Earthquake-induced fracture displacements and transmissivity changes in a 3D fracture network of crystalline rock for spent nuclear fuel disposal

During the long service period of a nuclear waste repository in crystalline rock,large earthquake(s)may occur nearby the repository site and coseismically alter the local stress field around pre-existing fractures within the geological formation.The resulting fracture normal/shear displacements may lead to fracture opening and further promote the transport of leaked radionuclides into the groundwater system.Thus,it is of central importance to analyze the consequences of potential future earthquake(s)on the hydrogeological properties of a repository site for spent nuclear fuel disposal.Based on the detailed site characterization data of the repository site at Forsmark,Sweden,we conduct a three-dimensional(3D)seismo-hydro-mechanical simulation using the 3Dimensional Distinct Element Code(3DEC).We explicitly represent a primary seismogenic fault zone and its surrounding secondary fracture network associated with a power-law size scaling and a Fisher orientation distribution.An earthquake with a magnitude of M_(w)=5.6 caused by the reactivation of the primary fault zone is modeled by simulating its transient rupture propagating radially outwards from a predefined hypocenter at a specified rupture speed,with the faulting dynamics controlled by a strength weakening law.We model the coseismic response of the off-fault fracture network subject to both static and dynamic triggering effects.We further diagnose the distribution of fracture hydro-mechanical properties(e.g.mechanical/hydraulic aperture,hydraulic transmissivity)before and after the earthquake in order to quantify earthquakeinduced hydraulic changes in the fracture network.It is found that earthquake-induced fracture transmissivity changes tend to follow a power-law decay with the distance to the earthquake fault.Our simulation results and insights obtained have important implications for the long-term performance assessment of nuclear waste repositories in fractured crystalline rocks.

A performance-based hybrid deep learning model for predicting TBM advance rate using Attention-ResNet-LSTM

The technology of tunnel boring machine(TBM)has been widely applied for underground construction worldwide;however,how to ensure the TBM tunneling process safe and efficient remains a major concern.Advance rate is a key parameter of TBM operation and reflects the TBM-ground interaction,for which a reliable prediction helps optimize the TBM performance.Here,we develop a hybrid neural network model,called Attention-ResNet-LSTM,for accurate prediction of the TBM advance rate.A database including geological properties and TBM operational parameters from the Yangtze River Natural Gas Pipeline Project is used to train and test this deep learning model.The evolutionary polynomial regression method is adopted to aid the selection of input parameters.The results of numerical exper-iments show that our Attention-ResNet-LSTM model outperforms other commonly-used intelligent models with a lower root mean square error and a lower mean absolute percentage error.Further,parametric analyses are conducted to explore the effects of the sequence length of historical data and the model architecture on the prediction accuracy.A correlation analysis between the input and output parameters is also implemented to provide guidance for adjusting relevant TBM operational parameters.The performance of our hybrid intelligent model is demonstrated in a case study of TBM tunneling through a complex ground with variable strata.Finally,data collected from the Baimang River Tunnel Project in Shenzhen of China are used to further test the generalization of our model.The results indicate that,compared to the conventional ResNet-LSTM model,our model has a better predictive capability for scenarios with unknown datasets due to its self-adaptive characteristic.

A stable implicit nodal integration-based particle finite element method(N-PFEM)for modelling saturated soil dynamics

In this study,we present a novel nodal integration-based particle finite element method(N-PFEM)designed for the dynamic analysis of saturated soils.Our approach incorporates the nodal integration technique into a generalised Hellinger-Reissner(HR)variational principle,creating an implicit PFEM formulation.To mitigate the volumetric locking issue in low-order elements,we employ a node-based strain smoothing technique.By discretising field variables at the centre of smoothing cells,we achieve nodal integration over cells,eliminating the need for sophisticated mapping operations after re-meshing in the PFEM.We express the discretised governing equations as a min-max optimisation problem,which is further reformulated as a standard second-order cone programming(SOCP)problem.Stresses,pore water pressure,and displacements are simultaneously determined using the advanced primal-dual interior point method.Consequently,our numerical model offers improved accuracy for stresses and pore water pressure compared to the displacement-based PFEM formulation.Numerical experiments demonstrate that the N-PFEM efficiently captures both transient and long-term hydro-mechanical behaviour of saturated soils with high accuracy,obviating the need for stabilisation or regularisation techniques commonly employed in other nodal integration-based PFEM approaches.This work holds significant implications for the development of robust and accurate numerical tools for studying saturated soil dynamics.

Modelling Hydrological Consequences of Climate Change—Progress and Challenges

The simulation of hydrological consequences of climate change has received increasing attention from the hydrology and land-surface modelling communities. There have been many studies of climate-change effects on hydrology and water resources which usually consist of three steps： （1） use of general circulation models （GCMs） to provide future global climate scenarios under the effect of increasing greenhouse gases, （2） use of downscaling techniques （both nested regional climate models, RCMs, and statistical methods） for ＂downscaling＂ the GCM output to the scales compatible with hydrological models, and （3） use of hydrologic models to simulate the effects of climate change on hydrological regimes at various scales. Great progress has been achieved in all three steps during the past few years, however, large uncertainties still exist in every stage of such study. This paper first reviews the present achievements in this field and then discusses the challenges for future studies of the hydrological impacts of climate change.

Decreasing Reference Evapotranspiration in a Warming Climate-A Case of Changjiang (Yangtze) River Catchment During 1970-2000

This study deals with temporal trends in the Penman-Monteith reference evapotranspiration estimated from standard meteorological observations, observed pan evaporation, and four related meteorological variables during 1970-2000 in the Yangtze River catchment. Relative contributions of the four meteorological variables to changes in the reference evapotranspiration are quantified. The results show that both the reference evapotranspiration and the pan evaporation have significant decreasing trends in the upper, the middle as well as in the whole Changjiang （Yangtze） River catchment at the 5% significance level, while the air temperature shows a significant increasing trend. The decreasing trend detected in the reference evapotranspiration can be attributed to the significant decreasing trends in the net radiation and the wind speed.

Spatial Interpolation of Daily Precipitation in China:1951-2005

Climate research relies heavily on good quality instrumental data; for modeling efforts gridded data are needed. So far, relatively little effort has been made to create gridded climate data for China. This is especially true for high-resolution daily data. This work, focuses on identifying an accurate method to produce gridded daily precipitation in China based on the observed data at 753 stations for the period 1951-2005. Five interpolation methods, including ordinary nearest neighbor, local polynomial, radial basis function, inverse distance weighting, and ordinary kriging, have been used and compared. Cross-validation shows that the ordinary kriging based on seasonal semi-variograms gives the best performance, closely followed by the inverse distance weighting with a power of 2. Finally the ordinary kriging is chosen to interpolate the station data to a 18 km× 18 km grid system covering the whole country. Precipitation for each 0.5°×0.5° latitude-longitude block is then obtained by averaging the values at the grid nodes within the block. Owing to the higher station density in the eastern part of the country, the interpolation errors are much smaller than those in the west （west of 100°E）. Excluding 145 stations in the western region, the daily, monthly, and annual relative mean absolute errors of the interpolation for the remaining 608 stations are 74%, 29%, and 16%, respectively. The interpolated daily precipitation has been made available on the internet for the scientific community.

A sensitivity study of the WRF model in offshore wind modeling over the Baltic Sea

Accurate wind modeling is important for wind resources assessment and wind power forecasting. To improve the WRF model configuration for the offshore wind modeling over the Baltic Sea, this study performed a sensitivity study of the WRF model to multiple model configurations, including domain setup,grid resolution, sea surface temperature, land surface data, and atmosphere-wave coupling. The simulated offshore wind was evaluated against LiDAR observations under different wind directions, atmospheric stabilities, and sea status. Generally, the simulated wind profiles matched observations, despite systematic underestimations. Strengthening the forcing from the reanalysis data through reducing the number of nested domains played the largest role in improving wind modeling. Atmosphere-wave coupling further improved the simulated wind, especially under the growing and mature sea conditions.Increasing the vertical resolution, and updating the sea surface temperature and the land surface information only had a slight impact, mainly visible during very stable conditions. Increasing the horizontal resolution also only had a slight impact, most visible during unstable conditions. Our study can help to improve the wind resources assessment and wind power forecasting over the Baltic Sea.

Amplitude Variation with Offset Responses Modeling Study of Walkaway Vertical Seismic Profile Data at CO_2 Geological Storage Site,Ketzin,Germany

An important component of any CO_2 sequestration project is seismic monitoring for tracking changes in subsurface physical properties,such as velocity and density.Different reservoirs have different amplitude variation with offset(AVO) responses,which can define underground conditions. In the present paper we investigate walkaway vertical seismic profile(VSP) AVO response to CO_2 injection at the Ketzin site,the first European onshore CO_2 sequestration pilot study dealing with research on geological storage of CO_2.First,we performed rock physics analysis to evaluate the effect of injected CO_2 on seismic velocity using the Biot-Gassmann equation.On the basis of this model,the seismic response for different CO_2 injection saturation was studied using ray tracing modeling.We then created synthetic walkaway VSP data,which we then processed.In contrast,synthetic seismic traces were created from borehole data.Finally,we found that the amplitude of CO_2 injected sand layer with different gas saturations were increased with the offset when compared with the original brine target layer.This is the typical classⅢAVO anomaly for gas sand layer.The AVO responses matched the synthetic seismic traces very well.Therefore,walkaway VSP AVO response can monitor CO_2 distribution in the Ketzin area.

Local topography-induced pressure gradient effects on the wake and power output of a model wind turbine

Wind-tunnel experiments were performed to study the effect of favorable and adverse constant pressure gradients(PG)from local changes in the topography right downwind of a model wind turbine.Particle image velocimetry was used to characterize the near and intermediate wake regions.We explored five scenarios,two favorable,two adverse PG,and a case with negligible PG.Results show that the PGs induce a wake deflection and modulate the wake.They imposed a relatively small impact on the turbulence kinetic energy and kinematic shear stress but a comparatively dominant effect on the bulk flow on the flow recovery.Based on this,a simple formulation is used to describe the impact of PG on the wake.We modeled the base flow through a linearized perturbation method;the wake is obtained by solving a simplified,integrated streamwise momentum equation.This approach reasonably estimated the flow profile and PG-induced power output variations.

How far away are accurate equations of state determinations? Some issues on pressure scales and non-hydrostaticity in diamond anvil cells

The equations of state(EOSs)of materials are the cornerstone of condensed matter physics,material science,and geophysics.However,acquiring an accurate EOS in diamond anvil cell(DAC)experiments continues to prove problematic because the current lack of an accurate pressure scale with clarified sources of uncertainty makes it difficult to determine a precise pressure value at high pressure,and nonhydrostaticity affects both the volume and pressure determination.This study will discuss the advantages and drawbacks of various pressure scales,and propose an absolute pressure scale and correction methods for the effects of non-hydrostaticity.At the end of this paper,we analyze the accuracy of the determined EOS in the DAC experiments we can achieve to date.

Improved significance testing of wavelet power spectrum near data boundaries as applied to polar research

When one applies the wavelet transform to analyze finite-length time series, discontinuities at the data boundaries will distort its wavelet power spectrum in some regions which are defined as a wavelength-dependent cone of influence （COI）. In the COI, significance tests are unreliable. At the same time, as many time series are short and noisy, the COI is a serious limitation in wavelet analysis of time series. In this paper, we will give a method to reduce boundary effects and discover significant frequencies in the COI. After that, we will apply our method to analyze Greenland winter temperature and Baltic sea ice. The new method makes use of line removal and odd extension of the time series. This causes the derivative of the series to be continuous （unlike the case for other padding methods）. This will give the most reasonable padding methodology if the time series being analyzed has red noise characteristics.

长江流域径流趋势变化及突变分析

选取长江流域重要控制站宜昌、汉口和大通站,分别应用1882～2000年、1870～2000年和1950～2000年的月平均流量资料,对年代际、月径流、季节性径流的变化以及径流的变化趋势及突变进行了分析研究,并使用非参数Mann-Kendall法来检验径流的趋势变化.趋势分析表明,20世纪90年代长江流域径流呈微弱增加趋势,但不显著且地区分布不均,中上游减少,下游增加;而季节性夏季和冬季径流增加趋势明显,尤其是7月和1月径流增加最突出;更重要的是90年代汛期径流也呈现出增加趋势,汛期径流的增加在一定程度上加大了洪灾发生的可能性,这可能是导致洪灾频繁的原因之一.突变分析指出,宜昌和汉口站从1926年开始径流经历了一个明显减少的变化,这与20世纪20年代初,北半球突然变暖,长江上游地区呈现降温、降水减少趋势一致.

同构造沉积速率对先存被动盐底辟挤压变形的影响:库车坳陷西秋里塔格构造带盐构造分析及物理模拟

文中构建了两组构造物理实验,对存在先存被动盐底辟构造的含盐盆地的厚皮挤压构造演化特征进行模拟,研究揭示了库车坳陷西段秋里塔格构造带新生代盐相关构造演化过程。实验结果表明,同构造沉积速率对库车坳陷西段秋里塔格构造带博孜—却勒区域(西段)和秋里塔格—克拉苏区域(东段)盐相关构造横向分段差异变形具有重要的控制影响作用。在挤压过程中,博孜—却勒区域慢速同构造沉积使得先存被动盐底辟北翼(拜城凹陷南翼)向南逆冲到底辟南翼之上,并促使却勒盐推覆体和米斯坎塔克盐背斜形成;而秋里塔格—克拉苏区域快速同构造沉积使得先存被动盐底辟北翼快速下沉,而其南翼在挤压应力作用下向北逆冲到底辟北翼(拜城凹陷南翼)之上,形成南秋里塔格盐背斜。

变网格间距速度层析成像方法

变网格间距速度层析成像,是指反演网格模型中采用不同的网格间距反演地下地层的速度分布,它可以在观测数据较少的情况下,提高浅部地层速度反演的分辨率和深层速度反演的精度。变网格间距与规则网格间距速度层析成像方法类似,但有两个最主要的不同之处:射线正演网格单元的射线段被划分到相应的较大反演网格单元中,平滑约束方程在变网格间距界面的上一平面和下一平面的网格处需要做出适当的修改。文中首先采用变网格方法对二维和三维检测板模型进行恢复测试,反演结果对大、小异常体的刻画效果均比规则网格方法好;然后,采用变网格方法对实际资料进行走时反演,反演结果对两个低速异常区的刻画比规则网格方法的效果好。因此,变网格方法反演的速度剖面分辨率较高,尤其对浅部地层的速度成像效果具有较大的改善作用;另外,在观测数据较少的情况下,通过调整不同网格的数量比例,变网格反演方法还可以克服层析成像过程中解的欠定问题。

剥蚀及同构造沉积作用对断层活动性影响的实验模拟研究

在统计分析内陆构造地震活动的空间分布特征时，容易发现构造地震活动带主要分布在造山带内部或者其盆山耦合带，如我国天山造山带、西昆仑造山带、龙门山褶皱造山带以及伊朗扎格罗斯褶皱造山带等。这些地震频发区域具有两个明显的构造特征，一是造山带隆升往往伴随着比较强烈的区域剥蚀作用，二是盆山耦合带容易沉积巨厚的同构造沉积地层。