Investigating the propagation mechanism of unmodelled systematic errors on coordinate time series estimated using least squares

The propagation of unmodelled systematic errors into coordinate time series computed using least squares is investigated, to improve the understanding of unexplained signals and apparent noise in geodetic (especially GPS) coordinate time series. Such coordinate time series are invariably based on a functional model linearised using only zero and first-order terms of a (Taylor) series expansion about the approximate coordinates of the unknown point. The effect of such truncation errors is investigated through the derivation of a generalised systematic error model for the simple case of range observations from a single known reference point to a point which is assumed to be at rest by the least squares model but is in fact in motion. The systematic error function for a one pseudo-satellite two-dimensional case, designed to be as simple but as analogous to GPS positioning as possible, is quantified. It is shown that the combination of a moving reference point and unmodelled periodic displacement at the unknown point of interest, due to ocean tide loading, for example, results in an output coordinate time series containing many periodic terms when only zero and first-order expansion terms are used in the linearisation of the functional model. The amplitude, phase and period of these terms is dependent on the input amplitude, the locations of the unknown point and reference point, and the period of the reference point's motion. The dominant output signals that arise due to truncation errors match those found in coordinate time series obtained from both simulated data and real three-dimensional GPS data.     

显式自由表面模型时间分裂格式的一个积分方案

讨论了有关显式自由表面模型的时间分裂格式中的分裂误差。在传统的积分方案中，由于采用蛙跳格式，斜压动量方程具有三层的时间离散结构，但是，正压动量方程在相应的时间层上只有二层的离散结构。因此，正压方程与斜压方程的时间离散结构是不相容的。分析结果表明，这是导致分裂误差的原因。本提出一种能保持时间离散结构相容的正压和斜压方程的时间积分方案。该积分方案的分裂误差很小因此特别适合于需要长期积分的气候研究。该方案在北太平洋的一个自由表面模型中得到了应用。     

Numerical Analysis of Space–Time Finite Element Formulations for Miscible Displacements

A finite element formulation is proposed to approximate a nonlinear system of partial differential equations, composed by an elliptic subsystem for the pressure–velocity and a transport equation (convection–diffusion) for the concentration, which models the incompressible miscible displacement of one fluid by another in a rigid porous media. The pressure is approximated by the classical Galerkin method and the velocity is calculated by a post-processing technique. Then, the concentration is obtained by a Galerkin/least-squares space–time (GLS/ST) finite element method. A numerical analysis is developed for the concentration approximation. Then, stability, convergence and numerical results are presented confirming the a priori error estimates.     

Ground truth seismic events and location capability at Degelen mountain, Kazakhstan

We utilized nuclear explosions from the Degelen Mountain sub-region of the Semipalatinsk Test Site (STS), Kazakhstan, to assess seismic location capability directly. Excellent ground truth information for these events was either known or was estimated from maps of the Degelen Mountain adit complex. Origin times were refined for events for which absolute origin time information was unknown using catalog arrival times, our ground truth location estimates, and a time baseline provided by fixing known origin times during a joint hypocenter determination (JHD). Precise arrival time picks were determined using a waveform cross-correlation process applied to the available digital data. These data were used in a JHD analysis. We found that very accurate locations were possible when high precision, waveform cross-correlation arrival times were combined with JHD. Relocation with our full digital data set resulted in a mean mislocation of 2 km and a mean 95% confidence ellipse (CE) area of 6.6 km² (90% CE: 5.1 km²), however, only 5 of the 18 computed error ellipses actually covered the associated ground truth location estimate. To test a more realistic nuclear test monitoring scenario, we applied our JHD analysis to a set of seven events (one fixed) using data only from seismic stations within 40° epicentral distance. Relocation with these data resulted in a mean mislocation of 7.4 km, with four of the 95% error ellipses covering less than 570 km² (90% CE: 438 km²), and the other two covering 1730 and 8869 km² (90% CE: 1331 and 6822 km²). Location uncertainties calculated using JHD often underestimated the true error, but a circular region with a radius equal to the mislocation covered less than 1000 km² for all events having more than three observations.     

ARTIFICIAL NEURAL NETWORK CORRECTION OF ROUGH ERRORS OF OBSERVATIONS*

In the context of tower measured radiation datasets.following the correction principle meeting a diagnostic equation in data quality control and in terms of a technique for model construction on data and ANN (artificial neural network) retrieval for BP correction of radiation measurements with rough errors available,a BP model is presented.Evidence suggests that the developed model works well and is superior to a convenient multivariate linear regression model,indicating its wide applications.     

应用VB+MapInfo开发的地震定位程序

利用OLE自动化方法，将MapInfo集成在VB中，在手工地震交切定位的基础上，开发了计算机定位程序，该程序与传统的定位方法相比，精度和效率都有较大幅度的提高。并在地震应急中发挥了作用。     

Earthquake—generating Structure Revealed by 1999 Sichuan mianzhu Earthquake Sequence with Ms=5.0

Through the accurate determination of hypocenter location,the measurement of the main focal mechanism solutions and the analyses of time dependent processes for Sichuan Mianzhu earthquake sequence with Ms=5.0 occurred along the middle segment of Longmenshan fault zone on November 30,1999,the distribution of focal depth section,the stress relase and seismicity features are given to reveal the earthquake-geneating structure of the earthquake sequence.The obtained results show the activity features for this sequence as follows:(1) There is no obvious foreshock,the accumulated strain energy releases in nearly pulse way,fluctuation of the seismic activity level is not quite evident during the duration of the sequence,and the statistical relation between the large events and the small events is less compatible with the traditional G-R estimation;(2) The epicenters of the earthquake sequence are not distributed on the main Longmenshan piedmont faults emerging out ground,but near the hidden Longmenshan piedmont faults.The direction of epicenter distribution is not very coincident with the fault strikes.The microscopic epicenters are relatively far from the macroscopic epicenters,The focal depths range from 5km to 16km;(3) The fractures of focal fault plane with the NE strike appear out the strike-slip displacement with a few overthrust components under the major principal compressive stress of NNE direction.From these,we consider it should be paid more attentions to the underground hidden faults near the ground fault zone on a large scale for their generating earthquake risk.     

河南豫北地震台网地区波速的探讨

为了解决河南豫北地区地震的定位问题 ,对豫北台网内的 10个典型地震 ,使用了 7个地震台站的资料 ,用波速比求出横波速度 ;用和达定位法 (有的同时使用高桥法 )进行了精确定位 ,求出震源深度 ;测量了震中至各台的震中距 ,以此反算出了纵波速度。通过计算 ,确定出了较为适合河南豫北地震台网地区的波速。     

Precise revision of the garnet-muscovite geothermometer

The garnet-muscovite geothermometer was refined through empirical calibration by using natural rocks metamorphosed under the physical conditions of 238—1306 MPa and 490—700℃. Input temperatures and pressures were determined through simultaneously applying the garnet-biotite geothermometer and the garnet-biotite-plagioclase-quartz barometer, assuming that all FeO in muscovite and garnet be ferrous. Garnet was treated as the asymmetric quaternary solid solution, and muscovite as the symmetric binary solid solution. Input muscovite compositions include Fe atoms between 0.03—0.19 and Mg atoms between 0.04—0.16 on the basis of 11 oxygen atoms, and input garnet compositions include spessartine fractions between 0.01—0.289, grossular fractions between 0.028—0.273, and the Fe/Mg ratio between 3.387-18.986. The resulting garnet-muscovite geothermometer reproduces temperatures within (50℃ compared with the garnet-biotite thermometer. Total random error of ±37℃ of the new thermometer may stem from the pressure uncertainty of ±200 MPa, and uncertainties of ±5% of Fe and Mg components in muscovite, and ±5% of Fe, Mg, Mn and Ca components in garnet, altogether. When there exist 10%, 20%, 30%, 40% and 50% Fe3+ in muscovite, respectively, the computed garnet-muscovite temperatures will be 1—6℃, 2—12℃, 3—16℃, 5—24℃ and 7—29℃, respectively, lower than those obtained when assuming that all FeO be ferrous. The new garnet-muscovite geothermometer can efficiently reflect temperature change of typical prograde sequences and contact aureole rocks, and may be applied to low- to high-grade and low- to high-pressure metamorphic rocks.     

The Mobile Street Food Service Practice in the Urban Economy of Kumba, Cameroon

The mobile food service practice is one of multiple survival strategies adopted by poor urban households in Cameroon to maintain and expand the base of subsistence incomes, especially in the current surge of economic crisis. Though a fast-growing informal sector enterprise, it is still at an artisanal stage in urban Cameroon, creating an urgent need for a supportive policy environment that could have measurable positive impacts on improving the productivity, welfare and income levels of the micro-entrepreneurs. This study looks at the mobile food service practice in Kumba, Cameroon, in terms of its basic characteristics, the locational factors influencing its socio-spatial distribution, the critical success factors (CSFs) determining customer choices, and its impacts on the local environmental resources and quality of urban life. The mobile food service practice creates employment, generates income, and acts as a food energy-support instrument to the urban poor and local economic activities operating in Kumba. The vendors, who are mostly women, can make incomes that are 405 per cent of the national minimum wage and, thus, contribute financially towards the education, health and survival of their families. The paper provides some recommendations on ways to improve the efficiency of this sector so as to achieve sustainable economic and social development and to enhance empowerment thereof.