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Doklady Earth Sciences - Oxidation decomposition of titanomagnetite grains to the magnetite–ilmenite lattice during the formation of igneous rock can lead to thermochemical remanent... 相似文献
2.
V. P. Shcherbakov A. V. Khokhlov N. K. Sycheva 《Izvestiya Physics of the Solid Earth》2014,50(2):222-228
The results of numerical modeling of the geomagnetic secular variation by the method of the Giant Gaussian Process (GGP) are presented and compared with the information derived from the presentday databases for paleointensity. The variances of the positions of the virtual geomagnetic pole (VGP) calculated from the synthetic and experimental data (Brunhes epoch, effusive rocks) are nearly similar, which supports the validity of the theoretical model. The average value of the virtual axial geomagnetic dipole (VADM) calculated from the PINT world database on paleointensity and the Sint-2000 model is lower than VADM calculated by the GGP model; at the same time, the estimates based on the archaeomagnetic data give the VADM value slightly above the model prediction. The largest difference is observed in the variances of VADM, which is for all the three databases noticeably higher than the value calculated from the GGP model. Most probably, this is due to the contribution of the neglected measurement errors of VADM. 相似文献
3.
Dynamics of interaction between fields of seismicity and surface deformations (Bishkek geodynamic test area) 总被引：1，自引：0，他引：1
G. A. Sobolev N. A. Zakrzhevskaya K. N. Akatova V. G. Gitis A. B. Derendyaev V. D. Bragin N. A. Sycheva S. I. Kuzikov 《Izvestiya Physics of the Solid Earth》2010,46(10):817-838
The spatial-temporal dynamics of surface crustal movements revealed from GPS data is compared with seismicity in the Bishkek
geodynamic test area documented in the regional KNET catalog. The geological information system (GIS) GeoTaim 2.0 is substantially
improved, which allowed variations in seismicity and deformation fields to be analyzed in the 3D raster. It is shown that
seismicity and surface deformations are correlative in the test area. The periods with extreme values of contraction and the
extension rates of the Earth’s surface areas are accompanied by enhanced seismicity and strong earthquakes. The increase in
the spatial gradient of surface crustal movements coincides with changes in the azimuths of compression axes indicated by
mechanisms of earthquakes that occurred at depths of up to 25 km. For a better geological—geophysical interpretation of interactions
between deformation and seismicity fields in the Bishkek geodynamic test area, the spatial system GPS stations and measurement
frequency need substantial improvement. 相似文献
4.
Coagulation of particles into aggregates during their deposition in a reservoir is numerically simulated with regard for Brownian motion, Van der Waals forces, gravitation, Stokes friction, and magnetostatic interaction, and the effect of this process on the depositional magnetization (DRM) is estimated. Clusters obtained due to random aggregation of smaller clusters have a loose and branching structure. The average fractal dimension of the clusters is d = 1.83 ± 0.23. In the process of coagulation, magnetic particles do not form chains or clusters, as was supposed in a number of preceding works, but become rather uniformly distributed among nonmagnetic particles, which provides an additional argument in favor of the fact that chains of magnetite particles in marine sediments are of biogenic origin rather than a result of mutual attraction of magnetic particles due to magnetostatic interaction. The deposition process is shown to obey a kind of the principle of scale invariance: the number of clusters and their average number of particles do not change if the basin depth H and the surface concentration of initial material c 0 simultaneously change (provided that temperature and the initial particle size r are constant) in such a way that Hc 0 = const. Coagulation is the most important factor forming the bottom layer structure and the magnetization of the suspension at a relatively high concentration c 0 Typical of redeposition conditions, lakes, and shelf seas. Coagulation virtually does not influence oceanic sediments because of the smallness of c 0. 相似文献
5.
V. I. Zhuravlev A. A. Lukk K. M. Mirzoev N. A. Sycheva 《Izvestiya Physics of the Solid Earth》2006,42(11):890-903
Data on the time moments and numbers of weak earthquakes (M ≥ 0) are analyzed in five regions of Central Asia where long-term extensive instrumental observations of seismicity were conducted. Spectra of time moments of seismic events were calculated in the range of periods from 1 to 48 h with a step of half an hour. The time variations in the numbers of these earthquakes were also calculated in windows of 4 to 48 h wide with a summation step of 1 h. The presence of significant high-quality spectral extrema at periods of 24 and 12 h is established for all catalogs used, and less significant extrema at a period of 8 h are established for some catalogs. These periodicities are observed in the analysis of weak earthquakes with M < 2.2 (K < 8) and are virtually absent for stronger seismic events. It is shown that lunisolar tides have no appreciable gravitational effect on the observed variations in seismic emission. Daily variations in the actual sensitivity of the observation network due to the daytime increase in the noise level as a factor responsible for the observed diurnal periodicity raise doubts. 相似文献
6.
The global database on the paleointensity, containing determinations of the virtual dipole moment (VDM) for a stable (normal) regime of the geomagnetic field in a time interval of up to 3.5 Ga, is supplemented by new VDM determinations and analyzed. The field generation process started no later than 3–3.5 Ga (earlier data are absent) at the stage of the Earth’s core formation. Since that time, the dipole value has differed from its present value by no more than an order of magnitude, and the deviations that have already been detected tend toward smaller values. The distribution of VDM values in the time interval 0–400 Ma is bimodal, which apparently reflects the presence of two different generation levels of the geomagnetic field distinguished by a relatively large value (close to the present field value) and a relatively small value (approximately half as large as the present value). The total duration of decreased VDM values appreciably exceeds that of increased VDM values (179.1 and 28.6 Myr, respectively). On the whole, data on the paleointensity do not contradict the hypothesis about the dipole nature of the field over the last 400 Myr; however, the number of determinations at high paleolatitudes is too small to draw decisive conclusions on the validity (or invalidity) of the dipole field approximation based solely on paleointensity data. 相似文献
7.
V. P. Shcherbakov N. K. Sycheva S. K. Gribov 《Izvestiya Physics of the Solid Earth》2017,53(5):645-657
The results of the Thellier–Coe experiments on paleointensity determination on the samples which contain chemical remanent magnetization (CRM) created by thermal annealing of titanomagnetites are reported. The results of the experiments are compared with the theoretical notions. For this purpose, Monte Carlo simulation of the process of CRM acquisition in the system of single-domain interacting particles was carried out; the paleointensity determination method based on the Thellier–Coe procedure was modeled; and the degree of paleointensity underestimation was quantitatively estimated based on the experimental data and on the numerical results. Both the experimental investigations and computer modeling suggest the following main conclusion: all the Arai–Nagata diagrams for CRM in the high-temperature area (in some cases up to the Curie temperature T c) contain a relatively long quasi-linear interval on which it is possible to estimate the slope coefficient k and, therefore, the paleointensity. Hence, if chemical magnetization (or remagnetization) took place in the course of the magnetomineralogical transformations of titanomagnetite- bearing igneous rocks during long-lasting cooling or during repeated heatings, it can lead to incorrect results in determining the intensity of the geomagnetic field in the geological past. 相似文献
8.
The paper is devoted to estimating the dynamical parameters of 14 earthquakes with intermediate magnitudes (energy class 11 to 14), which occurred in the Northern Tien Shan. For obtaining the estimates of these parameters, including the stress drop, which could be then applied in crustal stress reconstruction by the technique suggested by Yu.L. Rebetsky (Schmidt Institute of Physics of the Earth, Russian Academy of Sciences), we have improved the algorithms and programs for calculating the spectra of the seismograms. The updated products allow for the site responses and spectral transformations during the propagation of seismic waves through the medium (the effect of finite Q-factor). By applying the new approach to the analysis of seismograms recorded by the seismic KNET network, we calculated the radii of the sources (Brune radius), scalar seismic moment, and stress drop (release) for the studied 14 earthquakes. The analysis revealed a scatter in the source radii and stress drop even among the earthquakes that have almost identical energy classes. The stress drop by different earthquakes ranges from one to 75 bar. We have also determined the focal mechanisms and stress regime of the Earth’s crust. It is worth noting that during the considered period, strong seismic events with energy class above 14 were absent within the segment covered by the KNET stations. 相似文献
9.
N. A. Sycheva S. L. Yunga L. M. Bogomolov V. I. Makarov 《Izvestiya Physics of the Solid Earth》2008,44(5):351-363
Seismotectonic strains (STSs) are calculated on the basis of the catalog of focal mechanisms of earthquakes including more than 5000 events compiled at the Institute of Seismology, National Academy of Sciences of the Kyrgyz Republic, in order to investigate deformation processes in the Tien Shan (38°–44°N, 68°–80°E). A modern approach to STS classification based on the identification of 11 deformation settings (including four main, two extreme, and five transitional settings) is applied for constructing STS maps. Areal distributions of the Lode-Nadai coefficient, vertical component, and angle of the stress-state type are obtained. The results of the calculations are verified by comparing them with STS calculations using focal mechanisms of 116 strong earthquakes from the centroid moment tensor catalog of Harvard University that occurred in the studied region in 1976–2003. 相似文献
10.
The work continues the study of interrelations between strong flare-induced magnetic storms and variations of seismicity. Using data on the time dependences of the parameters of seismic noise (average level and root mean squared (RMS)), recorded by stations of the KNET seismic network during monitoring of the territory of Bishkek geodynamic site (North Tien Shan). The presented results indicate the high sensitivity of the seismic noise in the frequency range of 10–20 Hz to external and, in particular, electromagnetic effects in comparison to the seismic activity. We noted the manifestations of the effects of magnetic storms that occurred after strong and super-strong solar flares in 2000–2006. These were short-term increases in the RMS of seismic noise, preceding changes in the accumulation rate of the number of events. The obtained results agree with conclusions about the interrelation between seismicity and magnetic storms. A model is suggested to describe one of the possible mechanisms by which the electromagnetic pulses and the currents induced by them in a medium devoid of piezoelectric properties influence the seismic process. 相似文献