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161.
A major portion of the southern part of the Indian subcontinent is classified as a stable continental region. However, a few segments in this region are punctuated by rifts and shear zones that are seismically active. The Godavari rift that sutures the eastern Dharwar and the Bastar cratons is one such region, prone to seismic hazard. Estimation of the sedimentary thickness in these seismically active regions assumes importance since locales of thick and soft sediments are vulnerable to destruction due to surface waves generated by earthquakes. In the present study, data from five broadband seismological stations are utilized to estimate the average sedimentary thickness of the Godavari region using the difference in travel times of the direct S and converted Sp phases from local earthquakes. The thickness of sediments varies between 0.32 and 4.32 km. Also, the site-specific response in terms of the fundamental resonance frequency and the corresponding amplifications are estimated using the well-established Nakamura technique. The predominant frequencies are in the range of 1.3–4.61 Hz, and the amplifications are higher (>1.5) for the stations inside the Godavari basin. Both the thickness and amplification values clearly indicate that the sediments tend to get thicker toward the center of the basin, in good agreement with the geological distribution of the sedimentary units. 相似文献
162.
K. Giannopoulou M. Santamouris I. Livada C. Georgakis Y. Caouris 《Pure and Applied Geophysics》2010,167(11):1433-1449
The present paper investigates the impact of canyon geometry on the temperature regime and nocturnal heat island development
in the very dense urban area of Athens, Greece. Detailed measurements of air temperature have been carried out within three
deep urban canyons of different aspect ratios (H/W = 3, 2.1 and 1.7) during the night period of the summer and autumn of 2007. An analysis was carried out to investigate the
relative impact of the canyon geometry, the undisturbed wind velocity, ambient temperature, and cloud cover on the development
of a nocturnal heat island. A clear increase of the median, maximum and minimum values of the cooling rates has been observed
for decreasing aspect ratios. Under low ambient temperatures, high wind speeds correspond to a substantial rise of the cooling
rate in the urban canyons mainly because of the increased convective losses. On the contrary, cooling rates decrease substantially
under high-undisturbed wind speeds and ambient temperatures because of the important convective gains. The impact of cloud
cover was found to be important as cloudy skies cause a substantial decrease of the cooling rates in the urban canyons. Comparisons
were performed between the temperature data collected in the three studied urban canyons and temperatures recorded in an urban
as well as a suburban open space station. 相似文献
163.
Zircon and whole-rock Nd-Pb isotopic provenance of Middle and Upper Ordovician siliciclastic rocks, Argentine Precordillera 总被引:1,自引:0,他引:1
JAMES D. GLEASON STANLEY C. FINNEY† SILVIO H. PERALTA‡ GEORGE E. GEHRELS§ KATHLEEN M. MARSAGLIA¶ 《Sedimentology》2007,54(1):107-136
Graptolite‐bearing Middle and Upper Ordovician siliciclastic facies of the Argentine Precordillera fold‐thrust belt record the disintegration of a long‐lived Cambro‐Mid Ordovician carbonate platform into a series of tectonically partitioned basins. A combination of stratigraphic, petrographic, U‐Pb detrital zircon, and Nd‐Pb whole‐rock isotopic data provide evidence for a variety of clastic sediment sources. Four Upper Ordovician quartzo‐lithic sandstones collected in the eastern and central Precordillera yield complex U‐Pb zircon age spectra dominated by 1·05–1·10 Ga zircons, secondary populations of 1·22, 1·30, and 1·46 Ga, rare 2·2 and 1·8 Ga zircons, and a minor population (<2%) of concordant zircons in the 600–700 Ma range. Archaean‐age grains comprise <1% of all zircons analysed from these rocks. In contrast, a feldspathic arenite from the Middle Ordovician Estancia San Isidro Formation of the central Precordillera has two well‐defined peaks at 1·41 and 1·43 Ga, with no grains in the 600–1200 Ma range and none older than 1·70 Ga. The zircon age spectrum in this unit is similar to that of a Middle Cambrian quartz arenite from the La Laja Formation, suggesting that local basement rocks were a regional source of ca 1·4 Ga detrital zircons in the Precordillera Terrane from the Cambrian onwards. The lack of grains younger than 600 Ma in Upper Ordovician units reinforces petrographic data indicating that Ordovician volcanic arc sources did not supply significant material directly to these sedimentary basins. Nd isotopic data (n = 32) for Middle and Upper Ordovician graptolitic shales from six localities define a poorly mixed signal [ɛNd(450 Ma) = −9·6 to −4·5] that becomes more regionally homogenized in Upper Ordovician rocks (−6·2 ± 1·0; TDM = 1·51 ± 0·15 Ga; n = 17), a trend reinforced by the U‐Pb detrital zircon data. It is concluded that proximal, recycled orogenic sources dominated the siliciclastic sediment supply for these basins, consistent with rapid unroofing of the Precordillera Terrane platform succession and basement starting in Mid Ordovician time. Common Pb data for Middle and Upper Ordovician shales from the western and eastern Precordillera (n = 15) provide evidence for a minor (<30%) component that was likely derived from a high‐μ (U/Pb) terrane. 相似文献
164.
Meysam Fadaee I. Anastasopoulos G. Gazetas M.K. Jafari M. Kamalian 《地震工程与工程振动(英文版)》2013,12(3):473-486
When seismic thrust faults emerge on the ground surface,they are particularly damaging to buildings,bridges and lifelines that lie on the rupture path.To protect a structure founded on a rigid raft,a thick diaphragm-type soil bentonite wall(SBW) is installed in front of and near the foundation,at sufficient depth to intercept the propagating fault rupture.Extensive numerical analyses,verified against reduced–scale(1 g) split box physical model tests,reveal that such a wall,thanks to its high deformability and low shear resistance,"absorbs" the compressive thrust of the fault and forces the rupture to deviate upwards along its length.As a consequence,the foundation is left essentially intact.The effectiveness of SBW is demonstrated to depend on the exact location of the emerging fault and the magnitude of the fault offset.When the latter is large,the unprotected foundation experiences intolerable rigid-body rotation even if the foundation structural distress is not substantial. 相似文献
165.
An experiment is reported in which heat was released as a passive tracer from an elevated lateral line source within a model plant canopy, with h s = 0.85 h c (h s and h c being the source and canopy heights, respectively). A sensor assembly consisting of three coplanar hot wires and one cold wire was used to measure profiles of mean temperature % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaiikamaana% aabaGaeqiUdehaaiaacMcaaaa!390C!\[(\overline \theta )\], temperature variance (Σθ 2), vertical and streamwise turbulent heat fluxes, and third moments of wind and temperature fluctuations. Conclusions were:
- Despite the very heterogeneous flow within the canopy, the observed dispersive heat flux (due to spatial correlation between time-averaged temperature and vertical velocity) was small. However, there is evidence from the plume centroid (which was lower than h s at the source) of systematic recirculating motions within the canopy.
- The ratio % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Wdm3aaS% baaSqaaiabeI7aXjaab2gacaqGHbGaaeiEaaqabaGccaGGVaWaa0aa% aeaacqaH4oqCaaWaaSbaaSqaaiaab2gacaqGHbGaaeiEaaqabaaaaa!41DF!\[\sigma _{\theta {\text{max}}} /\overline \theta _{{\text{max}}} \] (of maximum values on vertical profiles) decreased from 1 near the source to an asymptotic value of 0.4 far downstream, in good agreement with previous experimental and theoretical work for concentration fluctuations in the surface layer well above the canopy.
- The eddy diffusivity for heat from the line source (K HL ) increased, downstream of the source, to a nearly constant ‘far-field’ vertical profile. Within the canopy, the far-field K HL was an order of magnitude larger than K HP , the equivalent diffusivity for a plane source; well above the canopy, the two were equal. The time scale defined by (far-field K HL )/(vertical velocity variance) was independent of height within the canopy.
- Budgets for temperature variance, vertical heat flux and streamwise heat flux are remarkably similar to the equivalent budgets for an elevated line source in the surface layer well above the canopy, except in the lower part of the canopy in the far field, where vertical transport is much more important than in the surface layer.
- A random flight simulation of the mean height and depth of the temperature plume was generally in good agreement with experiment. However, details of the temperature and streamwise turbulent heat flux profiles were not correct, suggesting that the model formulation needs to be improved.
166.
M. I. Vitorino P. L. da Silva Dias N. J. Ferreira 《Meteorology and Atmospheric Physics》2006,93(1-2):17-35
Summary Atmospheric variability in outgoing long-wave radiation (OLR) and tropospheric relative vorticity (VOR) over the South American
region was studied from 1979 to 1996 using the complex Morlet wavelet function. The analyses focus on spatial variation in
intraseasonal and submonthly scales. Scalograms were used to measure submonthly intraseasonal oscillations in convection,
which were found to be predominant in the tropical regions. However, 7-day and 15-day oscillations were observed at tropical
and extratropical latitudes in spring and winter, indicating that transient disturbances play a more prominent role. Regarding
VOR, tropical energy intensities were highest in the spring and summer, whereas subtropical and extratropical energy intensities
were highest in the autumn and winter. The dynamics of the 25-day and 45-day VOR oscillations indicates a possible correlation
with Rossby waves over the eastern tropical Pacific Ocean, mainly during the summer. During winter, the 7-day and 15-day VOR
oscillations are more frequent at higher latitudes and are enhanced along storm tracks. It was also observed that convection
amplitudes in the regions of maximum intensity change appreciably from year to year and from season to season, showing that
the behavior of the submonthly and intraseasonal oscillations is nonperiodic and correlates strongly with El Ni?o/Southern
Oscillation years. These results confirm the efficiency of wavelet analysis for time-scale studies of atmospheric variability. 相似文献
167.
A. V. Belov E. A. Eroshenko M. A. Abunina A. A. Abunin V. A. Oleneva V. G. Yanke 《Geomagnetism and Aeronomy》2016,56(6):645-651
Variations in the cosmic ray density during the initial phase of the Forbush effect during the first hours after the arrival of the interplanetary shock wave have been studied with the use of data on variations in the cosmic ray density with a rigidity of 10 GV obtained by the global survey method by the world network of neutron monitors in 1957?2012. It is found that behavior of this parameter after the arrival of the shock wave demonstrates high variability. A small (~1/5 of total number), though distinct, group of Forbush effects, in which the density of the cosmic ray increases (not decreases) after the arrival of the shock wave, is defined. As a whole, the initial variation in cosmic ray density is correlated with the Forbush effect magnitude and the strength of the associated geomagnetic disturbance. 相似文献
168.
M. G. Deminov G. F. Deminova G. A. Zherebtsov O. M. Pirog N. M. Polekh 《Geomagnetism and Aeronomy》2011,51(3):348-355
Results of statistical analysis of the properties of variability of F2-layer maximum parameters (critical frequency foF2 and the height hmF2) in quiet midlatitude ionosphere under low solar activity in the daytime (1000–1500 LT) and nighttime (2200–0300 LT) hours
are presented on the basis of Irkutsk station data for 2007–2008. It is found that the distribution density of δfoF2 could be presented as consisting of two distinctly different normal laws of this distribution, one of which corresponds
to weak (|δfoF2| < 10%) fluctuations in foF2 and the other corresponds to strong (30% > |δfoF2| > 10%) fluctuations. Weak fluctuations in foF2 to a substantial degree are related to ionospheric variability at times less of than 1–3 h and determine the δfoF2 variability in the daytime hours. Strong fluctuations in foF2 are mainly related to day-to-day variability of the ionosphere at a fixed local time, the variability increasing by approximately
a factor of 3 during the transition from day to night and determining the δfoF2 variability in the nighttime hours. The distribution density of ΔhmF2 is close to the normal distribution law. An interpretation of the different character of the distribution densities of δfoF2 and ΔhmF2 is given. 相似文献
169.
We present new counts of stars in M15, using plates inB, V andU. We are able to explore relatively close to the central parts of the cluster (0.1 pc) and we derive the best fitting parameters for the star distribution. 相似文献
170.
The Middle Miocene Tobe hornfels in the Sanbagawa metamorphic belt, western Shikoku, southwest Japan, is characterized by
an abnormally steep metamorphic gradient compared with other hornfelses associated with intrusive bodies. The basic hornfels,
originally Sanbagawa greenschist rocks, is divided into the following three metamorphic zones: plagioclase, hornblende, and
orthopyroxene. The plagioclase zone is defined by the appearance of calcic plagioclase, the hornblende zone by the assemblage
of hornblende+calcic plagioclase+quartz, and the orthopyroxene zone is characterized by the assemblage of orthopyroxene +
clinopyroxene + plagioclase + quartz. Calcic amphibole compositions change from actinolite to hornblende as a result of the
continuous reactions during prograde metamorphism. Petrographical and thermometric studies indicate a metamorphic temperature
range of 300–475°C for the plagioclase zone, 475–680°C for the hornblende zone, and 680–730°C for the orthopyroxene zone.
The temperature gradient based on petrological studies is approximately 5°C/m, which is unusually high. Geological and petrological
studies demonstrate that the hornfelses were formed by the focusing of high-temperature fluids through zones of relatively
high fracture permeability. The steep thermal gradient in the Tobe hornfels body is consistent with a large fluid flux, greater
than 8.3 × 10–7 m3 m–2S–1, over the relatively short duration of metamorphism, approximately 100 years.
Received: 10 October 1995 / Accepted: 28 May 1996 相似文献