Reevaluation of the earthquakes of 10 March and 19 May 1951 in southern Spain     

A.?UdíasEmail author  D.?Mu?oz  E.?Buforn  C.?Sanz?de?Galdeano  C.?del?Fresno  I.?Rodriguez 《Journal of Seismology》2005,9(1):99-110

Damage and parameters of the earthquakes of 10 March and 19 May 1951 in southern Spain have been reevaluated. Data available do not allow accurate depth determinations and previous estimates of larger depths are not confirmed, so depths have been fixed at 30 km for both shocks. Magnitudes (Ms) have been determined as 5.4 and 5.6, respectively. Intensities estimated at 22 and 29 sites from contemporary documentary sources give maximum values of VI–VII and VI (EMS Scale), lower than previous estimates. The focal mechanism for the May shock is right-lateral strike-slip with a normal component of motion, with planes with strikes 273° and 169°; seismic moment 1.9 × 10¹⁶ Nm and dimension 6 km (radius of circular fault). Shocks are located near the boundary between the Iberian plateau and the Guadalquivir Basin and may be related to faults connected with this boundary.  相似文献   

Distribution of platinum-group elements and Os isotopes in chromite ores from Mayarí-Baracoa Ophiolitic Belt (eastern Cuba)   总被引：1，自引：0，他引：1  

F.?GervillaEmail author  J.A.?Proenza  R.?Frei  J.M.?González-Jiménez  C.J.?Garrido  J.C.?Melgarejo  A.?Meibom  R.?Díaz-Martínez  W.?Lavaut 《Contributions to Mineralogy and Petrology》2005,150(6):589-607

The Mayarí-Baracoa ophiolitic belt in eastern Cuba hosts abundant chromite deposits of historical economic importance. Among these deposits, the chemistry of chromite ore is very variable, ranging from high Al (Cr#=0.43–0.55) to high Cr (Cr#=0.60–0.83) compositions. Platinum-group element (PGE) contents are also variable (from 33 ppb to 1.88 ppm) and correlate positively with the Cr# of the ore. Bulk PGE abundances correlate negatively with the Pd/Ir ratio showing that chromite concentrates mainly Os, Ir and Ru which gives rise to the characteristic negatively sloped, chrondrite-normalized PGE patterns in many chromitites. This is consistent with the mineralogy of PGEs, which is dominated by members of the laurite–erlichmanite solid solution series (RuS₂–OsS₂), with minor amounts of irarsite (IrAsS), Os–Ir alloys, Ru–Os–Ir–Fe–Ni alloys, Ni–Rh–As, and sulfides of Ir, Os, Rh, Cu, Ni, and/or Pd. Measured ¹⁸⁷Os/¹⁸⁸Os ratios (from 0.1304 to 0.1230) are among the lower values reported for podiform chromitites. The ¹⁸⁷Os/¹⁸⁸Os ratios decrease with increasing whole-rock PGE contents and Cr# of chromite. Furthermore, γOs values of all but one of the chromitite samples are negative indicating a subchondiritc mantle source. γOs decrease with increasing bulk Os content and decreasing ¹⁸⁷Re/¹⁸⁸Os ratios. These mineralogical and geochemical features are interpreted in terms of chromite crystallization from melts varying in composition from back-arc basalts (Al-rich chromite) to boninites (Cr-rich chromite) in a suprasubduction zone setting. Chromite crystallization occurs as a consequence of magma mixing and assimilation of preexisting gabbro sills at the mantle–crust transition zone. Cr#, PGE abundances, and bulk Os isotopic composition of chromitites are determined by the combined effects of mantle source heterogeneity, the degree of partial melting, the extent of melt-rock interactions, and the local sulfur fugacity. Small-scale (μm to cm) chemical and isotopic heterogeneities in the platinum-group minerals are controlled by the mechanism(s) of chromite crystallization in a heterogeneous environment created by the turbulent regime generated by successive inputs of different batches of melt.  相似文献   

Analysis of oscillations in the stable atmospheric boundary layer using wavelet methods     

E.?Terradellas  M.?R.?SolerEmail author  E.?Ferreres  M.?Bravo 《Boundary-Layer Meteorology》2005,114(3):489-518

A wavelet method is used to estimate kinetic energy and fluxes from data collected under stable conditions during the CASES-99 field campaign. Results in the high frequency range are compared with those obtained by the traditional method used to estimate turbulent moments, which is based on the Reynolds decomposition of variables into a mean and a turbulent part. The fact that the wavelet transform performs much better as a filter than the averaging process accounts for most of the disagreements between results. Since the wavelet method can be applied at very different spectral ranges, it is also used to analyse two different coherent structures: a density current and a train of internal gravity waves. The strong burst of turbulence related to the density current reflects the complexity of the first event. The wavelet method discriminates the different scales of motion, which are present in the perturbation, and is therefore an ideal tool for assessing the interactions between them. A method based on the phase difference between wavelet-transformed time series is then applied to the analysis of the horizontal and vertical structure of the gravity waves, and a three-dimensional image of the oscillations is provided.  相似文献   

Zooplankton succession during extraordinary drought–flood cycles: A case study in a South American floodplain lake     

Griselda Chaparro  María Cristina Marinone  Ruben J. Lombardo  María Romina Schiaffino  Alice de Souza Guimarães  Inés O’Farrell 《Limnologica》2011,41(4):371-381

We examined the zooplankton abundance and composition of Laguna Grande, a floodplain wetland of the Lower Paraná Basin (Argentina), during an extraordinary drought–flood cycle that affected both the environment and the biological conditions of the lake. Low waters were characterised by remarkably high conductivities and pH values, and high phytoplankton and bacterioplankton abundances with cyanobacterial blooms, while high waters showed opposite features. In relation to zooplankton, the mean abundances of all the taxonomic groups (rotifers, cladocerans, copepods, ciliates, and heterotrophic nanoflagellates) were slightly higher at low waters. Major changes were observed in the specific composition of metazooplankton: the euryhaline species assemblage that dominated in the dry warm period was replaced by several oligohaline littoral and planktonic species characteristic of the Paraná River Basin, when the water level rose. Mean species richness values at high waters doubled those of low waters and were directly correlated to water depth. Most of the rotifers of the genus Brachionus and the cladoceran Moina micrura switched from parthenogenetic to sexual reproduction during low waters, as a response to a harsh environment and crowding. We suggest that the main changes in the environmental conditions in this eutrophic floodplain lake are driven by the hydrology, which regulates the zooplankton succession. The herein described shifts in the zooplankton structure and dynamics of Laguna Grande over an extraordinary drought–flood cycle contribute to the understanding of the processes that might occur under the scenarios predicted by climate change models.  相似文献   

Paleoseismological analysis of an intraplate extensional structure: the Concud fault (Iberian Chain,eastern Spain)     

P. Lafuente  L. E. Arlegui  C. L. Liesa  J. L. Simón 《International Journal of Earth Sciences》2011,100(7):1713-1732

The Concud fault is a 13.5 km long, NW–SE striking normal fault at the eastern Iberian Chain. Its recent (Late Pleistocene) slip history is characterized from mapping and trench analysis and discussed in the context of the accretion/incision history of the Alfambra River. The fault has been active since Late Pliocene times, with slip rates ranging from 0.07 to 0.33 mm/year that are consistent with its present-day geomorphologic expression. The most likely empirical correlation suggests that the associated paleoseisms have potential magnitudes close to 6.8, coseismic displacements of 2.0 m, and recurrence intervals from 6.1 to 28.9 ka. At least six paleoseismic events have been identified between 113 and 32 ka. The first three events (U to W) involved displacement along the major fault plane. The last three events (X to Z) encompassed downthrow and hanging-wall synthetic bending prompting fissure opening. This change is accompanied by a decrease in slip rate (from 0.63 to 0.08–0.17 mm/year) and has been attributed to activation of a synthetic blind fault at the hanging wall. The average coseismic displacement (1.9–2.0 m) and recurrence period (6.7–7.9 ka) inferred from this paleoseismic succession are within the ranges predicted from empirical correlation. Such paleoseismic activity contrasts with the moderate present-day seismicity of the area (maximum instrumental Mb = 4.4), which can be explained by the long recurrence interval that characterizes intraplate regions.  相似文献   

Weathering fluxes of arsenic from a small catchment in Slovak Republic   总被引：1，自引：1，他引：0  

Ahmed Melegy  Igor Slaninka  Tomas Pa?es  Stanislav Rapant 《Environmental Earth Sciences》2011,64(2):549-555

Inputs of As to a small catchment due to chemical weathering of bedrock, mechanical weathering of bedrock, and atmospheric precipitation were 71.53, 23.98 and 0.02 g ha⁻¹ year⁻¹, respectively. The output fluxes of As due to mechanical erosion of soil, biological uptake, stream discharge, and groundwater flow were 6.32, 4.77, 0.37 and 0.02 g ha⁻¹ year⁻¹, respectively. The results indicate that arsenic accumulates in soil and regolith with a very high rate. This is attributed to the selective weathering and erosion with respect to arsenic and fixation of arsenic in the secondary solids produced by weathering. The output fluxes of As in stream and groundwater in Vydrica catchment in Slovak Republic (0.39 g ha⁻¹ year⁻¹) based on muscovite–biotite granites and granodiorites were much lower compared to catchments in a gold district in the Czech Republic. These results may be ascribed to the low levels of arsenic pollution measured in Vydrica catchment. The arsenic fluxes were estimated by calculation of mechanical and chemical weathering rates of the bedrocks in Vydrica catchment from mass balance data on sodium and silica. The justification of the steady state of Na and Si is that neither of the elements is appreciably accumulated in plants and in exchangeable pool of ions in soil.  相似文献   

Ernst Julius Öpik's (1916) note on the theory of explosion cratering on the Moon's surface—The complex case of a long‐overlooked benchmark paper     

Grzegorz Racki  Christian Koeberl  Tõnu Viik  Elena A. Jagt‐Yazykova  John W. M. Jagt 《Meteoritics & planetary science》2014,49(10):1851-1874

High‐velocity impact as a common phenomenon in planetary evolution was ignored until well into the twentieth century, mostly because of inadequate understanding of cratering processes. An eight‐page note, published in Russian by the young Ernst Julius Öpik, a great Estonian astronomer, was among the key selenological papers, but due to the language barrier, it was barely known and mostly incorrectly cited. This particular paper is here intended to serve as an explanatory supplement to an English translation of Öpik's article, but also to document an early stage in our understanding of cratering. First, we outline the historical–biographical background of this benchmark paper, and second, a comprehensive discussion of its merits is presented, from past and present perspectives alike. In his theoretical research, Öpik analyzed the explosive formation of craters numerically, albeit in a very simple way. For the first time, he approximated relationships among minimal meteorite size, impact energy, and crater diameter; this scaling focused solely on the gravitational energy of excavating the crater (a “useful” working approach). This initial physical model, with a rational mechanical basis, was developed in a series of papers up to 1961. Öpik should certainly be viewed as the founder of the numerical simulation approach in planetary sciences. In addition, the present note also briefly describes Nikolai A. Morozov as a remarkable man, a forgotten Russian scientist and, surprisingly, the true initiator of Öpik's explosive impact theory. In fact, already between 1909 and 1911, Morozov probably was the first to consider conclusively that explosion craters would be circular, bowl‐shaped depressions even when formed under different impact angles.  相似文献   

The geology of the Målingen structure: A probable doublet to the Lockne marine‐target impact crater,central Sweden     

J. Ormö  E. Sturkell  J. Nõlvak  I. Melero‐Asensio  Å. Frisk  T. Wikström 《Meteoritics & planetary science》2014,49(3):313-327

The Målingen structure is an approximately 700 m wide, rimmed, sediment‐filled, circular depression in Precambrian crystalline basement approximately 16.2 km from the concentric, marine‐target Lockne crater (inner, basement crater diameter approximately 7.5 km, total diameter in sedimentary strata approximately 13.5 km). We present here results from geologic mapping, a 148.8 m deep core drilling from the center of the structure, detailed biostratigraphic dating of the structure's formation and its age correlation with Lockne, chemostratigraphy of the sedimentary infill, and indication for shock metamorphism in quartz from breccias below the crater infill. The drill core reveals, from bottom to the top, approximately 33 m of basement rocks with increased fracturing upward, approximately 10 m of polymict crystalline breccia with shock features, approximately 97 m of slumped Cambrian mudstone, approximately 4.7 m of a normally graded, polymict sedimentary breccia that in its uppermost part grades into sandstone and siltstone (cf. resurge deposits), and approximately 1.6 m of secular sediments. The combined data set shows that the Målingen structure formed in conjunction with the Lockne crater in the same marine setting. The shape and depth of the basement crater and the cored sequence of crystalline breccias with shocked quartz, slumped sediments, and resurge deposits support an impact origin. The stratigraphic and geographic relationship with Lockne suggests the Lockne and Målingen craters to be the first described doublet impact structure by a binary asteroid into a marine‐target setting.  相似文献   

ATTITUDES AND ADJUSTMENTS TO THE FLOOD HAZARD IN A MIXED ETHNIC COMMUNITY IN MALACCA TOWN, PENINSULAR MALAYSIA     

Colin H. Leigh  M.A.  Ph.D.  Low Kwai Sim  B.A.  Ph.D. 《Singapore journal of tropical geography》1983,4(1):40-52

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Drought as an agri-environmental determinant of irrigation land: the case of Bardenas (Spain)     

J.?CausapéEmail author  I.?Clavería 《Environmental Geology》2007,51(7):1213-1220

Irrigated agriculture is causing certain deterioration of the quality of rivers and aquifers. The objective of this study is to analyse the agri-environmental repercussions caused by climatic changes in a typical irrigated land in the Ebro valley (Spain). The irrigation efficiency and agri-environmental impact in a basin of irrigated land (95 ha) were compared for two hydrological years with different pluviometry [October 2000/September 2001 (526 mm/year) vs. October 2004/September 2005 (211 mm/year)]. For this end, water balances were carried out in every plot and the quantity and quality (salinity and nitrates) of the water circulating through the drainage of the basin were gauged. The results indicate that in 2004/2005 farmers adjusted the irrigation doses better on each irrigation occasion, thus diminishing the fraction of drainage of the same (50% vs. 31%) and increasing the consumptive water use efficiency (56% vs. 79%). Nevertheless, the drought of 2004/2005 determined inappropriate irrigation management as the crops suffered a greater hydric deficit (3% vs. 23%). In 2004/2005, drainage waters presented higher electric conductivity (0.92 dS/m vs. 0.94 dS/m) and smaller nitrate concentration (96 mg/l vs. 74 mg/l). Last year, 55, 54 and 65% less of water, salts and N–NO₃⁻, respectively, were exported in the drainage. The lesser environmental impact in the year 2004/2005 was influenced by more appropriate use of water and agrichemical resources. Nevertheless, it is necessary to continue optimizing agricultural practices, mainly irrigation and fertilization, in order to minimize nitrate pollution and to confront years of drought.  相似文献