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91.
The Alban Hills, a Quaternary volcanic center lying west of the central Apennines, 15–25 km southeast of Rome, last erupted
19 ka and has produced approximately 290 km3 of eruptive deposits since the inception of volcanism at 580 ka. Earthquakes of moderate intensity have been generated there
at least since the Roman age. Modern observations show that intermittent periods of swarm activity originate primarily beneath
the youngest features, the phreatomagmatic craters on the west side of the volcano. Results from seismic tomography allow
identification of a low-velocity region, perhaps still hot or partially molten, more than 6 km beneath the youngest craters
and a high-velocity region, probably a solidified magma body, beneath the older central volcanic construct. Thirty centimeters
of uplift measured by releveling supports the contention that high levels of seismicity during the 1980s and 1990s resulted
from accumulation of magma beneath these craters. The volume of magma accumulation and the amount of maximum uplift was probably
at least 40×106 m3 and 40 cm, respectively. Comparison of newer levelings with those completed in 1891 and 1927 suggests earlier episodes of
uplift. The magma chamber beneath the western Alban Hills is probably responsible for much of the past 200 ka of eruptive
activity, is still receiving intermittent batches of magma, and is, therefore, continuing to generate modest levels of volcanic
unrest. Bending of overburden is the most likely cause of the persistent earthquakes, which generally have hypocenters above
the 6-km-deep top of the magma reservoir. In this view, the most recent uplift and seismicity are probably characteristic
and not precursors of more intense activity.
Received: 15 April 1997 / Accepted: 9 August 1997 相似文献
92.
本文对不同时期所建立的大地参考系进行了分析和比较,并预测了大地参考系的未来和发展以及如何满足许多有关学科在发展中提出的要求。对于不同的大地参考系之间的转换,本文就各种相似变换模型、多项式和逐次回归方程等模型及其精度进行了评述。 相似文献
93.
New solutions for the geodetic coordinate transformation 总被引:5,自引:2,他引:5
G. C. Jones 《Journal of Geodesy》2002,76(8):437-446
The Cartesian-to-geodetic-coordinate transformation is approached from a new perspective. Existence and uniqueness of geodetic
representation are presented, along with a clear geometric picture of the problem and the role of the ellipse evolute. A new
solution is found with a Newton-method iteration in the reduced latitude; this solution is proved to work for all points in
space. Care is given to error propagation when calculating the geodetic latitude and height.
Received: 9 August 2001 / Accepted: 27 March 2002
Acknowledgments. The author would like to thank the Clifford W.␣Tompson scholarship fund, Dr. Brian DeFacio, the University of Missouri College
of Arts &Sciences, and the United States Air Force. He also thanks a reviewer for suggesting and providing a prototype MATLAB
code. A MATLAB program for the iterative sequence is presented at the end of the paper (Appendix A). 相似文献
94.
The parameters of Earth free core nutation (FCN) are two relatively significant geophysical parameters. Sasao et al. (1980)
and Wahr and Bergen (1986) provided the theoretical estimation values of FCN parameters. Gwinn, Herring and Shapiro (1987)
first obtained the observational values of FCN parameters by very long base Interference (VLBI) at Cambridge University. In
the same year, Neuberg and Zürn in former West Germany and Hinderer in France began to retrieve FCN parameters by the observation
of gravity tides and introduced the stacking method. The other scholars who researched into the same geophysical problems
by applying the data of gravity tides basically followed the stacking method. The results they reached were similar to the
observational result of FCN parameters given by Neuberg et al. in 1987. But the observational results of FCN parameters gained
from gravity tides were not identical with those from VLBI, mainly because of the large difference of quality of FCN. So there
was not an affirmative observational result of FCN parameters since then. In this paper, The authors firstly introduce the
tri-frequency spectrum method with clearly geometrical and geophysical meaning for the resolution of FCN parameters, and the
observational results of FCN parameters obtained from tide data at three superconducting gravity stations were accordant with
those from VLBI, which will be relatively important to arriving at a certain observational result of FCN parameters. 相似文献
95.
The parameters of Earth free core nutation (FCN) are two relatively significant geophysical parameters. Sasao et al. (1980) and Wahr and Bergen (1986) provided the theoretical estimation values of FCN parameters. Gwinn, Herring and Shapiro (1987) first obtained the observational values of FCN parameters by very long base Interference (VLBI) at Cambridge University. In the same year, Neuberg and Zürn in former West Germany and Hinderer in France began to retrieve FCN parameters by the observation of gravity tides and introduced the stacking method. The other scholars who researched into the same geophysical problems by applying the data of gravity tides basically followed the stacking method. The results they reached were similar to the observational result of FCN parameters given by Neuberg et al. in 1987. But the observational results of FCN parameters gained from gravity tides were not identical with those from VLBI, mainly because of the large difference of quality of FCN. So there was not an affirmative observational result of FCN parameters since then. In this paper, The authors firstly introduce the tri-frequency spectrum method with clearly geometrical and geophysical meaning for the resolution of FCN parameters, and the observational results of FCN parameters obtained from tide data at three superconducting gravity stations were accordant with those from VLBI, which will be relatively important to arriving at a certain observational result of FCN parameters. 相似文献
96.
José Fernández José M. Carrasco John B. Rundle Vicente Araña 《Bulletin of Volcanology》1999,60(7):534-544
In this paper we study the application of different geodetic techniques to volcanic activity monitoring, using theoretical analysis. This methodology is very useful for obtaining an idea of the most appropriate (and efficient) monitoring method, mainly when there are no records of geodetic changes previous to volcanic activity. The analysis takes into account the crustal structure of the area, its geology, and its known volcanic activity to estimate the deformation and gravity changes that might precede eruptions. The deformation model used includes the existing gravity field and vertical changes in the crustal properties. Both factors can have a considerable effect on computed deformation and gravity changes. Topography should be considered when there is a steep slope (greater than 10°). The case study of Teide stratovolcano (Tenerife, Canary Islands), for which no deformation or gravity changes are available, is used as a test. To avoid considering topography, we worked at the lowest level of Las Cañadas and examined a smaller area than the whole caldera or island. Therefore, the results are only a first approach to the most adequate geodetic monitoring system. The methodology can also be applied to active areas where volcanic risk is not associated with a stratovolcano but instead with monogenetic scattered centers, especially when sites must be chosen in terms of detection efficiency or existing facilities. The Canary Islands provide a good example of this type of active volcanic areas, and we apply our model to the island of Lanzarote to evaluate the efficiency of the monitoring system installed at the existing geodynamic station. On this island topography is not important. The results of our study show clearly that the most appropriate geodetic volcano monitoring system is not the same for all different volcanic zones and types, and the particular properties of each volcano/zone must be taken into account when designing each system. 相似文献
97.
Precise geodesy with the Very Long Baseline Array 总被引:2,自引:2,他引:0
Leonid Petrov David Gordon John Gipson Dan MacMillan Chopo Ma Ed Fomalont R. Craig Walker Claudia Carabajal 《Journal of Geodesy》2009,83(9):859-876
We report on a program of geodetic measurements between 1994 and 2007 which used the Very Long Baseline Array (VLBA) and up
to ten globally distributed antennas. One of the goals of this program was to monitor positions of the array at a 1 mm level
of accuracy and to tie the VLBA into the international terrestrial reference frame. We describe the analysis of these data
and report several interesting geophysical results including measured station displacements due to crustal motion, earthquakes,
and antenna tilt. In terms of both formal errors and observed scatter, these sessions are among the very best geodetic very
long baseline interferometry experiments. 相似文献
98.
James D. Turner 《Journal of Geodesy》2009,83(2):139-145
The Cartesian-to-Geodetic coordinate transformation is re-cast as a minimization algorithm for the height of the Satellite
above the reference Earth surface. Optimal necessary conditions are obtained that fix the satellite ground track vector components
in the Earth surface. The introduction of an artificial perturbation variable yields a rapidly converging second order power
series solution. The initial starting guess for the solution provides 3–4 digits of precision. Convergence of the perturbation
series expansion is accelerated by replacing the series solution with a Padé approximation. For satellites with heights < 30,000 km
the second-order expansions yields ~mm satellite geodetic height errors and ~10−12 rad errors for the geodetic latitude. No quartic or cubic solutions are required: the algorithm is both non-iterative and
non-singular. Only two square root and two arc-tan calculations are required for the entire transformation. The proposed algorithm
has been measured to be ~41% faster than the celebrated Bowring method. Several numerical examples are provided to demonstrate
the effectiveness of the new algorithm. 相似文献
99.
On comparison of the Earth orientation parameters obtained from different VLBI networks and observing programs 总被引:1,自引:1,他引:0
Z. Malkin 《Journal of Geodesy》2009,83(6):547-556
In this paper, a new geometry index of very long baseline interferometry (VLBI) observing networks, the volume of network
V, is examined as an indicator of the errors in the Earth orientation parameters (EOP) obtained from VLBI observations. It
has been shown that both EOP precision and accuracy can be well described by the power law σ = aV
c
in a wide range of the network size from domestic to global VLBI networks. In other words, as the network volume grows, the
EOP errors become smaller following a power law. This should be taken into account for a proper comparison of EOP estimates
obtained from different VLBI networks. Thus, performing correct EOP comparison allows us to investigate accurately finer factors
affecting the EOP errors. In particular, it was found that the dependence of the EOP precision and accuracy on the recording
data rate can also be described by a power law. One important conclusion is that the EOP accuracy depends primarily on the
network geometry and to lesser extent on other factors, such as recording mode and data rate and scheduling parameters, whereas
these factors have a stronger impact on the EOP precision. 相似文献
100.
GPS定位技术的迅猛发展给测绘行业带来了革命性的变化,建于上世纪90年代初的厦门市首级控制网的升级换代摆上了议事日程。本文探讨厦门市三维、动态、高精度的现代大地基准建设及似大地水准面的精化。 相似文献