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1.
The homologues temperature of a crystalline material is defined as T/T_m, where T is temperature and T_m is the melting(solidus) temperature in Kelvin. It has been widely used to compare the creep strength of crystalline materials. The melting temperature of olivine system,(Mg,Fe)_2SiO_4, decreases with increasing iron content and water content, and increases with confining pressure. At high pressure, phase transition will lead to a sharp change in the melting curve of olivine. After calibrating previous melting experiments on fayalite(Fe_2SiO_4), the triple point of fayalite-Fe_2SiO_4 spinel-liquid is determined to be at 6.4 GPa and 1793 K. Using the generalized means, the solidus and liquidus of dry olivine are described as a function of iron content and pressure up to 6.4 GPa. The change of T/T_m of olivine with depth allows us to compare the strength of the upper mantle with different thermal states and olivine composition. The transition from semi-brittle to ductile deformation in the upper mantle occurs at a depth where T/T_m of olivine equals 0.5. The lithospheric mantle beneath cratons shows much smaller T/T_m of olivine than orogens and extensional basins until the lithosphere-asthenosphere boundary where T/T_m 0.66, suggesting a stronger lithosphere beneath cratons. In addition, T/T_m is used to analyze deformation experiments on olivine. The results indicate that the effect of water on fabric transitions in olivine is closely related with pressure. The hydrogen-weakening effect and its relationship with T/T_m of olivine need further investigation. Below 6.4 GPa(200 km), T/T_m of olivine controls the transition of dislocation glide from [100] slip to [001] slip. Under the strain rate of 10~(-12)–10~(-15) s~(-1) and low stress in the upper mantle, the [100](010) slip system(A-type fabric) becomes dominant when T/T_m 0.55–0.60. When T/T_m 0.55–0.60, [001] slip is easier and low T/T_m favors the operation of [001](100) slip system(C-type fabric). This is consistent with the widely observed A-type olivine fabric in naturally deformed peridotites, and the C-type olivine fabric in peridotites that experienced deep subduction in ultrahigh-pressure metamorphic terranes. However, the B-type fabric will develop under high stress and relatively low T/T_m. Therefore, the homologues temperature of olivine established a bridge to extrapolate deformation experiments to rheology of the upper mantle. Seismic anisotropy of the upper mantle beneath cratons should be simulated using a four-layer model with the relic A-type fabric in the upper lithospheric mantle, the B-type fabric in the middle layer, the newly formed A- or B-type fabric near the lithosphere-asthenosphere boundary, and the asthenosphere dominated by diffusion creep below the Lehmann discontinuity. Knowledge about transition mechanisms of olivine fabrics is critical for tracing the water distribution and mantle flow from seismic anisotropy.  相似文献   

2.
A method for determining medium quality factor is developed on the basis of analyzing the attenuation dispersion of the arrived first period P wave. In order to enhance signal to noise ratio, improve the resolution in measurement and reduce systematic error we applied the data resampling technique. The group velocity delay of P wave was derived by using an improved multi-filtering method. Based on a linear viscoelastic relaxation model we deduced the medium quality factor Q m, and associated error with 95% confidence level. Applying the method to the seismic record of the Xiuyan M=5.4 earthquake sequences we obtained the following result: (1) High Q m started to appear from Nov. 9, 1999. The events giving the deduced high Q m value clustered in a region with their epicenter distances being between 32 and 46 km to the Yingkou station. This Q m versus distance observation obviously deviates from the normal trend of Q m linearly increasing with distance. (2) The average Q m before the 29 Dec. 1999 M=5.4 earthquake is 460, while the average Q m between the M=5.4 event and the 12 Jan. 2000 M=5.1 earthquake is 391, and the average Q m after the M=5.1 event is 204.  相似文献   

3.
The deep structure of the upper mantle is determined from data on phase velocities of Love and Rayleigh waves measured by a differential method on traces between two stations in central Western Europe. One-dimensional velocity structures are first constructed from data of each pair of stations, after which two-dimensional distributions of SH and SV velocities are calculated by the method of two-dimensional tomography from S wave velocities at fixed depths. The results are presented in the form of 2-D vertical structures of the average S wave velocity (S = (SV + SH)/2) constructed along profiles crossing the region in directions of the best resolution. The main structural features are a higher velocity zone at depths of 60–80 km in the area (48°–50°N, 9°–11°E) and a lower velocity zone in the western part of the region at depths of 100–150 km, probably extending farther beyond the studied area.  相似文献   

4.
Based on the light-photosynthesis response measurement at leaf level, combined with over-and under-canopy eddy covariance measurements, research on photosynthetic characteristics of single trees and forest canopy was conducted. The relationship between light intensity and photosynthetic rates for leaves and canopy can be well fitted by a non-rectangular hyperbola model. Mongolian oak presented a high light compensation point, L cp (28 μmol·m?2·s?1), a light saturation point L sp (>1800 μmol·m?2·s?1), and a maximal net photosynthetic rate P max (9.96 μmol·m?2·s?1), which suggest that it is a typical heliophilous plant. Mono maple presented the highest apparent quantum efficiency α (0.066) but the lowest, L cp (16 μmol·m?2·s?1), L sp (≈800 μmol·m?2·s?1), and P max (4.51 μmol·m?2·s?1), which suggest that it is heliophilous plant. Korean pine showed the lowest α value but a higher P max, which suggest that it is a semi-heliophilous plant. At the canopy level, the values of both α and P max approached the upper limit of reported values in temperate forests, while L cp was within the lower limit. Canopy photosynthetic characteristics were well consistent with those of leaves. Both showed a high ability to photosynthesize. However, environmental stresses, especially high vapor pressure deficits, could significantly reduce the photosynthetic ability of leaves and canopy.  相似文献   

5.
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   

6.
The Dinghushan flux observation site, as one of the four forest sites of ChinaFLUX, aims to acquire long-term measurements of CO2 flux over a typical southern subtropical evergreen coniferous and broad-leaved mixed forest ecosystem using the open path eddy covariance method. Based on two years of data from 2003 to 2004, the characteristics of temporal variation in CO2 flux and its response to environmental factors in the forest ecosystem are analyzed. Provided two-dimensional coordinate rotation, WPL correction and quality control, poor energy-balance and underestimation of ecosystem respiration during nighttime implied that there could be a CO2 leak during the nighttime at the site. Using daytime (PAR > 1.0 μmol?1·m?2·s?1) flux data during windy conditions (u* > 0.2 m·s?1), monthly ecosystem respiration (Reco) was derived through the Michaelis-Menten equation modeling the relationship between net ecosystem C02 exchange (NEE) and photosynthetically active radiation (PAR). Exponential function was employed to describe the relationship between Reco and soil temperature at 5 cm depth (Ts05), then Reco of both daytime and nighttime was calculated respectively by the function. The major results are: (i) Derived from the Michaelis-Menten equation, the apparent quantum yield (α) was 0.0027±0.0011 mgCO2·μmol?1 photons, and the maximum photosynthetic assimilation rate (Amax) was 1.102±0.288 mgCO2·m?2·s?1. Indistinctive seasonal variation of α or Amax was consistent with weak seasonal dynamics of leaf area index (LAf) in such a lower subtropical evergreen mixed forest, (ii) Monthly accumulated Reco was estimated as 95.3±21.1 gC·m?2mon?1, accounting for about 68% of the gross primary product (GPP). Monthly accumulated WEE was estimated as ?43.2±29.6 gC·m?2·mon?1. The forest ecosystem acted as carbon sink all year round without any seasonal carbon efflux period. Annual NEE of 2003 and 2004 was estimated as ?563.0 and ?441.2 gC·m?2·a?1 respectively, accounting for about 32% of GPP.  相似文献   

7.
Recent estimates of fracture energy G ′ in earthquakes show a power-law dependence with slip u which can be summarized as G ′ ∝ u a where a is a positive real slightly larger than one. For cracks with sliding friction, fracture energy can be equated to G f : the post-failure integral of the dynamic weakening curve. If the dominant dissipative process in earthquakes is friction, G ′ and G f should be comparable and show a similar scaling with slip. We test this hypothesis by analyzing experiments performed on various cohesive and non-cohesive rock types, under wet and dry conditions, with imposed deformation typical of seismic slip (normal stress of tens of MPa, target slip velocity > 1 m/s and fast accelerations ≈ 6.5 m/s2). The resulting fracture energy G f is similar to the seismological estimates, with G f and G ′ being comparable over most of the slip range. However, G f appears to saturate after several meters of slip, while in most of the reported earthquake sequences, G ′ appears to increase further and surpasses G f at large magnitudes. We analyze several possible causes of such discrepancy, in particular, additional off-fault damage in large natural earthquakes.  相似文献   

8.
The dependence of the zonal geomagnetic indices (AE, Ap, Kp, Kn, and Dst) on the solar wind parameters (the electric field E y component, dynamic pressure P d and IMF irregularity σB) has been studied for two types of events: magnetic clouds and high-speed streams. Based on the empirical relationships, it has been established that the AE, Ap, Kp, and Kn indices are directly proportional to the E y value at E y < 12 mV m?1 and are inversely proportional to this value at E y > 12 mV m?1 for the first-type events. On the contrary, the dependence of Dst on E y is monotonous nonlinear. A linear dependence of all geomagnetic indices on E y is typical of the second-type events. It has been indicated that the specific features of geoeffectiveness of magnetic clouds and high-speed solar wind streams are caused by the dependence of the electric field potential across the polar cap on the electric field, solar wind dynamic pressure, and IMF fluctuations.  相似文献   

9.
Uncertainties in some key parameters in land surface models severely restrict the improvement of model capacity for successful simulation of surface-atmosphere interaction. These key parameters are related to soil moisture and heat transfer and physical processes in the vegetation canopy as well as other important aerodynamic processes. In the present study, measurements of surface-atmosphere interaction at two observation stations that are located in the typical semi-arid region of China, Tongyu Station in Jilin Province and Yuzhong Station in Gansu Province, are combined with the planetary boundary layer theory to estimate the value of two key aerodynamic parameters, i.e., surface roughness length z0m and excess resistance κB-1. Multiple parameterization schemes have been used in the study to obtain values for surface roughness length and excess resistance κB-1 at the two stations. Results indicate that z0m has distinct seasonal and inter-annual variability. For the type of surface with low-height vegetation, there is a large difference between the default value of z0m in the land surface model and that obtained from this study. κB-1 demonstrates a significant diurnal variation and seasonal variability. Using the modified scheme for the estimation of z0m and κB-1 in the land surface model, it is found that simulations of sensible heat flux over the semi-arid region have been greatly improved. These results suggest that it is necessary to further evaluate the default values of various parameters used in land surface models based on field measurements. The approach to combine field measurements with atmospheric boundary layer theory to retrieve realistic values for key parameters in land surface models presents a great potential in the improvement of modeling studies of surface-atmosphere interaction.  相似文献   

10.
This paper presents a stochastic model for multicomponent competitive monovalent cation exchange in hierarchical porous media. Reactive transport in porous media is highly sensitive to heterogeneities in physical and chemical properties, such as hydraulic conductivity (K), and cation exchange capacity (CEC). We use a conceptual model for multimodal reactive mineral facies and develop a Eulerian-based stochastic theory to analyze the transport of multiple cations in heterogeneous media with a hierarchical organization of reactive minerals. Numerical examples investigate the retardation factors and dispersivities in a chemical system made of three monovalent cations (Na+, K+, and Cs+). The results demonstrate how heterogeneity influences the transport of competitive monovalent cations, and highlight the importance of correlations between K and CEC. Further sensitivity analyses are presented investigating how the dispersion and retardation of each cation are affected by the means, variances, and integral scales of K and CEC. The volume fraction of organic matter is shown to be another important parameter. The Eulerian stochastic framework presented in this work clarifies the importance of each system parameters on the migration of cation plumes in formations with hierarchical organization of facies types. Our stochastic approach could be used as an alternative to numerical simulations for 3D reactive transport in hierarchical porous media, which become prohibitively expensive for the multicomponent applications considered in this work.  相似文献   

11.
To describe the cumulative distribution of the number of lithospheric plates over areas S, the dependence N(≥S) ～ S ?0.33 was proposed by Bird [2003]. Based on dimension considerations, the dependence N(≥S) ～ (?/S)1/3, where ? is the generation rate of kinetic energy of convection in the mantle estimated at 10?11 m2/s3, is proposed. The analogy of plate formation with developed hydrodynamic turbulence and other processes involving an energy input into the system and its dissipation is considered. Simple experiments on random partitioning of a surface into polygons gave their cumulative distributions over areas resembling those observed for lithospheric plates. This has led to the conclusion that the plate distribution pattern is characteristic of the random partitioning of surfaces.  相似文献   

12.
Solutions of P-SV equations of motion in a homogeneous transversely isotropic elastic layer contain a factor exp(±ν j z), where z is the vertical coordinate and j?=?1, 2. For computing Rayleigh wave dispersion in a multi-layered half space, ν j is computed at each layer. For a given phase velocity (c), ν j becomes complex depending on the transversely isotropic parameters. When ν j is complex, classical Rayleigh waves do not exist and generalised Rayleigh waves propagate along a path inclined to the interface. We use transversely isotropic parameters as α H , β V , ξ, ? and η and find their limits beyond which ν j becomes complex. It is seen that ν j depends on ? and η, but does not depend on ξ. The complex ν j occurs when ? is small and η is large. For a given c/β V , the region of complex ν j in a ? -η plane increases with the increase of α H /β V . Further, for a given α H /β V , the complex region of ν j increases significantly with the decrease of c/β V . This study is useful to compute dispersion parameters of Rayleigh waves in a layered medium.  相似文献   

13.
To alert the public to the possibility of tornado (T), hail (H), or convective wind (C), the National Weather Service (NWS) issues watches (V) and warnings (W). There are severe thunderstorm watches (SV), tornado watches (TV), and particularly dangerous situation watches (PV); and there are severe thunderstorm warnings (SW), and tornado warnings (TW). Two stochastic models are formulated that quantify uncertainty in severe weather alarms for the purpose of making decisions: a one-stage model for deciders who respond to warnings, and a two-stage model for deciders who respond to watches and warnings. The models identify all possible sequences of watches, warnings, and events, and characterize the associated uncertainties in terms of transition probabilities. The modeling approach is demonstrated on data from the NWS Norman, Oklahoma, warning area, years 2000–2007. The major findings are these. (i) Irrespective of its official designation, every warning type {SW, TW} predicts with a significant probability every event type {T, H, C}. (ii) An ordered intersection of SW and TW, defined as reinforced warning (RW), provides additional predictive information and outperforms SW and TW. (iii) A watch rarely leads directly to an event, and most frequently is false. But a watch that precedes a warning does matter. The watch type \(\{SV\), TV, \(PV\}\) is a predictor of the warning type \(\{SW\), RW, \(TW\}\) and of the warning performance: It sharpens the false alarm rate of the warning and the predictive probability of an event, and it increases the average lead time of the warning.  相似文献   

14.
The Aki-Utsu method of Gutenberg-Richter (G-R) b value estimation is often misapplied so that estimations not using the G-R histogram are often meaningless because they are not based on adequate samples. We propose a method to estimate the likelihood Pr(b?b m , N, M 1, M 2) that an observed b m estimate, based on a sample of N magnitudes within an [M 1????≤?ΔM/2,?M 2?+?ΔM/2) range, where ΔM?=?0.1 is the usual rounding applied to magnitudes, is due to a “true” source b value, b, and use these likelihoods to estimate source b ranges corresponding to various confidence levels. As an example of application of the method, we estimate the b values before and after the occurrence of a 7.4-magnitude earthquake in the Mexican subduction zone, and find a difference of 0.82 between them with 100% confidence that the b values are different.  相似文献   

15.
The purpose of this work is to define a seismic regionalization of Mexico for seismic hazard and risk analyses. This seismic regionalization is based on seismic, geologic, and tectonic characteristics. To this end, a seismic catalog was compiled using the more reliable sources available. The catalog was made homogeneous in magnitude in order to avoid the differences in the way this parameter is reported by various agencies. Instead of using a linear regression to converts from m b and M d to M s or M w , using only events for which estimates of both magnitudes are available (i.e., paired data), we used the frequency-magnitude relations relying on the a and b values of the Gutenberg-Richter relation. The seismic regions are divided into three main categories: seismicity associated with the subduction process along the Pacific coast of Mexico, in-slab events within the down-going COC and RIV plates, and crustal seismicity associated to various geologic and tectonic regions. In total, 18 seismic regions were identified and delimited. For each, the a and b values of the Gutenberg-Richter relation were determined using a maximum likelihood estimation. The a and b parameters were repeatedly estimated as a function of time for each region, in order to confirm their reliability and stability. The recurrence times predicted by the resulting Gutenberg-Richter relations obtained are compared with the observed recurrence times of the larger events in each region of both historical and instrumental earthquakes.  相似文献   

16.
We propose a method that employs the squared displacement integral (ID2) to estimate earthquake magnitudes in real time for use in earthquake early warning (EEW) systems. Moreover, using τ c and P d for comparison, we establish formulas for estimating the moment magnitudes of these three parameters based on the selected aftershocks (4.0 ≤ M s  ≤ 6.5) of the 2008 Wenchuan earthquake. In this comparison, the proposed ID2 method displays the highest accuracy. Furthermore, we investigate the applicability of the initial parameters to large earthquakes by estimating the magnitude of the Wenchuan M s 8.0 mainshock using a 3-s time window. Although these three parameters all display problems with saturation, the proposed ID2 parameter is relatively accurate. The evolutionary estimation of ID2 as a function of the time window shows that the estimation equation established with ID2 Ref determined from the first 8-s of P wave data can be directly applicable to predicate the magnitudes of 8.0. Therefore, the proposed ID2 parameter provides a robust estimator of earthquake moment magnitudes and can be used for EEW purposes.  相似文献   

17.
Using the foF2 database obtained from satellites and ground-based ionospheric stations, we have constructed a global empirical model of the critical frequency of the ionospheric F2-layer (SDMF2—Satellite and Digisonde Data Model of the F2 layer) for quiet geomagnetic conditions (Kp < 3). The input parameters of this model are the geographical coordinates, UT, day, month, year, and the integral index F10.7 (day, τ = 0.96) of solar activity for a given day. The SDMF2 model was based on the Legendre method for the spatial expansion of foF2 monthly medians to 12 in latitude and 8 in longitude of spherical harmonics. The resulting spatial coefficients have been expanded by the Fourier method in three spherical harmonics with respect to UT. The effect of the saturation of critical frequency of the ionospheric F2-layer at high solar activity was described in the SDMF2 model by foF2 as a logarithmic function of F10.7 (day, τ = 0.96). The difference between the SDMF2 and IRI models is a maximum at low solar activity as well as in the Southern Hemisphere and in the oceans. The testing on the basis of ground-based and satellite data has indicated that the SDMF2 model is more accurate than the IRI model.  相似文献   

18.
The authors have carried out the gamma-ray spectrometry of some Vesuvius lavas, by means of a S.E.L.O. equipment which consists of a 100 channels analyzer joined to a photomultiplier tube annexed to aNaI(T1) phosphor. TheU 238,Th 232,Ra 226 andK 2 O contents have been determined and the following conclusions have been drawn: theU 238 seems to be present in the examined lavas and the contents are fairly equal within the errors; also theTh 232 andK 2 O contents show no sensible variations in the different lavas. TheRa 226 content is remarkably higher than that necessary for the equilibrium with the observedU 238 content and shows a decrease with the age of the lavas. TheRa 226 content which exceeds that necessary for the equilibrium with the observedU 238 content decreases with a law similar to the natural radioactive decay ofRa 226.  相似文献   

19.
Long-term measurement of carbon metabolism of old-growth forests is critical to predict their behaviors and to reduce the uncertainties of carbon accounting under changing climate. Eddy covariance technology was applied to investigate the long-term carbon exchange over a 200 year-old Chinese broad-leaved Korean pine mixed forest in the Changbai Mountains (128°28′E and 42°24′N, Jilin Province, P. R. China) since August 2002. On the data obtained with open-path eddy covariance system and CO2 profile measurement system from Jan. 2003 to Dec. 2004, this paper reports (i) annual and seasonal variation of F NEE, F GPP and R E; (ii) regulation of environmental factors on phase and amplitude of ecosystem CO2 uptake and release Corrections due to storage and friction velocity were applied to the eddy carbon flux.LAI and soil temperature determined the seasonal and annual dynamics of FGPP and RE separately. VPD and air temperature regulated ecosystem photosynthesis at finer scales in growing seasons. Water condition at the root zone exerted a significant influence on ecosystem maintenance carbon metabolism of this forest in winter.The forest was a net sink of atmospheric CO2 and sequestered ?449 g C·m?2 during the study period; ?278 and ?171 gC·m?2 for 2003 and 2004 respectively. F GPP and F RE over 2003 and 2004 were ?1332, ?1294 g C·m?2. and 1054, 1124 g C·m?2 respectively. This study shows that old-growth forest can be a strong net carbon sink of atmospheric CO2.There was significant seasonal and annual variation in carbon metabolism. In winter, there was weak photosynthesis while the ecosystem emitted CO2. Carbon exchanges were active in spring and fall but contributed little to carbon sequestration on an annual scale. The summer is the most significant season as far as ecosystem carbon balance is concerned. The 90 days of summer contributed 66.9, 68.9% of F GPP, and 60.4, 62.1% of R E of the entire year.  相似文献   

20.
Solute transport in subsurface environments is controlled by geological heterogeneity over multiple scales. In reactive transport characterized by a low Damköhler number, it is also controlled by the rate of kinetic mass transfer. A theory for addressing the impact of sedimentary texture on the transport of kinetically sorbing solutes in heterogeneous porous formations is derived using the Lagrangian-based stochastic methodology. The resulting model represents the hierarchical organization of sedimentary textures and associated modes of log conductivity (K) for sedimentary units through a hierarchical Markov Chain. The model characterizes kinetic sorption using a spatially uniform linear reversible rate expression. Our main interest is to investigate the effect of sorption kinetics relative to the effects of K heterogeneity on the dispersion of a reactive plume. We study the contribution of each scale of stratal architecture to the dispersion of kinetically sorbing solutes in the case of a low Damköhler number. Examples are used to demonstrate the time evolution and relative contributions of the auto- and cross-transition probability terms to dispersion. Our analysis is focused on the model sensitivity to the parameters defined at each hierarchical level (scale) including the integral scales of K spatial correlation, the anisotropy ratio, the indicator correlation scales, and the contrast in mean K between facies defined at different scales. The results show that the anisotropy ratio and integral scales of K have negligible effect upon the longitudinal dispersion of sorbing solutes. Furthermore, dispersion of sorbing solutes depends mostly on indicator correlation scales, and the contrast of the mean conductivity between units at different scales.  相似文献   

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