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391.
392.
An anomalous high-velocity layer at shallow crustal depths in the Narmada zone, India 总被引:2,自引:0,他引:2
The Narmada zone in central India is a zone of weakness that separates the region of Vindhyan (Meso-Neoproterozoic) deposition to the north from Gondwana (Permo-Carboniferous–lower Cretaceous) deposits to the south. The reinterpretation of analogue seismic refraction data, acquired during the early 1980s, using 2-D ray-tracing techniques reveals a basement (velocity 5.8–6.0 km s−1 ) topography suggesting that the Narmada zone, bounded by the Narmada North and Narmada South faults is a region of basement uplift. A layer of anomalously high velocity (6.5–6.7 km s−1 ) at depths between 1.5 and 9.0 km appears to be present in the entire region. Within the Narmada zone this layer occurs at shallower depths than outside the Narmada zone. At two places within the Narmada zone this layer is at a depth of about 1.5 km. This layer cannot be considered as the top of the lower crust because in this case it should have produced large positive gravity anomalies at the shallowest parts. Instead, these parts correspond to Bouguer gravity lows. Furthermore, lower crust at such shallow depths has not been reported from any other part of the Indian shield. Therefore, this layer is likely to represent the top of a high-velocity mafic body that has different thicknesses in different places. 相似文献
393.
394.
The value of a physically based model versus an empirical approach in the prediction of ephemeral gully erosion for loess-derived soils 总被引:3,自引:0,他引:3
Jeroen Nachtergaele J. Poesen A. Steegen I. Takken L. Beuselinck L. Vandekerckhove G. Govers 《Geomorphology》2001,40(3-4)
A data set on soil losses and controlling factors for 58 ephemeral gullies has been collected in the Belgian loess belt from March 1997 to March 1999. Of the observed ephemeral gullies, 32 developed at the end of winter or in early spring (winter gullies) and 26 ephemeral gullies developed during summer (summer gullies). The assessed data have been used to test the physically based Ephemeral Gully Erosion Model (EGEM) and to compare its performance with the value of simple topographical and morphological indices in the prediction of ephemeral gully erosion.Analysis shows that EGEM is not capable of predicting ephemeral gully cross-sections well. Although conditions for input parameter assessment were ideal, some parameters such as channel erodibility, critical flow shear stress and local rainfall depth showed great uncertainty. Rather than revealing EGEM's inability of predicting ephemeral gully erosion, this analysis stresses the problematic nature of physically based models, since they often require input parameters that are not available or can hardly be obtained.With respect to the value of simple topographical and morphological indices in predicting ephemeral gully erosion, this study shows that for winter gullies and summer gullies, respectively, over 80% and about 75% of the variation in ephemeral gully volume can be explained when ephemeral gully length is known. Moreover, when previously collected data for ephemeral gullies in two Mediterranean study areas and the data for summer gullies formed in the Belgian loess belt are pooled, it appears that one single length (L)–volume (V) relation exists (V=0.048 L1.29; R2=0.91). These findings imply that predicting ephemeral gully length is a valuable alternative for the prediction of ephemeral gully volume. A simple procedure to predict ephemeral gully length based on topographical thresholds is presented here. Secondly, the empirical length–volume relation can also be used to convert ephemeral gully length data extracted from aerial photos into ephemeral gully volumes. 相似文献
395.
N. I. Alekseevskii K. M. Berkovich R. S. Chalov S. R. Chalov 《Geography and Natural Resources》2012,33(3):192-199
We assess the spatiotemporal changes in channel processes on rivers of Russia, determine the causes for vertical (incision or directional sediment accumulation) and horizontal (displacement of channel forms) deformations and show the distribution of stream channel of different morphodynamical types and with a different reconfiguration rate. The conditions are revealed, under which the channel types change over time. Particular emphasis is placed on the analysis of spatiotemporal changes in channels caused by anthropogenic disturbances and by direct technogenic interferences in the life of rivers (hydroelectric schemes, quarries in the river channels, and waterway dredging). 相似文献
396.
Vishal Chandr Jaunky 《Natural Resources Research》2012,21(2):265-278
The article attempts to test the aluminum consumption–economic growth nexus for 20 rich economies for the period 1970–2009.
Various panel data unit root and cointegration tests are applied. The series are found to be integrated of order one and cointegrated,
especially after controlling for cross-sectional dependence. Moreover, the Blundell–Bond system generalized methods-of-moments
is employed to conduct a panel causality test in a vector error-correction mechanism setting. Unidirectional causality running
from aluminum consumption to real GDP is uncovered in the short-run, while real GDP is found to Granger-cause aluminum consumption
in the long-run. Moreover, a 1% increase in real GDP generates an increase of 0.44% in aluminum consumption in the long-run
for the whole panel. 相似文献
397.
Developing approaches to automate the analysis of the massive amounts of data sent back from the Moon will generate significant benefits for the field of lunar geomorphology. In this paper, we outline an automated method for mapping lunar landforms that is based on digital terrain analysis. An iterative self-organizing (ISO) cluster unsupervised classification enables the automatic mapping of landforms via a series of input raster bands that utilize six geomorphometric parameters. These parameters divide landforms into a number of spatially extended, topographically homogeneous segments that exhibit similar terrain attributes and neighborhood properties. To illustrate the applicability of our approach, we apply it to three representative test sites on the Moon, automatically presenting our results as a thematic landform map. We also quantitatively evaluated this approach using a series of confusion matrices, achieving overall accuracies as high as 83.34% and Kappa coefficients (K) as high as 0.77. An immediate version of our algorithm can also be applied for automatically mapping large-scale lunar landforms and for the quantitative comparison of lunar surface morphologies. 相似文献
398.
Neolithic culture series in the Yishu River Basin developed in the order of Beixin culture-Dawenkou culture-Longshan culture-Yueshi culture. During the early and middle stage of Longshan culture (4600-4300 cal. yr BP), the climate in the Yishu River Basin was warm and wet. Paddy-oriented agriculture planted paddy was very developed. The society was flourishing with great amount of archaeological sites. The cooling starting in 4200 cal. yr BP made the paddies shortfall in output or even no seeds were gathered. This situation intensified the discrepancy between population and resource. The scarcity in natural resource led to substantial decrease in population and subsequent drop in archaeological sites. About 4000 cal. yr BP Longshan culture was displaced by Yueshi culture which was relatively un- derdeveloped, simple and unsophisticated. 相似文献
399.
V. M. Zobin E. I. Gordeev V. F. Bakhtiarov E. I. Ivanova Yu. M. Khatkevich V. N. Khodenko V. E. Levin V. P. Mityakin 《Natural Hazards》1992,6(1):51-70
The earthquake of 6 October 1987 (M = 6.6), which occurred near the Shipunsky Cape, Kamchatka, was the largest crustal event in the vicinity of the main city of Kamchatka — Petropavlovsk-Kamchatsky — during the last three decades. It was followed by numerous aftershocks. This earthquake allowed us to test the effectiveness of the seismic hazard monitoring in Kamchatka, including the seismological, geodetic and hydrogeochemical surveys. The seismic survey provided the location and source nature of the main shock and aftershocks and the seismic environment of the main shock. The geodetic and hydrogeochemical surveys have yielded data on the response to earthquakes of the Earth's surface deformations, water level, and chemical elements concentration in the underground water. As a result, the following data were obtained: The earthquake of 6 October had a seismic moment 4–10 E18 Nm, thrust type of faulting and the source volume of 20 × 20 × 10 km3. The maximum intensity was VI–VII (MSK-64 scale) and maximum acceleration 88 cm/s2. Before this event, a relative increase in the number of the upper mantle (depth more than 100 km) moderate magnitude earthquakes during 5 years and a one-year period of seismic quiescence for small shallow earthquakes, were recognized. Significant anomalies in HCO3 and H3BO3 concentrations in the underground waters were observed in the wells a week before the main shock. 相似文献
u
400.
T. A. Shatilina G. Sh. Tsitsiashvili T. V. Radchenkova 《Russian Meteorology and Hydrology》2010,35(11):740-743
Peculiarities are investigated of the air temperature variation tendencies at some stations of the Far East in 1976–2005.
The estimate of linear trend equation coefficients is computed according to the air temperature observation data using the
least squares method. It is demonstrated that the air temperature trend in northern regions possesses a small probability
at small values of residual variability. In the southern regions, the trend significance increases for almost all seasons
at small values of residual variability. At midlatitude stations, the trend significance in January and February decreases
considerably due to the large values of residual variability. 相似文献