首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 375 毫秒
1.
A 3D, two-time-level, σS-z-σB hybrid-coordinate Marine Science and Numerical Modeling numerical ocean circulation model (HyMOM) is developed in this paper. In HyMOM, the σ coordinate is employed in the surface and bottom regions, and the z coordinate is used in the intermediate layers. This method can overcome problems with vanishing surface cells and minimize the unwanted deviation in representing bottom topography. The connection between the σ and z layers vertically includes an expanded “ghost” method and the linear interpolation. The governing equations in the σS-z-σB hybrid coordinate based on the complete Reynolds-averaged Navier-Stokes equations are derived in detail. The two-level time staggered and Eulerian forward and backward schemes, which are of second-order of accuracy, are adopted for the temporal difference in internal and external mode, respectively. The computation of the baroclinic gradient force is tested in an analytic test problem; the errors for two methods in HyMOM, which are relatively large only in the bottom layers, are obviously smaller than those in the pure σ and z models in almost all of the vertical layers. A quasi-global climatologic numerical experiment is constructed to test the simulation performance of HyMOM. With the monthly mean Levitus climatology data as reference, the HyMOM can improve the simulating accuracy compared with its pure z or σ coordinate implementation.  相似文献   

2.
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   

3.
Conventional f?x empirical mode decomposition (EMD) is an effective random noise attenuation method for use with seismic profiles mainly containing horizontal events. However, when a seismic event is not horizontal, the use of f?x EMD is harmful to most useful signals. Based on the framework of f?x EMD, this study proposes an improved denoising approach that retrieves lost useful signals by detecting effective signal points in a noise section using local similarity and then designing a weighting operator for retrieving signals. Compared with conventional f?x EMD, f?x predictive filtering, and f?x empirical mode decomposition predictive filtering, the new approach can preserve more useful signals and obtain a relatively cleaner denoised image. Synthetic and field data examples are shown as test performances of the proposed approach, thereby verifying the effectiveness of this method.  相似文献   

4.
A key issue in the design of pile-supported structures on sloping ground is soil–pile interaction, which becomes more complicated in case of dynamic loading. This study aimed to evaluate the effect of slope on the dynamic behavior of pile-supported structures by performing a series of centrifuge tests. Three models were prepared by varying the slope and soil density of dry sand grounds. The mass supported on 3 by 3 group piles was shaken applying sinusoidal wave with various amplitudes. Test results showed that the location of maximum values and distribution shape of the bending moment below the ground surface varied noticeably with the pile position in the slope case. The relationship between the soil resistance and pile deflection (p–yp loops) was carefully evaluated by applying the piecewise cubic spline method to fit the measured bending moment curves along piles. It was found that the shape of the p–yp loops was irregular due to the effect of slope, and immensely influenced by the movement of the unstable zone. In addition, the effect of the pile group in the horizontal case was evaluated by comparing with the previously suggested curves that represent the relationship between the soil resistance and pile–soil relative displacement (p–y curves) to propose the multiplier coefficients.  相似文献   

5.
To understand physical mechanisms of generation of abnormally high peak ground acceleration (PGA; >1g) during the Tohoku earthquake, models of nonlinear soil behavior in the strong motion were constructed for 27 KiK-net stations located in the near-fault zones to the south of FKSH17. The method of data processing used was developed by Pavlenko and Irikura, Pure Appl Geophys 160:2365–2379, 2003 and previously applied for studying soil behavior at vertical array sites during the 1995 Kobe (М w ?=?6.8) and 2000 Tottori (М w ?=?6.7) earthquakes. During the Tohoku earthquake, we did not observe a widespread nonlinearity of soft soils and reduction at the beginning of strong motion and recovery at the end of strong motion of shear moduli in soil layers, as usually observed during strong earthquakes. Manifestations of soil nonlinearity and reduction of shear moduli during strong motion were observed at sites located close to the source, in coastal areas. At remote sites, where abnormally high PGAs were recorded, shear moduli in soil layers increased and reached their maxima at the moments of the highest intensity of the strong motion, indicating soil hardening. Then, shear moduli reduced with decreasing the intensity of the strong motion. At soft-soil sites, the reduction of shear moduli was accompanied by a step-like decrease of the predominant frequencies of motion. Evidently, the observed soil hardening at the moments of the highest intensity of the strong motion contributed to the occurrence of abnormally high PGA, recorded during the Tohoku earthquake.  相似文献   

6.
Homogeneous, nonrotating flow over a backward-facing rounded step is simulated using the 2D vertical version of two general circulation models, a z-coordinate model—the Massachusetts Institute of Technology general circulation model (MITgcm)—and a σ-coordinate model—the Bergen Ocean Model (BOM). The backward-facing step is a well-known testcase since it is geometrically simple but still embodies important flow characteristics such as separation point, reattachment length, and recirculation of the flow. The study compares the core of the two models and uses constant eddy viscosities and diffusivities. The Reynolds numbers ranges from 2·102 to 2·106. The results correspond with previously published results having a relatively stationary separation point and a fluctuating reattachment length due to downslope propagating eddies released from the reattachment zone for Reynolds numbers higher than or equal to 2 · 104. For Reynolds number within the laminar regime, the flow is stationary. The discrepancies between the models increase by enhancing Reynolds numbers. The σ-coordinate model experiences a reduction in eddy sizes with increasing resolution and Reynolds numbers in correspondence with published experiments, while the size of the eddies are independent of the Reynolds number using the MITgcm. Due to mixing generated by the staircase topography, the z-coordinate model gives a better convergence of the separation point and reattachment length compared with the BOM; however, this conclusion might change with the inclusion of a relevant turbulence scheme.  相似文献   

7.
Stable isotope paleoaltimetry has provided unprecedented insights into the topographic histories of many of the world’s highest mountain ranges. However, on the Tibetan Plateau (TP), stable isotopes from paleosols generally yield much higher paleoaltitudes than those based on fossils. It is therefore essential when attempting to interpret accurately this region’s paleoaltitudes that the empirical calibrations of local stable isotopes and the relations between them are established. Additionally, it is vital that careful estimations be made when estimate how different isotopes sourced from different areas may have been influenced by different controls. We present here 29 hydrogen isotopic values for leaf wax-derived n-alkanes (i.e., δDwax values, and abundance-weighted average δD values of C29 and C31) in surface soils, as well as the δD values of soil water (δDsw) samples (totaling 22) from Mount Longmen (LM), on the eastern TP (altitude ~0.8–4.0 km above sea level (asl), a region climatically affected by the East Asian Monsoon (EAM). We compared our results with published data from Mount Gongga (GG). In addition, 47 river water samples, 55 spring water samples, and the daily and monthly summer precipitation records (from May to October, 2015) from two precipitation observation stations were collected along the GG transect for δD analysis. LM soil δDwax values showed regional differences and responded strongly to altitude, varying from?160‰ to?219‰, with an altitudinal lapse rate (ALR) of?18‰ km?1 (R 2=0.83; p<0.0001; n=29). These δDwax values appeared more enriched than those from the GG transect by ~40‰. We found that both the climate and moisture sources led to the differences observed in soil δDwax values between the LM and GG transects. We found that, as a general rule, ε wax/rw, ε wax/p and ε wax/sw values (i.e., the isotopic fractionation of δDwax corresponding to δDrw, δDp and δDsw) increased with increasing altitude along both the LM and GG transects (up to 34‰and 50‰, respectively). Basing its research on a comparative study of δDwax, δDp, δDrw(δDspringw) and δDsw, this paper discusses the effects of moisture recycling, glacier-fed meltwater, relative humidity (RH), evapotranspiration (ET), vegetation cover, latitude, topography and/or other factors on ε wax/p values. Clearly, if ε wax-p values at higher altitudes are calculated using smaller ε wax-p values from lower altitudes, the calculated paleowaterδDp values are going to be more depleted than the actual δD values, and any paleoaltitude would therefore be overestimated.  相似文献   

8.
An earthquake with the moment magnitude M w ?=?5.8 occurred in the middle part of the Sakhalin Island, Russian Federation, on 14 August 2016, at 11:17 a.m. UTC. The earthquake source was located west of the Central Sakhalin Fault Zone, which is considered to mark the boundary between the Okhotsk and Eurasian (Amurian) plates. Moment tensor solution of the mainshock as well as the configuration of aftershock cloud suggests that the earthquake was caused by slip on a SW-dipping reverse fault. For the first time for Sakhalin, we have got the felt reports unified in accordance with DYFI. We also analyzed observed PGA values and, based on them, produced shaking maps.  相似文献   

9.
Spatiotemporal mapping the minimum magnitude of completeness Mc and b-value of the Gutenberg–Richter law is conducted for the earthquake catalog data of Greece. The data were recorded by the seismic network of the Institute of Geodynamics of the National Observatory of Athens (GINOA) in 1970–2010 and by the Hellenic Unified Seismic Network (HUSN) in 2011–2014. It is shown that with the beginning of the measurements at HUSN, the number of the recorded events more than quintupled. The magnitude of completeness Mc of the earthquake catalog for 1970–2010 varies within 2.7 to 3.5, whereas starting from April 2011 it decreases to 1.5–1.8 in the central part of the region and fluctuates around the average of 2.0 in the study region overall. The magnitude of completeness Mc and b-value for the catalogs of the earthquakes recorded by the old (GINOA) and new (HUSN) seismic networks are compared. It is hypothesized that the magnitude of completeness Mc may affect the b-value estimates. The spatial distribution of the b-value determined from the HUSN catalog data generally agrees with the main geotectonic features of the studied territory. It is shown that the b-value is below 1 in the zones of compression and is larger than or equal to 1 in the zones dominated by extension. The established depth dependence of the b-value is pretty much consistent with the hypothesis of a brittle–ductile transition zone existing in the Earth’s crust. It is assumed that the source depth of a strong earthquake can probably be estimated from the depth distribution of the b-value, which can be used for seismic hazard assessment.  相似文献   

10.
Upgrading of the electrical resistance variometer GEOMES-R6 of the Institute of Geophysics of the Poland Academy of Sciences, with enhancement of functional capabilities of the GEOMES assemblage for its application in laboratory measurements on rock samples, has been carried out. The assemblage operation principle, specifications, and theory of operation are given. Results of the assemblage test at measurements on marble sample and concrete model are presented. It is shown that the installation allows long-duration registration of variations of the value ρ k on high-ohmic samples.  相似文献   

11.
As the dominant primary producer in oligotrophic oceans, the unicellular picocyanobacterium Prochlorococcus is the smallest and most abundant photosynthetic phytoplankton in the world and plays an important role in marine carbon cycling. Cyanophages that infect Prochlorococcus influence the growth, carbon fixation, diversity, evolution, and environmental adaptation of their hosts. Here, we review studies on the isolation, genomics, and phylogenetic diversity of Prochlorococcus viruses and their interactions with Prochlorococcus. We also review the potential effects of Prochlorococcus viruses on biogeochemical cycling in the ocean.  相似文献   

12.
The algorithm for monitoring the magnetotelluric field has been briefly described, and the experimental data, obtained at the Bishkek geodynamic site, have been analyzed. The regularities in the seasonal behavior of the variations in the field vertical magnetic component have been revealed.  相似文献   

13.
During the 22nd Chinese Antarctic Research Expedition (CHINARE-22), the atmospheric gas samples above the oceanic surface and near the surface were collected on the track for the scientific ship “Xuelong” and on Millor Peninsula of eastern Antarctica, respectively, using the Tedlar gas bags. Every day the sampling times were 10:00 and 22:00 (local time), respectively. In the laboratory, high-precision measurement of the isotopic compositions for N2O in these gas samples was conducted using Thermo Finnigan MAT-253 Isotopic Mass Spectrometer with a fully automated interface for the pre-GC concentration (PreCon) of trace gases. The temporal and spatial variations of δ 15N and δ 18O in atmospheric N2O were analyzed. The mean δ 15N and δ 18O-N2O values above the oceanic surface were (7.21±0.50)‰ and (44.52±0.52)‰, respectively. From 30°N to Antarctica, the δ 15N (6.05‰–7.88‰) linearly increased with the rate of about 0.01‰ with the latitude while the δ 18O (43.05‰–48.78‰) showed a large fluctuation. The δ 15N negatively correlated with air temperature and N2O concentration, and slightly positively correlated with δ 18O. The summertime variations of δ 15N and δ 18O-N2O appeared the same trend on Millor Peninsula of eastern Antarctica. They significantly positively correlated with each other and negatively with N2O concentration. The δ 15N and δ 18O-N2O at different sites averaged (7.42±0.35)‰ and (44.69±0.49)‰, respectively, slightly higher than those above the oceanic surface, significantly higher than those of atmospheric N2O in the low-latitude regions of Northern Hemisphere. The predominant factors affecting the spatial variations of δ 15N and δ 18O values were also discussed. The isotopic data given in this study can help to investigate the global and regional N2O budgets. Supported by the National Natural Science Foundation of China (Grant Nos. 40676005 and 40406001)  相似文献   

14.
Oxygen stable isotope of atmospheric water vapor is widely used to study the modern process of climate. Atmospheric water vapor samples were collected at Dlingha, northeast of Tibetan Plateau during the period from July 2005 to February 2006. The variation of δ 18O and the relationships between δ 18O and both the temperature and specific humidity are analyzed in this paper. Results show that the seasonal variation of δ 18O of atmospheric water vapor at Delingha is remarkable with higher δ 18O in summer and lower δ 18O in winter. The temporal variation of vapor δ 18O shows obvious fluctuations, with magnitude of over 37‰ The daily variation of the δ 18O is highly correlated with air temperature. The relationship between δ 18O and atmospheric water vapor content is complex. Study shows that δ 18O of atmospheric water vapor is positively correlated with specific humidity in winter in seasonal scale and inversely correlated with specific humidity in summer rainy period. The δ 18O values of atmospheric water vapor are lower than those of precipitation at Delingha, and the average difference is 10.7‰ Variations of δ 18O of atmospheric water vapor is also found to be affected by precipitation events, The model results show that the precipitation effect could have caused the vapor δ 18O in the raining season to lower by 7% in average in July and August. Supported by the National Natural Science Foundation of China (Grant Nos. 40671043, 40571039 and 40771048) and National Basic Research Program of China (Grant No. 2005CB422002)  相似文献   

15.
The ocean takes up approximately 2 GT carbon per year due to the enhanced CO2 concentrations in the atmosphere. Several options have been suggested in order to reduce the emissions of CO2 into the atmosphere, and among these are CO2 storage in the deep ocean. Topographic effects of dissolution and transport from a CO2 lake located at 3,000-m depth have been studied using the z-coordinate model Massachusetts Institute of Technology general circulation model (MITgcm) and the σ-coordinate model Bergen ocean model (BOM). Both models have been coupled with the general ocean turbulence model (GOTM) in order to account for vertical subgrid processes. The chosen vertical turbulence mixing scheme includes the damping effect from stable stratification on the turbulence intensity. Three different topographic scenarios are presented: a flat bottom and the CO2 lake placed within a trench with depths of 10 and 20 m. The flat case scenario gives good correlation with previous numerical studies of dissolution from a CO2 lake. When topography is introduced, it is shown that the z-coordinate model and the σ-coordinate model give different circulation patterns in the trench. This leads to different dissolution rates, 0.1 μmol cm − 2 s − 1 for the scenario of a 20-m-deep trench using BOM and 0.005–0.02 μmol cm − 2 s − 1 for the same scenario using the MITgcm. The study is also relevant for leakages of CO2 stored in geological formations and to the ocean.  相似文献   

16.
This paper inspects the relationship betweenHomo erectus from Beijing, Nanjing and Chenjiawo on the viewpoint of environmental variations. Pieces of evidence show that Nanjing and ChenjiawoHomo erectus lived in glacial age at the Marine Oxygen Isotope Stage (MIS) 16, whileHomo erectus pekinensis in major interglacial age at MISs 15-13. It is also recovered that the cave deposits in Tangshan, Nanjing, and Zhoukoudian, Beijing, as well as the deposits at theHomo erectus site in Chenjiawo, have undergone some similar development process. All of them originated from early-middle Middle Pleistocene, and have gone through the test of the major glacial age at MIS 16 and the major interglacial period at the paleosol stage S5. At the same time, they were also closely connected with some environment events, such as the uplift of the Qinghai-Xizang Plateau, the formation of glaciations and the loess accumulations.  相似文献   

17.
Based on the results from seismogeological study, aeromagnetic inversion and deep seismic sounding (DSS), it is found that the M≥8.0 earthquakes in North China have three common deep structural characteristics, i.e., they all took place above the ultra-crustal deep faults or on the edges of the tectonic blocks with higher intensity, and there are low-velocity, low-density and high-conductive layers deep in the epicentral regions. The origins of the earthquakes are also discussed and the two possibilities of seismogenesis are proposed, i.e., tectonic movement and intracrustal explosion.  相似文献   

18.
We present results from a comparative analysis of empirical and synthetic shapes for isoseismals of low intensity (I = IV–VI on the MCS scale) for six Italian earthquakes of ML = 4.5–6. Our modeling of isoseismals is based on a plane-stratified earth model and on the double–couple point source approximation to calculate seismograms in the frequency range f 1 Hz. With a minimum of parameter variation we demonstrate that the low intensity isoseismals provide information on source geometry. We strive to avoid subjectivity in isoseismal constructions by using the new Diffuse Boundary method, which visualizes isoseismals with their uncertainty. Similar results in this direction are known for large earthquakes (ML 6 or greater) with extended sources and for the higher isoseismals (I VI on the MM scale). The latter studies disregard the earth structure, use a greater number of parameters, and therefore have greater possibilities for fitting the data than our approach.  相似文献   

19.
The structure of the averaged plasma pressure distribution in the plasma ring around the Earth at geocentric distances of ∼6–10R E has been determined. The distribution function moments measured on the international THEMIS mission satellites have been used. The plasma pressure distribution in the equatorial plane at 15R E > XSM > −15R E and 15R E > YSM > −15R E has been statistically studied. The radial dependence of the plasma pressure at the day-night and morning-evening meridians has been analyzed. It has been indicated that the plasma ring around the Earth has a structure, which is close to being azimuthally symmetric. The achieved results have been compared with the pressure distributions obtained previously. It has been indicated that in the overlapping regions, the achieved results agree with the previously obtained data within the pressure determination errors.  相似文献   

20.
The Iranian Plateau does not appear to be a single crustal block, but an assemblage of zones comprising the Alborz—Azerbaijan, Zagros, Kopeh—Dagh, Makran, and Central and East Iran. The Gumbel’s III asymptotic distribution method (GIII) and maximum magnitude expected by Kijko—Sellevoll method is applied in order to check the potentiality of the each seismogenic zone in the Iranian Plateau for the future occurrence of maximum magnitude (Mmax). For this purpose, a homogeneous and complete seismicity database of the instrumental period during 1900–2012 is used in 29 seismogenic zones of the examined region. The spatial mapping of hazard parameters (upper bound magnitude (ω), most probable earthquake magnitude in next 100 years (M100) and maximum magnitude expected by maximum magnitude estimated by Kijko—Sellevoll method (max MK ? Smax) reveals that Central and East Iran, Alborz and Azerbaijan, Kopeh—Dagh and SE Zagros are a dangerous place for the next occurrence of a large earthquake.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号