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61.
Yehuda Bock 《Journal of Geodesy》1983,57(1-4):294-311
The estimation of crustal deformations from repeated baseline measurements is a singular problem in the absence of prior information. One often applied solution is a free adjustment in which the singular normal matrix is augmented with a set of inner constraints. These constraints impose no net translation nor rotation for the estimated deformations X which may not be physically meaningful for a particular problem. The introduction of an available geophysical model from which an expected deformation vector \(\bar X\) and its covariance matrix \(\sum _{\bar X} \) can be computed will direct X to a physically more meaningful solution. Three possible estimators are investigated for estimating deformations from a combination of baseline measurements and geophysical models. 相似文献
62.
We present new in situ observations of systematic asymmetry in the pattern of damage expressed by fault zone rocks along sections of the San Andreas,
San Jacinto, and Punchbowl faults in southern California. The observed structural asymmetry has consistent manifestations
at a fault core scale of millimeters to meters, a fault zone scale of meters to tens of meters and related geomorphologic
features. The observed asymmetric signals are in agreement with other geological and geophysical observations of structural
asymmetry in a damage zone scale of tens to hundreds of meters. In all of those scales, more damage is found on the side of
the fault with faster seismic velocities at seismogenic depths. The observed correlation between the damage asymmetry and
local seismic velocity structure is compatible with theoretical predictions associated with preferred propagation direction
of earthquake ruptures along faults that separate different crustal blocks. The data are consistent with a preferred northwestward
propagation direction for ruptures on all three faults. If our results are supported by additional observations, asymmetry
of structural properties determined in field studies can be utilized to infer preferred propagation direction of large earthquake
ruptures along a given fault section. The property of a preferred rupture direction can explain anomalous behavior of historic
rupture events, and may have profound implications for many aspects of earthquake physics on large faults. 相似文献
63.
We analyze temporal variations of seismic velocity along the Karadere-Düzce branch of the north Anatolian fault using seismograms
generated by repeating earthquake clusters in the aftershock zones of the 1999 Mw7.4 İzmit and Mw7.1 Düzce earthquakes. The analysis employs 36 sets of highly repeating earthquakes, each containing 4–18 events. The events
in each cluster are relocated by detailed multi-step analysis and are likely to rupture approximately the same fault patch
at different times. The decay rates of the repeating events in individual clusters are compatible with the Omori's law for
the decay rate of regional aftershocks. A sliding window waveform cross-correlation technique is used to measure travel time
differences and evolving decorrelation in waveforms generated by each set of the repeating events. We find clear step-like
delays in the direct S and early S-coda waves (sharp seismic velocity reduction) immediately after the Düzce main shock, followed by gradual logarithmic-type
recoveries. A gradual increase of seismic velocities is also observed before the Düzce main shock, probably reflecting post-seismic
recovery from the earlier İzmit main shock. The temporal behavior is similar at each station for clusters at various source
locations, indicating that the temporal changes of material properties occur in the top most portion of the crust. The effects
are most prominent at stations situated in the immediate vicinity of the recently ruptured fault zones, and generally decrease
with normal distance from the fault. A strong correlation between the co-seismic delays and intensities of the strong ground
motion generated by the Düzce main shock implies that the radiated seismic waves produced the velocity reductions in the shallow
material. 相似文献
64.
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66.
Radosaw Wojtak Ewa L. okas Gary A. Mamon Stefan Gottlöber Anatoly Klypin Yehuda Hoffman 《Monthly notices of the Royal Astronomical Society》2008,388(2):815-828
We study the distribution function (DF) of dark matter particles in haloes of mass range 1014 –1015 M⊙ . In the numerical part of this work we measure the DF for a sample of relaxed haloes formed in the simulation of a standard Λ cold dark matter (ΛCDM) model. The DF is expressed as a function of energy E and the absolute value of the angular momentum L , a form suitable for comparison with theoretical models. By proper scaling we obtain the results that do not depend on the virial mass of the haloes. We demonstrate that the DF can be separated into energy and angular momentum components and propose a phenomenological model of the DF in the form . This formulation involves three parameters describing the anisotropy profile in terms of its asymptotic values (β0 and β∞ ) and the scale of transition between them ( L 0 ). The energy part f E ( E ) is obtained via inversion of the integral for spatial density. We provide a straightforward numerical scheme for this procedure as well as a simple analytical approximation for a typical halo formed in the simulation. The DF model is extensively compared with the simulations: using the model parameters obtained from fitting the anisotropy profile, we recover the DF from the simulation as well as the profiles of the dispersion and kurtosis of radial and tangential velocities. Finally, we show that our DF model reproduces the power-law behaviour of phase-space density Q =ρ( r )/σ3 ( r ) . 相似文献
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69.
Late Quaternary playa (stand-water) deposits are present in river channels upstream from dune fields in the northwestern Negev and represent a drainage disordering caused by dune migration during periods of aridity. These deposits are associated with modifications in the drainage system, including course changes and piracy, caused by dunes blocking drainage networks. Radiocarbon dates from the standing-water sediments indicate the occurrence of two periods of aridity: (1) 20,900 to 16,000 years B.P. and (2) 11,680 to 10,300 years B.P. These two periods indicate a correlation between glacial advances in Europe and dry intervals in the Near East during the Upper Pleistocene. We suggest that spatial and temporal associations between standing-water deposits, modifications in stream direction, soil formation and the dunes themselves can serve as a good indicator for the timing of dune migration. 相似文献
70.
Simulation of SH- and P-SV-wave propagation in fault zones 总被引:3,自引:0,他引:3
Seismic fault-zone (FZ) trapped waves provide a potentially high-resolution means for investigating FZ and earthquake properties. Seismic waves emitted within and travelling along low-velocity FZ layers may propagate many kilometres within the low-velocity structure associated with the fault. Waveform observation of FZ trapped waves can be modelled in terms of FZ layer velocities, thicknesses and attenuation coefficients. This can greatly improve the resolution of imaged FZ structure and microearthquake locations. At present, broad-band theoretical seismograms are restricted to plane-parallel layers of uniform properties. However, it is not clear how realistic these models are compared with actual fault structures which could, for example, flare outwards near the surface, have irregular boundaries, interior heterogeneities, etc. To address these interpretational uncertainties, we perform finite-difference simulations for irregular FZ geometries and non-uniform material properties within the layers. The accuracy of the numerical solutions are verified by comparison with the analytical solution of Ben-Zion & Aki (1990) for plane-parallel structures. Our main findings are: (1) FZs can widen at the ctustal surface only slightly modifying the trapped waves; (2) velocity variations with depth destroy trapped wave propagation at all wavelengths; (3) FZ trapped waves can be obscured by the presence of a low-velocity surface layer; (4) models with short-scale random structures suggest that trapped waves average out irregular FZ geometries, and hence can be effectively modelled by average-property plane-layered media for the observed range of wavelengths. 相似文献