frictional resistance of faults during accelerating and decelerating earthquake slip the dynamic friction along faults controls earthquake ruptures in the crust but many previous studies have quantified this value only for constant slip rates experiments accounting for the more realistic condition of changing slip rates suggest that faults undergo a sequence of strengthening weakening and healing during acceleration and deceleration of slip the dynamic friction of faults during earthquake slip is a critical control on earthquake ruptures in the crust extrapolation of brittle crack theories to natural earthquakes1 2 3 has led to the commonly held view that fault friction reduces during rapid earthquake slip a process known as slip weakening1 high velocity gouge experiments4 5 and recent analyses of thermal pressurization6 7 and frictional melting8 support such a notion however these studies dealt with constant rates of slip along faults here we present the results of experiments aimed at understanding the frictional behaviour of fault zone materials under variable slip rates conditions that are more representative of natural earthquakes our results show that faults undergo a sequence of strengthening weakening and healing during acceleration and deceleration of slip such a sequence may be explained by the extrapolation of rate and state frictional behaviour9 10 at low slip velocities to more realistic slip rates but involving different physical mechanisms and a different scale the initial strengthening should impose a barrier for rupture growth into large earthquakes the healing on decelerating fault motion may lead to pulse like earthquake ruptures11 12 13 14 and static stress drops that are low in comparison with the dynamic stress changes15

preseismic hydrogen gas anomalies caused by stress corrosion process preceding earthquakes simultaneous monitoring of he h2 ar n2 ch4 and rn in gas bubbles of groundwater from the 1 500 m deep nagashima well in the active yoro fault zone central japan reveals that three microearthquakes with m 1 6 2 6 in the fault zone are accompanied and preceded by increases of h2 as is a moderately large event with m 5 4 in the same fault zone all the focal distances of the earthquakes are within 25 km no comparable anomalies were seen in the gas species other than h2 we suggest that the selective and preseimic increases of h2 in groundwater gas bubbles are geochemical signals of the earthquake nucleation process of stress corrosion mechanism aseismic slips preceding earthquakes in the active fault zone are likely to have enhanced h2 production by mechanochemical reaction of fractured rock surface with water in pre existing fault planes as groundwater conduits

a constitutive law for the shear failure of rock under lithospheric conditions abstract this paper first reviews recent studies on constitutive formulations for shear failure which leads to the conclusion that revealing the constitutive property for not only frictional slip failure but also shear failure of intact rock in the brittle to brittle plastic transition regimes is critical to establish the constitutive law which governs earthquake shear failure that proceeds in the lithosphere to this end a unique high stiffness testing apparatus capable of applying polyaxial stress fields to rectangular rock specimens has been constructed for which a brief description is given the paper then presents new results of laboratory experiments on constitutive properties of shear fracture of intact granite at lithospheric conditions in view of the physical principles and constraints to be imposed on the constitutive law for shear failure the slip dependency is a more fundamental property than the time or rate dependency and hence the constitutive law for shear failure should primarily be slip dependent this slip dependent constitutive law which itself is self consistent can unifyingly and quantitatively treat the entire phases from stable quasistatic ruture growth to unstable dynamic fast speed rupture propagation for shear failure of any type whether it is frictional slip failure along a preexisting fault or shear fracture of intact materials the slip dependent constitutive law includes a scaling parameter dc critical slip displacement explicitly which in turn is scaled by a characteristic length c representing geometrical irregularities of the fault surfaces incorporation of dc or c enables this constitutive law to provide a common interpretation for shear failure of any size scale as an earthquake source from small scale in the laboratory to large scale in the earth the present experiments corroborate the slip dependent constitutive relation and other constitutive properties over the entire process from slip strengthening to slip weakening of intact granite under the conditions that confining pressure is in the range 440 to 500 mpa pore pressure is in the range 30 to 300 mpa temperature is in the range from room temperature to 456 c and strain rate is in the range 10 4 to 10 7 s it is found that some constitutive law parameters are not independent but mutually related the constitutive relation for shear failure and the parameters such as p breakdown stress drop and dc prescribing its relation are affected by ambient conditions such as temperature and strain rate

lithofacies classification and origin of the eocene lacustrine fine grained sedimentary rocks in the jiyang depression bohai bay basin eastern china abstract there are multiple sets of lacustrine source rocks in the paleogene of the jiyang depression bohai bay basin eastern china which are main targets in the terrestrial shale oil exploration compared with marine shales lacustrine fine grained rocks are more complex in their mineralogical compositions sedimentary structures and vertical stacking patterns therefore it is of great theoretical and practical significance to carry out petrological characterization and lithofacies classification in lacustrine fine grained rocks based on observations in cores and thin sections as well as elemental and organic geochemical analyses this study systematically analyzes petrological characteristics of eocene lacustrine fine grained sedimentary rocks in the jiyang depression from perspectives of mineralogical compositions sedimentary structures and organic matter abundance three end members carbonate minerals clay minerals and terrigenous clastic minerals together with organic matter abundance and sedimentary structure are employed to establish a lithofacies classification scheme that is suitable for fine grained rocks in the jiyang depression eastern china a total of 7 lithofacies types are recognized such as the organic matter rich laminated calcareous mudstone lithofacies and the moderately organic matter rich layered calcareous mudstone lithofacies through analysis of lithofacies from the bottom to the top of the drilling well sixth order sequence units are found to have good correspondence to lithofacies assemblages based on consideration of magnetic susceptibility mineral content and geochemical proxies these sixth order sequence units are divided into three types of lithofacies assemblages namely the type a lithofacies assemblage corresponding to the dominantly rising base level type b lithofacies assemblage corresponding to the dominantly falling base level and type c lithofacies assemblage with the isostatic base level among them the type c lithofacies assemblage is the most favorable for shale oil exploration and development results of this study are expected to not only deepen understanding of lithofacies and its genesis and origin of lacustrine fine grained rocks but also provide a theoretical basis for shale oil exploration and development

frictional changes induced by seismic slip on a non planar fault summary we propose a model which describes the formation of a strong asperity on a fault we consider a fault surface which differs slightly from a plane due to a jog like topographic variation the fault is placed in an elastic space and is subject to a uniform stress field the orientation of the fault is such that the normal traction which is compressive is greater on the topographic variation determining a higher static friction and hence an asperity the value of friction on this asperity depends on the magnitude of shear stress for times of seismological interest the increase in shear stress at rates typical of tectonic processes does not produce a sensible increase in friction with respect to the adjacent fault segments a considerable increase in friction and the formation of a strong asperity or even a barrier can occur due to repeated seismic slip episodes on the fault slip results in an elastic medium deformation causing an increase in normal traction on the asperity and hence in friction this process is described with the aid of a tensile somigliana dislocation regions with high friction undergo partial fracturing of the fault face material which can produce fault gouge the tensile dislocation introduces a small non double couple component in the seismic moment of the seismic event the magnitude of this component depending mainly on the relative size of the asperity

characteristic features of local breakdown near a crack tip in the transition zone from nucleation to unstable rupture during stick slip shear failure abstract characteristic features of local breakdown near a propagating crack tip during slip failure nucleation and its transition process to unstable rupture under mode ii conditions are experimentally studied using a rock sample with a simulated fault the size of which is large compared with the size of the breakdown zone in addition distinctive features in the nucleation zone are compared with those in the zone of steady dynamic rupture propagation it is found that the local breakdown stress drop the local dynamic stress drop the local stress increase immediately before the slip weakening process the dimensionless parameter s defined by das and aki and the shear fracture energy are functions of crack length in the transition zone from nucleation to unstable rupture i e they all increase with crack growth in the nucleation zone this is contrasted with the observations in the zone of steady dynamic rupture propagation where these physical parameters do not depend on crack length an increase in the magnitudes of these parameters with crack growth in the nucleation zone results in increasing resistance to crack extension with crack growth in the nucleation zone the reason for the increase in crack growth resistance in this zone is that a slip failure nucleus is formed at a point or zone where the local strength and the shear fracture energy are at a minimum this basic physical information can provide the key to earthquake prediction since the nucleation itself is a precursory phenomenon the ratio of the size of the breakdown zone to the crack length decreases abruptly beyond the critical crack length rupture velocity v accelerates with crack growth and reaches the shear wave velocity or super shear and v is found to be expressed empirically as a function of crack length in the nucleation zone a positive correlation is found between s and v in the nucleation zone v increases with increasing s however no such correlation was observed in the zone of steady dynamic rupture propagation where v seems to have reached the shear wave velocity of super shear for s 0 5 this is consistent with das and aki s numerical result the interrelationships between shear stress slip displacement slip velocity and acceleration near the crack tip during the breakdown in the nucleation zone are revealed and they are compared with those in the zone of dynamic rupture propagation the present experiments suggest that the relationship between shear stress and slip displacement is more fundamental during the breakdown process than the relationship between shear stress and slip velocity a model is presented to describe the breakdown process in the nucleation zone

constitutive relations between dynamic physical parameters near a tip of the propagating slip zone during stick slip shear failure abstract constitutive relations between physical parameters in the cohesive zone during stick slip shear failure are experimentally investigated stick slip was generated along a 40 cm long precut fault in tsukuba granite samples using a servocontrolled biaxial loading apparatus dynamic behavior during local breakdown processes near a tip of the slipping zone is revealed the slip velocity and acceleration are given as a function of the slip displacement and the cohesive or breakdown shear stress as a function of the slip velocity a cycle of the breakdown and restrengthening process of stick slip is composed of five phases characterized in terms of the cohesive strength and the slip velocity the cohesive strength can degrade regardless of the slip velocity during slip instabilities the maximum slip acceleration u max and the maximum slip velocity u max are obtained experimentally as u max 2 u c u max 2 and u max b g v where u c is the critical displacement b the breakdown stress drop g the rigidity and v the rupture velocity these relations are consistent with ida s theoretical estimation based on the cohesive zone model the above formula gives good estimates for the maximum slip acceleration of actual earthquakes the cutoff frequency max of the power spectral density of the slip acceleration increases with increasing normal stress in particular max is found to be directly proportional to the normal stress n within the normal stress range less than 17 mpa as max khz 4 0 n mpa n max increase with an increase in u max or u max all these results lead to the conclusion that u max u max and max increase with increasing normal stress this is consistent with a previous observation that b increases with increasing normal stress the above empirical linear relation between max and n can be explained by a linear dependence of b on n the size scale dependence of physical parameters is discussed and such size scale dependent parameters as u max and apparent fracture energy are scaled to the breakdown zone size regarded as a characteristic length to extend the results obtained in the laboratory to an earthquake failure in the earth

shale oil resource potential and oil mobility characteristics of the eocene oligocene shahejie formation jiyang super depression bohai bay basin of china abstract oil mobility in liquid rich shale is crucial for economic success of resource development the characteristics of the host rock and the properties of oil fluids are two primary factors controlling fluid mobility organic geochemistry data allows examination of both resource potential and oil mobility we propose data driven empirical models in this paper to describe hydrocarbon resource potential with respect to oil mobility the proposed methods were applied to a dataset collected from the eocene oligocene es3 and es4 source rock units in four recent shale oil exploration wells in the jiyang super depression of the bohai bay basin the dataset results from standard programmed pyrolysis of whole rock samples as well as solvent extracted replicates of 139 core samples was studied to examine the source rock characteristics and shale oil resource potential bulk geochemical characteristics and thermal decomposition trends allow for sub division of the samples into two groups a samples with high initial hydrogen index 800 mg hc g toc and average present day toc of 4 07 from ly1 and ny1 wells in a distal facies and b samples with slightly lower initial hydrogen index about 700 mg hc g toc and average toc of 3 11 from fy1 and l69 wells in a transitional facies three different categories of oil resource with respect to oil mobility can be defined adsorbed restricted and movable based on organic geochemical characteristics and their variations in the stratigraphic intervals represented by the samples in the four wells we show that expulsion efficiency is a good indicator of hydrocarbon retention in source rock reservoir and that the two wells in the distal facies have higher total resource potentials with abundant movable oil resource than the two wells in the transitional facies the total oil potential is separated into three types of oil resource to show oil mobility thus providing more information for business decision

the mechanics of lubricated faults insights from 3 d numerical models 1 the weakening mechanisms occurring during an earthquake failure are of prominent importance in determining the resulting energy release and the seismic waves excitation in this paper we consider the fully dynamic response of a seismogenic structure where lubrication processes take place in particular we numerically model the spontaneous propagation of a 3 d rupture in a fault zone where the frictional resistance is controlled by the properties of a low viscosity slurry formed by gouge particles and fluids this model allows for the description of the fault motion in the extreme case of vanishing effective normal stress by considering a viscous fault response and therefore without the need to invoke in the framework of coulomb friction the generation of the tensile mode of fracture we explore the effects of the parameters controlling the resulting governing law for such a lubricated fault the viscosity of the slurry the roughness of the fault surfaces and the thickness of the slurry film our results indicate that lubricated faults produce a nearly complete stress drop i e a very low residual friction coefficient 0 01 a high fracture energy density eg few 10s of mj m2 and significant slip velocities vpeak few 10s of m s the resulting values of the equivalent characteristic slip weakening distance d0eq 0 1 0 8 m depending on the adopted parameters are compatible with the seismological inferences moreover in the framework of our model we found that supershear ruptures are highly favored in the case of enlarging gap height we can have the healing of slip or even the inhibition of the rupture quantitative comparisons with different weakening mechanisms previously proposed in the literature such as the exponential weakening and the frictional melting are also discussed

roughness of natural fault surfaces the roughness of fault surfaces is important in the mechanics of fault slip and could play a role in determining whether sliding occurs via earthquakes or fault creep we have made preliminary measurements of the power spectral density of several fault surfaces over the wavelength range from 10 5 to 1 m using field and laboratory scale profilimeters the fault surfaces are strongly anisotropic profiles parallel to the slip direction have amplitudes about one order of magnitude lower than those perpendicular to the slip direction over most of the wavelength interval measured fault roughness perpendicular to the slip direction is similar to the roughness of natural joints the greater smoothness in the slip direction presumably represents wear resulting from slip combining our data with previous measurements of the roughness spectrum of the san andreas fault shows that fault surfaces are fractal over nearly eleven orders of magnitude in wavelength

slip dependent friction law and nucleation processes in earthquake rupture abstract matsu ura m kataoka h and shibazaki b 1992 slip dependent friction law and nucleation processes in earthquake rupture in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 135 148 we developed a physical model that interprets slip strengthening and slip weakening processes in brittle shear fracture by considering the microscopic interaction between statistically self similar fault surfaces our model successfully describes general features of the constitutive behaviour observed in laboratory experiments of stick slip with the progress of fault slip frictional stress first increases rapidly up to a peak value and then decreases gradually to a constant level the first slip strengthening process can be explained by the increase of frictional resistance in transition from the in phase contact to the random phase contact of fault surfaces the latter slip weakening process can be explained by the decrease of frictional resistance due to the abrasion of surface asperities the trade off between these two processes determines the peak stress and the critical displacement over which the slip weakening proceeds we examined the nucleation process proceeding in a seismogenic zone with the increase of external shear stress through numerical simulations in our model the seismogenic zone is represented by a broad weak zone with a locally strong part asperity on a fault plane the basic equations governing the nucleation process are the equation of equilibrium and the constitutive relation between frictional stress and fault slip we obtained the following results the nucleation process first proceeds quasi statically at the weak portions with the increase of external shear stress then if the constitutive relation at the asperity has a high and narrow peak of stress brittle dynamic rupture occurs in a limited area around the asperity when the constitutive relation has a low and broad peak the dynamic rupture of the asperity does not occur the process is completely aseismic when the peak of stress is high and broad the dynamic rupture of the asperity leads to the catastrophic rupture which extends over the whole region from these results it is concluded that diversity in the nucleation process can be ascribed to difference in the variation of constitutive behaviour along the fault

constraint of fault parameters inferred from nonplanar fault modeling 1 we study the distribution of initial stress and frictional parameters for the 28 june 1992 landers california earthquake through dynamic rupture simulation along a nonplanar fault system we find that observational evidence of large slip distribution near the ground surface requires large nonzero cohesive forces in the depth dependent friction law this is the only way that stress can accumulate and be released at shallow depths we then study the variation of frictional parameters along the strike of the fault for this purpose we mapped into our segmented fault model the initial stress heterogeneity inverted by peyrat et al 2001 using a planar fault model simulations with this initial stress field improved the overall fit of the rupture process to that inferred from kinematic inversions and also improved the fit to the ground motion observed in southern california in order to obtain this fit we had to introduce an additional variations of frictional parameters along the fault the most important is a weak kickapoo fault and a strong johnson valley fault

nucleation of rupture under slip dependent friction law simple models of fault zone the initiation of frictional instability is investigated for simple models of fault zone using a linearized perturbation analysis the fault interface is assumed to obey a linear slip weakening law the fault is initially prestressed uniformly at the sliding threshold in the case of antiplane shear between two homogeneous linearly elastic media space time and spectral solutions are obtained and shown to be consistent the nucleation is characterized by 1 a long wavelength unstable spectrum bounded by a critical wave number 2 an exponential growth of the unstable modes and 3 an induced off fault deformation that remains trapped within a bounded zone in the vicinity of the fault these phenomena are characterized in terms of the elastic parameters of the surrounding medium and a nucleation length that results from the coupling between the frictional interface and the bulk elasticity these results are extended to other geometries within the same formalism and implications for three dimensional rupture are discussed finally internal fault structures are investigated in terms of a fault parallel damaged zone spectral solutions are obtained for both a smooth and a layered distribution of damage for natural faults the nucleation is shown to depend strongly on the existence of a internal damaged layer this nucleation can be described in terms of an effective homogeneous model in all cases frictional trapping of the deformation out of the fault can lead to the property that arbitrarily long wavelengths remain sensitive to the existence of a fault zone

geologic characteristics of hydrocarbon bearing marine transitional and lacustrine shales in china abstract organic rich shales spanning in age from pre cambrian to quaternary were widely deposited in china this paper elaborates the geology and unique characteristics of emerging and potential hydrocarbon bearing shales in china the pre cambrian sinian doushantuo to silurian black marine shales in the intra shelf low to slope environments were accumulated in south china and tarim platform in northwest china these marine shales with maturity ro of 1 3 5 are in dry gas window during carboniferous to permian the shales associated with coal and sandstones were mainly deposited in coastal swamp transitional setting in north china ne china nw china and yangtze platform in south china these transitional shales are generally clay rich and are potential gas bearing reservoirs since middle permian the lacustrine shales with total carbon content toc up to 30 and ro mainly in oil window are widely distributed in all the producing basins in china the lacustrine shales usually have more clay mineral content than marine shales and are characterized by rapid facies change and are interbedded with carbonates and sandstone the high quality shale reservoir with high toc hydrocarbon content and brittle minerals content is usually located at transgressive systems tract tst to early highstand systems tract ehst interval deposited in anoxic depositional setting recent commercial shale gas production from the silurian longmaxi marine shale in the southeastern sichuan basin preliminary tight oil production associated with lacustrine hydrocarbon bearing shale intervals and hydrocarbon shows from many other shales have proven the hydrocarbon bearing shales in china are emerging and potential shale gas and tight shale oil plays tectonic movements could have breached the early hydrocarbon accumulation in shales and tectonically stable areas are suggested to be favorable prospects for china shale plays exploration and production

maximizing information from fine grained sedimentary rocks an inclusive nomenclature for mudstones abstract a simple nomenclature for fine grained sedimentary rocks is proposed based on sedimentary structures present and abundance of all materials forming more than 10 of rock volume irrespective of their origin allochthonous autochthonous and diagenetic a mudstone sedimentary rock that comprises 50 grains 90 clay silt and sand bearing clay rich mudstone 50 to 90 clay 10 to 50 sand 10 to 50 silt and calcite ce ment calcareous nannoplankton and clay bearing mudstone all components 10 to 50 textural information can and should be incorporated into this scheme by prefixing the rock name with descriptions such as bioturbated and thin bedded such a nomenclature is necessary to fully describe variability within fine grained sedimentary rocks that hitherto have typically been described using selected constituents of varying significance such as total organic carbon fissility parting spacing ray signature and lamination using the inclusive nomenclature proposed here will improve opportunities to compare all fine grained sediments aid interpretation of depositional and diagenetic controls of variability and enable these rocks to be more easily integrated into basin scale facies models

diagenetic variation at the lamina scale in lacustrine organic rich shales implications for hydrocarbon migration and accumulation abstract lacustrine carbonate rich shales are well developed within the mesozoic cenozoic strata of the bohai bay basin bbb of eastern china and across southeast asia developing an understanding of the diagenesis of these shales is essential to research on mass balance diagenetic fluid transport and exchange and organic inorganic interactions in black shales this study investigates the origin and distribution of authigenic minerals and their diagenetic characteristics processes and pathways at the scale of lacustrine laminae within the es4s es3x shale sequence of the bbb the research presented in this study is based on thin sections field emission scanning electron microscope fesem and sem catholuminescence cl observations of well core samples combined with the use of x ray diffraction xrd energy dispersive spectroscopy electron microprobe analysis and carbon and oxygen isotope analyses performed using a laser microprobe mass spectrometer the dominant lithofacies within the es4s es3x sequence are a laminated calcareous shale lcs 1 and a laminated clay shale lcs 2 the results of this study show that calcite recrystallization1 is the overarching diagenetic process affecting the lcs 1 related to acid generation from organic matter om thermal evolution this evolutionary transition is the key factor driving the diagenesis of this lithofacies while the transformation of clay minerals is the main diagenetic attribute of the lcs 2 diagenetic differences occur within different laminae and at variable locations within the same lamina level controlled by variations in mineral composition and the properties of laminae interfaces the diagenetic fluid migration scale is vertical and responses dissolution and replacement are limited to individual laminae between zero and 100 m in width in contrast the dominant migration pathway for diagenetic fluid is lateral along the abrupt interfaces between laminae boundaries which leads to the vertical transmission of diagenetic responses the recrystallization boundaries between calcite laminae act as the main migration pathways for the expulsion of hydrocarbons from these carbonate rich lacustrine shales however because the interaction between diagenetic fluids and the shales themselves is limited to the scale of individual lamina this system is normally closed the occurrence of abnormal pressure fractures can open the diagenetic system however and cause interactions to occur throughout laminae in particular the closed open c o diagenetic process at this scale is critical to this shale interval multi scale c o systems are ubiquitous and episodic ranging from the scale of laminae to the whole basin observations show that such small scale systems are often superimposed onto larger ones to constitute the complex diagenetic system seen within the bbb combining fluid transport material and energy exchange and solid liquid and organic inorganic interactions

a compositional classification for grain assemblages in fine grained sediments and sedimentary rocks reply abstract a tripartite compositional classification is proposed for sediments and sedimentary rocks that have grain assemblages with greater than 50 percent of a weight or volume of particles smaller than 62 5 m 4 phi tarl terrigenous argillaceous contains a grain assemblage dominated by more than 75 percent of particles of extrabasinal derivation including grains derived from continental weathering and also volcanogenic debris carl calcareous argillaceous contains less than 75 percent of particles of extrabasinal derivation debris and among its intrabasinal grains contains a preponderance of biogenic carbonate particles including carbonate aggregates sarl siliceous argillaceous contains less than 75 percent of particles of extrabasinal derivation and contains a preponderance of biogenic siliceous particles over carbonate grains these three classes of fine grained particulate sediments and rocks effectively separate materials that have distinct depositional settings and systematic contrasts in organic matter content and minor grain types in the subsurface the grain assemblages that define these classes follow contrasting and predictable diagenetic pathways that have significant implications for the evolution of bulk rock properties and thus assigning a fine grained rock to one of these classes is an important first step for predicting its economic and engineering qualities for purposes of description these three class names can be joined to modifier terms denoting rock texture more precise compositional divisions specific grain types of notable importance and diagenetic features

grain assemblages and strong diagenetic overprinting in siliceous mudrocks barnett shale mississippian fort worth basin texas porosity permeability and total organic carbon toc in a heterogeneous suite of 21 high maturity samples vitrinite reflectance 1 52 2 15 from the barnett shale in the eastern fort worth basin display few correlations with parameters of rock texture fabric and composition these factors being mostly obscured by the effects of a protracted history of diagenesis diagenesis in these rocks includes mechanical and chemical modifications that occurred across a wide range of burial conditions compaction and cementation have mostly destroyed primary intergranular porosity the porosity average 5 vol by gas research institute helium porosimetry and pore size 8 nm median pore throat diameter are reduced to a degree such that pores are difficult to detect even by imaging ar ion milled surfaces with a field emission scanning electron microscope the existing porosity that can be imaged is mostly secondary and is localized dominantly within organic particulate debris and solid bitumen the grain assemblage is highly modified by replacement a weak pattern of correlation survives between bulk rock properties and the ratio of extrabasinal to intrabasinal sources of siliciclastic debris higher porosity permeability and toc are observed in samples representing the extreme end members of mixing between extrabasinal siliciclastic sediment and intrabasinal derived biosiliceous debris reservoir quality in these rocks is neither more strongly nor more simply related to variations in primary texture and composition because the interrelationships between texture and composition are complex and importantly the diagenetic overprint is too strong

time dependent friction of granite implications for precursory slip on faults frictional forces were measured during sliding between saw cut cylinders of barre granite deformed in a servo controlled triaxial loading machine two different effects occur depending on the type of loading when steady shortening of a stably sliding sample is halted suddenly slip continues at a diminishing rate which depends on the logarithm of the initial sliding velocity thus the frictional strength of the surface is decreasing with time when shortening at a constant rate resumes after the holding period however the frictional resistance temporarily rises to a peak proportional to the logarithm of time of no driving showing a well known increase in friction with time the subsequent decrease in resistance from this peak is continuous the observed frictional resistance of a surface thus results from the interaction of several processes and is not a constant in general but depends on the immediate and preceding deformation when shortening is resumed after a period of holding slip rate across the friction surface temporarily accelerates above the driving rate the slip rate can then either decrease to the driving rate and remain stable or accelerate further and lead to stick slip motion at stress levels below the peak value there is no apparent difference in the frictional resistance until the unloading rate of the loading machine is exceeded between slip episodes which settle stably to the constant driving rate and those which become unstable and result in stick slip the stick slip failure criterion is not a peak stress but rather loss of strength more rapidly that the unloading rate of the loading machine the evidence that accelerating motion before stick slip is due to the time variable strength of rock suggests that accelerating slip will occur before earthquakes unfortunately for easy observation experiments indicate that slip need not be uniform over a fault surface also to be established is whether slip will be sufficiently large in the earth to be detectable nevertheless a plausible mechanism for generating observable phenomena prior to earthquakes is suggested by the laboratory observations

geochemistry of recent toc rich sediments from the gulf of california and the black sea major and minor elements incl ag as ba cd co cr cu mn mo ni pb sr v zn have been determined in recent sediments from the gulf of california upwelling area and black sea sapropels in order to reinterpret their chemical composition in view of reliable seawater and plankton data the chemistry of the gulf of california sediments reflects regeneration processes which occur in the water column i e only a small fraction 10 of elements like cd which in seawater are coupled to the labile nutrients c n p is buried in the sedimentary column in contrast elements like the more resistant nutrients si undergo a deeper regeneration cycle ba several trace metals which are present in comparatively higher concentrations in seawater as mo u v and at the same time are reactive under reducing conditions and or are able to form stable sulfides are fixed in the sediments during early diagenesis the early diagenetic behavior of ba is closely related to bacterial sulfate reduction the formation of barite concretions is discussed anoxic conditions in the water column act as ideal traps for a number of redox sensitive and or stable sulfide forming elements a simple trace metal balance calculation shows that the chemical composition of black sea sapropels is controlled by fluvial and mediterranean seawater element input and the accumulation rate of terrigenous detrital material

sedimentary characteristics of thick layer lacustrine beach bars in the cenozoic banqiao sag of the bohai bay basin east china abstract lacustrine beach bar reservoirs have become important exploration targets in the bohai bay basin in china especially in the banqiao sag within the huanghua depression where some typical thick layer beach bar reservoirs have been discovered recently the average single layer thickness of the beach bar sand bodies in the second member of the paleogene shahejie formation within the sag is greater than 10 m and the cumulative thickness of these sands reach up to 100 m the second member of the shahejie formation in the banqiao sag consists of a third order sequence of three systems tracts a lowstand systems tract a transgressive systems tract and a highstand systems tract beach bar sand bodies were deposited widely in the sag in the lowstand systems tract but were less deposited in the other systems tracts the sedimentary characteristics distribution patterns and formation mechanisms of the beach bar sand bodies in the lowstand systems tract of the second member of the shahejie formation were systemically studied using cores wireline logs and 3d seismic data the beach bar was divided into five sedimentary microfacies namely sandy bar centre sandy bar flank interbar deposit coastal beach and infralittoral beach based on the integrated analysis of the paleostructure and sedimentary environment it was inferred that the thick layer beach bars in this area resulted from the combination and joint control of the sediment source system hydrodynamic environment lake level variations and contemporaneous fault activity firstly the sands in the braided river delta of the beidagang buried hill structural belt served as the provenance that provided the material basis for the beach bars in the banqiao sag secondly the wave effects in the gentle slope belt controlled the scale and distribution of the beach bars under the control of waves various sedimentary microfacies were regularly distributed in particular the continuous activity of the contemporaneous dazhangtuo fault contributed to the formation of the thick layer beach bars in the banqiao sag the contemporaneous fault controlled the allocation of the sediments providing abundant sands in the downthrown side of the fault in addition there was a constant high energy hydrodynamic environment near the fault plane where the sand bodies experienced long term reworking by waves and gradually formed beach bars with large thickness the activity of the contemporaneous fault increased the accommodation space in the lowstand systems tract of the second member of the shahejie formation which resulted in continuous sand deposition and provided the necessary conditions for forming the thick layer beach bars

exploration breakthroughs and geological characteristics of continental shale oil a case study of the kongdian formation in the cangdong sag china abstract petroleum geology and deposition features of the fine grain phase region in the second member of the kongdian formation were investigated using traditional petroleum geology and sedimentary petrology new theories for shale oil and gas formation based on data from 500 m continuous coring systematic analysis of over ten thousand core samples and logging data in the center of the lake basin in the cangdong sag bohai bay basin china were developed to determine the distribution of shale oil and provide a basis for shale oil exploration deployment results showed that a wide distribution of semi deep to deep lake sub facies fine grained sediment shale was deposited in the study area during the largest lake flooding period this sediment consists of felsic shale mixed shale and dolomites but no clay shale the shale features multiple rock components with few dominant minerals high clastic mineral content and low clay mineral content rich analcite and lean pyrite rich brittle minerals with lean quartz diverse rock types with limited shale oil more tight reservoirs and fewer reservoirs with no fractures more high quality source rock with less non hydrocarbon source rock and more high frequency cycles with fewer monolithic deposits results indicate that dolomites are located in strips on the plane and are locally enriched contradicting the understanding that only hydrocarbon source rock and no reservoirs develop in the middle of a continental closed lake basin the study region demonstrates good conditions for shale oil formation a favorable configuration of source rock and reservoirs and 260 km2 of sweet spots indicating high exploration value several prospecting wells have obtained industrial oil flow with guidance based on geological knowledge and engineering technology support

genesis and distribution pattern of carbonate cements in lacustrine deep water gravity flow sandstone reservoirs in the third member of the shahejie formation in the dongying sag jiyang depression eastern china abstract the lacustrine deep water gravity flow sandstone reservoirs in the third member of the shahejie formation are the main exploration target for hydrocarbons in the dongying sag eastern china carbonate cementation is responsible for much of the porosity and permeability reduction in the lacustrine deep water gravity flow sandstone reservoirs the sandstones are mainly lithic arkose with an average framework composition of q43f33l24 the carbonate cements are dominated by calcite ferroan calcite ankerite and a small amount of dolomite the calcite and ferroan calcite are mainly poikilotopic blocky crystals while the dolomite and ankerite are mainly euhedral rhombohedra crystals filling intergranular and intragranular pores the relatively positive 13c values 2 to 3 9 of the carbonate cements in the sandstone reflect a mainly inorganically sourced carbon from 32 ma to 25 ma the pore water was rich in bicarbonate and ca2 due to carbonate dissolution in mudstone and which were transported with the pore water from mudstone to sandstone via advection and precipitated calcite cementation in thinly bedded sandstones and some high permeability zones in the middle of medium to thick sandstone beds from 12 ma to present abundant ca2 fe3 fe2 mg2 and bicarbonate had been transported from mudstone to sandstone via diffusion to form tight ferroan calcite cementation in the upper and lower parts of the medium to thick bedded sandstones ankerite is mainly distributed in the reservoirs associated with oil migration or charge because change of fe3 to fe2 from oil charge may supply sufficient fe2 for ankerite precipitation the center of sandstone beds 0 6 m is with potential of high quality reservoirs in the research area carbonate cementation appears to be an important factor that controls the accumulation of oil in deep water gravity flow sandstone reservoirs in the study area

effects of physical fault properties on frictional instabilities produced on simulated faults laboratory studies of large scale simulated faults show that physical properties of the fault specifically normal stress and fault roughness significantly influence the unstable shear failure behavior of the fault in addition the experiments provide insights into important length scaling effects that are useful for assessing concepts such as critical crack length or rupture nucleation dimension stick slip shear failures have been generated along a 2 m long simulated fault in a block of sierra white granite experiments were conducted at normal stresses between 0 6 and 4 mpa with two different prepared roughnesses of the simulated fault a smooth fault with a profilometer measured roughness of 0 2 m and a rough fault with a measured roughness of 80 m high speed records of shear strains and slip velocities clearly show both the propagation of the stick slip failures and details of the local deformations and motions from which slip weakening of the fault at the onset of sliding can be resolved both the dynamic stress drops of the stick slip events and the apparent fracture energies of the events determined from the records of the fault slip weakening increase with increasing normal stress although critical slip weakening displacements are insensitive to normal stress they increase with increased fault roughness such that the apparent fracture energies are also larger on the rough fault than on the smooth fault slip velocities in these experiments are influenced by roughness and are proportional to stress drop although the onset of slip is sharply defined the termination of slip is more gradual without a clear stopping phase measured rupture velocities on the rough fault are lower than those on the smooth fault when a length scale based on rupture nucleation dimensions directly proportional to critical displacements is introduced the data suggest that at fault lengths close to the nucleation lengths rupture velocity and slip velocity increase with increasing fault length

geology of gulf coast lignites edited by r b finkelman and d j casagrande environmental and coal associates houston 1986 224 pp 39 00

sedimentology geodynamics resources and environments of china and adjacent areas a special issue in memory of professor shu sun for his scientific contributions and academic services

fracture energy of stick slip events in a large scale biaxial experiment the concept of apparent fracture energy for the shear failure process is employed by many authors in modeling earthquake sources as dynamically extending shear cracks using records of shear strain and relative displacement from stick slip events generated along a simulated prepared fault surface in a large 1 5m x 1 5m x 0 4m granite block and a slip weakening model for the fault direct estimates of the apparent shear fracture energy of the stick slip events have been obtained for events generated on a finely ground fault surface apparent fracture energy ranges from 0 06 j m sup 2 at a normal stress of 1 1 mpa to 0 8 j m sup 2 at a normal stress of 4 6 mpa in contrast to estimates for tensile crack formation we find that the apparent fracture energy of stick slip events increases linearly with normal stress the results for the slip weakening model for the stick slip events are generally consistent with constitutive fault models suggested by observations of stable sliding in smaller scale experiments

mineralogical and chemical distribution of the es3l oil shale in the jiyang depression bohai bay basin e china implications for paleoenvironmental reconstruction and organic matter accumulation abstract the es3l lower sub member of the third member of the eocene shahejie formation shale in the jiyang depression is a set of relatively thick and widely deposited lacustrine sediments with elevated organic carbon and is considered to be one of the most important source rocks in east china we can determine the mineralogy organic and inorganic geochemistry of the es3l shale and calculate paleoclimate indexes by using multiple geochemical proxies based on organic chemistry total organic carbon toc and rock eval pyrolysis major and trace elements x ray diffraction and carbon and oxygen isotope data from key wells alongside ecs elemental capture spectroscopy well log data these indicators can be used to analyze the evolution of the paleoenvironment and provide a mechanism of organic matter om accumulation the es3l oil shale has high toc abundance most samples 3 0 and is dominated by type i kerogens additionally the organic rich shale is rich in cao and enrichment in some trace metals is present such as sr ba and u the positive 13c and negative 18o values high sr ba b ga and ca ca fe ratios and low c s ratios indicate that the es3l shales were mainly deposited in a semi closed freshwater brackish water lacustrine environment the consistently low ti al and si al ratios reflect a restricted but rather homogeneous nature for the detrital supply many redox indicators including the th u v v ni and u ratios pyrite morphology and toc ts fe diagrams suggest deposition under dysoxic to suboxic conditions subsequently the brackish saline bottom water evolved into an anoxic water body under a relatively arid environment during which organic lean marls were deposited in the early stage later an enhanced warm humid climate provided an abundant mineral nutrient supply and promoted the accumulation of algal material om input from algal blooms reached a maximum during the deposition of the organic rich calcareous shale with seasonal laminations high p ti ratios and a strongly positive relationship between the p and toc contents indicate that om accumulation in the oil shale was mainly controlled by the high primary productivity of surface waters with help from a less stratified water column factors such as the physical protection of clay minerals and the dilution of detrital influx show less influence on om enrichment

static shear crack with a zone of slip weakening summary as a prologue to our investigation of the nature of sequences of earthquake events we investigate the problem of a finite 2 d antiplane static shear crack for two different models of a slip weakening zone near the crack tip the crack is imbedded in an infinite elastic medium in the limit as the size of the slip weakening zone vanishes the problem becomes one considered by knopoff for a finite shear crack in a uniform field we solve for the displacement and the stress for representative values of dimension less stress drop for the two models our results indicate that these quantities are not strongly dependent on the details of the constitutive relation in the transition zone with decreasing dimensionless stress drop the crack length increases monotonically and the size of the slip weakening zone decreases monotonically these results can be interpreted as the critical conditions for the further extension of an initial earthquake fault in this interpretation these results imply that the initiation of an earthquake is not only controlled by the stress drop on the fault plane but also by the size of a pre existing fracture an earthquake can be initiated from a small pre existing fracture if the stress drop on the initial fault is large enough conversely it can be initiated under the influence of a lower stress drop if the initial fault is large enough no solution to the static problem exists if the dimensionless stress drop is greater than a certain value this maximum dimensionless stress drop corresponds to a minimum crack length for which the slip weakening zone occupies the entire crack in the small dimensionless stress drop or small scale yielding limit the dimensionless half length of the crack is inversely proportional to the square of the dimensionless stress drop the dimensionless length of the slip weakening zone has been calculated we generalize the formula for the effective shear fracture energy obtained by palmer rice and andrews to include the effect of the size of the slip weakening zone our results indicate that because the influence of the size of of the slip weakening zone has not been taken into account earlier estimates of the effective shear fracture energy may have been overestimated by as much as 67 per cent

climate driven paleolimnological change controls lacustrine mudstone depositional process and organic matter accumulation constraints from lithofacies and geochemical studies in the zhanhua depression eastern china abstract the influence of paleoclimate on the depositional process of lacustrine mudstone and organic matter accumulation is important to both paleoclimate reconstruction and hydrocarbon exploration here we study the lower third member es3l of the eocene shahejie formation in the zhanhua depression bohai bay basin eastern china in order to understand how paleoclimate influenced depositional processes and organic matter accumulation of lacustrine organic rich mudstone by combining detailed core descriptions and microscopic observations and high resolution mineralogical and geochemical analyses we identified two major lithofacies including massive calcareous mudstone and laminated calcareous mudstone from the luo 69 drilling core the sedimentologic observations and changes of geochemical proxies including detritus index ln al2o3 na2o b ga and v v ni suggest that the massive calcareous mudstone was deposited in a small shallow salt lake that was dysoxic anoxic and the paleoclimate in the lake catchment was cool and arid and the laminated calcareous mudstone was deposited in a large and deep stratified lake which has anoxic highly saline bottom and oxic less saline surface water and the lake catchment was more humid and warm the dominant lithofacies changed from laminated calcareous mudstone to massive calcareous mudstone in the studied core suggesting that the lake became shallower and smaller when the paleoclimate became cooler and drier through time such a climate trend may be a response to global cooling during the middle eocene the average total organic content toc in both lacustrine highstand and lowstand are comparable even though the lake water chemistry and amount of terrigenous input are different we infer that the accumulation of organic matter within the lacustrine highstand was controlled by the combination of primary productivity carbonate production and preservation in anoxic bottom water while accumulation within lacustrine lowstand was only controlled by primary productivity

earthquake aftereffects and triggered seismic phenomena the physical basis for delayed aftereffects of large crustal earthquakes is analyzed these effects apparently range in scale from typical aftershocks near the source region of a prior earthquake to the triggering of groundwater and deformation related anomalies possibly including other large earthquakes at locations as much as a few hundred kilometers from the source of a great earthquake observational reports of such aftereffects are reviewed and possible mechanisms for their occurrence are discussed

hierarchical asperity model for multiscale characteristic earthquakes a numerical study for the off kamaishi earthquake sequence in the ne japan subduction zone 1 we develop a numerical model to simulate the occurrence of multiscale characteristic earthquakes in the off kamaishi area of the northeast japan subduction zone a notable feature of these earthquake sequences is that microearthquakes occur during the later half of interseismic period between two successive m 4 9 characteristic earthquakes which we call moderate earthquakes we introduce a microasperity the rupture area of the microearthquakes with a significantly smaller nucleation size than the size of a hyper asperity the rupture area for moderate earthquakes in contrast the nucleation size in the rest of the hyper asperity which we call a conditional asperity is set to be comparable to the spatial size of the hyper asperity such a hierarchical asperity model successfully reproduces the observed earthquake sequences the simulation results show that both microearthquakes and moderate earthquakes nucleate at the microasperity the stress level in the conditional asperity determines whether a rupture terminates just outside the microasperity or propagates out into the conditional asperity