Preliminary Sr and Nd isotopic data for recent lavas from Vesuvius volcano     

Graziella Caprarelli  Shigeko Togashi  Benedetto De Vivo 《Journal of Volcanology and Geothermal Research》1993,58(1-4)

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Ground deformations in collapsed caldera structures     

Giuseppe De Natale  Folco Pingue 《Journal of Volcanology and Geothermal Research》1993,57(1-2)

A method is presented to analyze the effect of stress-strain discontinuities on the ground deformations generated by a pressure source. This is meant to simulate the effects due to caldera structures, likely to present fractured zones at the borders of the collapsed area. A method originally developed by Crouch (1976) to solve plane-strain problems has been used to simulate deformation curves for several source and discontinuity geometries. The main result is that the location of the discontinuities controls the extension of the deformed zone, and always reduces it with respect to a continuous medium. With respect to a homogeneous medium the presence of lateral discontinuities also acts towards lowering the overpressure required to produce a given amount of deformation. These results indicate that, when analyzing ground deformations in calderas, the use of classical methods involving continuous media should be avoided, or at least taken with caution. These methods, in fact, assume that the extension of the deformed zone is only linked to the source depth.Some examples of ground deformations in active calderas have been analyzed in the framework of the results obtained from theoretical modeling. Four calderas recently affected by ground deformations have been considered: Rabaul (New Guinea), Campi Flegrei (Italy), Long Valley and Yellowstone (U.S.A.). The effects of collapsed structures on the deformation field are possibly evidenced for all the four calderas. At Rabaul and Campi Flegrei, the fracture systems mainly affecting the ground deformations probably represent younger, innermost collapses and are well evidenced by seismicity studies. Ground deformations are here concentrated in an area much smaller than the one enclosed by geologically visible caldera rims. In particular, at Rabaul, the effect of the innermost collapse can explain the high concentration of the uplift in the period 1971–1985, previously modeled by a very shallow source (1–3 km) in terms of overpressure in the main magma chamber, probably located at 4–5 km of depth.  相似文献   

The Crust of the Western Mediterranean Ridge From Deep Seismic Data and Gravity Modelling   总被引：2，自引：0，他引：2  

C. Truffert  N. Chamot-Rooke  S. Lallemant  B. De  Voogd  P. Huchon  X. Le  Pichon 《Geophysical Journal International》1993,114(2):360-372

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Reply to Takayama's comment     

Francesco Mulargia  Paolo Gasperini 《Geophysical Journal International》1993,115(3):1199-1201

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Derivation of vegetative variables from a landsat tm image for modelling soil erosion   总被引：1，自引：0，他引：1  

Steven M. De Jong 《地球表面变化过程与地形》1994,19(2):165-178

A study was carried out to assess the potential use of satellite thematic mapper (TM) images to produce maps of vegetation-related variables for erosion modelling. In a Mediterranean study area in southern France the (semi-)natural vegetation was described at 33 field plots using four quantitative methods: the Fosberg structural classification system, the cover and management factor of the Universal Soil Loss Equation, the leaf area index and the total percentage cover. After radiometric correction of the image, the spectral TM bands were processed following three different methods. Each method aimed at combining the data of the six spectral TM bands into a single band in such a way that the resulting image displayed optimal information on green vegetation cover. The algorithms used comprise the normalized difference vegetation index, the conventional ‘tasselled cap’ transformation and a locally tuned tasselled cap transformation. Only slight differences were found between the different methods to calculate spectral vegetation indices for this particular case. Furthermore, the correlations between the field variables and image-derived spectral indices are generally small. The largest correlations were found for the normalized vegetation index and the leaf area index (r + 0·71) and for the normalized vegetation index and Fosberg's structural vegetation classes (r + 0·76). However, Fosberg's method results in very general classes, which are of little use for soil erosion models. Furthermore, the spectral indices appeared to be sensitive for the vitality of the vegetation. Consequently, an area covered by a sensed, senescent vegetation will not yield a large value for the spectral index, but its soil is protected against splash erosion. This might lead to a misinterpretation of the soil protective cover when satellite images are used. A final conclusion is that a balance has to be found between the more accurate, but time-consuming field surveys to gather information on erosion-controlling factors and a certain loss of accuracy associated with the use of quick and easy remote sensing methods.  相似文献   

Undications of current action in late Jurassic limestones,radiolarian limestones,saccocoma limestones and associated rocks from the subbetic of SE Spain     

B. Kuhry  S.W.G. De Clercq  L. Dekker 《Sedimentary Geology》1976,15(3):235-258

In the Vélez Blanco region (province of Almeia), filament limestones occur associated with pellet limestones, crinoidal limestones, radiolarian limestones, Saccocoma limestones and tintinnid limestones. These predominantly Late Jurassic rocks are underlain by Middle Jurassic oolitic limestones and overlain by Cretaceous pelagic limestones and marls.A distinction can be made between long and short filaments. The former are interpreted as undamaged valves, the latter as shell fragments of the pelagic pelecypod Bositra buchi. Bositra valves and fragments have been sorted by weak current (and/or wave) action.In the Saccocoma limestones, evidence for similar sorting of Saccocoma debris has been found.The radiolarian limestones represent a low-energy basin environment, but are not comparable with recent deep-sea radiolarian oozes.Nodular limestone intercalations and hiatuses represent a current- (and/or wave-) swept environment.The occurrence of filament-rich and Radiolaria-bearing, but benthos-poor, intervals within the oolitic limestone indicates that the deposition of such rocks can take place at moderate sea depths.  相似文献   

Size distribution models of stratospheric particles in terms of the modified gamma function     

Dr. Francesco Tampieri  Dr. Claudio Tomasi 《Meteorology and Atmospheric Physics》1976,25(1):47-54

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Bioaccumulation factors of chlorinated hydrocarbons between mussels and seawater     

Robert W Risebrough  Brock W De Lappe  Timothy T Schmidt 《Marine pollution bulletin》1976,7(12):225-228

The bioaccumulation of PCB and DDT compounds by mussels, Mytilus spp., from ambient seawater was determined by measuring concentrations of these chlorinated hydrocarbons in both mussels and seawater at four sites on the Mediterranean coast of France and two sites in California. Bioaccumulation factors were found to vary over an order of magnitude. Ratios of the concentrations of PCB in mussels, consisting predominantly of pentachloro-and hexachlorobiphenyls, to concentrations in ambient seawater ranged between 69 000 and 690 000; the corresponding ratios of concentrations of p,p′-DDE or p,p′-DDT ranged from 40 000 to 690 000. Although mussels appear to be appropriate and convenient indicator organisms of local chlorinated hydrocarbon contamination levels, the factors contributing to this variance must be determined before mussels are widely used in global monitoring programmes.  相似文献   

Paleomagnetic record of two successive Miocene geomagnetic reversals in western Crete     

Jean-Pierre Valet  Carlo Laj 《Earth and Planetary Science Letters》1981,54(1):53-63

Two geomagnetic reversals(R→N followed by N→R) have been recorded in a sequence of Miocene marine clays of Tortonian-Messinian age in western Crete (Greece). The time span of each transition is found to be of the order of 5000–10,000 years. The transitional VGP paths are largely constrained in longitude either near the site longitude(R→N) or opposite to it(N→R). A normalized magnetization intensity record has also been obtained and its variations during reversals are found to be in excellent agreement with the predictions of Hoffman's phenomenological model.  相似文献   

Formation of artifacts in sediments upon freeze-drying     

D. Van de Meent  W.L. Maters  J.W. De Leeuw  P.A. Schenck 《Organic Geochemistry》1977,1(1):7-9

Comparison of the analytical data on the alkenes extracted from both dried and wet Messel shale sediment points to the formation of artifacts, presumably as a result of clay-catalyzed dehydration reactions.  相似文献