Surface effects of triggered fault slip on Reykjanes Peninsula, SW Iceland     

Amy E. Clifton  Carolina Pagli  Jna Finndís Jnsdttir  Kristjana Eythorsdttir  Kristin Vogfjr 《Tectonophysics》2003,369(3-4):145-154

Three large earthquakes (M_w>4.5) were triggered within 5 min, 85 km west of a M_w 6.5 earthquake in the South Iceland Seismic Zone (SISZ). We report on surface effects of these triggered earthquakes, which include fresh rupture, widespread rockfall, disrupted rockslides and block slides. Field data confirm that the earthquakes occurred along N-striking right-lateral strike-slip faults. Field data also support the conclusion from modeling of InSAR data that deformation from the second triggered event was more significant than for the other two. A major hydrological effect was the draining of water through an open fissure on a lake bed, lowering the lake level by greater than 4 m. Field relationships suggest that a component of aseismic slip could have been facilitated by water draining into the fault zone.  相似文献   

Layer parallel shortening in salt-detached folds: constraint on cross-section restoration     

M. Sans  J. Vergs  E. Gomis  J. M. Pars  M. Schiattarella  A. Trav  F. Calvet  P. Santanach  A. Doulcet 《Tectonophysics》2003,372(1-2):85-104

Cleavage-fissility perpendicular to bedding is a common feature in the external part of fold-and-thrust belts. Three techniques were used to determine the internal distortion in the frontal Southern Pyrenees: the analysis of strain markers such as burrows and rain drops, the measurement of fissility, and the measurement of anisotropy of magnetic susceptibility (AMS). The comparison of the three techniques showed a good fit although they differ in sensitivity to penetrative strain variations in the range of deformation values explored in the study case. On the regional scale, the values of layer parallel shortening (LPS) derived from the markers analysis are very constant and account for 16–23% of shortening. These values are two to three times larger than the shortening values calculated from the restoration of the macroscopic scale structures and indicate a good decoupling above the Cardona salt Formation. This study permitted an accurate restoration of the low-amplitude el Guix detached anticline.  相似文献   

Tracing the flow of organic matter from primary producers to filter feeders in Ria Formosa lagoon, Southern Portugal     

Raquel Machás  Rui Santos  Bruce Peterson 《Estuaries and Coasts》2003,26(4):846-856

The flow of organic matter along the main navigation channel of Ria Formosa, Portugal, was assessed using determinations of suspended particulate matter (SPM), particulate organic matter (POM), and chlorophyll a (chla) concentrations in conjunction with stable isotope values of primary producers, particulate matter, and two filter feeders. SPM in the lagoon is dominated by inorganic particles comprising 80% of total weight with organic matter averaging about 20%. The algal component of the POM averaged about 5% with the remainder comprised of detritus. The δ¹³C values of primary producers ranged from ?9.1‰ in the intertidal seagrassZostera noltii to ?30.7‰ in the red seaweedBostrychia scorpioides revealing underlying differences in the mechanisms of carbon uptake. The δ¹³C value ofB. scorpioides, which develops entangled on the salt marsh speciesSpartina maritima, suggests that its main source of inorganic carbon is atmospheric CO₂. The δ¹³C values of the high marsh macrophyteSarcocornia perennis significantly increased with distance from the ocean while δ¹³C values ofZ. noltii decreased, probably because higher decomposition of organic matter at inner stations lowers the δ¹³CO₂ value in the water. The δ¹⁵N values of Ulvales, seagrasses, and marsh plants significantly increased from outer stations to inner stations. This increase may be due either to recycling of nitrogen (N) within the marsh (with loss of light N₂ or NH₄) or to inputs of isotopically heavy N from sewage. The δ¹⁵N values of particulate matter showed an opposite trend, which indicates higher microbial degradation of organic matter at the inner lagoon. The data demonstrate that the seston in the lagoon is a mixture of detritus from lagoon primary producers with a minor contribution of microalgae. The filter feeders are most likely assimilating a mixture of phytoplankton and microphytobenthos. Digestion of lagoon seston is selective. The δ¹⁵N values of both muscle and digestive gland of filter feeders showed the opposite gradient of particulate matter indicating that the depleted δ¹⁵N of SPM at inner stations was not assimilated or even ingested. Stable isotopes values did not differ between the filter-feeders—the musselMytilus galloprovincialis collected on buoys and the clamTapes decussatus collected in the sediment—suggesting a considerable mixture of benthic-pelagic organic matter throughout the water column. Assessment of the changes in isotopic decomposition of detritus as it decays is required to refine our understanding of organic matter transfers in detrital food webs.  相似文献   

Private property—national legacy: Protecting privately owned archaeological sites in the united states     

Mark Michel 《Natural Resources Research》1997,6(2):131-136

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A model for the Am (Km) planetary geomagnetic activity index and application to prediction     

Christian Francq  Michel Menvielle 《Geophysical Journal International》1996,125(3):729-746

We studied the existence of dynamical stochastic relations in the evolution of the am index. A first analysis of the autocorrelation functions showed evidence of several seasonalities. We first used linear (ARMA) models, and it was found that these do not account for the whole internal dynamics of the data series. We then used various non-linear models to provide a better fit to reality. The forecast performances of the non-linear models are not significantly different from those of the linear model. We give a tentative explanation for the failure of the non-linear predictions. Finally, ARCH models were used in order to take into account the fact that the confidence interval for the predicted value depends on past observations.  相似文献   

Reinterpretation of the RRISP-77 Iceland shear-wave profiles   总被引：1，自引：0，他引：1  

William Menke  Bryndís Brandsdóttir  Páll Einarsson  Ingi Th. Bjarnason 《Geophysical Journal International》1996,126(1):166-172

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Nest microhabitat selection in larks from a European semi-arid shrub-steppe: the role of sunlight and predation     

Miguel Yanes  Jesús Herranz  Francisco Suárez 《Journal of Arid Environments》1996,32(4):469-478

We analysed nest site selection in two shrub-steppe larks, the lesser short-toed larkCalandrella rufescensand the Thekla larkGalerida theklae. Both species nest on the ground next to a bush preferably facing north or north-east. Nestling growth and fledging weight are greater when the nest faces these directions. Both species prefer to nest next to camephytes with little foliage, and the lesser short-toed lark chooses sites with high visibility. We conclude that sunlight and nest predation are fundamental selective pressures determining nest microhabitat selection in larks in semi-arid areas.  相似文献   

Effects of early season defoliation ofAnthyllis cytisoides(a Mediterranean browse species) on further herbivore attack     

Concepción L. Alados  Fernando G. Barroso  Antonio Aguirre  Juan Escós 《Journal of Arid Environments》1996,34(4):455-463

To determine if defoliation of a woody plant affects foraging by folivorous insects, we examined the infection rate (number of leaves damaged per total number of leaves sampled on marked stems) ofAnthyllis cytisoidesunder three experimental treatments: 10, 50 and 90% plant defoliation. Observations were made for three age classes, established by trunk base perimeter (equal to or lower than 11 cm, between 11 and 20 cm, larger than 20 cm). Plants respond positively to artificial defoliation by increasing total vegetative length of the stem and total inflorescence length. This response is most evident in young individuals.Response to herbivory was measured as overall infection rate and also as infection rate by different feeding guilds—chewing, mining, or sucking insects. We found that increased defoliation elicited increased resistance of leaves to insect attack. This was particularly evident in young plants. Different insect guilds respond in different ways. Attack by chewing insects declines with defoliation for all plant age classes; only sucking insects which feed on the oldest plants reduce feeding rate with plant defoliation. Finally, mining insects present the opposite trend in young and senescent plants.  相似文献   

Transport in a 2-D saturated porous medium: A new method for particle tracking   总被引：2，自引：0，他引：2  

Frédérick Delay  Hélène Housset-Resche  Gilles Porel  Ghislain de Marsily 《Mathematical Geology》1996,28(1):45-71

A new method for solving the transport equation based on the management of a large numbe of particles in a discretized 2-D domain is presented. The method uses numerical variables to represent the number of particles in a given mesh and is more complex than the 1-D problem. The first part of the paper focuses on the specific management of particles in a 2-D problem. The method also would be valid for three dimensions as long as the medium can be modeled similar to a layered system. As the particles are no longer tracked individually, the algorithm is fast and does not depend on the number of particles present. The numerical tests show that the method is nearly numerical dispersion free and permits accurate calculations even for simulations of low-concentration transport. Because each mesh is considered as a closed system between two successive time steps, it is easy to add adsorption phenomenon without any problem of numerical stability. The model is tested under conditions that are extremely demanding for its operating mode and gives a good fit to analytical solutions. The conditions in which it can be used to best advantage are discussed.  相似文献   

The age and thermal history of Cerro Rico de Potosi, Bolivia   总被引：1，自引：0，他引：1  

C. G. Cunningham  R. E. Zartman  E. H. McKee  R. O. Rye  C. W. Naeser  O. Sanjinés V  G. E. Ericksen  F. Tavera V 《Mineralium Deposita》1996,31(5):374-385

 Cerro Rico de Potosi, Bolivia, is the world’s largest silver deposit and has been mined since the sixteenth century for silver, and for tin and zinc during the twentieth century, together with by-product copper and lead. The deposit consists primarily of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and explosion breccia. The deposit is compositionally and thermally zoned, having a core of cassiterite, wolframite, bismuthinite, and arsenopyrite surrounded by a peripheral, lower-temperature mineral assemblage consisting principally of sphalerite, galena, lead sulfosalt, and silver minerals. The low-temperature assemblage also was superimposed on the high-temperature assemblage in response to cooling of the main hydrothermal system. Both the dacite dome and the ore fluids were derived from a larger magmatic/hydrothermal source at depth. The dome was repeatedly fractured by recurrent movement on the fault system that guided its initial emplacement. The dome was extruded at 13.8±0.2 Ma (2σ), based on U-Th-Pb dating of zircon. Mineralization and alteration occurred within about 0.3 my of dome emplacement, as indicated by a ⁴⁰Ar/³⁹Ar date of 13.76±0.10 Ma (1σ) for sericite from the pervasive quartz-sericite-pyrite alteration associated with the main-stage, high-temperature, mineralization. The last thermal event able to reset zircon fission tracks occurred no later than 12.5±1.1 Ma (1σ), as indicated by fission-tract dating. Minor sericite, and magmatic-steam alunite veins, were episodically formed around 11 Ma and between 8.3 and 5.7 Ma; the younger episodes occurring at the time of extensional fracturing at Cerro Rico and widespread volcanism in the adjacent Los Frailes volcanic field. None of these younger events appear to be significant thermal/mineralizing events; the exceptionally flat thermal release pattern of ³⁹Ar from sericite and the results of the fission-tract dating of zircon show that none of the younger events was hot enough, and lasted long enough, to cause significant loss of Ar or annealing of zircon fission tracks. U-Th-Pb dating of zircon cores indicates a Precambrian progenitor for some zircons, and REE analyses of dated samples of hydrothermally altered dacite show the presence of a prominent positive Eu anomaly, which constrains interpretations of the origin and evolution of the magmatic/hydrothermal system. Received: 14 October 1995/Accepted: 29 January 1996  相似文献