DESIGN AND IMPLEMENTATION OF DYNAMIC SYMBOLS IN DYNAMIC GIS

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Velocity structure of the shallow lunar crust

The data from the Apollo-14 and Apollo-16 Active Seismic Experiments have been reanalyzed and show that a power-law velocity variation with depth,v(z)110z ^1/6 m s^–1 (0<z<10 m), is consistent with both the travel times and amplitudes of the first arrivals for source-to-geophone separations up to 32 m. The data were improved by removing spurious glitches, by filtering and stacking. While this improved the signal-to-noise ratios, it was not possible to measure the arrival times or amplitudes of the first arrivals beyond 32 m. The data quality precludes a definitive distinction between the power-law velocity variation and the layered-velocity model proposed previously. However, the physical evidence that the shallow lunar regolith is made up of fine particles adds weight to the 1/6-power velocity model because this is the variation predicted theoretically for self-compacting spheres.The 1/6-power law predicts the travel time,t(x), varies with separation,x, ast(x)=t ₀(x/x ₀)^5/6 and, using a first-order theory, the amplitude,A(x), varies asA(x)=A ₀(x/x ₀)^{–(13–m)/12},m>1; the layervelocity model predictst(x)=t ₀(x/x ₀) andA(x)=A ₀(x/x ₀)^–2, respectively. The measured exponents for the arrival times were between 0.63 and 0.84 while those for the amplitudes were between –1.5 and –2.2. The large variability in the amplitude exponent is due, in part, to the coarseness with which the amplitudes are measured (only five bits are used per amplitude measurement) and the variability in geophone sensitivity and thumper-shot strengths.A least-squares analysis was devised which uses redundancy in the amplitude data to extract the geophone sensitivities, shot strengths and amplitude exponent. The method was used on the Apollo-16 ASE data and it indicates there may be as much as 30 to 40% variation in geophone sensitivities (due to siting and coupling effects) and 15 to 20% variability in the thumper-shot strengths. However, because of the low signal-to-noise ratios in the data, there is not sufficient accuracy or redundancy in the data to allow high confidence in these results.     

关于在基础设施抗震规范中规定最低设防要求的一点建议

作者针对目前我国基础设施抗震设计时遇到的问题,给出了以下建议:①根据地震作用水平,对结构不同部位、不同构件制定不同的设计目标,明确设计构件所用的强度、延性参数指标;②我国地震动区划图提供的地震动参数仅仅是中震水平(地震重现期475年),实际发生的地震可能远远超过中震水平,在基础设施设计时应对大震(罕遇地震)有所考虑,甚至应考虑超预期地震发生后的应对、应急措施;③提高最低设防水准,并非是提高一度设防,应通过确定最小地震动参数满足最低设防要求,并在地震动区划图中以地震重现期代表地震危险程度;④对于Ⅵ度以下设防地区的基础设施结构物,都应按照Ⅵ度设防标准设计并考虑采取相应的抗震措施.     

Surface Deformation and Seismic Rebound: Implications and Applications

An earthquake process includes pre-seismic stress accumulation, co-seismic rock rupture and post-seismic elastic and/or viscoelastic rebound. Although co-seismic and post-seismic deformations have been readily observed using the global positioning system (GPS), detecting pre-seismic stress accumulation hidden in time-series data remains challenging. This study applies the Hilbert–Huang transform to extract non-linear and non-stationary pre-earthquake deformation data from GPS records for central Taiwan. By converting the derived surface deformation into horizontal azimuths, the randomly oriented GPS-azimuths are reoriented in a similar direction several days before and after earthquakes due to loading and rebound stress, respectively. Analytical results demonstrate that the stress accumulation and release along the entire course of an earthquake process provide significant evidence supporting the seismic rebound theory. This finding would be applicable to areas with dense GPS networks and active plate interactions. Surface deformations detected by the proposed analytical technique have encouraging potential for mitigating future seismic hazards.     

Application of Persistent Scatterer Interferometry (PSI) in monitoring slope movements in Nainital,Uttarakhand Lesser Himalaya,India

Orogenic movements and sub-tropical climate have rendered the slopes of the Himalayan region intensely deformed and weathered. As a result, the incidences of slope failure are quite common all along the Himalayan region. The Lesser Himalayan terrane is particularly vulnerable to mass-movements owing to geological fragility, and many parts of it are bearing a high-risk of associated disaster owing to the high population density. An important step towards mitigation of such disasters is the monitoring of slope movement. Towards this, the Persistent Scatterer Interferometry (PSI) technique can be applied. In the present study, the PSI technique is employed in Lesser Himalayan town of Nainital in Uttarakhand state of India to decipher and monitor slope movements. A total of 15 multi-date ENVISAT ASAR satellite images, acquired during August 2008 to August 2010 period, were subjected to PSI, which revealed a continuous creep movement along the hillslopes located towards the eastern side of the Nainital lake. The higher reaches of the hill seem to be experiencing accelerated creep of \({\sim }21\) mm/year, which decreases downslope to \({\sim }5\) mm/year. Based on spatial pattern of varying PSI Mean LOS Velocity (MLV) values, high (H), moderate (M), low (L) and very low (S) creeping zones have been delineated in the hillslopes. Given the long history of mass movements and continuously increasing anthropogenic activities in Nainital, these results call for immediate measures to avert any future disaster in the town.     

Estimation of ecological high flow

Floods can destroy fish habitat. During a flood a fish has to seek shelters (refuges) to survive. It is necessary to know the maximum discharge that the fish can sustain against the strong current. Ecological and hydraulic engineers can simulate the flow condition of high flow for designing the refuge when restoring and enhancing the rivers are needed. Based on the average ratio of the mean and maximum velocities invariant with time, discharge and water level, this paper tries to introduce the concept of ecological high flow. The mean‐maximum velocity ratio can be used to estimate the mean velocity of the river. If the maximum velocity of the cross section is replaced by the maximum sustained swimming speeds of fish, the mean velocity of ecological high flow can be calculated with the constant ratio. The cross‐sectional area can be estimated by the gage height. Then the ecological high flow can be estimated as the product of mean velocity of ecological high flow multiplied by the cross‐sectional area. The available data of the upstream of the Dacha River where is the habitat of the Formosan landlocked salmon were used to illustrate the estimation of the ecological high flow. Any restoration project at Sonmou that try to improve the stream habitat can use the ecological high flow to design the hydraulic structure at suitable location to offer refuges for the Formosan landlocked salmon that is an endangered species in Taiwan Copyright © 2005 John Wiley & Sons, Ltd.     

Semi‐analytical solution for a slug test in partially penetrating wells including the effect of finite‐thickness skin

This paper presents a new semi‐analytical solution for a slug test in a well partially penetrating a confined aquifer, accounting for the skin effect. This solution is developed based on the solution for a constant‐flux pumping test and a formula given by Peres and co‐workers in 1989. The solution agrees with that of Cooper and co‐workers and the KGS model when the well is fully penetrating. The present solution can be applied to simulate the temporal and spatial head distributions in both the skin and formation zones. It can also be used to demonstrate the influences of skin type or skin thickness on the well water level and to estimate the hydraulic parameters of the skin and formation zones using a least‐squares approach. The results of this study indicate that the determination of hydraulic conductivity using a conventional slug‐test data analysis that neglects the presence of a skin zone will give an incorrect result if the aquifer has a skin zone. Copyright © 2008 John Wiley & Sons, Ltd.     

Investigating the impact of the Chi‐Chi earthquake on the occurrence of debris flows using artificial neural networks

Debris flows have caused enormous losses of property and human life in Taiwan during the last two decades. An efficient and reliable method for predicting the occurrence of debris flows is required. The major goal of this study is to explore the impact of the Chi‐Chi earthquake on the occurrence of debris flows by applying the artificial neural network (ANN) that takes both hydrological and geomorphologic influences into account. The Chen‐Yu‐Lan River watershed, which is located in central Taiwan, is chosen for evaluating the critical rainfall triggering debris flows. A total of 1151 data sets were collected for calibrating model parameters with two training strategies. Significant differences before and after the earthquake have been found: (1) The size of landslide area is proportioned to the occurrence of debris flows; (2) the amount of critical rainfall required for triggering debris flows has reduced significantly, about half of the original critical rainfall in the study case; and (3) the frequency of the occurrence of debris flows is largely increased. The overall accuracy of model prediction in testing phase has reached 96·5%; moreover, the accuracy of occurrence prediction is largely increased from 24 to 80% as the network trained with data from before the Chi‐Chi earthquake sets and with data from the lumped before and after the earthquake sets. The results demonstrated that the ANN is capable of learning the complex mechanism of debris flows and producing satisfactory predictions. Copyright © 2009 John Wiley & Sons, Ltd.     

A fast method of flood discharge estimation

Discharge, especially during flood periods, is among the most important information necessary for flood control, water resources planning and management. Owing to the high flood velocities, flood discharge usually cannot be measured efficiently by conventional methods, which explains why records of flood discharge are scarce or do not exist for the watersheds in Taiwan. A fast method of flood discharge estimation is presented. The greatest advantage of the proposed method is its application to estimate flood discharge that cannot be measured by conventional methods. It has as its basis the regularity of open‐channel flows, i.e. that nature maintains a constant ratio of mean to maximum velocities at a given channel section by adjusting the velocity distribution and the channel geometry. The maximum velocity at a given section can be determined easily over a single vertical profile, which tends to remain invariant with time and discharge, and can be converted to the mean velocity of the entire cross‐section by multying by the constant ratio. Therefore the mean velocity is a common multiple of maximum velocity and the mean/maximum velocity ratio. The channel cross‐sectional area can be determined from the gauge height, the water depth at the y‐axis or the product of the channel width multiplied by the water depth at the y‐axis. Then the most commonly used method, i.e. the velocity–area method, which determines discharge as the product of the cross‐sectional area multiplied by mean velocity, is applied to estimate the flood discharge. Only a few velocity measurements on the y‐axis are necessary to estimate flood discharge. Moreover the location of the y‐axis will not vary with time and water stage. Once the relationship of mean and maximum velocities is established, the flood estimation can be determined efficiently. This method avoids exposure to hazardous environments and sharply reduces the measurement time and cost. The method can be applied in both high and low flows in rivers. Available laboratory flume and stream‐flow data are used to illustrate accuracy and reliability, and results show that this method can quickly and accurately estimate flood discharges. Copyright © 2004 John Wiley & Sons, Ltd.     

对研制云南山地水土流失动态监测系统的初步尝试

采用基于3S技术的定量遥感方法，对1998年和1999年金沙江一级支流龙川江上游小流域进行了水土流失动态监测和防治决策分析。结果表明，1999年为涝年，侵蚀总量高达869008.97t，强度及其以上侵蚀级别的侵蚀量占总量的86．39％，侵蚀模数平均为7703.87t/km^2。1998年为旱年，流失情况较1999年的轻微。1999年中度及其以上侵蚀级别的侵蚀面积占流失总面积的32．41％，而1998年只占26．09％。1999年需要治理和急需治理的面积占侵蚀总面积的15．45％和0．82％，而998年的治理面积较低。本研究采用的技术在国内具有先进性和快速，准确，经济等优点，在云南山地有广阔的运用推广前景。