黄土和红粘土中宇宙成因核素定年的潜力:^(10)Be浓度与化学成分的关系

宇宙成因核素10Be(半衰期1.5M a)不但是古环境变化的示踪剂,而且具有确定地质年龄的能力。80个全岩样品的10Be和化学分析数据表明,黄土高原约6M a以来的红粘土和黄土序列中年龄校正的10Be浓度与沉积物粒度和风化程度的化学指标具有显著的关系。根据这种关系建立的10Be浓度与化学指标的经验回归线性模型,可以估计红粘土和黄土形成时的10Be浓度,确定红粘土和黄土形成的10Be放射性年龄。

Influence of hysteretic stress path behavior on seal integrity during gas storage operation in a depleted reservoir

In this study,we numerically investigate the influence of hysteretic stress path behavior on the seal integrity during underground gas storage operations in a depleted reservoir.Our study area is the Honor Rancho Underground Storage Facility in Los Angeles County(California,USA),which was converted into an underground gas storage facility in 1975 after 20 years of oil and gas production.In our simulations,the geomechanical behavior of the sand reservoir is modeled using two models:(1)a linear elastic model(non-hysteretic stress path)that does not take into consideration irreversible deformation,and(2)a plastic cap mechanical model which considers changes in rock elastic properties due to irreversible deformations caused by plastic reservoir compaction(hysteretic stress path).It shows that the irreversible compaction of the geological layer over geologic time and during the reservoir depletion can have important consequences on stress tensor orientation and magnitude.Ignoring depletion-induced irreversible compaction can lead to an over-estimation of the calculation of the maximum working reservoir pressure.Moreover,this irreversible compaction may bring the nearby faults closer to reactivation.However,regardless of the two models applied,the geomechanical analysis shows that for the estimated stress conditions applied in this study,the Honor Rancho Underground Storage Facility is being safely operated at pressures much below what would be required to compromise the seal integrity.

Fault activation and induced seismicity in geological carbon storage--Lessons learned from recent modeling studies

In the light of current concerns related to induced seismicity associated with geological carbon sequestration(GCS),this paper summarizes lessons learned from recent modeling studies on fault activation,induced seismicity,and potential for leakage associated with deep underground carbon dioxide(CO2) injection.Model simulations demonstrate that seismic events large enough to be felt by humans require brittle fault properties and continuous fault permeability allowing pressure to be distributed over a large fault patch to be ruptured at once.Heterogeneous fault properties,which are commonly encountered in faults intersecting multilayered shale/sandstone sequences,effectively reduce the likelihood of inducing felt seismicity and also effectively impede upward CO2leakage.A number of simulations show that even a sizable seismic event that could be felt may not be capable of opening a new flow path across the entire thickness of an overlying caprock and it is very unlikely to cross a system of multiple overlying caprock units.Site-specific model simulations of the In Salah CO2storage demonstration site showed that deep fractured zone responses and associated microseismicity occurred in the brittle fractured sandstone reservoir,but at a very substantial reservoir overpressure close to the magnitude of the least principal stress.We conclude by emphasizing the importance of site investigation to characterize rock properties and if at all possible to avoid brittle rock such as proximity of crystalline basement or sites in hard and brittle sedimentary sequences that are more prone to injection-induced seismicity and permanent damage.

Interactive roles of geometrical distribution and geomechanical deformation of fracture networks in fluid flow through fractured geological media

In this study,the combined effects of geometrical distribution and geomechanical deformation of fracture networks on fluid flow through fractured geological media are investigated numerically.We consider a finite-sized model domain in which the geometry of fracture systems follows a power-law length scaling.The geomechanical response of the fractured rock is simulated using a hybrid finitediscrete element model,which can capture the deformation of intact rocks,the interaction of matrix blocks,the displacement of discrete fractures and the propagation of new cracks.Under far-field stress loading,the locally variable stress distribution in the fractured rock leads to a stress-dependent variable aperture field controlled by compression-induced closure and shear-induced dilatancy of rough fractures.The equivalent permeability of the deformed fractured rock is calculated by solving for the fracture-matrix flow considering the cubic relationship between fracture aperture and flow rate at each local fracture segment.We report that the geometrical connectivity of fracture networks plays a critical role in the hydromechanical processes in fractured rocks.A well-connected fracture system under a high stress ratio condition exhibits intense frictional sliding and large fracture dilation/opening,leading to greater rock mass permeability.However,a disconnected fracture network accommodates much less fracture shearing and opening,and has much lower bulk permeability.We further propose an analytical solution for the relationship between the equivalent permeability of fractured rocks and the connectivity metric(i.e.percolation parameter)of fracture networks,which yields an excellent match to the numerical results.We infer that fluid flow through a well-connected system is governed by traversing channels(forming an“in parallel”architecture)and thus equivalent permeability is sensitive to stress loading(due to stress-dependent fracture permeability),whilst fluid flow through a disconnected system is more ruled by matrix(linking isolated clusters“in series”)and has much less stress dependency.

Evaluation of deep learning algorithms for national scale landslide susceptibility mapping of Iran

The identification of landslide-prone areas is an essential step in landslide hazard assessment and mitigation of landslide-related losses.In this study,we applied two novel deep learning algorithms,the recurrent neural network(RNN)and convolutional neural network(CNN),for national-scale landslide susceptibility mapping of Iran.We prepared a dataset comprising 4069 historical landslide locations and 11 conditioning factors(altitude,slope degree,profile curvature,distance to river,aspect,plan curvature,distance to road,distance to fault,rainfall,geology and land-sue)to construct a geospatial database and divided the data into the training and the testing dataset.We then developed RNN and CNN algorithms to generate landslide susceptibility maps of Iran using the training dataset.We calculated the receiver operating characteristic(ROC)curve and used the area under the curve(AUC)for the quantitative evaluation of the landslide susceptibility maps using the testing dataset.Better performance in both the training and testing phases was provided by the RNN algorithm(AUC=0.88)than by the CNN algorithm(AUC=0.85).Finally,we calculated areas of susceptibility for each province and found that 6%and 14%of the land area of Iran is very highly and highly susceptible to future landslide events,respectively,with the highest susceptibility in Chaharmahal and Bakhtiari Province(33.8%).About 31%of cities of Iran are located in areas with high and very high landslide susceptibility.The results of the present study will be useful for the development of landslide hazard mitigation strategies.

Effects of change of use of land on an aquifer in a tectonically active region

This paper shows the effects caused by the combination of two factors: an anthropic factor and one natural. The leading causes of imbalance in the subsoil due to drawdown of the aquifer is reflected on the surface with the appearance of cracks on ground, then came the lateral and vertical movements called faulting. This geological phenomenon is due to a pattern of orientation is associated with a regional fault system, lateral movement is almost imperceptible but the vertical displacement becomes important because it is the most conspicuous and be responsible for the damage caused to the urban infrastructure, vertical faulting is related to the drawdown generated by intense extraction of groundwater. The demand for groundwater, increasing year by year in the past four decades because of the change in land use, the most significant change was the shift from rain feed crop to irrigated crop agriculture, this change in land use occurred on Celaya’s Valley between year period 1976-2009 was quantified by use of remote sensing and geographic information systems (GIS).

Mesh generation and optimization from digital rock fractures based on neural style transfer

The complex geometric features of subsurface fractures at different scales makes mesh generation challenging and/or expensive.In this paper,we make use of neural style transfer(NST),a machine learning technique,to generate mesh from rock fracture images.In this new approach,we use digital rock fractures at multiple scales that represent’content’and define uniformly shaped and sized triangles to represent’style’.The 19-layer convolutional neural network(CNN)learns the content from the rock image,including lower-level features(such as edges and corners)and higher-level features(such as rock,fractures,or other mineral fillings),and learns the style from the triangular grids.By optimizing the cost function to achieve approximation to represent both the content and the style,numerical meshes can be generated and optimized.We utilize the NST to generate meshes for rough fractures with asperities formed in rock,a network of fractures embedded in rock,and a sand aggregate with multiple grains.Based on the examples,we show that this new NST technique can make mesh generation and optimization much more efficient by achieving a good balance between the density of the mesh and the presentation of the geometric features.Finally,we discuss future applications of this approach and perspectives of applying machine learning to bridge the gaps between numerical modeling and experiments.

Effects of the type of forest alteration on gross nitrogen mineralization in soils of southern India

Change in land-use practices can result in major shifts in the cycling of various elements,particularly nitrogen(N),which is prone to anthropogenic perturbations.For quantifying these shifts,accurate measurements of rates of biogeochemical transformations of N are needed.We used the(^(15)N) isotope dilution technique to understand the effects of the types of forest alteration on(N) transformation rates by comparing gross N mineralization and ammonium(NH_(4)^(+)) consumption rates in soils of a managed forest,an unmanaged forest,and a rubber plantation in Kerala,India.Overall,nitrate(NO_3~-) dominated soils of the managed and unmanaged forests,whereas soils in the rubber plantation showed relatively higher NH_(4)^(+) concentration.Total N(TN) and total organic carbon(TOC) concentrations were the highest under the rubber canopy(TN:1.49±0.02 mg N g^(-1);TOC:7.96±0.86 mg C g^(-1)).In soils of all three forest types,gross N mineralization rates were higher compared to NH_(4)^(+) consumption rates.Despite high TN and TOC concentrations,the rates of gross N mineralization and NH_(4)^(+) consumption were considerably lower in the rubber plantation(mineralization:1.08±0.08 mg N kg^(-1)d^(-1);consumption:0.85±0.09 mg N kg^(-1) d^(-)) compared to the managed(mineralization:3.71±0.35 mg N kg^(-1) d^(-1);consumption:2.20±1.41 mg N kg^(-1) d^(-1)) and unmanaged(mineralization:2.20±1.07 mg N kg^(-1) d^(-1);consumption:1.39±0.27 mg N kg^(-1) d^(-1)) forests.The lower NH_(4)^(+) consumption rates in the rubber plantation led to significantly higher(p<0.05) residence time of NH_(4)^(+)(~4 days) compared to the managed and unmanaged forests(<2 days),possibly contributing to acidification of rubber soils(pH~4.8).These results together suggest that replacement of naturally grown forests with a mono-cropped plantation such as rubber negatively impact rates of N transformation processes in tropical soils and imply that change in tree species composition of naturally grown forests can adversely affect soil microbial activity.We recommend intercropping these plantations with commercial crops to maintain soil microbial diversity and biogeochemical cycling for sustainable forest management.

Eocene Crustal Thickening and Uplifting of the Tibetan Plateau:Evidence from Adakitic Volcanic Rocks

Changes in oceanic O-Sr-C isotopic compositions, global cooling and Asian continental aridification beginning in the Middle-Late Eocene(47-34 Ma) are considered to have been caused by the uplift of the Tibetan plateau.The specific timing and uplift mechanism,however,have long been subjects of debate.We investigated the Duogecuoren lavas of the central-western Qiangtang block,which form the largest outcrops among Cenozoic lavas in north-

Effects of in situ stress measurement uncertainties on assessment of predicted seismic activity and risk associated with a hypothetical industrial-scale geologic CO_2 sequestration operation

Carbon capture and storage(CCS) in geologic formations has been recognized as a promising option for reducing carbon dioxide(CO) emissions from large stationary sources.However,the pressure buildup inside the storage formation can potentially induce slip along preexisting faults,which could lead to felt seismic ground motion and also provide pathways for brine/COleakage into shallow drinking water aquifers.To assess the geomechanical stability of faults,it is of crucial importance to know the in situ state of stress.In situ stress measurements can provide some information on the stresses acting on faults but with considerable uncertainties.In this paper,we investigate how such uncertainties,as defined by the variation of stress measurements obtained within the study area,could influence the assessment of the geomechanical stability of faults and the characteristics of potential injection-induced seismic events.Our modeling study is based on a hypothetical industrial-scale carbon sequestration project assumed to be located in the Southern San Joaquin Basin in California,USA.We assess the stability on the major(25 km long) fault that bounds the sequestration site and is subjected to significant reservoir pressure changes as a result of 50 years of COinjection.We present a series of geomechanical simulations in which the resolved stresses on the fault were varied over ranges of values corresponding to various stress measurements performed around the study area.The simulation results are analyzed by a statistical approach.Our main results are that the variations in resolved stresses as defined by the range of stress measurements had a negligible effect on the prediction of the seismic risk(maximum magnitude),but an important effect on the timing,the seismicity rate(number of seismic events) and the location of seismic activity.

Ground motion parameters of Shillong plateau: One of the most seismically active zones of northeastern India

Strong ground motion parameters for Shillong plateau of northeastern India are examined. Empirical relations are obtained for main parameters of ground motions as a function of earthquake magnitude, fault type, source depth, velocity characterization of medium and distance. Correlation between ground motion parameters and characteristics of seismogenic zones are established. A new attenuation relation for peak ground acceleration is developed, which predicts higher expected PGA in the region. Parameters of strong motions, particularly the predominant periods and duration of vibrations, depend on the morphology of the studied area. The study measures low estimates of logarithmic width in Shillong plateau. The attenuation relation estimated for pulse width critically indicates increased pulse width dependence on the logarithmic distance which accounts for geometrical spreading and anelastic attenuation.

Issues and Limitations of Broad Band Remote Sensing of Kimberlite—A Case Example from Kimberlites of Dharwar Craton, India

Present study attempts to understand the potential of multispectral ASTER (Advanced space borne thermal emission and reflection radiometer) data for spatial mapping of kimberlite. Kimberlite is an economic rock known for hosting diamond. Kimberlite also has petrogenetic importance for giving us clue on the composition of lower part of the mantle. Kimberlites often contain serpentine, carbonate minerals;which have their diagnostic spectral signatures in short wave infrared (SWIR) domain. In the present study, attempt is made to delineate kimberlite from adjacent granite-granodiorite gneiss based on processing of the ASTER data as ASTER’s spectral channels can detect some of the diagnostic absorption features of kimberlites. But it has been observed that the kimberlites are difficult to be delineated by processing the ASTER data using correlative information of both sub-pixel and per-pixel mapping. Moreover, smaller spatial size of kimberlites with respect to pixel size of ASTER SWIR channels further obscures the spectral feature of kimberlite. Therefore, an attempt is also made to understand how intra pixel spectral mixing of kimberlite and granite granodiorite-gneiss modifies the diagnostic spectral feature of kimberlite. It is observed that spectral feature of kimberlites would be obscured when it is has very small spatial size (one-tenth of pixel) with respect to pixel size. Moreover, calcrete developed in the adjacent soil has identical absorption feature similar to the spectral features of kimberlites imprinted in the respective ASTER convolved spectral profiles. This also has resulted false-positives in ASTER image when we use spectral feature as a tool for spatial mapping of kimberlite. Therefore hyperspectral data with high spatial and spectral resolution is required for targeting kimberlites instead of using broad band spectral feature of kimberlites.

Mountain highway stability threading on the fragile terrain of upper Ganga catchment(Uttarakhand Himalaya),India

Roads are the most critical means of connectivity in Himalayan villages.However,the terrain is inherently fragile with varied geological,geomorphological,ecological,and climate regimes,that result in frequent slope failure and disruption in connectivity.The risk is further to be increased by extreme events-generated hazards,which are expected to rise in frequency and magnitude with ongoing intervention,however,can improve the sustainability of road networks.The present study attempts to analyse and quantify the impacts of a major road widening project initiated in 2018 in the upper Ganga catchment,Uttarakhand Himalaya which has destabilised valley slopes along the widened segments.Also,a large quantity of excavated sediments is dumped down slopes,which is posing a threat to aquatic biodiversity.The estimates are based on Google Earth imagery of a few representative road segments recently widened in the upper Ganga catchment,which indicate a substantial increase in the landslide and unstable slope area following the road widening.The increase in unstable slope area is attributed to improper road widening approaches and poor slope management in seismically active Himalayan terrain.Further,the mean velocity plots of Persistent Scatterer Interferometric Synthetic Aperture Radar(PSInSAR)indicate that the segments undergoing road widening are coherent with areas of significant earth surface change.A broad correlation between the road width and sediment yield indicates that even a slight increase in road width can result in a large-scale mass removal from the toe of the hillslope,inflicting cascading impact on hillslopes.The study recommends a more flexible road construction approach based on the environmental and geological aspects of the terrain for sustainable road networks.Further,the impact of climate change is looming over the Himalayas,and the relation between climate change and its potential effects on the stability of slopes remains an open issue.

Subsidence associated with land use changes in urban aquifers with intensive extraction

Land use change is a major factor in alterations in natural processes and cycles. Remote sensing has become an excellent tool to evaluate technological changes in land cover and land use changes over large areas, such as those occurring in the Valley of San Luis Potosi (VSLP). Here, such changes have impacted a system which is 95% dependent on the aquifer. The methodology for the present study is based on the use of satellite images for the years 1976, 1986, 1995 and 2000. To asses land use change, a supervised classification process was used with a decision tree technique and ENVI 4.3 software. The evolution of groundwater levels for the years 1977, 1986, 1995, 1998 and 2007 was also analyzed, as well as problems of subsidence and fissuring in the urban area of the valley in 2006. With the support of remote sensing, it was possible to analyze the dynamic changes in land use over large areas and highlight their impact on the environment.

Geochemical Characterization and Mineralogy of Babouri-Figuil Oil Shale,North-Cameroon

Organic geochemistry methods such as high temperature combustion, Rock-Eval pyrolysis and gas analysis were used to analyze oil shale from Babouri-Figuil Basin. Results show that the average content of organic matter is 36.25 %wt, while that of mineral matter is 63.75 %wt. The total organic carbon (TOC) is between 15.93 %wt and 26.82 %wt. The HI vs. Tmax diagram indicates an immature Type I kerogen. The average value of the oil potential (S2b) is 149.95 mg HC/g rock. The gases obtained by retort process are H2, CO2, CO and CnH2n, CnH2n+2. Finally, it emerges that, the organic matter of Babouri-Figuil shales was immature or has just reached the beginning of the oil window. The mineralogical study of Babouri-Figuil oil shale has been carried out by means of XRD (X-Ray Diffractometry) and XRF (X-Ray Fluorescence spectrometry). The results show that mineral matrix contains silica, carbonates, sulphates, oxides and clay minerals. Besides, compounds contain metals and metalloids like Fe, In, Ca. The main oxides are SiO2 (majority), CaO, Fe2O3, Al2O3, SO3, and K2O.

单畴和多畴磁铁矿合成样品的部分非磁滞剩磁研究

应用部分非磁滞剩磁(pARM)谱,对单畴和多畴亚铁磁性矿物携带的磁信息研究表明,多畴颗粒明显具有软的矫顽力谱,高于20mT的pARM可以有效地压抑多畴颗粒的信息.此外,pARM的比值,如pARM(5,10mT)/pARM(0,5mT),与单畴和多畴亚铁磁性矿物的相对含量呈正相关.因此,利用这些新参数能够快速地判断岩石或沉积物中单畴亚铁磁性矿物的相对含量,从而有助于沉积物的古气候和古地磁学研究.

An experimental investigation on acoustic emission characteristics of sandstone rockburst with different moisture contents

Rockburst occurred frequently during deep mining in China. The mechanism of rockburst is very complicated and related to many factors. In order to investigate the influence of moisture contents of rockmass on rockburst, we conducted a series of laboratory rockburst experiments of sandstone under three different moisture contents by the Modified True-Triaxial Apparatus (MTTA),in which the acoustic emission (AE) system was employed to monitor the internal damage of rock mass. A high-speed video camera was utilized to record the detail of rockburst. Based on the experimental results, the AE characteristics, such as AE count,AE energy, and AE frequency, were analyzed. The rockburst process, type, and indensity under different moisture contents were discussed. The research results show that with the increase of moisture contents, rock strength was soften, the elastic and the cumulative damage of the rock were reduced, resulting in a gradual decrease in AE cumulative counts and cumulative energy over the course of rockburst. This study provides an experimental basis and reference for better understanding to the rockburst mechanism and control.

Structural defects in MAX phases and their derivative MXenes:A look forward

MAX phases and corresponding 2 D derivative MXenes have attracted considerable interests due to not only their fascinating mechanical,physical and chemical properties but also their unique atomically laminated structures.As the most important way to tailor the materials properties,the structural defects in MAX phases and MXenes have been extensively investigated but lack of systematic survey although six reviews and two books in this field have been published.To make the defect-engineering based materials design and exploration more efficient and targeted,this paper provides a review of the recent progress on the nature of different-dimensional structural defects and their influence on the properties,in the hope of facilitating the conversion of established experiment and simulation results into practical guideline for optimizing defects in a broad range of demand-oriented materials development in the future.Also,unsolved issues on the structural defects of these scientifically and technologically important materials are also highlighted for the future study.

Partial anhysteretic remanent magnetization (pARM) of synthetic single-and multidomain magnetites and its paleoenvironmental significance

In order to isolate magnetic signals carried by single-domain (SD) ferrimagnetic (FM) minerals from multi-domain (MD) FM minerals, we developed a few pa- rameters using partial anhysteretic remanent magnetization (pARM). Because MD fraction contains only soft (easy to be demagnetized) coercivity spectrum, pARM(>20 mT) was sensitive in eliminating MD contributions. Ratio of pARM(5 mT, 10 mT)/pARM(0, 5 mT) is useful in quantifying a rela- tive abundance of mass ratio between SD and MD fractions. These new proxies can quickly characterize the details of grain size distribution of magnetic minerals in paleoclimatic and paleomagnetic studies.