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 140 毫秒
1.
We investigate the nature of temporal variations in the statistical properties of seismicity associated with the North Anatolian Fault Zone between longitudes 31°–41°E during the instrumental period 1900–1992. Temporal variations in the seismicb value and the fractal (correlation) dimensionD c of earthquake epicenters are examined for earthquakes of magnitudeM S 4.5, using sliding windows of 100 consecutive events.b varies temporally between 0.6 and 1.0, andD c between 0.6 and 1.4, both representing significant fluctuations above the errors in measurement technique. A strong negative correlation (r=–0.85) is observed betweenb andD c , consistent with previous observation of seismicity in Japan and southern California. Major events early in this century (M S 7) are associated with lowb and highD c , respectively consistent with greater stress intensity and greater spatial clustering of epicenters—both implying a greater degree of stress concentration at this time.  相似文献   

2.
One of the main morphological changes along the Southern Central Andes occurs from 36° to 39°S. The northern portion is characterized by prominent basement structures and a thick-skinned orogenic front with relief of over 2000 m with a deep level of exhumation where more than 4 km of section has been eroded. Contrastingly, the southern part is formed by mildly inverted basement structures restricted mainly to the hinterland zone, which reaches only 1500–1700 m relief. We quantify the variable contributions of two main contractional stages through the construction of three regionally balanced sections across the Andes, constrained by field and geophysical data. Extensional re-activation described for this segment in late Oligocene-early Miocene and Pliocene to Quaternary times, after the two main contractional episodes, suggests only 3 km of stretching that represents 30–10% of the original longitude. We, therefore, conclude that while initial Late Cretaceous to Eocene compression was similar along strike (∼10–7 km), it is the contrasting degrees of Neogene shortening (∼16–6 km) that have played the largest role in the along strike differences in structure and morphology along this portion of the southern Andes. Variable Neogene arc expansion could be responsible for the contrasting contractional deformation: In the north, late Miocene arc-related rocks cover most of the retroarc zone (>200 km with respect to the late Miocene arc front in the south), presumably driven by a shallow subduction episode in the area, whereas to the south they remain restricted to the continental drainage divide. Other factors involving architecture of previous rift structures, are proposed as additional mechanisms that accommodated variable shortening magnitudes through inversion.  相似文献   

3.
The identification of the center acting as electron source for the well-known 110 °C thermoluminescence (TL) peak of quartz is of fundamental importance for practical applications in dating and dosimetry. This TL peak was studied in parallel with the electron paramagnetic resonance (EPR) signal of the [GeO4]− center on natural colourless quartz irradiated at room temperature. Immediately after irradiation, the signals of the 110 °C TL peak and of [GeO4]− center decay exponentially in the same way, yielding a lifetime of 50.4 ± 0.9 min at room temperature. Besides, we acquired the isothermal decay curves for the 110 °C TL peak and [GeO4]− center at different temperatures (the samples were held at the selected temperature in the range of 260–308 K). The lifetimes extracted by the isothermal decays were plotted as a function of reciprocal temperature, revealing again the same behavior of the 110 °C TL peak and [GeO4]− center, both characterized by activation energies very close of 0.76 ± 0.07 eV and 0.77 ± 0.07 eV, respectively. All results of the present work clearly show the role of electron source of [GeO4]− center in the emission mechanism of the 110 °C TL peak in quartz.  相似文献   

4.
Tomczak  Matthias 《Ocean Dynamics》2019,69(3):301-311
Ocean Dynamics - The concept of water type richness wtr and inversion count inv is introduced and applied to high-resolution Argo float data in a meridional strip in the southern Indian Ocean as a...  相似文献   

5.
The climatology of mean wind, diurnal and semidiurnal tide during the first year (1996–1997) of simultaneous wind observations at Wakkanai (45.4°N, 141.7°E) and Yamagawa (31.2°N, 130.6°E) is presented. The locations of the radars allow us to describe the latitudinal dependence of the tides. Tidal amplitude and phase profiles are compared with those of the global scale wave model (GSWM). While the observed amplitude profiles of the diurnal tide agree well with the GSWM values, the observed phase profiles often indicate longer vertical wavelengths than the GSWM phase profiles. In contrast to the GSWM simulation, the observations show a strong bimodal structure of the diurnal tide, with the phase advancing about 6 hours from summer to winter.  相似文献   

6.
Three thousand kilometres of multichannel (MCS) and wide-angle seismic profiles, gravity and magnetic, multibeam bathymetry and backscatter data were recorded in the offshore area of the west coast of Mexico and the Gulf of California during the spring 1996 (CORTES survey). The seismic images obtained off Puerto Vallarta, Mexico, in the Jalisco subduction zone extend from the oceanic domain up to the continental shelf, and significantly improve the knowledge of the internal crustal structure of the subduction zone between the Rivera and North American (NA) Plates. Analyzing the crustal images, we differentiate: (1) An oceanic domain with an important variation in sediment thickness ranging from 2.5 to 1 km southwards; (2) an accretionary prism comprised of highly deformed sediments, extending for a maximum width of 15 km; (3) a deformed forearc basin domain which is 25 km wide in the northern section, and is not seen towards the south where the continental slope connects directly with the accretionary prism and trench, thus suggesting a different deformational process; and (4) a continental domain consisting of a continental slope and a mid slope terrace, with a bottom simulating reflector (BSR) identified in the first second of the MCS profiles. The existence of a developed accretionary prism suggests a subduction–accretion type tectonic regime. Detailed analysis of the seismic reflection data in the oceanic domain reveals high amplitude reflections at around 6 s [two way travel time (twtt)] that clearly define the subduction plane. At 2 s (twtt) depth we identify a strong reflection which we interpret as the Moho discontinuity. We have measured a mean dip angle of 7° ± 1° at the subduction zone where the Rivera Plate begins to subduct, with the dip angle gently increasing towards the south. The oceanic crust has a mean crustal thickness of 6.0–6.5 km. We also find evidence indicating that the Rivera Plate possibly subducts at very low angles beneath the Tres Marias Islands.  相似文献   

7.
  相似文献   

8.
The changes of NH3-N, NO3-N, NO2-N and TN/TP were studied during growth and non-growth season in 33 subtropical shallow lakes in the middle and lower reaches of the Yangtze River. There were significant positive correlations among all nutrient concentrations, and the correlations were better in growth season than in non-growth season. When TP>0.1 mgL-1, NH3-N increased sharply in non-growth season with increasing TP, and NO3-N increased in growth season but decreased in non-growth season with TP. These might be attributed to lower dissolved oxygen and low temperature in non-growth season of the hypereutrophic lakes, since nitrification is more sensitive to dissolved oxygen and temperature than antinitrification. When 0.1 mgL-1>TP>0.035 mgL-1, TN and all kinds of inorganic nitrogen were lower in growth season than in non-growth season, and phytoplank-ton might be the vital regulating factor. When TP<0.035 mgL-1, inorganic nitrogen concentrations were relatively low and NH3-N, NO2-N had significant correlations with phytoplankton, indicating that NH3-N and NO2-N might be limiting factors to phytoplankton. In addition, TN/TP went down with decline in TP concentration, and TN and inorganic nitrogen concentrations were obviously lower in growth season than in non-growth season, suggesting that decreasing nitrogen (especially NH3-N and NO3-N) was an important reason for the decreasing TN/TP in growth season. The ranges of TN/TP were closely related to trophic level in both growth and non-growth seasons, and it is apparent that in the eutrophic and hypertrophic state the TN/TP ratio was obviously lower in growth season than in non-growth season. The changes of the TN/TP ratio were closely correlated with trophic levels, and both declines of TN in the water column and TP release from the sediment were important factors for the decline of the TN/TP ratio in growth season.  相似文献   

9.
  相似文献   

10.
The results of studies of the shear wave attenuation field in source zones of the 2003 Chuya, 1970 Ureg-Nur, 1991 Busingol, 2011 Sayan, and 2011–2012 Tuva earthquakes are presented. Attenuation fields in these source zones include blocks with a high Q-factor and linear weakened zones. The surface ruptures from the mainshocks of the 2003 Chuya and 2011–2012 Tuva earthquakes are located in the zones of strong attenuation. Epicenters of the mainshocks are located where the maximum contrast in attenuation is observed. In the source zones of large earthquakes in the Altai–Sayan region or near them, the zones similar to so-called seimogenic bodies described in the literature are found. These objects tend to linear zones with high attenuation and are characterized by an increased density of deepened earthquakes and also by deformations of near-vertical elongation. The obtained data suggest that the fluid factor could play certain role in the occurrence of large earthquakes in the Altai–Sayan region.  相似文献   

11.
The investigation and continuous monitoring with an innovative iron oxide embedded cellulose acetate membrane (FeO/CAM) on the concentrations of biologically available phosphorus (BAP) were conducted in the Meiliang Bay of the Taihu Lake during summer in 2004. The results showed that the concentrations of dissolved (FeO-DP), particulate (FeO-PP) and total bioavailable phosphorus (FeO-P) had similar horizontal distribution. The BAP concentrations were the highest in those estuaries in the northern bay. With the decrease of the distance to the estuary or long shore, there was little difference between BAP concentrations in an open lake area. During the observation period, algal blooms occurred in most waters of the northern bay, which was reflected from the high concentrations of chlorophyll a (Chl-a). While they were not highest in the estuarine waters of those major rivers, this is the case for the BAP concentrations. The concentrations of Chl-a had a significantly positive correlation with those of bioavailable phosphorus in the open area of the Meiliang Bay. With the sediment resuspension induced by wind and wave, BAP concentrations increased in a short-term, indicating that the riverine P inputs mainly contribute to the concentrations of BAP in the estuarine water while internal P release was the major source of BAP in the open lake area. In the eutrophic shallow lake, the blooms of alga may cause pH increase and further result in internal P release. The above results showed that the new membrane of FeO/CAM can be used to monitor the concentrations of BAP and provide the scientific justifications for the control strategy of the lake eu-trophication.  相似文献   

12.
Observations of wave-driven fluctuations in emissions from the OH Meinel (OHM) and O2 Atmospheric band were made with a narrow-band airglow imager located at Adelaide, Australia (35S, 138E) during the period April 1995 to January 1996. Simultaneous wind measurements in the 80–100 km region were made with a co-located MF radar. The directionality of quasi-monochromatic (QM) waves in the mesopause region is found to be highly anisotropic, especially during the solstices. During the summer, small-scale QM waves in the airglow are predominately poleward propagating, while during winter they are predominately equatorward. The directionality inferred from a Stokes analysis applied to the radar data also indicates a strong N–S anisotropy in summer and winter, but whether propagation is from the north or south cannot be determined from the analysis. The directionality of the total wave field (which contains incoherent as well as coherent features) derived from a spectral analysis of the images shows a strong E–W component, whereas, an E–W component is essentially absent for QM waves. The prevalence of QM waves is also strongly seasonally dependent. The prevalence is greatest in the summer and the least in winter and correlates with the height of the mesopause; whether it is above or below the airglow layers. The height of the mesopause is significant because for nominal thermal structures it is associated with a steep gradient in the Brunt-Väisälä frequency that causes the base of a lower thermospheric thermal duct to be located in the vicinity of the mesopause. We interpret the QM waves as waves trapped in the lower thermosphere thermal duct or between the ground and the layer of evanescence above the duct. Zonal winds can deplete the thermal duct by limiting access to the duct or by negating the thermal trapping. Radar measurements of the prevailing zonal wind are consistent with depletion of zonally propagating waves. During winter, meridional winds in the upper mesophere and lower thermosphere are weak and have no significant effect on meridionally propagating waves. However, during summer the winds in the duct region can significantly enhance ducting of southward propagating waves. The observed directionality of the waves can be explained in terms of the prevailing wind at mesopause altitudes and the seasonal variation of distant sources.  相似文献   

13.
Introduction The medium of the earth is made up of gas, liquid, and solid. The solid is the main material to form the structure of the earth, so it is very significant to study the solid matter of the earth. Rock, as a solid medium of the earth is a common object studied by geophysicists. The measurement of the comprehensive physical properties of rocks (ZHAO, et al, 1996; GUO, et al, 1989) considered that the minimal cell of rock is the atoms of chemical element, and all sorts of the rock …  相似文献   

14.
A critical factor controlling changes in the acidity of coastal waters is the alkalinity of the water. Concentrations of alkalinity are determined by supply from rivers and by in situ processes such as biological production and denitrification. A 2-year study based on 15 cruises in Liverpool Bay followed the seasonal cycles of changing concentrations of total alkalinity (TA) and total dissolved inorganic carbon (DIC) in relation to changes caused by the annual cycle of biological production during the mixing of river water into the Bay. Consistent annual cycles in concentrations of nutrients, TA and DIC were observed in both years. At a salinity of 31.5, the locus of primary production during the spring bloom, concentrations of NO x decreased by 25 ± 4 μmol kg−1 and DIC by 106 ± 16 μmol kg−1. Observed changes in TA were consistent with the uptake of protons during primary biological production. Concentrations of TA increased by 33 ± 8 μmol kg−1 (2009) and 33 ± 15 μmol kg−1 (2010). The impact of changes in organic matter on the measured TA appears likely to be small in this area. Thomas et al. (2009) suggested that denitrification may enhance the CO2 uptake of the North Sea by 25%, in contrast we find that although denitrification is a significant process in itself, it does not increase concentrations of TA relative to those of DIC and so does not increase buffer capacity and potential uptake of CO2 into shelf seawaters. For Liverpool Bay historical data suggest that higher concentrations of TA during periods of low flow are likely to contribute in part to the observed change in TA between winter and summer but the appropriate pattern cannot be identified in recent low-frequency river data. On a wider scale, data for the rivers Mersey, Rhine, Elbe and Weser show that patterns of seasonal change in concentrations of TA in river inputs differ between river systems.  相似文献   

15.
  相似文献   

16.
  相似文献   

17.
RS-monitoring index systems of ecological environment changes at a large scale, based on empirical data and trends in environmental change in Central Asia, are developed using NOAA and MODIS data. Moreover, with the help of mathematical statistics and GIS spatial analysis, the degrees, hazards and distribution extent of various possible ecological problems are discussed, environmental changes in Central Asia in 1990 and 2005 are separately evaluated, and dynamic changes in the environment in Central Asia over a 15-year period are analyzed. The results reveal that during the 15-year period from 1990 to 2005, areas of degenerated vegetation in Kazakhstan, Uzbekistan, Turkmenistan, Kirghizstan and Tadzhikistan were enlarged by 0.069×105 km2, 0.081×105 km2, 0.296×105 km2, 0.022×105 km2 and 0.112×105 km2, respectively. The ecological environment in Central Asia was in the state of significant degeneration and even deterioration. This study proves that NOAA and MODIS data can be used to successfully monitor the environment and provide useful results.  相似文献   

18.
ＣｏｍｐａｒｉｓｏｎａｎｄａｎａｌｙｓｉｓｏｆｔｈｅｓｔｒｅｓｓｆｉｅｌｄｉｎｔｈｅｓｏｕｒｃｅｒｅｇｉｏｎｏｆＴａｎｇｓｈａｎａｎｄＬａｎｃａｎｇｅａｒｔｈｑｕａｋｅｓｅｑｕｅｎｃｅｓＧｕｉ－ＬｉｎｇＤＩＡＯ；（刁桂苓）Ｌｉ－ＭｉｎＹＵ；（于利民）...  相似文献   

19.
Iodine is a trace element playing an important role in vital activities of organisms. It is im-portant for human bodys thyroid gland. Deficient or excessive iodine will not only influence hu-man health but also cause feeblemindedness, so great attention h…  相似文献   

20.
Although the Arctic methane reservoir is large,the emission of methane from the Arctic Ocean into the atmosphere remains poorly constrained.Continuous ship-borne measurements of atmospheric methane near the surface ocean were carried out during two cruises to investigate methane emission from the Arctic Ocean up to the latitude of 87°N.Three-day air mass back trajectories along the cruise tracks indicated that the surface Arctic Ocean could be a potentially important source of methane to the atmosphere.Rapid bursts in methane concentration occurred mainly along the ocean frontal area,suggesting that frontal upwelling in the upper layer of the Arctic Ocean might contribute to methane emissions into the atmosphere.  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