No 5 (2019)

ARTICLES
Estimates of the lithospheric failure cycle parameters based on regional earthquake catalogs
Smirnov V.B., Ommi S., Potanina M.G., Mikhailov V.O., Petrov A.G., Shapiro N.M., Ponomarev A.V.

Abstract

Based on the generalized magnitude-frequency relation, the failure cycle parameters are estimated from regional earthquake catalogs for the zones with different characteristic tectonic regimes: subduction and shear faults. For the subduction zones, the Kamchatka and Japan catalogs are used. The shear zones considered in the study are the San Andreas fault (Northern California catalog), North Anatolian fault (catalog for Greece), and Zagros shear zone (Iran catalog). The distribution maps for failure cycle duration and for parameter q characterizing the dependence of failure cycle duration on the size of the fracture area are constructed. It is shown that on average for each region, the q values are close to zero which indicates that the probability of fracture for structural elements of the medium does not depend on their size and that the strength and stress distributions by size of inhomogeneities are, on average, consistent with each other.

Intraregional spatial variations of parameter q exceed the statistical error of estimates, which can be interpreted as the presence of variations in stress distribution by size of inhomogeneities. The intensities of these variations estimated under the Zhurkov's kinetic fracture concept are comparable to the stresses released by the earthquakes.

Regional variations in the duration of failure cycle statistically range within approximately two orders of magnitude; the durations are inversely proportional to the region-mean velocities of relative plate motion along the fault zones. This indicates that the durations of failure cycle are mainly determined by the rates of tectonic deformations. The significant scatter in the durations of the failure cycle within regions testifies to the substantially heterogeneous intraregional distribution of the strain rates and strengths which is consistent with the up-to-date notions concerning the hierarchical structure of the geological medium and the mosaicity of the stress field.

Физика Земли. 2019;(5):3-21
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Forecasting aftershock activity: 5. Estimating the duration of hazardous period
Shebalin P.N., Baranov S.V.

Abstract

Continuing the series of publications on aftershock hazard assessment, we consider the problem of estimating the time interval after a strong earthquake that is prone to the aftershocks which may pose an independent hazard. The distribution model of this quantity is constructed which depends on three parameters of the Omori–Utsu law. With appropriate averaged parameter estimates, the model fairly closely fits the real (empirical) distributions of this quantity on the global and regional scale. A key parameter in the model is the expected number of aftershocks of a given magnitude. This number broadly varies from earthquake to earthquake which determines a wide confidence variant of the estimates based on the averaged parameters. Therefore, for forecasting the duration of the hazardous aftershock-prone period we propose to use two variants of the estimates. The first variant is based only on the averaged parameter estimates for a region under study and on the value of the magnitude of the earthquake. This variant is applicable immediately after a strong earthquake. The second variant employs information about the aftershocks that occurred during the first few hours after the earthquake, which improves the forecast considerably.

Физика Земли. 2019;(5):22-37
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Declustering of seismicity flow: statistical analysis
Pisarenko V.F., Rodkin M.V.

Abstract

The known methods for identifying the clusters of seismic events that are mainly formed by the aftershocks frequently include debatable initial assumptions or a complicated system of successive approximations. One of the most recent and the most logically consistent method for identifying the clusters of aftershocks is the nearest neighbor distance (NND) method which is however algorithmically most challenging. In this paper, we propose a new declustering method based on a generalized distance (GD) metric, which employs some assumptions of the NDD method but is as simple in practical implementation as the window methods previously proposed for this purpose. In analyzing and substantiating this new method, a procedure of random shuffling of seismic events with respect to time is used for generating a real catalog which is however free of genetic relations between different events. The efficiency of the existing window methods, the GD method, and the NND methods is compared by a number of the criteria for 17 regions. It is shown that the GD method is, on average, noticeably more efficient than the standard window methods and compares very favorably with the NND method. In the conclusions, a certain speculativeness of separating the events into main and dependent shocks is discussed.

Физика Земли. 2019;(5):38-52
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Some problems of joint inversion of temporal gravity variations with data on land and seafloor displacements: a case study of the Tohoku-Oki earthquake of march 11, 2011
Mikhailov V.O., Timoshkina E.P., Khairetdinov S.A., Dmitriev P.N., Kartashov I.M., Smirnov V.B.

Abstract

The methodology for joint inversion of various types of data on the Tohoku-Oki earthquake is presented. It is shown that data of satellite geodesy (GPS), SAR interferometry, and co-seismic GRACE gravity anomalies are overall fairly well consistent with each other. However, the resolution of these data is not high and the rupture surface model based on them is smoothed. Meanwhile, the measured and calculated data agree very well which creates the illusion that the resulting solution is close to the real process. The solution of the inverse problem based on displacements of the ocean bottom stations shows that the rupture surface models based on the measurement data on land and/or GRACE gravity anomalies alone may significantly differ from the real co-seismic displacement field. If the rupture surface is specified inaccurately, then the high quality of data fitting and the chessboard test do not guarantee high accuracy of the solution. A similar situation is also observed in estimating the degree of locking along the plate contact within locked segments of a subduction zone. In the paper it is emphasized that the accuracy of inverse problem solution mostly depends on how the geodynamic model matches the real process. For increasing the accuracy and degree of detail of the solution, the efforts need to be focused on a more adequate description of the physics of the co-seismic and post-seismic process in parallel with a more detailed description of the geological structure of a rupture area with allowance for the discontinuities of the medium and a more detailed assignment of the distribution of physical parameters.

Физика Земли. 2019;(5):53-60
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Induced deformations of fault zones
Kuzmin Y.O.

Abstract

Empirical data obtained by studying the Earth’s surface deformations in the fault zones induced by exogenous, endogenous, and manmade processes are presented. It is suggested to analyze induced deformations in the fault zones caused by different factors using a unified approach based on the notions of parametric excitation of processes. Two variants (types) of the formation of induced phenomena are considered. In the first variant, deformational response of faults occurs linearly when an influence directly causes a fault to deform. The second variant is a nonlinear parametric amplifier when the deformational response of a fault zone is anomalously high and induced (excited) by small influences.
In accordance with this approach, definitions are given of exogenously induced, endogenously induced, and technology-induced deformations of the fault zones. The examples are presented when both scenarios of process formation, e.g., exogenous and exogenously-induced surface deformations, are simultaneously observed within a single measurement system.

Физика Земли. 2019;(5):61-75
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Joint perturbation in geoacoustic emission, radon, thoron, and atmospheric electric field based on observations in Kamchatka
Rulenko O.P., Marapulets Y.V., Kuz`min Y.D., Solodchuk A.A.

Abstract

Based on the integration and analysis of the published theoretical results and field observations, the possibility is considered of a joint perturbation in geoacoustic emission, radon, thoron, and atmospheric electric field before an earthquake. A scheme is proposed for the formation of this perturbation in the presence of near-surface sedimentary rocks at the observation point and their extension. For detecting such a perturbation, simultaneous measurements of geoacoustic emission, radon, thoron, and atmospheric electric field have been carried out for the first time in Kamchatka in summer and autumn of 2012–2013, and a joint anomalous perturbation in these parameters was recorded.

Физика Земли. 2019;(5):76-86
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Studying the causes of similarity between blocking temperature spectra of chemical and thermoremanent magnetization by computer simulation
Shcherbakov V.P., Sycheva N.K.

Abstract

Monte Carlo numerical simulation of the formation of chemical remanent magnetization (CRM) by the mechanism of the growth of volumes from superparamagnetic (SPM) to single-domain (SD) in the ensembles of magnetostatically interacting particles, thermoremanent magnetization (TRM) and the experiments on paleointensity determination by the Thellier–Coe and Wilson–Burakov methods are carried out. The obtained results agree with the Smirnov–Tarduno hypothesis (Smirnov and Tarduno, 2005) that the similarity of the spectra of blocking temperatures Tb of CRM and TRM can be due to the narrowness of the interval of the blocking temperatures Tb of CRM and TRM with a reserve that the similarity can be observed on a part of the total interval of the Tb spectrum provided that this interval accommodates a significant fraction of total CRM intensity. The analytical examination of the case of non-interacting particles (sparse concentration of grains) has shown that in this case, (quasi)linearity of the Arai–Nagata diagrams is due to the presence of a plateau on the curves of the derivative dCRM/dpTRM (pTRM is partial thermoremanent magnetization) which emerges at narrow spectrum of blocking temperatures. The results of the numerical experiments suggest that at particle concentration above 0.2% magnetostatic interaction leads to the practically full linearity of the Arai–Nagata diagram over a significant interval of the total spectrum of blocking temperatures for CRM. At the same time, on the remaining temperature interval, both the Arai–Nagata diagrams and the CRM(TRM) curves are substantially concave indicating the lack of similarity between the spectra of blocking temperatures for CRM and TRM. The analysis of the empirical data revealed their certain resemblance to the results of simulation but at the same time clearly demonstrated their noticeable distinction associated with the significant differences in the conditions of the numerical and laboratory experiments.

Физика Земли. 2019;(5):87-103
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Meteotsunami manifestations in geospheres
Dolgikh S.G., Dolgikh G.I.

Abstract

The results of processing synchronous records from two laser strainmeters, a broadband seismograph, a laser nanobarograph, and a laser meter of hydrospheric pressure variations are discussed. It is established that a sharp change in the atmospheric pressure which was recorded by the laser nanobarograph resulted in the generation of solitary waves in the hydrosphere detected by the laser meter of hydrosphere pressure variations. These waves were accompanied by intense deformational perturbations with periods of about 2–2.5 min observed by the laser strainmeters and broadband seismograph. The identification of this phenomenon as a meteotsunami is supported by the subsequent arrival of powerful 1.5-h oscillations in the zone of the location of instrumental complexes, which were recorded by the laser nanobarograph and laser strainmeter.

Физика Земли. 2019;(5):104-109
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Infrasound strain perturbations caused by typhoons
Dolgikh G.I., Chupin V.A., Gusev E.S.

Abstract

The paper addresses excitation of high-power infrasound disturbances in the 7–9 Hz frequency band associated with passage of tropical cyclones (typhoons) in the zone of operation of laser strainmeters installed at Cape Shultz in Primorskii krai.

Физика Земли. 2019;(5):110-117
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Errors of Earth gravity models depending on seafloor morphology
Bekhterev S.V., Drobyshev M.N., Zheleznyak L.K., Koneshov V.N., Mikhailov P.S., Solov`ev V.N.

Abstract

The empirical results on estimating the resolution and high-frequency noise in the Earth gravity field models are presented. The Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences (IPE RAS) participated in the marine areal surveys in the Indian Ocean. Maps of ten regions with a total of 611 986 gravimetric points were obtained. The root mean square measurement error is within 0.27 mGal. The differences between the measured gravity field values and EGM2008 model predictions are calculated. The statistical processing of these differences has shown that they vary from –25 to 44 mGal on the shelf and continental slope and from –7.4 to 6.2 mGal on the abyssal plain with the root mean square value of 1.33 mGal. From the results of the experimental studies it follows that that gravity anomalies provided by the ultra-high-order gravity model can only be used for constructing gravity maps on a scale of 1:500 000 or smaller.

Физика Земли. 2019;(5):118-122
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