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31.
32.
Explicit, approximate expressions for the resolution and a posteriori covariance of massive tomographic systems 总被引:2,自引:0,他引:2
We present an approximate method to estimate the resolution, covariance and correlation matrix for linear tomographic systems Ax = b that are too large to be solved by singular value decomposition. An explicit expression for the approximate inverse matrix A − is found using one-step backprojections on the Penrose condition AA − ≈ I , from which we calculate the statistical properties of the solution. The computation of A − can easily be parallelized, each column being constructed independently.
The method is validated on small systems for which the exact covariance can still be computed with singular value decomposition. Though A− is not accurate enough to actually compute the solution x , the qualitative agreement obtained for resolution and covariance is sufficient for many purposes, such as rough assessment of model precision or the reparametrization of the model by the grouping of correlating parameters. We present an example for the computation of the complete covariance matrix of a very large (69 043 × 9610) system with 5.9 × 106 non-zero elements in A . Computation time is proportional to the number of non-zero elements in A . If the correlation matrix is computed for the purpose of reparametrization by combining highly correlating unknowns x i , a further gain in efficiency can be obtained by neglecting the small elements in A , but a more accurate estimation of the correlation requires a full treatment of even the smaller A ij . We finally develop a formalism to compute a damped version of A − . 相似文献
The method is validated on small systems for which the exact covariance can still be computed with singular value decomposition. Though A
33.
Evolution of an early Eocene pull‐apart basin in the Central Pontides (Northern Turkey): New insights into the origin of the North Anatolian Shear Zone
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Giuseppe Ottria Luca Pandolfi Rita Catanzariti Simone Da Prato Alessandro Ellero Chiara Frassi Mehmet Cemal Göncüoğlu Michele Marroni Leonardo Ruffini Kaan Sayit 《地学学报》2017,29(6):392-400
Although the North Anatolian Shear Zone is one of the main lithospheric‐scale strike‐slip deformation zone in the world, playing a prominent role in the complex geodynamic interaction among the Eurasian, Anatolian and Arabian plates, the onset time of its activity remains highly controversial. Here, we tackle this issue by utilizing nannofossil biostratigraphy on deposits from the Ta?cilar basin, a pull‐apart basin that we have identified inside the North Anatolian Shear Zone overprinting the Intra‐Pontide suture zone. The syn‐tectonic sedimentary succession of the Ta?cilar basin developed completely during the early Eocene (Ypresian; CNE4–CNE5 Zones). The strike‐slip faulting related to the initial onset of the North Anatolian Shear Zone can likely be constrained within the Ypresian, suggesting that the westward escape of the Anatolian plate along the North Anatolian Shear Zone started in the early Eocene. 相似文献
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Raffaella De Matteis Annalisa Romeo Giuseppe Pasquale Giovanni Iannaccone Aldo Zollo 《Studia Geophysica et Geodaetica》2010,54(3):367-387
A new dataset of first P-wave arrival times is used to derive the 3D tomographic model of the Campania-Lucania region in the
southern Apennines (Italy). We address the issue related to the non-uniqueness of the tomographic inversion solution through
massive numerical experimentation based on the global exploration of the model parameter space starting from a large variety
of physically plausible initial models. The average of all the realizations is adopted as the best-fit solution and the uncertainty
of the model parameters is studied using a statistical approach based on a Monte Carlo-type analysis. How the uncertainty
in the initial model, earthquake locations, and data influences the inversion result is studied by considering separately
the individual effects. Checkerboard tests are performed to estimate the resolving power of the dataset. Re-located seismicity
in a reliable new 3D tomographic model allows us to correlate the earthquake distribution with the main seismogenic structures
present in the area. 相似文献
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Anne-Marie Weijmans Davor Krajnovi Glenn van de Ven † Tom A. Oosterloo Raffaella Morganti P. T. de Zeeuw 《Monthly notices of the Royal Astronomical Society》2008,383(4):1343-1358
We present H i observations of the elliptical galaxy NGC 2974, obtained with the Very Large Array. These observations reveal that the previously detected H i disc in this galaxy is in fact a ring. By studying the harmonic expansion of the velocity field along the ring, we constrain the elongation of the halo and find that the underlying gravitational potential is consistent with an axisymmetric shape.
We construct mass models of NGC 2974 by combining the H i rotation curve with the central kinematics of the ionized gas, obtained with the integral-field spectrograph SAURON. We introduce a new way of correcting the observed velocities of the ionized gas for asymmetric drift, and hereby disentangle the random motions of the gas caused by gravitational interaction from those caused by turbulence. To reproduce the observed flat rotation curve of the H i gas, we need to include a dark halo in our mass models. A pseudo-isothermal sphere provides the best model to fit our data, but we also tested an NFW halo and modified Newtonian dynamics, which fit the data marginally worse.
The mass-to-light ratio M / L I increases in NGC 2974 from 4.3 M⊙ /L⊙ , I at one effective radius to 8.5 M⊙ /L⊙ , I at 5 R e . This increase of M / L already suggests the presence of dark matter: we find that within 5 R e at least 55 per cent of the total mass is dark. 相似文献
We construct mass models of NGC 2974 by combining the H i rotation curve with the central kinematics of the ionized gas, obtained with the integral-field spectrograph SAURON. We introduce a new way of correcting the observed velocities of the ionized gas for asymmetric drift, and hereby disentangle the random motions of the gas caused by gravitational interaction from those caused by turbulence. To reproduce the observed flat rotation curve of the H i gas, we need to include a dark halo in our mass models. A pseudo-isothermal sphere provides the best model to fit our data, but we also tested an NFW halo and modified Newtonian dynamics, which fit the data marginally worse.
The mass-to-light ratio M / L
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Palaeomagnetic study of the El Quemado complex and Marifil formation, Patagonian Jurassic igneous province, Argentina 总被引:1,自引:0,他引:1