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1.
The analysis of earthquake-related signals in hydrochemical time series is still a challenging task. Mostly it is unclear how the geometrical and energetic distribution of earthquakes is influencing variation in the hydrochemical composition of monitoring sites, e.g. located close to volcanoes. Past research showed that linear stress-release models alone are not capable to explain sufficiently observed variation in hydrochemical time series due to earthquake activity. A spring located at the base of Koryaksky Volcano, which has shown hydrochemical variation close to 5, major earthquakes, was chosen to analyse relation patterns between hydrochemical variation and seismicity. A possible mechanism, explaining observed hydrochemical variation, that seismic waves trigger an underground water pumping caused by nucleation of gas bubbles in magma was proposed. Consequences are an increase of discharge, gas content in water and changes in the mixing ratios of waters of different genesis. Based on functions of aggregated earthquake information (E) it is herein shown that seismotectonic-triggered processes have a significant influence on the variation of the hydrochemistry of the spring, lasting longer than two decades. At least seven categories of relation patterns between hydrochemical variation and seismotectonic activity E can be identified. A conducted spectral analysis shows that earthquake activity and hydrochemistry share spikes in frequencies. Results prove that the use of functions of transformed aggregated seismic observations is useful to represent the seismotectonic activity for analysing earthquake-related signals in hydrochemical time series.  相似文献   

2.
An investigation of seagrass-epiphyte controlling factors was conducted within aThalassia testudinum meadow in Florida Bay from March 2000 to April 2001. Univariate and multivariate analyses were performed using water column nutrient concentrations, temperature, salinity, and turbidity, and gastropod grazer abundances, seagrass leaf area index, and leaf turnover rate data to explain the variation in total epiphyte standing stock, epiphyte chlorophylla, and epiphyte autotrophic index. Turbidity was positively correlated with total epiphyte standing stock and accounted for the most variation. Observations of adhered sediment onT. testudinum leaves and the combination, of increased total epiphyte standing stocks and low autotrophic indices observed in February and April 2001 suggest that the settling of resuspended sediments following turbidity events is one of the temporal mechanisms for increased epiphyte accumulation. Total epiphyte standing stock was also negatively correlated with the abundance of a robust gastropod grazer community dominated byTurbo castanea, Tegula fasciata, andModulus modulus. Distinct temporal size cohorts ofT. castanea andT. fasciata throughout the study period suggest recruitment in spring and an annual lifespan. Nutrient concentrations can also account for some of the temporal variation in total epiphyte standing stock, epiphyte chlorophylla, and autotrophic index. The low variation ofT. testudinum leaf turnover rates was unable to account for any of the variation in the epiphyte parameters.  相似文献   

3.
The detection of long-term shifts in species composition and spatial structuring of aquatic communities may be obscured by high levels of interannual variation. Estuarine fish communities are likely to exhibit high levels of variation owing to the influence of riverine forcing and the importance of anadromous and transient species, whose abundances may not be locally controlled. We describe patterns of interannual variation and long-term shifts in the nearshore fish community of the mesohaline Hudson River estuary based on 21 yr of beach seine sampling conducted annually between late August and mid November. Of the 60 species encountered, the most abundant were Atlantic silversides (Menidia menidia), striped bass (Morone saxatilis), white perch (Morone americana), American shad (Alosa sapidissima), and blueback herring (Alosa aestivalis). Relationships between annual community composition and seasonal flow and temperature regimes were examined with canonical correspondence analysis. Annual variation was most closely correlated with river flows in the 3-mo period preceding fish sampling, indicating a persistent effect of environmental conditions on community structure. Despite significant interannual variation in composition, longer-term trends in community structure were observed. These included declines in catch rates of freshwater and estuarine species and a dramatic increase in the catch of Atlantic silversides, an annual marine species. Associated with these changes were declines in community diversity and increased compositional variation. These results indicate that analyses of temporal changes in community structure need to account for the multiple time scales under which forcing factors and community composition vary.  相似文献   

4.
Temporal variation in abundance and mean proloculus diameter of the benthic foraminiferal speciesEpistominella exigua has been reconstructed over the last ∼ 50,000 yr BP, from a core collected from the distal Bay of Bengal fan, to assess its potential application in palaeoceanographic reconstruction studies. The down-core variation shows significant change in abundance ofE. exigua during the last ∼ 50,000 yr BP. In view of the present day abundance of this species from areas with strong seasonal organic matter supply, we conclude that at ∼ 7, ∼ 22, ∼ 33 and ∼ 46kyr BP, strong seasonality prevailed in the distal Bay of Bengal fan, probably indicating either strong or prolonged north-east monsoon or weakened south-west monsoon. For the first time, a strong correlation is observed in abundance and mean proloculus diameter ofE. exigua. Based on coherent variation in mean proloculus diameter and abundance, it is postulated that mean proloculus diameter can also be used to infer increased seasonality in organic matter production, thus variation in strength or duration of monsoon. Thus, this study establishes that the down-core variation in the abundance and mean proloculus diameter ofEpistominella exigua can be used to infer past climatic variations from the distal Bay of Bengal fan.  相似文献   

5.
SOHO-MDI daily magnetic field synoptic data (a 14-year series of daily maps of the solar magnetic field intensity B available at the site ) have been used to analyze the dynamics of the photospheric magnetic field in the vicinity of the solar equator. The standard deviation s B of the field B calculated over areas of tens of square degrees on the solar disk was taken as a basic index. An 11-year variation similar to that observed at higher latitudes is observed in the vicinity of the equator, and is similar for weak and strong fields; i.e., the solar cycle exists in the sunspot-free zone. New qualitative data support the idea that the weak background magnetic field increases toward the solar limb. This angular dependence suggests the existence of a transverse component of the background field. The magnetic fields in the vicinity of the equator were significantly different in the initial phases of Cycles 23 and 24. Annual variations of s B were observed near the center of the solar disk. These variations are due to two factors: the annual variation of the distance from the equator to the disk center and the increase of s B with with distance from the equator. Reliable detection of these variations is an evidence of high accuracy of the s B estimates.  相似文献   

6.
Transmission electron microscopy of various natural and synthetic sapphirines shows the existence of extensive polytypic variation in some samples. In addition to the previously described 1Tc and 2M polytypes, 3Tc, 4M and 5Tc structures are observed. The structural principles underlying the polytypism and the associated diffraction behaviour are reviewed, and the correlation between the nature of the observed stacking faults and their origin during crystal growth, in deformation or as a result of solid-state transformation is discussed. Pairs of c/2 partial dislocations observed in synthetic material provide a likely solid-state transformation mechanism, although the evidence suggests that most observed stacking variation arises during growth.A new type of non-conservative planar defect has been found in sapphirine from Finero, Italy, suggestive of unit-cell scale intergrowth with a surinamite- or pyroxene-like structure. A polysomatic model of the sapphirine and surinamite structures as stackings of pyroxene P and spinel S modules is proposed.  相似文献   

7.
During the month of March 2006, a short campaign was conducted to measure fair-weather atmospheric electricity parameters in Tripura, Northeast India (23.50°N, 91.25°E). The campaign was the first of its kind in this region of the globe. The main objective of the campaign was to characterize the diurnal variation of three parameters namely vertical potential gradient (E), vertical air-earth current density (J z ) and atmospheric electrical conductivity (σ) in fair-weather conditions. The diurnal variation of E and J z over sixteen fair-weather days shows two distinct maxima around 14UT and 20UT and a minimum around 03UT. The average vertical potential gradient is found to be 108V·m−1 and air-earth current density 1.85 pA·m−2. The average bipolar atmospheric electrical conductivity at the ground level is found to be 19.6 fS·m−1. An excellent positive correlation between E and J z is found, with a correlation coefficient of 0.96. A comparative study with Carnegie universal variation shows 70% correlation with observed variation of vertical potential gradient during the period of the campaign. The results are discussed in view of difficulty as well as possibility of getting global signatures in atmospheric electricity measurements made from tropical land stations.  相似文献   

8.
Abstract: The paper introduces the anomalies observed by digital tiltmeter, cross-fault deformation meter, 4-component borehole strainmeter and geothermometer before May 12, 2008, Ms8.0 Wenchuan earthquake, Sichuan. The digital tiltmeter installed in the epicentral region in Shifang County recorded the tilt anomalies 15 days before the earthquake with variation amplitude of 3.7 times larger than the annual deviation of 2007. The cross-fault deformation meter installed at Zimakua station on the Xianshuihe-Anninghe fault zone detected displacement anomaly occurring since 2006 with the variation amplitude exceeding the cumulative value of the last ten years. Five borehole strainmeter stations in the Chongqing section of Three Gorges Reservoir area observed unconventional strain changes occurring in the period from May 1 through 12, 2008. Among them, the strainmeter at Wanzhou station recorded the great compression strain rate on the EW component at 14:00 o'clock of May 10, and the anomaly amplitude was so large that the instrument output exceeded its dynamic range, corresponding to a level of ~104 nanostrains. The geothermometers installed in Xi’an, Chongqing and Xichang recorded the sudden temperature changes from November 2007 to January 2008 with the variation amplitudes several times larger than the ordinary deviation. The above phenomena and the criteria for distinguishing the anomalies from background fluctuations are discussed in this paper.  相似文献   

9.
We explored to what extent morphological variation and habitat modification are correlated for an autogenic ecosystem engineer, which is an organism that modifies its habitat via its own physical structures. The intertidal salt marsh speciesSpartina anglica is well known for its capacity to enhance sediment accretion within its canopy by reducing hydrodynamic energy. Sediment accretion is favorable toSpartina, as it reduces inundation stress, enhances soil drainage, and enhances nutrient availability. Shoot density and clonal architecture showed a large variation that was strongly correlated with the marsh elevation and sediment type. This correlation showed that at the lowest elevations at the muddy site,Spartina tussocks had the highest shoot density, which is known to be favorable for sediment accretion by reduction of hydrodynamic energy. There was also a strong positive correlation between the amount of sediment that accumulated within a tussock and gully formation around thatSpartina tussock. The tussocks at the lowest elevations at the muddy site had the lowest lateral tussock growth. At the highest elevations at the sandy site, stem densities were lower and there was a relatively high rate of clonal expansion and marsh formation. At this location, we also observed tussock mortality due to erosion of several of these openly structured tussocks. Based on the observed correlations, we hypothesize that the morphology ofSpartina represents trade-offs between the capacity to maximize habitat modification through sediment trapping by having a high shoot density versus the capacity to maximize clonal expansion by spreading shoots widely and the capacity of maximal clonal expansion by spreading shoots widely versus the risk of tussock mortality due to insufficient modification of the habitat that makes the tussock vulnerable to erosion. Our results indicated that morphological variation and habitat modification are strongly correlated for the autogenic ecosystem engineerS. anglica.  相似文献   

10.
The sandbuilder worm Sabellaria vulgaris is widely found along the Mid-Atlantic region of the USA, but occurs in dense, reef-like structures in only one estuary. Reef formation and persistence was monitored in lower Delaware Bay along the western shoreline between 2001 and 2009 using ground surveys and aerial photography. These observations were combined with field larval settlement studies, laboratory low temperature susceptibility experiments, and an examination of the physical properties of the individual beaches to attempt to explain the location and persistence of the reefs. Neither exposure to temperature minima during spring low tides nor yearly variations in recruitment accounted for the observed reef distribution patterns. This study suggests that two physical factors, the distance from the beach to the 2-m isobath and the presence of coarse substratum >2 mm explain the greatest amount of variation in the observed distribution of intertidal S. vulgaris reefs and small aggregations.  相似文献   

11.
Ecological data indicate that as the amount of precipitation in an arid areas increases, so too does mammalian taxonomic richness. This correspondence has been found in two late-Quaternary mammalian faunas from Utah, one from Homestead Cave in the Bonneville Basin. We use the remains of two species of woodrat (Neotoma cinerea and Neotoma lepida) from Homestead Cave to test the hypothesis that as the amount of precipitation in an arid area increases, so too does morphological diversity within individual mammalian taxa. Morphological diversity is measured as corrected coefficients of variation and as richness of size classes of mandibular alveolar lengths. Coefficients of variation for N. cinerea are few and coincide with moisture history if temporally successive small samples are lumped together. More abundant coefficients of variation for N. lepida coincide only loosely with moisture history, likely because such coefficients measure dispersion but not necessarily other aspects of variation. Richness of size classes of N. lepida is high during the early and late Holocene when moisture was high, and lowest during the middle Holocene when climate was most arid.  相似文献   

12.
Su  Zhengan  Xiong  Donghong  Dong  Yifan  Yang  Dan  Zhang  Su  Zhang  Baojun  Zheng  Xueyong  Zhang  Jianhui  Shi  Liangtao 《Natural Hazards》2015,79(1):183-202

This study assessed temporal variation in soil erosion rates in response to energy consumption of flow (ΔE). It employed an in situ bank gully field flume experiment with upstream catchment areas with bare (BLG) or cultivated land (CLG) that drained down to bare gully headcuts. Water discharge treatments ranged from 30 to 120 L Min−1. Concentrated flow discharge clearly affected bank gully soil erosion rates. Excluding minimal discharge in the CLG upstream catchment area (30 L min−1), a declining power function trend (p ≤ 0.1) was observed with time in soil erosion rates for both BLG and CLG upstream catchment areas and downstream gully beds. Non-steady state soil erosion rates were observed after an abrupt collapse along the headcut slope after prolonged scouring treatments. However, as the experiment progressed, ΔE and energy consumption of flow per unit soil loss (ΔEu) exhibited a logarithmic growth trend (p < 0.1) at each BLG and CLG position. Although similar temporal trends in soil erosion and infiltration rates were observed, values clearly differed between BLG and CLG upstream catchment areas. Furthermore, Darcy–Weisbach friction factor (f) values in the CLG upstream catchment area were higher than the corresponding BLG area. In contrast to the BLG upstream catchment area, lower ΔEu and higher soil erosion rates were observed in the CLG upstream catchment area as a result of soil disturbances. This indicated that intensive land use changes accelerate soil erosion rates in upstream catchment areas of bank gullies and increase soil sediment transport to downstream gullies. Accordingly, reducing tillage disturbances and increasing vegetation cover in upstream catchment areas of bank gullies are essential in the dry-hot valley region of Southwest China.

  相似文献   

13.
Monthly scenarios of relative humidity (R H) were obtained for the Malaprabha river basin in India using a statistical downscaling technique. Large-scale atmospheric variables (air temperature and specific humidity at 925 mb, surface air temperature and latent heat flux) were chosen as predictors. The predictor variables are extracted from the (1) National Centers for Environmental Prediction reanalysis dataset for the period 1978–2000, and (2) simulations of the third generation Canadian Coupled Global Climate Model for the period 1978–2100. The objective of this study was to investigate the uncertainties in regional scenarios developed for R H due to the choice of emission scenarios (A1B, A2, B1 and COMMIT) and the predictors selected. Multi-linear regression with stepwise screening is the downscaling technique used in this study. To study the uncertainty in the regional scenarios of R H, due to the selected predictors, eight sets of predictors were chosen and a downscaling model was developed for each set. Performance of the downscaling models in the baseline period (1978–2000) was studied using three measures (1) Nash–Sutcliffe error estimate (E f), (2) mean absolute error (MAE), and (3) product moment correlation (P). Results show that the performances vary between 0.59 and 0.68, 0.42 and 0.50 and 0.77 and 0.82 for E f, MAE and P. Cumulative distribution functions were prepared from the regional scenarios of R H developed for combinations of predictors and emission scenarios. Results show a variation of 1 to 6% R H in the scenarios developed for combination of predictor sets for baseline period. For a future period (2001–2100), a variation of 6 to 15% R H was observed for the combination of emission scenarios and predictors. The variation was highest for A2 scenario and least for COMMIT and B1 scenario.  相似文献   

14.
We analyse the seismicity pattern including b-value in the north Sumatra-Great Nicobar region from 1976 to 2004. The analysis suggests that there were a number of significant, intermediate and short-term precursors before the magnitude 7.6 earthquake of 2 November 2002. However, they were not found to be so prominent prior to the magnitude 9.0 earthquake of 26 December 2004 though downward migration of activity and a 50-day short-term quiescence was observed before the event. The various precursors identified include post-seismic and intermediate-term quiescence of 13 and 10 years respectively, between the 1976 (magnitude 6.3) and 2002 earthquakes with two years (1990–1991) of increase in background seismicity; renewed seismicity, downward migration of seismic activity and foreshocks in 2002, just before the mainshock. Spatial variation in b-value with time indicates precursory changes in the form of high b-value zone near the epicenter preceding the mainshocks of 2004 and 2002 and temporal rise in b-value in the epicentral area before the 2002 earthquake.  相似文献   

15.
The unsaturated poromechanical behavior of Callovo-Oxfordian argillite (also referred to as Meuse/Haute–Marne argillite) is analyzed by means of indentation tests at different hygrometries. Numerical simulations carried out with a finite element code are then used to simulate flat punch indentation tests at different controlled hygrometries. The numerical response F(h) is compared to experimental data in order to estimate the drained Young’s modulus E and the internal friction angle \Upphi\Upphi (at high confinement) by means of a back analysis. A linear decrease in the drained Young’s modulus and quasi-constant values of the internal friction angle are observed when the relative humidity ranges. Some predictions of the model are also presented to quantify the activation of hydraulic phenomena. Indeed, the maximal variation of the saturation and porosity relative to the initial state of the specimen are lower than 10% and 8%, respectively.  相似文献   

16.
Bogdan Enescu  Kiyoshi Ito   《Tectonophysics》2005,409(1-4):147-157
By using the double-difference relocation technique, we have determined the fine structure of seismicity during the 1998 Hida Mountain earthquake swarm. The distribution of seismic activity defines two main directions (N–S and E–W) that probably correspond to the regional stress pattern. The detailed structure of seismicity reveals intense spatio-temporal clustering and earthquake lineations. Each cluster of events contains a mainshock and subsequent aftershock activity that decays according to the Omori law. The seismicity and the b-value temporal and spatial patterns reflect the evolution of the static stress changes during the earthquake swarm. About 80% of the swarm's best-relocated events occur in regions of increased ΔCFF. The smaller value of b found in the northern part of the swarm region and a larger b-value observed to the south, for the same period of time, could be well explained by the static stress changes caused by the larger events of the sequence. We argue that the state of stress in the crust is the main factor that controls the variation of b-value.  相似文献   

17.
Garnet-biotite gneisses, some of which contain sillimanite or hornblende, are widespread within the Otter Lake terrain, a portion of the Grenville Province of the Canadian Shield. The metamorphic grade is upper amphibolite to, locally, lower granulite facies. The atomic ratio Fe2+/(Fe2++ Fe3+) in biotite ranges from 0.79 to 0.89 (ferrous iron determinations in 10 highly pure separates), with a mean of 0.86. Mg and Fe2+ atoms occupy 67–78% of the octahedral sites, the remainder are occupied by Fe3+, Ti, and Al, and some are vacant. Mg/(Mg + Fe2+), denoted X, in the analysed samples ranges from 0.32 to 0.65. Garnet contains 1–24% grossular, 1–12% spessartine and X ranges from 0.07 to 0.34. Compositional variation in biotite and garnet is examined in relation to three mineral equilibria: (I) biotite + sillimanite + quartz = garnet + K-feldspar + H2O; (II) pyrope + annite = almandine + phlogopite; (III) anorthite = grossular + sillimanite + quartz. Measurements of X (biotite) and X (garnet) are used to construct an illustrative model for equilibrium (I) which relates the observed variation in X to a temperature range of 70°C or a range in H2O activity of 0.6; the latter interpretation is preferred. In sillimanite-free gneisses, the distribution of Mg and Fe2+ between garnet (low in Ca and Mn) and biotite is adequately described by a distribution coefficient (KD) of 4.1 (equilibrium II). The observed increase in the distribution coefficient with increasing Ca in garnet is ln KD= 1.3 + 2.5 × 10?2 [Ca] where [Ca] = 100 Ca/(Mg + Fe2++ Mn + Ca). The distribution coefficient is apparently unaffected by the presence of up to 12% spessartine in garnet. In several specimens of garnet-sillimanite-plagioclase gneiss, the Ca contents of garnet and of plagioclase increase in unison, as required by equilibrium (III). The mean pressure calculated from these data (n= 17) is 5.9 kbar, and the 95% confidence limits are ±0.5 kbar.  相似文献   

18.
We have studied the relation log M0+ versus ML in Friuli (Italy) by considering the amplitude spectra of local earthquakes. We show a possible time variation of the apparent average stress in the focal region between the two periods of May and November, 1976. Furthermore, the quality factor Qp obtained from the same spectra indicates a spatial variation which could be correlated to the difference in the seismicity level.  相似文献   

19.
Although grasshoppers are common salt marsh herbivores, we know little about geographic variation in their species composition. We documented latitudinal variation in species composition of the tettigoniid grasshopper fauna of Atlantic Coast salt marshes. Tettigoniids (N = 740 adults) were collected from the Spartina alterniflora zone of 31 salt marsh sites across a latitudinal range of 13.19° (Florida to Maine), with an additional 52 individuals collected from the Juncus roemerianus zone of low-latitude marshes for comparative purposes. Eight species were collected, but some were common only at a few sites or rare throughout the entire collection range. The tettigoniid community was dominated by Orchelimum fidicinium at low latitudes and Conocephalus spartinae at high latitudes. Several factors might explain this shift, including changes in climate, plant phenology, and plant zonation patterns. O. fidicinium and C. spartinae increased in body size toward low latitudes. In laboratory feeding assays, O. fidicinium readily ate S. alterniflora and J. roemerianus leaves, Orchelimum concinnum, which is largely restricted to the J. roemerianus zone, ate only J. roemerianus leaves, and Conocephalus spp. ate neither, consistent with literature suggestions that they mainly consume seeds and flowers. Geographic variation in species composition and body size of grasshoppers may help explain documented patterns of geographic variation in plant palatability and plant–herbivore interactions in Atlantic Coast salt marshes. Because it can be difficult to identify tettigoniids to species, we present a guide to aid future workers in identifying the tettigoniid species common in these marshes.  相似文献   

20.
An extremely differentiated suite of unaltered volcanic rocks dredged from the Galapagos Spreading Center ranges in 18O from 5.7 to 7.1 At 95°W, low K-tholeiites, FeTi-basalts, andesites and rhyodacites were recovered. Their lithologic and major element geochemical variation can be accounted for by crystal fractionation of plagioclase, pyroxenes, olivine and titanomagnetite in the same proportions and amounts needed to model the 18O variation by simple Rayleigh fractionation. More complicated behaviour was observed in a FeTi-basalt suite from 85°W. This study shows that 90% fractionation only enriches the residual melt by about 1.2 in 18O. It also implies that the magma chambers along parts of the Galapagos Spreading Center were static and isolated such that extreme differentiation could occur.  相似文献   

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