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1.
Airglow all sky imaging observation has been carried out in three different locations in south America, at Cachoeira Paulista (22.7°S, 45.0°W) in 1999, São João do Cariri (7.5°S, 36.5°W) in 2001 and Boa Vista (2.8°N, 60.7°W) in 2002. Comparing the atmospheric gravity wave characteristics retrieved from the image data for the three different sites and including a previous work at Alcântara (2.3°S, 44.5°W) carried out by Taylor et al. [1997. Journal of Geophysical Research 102 (D22) 26,283–26,299], we found that there is a preferential propagation direction, from the Continent to the Atlantic Ocean. The observed wave propagation directions reveal that a major part of the waves have their direction from Continent toward Ocean. The possible source of the wave generation is discussed.  相似文献   

2.
Continuous MF and meteor radar observations allow detailed studies of winds in the mesosphere and lower thermosphere (MLT) as well as temperatures around the mesopause. This height region is characterized by a strong variability in winter due to enhanced planetary wave activity and related stratospheric warming events, which are distinct coupling processes between lower, middle and upper atmosphere. Here the variability of mesospheric winds and temperatures is discussed in relation with major and minor stratospheric warmings as observed during winter 2005/06 in comparison with results during winter 1998/99.Our studies are based on MF radar wind measurements at Andenes (69°N, 16°E), Poker Flat (65°N, 147°W) and Juliusruh (55°N, 13°E) as well as on meteor radar observations of winds and temperatures at Resolute Bay (75°N, 95°W), Andenes (69°N, 16°E) and Kühlungsborn (54°N, 12°E). Additionally, energy dissipation rates have been estimated from spectral width measurements using a 3 MHz Doppler radar near Andenes. Particular attention is directed to the changes of winds, turbulence and the gravity wave activity in the mesosphere in relation to the planetary wave activity in the stratosphere.Observations indicate an enhancement of planetary wave 1 activity in the mesosphere at high latitudes during major stratospheric warmings. Daily mean temperatures derived from meteor decay times indicate that strong warming events are connected with a cooling of the 90 km region by about 10–20 K. The onset of these cooling processes and the reversals of the mesospheric circulation to easterly winds occur some days before the changes of the zonal circulation in the stratosphere start indicating a downward propagation of the circulation disturbances from the MLT region to the stratosphere and troposphere during the stratospheric warming events. The short-term reversal of the mesospheric winds is followed by a period of strong westerly winds connected with enhanced turbulence rates and an increase of gravity wave activity in the altitude range 70–85 km.  相似文献   

3.
The geological evolution of the Mesozoic Troodos Ophiolite Complex in Cyprus, and the tectonic nature and timing of the palaeomagnetically indicated anticlockwise rotation of Cyprus of some 80° and ca. 15° northward translation, have been open for debate for some time. New palaeomagnetic data from 18 sites ( 180samples) in the post-ophiolite sediments, ranging in age from Upper Cretaceous to Upper Miocene, are presented. Most of the sites are of normal geomagnetic polarity, but indications of reversed polarity have been found in an older group of sediments (the Lefkara Formation of Upper Palaeocene age).Six sites from the older group of sediments (Upper Cretaceous to Eocene in age) give a site mean direction of the AF cleaned sediments of (D, I) = (323°, 29°) with α95 = 18°, while 5 sites from a younger group of sediments (Oligocene to Miocene in age) give a cleaned site mean direction of (D, I) = (334°, 58°) with α95 = 9°. These and published data suggest that an anticlockwise rotation of Cyprus of 60 ± 10° occurred early during the post-igneous evolution of the Cyprus oceanic crust between 90 and 50Ma, leaving only a minor anticlockwise rotation of 20 ± 10° to occur during the last 50 Ma. It is furthermore concluded that the northward translation of Cyprus of 15° mostly took place during the last 30Ma.It thus appears that a fairly rapid rotation of the Cyprus microplate first took place in the Late Cretaceous and Early Tertiary time with an average angular velocity of 1–2°/Ma, during which the northward translation was minor or negligible. In the latter half of the Tertiary, the sense of movement appears to have radically changed, the northward translation now being dominant with an average velocity of 5–6cm/yr. This temporal evolution is found to be in good agreement with the Mesozoic and Tertiary movements of the African lithospheric plate relative to Europe, as evidenced from the Atlantic sea-floor magnetic anomaly spreading history.  相似文献   

4.
The present paper aims to synthesize results of a systematic paleomagnetic investigation performed on metamorphic, plutonic and volcanic series from the Central Massif. Detailed, thermal and alternating field demagnetizations yield a large set of paleomagnetic directions. Several groups of directions corresponding to different age intervals are identified. The group D mean direction: D = 288°, I = 57° (37°S, 110°E), characterizes Late Devonian/Early Carboniferous metamorphic and plutonic rocks from Limousin. The group C′ directions: D = 301°, I = 24° (30°S, 79°E), represent Late Visean/Namurian magnetizations, present in the major investigated areas. The group B directions: D = 249°, I = 7° (12°N, 111°E), exist not only in the whole Central Massif, but also in other Paleozoic outcrops of the Variscan belt. They were acquired during the Namurian/Westphalian. The group A′-A directions are the only typically “European” magnetic directions. They have taken place in Stephanian/Autunian times, mainly during the Kiaman reversed interval. Interpretation of these directions in terms of geodynamics leads to a probable large S-N drift of the massif during the Latest Devonian/Early Carboniferous followed by two important rotation phases, first in the Middle Carboniferous, then at the end of the Westphalian. These rotations have also affected other massifs of the Variscan belt.  相似文献   

5.
The non-hydrostatic part of the second zonal harmonic term has been included in the Indian gravity anomaly. The interpretation of the potential, gravity and deflection of the vertical has been produced by a new method. The depth of the source is 580 km and the solution satisfies the temperature gradient of 1°K/km. The ratio Δ Vp/Δp > 0 shows the thermal nature of the density distribution near 670 km.  相似文献   

6.
Loading by atmosphere and by the Baltic Sea cause gravity change at Metsähovi, located 15 km from the open sea. Gravity is changed by both the Newtonian attraction of the loading mass and by the crustal deformation. We have performed loading calculations using appropriate Green's function for both gravity and deformation, for both atmospheric and Baltic loading. The loading by atmosphere has been computed using a detailed surface pressure field from high resolution limited area model (HIRLAM) for north Europe up to 10° distances. Baltic Sea level is modelled using tide gauge records. Calculations show that 1 m of uniform layer of water corresponds to 31 nm s−2 in gravity and −11 mm in height. Modelled loading is compared with observations of the superconducting gravimeter T020 for years 1994–2002. The combination of HIRLAM and a tide gauge record decreases RMS of gravity residuals by 14% compared to single admittance in air pressure corrections without sea level data. Regression of gravity residuals on the tide gauge record at Helsinki (at 30 km distance) gives a gravity effect of 26 nm s−2 m−1 for Baltic loading.The gravity station is co-located with a permanent GPS station. We have also associated the loading effects of the atmosphere and of the Baltic Sea with temporal height variations. The range of modelled vertical motion due to air pressure was 46 mm and that due to sea level 18 mm. The total range was 38 mm. The effects of the Baltic Sea and of the atmosphere partly cancel each other, since at longer periods the inverse barometer assumption is valid. Regression of the modelled height on local air pressure gives −0.37 mm hPa−1, corresponding approximately to width 6° for pressure system.We have tested the models using one year of daily GPS data. Multilinear regression on local air pressure and sea level in Helsinki gives the coefficient −0.34 mm hPa−1 for pressure, and −11 mm m−1 for sea level. These match model values. Loading by air pressure and Baltic Sea explains nearly 40% of the variance of daily GPS height solutions.  相似文献   

7.
The interpretation of the Jarrafa magnetic and gravity highs, NW Libyan offshore, suggests that it may be caused by a body of high-density and high magnetization. Analysis of their power spectra indicates two groups of sources at: (1) 2.7 km depth, probably related to the igneous rocks, some of which were penetrated in the JA-1 borehole, (2) 5 km depth, corresponding to the top of the causative body and (3) 10 km depth, probably referring to the local basement depth. The boundary analysis derived from applied horizontal gradient to both gravity and magnetic data reveals lineaments many of which can be related to geological structures (grabens, horsts and faults).The poor correlation between pseudogravity fields for induced magnetization and observed gravity fields strongly suggests that the causative structure has a remanent magnetization (D = −16°, I = 23°) of Early Cretaceous age, fitting with the opening of the Neo Tethys 3 Ocean.Three-dimensional interpretation techniques indicate that the magnetic source of the Jarrafa magnetic anomaly has a magnetization intensity of 0.46 A/m, which is required to simulate the amplitude of the observed magnetic anomaly. The magnetic model shows that it has a base level at 15 km.The history of the area combined with the analysis and interpretation of the gravity and magnetic data suggests that: (1) the source of the Jarrafa anomaly is a mafic igneous rock and it may have formed during an Early Cretaceous extensional phase and (2) the Jarrafa basin was left-laterally sheared along the WNW Hercynian North Graben Fault Zone, during its reactivation in the Early Cretaceous.  相似文献   

8.
In this paper, data obtained by the 1995, 1996 and 1999 three GPS campaigns in North China have been used to study intraplate tectonic block movements in this area (N36°–N42°, and E112°–E120°). By a Bayesian inversion method, negative dislocation distributions on three main fault zones and individual relative movements between four intraplate tectonic blocks have been obtained based on these GPS data. The results show that the relative movements between four intraplate tectonic plates are several millimeters per year. The obtained negative dislocation values on the Front Tai-Hong Mountain fault are −5±2 mm/a in tensile component, and 2±2 mm/a in both strike and dip component, which indicates that this fault mainly suffers pull apart tectonic movements. On the Tangshan–Ninghe fault, the obtained negative dislocation values are −3±3 mm/a in dip, −2±2 mm/a in tensile and −1±3 mm/a in strike, which indicates that the east part of this fault still undergoes upward movement. On the Zhangjiako–Beipiao fault, the obtained negative dislocation values are −4±2 mm/a in strike, 0±2 mm/a in dip, and 1±2 mm/a in tensile, which indicates that this fault has sinistral strike movement. According to the inversion results, the southern part of the Zhangjiako-Beipiao fault suffers pull tectonic movements caused by recent upward movement of the eastern part. The pulling tectonic movements are almost totally blocked on the Front Tai-Hong Mountain fault and this fault is more likely to be a potential earthquake source.  相似文献   

9.
Paleomagnetic data from 46 sites (674 specimens) of the Westcoast Crystalline Gneiss Complex on the west coast of Vancouver Island using AF and thermal demagnetization methods yields a high blocking temperature WCB component (> 560°C) with a pole at 335°W, 66°N (δp = 4°, δm = 6°) and a lower coercivity WCA component ( 25 mT, < 500°C) with a pole at 52°W, 79°N (δp = 7°, δm = 8°). Further thermal demagnetization data from 24 sites in the Jurassic Island Intrusions also defines two high blocking temperature components. The IIA component pole is at 59°W, 79°N (δp = 7°, δm = 8°) and IIB pole at 130°W, 73°N (δp = 12°, δm = 13°). Combined with previous data from the Karmutsen Basalts and mid-Tertiary units on Vancouver Island and from the adjacent Coast Plutonic Complex, the geotectonic motions are examined for the Vancouver Island segment of the Wrangellian Subterrane of composite Terrane II of the Cordillera. The simplest hypothesis invokes relatively uniform translation for Terrane II from Upper Triassic to Eocene time producing 39° ± 6° of northward motion relative to the North American craton, combined with 40° of clockwise rotation during the Lower Tertiary.  相似文献   

10.
Various kinds of geophysical surveys have been carried out in the Mizuho Plateau, East Antarctica by the Japanese Antarctic Research Expeditions (JARE). The correlation between the high-level gravity anomaly and the bedrock elevation is examined along a route where both data are sufficient to permit deriving a crustal model from gravity, radio-echo sounding and explosion seismic data. The bedrock elevation usually correlates well with the high-level gravity anomaly. However, along the traverse route S-H-Z from the Syowa to Mizuho stations, the bedrock elevation has a weak negative correlation with the high-level gravity anomaly. Such a weak negative correlation is attributed to the deeper part of the crust.The crustal structure between the Syowa and Mizuho stations is modeled from the gravimetric data and the radio-echo sounding of bedrock elevations, so as to fit the P-wave velocity structure derived from the data of explosion seismic experiments. Then the structure is extended from Syowa Station seaward across Lützow-Holm Bay and from Mizuho Station southeastwards inland, where only gravimetric data are available. Thus, a crustal section about 600 km long is obtained on a margin of East Antarctica. The depth of the Moho increases by about 7 km from Syowa Station to the point Y200 (71° 46′S, 48° 56′E), about 500 km from the coast. A graben-like structure is obtained along the line across Lützow-Holm Bay. This suggests that both sides of the bay are bounded by faults.  相似文献   

11.
Samples of the Dhajala H3.8 chondrite have been annealed for 10 hours at 600, 700, 800, 900 and 1000°C and at 1000°C for 1, 2, 20 and 100 h and their thermoluminescence (TL) properties measured. The TL sensitivity decreased by a factor of 2 after annealing at < 900°, but at higher temperatures fell by an order of magnitude. An abrupt increase in the temperature of the TL peak from 172 ± 9°Cto231 ± 8°C and a steady increase in the width of the peak from 169 ± 7°Cto212 ± 5°C were caused by the annealing treatment. The TL phosphor in Dhajala is thought to be feldspar predominantly in the high-temperature (disordered) form, but the present data indicate that a contribution from the low-temperature form is also present and that this low-temperature component is converted to the high form by the annealing treatment. The low-temperature feldspar is located in a few of the chondrules ( 20% of those separated from the meteorite) which are also noteworthy for having high TL sensitivities. These chondrules must have suffered greater crystallization of their mesostasis than the other chondrules, and equilibrated to lower temperatures. It is argued that, for compositional reasons, their mesostasis constituted less of a barrier to diffusion and therefore equilibration. Presumably the post-metamorphic cooling rate of the meteorite through the stability field of the low form was slow enough to permit some crystallization, and the width and temperature of the TL peaks for petrologic types 3.5–3.9 are somehow related to cooling rate. Based on TL, there is no indication of a correlation between petrologic type and cooling rate for types 3.5–3.9; this is not consistent with a simple, single internally heated meteorite parent body.  相似文献   

12.
All previous accounts of the spiral patterns at the Martian poles emphasize that the north polar spiral is centered about the geographic pole, whereas that of the south polar region is off-set by about 4°. This paper demonstrates that the patterns near both poles are centered on topographic highs rather than the spin poles themselves. This is circumstantial evidence in favour of the relatively unexplored mechanism of radial outflow of viscous rock by gravity spreading.The hypothesis developed here is that the spiral patterns are essentially due to crevasse patterns formed perpendicular to flow lines which are perturbed by Coriolis forces. In order to account for a crevasse pattern that has a form concave to the east the angular deflection of an hypothetical ice flow emanating from the topographic high centered about the geographical north pole, must be about 40° or 0.7 radians in a westward direction at 85°N latitude.The polar cap rock has previously been assumed to consist mainly of either frozen carbondioxide or water ice. Corresponding viscosities (at 190 K) allow for the occurrence of radial outflow or gravity driven tectonics at a maximum rate of 1 cm a−1, but the flow pattern remains unaffected by Coriolis forces.The spiral patterns of the Martian poles can be explained if the flowing mass has an occasional effective kinematic viscosity as low as about 7 × 106 m2 s−1, because gravity tectonics will then be deflected by Coriolis forces resulting in appropriately curved flowlines. A tensile fracture pattern, resembling an anticlockwise spiral pattern perpendicular to the clockwise deflected flowlines may subsequently form by local brittle failure.The occasional kinematic viscosity 7 × 106 m2 s−1 would cause flow rates of 0.2 m s−1 along the slopes of the topographic highs. This velocity and the corresponding viscosity is tentatively thought to be possible when thermal and pressure runaway occurs in the polar layered deposits. This would mean glacier surges on the Martian poles are two orders of magnitude faster than those hitherto observed on Earth.  相似文献   

13.
For the Central European area three-dimensional model techniques are used to estimate the temperature-depth distribution within the Earth's crust, the temperature at the crust-mantle boundary, the MOHO heat flow density, and the lateral variations of the heat production within the granitic upper crust. Regularization methods are used for the inversion of the surface heat flow density. The calculations were done for a 1 × 1 degree grid. Evidently, for single geothermal provinces the 200°, 400°, 600°, and 800° isotherms are running parallel to the crust-mantle boundary which implies that this discontinuity might be interpreted in terms of an isotherm.  相似文献   

14.
The equilibrium distribution of CO2H2O fluids in synthetic rock samples (principally dunite and quartzite) has been characterized by measurements of the dihedral wetting angle, θ, resulting from 5-day annealing periods at 950–1150°C and 1 GPa. For fluids in equilibrium with polycrystalline quartz, θ varies systematically from 57° for pure H2O to 90° at XCO2 0.9. Similarly, for San Carlos olivine, θ varies from 65° for pure H2O to 90° at XCO2 0.9. The addition of solutes (NaCl, KCl, CaF2, Na2CO3) to H2O causes a major decrease in θ in the quartz/fluid system (to values as low as 40°), but has no effect on fluid wetting in dunite. Reconnaissance experiments on other mono- and polymineralic aggregates indicate universally high wetting angles (θ 60°) in upper mantle assemblages and for CO2 in felsic compositions. For diopside + H2O, θ 80°, with large variation due to crystalline anisotropy. In no case does θ approach 0°, the condition necessary for fluid to be present along all grain boundaries.Because a value of θ greater than 60° precludes the existence of an interconnected fluid phase in a rock, our results have important implications not only for fluid transport but also for the physical properties of the bulk fluid/rock system. Any static fluid present in the upper mantle must exist as isolated pores located primarily at grain corners, and transport can occur only by hydrofracture. In the continental crust, aqueous fluids (especially saline ones) are likely to form an interconnected network along grain edges, thus contributing to high electrical conductivity and allowing the possibility of fluid transport by porous flow or surface energy-driven infiltration.  相似文献   

15.
The gravimetric parameters of the gravity pole tide are the amplitude factor δ, which is the ratio of gravity variations induced by polar motion for a real Earth to variations computed for a rigid one, and the phase difference κ between the observed and the rigid gravity pole tide. They can be estimated from the records of superconducting gravimeters (SGs). However, they are affected by the loading effect of the ocean pole tide. Recent results from TOPEX/Poseidon (TP) altimeter confirm that the ocean pole tide has a self-consistent equilibrium response. Accordingly, we calculate the gravity loading effects as well as their influence on the gravimetric parameters of gravity pole tide at all the 26 SG stations in the world on the assumption of a self-consistent equilibrium ocean pole tide model. The gravity loading effect is evaluated between 1 January 1997 and 31 December 2006. Numerical results show that the amplitude of the gravity loading effect reaches 10−9 m s−2, which is larger than the accuracy (10−10 m s−2) of a SG. The gravimetric factor δ is 1% larger at all SG stations. Then, the contribution of a self-consistent ocean pole tide to the pole tide gravimetric parameters cannot be ignored as it exceeds the current accuracy of the estimation of the pole tide gravity factors. For the nine stations studied in Ducarme et al. [Ducarme, B., Venedikov, A.P., Arnoso, J., et al., 2006. Global analysis of the GGP superconducting gravimeters network for the estimation of the pole tide gravimetric amplitude factor. J. Geodyn. 41, 334–344.], the mean of the modeled tidal factors δm = 1.1813 agrees very well with the result of a global analysis δCH = 1.1816 ± 0.0047 in that paper. On the other hand, the modeled phase difference κm varies from −0.273° to 0.351°. Comparing to the two main periods of the gravity pole tide, annual period and Chandler period, κm is too small to be considered. Therefore, The computed time difference κL induced by a self-consistent ocean pole tide produces a negligible effect on κm. It confirms the results of Ducarme et al., 2006, where no convincing time difference was found in the SG records.  相似文献   

16.
The redistribution of air masses induces gravity variations (atmospheric pressure effect) up to about 20 μgal. These variations are disturbing signals in gravity records and they must be removed very carefully for detecting weak gravity signals. In the past, different methods have been developed for modelling of the atmospheric pressure effect. These methods use local or two-dimensional (2D) surface atmospheric pressure data and a standard height-dependent air density distribution. The atmospheric pressure effect is consisting of the elastic deformation and attraction term. The deformation term can be well modelled with 2D surface atmospheric pressure data, for instance with the Green's function method. For modelling of the attraction term, three-dimensional (3D) data are required. Results with 2D data are insufficient.From European Centre for Medium-Range Weather Forecasts (ECMWF) 3D atmospheric pressure data are now available. The ECMWF data used here are characterised by a spacing of Δ and Δλ = 0.5°, 60 pressure levels up to a height of 60 km and an interval of 6 h. These data are used for modelling of the atmospheric attraction term. Two attraction models have been developed based on the point mass attraction of air segments and the gravity potential of the air masses. The modelling shows a surface pressure-independent part of gravity variations induced by mass redistribution of the atmosphere in the order of some μgal. This part can only be determined by using 3D atmospheric pressure data. It has been calculated for the Vienna Superconducting Gravimeter site.From this follows that the gravity reduction can be improved by applying the 3D atmospheric attraction model for analysing long-periodic tidal waves including the polar tide. The same improvement is expected for reduction of long-term absolute gravity measurements or comparison of gravity measurements at different seasonal times. By using 3D atmospheric pressure data, the gravity correction can be improved up to some μgal.  相似文献   

17.
An all-sky CCD imager designed to measure wave structure of the OH, O2b(0,1) and OI557.7 nm airglow emission layers in the mesosphere and lower thermosphere (MLT) region has been operated near the equatorial region at São João do Cariri (Cariri), Brazil, (7.5°S, 36.5°W). A large number of gravity wave was observed from September 2000 to September 2002 and among them 64 wave events were identified as mesospheric bores. The bore front shows a horizontal extension greater than 1000 km, and observed in the airglow layers as a complementary brilliance between the three emissions. At the first time mesospheric bore events were observed and analyzed in the equatorial region. Their predominant characteristics, occurrence, local time dependency, morphology and propagation direction will be presented and discussed.  相似文献   

18.
Measurement of the depth-mean PAR (photosynthetically active radiation) extinction coefficient, ° Ko, is important in the study of estuarine productivity. Measurements of ° Ko, beam attenuation coefficient and Secchi disc depth are presented for the turbid waters of the Tamar Estuary. Equations are formulated which allow good estimates of ° Ko to be determined both from the beam attenuation coefficient (at 660 nm) and from the Secchi disc depth. For comparison, similar data are presented for the clearer waters of the northeast Atlantic.  相似文献   

19.
The Teide volcano (3717 m) is the central structure of the island of Tenerife and at present its morphology is that of a stratovolcano which has grown on a large caldera with a collapse 17 km in diameter, which was generated some 0.6 million years ago.The different studies that have been carried out seem to indicate that, in a oversimplified model, there is an intermediate magma chamber with an approximate volume of 30 km3 and located 2–3 km below the actual base of the caldera, i.e., almost at sea level, with a temperature of 430 ± 50°C, and a pressure of 400 ± 100 bar.The summit fumarole emissions are 85°C and are formed mainly of CO2 with small amounts of sulphur species, H2, CH4 and He. The water vapor (68–82%) emitted with the gases comes from the vaporization of a perched aquifer in the upper cone, as shown by the isotopic analyses.  相似文献   

20.
Basalts dredged along the Mid-Atlantic Ridge axis between 10°N and 17°N have been studied for their trace element characteristics [1]. To give complementary information on mantle source history and magma genesis, these samples have been analysed for their SrNdPb isotopic compositions. There is a good correlation between the structure of the ridge axis which shows a topographic anomaly centered around 14°N and hygromagmaphile element ratios such as Rb/Sr, (Nb/Zr)N or Sm/Nd as well as isotopic ratios plotted as a function of latitude. The samples coming from the 14°N topographic high show new MORB SrNd isotopic characteristics which pictured in a classical mantle array diagram, put their representative points close to HIMU sources of ocean islands such as St. Helena, Tubuaïand Mangaia. The 14°N mantle source presents geochemical characteristics which indicate mantle differentiation processes and a mantle history that are more distinct than so far envisaged from typical MORB data. Pb data indicates that the 14°N mantle source cannot be the result of binary mixing between a depleted mantle and a HIMU-type source. Rather, the enriched endmember could itself be a mixture of Walvis-like and HIMU-like materials. The geochimical observations presented favour the model of an incipient ridge-centered plume, in agreement with [1].  相似文献   

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