关中平原地下水水位变化规律与影响因素分析

根据关中平原148个潜水监测点和116个承压水监测点近年地下水统测资料,分析潜水和承压水的地下水水位变化规律。对潜水水位变化规律按照地貌分区进行研究,对承压水变化规律按照各城市集中供水水源地进行研究。分析各区域潜水和承压水的变化规律和影响因素。研究表明:西安市城区南郊和西郊以及咸阳市水位目前处于上升趋势。承压水水位上升幅度较大,潜水也有一定幅度上升。周至户县长安南部一带由于农业发展,承压水和潜水下降幅度较大。研究结果为地下水开采和调节地下水位起到一定的指导作用。     

Dry-season vegetation mass and cover fraction from SWIR1.6 and SWIR2.1 band ratio: Ground-radiometer and MODIS data in the Sahel

The potential of the short-wave infrared (SWIR) bands to detect dry-season vegetation mass and cover fraction is investigated with ground radiometry and MODIS data, confronted to vegetation data collected in rangeland and cropland sites in the Sahel (Senegal, Niger, Mali). The ratio of the 1.6 and 2.1 μm bands (called STI) acquired with a ground radiometer proved well suited for grassland mass estimation up to 2500 kg/ha with a linear relation (r² = 0.89). A curvilinear regression is accurate for masses ranging up to 3500 kg/ha. STI proved also well suited to retrieve vegetation cover fraction in crop fields, fallows and rangelands. Such dry-season monitoring, with either ground or satellite data, has important applications for forage, erosion risk and fire risk assessment in semi-arid areas.     

Seismic analysis of laterally loaded pile under influence of vertical loading using finite element method

An efficient analytical approach using the finite element (FE) method, is proposed to calculate the bending moment and deflection response of a single pile under the combined influence of lateral and axial compressive loading during an earthquake, in both saturated and dry homogenous soil, and in a typical layered soil. Applying a pseudo-static method, seismic loads are calculated using the maximum horizontal acceleration (MHA) obtained from a seismic ground response analysis and a lateral load coefficient (a) for both liquefying and non-liquefying soils. It is observed that for a pile having l/d ratio 40 and embedded in dry dense sand, the normalized moment and displacement increase when the input motion becomes more severe, as expected. Further increasing of a from 0.1 to 0.3 leads to increase in the normalized moment and displacement from 0.033 to 0.042, and 0.009 to 0.035, respectively. The validity of the proposed FE based solution for estimating seismic response of pile is also assessed through dynamic centrifuge test results.     

多级多源控制点影像数据库建立数据分析与处理

地面控制点GCP（Ground Control Point）是表达地理空间位置的信息数据,归结为空间位置坐标、点位局部影像、点位特征描述及说明（点之记）、辅助信息。本文基于＂多级多源控制点影像数据库系统的建立研究＂课题,重点阐述多级多源控制点（GCP）的数据内容及形式、数据的获取方法、数据的组织方案及数据库的概念设计。     

A new approximation in determination of zonation boundaries of ignimbrite by ground penetrating radar: Kayseri,Central Anatolia,Turkey

Ground penetrating radar (GPR) method is used as a tool to identify the zonation boundaries in ignimbrite series through their columnar section. Ignimbrites can be classified in terms of welding degree, colour, texture and mineralogical compositions. The research area comprises a part of İncesu (Kayseri) ignimbrite at Central Anatolia, Turkey. This ignimbrite is divided into three levels and each level has clear differences in terms of macroscopic and microscopic views. This paper presents the results of an application of GPR for the determination of zonation boundary within the ignimbrite flow unit in the view of their textural and petrological features. RAMAC CU II equipment was used with 250 MHz shielded antenna on parallel ten profiles to observe the physical difference among the ignimbrite levels of the study area. Two levels out of three have been defined at the İncesu ignimbrite and supported by field geology and petrographical studies. The first level, which is extremely fractured structure, is about 1.5 m thick and matches with middle level of the İncesu ignimbrite. The second level has an average 50–75 cm thickness and matches with lower level of the ignimbrite. In this manner, vertical lithological variations should be taken into consideration during petrological investigation of the ignimbrites.     

Modeled impacts of changes in tundra snow thickness on ground thermal regime and heat flow to the atmosphere in Northernmost Alaska

Seasonal snow covers the tundra surface for up to nine months of each year on the Alaskan North Slope. Variations in the snow thickness could strongly influence the thermal regime of the underlying soil and permafrost, and the surface energy balance. The impacts of increases and decreases in the tundra snow thickness on the thermal regime of snow surface, active layer, and permafrost, and on the conductive heat flow to the atmosphere were investigated numerically, by using an improved surface energy balance approach based one-dimensional heat transfer model. The baseline inputs for the numerical model are mean daily meteorological data and surface albedos collected at Barrow, Alaska from 1995 through 1999. Based on a study for the long-term mean daily maximum and minimum snow thickness distributions at Barrow in the snow season of 1948 through 1997, a snow thickness factor was defined and five simulation cases were run for the snow season of 1997–1998 by changing the snow thickness factor. The modeled results indicate that changes in snow thickness have significant impacts on ground thermal regimes and conductive heat flow to the atmosphere. Decreasing the snow thickness by 50% led to the maximum ground temperature decrease of 1.48 °C at 0.29 m depth, and 0.72 °C at 3.0 m depth; the magnitude of the mean conductive heat flow to the atmosphere for December increase of 4.3 Wm^− 2. Increasing the snow thickness by 50% resulted in the maximum ground temperature increase of 1.44 °C at 0.29 m depth, and 0.66 °C at 3.0 m depth; the magnitude of the mean conductive heat flow to the atmosphere for December decrease of 1.57 W m^− 2. On an annual basis, variation in the snow thickness by 50%, the ground temperature variations of more than 0.25 °C occurred as deep as 8.0 m below the ground surface. The modeled results also show that changes in snow thickness have a relatively small influence on the snow surface temperature.     

About the Symmetry of the Upscaled Equivalent Transmissivity Tensor

This paper provides a proof of the symmetry of the equivalent transmissivity tensor computed with a method based on the solution of the balance equation at the fine scale with integrated finite differences. The basic hypotheses are that the balance equation is solved on a block assigning Dirichlet boundary conditions that vary linearly with the space coordinates and the equivalent transmissivity tensor is computed as the linear tensor relating average flux and hydraulic gradient.     

Stratigraphy, chronology, and sedimentology of ignimbrites from the white trachytic tuff, Roccamonfina Volcano, Italy

We describe the stratigraphy, chronology, and grain size characteristics of the white trachytic tuff (WTT) of Roccamonfina Volcano (Italy). The pyroclastic rock was emplaced between 317 and 230 Ma BP during seven major eruptive events (units A to G) and three minor events (units BC, CD, and DE). These units are separated by paleosol layers and compositionally well-differentiated pyroclastic successions. Stratigraphic control is favored by the occurrence at the base of major units of marker layers. Four WTT units (1 to 4) occur within the central caldera. These are not positively correlated with specific extracaldera units.The source of most of the WTT units was the central caldera. Units B and C were controlled by the western wall of the caldera, whereas units D and E were able to overcome this barrier, spreading symmetrically along the flanks of MC. The maximum pumice size (MP) of units increases with distance from the caldera, whereas the maximum lithic size (ML) decreases. MP and ML of the marker layer of unit D (MKDa–MKDp) do not show any systematic variations with respect to the central caldera. In contrast, the thickness of surge MKDa decreases with distance from the source, and MKDp accumulates to the north of MC probably controlled, respectively, by mobility-transport power and by wind blowing northwards.The grain size characteristics of the WTT deposits are used for classifying the units. There is no systematic variation of the grain size as a function of stratigraphic height either among units or within single units. Large variation of components in subunit E1, with repetitive alternation of pyroclastic flow to surge through fallout vs. surge deposits, suggests that the process of eruption took place in a complex or piecemeal fashion.Pumice concentration zones (PCZ) occur at all WTT levels on the volcano, but they are much thicker and pumice clasts are much larger within the central caldera. These were probably originated by the disruption of lava (flow or dome) to pumice fragments and fine ash due to sudden depressurization and interaction with lake waters of the molten lava. Local basal PCZ are, in some cases, similar to the lapilli-rich “layer 1P” that has been described elsewhere, and may have been deposited from currents transitional between pyroclastic surge and flow. Other basal PCZ formed in response to small undulations in the substrate, or can be originated by fallout. Lenticular PCZ within ignimbrite interiors and tops are interpreted to record marginal pumice levees and pumice rafts, some of which were buried by subsequant pyroclastic flows.Lithic concentration zones (LCZ) also occur at various stratigraphic height within the extracaldera ignimbrites, whereas intracaldera LCZ are absent, probably due to the fact that ignimbrite currents are strongly energetic and erosive near vent. LCZ at the top of basal inversely graded layers are formed by mechanical sieving or dispersive pressure in response to variable velocity gradients and particle concentration gradients (a segregation process). Coarse LCZ and coarse lithic breccias (LB), that reside in the interior or tops of pyroclastic flows and that occur in medial to distal areas, are interpreted to be the result of slugs of lithic-rich debris introduced by vent collapse or rockslides into the moving pyroclastic flows along their flow paths. These LCZ become mixed to varying degrees due to differential densities and velocities relative to the pyroclastic flows (desegregation processes).     

地应力观测井中元件标定及应力场计算方法

在地应力长期观测中,对井下现场标定观测元件的布设以及计算应力的相对变化是一个困难的问题。针对这个问题,提出了在钻孔内布设四个应力测量元件,而非传统三个元件的测量方法。在井下其中一个元件大体标定的情况下,对其他元件进行了相对精密标定,并给出了应力变化以及实现应力观测数据可靠性自校的计算公式。     

山西大同—阳高6.1级地震前的地电阻率异常

分析了 1989年 10月 18日山西省大同—阳高 Ms6 .1地震前 ,距震中 15 0 km的内蒙呼和浩特地震台和距震中 2 5 0 km的内蒙宝昌地震台地电阻率的异常特征 ,研究了引起地电阻率异常的可能原因 ,认为这些异常是该次地震的前兆反映。