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1.
In this study a new method is presented to determine model parameters from magnetic anomalies caused by dipping dikes. The proposed method is applied by employing only the even component of the anomaly. First, the maximum of the even component is divided to its value at any distance x in order to obtain S1. Then, theoretical even component values are computed for the minimal depth (h) and half-width (b) values. S2 is obtained by dividing their maximum to the value computed for the same distance x. A set of S2 values is calculated by slowly increasing the half-width, and h and b for the S2 closest to S1 are determined. The same procedure is repeated by increasing the depth. The determined b values are plotted against the corresponding values of h. After repeating the process and plotting curves for different distances, it is possible to determine the actual depth and half-width values.  相似文献   

2.
We have analyzed the behavior of the F2 layer parameters during nighttime periods of enhanced electron concentration by the results of vertical sounding of the ionosphere carried out with five-minute periodicity in Almaty (76°55′ E, 43°15′ N) in 2001–2012. The results are obtained within the frameworks of the unified concept of different types of ionospheric plasma disturbances manifested as variations in the height and half-thickness of the layer accompanied by an increase and decrease of N m F2 at the moments of maximum compression and expansion of the layer. A good correlation is found between height h Am , which corresponds to the maximum increase, and layer peak height h m F, while h Am is always less than h m F. The difference between h Am and h m F linearly increases with increasing h m F. Whereas the difference is ~38 km for h m F = 280 km, it is ~54 km for h m F = 380 km. Additionally, the correlation is good between the increase in the electron concentration in the layer maximum ΔN m and the maximum enhancement at the fixed height ΔN; the electron concentration enhancement in the layer maximum is about two to three times lower than its maximum enhancement at the fixed height.  相似文献   

3.
The celebrated Boltzmann-Gibbs (BG) entropy, S BG = ?kΣ i p i ln p i , and associated statistical mechanics are essentially based on hypotheses such as ergodicity, i.e., when ensemble averages coincide with time averages. This dynamical simplification occurs in classical systems (and quantum counterparts) whose microscopic evolution is governed by a positive largest Lyapunov exponent (LLE). Under such circumstances, relevant microscopic variables behave, from the probabilistic viewpoint, as (nearly) independent. Many phenomena exist, however, in natural, artificial and social systems (geophysics, astrophysics, biophysics, economics, and others) that violate ergodicity. To cover a (possibly) wide class of such systems, a generalization (nonextensive statistical mechanics) of the BG theory was proposed in 1988. This theory is based on nonadditive entropies such as \(S_q = k\frac{{1 - \sum\nolimits_i {p_i^q } }}{{q - 1}}\left( {S_1 = S_{BG} } \right)\). Here we comment some central aspects of this theory, and briefly review typical predictions, verifications and applications in geophysics and elsewhere, as illustrated through theoretical, experimental, observational, and computational results.  相似文献   

4.
Effects of temporally correlated infiltration on water flow in an unsaturated–saturated system were investigated. Both white noise and exponentially correlated infiltration processes were considered. The moment equations of the pressure head (ψ) were solved numerically to obtain the variance and autocorrelation functions of ψ at 14 observation points. Monte Carlo simulations were conducted to verify the numerical results and to estimate the power spectrum of ψ (S ψψ ). It was found that as the water flows through the system, the variance of the ψ (\( \sigma_{\psi }^{2} \)) were damped by the system: the deeper in the system, the smaller the \( \sigma_{\psi }^{2} \), and the larger the correlation timescale of the infiltration process (λ I ), the larger the \( \sigma_{\psi }^{2} \). The unsaturated–saturated system gradually filters out the short-term fluctuations of ψ and the damping effect is most significant in the upper part of the system. The fluctuations of ψ is non-stationary at early time and becomes stationary as time progresses: the larger the value of λ I , the longer the non-stationary period. The correlation timescale of the ψ (λ ψ ) increases with depth and approaches a constant value at depth: the larger the value of λ I , the larger the value of λ ψ . The results of the estimated S ψψ is consistent with those of the variance and autocorrelation function.  相似文献   

5.
An attempt has been made to study the behavior of nailed vertical excavations in medium dense to dense cohesionless soil under seismic conditions using a pseudo-dynamic approach. The effect of several parameters such as angle of internal friction of soil(Φ), horizontal(k_h) and vertical(k_v) earthquake acceleration coefficients, amplification factor(f_a), length of nails(L), angle of nail inclination(α) and vertical spacing of nails(S_v) on the stability of nailed vertical excavations has been explored. The limit equilibrium method along with a planar failure surface is used to derive the formulation involved with the pseudo-dynamic approach, considering axial pullout of the installed nails. A comparison of the pseudo-static and pseudo-dynamic approaches has been established in order to explore the effectiveness of the pseudo-dynamic approach over pseudo-static analysis, since most of the seismic stability studies on nailed vertical excavations are based on the latter. The results are expressed in terms of the global factor of safety(FOS). Seismic stability, i.e., the FOS of nailed vertical excavations is found to decrease with increase in the horizontal and vertical earthquake forces. The present values of FOS are compared with those available in the literature.  相似文献   

6.
Thermal waters contain small amounts of dissolved sulfides which in places precipitate at or near the earth’s surface. Knowledge of the physical chemistry of hydrothermal solutions is needed at elevated temperatures and pressures. Therefore, solubilities of the epithermal minerals cinnabar, stibnite, quartz, and orpiment in aqueousNa 2 S solutions was determined from 25–250° C, 1–2000 bars, and at severalNa 2 S concentrations. All the minerals are appreciably soluble inNa 2 S solutions. Pressure increase decreases solubilities of metallic sulfides but slightly increases quartz solubility. Temperature increase causes increased solubility at temperatures above 150° C, but at lower temperatures, cinnabar, orpiment and quartz show solubility decreases with increasing temperatures. Quartz and cinnabar are mutually soluble, but in the presence of stibnite only a small amount of cinnabar dissolves. The second ionization constant ofH 2 S as calculated from the solubility data ranges from 10?16,21 at 0°C to 10?12,59 at 250°C. TheK 2 ofH 2 S is lower according to this study than any reported before, and the variation with temperature is several orders of magnitude greater than had been predicted.  相似文献   

7.
In this study, continuous wavelet transform is applied to estimate the frequency-dependent quality factor of shear waves, Q S , in northwestern Iran. The dataset used in this study includes velocigrams of more than 50 events with magnitudes between 4.0 and 6.5, which have occurred in the study area. The CWT-based method shows a high-resolution technique for the estimation of S-wave frequency-dependent attenuation. The quality factor values are determined in the form of a power law as Q S (f)?=?(147?±?16)f 0.71?±?0.02 and (126?±?12)f 0.73?±?0.02 for vertical and horizontal components, respectively, where f is between 0.9 and 12 Hz. Furthermore, in order to verify the reliability of the suggested Q S estimator method, an additional test is performed by using accelerograms of Ahar-Varzaghan dual earthquakes on August 11, 2012, of moment magnitudes 6.4 and 6.3 and their aftershocks. Results indicate that the estimated Q S values from CWT-based method are not very sensitive to the numbers and types of waveforms used (velocity or acceleration).  相似文献   

8.
Between 2013 June and 2015 January, 35 earthquakes with local magnitude M L ranging from 1.1 to 4.2 occurred in Nógrád county, Hungary. This earthquake sequence represents above average seismic activity in the region and is the first one that was recorded by a significant number of three-component digital seismographs in the county. Using a Bayesian multiple-event location algorithm, we have estimated the hypocenters of 30 earthquakes with M L ≥1.5. The events occurred in two small regions of a few squared kilometers: one to the east of Érsekvadkert and the other at Iliny. The uncertainty of the epicenters is about 1.5–1.7 km in the E-W direction and 1.8–2.1 km in the N-S direction at the 95 % confidence level. The estimated event depths are confined to the upper 3 km of the crust. We have successfully estimated the full moment tensors of 4 M w ≥3.6 earthquakes using a probabilistic waveform inversion procedure. The non-double-couple components of the retrieved moment tensor solutions are statistically insignificant. The negligible amount of the isotropic component implies the tectonic nature of the investigated events. All of the analyzed earthquakes have strike-slip mechanism with either right-lateral slip on an approximately N-S striking or left-lateral movement on a roughly E-W striking nodal plane. The orientations of the obtained focal mechanisms are in good agreement with the main stress pattern published for the epicentral region. Both the P and T principal axes are horizontal, and the P axis is oriented along a NE-SW direction.  相似文献   

9.
In this paper changes in focal mechanisms, parameters of wave spectra, and stress drops for the M S=5.0 foreshock and M S=6.0 mainshock in February 2001 in Yajiang County, Sichuan, and seismicity in epicentral region are studied. Comparison of focal mechanisms for the Yajiang earthquakes with distribution patterns of aftershocks, the nodal plane I, striking in the direction of NEN, of the Yajiang M=5.0 event is chosen as the faulting plane; the nodal plane II, striking in the direction of WNW, of the M=6.0 event as the faulting plane. The strikes of the two faulting planes are nearly perpendicular to each other. The level of stress drops in the epicentral region before the occurrence of the M=6.0 earthquake increases, which is consistent with increase of seismicity in the epicentral region. The rate decay of the Yajiang earthquake sequence, changes in wave spectra for foreshocks and aftershocks, and focal mechanisms are complex.  相似文献   

10.
This study analyzes and compares the P- and S-wave displacement spectra from local earthquakes and explosions of similar magnitudes. We propose a new approach to discrimination between low-magnitude shallow earthquakes and explosions by using ratios of P- to S-wave corner frequencies as a criterion. We have explored 2430 digital records of the Israeli Seismic Network (ISN) from 456 local events (226 earthquakes, 230 quarry blasts, and a few underwater explosions) of magnitudes Md?=?1.4–3.4, which occurred at distances up to 250 km during 2001–2013 years. P-wave and S-wave displacement spectra were computed for all events following Brune’s source model of earthquakes (1970, 1971) and applying the distance correction coefficients (Shapira and Hofstetter, Teconophysics 217:217–226, 1993; Ataeva G, Shapira A, Hofstetter A, J Seismol 19:389-401, 2015), The corner frequencies and moment magnitudes were determined using multiple stations for each event, and then the comparative analysis was performed.The analysis showed that both P-wave and especially S-wave displacement spectra of quarry blasts demonstrate the corner frequencies lower than those obtained from earthquakes of similar magnitudes. A clear separation between earthquake and explosion populations was obtained for ratios of P- to S-wave corner frequency f 0(P)/f 0(S). The ratios were computed for each event with corner frequencies f 0 of P- and S-wave, which were obtained from the measured f 0 I at individual stations, then corrected for distance and finally averaged. We obtained empirically the average estimation of f 0(P)/f 0(S)?=?1.23 for all used earthquakes, and 1.86 for all explosions. We found that the difference in the ratios can be an effective discrimination parameter which does not depend on estimated moment magnitude M w .The new multi-station Corner Frequency Discriminant (CFD) for earthquakes and explosions in Israel was developed based on ratios P- to S-wave corner frequencies f 0(P)/f 0(S), with the empirical threshold value of the ratio for Israel as 1.48.  相似文献   

11.
A semiempirical mathematical model of iron and manganese migration from bottom sediments into the water mass of water bodies has been proposed based on some basic regularities in the geochemistry of those elements. The entry of dissolved forms of iron and manganese under aeration conditions is assumed negligible. When dissolved-oxygen concentration is <0.5 mg/L, the elements start releasing from bottom sediments, their release rate reaching its maximum under anoxic conditions. The fluxes of dissolved iron and manganese (Me) from bottom sediments into the water mass (J Me) are governed by the gradients of their concentrations in diffusion water sublayer adjacent to sediment surface and having an average thickness of h = 0.025 cm: \({J_{Me}} = - {D_{Me}}\frac{{{C_{Me\left( {ss} \right)}} - {C_{Me\left( w \right)}}}}{h}\) (D Me ≈ 1 × 10–9 m2/s is molecular diffusion coefficient of component Me in solution; C Me(ss) and C Me(w) ≈ 0 are Me concentrations on sediment surface, i.e., on the bottom boundary of the diffusion water sublayer, and in the water mass, i.e., on the upper boundary of the diffusion water sublayer). The value of depends on water saturation with dissolved oxygen (\({\eta _{{O_2}}}\)) in accordance with the empiric relationship \({C_{Me\left( {ss} \right)}} = \frac{{C_{_{Me\left( {ss} \right)}}^{\max }}}{{1 + k{\eta _{{O_2}}}}}\) (k is a constant factor equal to 300 for iron and 100 for manganese; C Me(ss) max is the maximal concentration of Me on the bottom boundary of the diffusion water sublayer with C Fe(ss) max ≈ 200 μM (11 mg/L), and C Mn(ss) max ≈ 100 μM (5.5 mg/L).  相似文献   

12.
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13.
The Q-factor estimates of the Earth’s crust and upper mantle as the functions of frequency (Q(f)) are obtained for the seismic S-waves at frequencies up to ~35 Hz. The estimates are based on the data for ~40 earthquakes recorded by the Kislovodsk seismic station since 2000. The magnitudes of these events are MW > 3.8, the sources are located in the depth interval from 1 to 165 km, and the epicentral distances range from ~100 to 300 km. The Q-factor estimates are obtained by the methods developed by Aki and Rautian et al., which employ the suppression of the effects of the source radiation spectrum and local site responses in the S-wave spectra by the coda waves measured at a fixed lapse time (time from the first arrival). The radiation pattern effects are cancelled by averaging over many events whose sources are distributed in a wide azimuthal sector centered at the receiving site. The geometrical spreading was specified in the form of a piecewise-continuous function of distance which behaves as 1/R at the distances from 1 to 50 km from the source, has a plateau at 1/50 in the interval from 50–70 km to 130–150 km, and decays as \({\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 {\sqrt R }}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${\sqrt R }$}}\) beyond 130–150 km. For this geometrical spreading model and some of its modifications, the following Q-factor estimates are obtained: Q(f) ~ 85f0.9 at the frequencies ranging from ~1 to 20 Hz and Q(f) ~ 75f1.0 at the frequencies ranging from ~1 to 35 Hz.  相似文献   

14.
The reaction of the lower ionosphere to the solar proton events that occurred in 2011–2012 is studied in this paper based on the results of measurements of the propagation velocity and the E z /H τ ratio of the low-frequency electromagnetic pulses (atmospherics) in the ELF range at the high-latitude observatories Lovozero and Barentsburg. With numerical modeling methods, it is shown that horizontal local irregularities of the lower ionosphere conductivity profile could be a cause of the splashes in the E z /H τ ratio observed in the experiment during the solar proton event of March 7, 2012, which was a unique event in both the proton flux value and energy.  相似文献   

15.
We made an attempt to assess the shear wave velocity values V S and, to a lesser extent, the V P values from ambient noise recordings in an array configuration. Five array sites were situated in the close proximity to borehole sites. Shear wave velocity profiles were modeled at these five array sites with the aid of two computational techniques, viz. spatial autocorrelation (SPAC) and H/V ellipticity. Out of these five array sites, velocity estimates could be reliably inferred at three locations. The shear wave velocities estimated by these methods are found to be quite consistent with each other. The computed V S values up to 30 m depth are in the range from 275 to 375 m/s in most of the sites, which implies prevalence of a low velocity zone at some pocket areas. The results were corroborated by evidence of site geology as well as geotechnical information.  相似文献   

16.
Aftershock sequences of some strong earthquakes of Kamchatka, the Kurile Islands, and Japan are examined. Such source parameters as the length L, along-dip width W, motion on fault D, and stress drop Δσ are determined from the aftershock sequences considered. The values of these parameters were obtained by the formal estimation of linear source parameters (lower bound estimates) and visually (upper bound estimates). The correlation dependences of the obtained parameters on the surface wave (M S ) and seismic moment (M W ) magnitudes are calculated.  相似文献   

17.
Theory of wave boundary layers (WBLs) developed by Reznik (J Mar Res 71: 253–288, 2013, J Fluid Mech 747: 605–634, 2014, J Fluid Mech 833: 512–537, 2017) is extended to a rotating stratified fluid. In this case, the WBLs arise in the field of near-inertial oscillations (NIOs) driven by a tangential wind stress of finite duration. Near-surface Ekman layer is specified in the most general form; tangential stresses are zero at the lower boundary of Ekman layer and viscosity is neglected below the boundary. After the wind ceases, the Ekman pumping at the boundary becomes a linear superposition of inertial oscillations with coefficients dependent on the horizontal coordinates. The solution under the Ekman layer is obtained in the form of expansions in the vertical wave modes. We separate from the solution a part representing NIO and demonstrate development of a WBL near the Ekman layer boundary. With increasing time t, the WBL width decays inversely proportional to \( \sqrt{t} \) and gradients of fields in the WBL grow proportionally to \( \sqrt{t} \); the most part of NIO is concentrated in the WBL. Structure of the WBL depends strongly on its horizontal scale L determined by scale of the wind stress. The shorter the NIO is, the thinner and sharper the WBL is; the short-wave NIO with L smaller than the baroclinic Rossby scale LR does not penetrate deep into the ocean. On the contrary, for L?≥?LR, the WBL has a smoother vertical structure; a significant long-wave NIO signal is able to reach the oceanic bottom. An asymptotic theory of the WBL in rotating stratified fluid is suggested.  相似文献   

18.
Cushion is a layer of granular materials between the raft and the ground. The shear behavior of the interface between the cushion and the raft may influence the seismic performance of the superstructure. In order to quantify such influences, horizontal shear tests on the interfaces between different cushion materials and concrete raft under monotonic and cyclic loading were carried out. The vertical pressure P_v, material type and cushion thickness h_c were taken as variables. Conclusions include: 1) under monotonic loading, P_v is the most significant factor; the shear resistance P_(hmax) increases as P_v increases, but the normalized factor of resistance μ_n has an opposite tendency; 2) for the materials used in this study, μ_n varies from 0.40 to 0.70, the interface friction angle δ_s varies from 20° to 35°, while u_(max) varies from 3 mm to 15 mm; 3) under cyclic loading, the interface behavior can be abstracted as a "three-segment" back-bone curve, the main parameters include μ_n, the displacement u_1 and stiffness K_1 of the elastic stage, the displacement u_2 and stiffness K_2 of the plastic stage; 4) by observation and statistical analysis, the significance of different factors, together with values of K_1, K_2 and μ_n have been obtained.  相似文献   

19.
An alternative model for the nonlinear interaction term Snl in spectral wave models, the so called generalized kinetic equation (Janssen J Phys Oceanogr 33(4):863–884, 2003; Annenkov and Shrira J Fluid Mech 561:181–207, 2006b; Gramstad and Stiassnie J Fluid Mech 718:280–303, 2013), is discussed and implemented in the third generation wave model WAVEWATCH-III. The generalized kinetic equation includes the effects of near-resonant nonlinear interactions, and is therefore able, in theory, to describe faster nonlinear evolution than the existing forms of Snl which are based on the standard Hasselmann kinetic equation (Hasselmann J Fluid Mech 12:481–500, 1962). Numerical simulations with WAVEWATCH have been carried out to thoroughly test the performance of the new form of Snl, and to compare it to the existing models for Snl in WAVEWATCH; the DIA and WRT. Some differences between the different models for Snl are observed. As expected, the DIA is shown to perform less well compared to the exact terms in certain situations, in particular for narrow wave spectra. Also for the case of turning wind significant differences between the different models are observed. Nevertheless, different from the case of unidirectional waves where the generalized kinetic equation represents a obvious improvement to the standard forms of Snl (Gramstad and Stiassnie 2013), the differences seems to be less pronounced for the more realistic cases considered in this paper.  相似文献   

20.
Over the past decade, the H-κ stacking technique of Zhu and Kanamori (J Geophys Res 105:2969–2980, 2000) has become a standard tool to determine the crustal thickness H and the bulk crustal vP/vS ratio κ from teleseismic receiver functions. It is obvious that unfavorable noise conditions as well as a complex 3D velocity structure can severely hamper the interpretation of receiver-function data. However, we observe that ambiguities can even arise from a simple 1D layered velocity structure which raises a high potential for misinterpretations. To analyze the feasibility and basic limitations of the H-κ stacking method, we conduct a series of tests based on synthetic data. The impact of different given elementary parameters, related either to the velocity structure or to the data processing, is evaluated in a series of eight individual tests. We deliberately exclude complications such as 3D structural variations and/or noise to show that even a simple 1D velocity structure, involving, e.g., an additional inter-crustal discontinuity, can have significant consequences for the interpretation of the results. However, our modeling suggests that more complex crustal structures may lead to even less reliable results. Additionally, our tests illustrate that time shifts of the maxima in the H-κ domain due to the superposition and merging of individual phases can lead to significantly overestimated vP/vS ratios. In general, the depth to the Moho (or other discontinuities of interest) is less significantly affected. Our tests indicate the necessity to accurately check delay times derived from the maxima of the H-κ stacks against corresponding phases in the receiver functions. Repeating the stacking with varied weighting factors and filter ranges can help to reduce the ambiguities and to avoid possible misinterpretation.  相似文献   

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