Estimation of the 3D correlation structure of an alluvial aquifer from surface-based multi-frequency ground-penetrating radar reflection data     

Zhiwei Xu  James Irving  Kyle Lindsay  John Bradford  Peimin Zhu  Klaus Holliger 《Geophysical Prospecting》2020,68(2):678-689

Knowledge about the stochastic nature of heterogeneity in subsurface hydraulic properties is critical for aquifer characterization and the corresponding prediction of groundwater flow and contaminant transport. Whereas the vertical correlation structure of the heterogeneity is often well constrained by borehole information, the lateral correlation structure is generally unknown because the spacing between boreholes is too large to allow for its meaningful inference. There is, however, evidence to suggest that information on the lateral correlation structure may be extracted from the correlation statistics of the subsurface reflectivity structure imaged by surface-based ground-penetrating radar measurements. To date, case studies involving this approach have been limited to 2D profiles acquired at a single antenna centre frequency in areas with limited complementary information. As a result, the practical reliability of this methodology has been difficult to assess. Here, we extend previous work to 3D and consider reflection ground-penetrating radar data acquired using two antenna centre frequencies at the extensively explored and well-constrained Boise Hydrogeophysical Research Site. We find that the results obtained using the two ground-penetrating radar frequencies are consistent with each other, as well as with information from a number of other studies at the Boise Hydrogeophysical Research Site. In addition, contrary to previous 2D work, our results indicate that the surface-based reflection ground-penetrating radar data are not only sensitive to the aspect ratio of the underlying heterogeneity, but also, albeit to a lesser extent, to the so-called Hurst number, which is a key parameter characterizing the local variability of the fine-scale structure.  相似文献   

Characterization of sudden and sustained base flow jump hydrologic behaviour in the humid seasonal tropics of the Panama Canal Watershed     

Yanyan Cheng  Fred L. Ogden  Jianting Zhu 《水文研究》2020,34(3):569-582

Base flows are important for tropical regions with pronounced dry seasons, which are facing increasing water demands. Base flow generation, however, is one of the most challenging hydrological processes to characterize in the tropics. In many years during the May–December wet season in the Panama Canal Watershed (PCW), base flows in rivers abruptly increase. This increase persists until the start of the December–April dry season. Understanding this unusual base flow jump (BFJ) behaviour is critical to improve water provisioning in the seasonal tropics, especially during droughts and extended dry seasons. This study developed an integrated approach combining piecewise regression on cumulative average base flow and sensitivity analysis to calculate the timing and magnitude of BFJ. Rainfall, forest cover, mean land surface slope, catchment area, and estimated subsurface storage were tested as predictors for the occurrence and magnitude of the BFJs in seven subcatchments of the PCW. Sensitivity analysis on correlated predictors allowed ranking of predictor contributions due to isolated and cross-correlation effects. Correlations between observed BFJs and BFJs predicted by watershed and rainfall-related predictors were 0.92 and 0.65 for BFJ timing and magnitude, respectively. Forest cover was the second most significant predictor after cumulative rainfall for jump magnitude, owing to larger subsurface storage and groundwater recharge in forests than pastures. Catchments in the mountainous eastern PCW always generated larger jumps due to their higher rainfall and greater forest cover than the western PCW catchments. The cross-correlations between predictors contributed to more than 50% of the jump variances. The results demonstrate the importance of rainfall gradient and catchment characteristics in affecting the sudden and sustained BFJs, which can help inform land management decisions intended to enhance water supplies in the tropics. This study underscores the need for more research to further understand the hydrological processes involved in the BFJ phenomenon, including better BFJ models and field characterizations, to help improve tropical ecosystem services under a changing environment.  相似文献   

游客-环境互动视角下旅游者目的地环境恢复性效应     

朱芳  苏勤  陶云  沈惊宏 《热带地理》2020,40(4):636-648

日常生活环境和旅游目的地环境都可以为个体提供恢复的机会，不同环境的属性特征导致不同程度的恢复。为了探究环境类型与恢复性效应之间的关系及停留时间的调节作用，文章采用问卷调查方式，利用配对样本t检验和混合设计方差分析相结合的方法，探讨游客在不同环境中的恢复性效应，并对这一现象提供心理上的解释。结果表明：1）恢复体验的4个维度（放松体验、心理脱离、掌握体验、控制体验）在旅游目的地环境中的得分均高于日常生活环境。2）掌握和控制体验维度在城市旅游目的地中的变化程度高于乡村旅游目的地，两种类型目的地的放松和心理脱离维度差异较小。3）随着在目的地停留时间的延长，乡村旅游目的地放松体验和心理脱离维度变化程度高于城市旅游目的地，两种类型目的地环境恢复性效应会相互靠近。因此，游客的环境恢复性效应不仅受到环境和目的地类型的影响，同时还与游客的适应程度有关，且受到其停留时间的调节作用。  相似文献   

Analysis of city centrality based on entropy weight TOPSIS and population mobility:A case study of cities in the Yangtze River Economic Belt     

罗静  陈四云  孙璇  朱媛媛  曾菊新  陈广平 《地理学报(英文版)》2020,30(4):515-534

Based on statistical data and population flow data for 2016,and using entropy weight TOPSIS and the obstacle degree model,the centrality of cities in the Yangtze River Economic Belt(YREB)together with the factors influencing centrality were measured.In addition,data for the population flow were used to analyze the relationships between cities and to verify centrality.The results showed that:(1)The pattern of centrality conforms closely to the pole-axis theory and the central geography theory.Two axes,corresponding to the Yangtze River and the Shanghai-Kunming railway line,interconnect cities of different classes.On the whole,the downstream cities have higher centrality,well-defined gradients and better development of city infrastructure compared with cities in the middle and upper reaches.(2)The economic scale and size of the population play a fundamental role in the centrality of cities,and other factors reflect differences due to different city classes.For most of the coastal cities or the capital cities in the central and western regions,factors that require long-term development such as industrial facilities,consumption,research and education provide the main competitive advantages.For cities that are lagging behind in development,transportation facilities,construction of infrastructure and fixed asset investment have become the main methods to achieve development and enhance competitiveness.(3)The mobility of city populations has a significant correlation with the centrality score,the correlation coefficients for the relationships between population mobility and centrality are all greater than 0.86(P<0.01).The population flow is mainly between high-class cities,or high-class and low-class cities,reflecting the high centrality and huge radiating effects of high-class cities.Furthermore,the cities in the YREB are closely linked to Guangdong and Beijing,reflecting the dominant economic status of Guangdong with its geographical proximity to the YREB and Beijing's enormous influence as the national political and cultural center,respectively.  相似文献   

Influence of Stress on Void Ratios of Compacted Crushed Rock Masses in Coal Mine Gobs     

Hu  Shengyong  Han  Dandan  Feng  Guorui  Zhang  Ao  Hao  Guocai  Hu  Lanqing  Zhu  Liping  Li  Bo 《Natural Resources Research》2020,29(2):1361-1373

The transfer and evolution of stress among rock blocks directly change the void ratios of crushed rock masses and affect the flow of methane in coal mine gobs. In this study, a Lagrange framework and a discrete element method, along with the soft-sphere model and EDEM numerical software, were used. The compaction processes of rock blocks with diameters of 0.6, 0.8, and 1.0 m were simulated with the degrees of compression set at 0%, 5%, 10%, 15%, 20%, and 25%. This study examines the influence of stress on void ratios of compacted crushed rock masses in coal mine gobs. The results showed that stress was mainly transmitted downward through strong force chains. As the degree of compression increased, the strong force chains extended downward, which resulted in the stress at the upper rock mass to become significantly higher than that at the lower rock mass. It was determined that under different degrees of compression, the rock mass of coal mine gobs could be divided, from the bottom to the top, into a lower insufficient compression zone (ICZ) and an upper sufficient compression zone (SCZ). From bottom to top, the void ratios in the ICZ sharply decreased and those in the SCZ slowly decreased. Void ratios in the ICZ were 1.2–1.7 times higher than those in the SCZ.

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Seismic design of floor–wall joints of multi-storey CLT buildings to comply with regularity in elevation     

Davide Trutalli  Luca Pozza 《Bulletin of Earthquake Engineering》2018,16(1):183-201

The effects of irregularity in elevation of cross-laminated timber buildings have not been fully analysed in literature to provide useful information for the design. In this work, a number of building configurations, regular or irregular in elevation, characterized by a different arrangement per storey of the floor–wall joints have been analysed by means of non-linear dynamic analyses. Comparative results in terms of ratio between the behaviour q-factor of the investigated irregular configurations and that of reference regular ones, show that less dissipative capacity can be expected if the building is irregular due to a disequilibrium among storeys between the actual and the required strength provided by the floor–wall joints. A correlation method to estimate the behaviour q-factor for perfectly regular cross-laminated timber buildings is here presented and extended to in-elevation irregular ones. A new empirical formulation to assess the reliable corrective factor accounting for the irregularity in elevation of cross-laminated timber buildings, according to Eurocode 8 provisions, is also proposed. A final discussion about the implications of in-elevation irregularity on the building design is reported.  相似文献   

Seismic performance and damage incurred by monolithic concrete self-centering rocking walls under the effect of axial stress ratio     

Abouzar Jafari  Mohammad Reza Ghasemi  Habib Akbarzadeh Bengar  Behrooz Hassani 《Bulletin of Earthquake Engineering》2018,16(2):831-858

Self-centering rocking walls offer the possibility of minimizing repair costs and downtimes, and also nullify the residual drift after seismic events, thanks to their self-centering properties. In this paper, the effect of axial stress ratio on the behavior of monolithic self-centering rocking walls is investigated by utilizing a developed finite element model. To verify the validity of the finite element model, results and observed damage in the model are compared with those of a full-scale wall test. The axial stress ratio is varied from 0.024 to 0.30 while keeping the other structural parameters constant. For qualitative damage evaluation, the observed damage in the model compared with expected damage states of desired performance levels. In order to evaluate the incurred damage quantitatively, the amount of crushing and damage in the wall is calculated by utilizing several ratios (crushing ratio and damage ratio). Furthermore, seismic response factors (i.e., μ, R and C_d) are calculated for different axial stress ratio values. The obtained results showed that, in order to satisfy the requirements of desired performance levels, the maximum axial stress ratio should be approximately within the range of 0.10–0.15. In addition, the maximum overall damage ratio and crushing ratio are suggested to be less than 5%. For axial stress ratio higher than 0.15, the flag-shaped pattern of hysteresis curves completely disappeared and the variation of displacement ductility is less sensitive to axial stress ratio. Considering the maximum axial stress ratio limited to 0.150, values of 4 and 3.5 are conservatively proposed as a period-independent response modification factor and displacement modification factor of the investigated structural wall, respectively.  相似文献   

The 2014 Earthquake Model of the Middle East: seismogenic sources     

Laurentiu Danciu  Karin Şeşetyan  Mine Demircioglu  Levent Gülen  Mehdi Zare  Roberto Basili  Ata Elias  Shota Adamia  Nino Tsereteli  Hilal Yalçın  Murat Utkucu  Muhammad Asif Khan  Mohammad Sayab  Khaled Hessami  Andrea N. Rovida  Massimiliano Stucchi  Jean-Pierre Burg  Arkady Karakhanian  Hektor Babayan  Mher Avanesyan  Tahir Mammadli  Mahmood Al-Qaryouti  Doğan Kalafat  Otar Varazanashvili  Mustafa Erdik  Domenico Giardini 《Bulletin of Earthquake Engineering》2018,16(8):3465-3496

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Probabilistic seismic hazard assessment for South-Eastern France     

Christophe Martin  Gabriele Ameri  David Baumont  David Carbon  Gloria Senfaute  Jean-Michel Thiry  Ezio Faccioli  Jean Savy 《Bulletin of Earthquake Engineering》2018,16(6):2477-2511

The accurate evaluation and appropriate treatment of uncertainties is of primary importance in modern probabilistic seismic hazard assessment (PSHA). One of the objectives of the SIGMA project was to establish a framework to improve knowledge and data on two target regions characterized by low-to-moderate seismic activity. In this paper, for South-Eastern France, we present the final PSHA performed within the SIGMA project. A new earthquake catalogue for France covering instrumental and historical periods was used for the calculation of the magnitude-frequency distributions. The hazard model incorporates area sources, smoothed seismicity and a 3D faults model. A set of recently developed ground motion prediction equations (GMPEs) from global and regional data, evaluated as adequately representing the ground motion characteristics in the region, was used to calculate the hazard. The magnitude-frequency distributions, maximum magnitude, faults slip rate and style-of-faulting are considered as additional source of epistemic uncertainties. The hazard results for generic rock condition (Vs30 = 800 m/s) are displayed for 20 sites in terms of uniform hazard spectra at two return periods (475 years and 10,000 years). The contributions of the epistemic uncertainties in the ground motion characterizations and in the seismic source characterization to the total hazard uncertainties are analyzed. Finally, we compare the results with existing models developed at national scale in the framework of the first generation of models supporting the Eurocode 8 enforcement, (MEDD 2002 and AFPS06) and at the European scale (within the SHARE project), highlighting significant discrepancies at short return periods.  相似文献   

Assessment of the influence of horizontal diaphragms on the seismic performance of vernacular buildings     

Javier Ortega  Graça Vasconcelos  Hugo Rodrigues  Mariana Correia 《Bulletin of Earthquake Engineering》2018,16(9):3871-3904

The awareness and preservation of the vernacular heritage and traditional construction techniques and materials is crucial as a key element of cultural identity. However, vernacular architecture located in earthquake prone areas can show a particularly poor seismic performance because of inadequate construction practices resulting from economic restraints and lack of resources. The horizontal diaphragms are one of the key aspects influencing the seismic behavior of buildings because of their major role transmitting the seismic actions to the vertical resisting elements of the structure. This paper presents a numerical parametric study adopted to understand the seismic behavior and resisting mechanisms of vernacular buildings according to the type of horizontal diaphragm considered. Detailed finite element modeling and nonlinear static (pushover) analyses were used to perform the thorough parametric study aimed at the evaluation and quantification of the influence of the type of diaphragm in the seismic behavior of vernacular buildings. The reference models used for this study simulate representative rammed earth and stone masonry vernacular buildings commonly found in the South of Portugal. Therefore, this paper also contributes for a better insight of the structural behavior of vernacular earthen and stone masonry typologies under seismic loading.  相似文献