This article aims to reveal the control rules of pre-existing faults in the Cambrian-Ordovician carbonate rocks in the Manjiaer Sag of the Tarim Basin on the development density of structural fractures,and to provide geological basis for reservoir fracture prediction and oil and gas exploration and development.This study is based on cores,FMI imaging logging and regional geological data,and uses quantitative characterization of fracture surface density,curve fitting analysis and mechanical property comparison methods to systematically analyze the control effects of fault distance,length,dip angle and mechanical properties on fracture density.The results show that the fracture surface density decays exponentially as the fault distance increases,and the fitting coefficient of determination reaches 0.999 7.The density in the near-fault area can reach up to 2.81 m-1,and the far-end area is stable at 0.96～1.03 m-1.The fracture density increases linearly with the fault length and slowly increases with the fault inclination angle.The fitting coefficients of determination are 0.999 7 and 0.9160 7 respectively,both of which are secondary control factors.There are differences in the control effects of faults with different mechanical properties.The median fracture surface densities in tension,torsion,and compression fault control areas are 2.75 m-1,2.00 m-1,and 1.30 m-1,respectively.Pre-existing faults control the spatial distribution of fracture density through stress redistribution and damage zone development,and the fault mechanical properties determine the control strength and attenuation mode.The research results can provide support for carbonate reservoir evaluation and exploration deployment in the study area.
The Late Pleistocene-Holocene transition was a pivotal interval of climate-environment reorganization.The Nihewan Basin in northern China,where more than 400 archaeological sites are distributed,provides an ideal setting for investigating prehistoric human-environment interactions.Based on 12.5 m DEM data,this study used GIS-based spatial analysis to extract environmental variables,including elevation,aspect,slope,TRI,and distance to rivers.Non-parametric tests,Cliff's Delta effect size analysis,and principal component analysis were employed to compare environmental preferences between the late stage of the Late Pleistocene and the Early-Middle Holocene and to explore the mechanisms underlying human-environment coupling.The results show that(1)occupations in both periods were concentrated at elevations of 800-1 000 m and within 2 km of rivers.In the Early-Middle Holocene,settlement preference shifted toward areas with lower surface roughness(<4),gentler slopes(<7°),and sunny aspects.(2)PCA further indicates that prehistoric human activities were mainly concentrated in areas close to water,with gentle slopes and relatively flat terrain.During the Early-Middle Holocene,the environmental adaptation range of prehistoric humans narrowed compared with that in the Late Pleistocene,and they showed a greater preference for more humid environments and lower topographic positions.(3)The habitat selection and subsistence strategies of prehistoric humans shifted from highly mobile hunter-gathering to agricultural production with a degree of sedentary settlement,providing new quantitative evidence for understanding how prehistoric populations in East Asia adapted to environmental change.
Classical travel-time tomography struggles to resolve the heterogeneity within the medium.To address this challenge,this paper proposes a tomography method based on Hamiltonian Monte Carlo(HMC)sampling.In this method,forward modeling utilizes the fast marching method(FMM),governed by the Eikonal equation.For inversion,velocity parameters are expressed as probability distributions,and samples representing these parameters are obtained by employing a Markov chain.This chain is generated from the distributions.The Markov chain is controlled by an artificial Hamiltonian system.In this system,the models are treated as high-dimensional particles.These particles advance through trajectories in the extended phase space.HMC uses the derivatives of the forward equations to enable long-distance transitions between models.This approach enhances sample independence and maintains a high acceptance rate.Results demonstrate that this tomography method can accurately invert the position and shape of velocity anomalies,as well as the heterogeneity in stochastic medium models.This method provides a novel approach for seismic tomography.It can accurately characterize subsurface structures and is valuable for seismic exploration and geophysical studies.
Electrical resistivity tomography(ERT)and seismic refraction tomography(SRT)are two important near-surface geophysical imaging methods.The resistivity is highly sensitive to factors such as water content and porosity,whereas the seismic velocity provides high-resolution imaging of layer interfaces and velocity structures.Due to the strong heterogeneity and multi-scale structural characteristics of near-surface media,as well as environmental noise and human activity interference,a single method is prone to generating multiple solutions and resulting in low imaging accuracy,making it difficult to accurately characterize complex near-surface structures.In this study,the authors propose an ERT and SRT joint inversion method based on the ensemble Kalman filter(EnKF),which enables the jointy constrained inversion of resistivity and velocity and provides uncertainty quantification results.By introducing structural consistency constraints during the inversion update process,the inversion accuracy of the resistivity and velocity models at layer interfaces and anomalous structures is improved,enhancing interface continuity.Model testing and field data from the Northeast Black Soil Test Field demonstrate that the proposed EnKF joint inversion strategy can effectively improve imaging resolution,providing a reliable framework for geophysical imaging and interpretation in complex near-surface applications.
Groundwater in basalt-covered areas primarily occurs within pore zones,cooling contraction fractures,primary joints,tectonic fractures,and weathered layers,resulting in a highly heterogeneous and discontinuous distribution pattern of the aquifers.This work investigates the groundwater system in the Changbai Mountain basalt region using electrical resistivity tomography(ERT).The study area is located in Baili Village,Longcheng Town,Helong City,Jilin Province,where three parallel survey lines of ERT were deployed.The subsurface electrical model of the study area was obtained using a smooth-constrained least-squares inversion method.The results revealed the presence of a localized shallow aquifer and a regionally developed fault zone.The regional fault zone plays a dominant role in controlling shallow groundwater migration and serves as a pathway for groundwater accumulation.The findings demonstrate that ERT is an effective tool for revealing the spatial distribution patterns of discrete groundwater in basalt-covered areas.
