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131.
Petr Vaníček Mehdi Najafi Zdeněk Martinec Lars Harrie Lars E. Sjöberg 《Journal of Geodesy》1995,70(3):176-182
In this paper we formulate two corrections that have to be applied to the higher-degree reference spheroid if one wants to use it in conjunction with the Stokes-Helmert scheme for geoid determination. We show that in a precise geoid determination one has to apply the correction for the residual topographical potential and the correction for the earth ellipticity. Both these corrections may reach several decimetres; we show how their magnitudes vary within Canada and we give their global ranges. 相似文献
132.
Water Resources - Evaporation from soil surface plays a significant role in water resources management. Evaporation is an important component of hydrological cycle and is needed for most soil,... 相似文献
133.
Davoudi Nader Tavakoli Hamid Reza Zare Mehdi Jalilian Abdollah 《Natural Hazards》2020,100(3):1159-1170
Natural Hazards - Aftershock probabilistic seismic hazard analysis (APSHA) has a key role in risk management after a major earthquake. The main goal of the current study is to assess aftershock... 相似文献
134.
The effect of plastic fines on the pore pressure generation characteristics of saturated sands 总被引:2,自引:0,他引:2
Mehdi Derakhshandi Ellen M. Rathje Kenan Hazirbaba S.M. Mirhosseini 《Soil Dynamics and Earthquake Engineering》2008,28(5):376-386
Pore water pressure generation during earthquake shaking initiates liquefaction and affects the shear strength, shear stiffness, deformation, and settlement characteristics of soil deposits. The effect of plastic fines (kaolinite) on pore pressure generation in saturated sands was studied through strain-controlled cyclic triaxial tests. In addition to pore pressure generation, this experimental study also focused on evaluating the threshold shear strain for pore pressure generation and the volumetric compressibility of specimens during pore pressure dissipation. The results reveal that specimens having up to 20% plastic fines content generated larger values of pore water pressure than clean sand specimens. At 30% fines content, the excess pore water pressure decreased below that of clean sand. The threshold shear strain, which indicates the strain level above which pore pressures begin to generate, was assessed for different kaolinite–sand mixtures. The threshold shear strain was similar for 0–20% fines (γt0.006–0.008%), but increased to about 0.025% for 30% fines. The volumetric compressibility, measured after pore pressure generation, was similar for all specimens. The transition of behavior at fines contents between 20% and 30% can be attributed to a change in the soil structure from one dominated by sand grains to one dominated by fines. 相似文献
135.
An investigation on Balakot, Muzaffarabad (Pakistan) earthquake, 8 Oct. 2005, Mw 7.6; geological aspects and intensity distribution 总被引:1,自引:0,他引:1
In this paper, the investigations on seismotectonic and intensity evaluations of epicentral and meizoseismal regions in Muzaffarabad
earthquake—8 Oct. 2005, Mw 7.6—are summarized using The European Macroseismic Scale (EMS-98). The observations are compiled
based on the field investigations and isoseismal map. The results show that the isoseismals are elongated parallel to the
reactivated Muzaffarabad fault, and the attenuation is high in the direction normal to the fault compared with the direction
parallel to it. The geotechnical investigations in Muzaffarabad Valley have helped the authors to assign intensity values
in the localities where some huge landslides are observed. Finally, the empirical laws, previously developed for intensity
attenuation in Iran in EMS-98 scale, are compared with the intensity observations here. The results are roughly consistent
with the general form of attenuation laws. However, it is found that the intensity attenuations are different in the directions
normal and parallel to the fault. 相似文献
136.
Satellite gradiometry is an observation technique providing data that allow for evaluation of Stokes’ (geopotential) coefficients.
This technique is capable of determining higher degrees/orders of the geopotential coefficients than can be achieved by traditional
dynamic satellite geodesy. The satellite gradiometry data include topographic and atmospheric effects. By removing those effects,
the satellite data becomes smoother and harmonic outside sea level and therefore more suitable for downward continuation to
the Earth’s surface. For example, in this way one may determine a set of spherical harmonics of the gravity field that is
harmonic in the exterior to sea level.
This article deals with the above effects on the satellite gravity gradients in the local north-oriented frame. The conventional
expressions of the gradients in this frame have a rather complicated form, depending on the first-and second-order derivatives
of the associated Legendre functions, which contain singular factors when approaching the poles. On the contrary, we express
the harmonic series of atmospheric and topographic effects as non-singular expressions. The theory is applied to the regions
of Fennoscandia and Iran, where maps of such effects and their statistics are presented and discussed. 相似文献
137.
In this study, a scheme to estimate oceanic and hydrological effects in the GRACE (Gravity Recovery and Climate Experiment) data is presented. The aim is to reveal tectonic signals for the case of the Sumatra earthquake on 26 December 2004. The variations of hydrological and oceanic effects are estimated with the aid of data set of GRACE, altimetry, World Ocean Atlas, and the GLDAS model for a period of January 2003 to December 2006. The time series of computed gravity changes over Sumatra region show some correlations to the deformation resulting from the earthquake occurred in December 2004. The maximum and minimum impacts of hydrological and oceanic effects on gravity changes are about 3 μGal in radial direction and–5 μGal in northward direction. The maximum and minimum amounts of gravitational gradient changes after the correction are 0.2 and–0.25 mE, which indicates the significant influences of hydrological and oceanic sources on the desired signal. 相似文献
138.
Two integral transformations between the stress function, differentiation of which gives the meridian and prime vertical components of the sub-crustal stress due to mantle convection, and the satellite-to-satellite tracking (SST) data are presented in this article. In the first one, the SST data are the disturbing potential differences between twin-satellites and in the second one the line-of-sight (LOS) gravity disturbances. It is shown that the corresponding integral kernels are well-behaving and therefore suitable for inversion and recovery of the stress function from the SST data. Recovery of the stress function and the stress components is also tested in numerical experiments using simulated SST data. Numerical studies over the Himalayas show that inverting the disturbing potential differences leads to a smoother stress function than from inverting LOS gravity disturbances. Application of the presented integral formulae allows for recovery of the stress from the satellite mission GRACE and its planned successor. 相似文献
139.
Farhad Behnamfar Sayed Mehdi Taherian Arash Sahraei 《Bulletin of Earthquake Engineering》2016,14(11):3025-3046
In this study a new method for nonlinear static analysis based on the relative displacements of stories is proposed that is able to be implemented in a single stage analysis and considers the effects of an arbitrary number of higher modes. The method is called the extended drift pushover analysis procedure (EDPA). To define the lateral load pattern, values of the relative displacements of stories are calculated using the elastic modal analysis and the modal combination factors introduced. For determining the combination factors, six different approaches are examined. Buildings evaluated in this study consist of four special steel moment-resisting frames with 10–30 stories. Responses including relative displacements of stories, story shear forces and rotation of plastic hinges in each story are calculated using the proposed approaches in addition to modal pushover analysis and nonlinear dynamic time history analyses. The nonlinear dynamic analysis is implemented using ten consistent earthquake records that have been scaled with regard to ASCE7-10. Distribution of response errors of story shears and plastic hinge rotations show that a major part of error corresponds to the second half of the buildings studied. Thus, the mentioned responses are corrected systematically. The final results of this study show that implementing the EDPA procedure using the third approach of this research is able to effectively overcome the limitations of both the traditional and the modal pushover analyses methods and predict the seismic demands of tall buildings with good accuracy. 相似文献
140.
Nima Aein Najarchi Mohsen Hezaveh Seyyed Mohammad Mirhosseini Mehdi NajafiZadeh Mohammad Zeighami Ehsanollah 《Water Resources》2020,47(4):537-549
Water Resources - Combined weir-gate structure is one of the important structures which are control the water level, measure discharge and avoid sediment deposition behind the weir. In this study,... 相似文献