions between the high pressure regime and principal in situ stresses appear to be fundamental the processes which induce open faulting and fluid pressure build up in the direction of reservoirs with lower pressure regimes occur preferentially during phases of lateral tectonic stress relaxation as soon as the effective minimum stress component becomes negative the analysis of this case study gives a better understanding of the dynamic phenomena involving secondary hydrocarbon migration and caprock efficiency the results obtained will help to optimize the overpressure prediction approach in comparable geological contexts

locating microseismic events using borehole data constraining microseismic hypocentres in and around hydrocarbon reservoirs and their overburdens is essential for the monitoring of deformation related to hydraulic fracturing production and injection and the assessment of reservoir security for co2 and wastewater storage microseismic monitoring in hydrocarbon reservoirs can be achieved via a variety of surface and subsurface acquisition geometries in this study we use data from a single subsurface vertical array of sensors we test an existing technique that uses a 1d velocity model to constrain locations by minimizing differential s to p arrival times for individual sensors we show that small errors in either arrival time picks or the velocity model can lead to large errors in depth especially near velocity model discontinuities where events tend to cluster to address this issue we develop two methods that use all available arrival times simultaneously in the inversion thus maximizing the number of potential constraints from n 2 to n where nis the number of phase picks the first approach minimizes all available arrival time pairs whilst the second approach the equal distance time edt method defines the hypocentre as the point where the maximum number of arrival time surfaces intersect we test and compare the new location procedures with locations using differential s to p times at each individual sensor on a microseismic data set recorded by a vertical array of sensors at the ekofisk reservoir in the north sea specifically we test each procedure s sensitivity to perturbations in measured arrival times and the velocity model using monte carlo analysis in general location uncertainties increase with increasing raypath length we show that errors in velocity model estimates are the most significant source of uncertainty in source location with these experiments our tests show that hypocentres determined by the new procedures are less sensitive to erroneous measurements and velocity model uncertainties thus reducing the potential for misinterpretation of the results

santorini luminescence dating of a volcanic province using quartz abstract we have investigated the application of luminescence dating to the palaeosol underlying the cape riva ignimbrite from the volcanic island of santorini 36 40 n 25 40 e in the aegean sea the history of volcanism in this area is of intrinsic interest and is also of importance to archaeology in the eastern mediterranean a flourishing late bronze age settlement was buried under the volcanic products of the minoan eruption 1640 bc volcanic provinces are notoriously difficult to date using luminescence techniques because volcanic feldspars almost invariably show anomalous fading which can lead to age underestimates of more than 50 quartz does not show anomalous fading but unfortunately it is rare or non existent in volcanic sediments and so it is usually not considered as a potential chronometer we have studied the luminescence characteristics of material extracted from the cape riva palaeosol with good independent age control all samples contain detectable quartz but usually

cyclostratigraphy and astronomical tuning during the oligocene in the jizhong depression bohai bay basin northeastern china abstract the dongying formation ed and the first member of the shahejie formation es1 in the central raoyang sag cover about 1705 m long sedimentary series of terrestrial lacustrine infill we employed the gamma ray gr log data as a paleoclimatic and paleoenvironmental proxy to conduct the high resolution cyclostratigraphy research in well w33 and w62 prominent sedimentary cycles in decameters and meters were revealed by multi taper mtm power spectra evolutionary fast flourier transformation fft and correlation coefficient analyses in the es1 and ed intervals the 405 kyr long eccentricity 125 kyr and 100 kyr short eccentricity 40 kyr obliquity and 23 kyr precession can be recognized with a wavelength ratio of approximately 20 5 2 1 respectively by tuning the 405 kyr filter output in well w33 to the orbital target curve of la2010d astronomical solution we established an astronomical time scale ats that provided absolute age controls during the oligocene and shed light on the event correlation among isolated depressions in the bohai bay basin sediment accumulation rates sars were derived from the extracted 405 kyr long eccentricity and were tested with an average of 17 cm kyr age boundaries of ng ed1 ed1 ed2 ed2 ed3 ed3 es1 and es1 es2 are 23 03 ma 24 34 ma 25 53 ma 29 05 ma and 33 10 ma respectively based on the ats and sars we discussed the depositional evolution within age boundaries cause of high sars and origin of formation overpressure after the largest lake transgression shallow water deltas and fluvial plains transitionally dominate the central raoyang sag with shallowing water depth thin interlayers of mudstones and sandstones originate from shallow water deltaic systems with low sand to mud ratios under high sars enhanced by mountain uplift and low sand to mud ratios formation overpressure results mainly from high porosities in under compacted mudstone intervals

direct dating of quaternary phreatic maar eruptions by luminescence methods the suitability of quartz optically stimulated luminescence osl and feldspar infrared stimulated luminescence irsl for the direct dating of phreatic eruptions was tested on examples from the eifel volcanic field germany the mean irsl age of 11 6 0 5 ka for ulmener maar tephra is in excellent agreement with the independent age control 11 0 1 ka but the mean osl age of 14 2 0 6 ka overestimates the known age by 3 ka for meerfelder maar tephra consistent irsl mean 74 9 5 0 ka and osl ages 74 9 5 5 ka have been observed the consistent results from meerfelder maar imply that the overestimation observed for ulmener maar quartz osl might not be relative to the eruption age but rather represents a small absolute offset in samples taken from deposits of the eruption of laacher see volcano no resetting of the osl signal and highly scattered irsl estimates were found this implies that phreatomagmatic eruptions are less well suited for this dating approach compared to pure phreatic maar eruptions where the effect of high pressure shock waves probably dominates the process of resetting the luminescence signal

source parameters for 11 earthquakes in the tien shan central asia determined by p and sh waveform inversion the tien shan mountain belt of central asia was formed in late paleozoic time and reactivated in tertiary time following the collision of india with eurasia more than 1500 km to the south to study the style and distribution of faulting occurring today in the tien shan we digitized long period world wide standard seismograph network p and sh waveforms of 11 of the largest tien shan earthquakes between 1965 and 1982 and then used a least squares inversion routine to constrain their fault plane solutions and depths four of the earthquakes occurred near the southern edge of the tien shan and two occurred in the intermontane fergana basin these earthquakes occurred at depths of 10 20 km and are associated with thrust faulting on east west to southwest northeast striking fault planes that dip moderately 35 55 the other five earthquakes in the northern tien shan were mostly deeper 15 44 km and the fault plane solutions of four of them are similar to the events farther south the exception an event on june 2 1973 probably occurred on a gently northward dipping east west striking fault plane all events occur within the basement at depths of 10 km or greater waveforms for earthquakes near the edges of the dzungarian fergana and kucha basins are fit best using velocity structures with thick sediment layers implying that sediments from these basins have been and are being underthrust beneath the neighboring mountains we examined only the relatively small mb 5 5 6 2 events after 1965 and did not study any of the largest events ms 8 that occurred in the tien shan earlier in this century still we can conclude that north south shortening is presently occurring in the tien shan with the formation of basement uplifts flanked by moderately dipping thrust faults the present day tectonics of the tien shan seem to be analogous to those of the rocky mountains in colorado wyoming and utah during the laramide orogeny in late cretaceous and early tertiary time

luminescence dating of late pleistocene eruptions in the eifel volcanic field germany robust chronologies of late pleistocene and holocene volcanic eruptions are vital for hazard analysis but accurate and precise dating of these events is often difficult here we apply various luminescence techniques to quartz and polymineral extracts from heated crustal xenoliths enclosed in scoria and volcanically heated bedrock in the quaternary eifel volcanic field evf germany consistent results from red thermoluminescence rtl and optically stimulated luminescence osl of quartz and from post infrared infrared stimulated luminescence of polymineral material demonstrate complete luminescence signal resetting during lava emplacement and sufficient signal stability rtl and osl age underestimation of one sample with independently known age from the lava contact zone could be eliminated by annealing before laboratory regenerative irradiation the average luminescence age of 33 6 2 4 ka for the wartgesberg eruption is in good agreement with independent age control while the average age of 15 5 1 1 ka for the facher hohe scoria cone is much younger than previously assumed this result represents the third youngest known eruption in the evf our new data are in line with the hypothesized climate controlled triggering of eifel volcanism and confirm that active volcanism related to asthenosphere upwelling migrates from nw to se in the evf

seismicity triggered by fluid injection induced aseismic slip anthropogenic fluid injections are known to induce earthquakes the mechanisms involved are poorly understood and our ability to assess the seismic hazard associated with geothermal energy or unconventional hydrocarbon production remains limited we directly measure fault slip and seismicity induced by fluid injection into a natural fault we observe highly dilatant and slow 4 micrometers per second m s aseismic slip associated with a 20 fold increase of permeability which transitions to faster slip 10 m s associated with reduced dilatancy and micro earthquakes most aseismic slip occurs within the fluid pressurized zone and obeys a rate strengthening friction law 0 67 0 045ln v v with v 0 1 m s fluid injection primarily triggers aseismic slip in this experiment with micro earthquakes being an indirect effect mediated by aseismic creep

frictional properties of shale reservoir rocks 1 we performed laboratory friction experiments on shale samples from three hydrocarbon reservoirs to assess compositional controls on fault slip behavior accompanying hydraulic stimulation the samples span a range of clay and total organic content from 10 to 60 by weight and demonstrate fine scale heterogeneity within each reservoir friction measurements demonstrate strong dependence of strength and rate state constitutive properties on shale composition shale samples with clay and organic content above 30 by weight show coefficient of friction 0 4 and consistently velocity strengthening behavior while those below this threshold show increased strength and velocity weakening behavior this transition in frictional strength and stability suggests a change in the shale grain packing framework from rigid clast supported to clay mineral and organic matter supported measurements of gouge dilatancy further support these relationships showing a negative correlation with clay and organic content critical slip evolution distance exhibits similar dependence on composition implying common micromechanical mechanisms for the observed transition in frictional behavior we performed microstructural characterization of the experimental samples and observe changes in the gouge load bearing framework and shear localization features consistent with these mechanical data while these results can be applied generally to infer slip stability on faults in clay bearing sedimentary rock we employ the experimental data to place constraints on microearthquake magnitudes and the occurrence of slow shear slip on preexisting faults during hydraulic stimulation in shale reservoirs

characterization of lacustrine mixed fine grained sedimentary rocks using coupled chemostratigraphic petrographic analysis a case study from a tight oil reservoir in the jimusar sag junggar basin abstract mixed deposits are sediments consisting of external clastic epiclastic or terrigenous intrabasinal components and pyroclastic components the mixture comprising variable amounts of the three components is defined as mixed sedimentary rocks the permian lucaogou formation p2l in the jimusar sag of the junggar basin is a promising tight oil target in western china the fine grained mixed sedimentary rocks of which are rich in organic matter om and two sweet spot intervals with relatively high porosity however the sediment composition provenance and deposition environmental settings have not been studied in detail in this study coupled chemostratigraphic petrographic analysis were used to reconstruct their depositional environments the results show that the fine grained sedimentary rocks have three major sediment sources external clastic input terrigenous clastics intrabasinal autochthonous to parautochthonous components carbonates siliceous skeletal debris and om and pyroclastic input main lithofacies include siltstone fine sandstone mudstone dolomite and tuffite the silt sandstones were mainly sourced from rocks with calc alkaline composition while the tuffaceous sedimentary rocks were sourced from high k calc alkaline rocks elemental proxies suggest that the carbonate rocks were generally deposited under warm and arid conditions whereas the fine grained clastic sediments were deposited under relatively humid conditions the muddy or silty tuffaceous mixed rocks were deposited under relatively reducing conditions compared with carbonates and sandstones variations of lithofacies and om accumulation of different intervals reflect changing deposition environmental settings and the frequently altered high toc content rocks and good reservoirs are benefit for tight oil formation the work may provide some useful insights and serve as a reference for studying other mixed fine grained sedimentary rocks and tight oil plays in similar lacustrine basins elsewhere

fault activation by hydraulic fracturing in western canada hydraulic fracturing has been inferred to trigger the majority of injection induced earthquakes in western canada in contrast to the midwestern united states where massive saltwater disposal is the dominant triggering mechanism a template based earthquake catalog from a seismically active canadian shale play combined with comprehensive injection data during a 4 month interval shows that earthquakes are tightly clustered in space and time near hydraulic fracturing sites the largest event moment magnitude mw 3 9 occurred several weeks after injection along a fault that appears to extend from the injection zone into crystalline basement patterns of seismicity indicate that stress changes during operations can activate fault slip to an offset distance of 1 km whereas pressurization by hydraulic fracturing into a fault yields episodic seismicity that can persist for months

foreland basin stratigraphic control on thrust belt evolution the link between orogenic activity and foreland basin stratigraphy is well established however potential controls by foreland basin stratigraphy on thrust belt architecture have not been fully evaluated mechanical properties of typical foreland basin stratigraphic successions influence the structural development of fold thrust belts in predictable ways fundamental features of foreland basins include the onset of rapid subsidence and deposition of a coarsening upward sedimentary succession in the lower part of this succession are fine grained distal foreland basin deposits enlargement of the orogenic wedge through frontal accretion incorporates the foreland basin strata into the thrust belt and distal foreland basin depositional units may be preferentially exploited as a thrust detachment zone resulting in multiple detachment levels we propose that foreland basin stratigraphic architecture has significant influence on the structural development of thrust belts and that by extension processes that influence foreland basin sedimentation may ultimately influence orogenic evolution far removed in time and space

venture gas field offshore nova scotia case study of overpressuring in region of low sedimentation rate the venture gas field is a deep overpressured gas reservoir on the scotian shelf off eastern canada overpressuring occurs at depths below 4 5 km and is associated with significant quantities of gaseous hydrocarbons the overpressured zone is composed of high porosity sandstones interbedded with low porosity low permeability shales which have nearly normal levels of compaction pore pressures in this zone show a step wise increase with depth where pressure jumps correlate with low permeability 10 20m2 where 10 12m2 1 01 d shale beds petrophysical and lithological data for sandstones and shales in the overpressured zone are used to constrain a one dimensional single phase model of pore pressure development the con ersion of kerogen to hydrocarbons is simulated by simple kinetic reaction theory estimates of the effects on overpressuring of sediment compaction temperature changes and hydrocarbon generation were obtained from this model using the above data 2 disequilibrium compaction apparently is responsible for much of the overpressuring in the venture gas field in our simple single phase model the contribution of hydrocarbon generation to overpressuring was slight

petrography and isotopic geochemistry of bedding parallel fibrous gypsum veins in the neogene qingshuiying formation of the ningnan basin north china insights for growth model of antitaxial fibrous veins abstract bedding parallel fibrous gypsum veins which are widely developed in the neogene qingshuiying formation of the ningnan basin a tertiary basin located in the northeastern margin of the tibetan plateau provide valuable information on stress field fluid origin and host rock deformation during their formation the systematic petrographic observation and isotope analysis of both of veins and wall rocks were carried out to investigate the formation mechanism of bedding parallel fibrous gypsum veins the distribution of fibrous gypsum veins shows vertical heterogeneity and mainly occurs in the middle and lower part of the qingshuiying formation with relatively high gypsum content single fibrous gypsum veins consist of a median zone and two fibrous zones the median zone is characterized by blocky gypsum crystals and multiple host rock fragments formed by crack seal events the fibrous zone is composed of parallel gypsum fibres a high angle to the vein walls indicating shear component vein opening is considered to be the result of fluid overpressure caused by horizontal compression in low permeability mudstone during basin inversion fibrous gypsum crystals grow continuously without obvious growth competition between adjacent crystals this indicates that growth of gypsum fibres occurs in limited space even without fractures the main driving force for vein dilation is force of crystallization of gypsum fibre growth and fluid pressure also has a certain contribution the sulfur and strontium isotopes of gypsum veins exhibit a high degree of consistency with wall rocks which indicates the material of the fibrous gypsum veins is derived from the wall rock a suitable growth model of bedding parallel fibrous gypsum veins in the ningnan basin is established which explains the process of vein interaction and the formation of v shaped or u shaped solid inclusions

contributions of compaction and aquathermal pressuring to geopressure and the influence of environmental conditions reply luo and vasseur 1992 presented a useful methodology of simplifying the complex equations that describe basin compaction and thereby directly assessing the contribution of aquathermal effects in the development of abnormal pressures their methodology leads to the conclusion that aquathermal pressuring plays only a small role in the development of overpressures in sedimentary basins although this conclusion follows from the cases studied it is possible to conclude otherwise using 1 a more general model of sediment compaction and 2 material properties that are more representative of conditions at depth the primary factor behind objection to the conclusion in luo and vasseur 1992 is that is fundamental equations which formed the basis for the simplifying methodology do not account fully for conditions in which a sediment s effective stresses are reduced we emphasize here that we do not claim that thermal effects are the dominant cause of overpressures rather our calculations suggest that they are not negligible in all cases there is a complex interplay of the various mechanisms that cause excess pore water pressures no one mechanism of overpressuring dominates all others for all situations because thermal effects not only cause higher excess pore pressures but also reduce effective stresses thermal effectsmore will be minimized by default in calculations that do not account for effective stress reduction the resulting reduced effective stresses also have important implications for geological questions such as acoustic velocities and fracture potential less

vent evolution and lag breccia formation during the cape riva eruption of santorini greece the 18 500 yr b p cape riva cr eruption of santorini vented several km3 or more of magma generating four eruption units a basal plinian fall deposit cr a and three pyroclastic flow deposits cr b to cr d upwards cr b and cr d are welded ignimbrites cr c consists predominantly of up to 25 m thick coarse lithic rich co ignimbrite lag breccias resulting from a climactic phase of the eruption the initial plinian phase occurred from a localized vent in n santorini and subsequent column collapse resulted in emplacement of cr b towards the end of cr b new conduits were activated and pyroclastic flows discharged from multiple vents to generate the lag breccias cr c cr d probably records a return to a localized vent as the eruption waned the eruption sampled a zoned magma chamber containing rhyodacite overlying andesite and leaks of these magmas were manifested as the skaros therasia lavas preceding the cr eruption plinian and initial ignimbrite stages occurred while the magma chamber was ove

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

anatomy of a buried thrust belt activated during hydraulic fracturing abstract tectonically active fault networks are often inter connected but in the case of injection induced seismicity prior knowledge of fault architecture tends to be severely limited in most cases reactivated faults due to fluid injection are inferred after the fact by the spatial distribution of induced seismicity hypocenters such reliance on post injection seismicity impedes any pre operational risk analysis as well as development of a more holistic understanding of fault system models by combining high resolution depth migrated 3 d seismic data with a new focal depth estimation method that reduces spatial uncertainty of hypocenters this study pinpoints microearthquake fault activation within a buried thrust belt in the montney formation in western canada british columbia during hydraulic fracturing operations rupture nucleation occurred on seismically imaged thrust ramps that cut through the debolt formation a massive carbonate layer that underlies the stimulated zone high resolution seismic images reveal transverse structures interpreted as basement controlled fold hinges or tear faults that transferred displacement between thrust faults during late cretaceous paleogene compressional shortening the spatio temporal pattern of induced seismicity suggests that these transverse structures provide permeable pathways for aseismic pore pressure diffusion thus connecting distinct thrust faults and enabling earthquake triggering on a timescale of days and at distances of up to 2 km from the injection wells inferred relationships highlight how the fault system is connected including apparent stress concentrations at the intersections of transverse structures and orogen parallel thrust ramps

seismic indicators of focused fluid flow and cross evaporitic seepage in the eastern mediterranean abstract we present for the first time a synthesis of the evidence of focused fluid flow in the eastern mediterranean providing an updated record that includes recent and past occurrences through the last ca 6 my of evolution of the basin we do this by adding the interpretation of a previously unpublished regional 2d seismic dataset to the existing occurrences of focused fluid flow reported in the literature our interpretation shows a high number 141 of focused fluid flow features which span the stratigraphic interval from late miocene to recent of these features 82 are at the seabed and 59 are buried the previous published record is more difficult to quantify but in comparison shows an overwhelming majority of seabed features with only rare examples of buried features the spectrum of the buried and seabed features covers pockmarks pipes mud volcanoes clastic intrusions and collapse structures clustering of the fluid flow features is observed at different times in specific areas including the nile cone and the levant herodotus cyprus and latakia basins with the buried record we are able to highlight the evolution of the leakage points through time focused fluid flow venting has been occurring since the onset of the messinian salinity crisis and the start of basinwide deposition of evaporites we focus in particular on seismic indicators of leakage through evaporites and of sub evaporitic source for fluids and remobilised sediments we also discuss the role of the evaporites as a seal to ascending fluids and in which circumstances they can be breached fluids and associated remobilised sediments are sourced from different intervals from the sub and supra evaporitic section and possibly within the evaporites only a minor proportion of the fluid flow features are certainly sourced from below the messinian evaporites and most of them are located in the nile levant eratosthenes areas the few examples of pathways that are able to cross thick undeformed and well preserved evaporites are typically correlated to overpressure release and hydrofracturing this confirms that the evaporites do act regionally as a very good seal as expected while fluids are able to cross the evaporites only in their most extreme expression i e in near lithostathic overpressure conditions this is confirmed by our observations made in the eastern mediterranean where in the presence of relatively undisturbed evaporites cross evaporite vertical fluid pathways are only observed at the high end of the flux pressure range and involve sediment remobilisation maps combining these different elements can be used to detect areas potentially more prone to breaching

the robustness of seismic moment and magnitudes estimated using spectral analysis we present an assessment of how microseismic moment magnitude mw e stimates vary with the method and parameters used to calculate seismic moment this is an important topic for operators and regulators who require good magnitude estimates when monitoring induced seismicity it is therefore imperative that these parties know and understand what errors exist in given magnitude values something that is poorly reported this study concentrates on spectral analysis techniques and compares mw computed in the time and frequency domains using recordings of mw 1 5e vents at cotton valley east texas the maximum discrepancy between mw estimated using the different methods is 0 6 units a significant variation by adjusting parameters in the mw calculation we find that the radiation pattern correction term can have the most significant effect on m w generally up to 0 8 units following this investigation we make a series of recommendations for estimating microseismic m w using spectral methods noise should be estimated and removed from recordings and an attenuation correction should be applied the spectral level can be measured by spectral fitting or taken from the low frequency level significant factors in obtaining reliable microseismic mw estimates include using at least four receivers recording at 1000 hz and making radiation pattern corrections based on focal mechanism solutions not average values

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

a dual aliquot regenerative dose protocol dap for thermoluminescence tl dating of quartz sediments using the light sensitive and isothermally stimulated red emissions abstract quartz sediments collected from a cave deposit in eastern indonesia display very weak optically stimulated luminescence osl ultraviolet emissions which we attribute to their volcanic provenance they do however emit at longer red wavelengths here we provide details of a new method of using a light sensitive red thermoluminescence tl signal to date the last time of exposure of quartz grains to natural sunlight which we have used previously to constrain the burial age of homo floresiensis remains found on the indonesian island of flores the samples examined typically contained a rapidly bleaching bleachable signal a slowly bleaching signal and a light insensitive heat reset signal we isolated the bleachable tl signal from the other unbleachable tl signals by means of a dual aliquot regenerative dose protocol dap and the bleachable dose was estimated by subtracting the unbleachable dose from the total dose taking into account the dose response differences between these signals the bleachable tl signal was found to be stable over geological timescales 17 5 million years to display minimal sensitivity change during successive cycles of dosing bleaching and heating and to exhibit reproducible dose response behaviour red tl measurements are commonly plagued by poor signal to noise ratios due to incandescence and possibly thermal quenching at high temperatures such difficulties have been minimised in this study by measuring the red tl isothermally at 260 c for an extended duration 1000 s red tl dating results are presented for eight samples of quartz from diverse sedimentary environments to illustrate the potential of this dating procedure in particular but not exclusively for quartz that has been heated in the past e g due to volcanic activity

fault interaction at the junction of the transverse ranges and eastern california shear zone a case study of intersecting faults abstract a case study from southern california illustrates the value of detailed geologic data for understanding the kinematics of complex fault systems the neotectonic behavior of faults at the junction of the eastern california shear zone ecsz and transverse ranges has implications for the interaction of intersecting segmented fault systems and regional plate boundary evolution paleoseismic observations indicate that the north frontal thrust system nfts has ruptured once in the holocene with 1 7 m displacement despite previous speculations of inactivity based on its dissection by younger strike slip faults simple polyphase deformation in which dextral shear has replaced and overprinted thrusting is thus not a valid explanation for this system of intersecting faults this illustrates the limitations of inferring rupture behavior from mapped fault patterns alone neotectonic and geomorphic observations along the thrust system also suggest that the thrust segment west of the intersection with the dextral helendale fault is significantly more active than the segment to the east this is consistent with a simple block velocity model in which dextral slip on the helendale fault is balanced by convergence on the western thrust segment dextral motion on the poorly studied pipes creek fault to the southeast and inactivity on the eastern thrust segment this divides the san bernardino mountains into domains dominated by thrusting west and strike slip east the union of which is a quasi stable triple junction we speculate that this union has migrated to the west as the mojave desert has been translated southwards along the san andreas fault

applying luminescence methodology to key sites of alpine glaciations in southern germany abstract this paper investigates the properties of quartz sampled at different sites in the riss iller mindel and isar valley of the northern alpine foreland of germany and ties in with a previous study of optically stimulated luminescence osl dating of glaciofluvial sediments from the type regions of the wurmian the rissian and the mindelian glaciations the previous investigation showed severe underestimation of quartz ages compared to the existing tentative chronology based on morphostratigraphic evidence as well as fading uncorrected feldspar infrared stimulated luminescence irsl ages in this paper we present laboratory experiments and data analyses such as pulse annealing and isothermal decay measurements d e t and nr t plots as well as curve fitting analyses to demonstrate that the quartz has unfavourable luminescence characteristics we conclude that the quartz from the study area is not suitable for osl dating using standard single aliquot regenerative dose techniques

quartz as a natural luminescence dosimeter abstract luminescence from quartz is commonly used in retrospective dosimetry in particular for the dating of archaeological materials and sediments from the quaternary period the phenomenon of luminescence is related to the interaction of natural radiation with mineral grains by the activation of and subsequent trapping of electrons at defects within the quartz lattice the latent luminescence signal i e the trapped electrons is released when the grains are exposed to stimulation energy in the form of light or heat despite the fact that quartz is most nominally pure sio2 the mineral forms in several different geological settings i e under different pressure and temperature conditions the luminescence emitted from quartz is complex and shows a variety of different components with diverse physical properties this complexity is explained by the variety of defects in quartz that are either intrinsic e g si and o vacancies or related to impurity atoms e g al or ti the concentration of impurity related defects is dependent on the conditions of mineral formation or subsequent alteration experimental data have shown that the luminescence properties of quartz are highly variable with geological source and vary even at a grain to grain level within a sediment as a consequence caution is needed when making any general statements about the luminescence properties of quartz when using luminescence measurements as a dating technique it is necessary to adjust the measurement procedures for each geological provenance furthermore some quartz has luminescence properties that make it problematic or even unsuitable for certain applications these problems can arise from low and changing luminescence sensitivity thermal transfer of trapped electrons thermal instability of the trapped electrons and low saturation dose reviewing the present knowledge reveals that insufficient information is available either to unambiguously link distinctive lattice defects with characteristic luminescence components or even to explain problems observed in application studies by potential dynamics of the defects within the crystal this paper gives some ideas on how future research could utilise innovative analytical tools to identify or map the distribution of lattice defects and how practitioners could relate lattice defects to measured luminescence properties of quartz

human footprints in central mexico older than 40 000 years abstract the timing route and origin of the first colonization to the americas remains one of the most contentious topics in human evolution a number of migration routes have been suggested and there are different views as to the antiquity of the earliest human occupation some believe that settlement happened as early as 30 ka bp but most of the currently accepted early sites in north america date to the latest pleistocene related to the expansion of the clovis culture while the oldest directly radiocarbon dated human remains are 11 5 ka bp in this context new evidence is presented in this paper in the form of human footprints preserved in indurated volcanic ash to suggest that central mexico was inhabited as early as over 40 ka bp human and animal footprints have been found within the upper bedding surfaces of the xalnene volcanic ash layer that outcrops in the valsequillo basin south of puebla mexico this ash layer was produced by a subaqueous monogenetic volcano erupting within a palaeo lake dammed by lava within the valsequillo basin during the pleistocene the footprints were formed during low stands in lake level along the former shorelines and indicate the presence of humans deer canids big felids and probably camels and bovids the footprints were buried by ash and lake sediments as lake levels rose and transgressed across the site the ash has been dated to at least 40 ka bp by osl dating of incorporated baked lake sediments

timing and nature of alluvial fan development along the chajnantor plateau northern chile abstract alluvial systems in the atacama desert provide a unique opportunity to elucidate the sedimentary response to climate variability particularly changes in precipitation in hyperarid environments alluvial fans along the eastern margin of the salar de atacama adjacent to the chajnantor plateau in the atacama desert of northern chile provide an archive of climate modulated sediment transfer and erosion at an extreme of earth s climate three regional alluvial fan surfaces qf1 oldest to qf3 youngest were mapped along the western flank of the chajnantor plateau the alluvial fans were examined with geomorphic and terrestrial cosmogenic 36 cl surface exposure dating methods to define the timing of alluvial fan formation and to determine the role of climatic processes on fan development in a hyperarid environment alluvial fans in the study area are comprised of hyperconcentrated flow and boulder rich debris flow deposits that reflect deposition transitioning between cohesive and noncohesive regimes alluvial fan surfaces yield exposure ages that range from 49 6 4 4 to 194 12 ka while debris flow boulders yield exposure ages ranging from 12 4 2 1 to 229 53 ka cosmogenic 36 cl exposure ages indicate that abandonment of alluvial fan surfaces qf1 qf2 and qf3 date to 175 22 6 ka mis 6 134 5 9 18 ka mis 6 and 20 07 6 26 ka mis 2 respectively a 36 cl concentration depth profile through alluvial fan qf1 suggests a simple depositional history with minimal nuclide inheritance implying relatively rapid aggradation 6 m in ca 25 kyr followed by surface abandonment ca 180 200 ka our data support a strong climatic control on alluvial fan evolution in the region and we propose that the alluvial fans along the margins of the salar de atacama form according to the humid model of fan formation

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

generation and evolution of overpressure caused by hydrocarbon generation in the jurassic source rocks of the central junggar basin northwestern china the jurassic black mudstone and coal beds in the central junggar basin northwestern china are the major source rocks for the basin with type ii2 and type iii gas prone kerogens widespread overpressures are developed in the jurassic stratigraphic interval sonic and resistivity logs display strong characteristic responses of overpressure in the mudstones with anomalously high acoustic traveltimes and low resistivity compared with the normally pressured mudstones the overpressured jurassic sediment sequences appear to have undergone normal compaction because the mudstones exhibit no anomalously low bulk density the overpressured mudstones deviate from the normally pressured mudstones in density effective vertical stress space the overpressure in the jurassic source rocks is therefore not caused by disequilibrium compaction the overpressured jurassic sandstone reservoirs are predominantly oil and gas saturated or oil bearing the well log responses of the overpressured mudstones and seismic velocity characteristics indicate that the top depth of the overpressure zone ranges from 3800 to 4600 m 12 500 to 15 100 ft corresponding to formation temperatures of approximately 94 c to 111 c 201 f to 232 f with estimated vitrinite reflectance values of 0 6 to 0 75 the jurassic source rocks with overpressure are capable of generating hydrocarbons at present and are currently overpressured all the evidence suggests that the overpressure in the jurassic source rocks in the central junggar basin is caused by hydrocarbon hc generation the overpressure evolution was modeled quantitatively in response to pressure changes caused by hc generation during basin evolution the results indicate that multiple episodes of overpressure development and release occurred within the jurassic source rocks suggesting multiple episodes of hc expulsion the timing and numbers of these episodes of hc expulsion were thus determined from the modeled overpressure evolution

overpressuring mechanisms in the yinggehai basin south china sea yinggehai basin is an elongate cenozoic rift basin on the northwestern margin of the south china sea continental shelf its thick 17 km basin fill is characterized by high geothermal gradient and high overpressure overpressure associated with nonequilibrium compaction mainly occurs at depths more than 2800 m at the basin center and more than 4000 m at the basin margin because the shallow buried neogene and quaternary strata lack effective seals this regional overpressure distribution however is disrupted at basin center where high overpressure occurs in permeable formations at a depth as shallow as 1400 m on top of a series of deep seated faults and fractures we studied the processes and mechanisms of overpressuring via numerical modeling that couples basin filling sediment compaction and thermal and pressure fields to approach the origin of the shallow high overpressure model results indicated that an increase of fluid volume due to natural gas generation by organic cracking is not large enough to generate the overpressure because of the limited amount of organic matter the shallow overpressure has probably been generated allogenically deep open faults have served as vertical hydraulic conduits and channeled the deep high pressure into shallow permeable formations

genesis of natural hydraulic fractures as an indicator of basin inversion abstract satin spar fibrous gypsum veins which occur in evaporite basins worldwide provide significant insights into host rock deformation and fluid flow although the genetic mechanism remains obscure satin spar veins in the red marls of the triassic mercia mudstone of the bristol channel basin were characterized in the context of regional and local setting the vein network in the keuper marl lower mercia exhibits a lack of systematic cross cutting between three distinct vein sets two sets of veins are observed in the overlying tea green marl with one set clearly crossing the other the gypsum veins commonly contain a blocky median zone of multiple thin bands of host rock inclusions and alabastrine gypsum crystals exhibiting crack seal patterns fibrous zones on either side of the median zone consist of pure parallel aligned gypsum fibres that are oblique to vein walls indicating a hybrid shear extensional mode of vein widening veins developed within reverse reactivated faults contain fibre lineations in the median zones and also on vein surfaces suggesting a minimum of two phases of fault slip the veins are interpreted to have formed as a result of overpressure in the low permeability mudstones by tectonic compression during basin inversion giving rise to the median zone growth of gypsum fibres commenced when the initial fractures were completely sealed the timing of vein formation is suggested to be miocene based on cross cutting relationships with folds formed during the latest phase of basin inversion because the fractures initiated in response to fluid overpressures they provide a useful analog to subsurface hydraulic fracture systems in low permeability rocks subjected to tectonic compression the fibrous widening of the veins post dates their initiation and led to continued propagation and increased connectivity

quantitative evaluation of the transporting capacity of unconformities a case study from the zhongguai area junggar basin nw china abstract unconformities are special geologic bodies with a three layer structure including the rock above the unconformity a weathered clay layer and a leached rock the upper wuerhe upper permian bottom unconformity in northwest junggar basin is the main pathway system linking the zhongguai zg lift with hydrocarbon source kitchens based on the log response characteristics of the unconformity s vertical structure and core calibration a principal component analysis pca was applied to extract and identify the evaluation parameters of the unconformity s vertical structure on the basis of darcy s law the quantitative characterization formula of the unconformity s transport capacity with an actual geological significance was established after taking several factors into consideration the migration probability of the unconformity was used to evaluate the possibility that the unconformity acted as a migration pathway consequently a relationship between the migration probability and the evaluation parameters was developed to analyze the effectiveness of these parameters in characterizing the transporting capacity of the unconformity this study shows that the quotient of the two principal components extracted from the conventional logging curves pc1 pc2 have different reference values in the leached and parent rocks the distribution of thicknesses of the weathered clay layer and the leached rock is well matched with the distribution of paleogeomorphology the parameters representing only a single geological factor are not enough to determine whether the unconformity acted as a migration pathway the flow coefficient cf containing multiple factors can effectively and clearly identify the transporting capacity of the unconformity considering the positive correlation between the parameter cf and the migration probability of the unconformity the oil and gas shows of the area with a parameter cf greater than 10 10 4 cm2 s are abundant which is the superior transporting area of the unconformity and there is a good matching relationship between the distribution of the superior transporting area of the unconformity and that of the hydrocarbon distribution

contemporary tectonics of the himalayan frontal fault system folds blind thrusts and the 1905 kangra earthquake the sub himalayan fold thrust belt consists of deformed late cenozoic and older deposits south of the main boundary thrust mbt in pakistan east of the indus river the sub himalaya comprises the potwar plateau and the salt range which is thrust southward over the jhelum river floodplain along the salt range thrust although an estimated 9 14 mm a 1 shortening has been taken up on the salt range thrust during the last 2 ma the range front scarp does not show signs of recent faulting shortening may be shifting southward to the lilla overpressured anticline which rises from the jhelum floodplain as a fault propagation fold farther east shortening is partitioned among several anticlines underlain by foreland and hinterland dipping blind thrusts southeast of the main deformation zone the pabbi hills overpressured anticline is best explained as a fault propagation fold throughout the potwar plateau and salt range thrusts and folds rise from a basal decollement horizon in eocambrian evaporites the pakistani part of the decollement horizon could generate large earthquakes only if these evaporites die out northward at seismogenic depths in india and nepal the sub himalaya is narrower reflecting the absence of evaporites and a steeper slope of the basement towards the hinterland the southern boundary of the sub himalaya is the himalayan front fault discontinuous because part of the shortening is expressed at the surface by folding broad alluvial synclinal valleys dun valleys are bounded on the south by rising barrier anticlines of siwalik molasse the 1905 kangra earthquake m8 produced uplift on the mohand anticline and the dehra dun valley suggesting that this earthquake occurred on a decollement horizon above basement downdip from the fold if so the kangra event is the largest known earthquake on a blind thrust expressed at the surface as a fold

deformation character and palaeo fluid flow across a wrench fault within a palaeozoic subduction accretion system waratah fault zone southeastern australia abstract melange formation cataclasis meso to micro scale faulting and veining reflect faulting processes within turbidite and limestone sequences juxtaposed along a steeply dipping sinistral wrench fault zone in the lachlan orogen southeastern australia fault damage occurs across a zone up to 600 m wide effects of faulting in the turbidites are shown by a 100 150 m wide zone of scaly mudstone matrix melange mud injection dykes and veinlets and refolding of melange fabrics with minor subsidiary brittle faulting and cataclasis extending up to 500 m from the major fault plane veining and cataclastic zones occur in the limestone and are most pronounced up to 100 m from the main brittle fault fluid inclusion data from quartz and calcite veins suggest faulting took place at temperatures between 160 and 200 c whereas folding is inferred to have taken place at temperatures above 300 c fluid assisted fault zone weakening mechanisms pressure solution solution transfer were active over the whole fault zone veining characteristic of fluid assisted fault zone strengthening processes i e rock mass cementation is confined to the limestone sequence here calcite precipation led to fault rocks with lower porosity and permeability than in the turbidite sequence overprinting between different veins and fractures and zonation in vein cement suggest cyclic deformation and fluid flow the repeated change between brittle fracturing and veining cementation led to a combined conduit barrier system in the limestone sequence whereas the melange zone in the turbidites acted as a fluid conduit only

jurassic tectonostratigraphic evolution of the junggar basin nw china a record of mesozoic intraplate deformation in central asia mesozoic basins in northwest china provide important records for investigating relationships between intraplate deformation in central asia and tectonic processes at asian boundaries the present study using well seismic outcrop and thermochronology data in the junggar basin and neighboring areas describes the main features of jurassic strata in the basin analyzes the jurassic evolution of the basin and neighboring mountain belts and discusses possible mechanisms of jurassic intraplate deformation in central asia during the early middle jurassic episodic uplift of surrounding mountain belts kept the junggar basin a contractional closed basin and alluvial fan fluvial delta and lacustrine depositional environments successively developed from surrounding ranges to the central basin during the late jurassic the western and central parts of the basin were folded and uplifted and deposition migrated mainly to the eastern basin during the latest jurassic earliest cretaceous pre cretaceous strata in the eastern and northeastern junggar basin were folded and uplifted and coarse grained sediments were transported from surrounding uplifts to the central basin we suggest that jurassic episodic deformation events in the junggar basin and other areas of central asia are related to the qiangtang collision during the late triassic early jurassic the closure of the western mongol okhotsk ocean at the early middle jurassic boundary a collision of a microcontinent in the pamir with the southern asian margin during the late middle jurassic early late jurassic the collision of the kolyma omolon block with siberia at the end of the jurassic and the subsequent closure of the eastern mongol okhotsk ocean during the latest jurassic earliest cretaceous

a comparison of the volcanic records over the past 4000 years from the greenland ice core project and dye 3 greenland ice cores since 1980 the electrical conductivity method ecm has been used to infer volcanic acid signals in greenland ice cores the method reveals the great majority of major volcanic eruptions including several known from historic records subsequent ion chromatographic analyses of the acid volcanic layers show the chemical composition i e the concentration of the volcanic acids h2so4 hci and hf plus e g the nonvolcanically derived hno3 while ecm data are available from a large number of shallow depth greenland ice cores covering the past 500 1500 years only the greenland ice core project grip greenland ice sheet project 2 gisp2 and dye 3 deep ice cores exist for a detailed comparative study of volcanic signals in greenland ice cores representing several thousand years comparison of the volcanic signals registered in the grip and gisp2 cores will be presented elsewhere the latter cores were augered 30 km apart and essentially represent the same atmospheric conditions such as temperature snow accumulation and chemical composition of the air here we present a comparison between the major volcanic signals over the past 4000 years in the grip core from central greenland and the dye 3 core from se greenland in order to investigate the depositional differences many of the major signals are detected in both cores but some of the differences in the records can be used to infer the latitudinal band of some eruption sites furthermore the influence of the amount of annual precipitation and glaciological postdepositional processes on the volcanic signals is discussed

hydrocarbon generation as a mechanism for overpressuring in rocky mountain region overpressured reservoirs are present in the deeper parts of most basins in the rocky mountain region a variety of conditions can cause overpressuring however most high pressures in the region are caused by present day or recently active oil and gas generation or generation in the last few million years in low permeability rock successions that still contain organic matter capable of yielding thermally generated hydrocarbons rocks with above normal pressure range from devonian to tertiary and commonly are associated with low permeability tight reservoirs most of the overpressuring occurs in cretaceous and tertiary rocks overpressuring in rocks older than cretaceous is rare and where present only occurs in strata with very rich hydrocarbon source beds such as the d vonian mississippian bakken formation most organically lean pre cretaceous source beds are no longer capable of yielding enough hydrocarbons to maintain abnormal pressure nearly all overpressured reservoirs and source rocks have temperatures of approximately 200 f 93 c or higher in addition available data indicate that hydrocarbon related overpressuring does not generally occur if vitrinite reflectance ro values are less than 0 6 in oil prone strata or less than 0 7 in gas prone strata overpressured gas bearing strata generally have ro values of 0 8 or higher maximum reservoir pressures are about equal to the fracture gradient pressure in the reservoir rocks some vertical fractures in reservoir rocks are probably caused by rapid expulsion of hydrocarbons from the source beds high pressures in the rocky mountain region means that the rock succession is gas or oil saturated and discrete hydrocarbon water contacts are generally not present classical concepts of hydrodynamics do not appear to be applicable to these overpressured successions the optimum depths for exploration are generally the upper 1 000 2 000 ft 305 610 m of the overpressured succession

late quaternary history of the vakinankaratra volcanic field central madagascar insights from luminescence dating of phreatomagmatic eruption deposits the quaternary vakinankaratra volcanic field in the central madagascar highlands consists of scoria cones lava flows tuff rings and maars these volcanic landforms are the result of processes triggered by intracontinental rifting and overlie precambrian basement or neogene volcanic rocks infrared stimulated luminescence irsl dating was applied to 13 samples taken from phreatomagmatic eruption deposits in the antsirabe betafo region with the aim of constraining the chronology of the volcanic activity establishing such a chronology is important for evaluating volcanic hazards in this densely populated area stratigraphic correlations of eruption deposits and irsl ages suggest at least five phreatomagmatic eruption events in late pleistocene times in the lake andraikiba region two such eruption layers can be clearly distinguished the older one yields ages between 109 15 and 90 11 ka and is possibly related to an eruption at the amboniloha volcanic complex to the north the younger one gives ages between 58 4 and 47 7 ka and is clearly related to the phreatomagmatic eruption that formed lake andraikiba irsl ages of a similar eruption deposit directly overlying basement laterite in the vicinity of the fizinana and ampasamihaiky volcanic complexes yield coherent ages of 68 7 and 65 8 ka these ages provide the upper age limit for the subsequently developed iavoko antsifotra and fizinana scoria cones and their associated lava flows two phreatomagmatic deposits identified near lake tritrivakely yield the youngest irsl ages in the region with respective ages of 32 3 and 19 2 ka the reported k feldspar irsl ages are the first recorded numerical ages of phreatomagmatic eruption deposits in madagascar and our results confirm the huge potential of this dating approach for reconstructing the volcanic activity of late pleistocene to holocene volcanic provinces

deep transverse basement structural control of mineral systems in the southeastern canadian cordillera1geological survey of canada contribution 20110294 intermittent reactivation of deep paleoproterozoic and archean aged transverse structures in the north american cratonic basement beneath the southeastern canadian cordillera exerted an important influence on the subsequent sedimentary intrusive deformation and mineralization history two regional crossbelt transverse structural corridors recognized by recurrent episodic changes in sediment thickness and facies and anomalous transverse structural trends occur within the thrust and fold belt palinspastic restoration of the exposed transported structural corridors showed that the northern and southern structural corridors are cover expressions of the red deer zone and vulcan low structures in the cratonic basement respectively transverse basement controlled structural corridors enhanced the mineral potential and mineralization systems along them by localization of sedimentary facies favourable for mineralization hydrothermal flow intrusions and favourable structures for mineralization greatest enhancement of hydrothermal flow and mineralization occurred near the intersection of basin parallel and transverse structures greater opportunity for mineralization and intrusion occurred not only along the exposed corridors but also in the west above their undeformed root in the basement the processes that intensified mineralization and localized intrusions along transverse basement controlled structural corridors in the southeastern canadian cordillera should have occurred in thrust and fold belts elsewhere the niobium bearing aley carbonatite complex in the eastern cordillera of northeastern british columbia may be an example of this

in situ stress and active faulting in oklahoma abstract appreciable injection induced seismicity has been occurring in north central oklahoma since 2009 to better understand these earthquakes we have compiled new information on the state of stress in the state to compare it with both mapped faults and faults inferred from earthquake epicenters and focal plane mechanisms seventy five new in situ stress orientations are available from wellbores throughout the state in the north central part of the state where the induced seismicity is occurring stress orientation and relative magnitude from focal mechanism inversions show excellent agreement with the wellbore stress orientations all of the data show remarkably uniform stress directions the azimuth of s hmax the maximum horizontal stress is about n85 5 e strike slip faulting is occurring in central oklahoma with strike slip normal and normal faulting observed in northern oklahoma and southern kansas as very few of the thousands of m 2 5 earthquakes that have recently occurred are located on or near already mapped faults we utilize the stress information to interpret the likely fault planes associated with over 300 well constrained focal plane mechanisms in the vicinity of the january 2016 sequence of magnitude 4 and 5 earthquakes in the fairview oklahoma region we illustrate how knowledge of the stress field can be used to identify the faults responsible for the seismicity and better evaluate the potential hazard associated with possible future earthquakes in the area the september 2016 m w 5 8 pawnee event occurred on an unmapped n70 w trending strike slip fault expected to be active in the local stress field

conceptual model for origin of abnormally pressured gas accumulations in low permeability reservoirs the largest gas fields in the rocky mountain region occur in abnormally pressured reservoirs these gas accumulations are different from more conventional gas accumulations in that they are commonly located in basin center positions they occur downdip from water bearing rocks and they are in overpressured or underpressured low permeability reservoirs we suggest that overpressured and underpressured gas accumulations of this type have a common origin in basins containing overpressured gas accumulations rates of thermogenic gas accumulation exceed gas loss causing fluid gas pressure to rise above the regional hydrostatic pressure within the overpressured gas generation zone free water in the larger pores is forced out of the gas generation zone into overlying and updip normally pressured water bearing rocks the remaining tightly bound water at irreducible saturation levels cannot remove dissolution products precluding significant permeability and porosity enhancement thus while other diagenetic processes continue a pore network with very low permeability develops as a result gas accumulates in these low permeability reservoirs at rates higher than it is lost in basins containing underpressured gas accumulations rates of gas generation and accumulation are less than gas loss these basins have typically experienced significant uplift and erosion and or temporal variations of paleotemperature despite these modifications the basin center gas accumulation persists but because of changes in the basin dynamics the overpressured accumulation evolves into an underpressured system

on the relationship between fault permeability increases induced stress perturbation and the growth of aseismic slip during fluid injection author s cappa f guglielmi y nussbaum c birkholzer j abstract 2018 american geophysical union all rights reserved fluid injections into the deep subsurface can at times generate earthquakes but often they only produce aseismic deformations here we analyze the influence of fault hydromechanical properties on the growth of injection induced aseismic slip using hydromechanical modeling we show how permeability enhancement in addition to the background stress and frictional weakening has an important effect on the pressure diffusion and slip growth during injection we find that the more pronounced the fault permeability enhancement the stronger is the growth of the aseismic slip zone the effect of enhanced permeability is more pronounced when the fault is initially close to failure our results show that aseismic slip grows beyond the pressurized zone when the fault permeability increases while slip remains behind the pressurized zone when permeability does not vary from its initial preslip value thus fault permeability increases should be considered as complementary mechanism to current models of fluid induced aseismic slip

geopressuring mechanism of organic matter cracking numerical modeling since the 1950s hydrocarbon generation has been considered as one of the most important abnormal pressuring mechanisms hydrocarbon generation effects on pore pressure evolution 1 it increases the pore fluid volume through the conversion of solid kerogen into liquid or gaseous hydrocarbon and 2 it decreases the sediment permeability because hydrocarbons remain an immiscible phase in pore water in this paper the two products of organic matter decomposition liquid hydrocarbon oil and gaseous hydrocarbon methane are assumed to occur in sequence as a supplementary phase in pores as a basis for evaluating the effect of this pressuring mechanism a simplified three stage first order kinetic reaction model is applied to simulate the generation of oil and gas we u e a numerical basin model with a two phase hydrodynamic formulation to calculate the effect of organic maturation on geopressure evolution oil generation does not play an important role except when the organic matter content of rocks is relatively large 5 however the generation of gas has a large influence the results show that beneath a certain depth oil to gas cracking strongly influences overpressuring the effect of this mechanism becomes more important with increasing organic matter content of rocks several environmental conditions such as kerogen type temperature gradient and lithological characteristics influence to various degrees the effect of organic matter maturation on overpressure development

natural fractures in carbonate rich tight oil reservoirs from the permian lucaogou formation southern junggar basin nw china insights from fluid inclusion microthermometry and isotopic geochemistry abstract natural fractures within tight reservoirs form preferred pathways for hydrocarbon charge and provide space for hydrocarbon preservation however the mechanism that controls the formation of natural fractures in tight reservoirs remains controversial this study investigates natural fractures within carbonate rich tight oil reservoirs from the permian lucaogou formation in the jimsar sag southern junggar basin drill core and image log observations show that fractures in the lucaogou formation can be categorized into two types bedding parallel fractures and inclined fractures the carbon and oxygen isotopic compositions of calcite cements in the bedding parallel fractures range from 0 6 to 6 0 13cpdb and from 15 5 to 8 9 18opdb respectively which are similar to those of the organic rich host rock this suggests that the bedding parallel fractures likely formed in a closed fluid system fluid inclusion analyses of the aqueous inclusions in calcite cements from the bedding parallel fractures record homogenization temperatures of 91 5 c 130 4 c indicating that they formed at the cretaceous to cenozoic during when the lucaogou formation reached peak oil generation stage therefore the bedding parallel fractures were most likely generated by hydrocarbon generation overpressure the presence of hydrocarbon inclusions in bedding parallel fracture cements supports natural fracturing by high pore fluid pressure the 13cpdb and 18opdb of calcite cements within the inclined fractures vary from 3 6 to 9 6 and from 11 0 to 2 9 respectively which are close to those of the carbonate rich parent rock this also supports a closed fluid system scenario the relatively lower fluid inclusion trapping temperatures 70 5 c 109 7 c suggest that they were likely generated by decrease of confining stress during uplift processes therefore both an increase in pore fluid pressure and a decrease in confining stress contribute to the formation of natural fractures in the lucaogou formation tight oil reservoirs

chronology and the upper dating limit for loess samples from luochuan section in the chinese loess plateau using quartz osl sar protocol abstract luminescence dating of loess older than 100 ka has long been a challenge it has been recently reported that using optically stimulated luminescence osl of fine grained quartz 4 11 m extracted from loess the range of luminescence dating could be pushed to 0 6 ma with osl ages being in agreement with independent ages watanuki t murray a s tsukamoto s 2005 quartz and polymineral luminescence dating of japanese loess over the last 0 6 ma comparison with an independent chronology earth and planetary science letters 240 774 789 the aim of this study is to provide a luminescence chronology 20 samples for the standard luochuan loess section and to further examine the upper limit of quartz osl dating for chinese loess the growth curve does not saturate at 700 gy and should allow reliable equivalent dose d e determination up to at least 400 gy however when compared with independent chronological control the d e that could be treated as reliable is less than 230 gy corresponding to 70 ka in age for chinese loess and the d e larger than 230 gy should be underestimated ages for samples from the lower part of palaeosol s1 are severely underestimated with the maximum age of 95 ka for a sample from the bottom of this palaeosol much younger than the expected age of 128 ka the maximum d e obtained for sample l9 m collected from loess layer l9 which is below the matuyama brunhes b m boundary whose age is 780 ka is only 403 gy which corresponds to an age of 107 ka the cause of underestimation is not yet clear the previous results by watunuki et al 2005 on the extension of osl dating of loess to 0 6 ma is not confirmed when evaluating the validity of osl ages in s1 another possibility is to question the already established chronological frame for luochuan section which is based on the hypothesis of continuous dust deposition the assumption of an erosion hiatus between l2 and s1 could make the osl ages look reasonable however if this is the case then it is difficult to explain why the age of sample l9 m is only 107 ka which could be treated as a saturation age while the osl can provide a correct age for loess as old as 94 9 ka for sample lc22 collected from the bottom of s1 much work is required to clarify these confusions

geochemical characteristics of crude oil from a tight oil reservoir in the lucaogou formation jimusar sag junggar basin jimusar sag which lies in the junggar basin is an important tight oil study area in china however the properties and origin of the crude oil and the geochemical characteristics of the tight oil from the lucaogou formation have not yet been studied in the present study 23 crude oil samples from the lucaogou formation were collected for analysis including physical properties density and viscosity bulk composition saturated hydrocarbon gas chromatography mass spectrometry and calculation of various biomarker parameters source rock evaluation and porosity permeability analysis were applied to the mudstones and siltstones to analyze the hydrocarbon generation history of the lucaogou source rocks one dimensional basin modeling was performed the oil filling history was also investigated by means of basin modeling and microthermometry biomarkers of suitable source rocks total organic carbon content is 1 summation of the free and volatile hydrocarbon and remaining hydrocarbon generative potential is 6 mg hc g rock and vitrinite reflectance is between 0 7 and 1 were analyzed for oil source correlation the results indicate that low maturity to mature crude oils originated from the source rocks containing terrigenous organic matter which were deposited in a saline lake the source rocks are of mainly type ii kerogen oil in the lower section of the lucaogou formation is relatively dense and viscous and has elevated nonhydrocarbon content in addition a higher proportion of bacteria and algae is shown to have contributed to the formation of crude oil in the lower section when compared with the upper section of the lucaogou formation oil source correlations demonstrate that not all mudstones within the lucaogou formation contribute to oil accumulation thin section observation indicates organic macerals surround the grains of some siltstones within the porous and permeable subsections which proves the siltstones contribute to hydrocarbon generation crude oils from the upper and lower sections mainly originate from thin bedded mudstones interbedded and siltstones within the porous and permeable subsections the mudstones over or beneath the porous and permeable subsections consist of seals and prevent the vertical movement of oil by capillary forces despite being thicker mudstones between the two porous and permeable subsections make no obvious contribution to the oil accumulation because of their low permeability and distance from the porous and permeable subsections which is consistent with the principle of near source charging for tight oil accumulations lucaogou oil has been charged twice once from 235 to 210 ma and again from 180 to 150 ma coinciding with oil generation time

faults and associated karst collapse suggest conduits for fluid flow that influence hydraulic fracturing induced seismicity during december 2011 a swarm of moderate magnitude earthquakes was induced by hydraulic fracturing hf near cardston alberta despite seismological associations linking these two processes the hydrological and tectonic mechanisms involved remain unclear in this study we interpret a 3d reflection seismic survey to delve into the geological factors related to these earthquakes first we document a basement rooted fault on which the earthquake rupture occurred that extends above the targeted reservoir second at the reservoir s stratigraphic level anomalous subcircular features are recognized along the fault and are interpreted as resulting from fault associated karst processes these observations have implications for hf induced seismicity as they suggest hydraulic communication over a large vertical distance reconciling the discrepancy between the culprit well trajectory and earthquake hypocenters we speculate on how these newly identified geological factors could drive the sporadic appearance of induced seismicity and thus be utilized to avoid earthquake hazards

astronomical forcing of middle permian terrestrial climate recorded in a large paleolake in northwestern china abstract geological records of milankovitch cycles provide a temporal framework for reconstructing earth climate evolution and mapping out the history of the ancient solar system understanding the fundamental celestial mechanics driving astronomical rhythms during the permian period from stratigraphic record is challenging because of the inherent limitations of astronomical solutions the chaotic nature of solar system motion and the paucity of cyclostratigraphic studies of geological records the junggar and adjacent basins of northwestern china constituted a large tectonic lake in the middle permian which deposited one of the thickest and richest petroleum source rock intervals in the world constructing an accurate timescale for the permian junggar basin is critical to understand the processes that controlled organic carbon burial as well as paleoclimatic and paleoenvironmental background conditions in this study detailed spectral analyses of natural gamma ray ngr data were performed on the lacustrine muddy dominated lucaogou formation from five exploitation wells the results reveal significant meter scale sedimentary cycles of 37 8 m 10 7 10 m 3 85 3 2 m and 2 0 1 58 m reflecting oscillations in lithologies variations in changing clay content within the mudstone sandstone and dolomite these cycle wavelength ratios match well with those of the milankovitch cycles predicted for middle permian period the depositional duration of the lucaogou formation was estimated at 3 myr correlation of the 1 2 myr obliquity modulation cycles among the ngr logs sedimentation rates and lake levels of the junggar basin as well as with the middle permian global sea level suggests that long term astronomical grand cycles tightly forced climatic and sedimentary processes throughout the lucaogou formation according to two independent approaches we reconstruct middle permian astronomical parameters earth precession constant k and fundamental frequencies terms gi i 1 2 3 4 5 and calculate astronomical periods eccentricity obliquity and precession these results document astronomical forcing of paleozoic lake systems constrain earth moon orbital evolution and refine the fundamental astronomical frequencies of the solar system during the middle permian

quantitative modelling of hydrocarbon expulsion and quality grading of tight oil lacustrine source rocks case study of qingshankou 1 member central depression southern songliao basin china the quality of source rocks plays an important role in the distribution of tight and conventional oil and gas resources despite voluminous studies on source rock hydrocarbon generation expulsion and overpressure a quality grading system based on hydrocarbon expulsion capacity is yet to be explored such a grading system is expected to be instrumental for tight oil and gas exploration and sweet spot prediction this study tackles the problem by examining late cretaceous lacustrine source rocks of the qingshankou 1 member in the southern songliao basin china by evaluating generated and residual hydrocarbon amounts of the source rock the extent of hydrocarbon expulsion is modelled through a mass balance method the overpressure is estimated using petromod software through correlation between the hydrocarbon expulsion and source rock evaluation parameters total organic carbon toc kerogen type vitrinite reflectance ro and overpressure three classes of high quality effective and ineffective source rocks are established high quality class contains toc 2 type i kerogen ro 1 0 overpressure 7mpa sharp increase of hydrocarbon expulsion along with increasing toc and overpressure and high expulsion value at ro 1 source rocks with toc and ro 0 8 type ii2 iii kerogen overpressure 3mpa and low hydrocarbon expulsion volume are considered ineffective rocks with parameters between the two are considered effective the high quality class shows a strong empirical control on the distribution of tight oil in the songliao basin this is followed by the effective source rock class the ineffective class has no measurable contribution to the tight oil reserves because the hydrocarbon expulsion efficiency of source rocks is controlled by many factors the lower limits of the evaluation parameters in different basins may vary however the classification method of tight source rocks proposed in this paper should be widely applicable

timing and displacement of holocene faulting on the median tectonic line in central shikoku southwest japan abstract the median tectonic line mtl extends about 900 km parallel to the general trend of the southwest japan island arc the central segment of the mtl has been active during the quaternary although the average slip rate along the mtl is up to several mm a 1 there is no historical record of destructive earthquakes along it in order to collect data on the behavior of the mtl during late holocene times especially on the timing of seismic events and the amount of displacement during each event trench studies were conducted on the active segment in central shikoku in 1984 and 1988 the results are summarized as follows 1 the latest two seismic events produced by slip on the mtl in central shikoku occurred during the early 8th century a d and between 3250 and 2820 years b p 2 the amount of displacement during the latest event is inferred to have been about 5 7 m 3 the earthquake magnitude for the latest event is estimated at 7 9 richter scale and a fault segment trace about 70 km long ruptured during that event 4 an average slip rate along the active trace of the mtl in central shikoku during the late quaternary is estimated to be 5 8 mm a 1

a reanalysis of the hypocentral location and related observations for the great 1906 california earthquake we determine probabilistic hypocentral locations for the foreshock and mainshock of the great 1906 california earthquake through reanalysis of arrival time observations in conjunction with modern velocity models and advanced event location techniques we obtain two additional observations for the mainshock and one for the foreshock that were not used in previous location studies using a robust likelihood function for event location we generate a usable subset of the predominantly unreliable teleseismic readings and determine new wave type identifications for some of the local and teleseismic readings our locations are much better constrained than those of earlier studies even though we do not assume that the epicenter lies on the san andreas fault as did previous authors we confirm the conclusions of earlier studies that the local and teleseismic arrival time observations can be explained by a single foreshock focus and a single mainshock focus on the san andreas fault and that there is no single unique hypocenter that satisfies all available local observations the maximum likelihood point latitude 37 78 n longitude 122 51 w for our preferred mainshock location indicates a hypocenter to the west of san francisco close to the san andreas fault zone this hypocenter has a 68 confidence error of about 8 km parallel to the san andreas fault and about 24 km perpendicular to the fault and a depth in the midcrust of about 12 7 km the closest point on the san andreas fault to this hypocenter lies about 10 km to the northwest of the widely accepted mainshock epicenter of bolt 1968 our mainshock location is consistent with the association of initial rupture of the 1906 mainshock with a dilatational right bend or step over in the submerged san andreas fault system offshore of the golden gate our foreshock location is less well constrained than our mainshock location but is consistent with the foreshock hypocenter being at the same location as the mainshock hypocenter online material visualization of 3d probabilistic hypocentral locations associated with the 1906 earthquake

an overview of canadian shale gas production and environmental concerns abstract production of hydrocarbons from canadian shales started slowly in 2005 and has significantly increased since natural gas is mainly being produced from devonian shales in the horn river basin and from the triassic montney shales and siltstones both located in northeastern british columbia and to a lesser extent in the devonian duvernay formation in alberta western canada other shales with natural gas potential are currently being evaluated including the upper ordovician utica shale in southern quebec and the mississippian frederick brook shale in new brunswick eastern canada this paper describes the status of shale gas exploration and production in canada including discussions on geological contexts of the main shale formations containing natural gas water use for hydraulic fracturing the types of hydraulic fracturing public concerns and on going research efforts as the environmental debate concerning the shale gas industry is rather intense in quebec the utica shale context is presented in more detail