Calibration of Local Magnitude M<Subscript>L</Subscript> in the Azores Archipelago Based on Recent Digital Recordings     

Eva?GóngoraEmail author  Fernando?Carrilho  Carlos S.?Oliveira 《Pure and Applied Geophysics》2004,161(3):647-659

—The development of the digital seismic network in the Azores Archipelago during recent years made it possible to obtain the amplitudes (waveform) of recorded motion in a large set of stations. With this new data, maximum amplitudes of the Wood Anderson seismograph are computed, for each station/component, which, together with epicentral distances, allows for the estimation of local magnitude M _L . We used data recorded in 8 digital permanent three-component stations, with inter-stations distances up to 300 km, in the period June 1998 – June 2000, corresponding to a set of 1315 events with magnitude (M _L or M _D ) 2<M<5.8 and epicenters located in the Azores region, to estimate the coefficients of the equation to compute M _L , as well as to determine the corrections to be applied to each station. The new set of parameters, formed by attenuation coefficients and station corrections, were introduced in the calculations of the M _L , leading to smaller dispersions in the analyzed dataset. We also conclude that the attenuation in the first 150 km is similar to the California values, although higher for longer distances.  相似文献   

Hydrothermal mixing,carbonate dissolution and sulfide precipitation in Mississippi Valley-type deposits   总被引：1，自引：0，他引：1  

Mercè?CorbellaEmail author  Carlos?Ayora  Esteve?Cardellach 《Mineralium Deposita》2004,39(3):344-357

A large number of Mississippi Valley-Type (MVT) deposits are located within dissolution zones in carbonate host rocks. Some genetic models propose the existence of cavities generated by an earlier event such as a shallow karstification, that were subsequently filled with hydrothermal minerals. Alternative models propose carbonate dissolution caused by the simultaneous precipitation of sulfides. These models fail to explain either the deep geological setting of the cavities, or the observational features which suggest that the dissolution of carbonates and the precipitation of minerals filling the cavities are not strictly coeval. We present a genetic model inspired by the textural characteristics of MVT deposits that accounts for both the dissolution of carbonate and precipitation of sulfides and later carbonates in variable volumes. The model is based on the mixing of two hydrothermal fluids with a different chemistry. Depending on the proportion of the end members, the mixture dissolves and precipitates carbonates even though the two mixing solutions are both independently saturated in carbonates. We perform reactive transport simulations of mixing of a regional groundwater and brine ascending through a fracture, both saturated in calcite, but with different overall chemistries (Ca and carbonate concentrations, pH, etc). As a result of the intrinsic effects of chemical mixing, a carbonate dissolution zone, which is enhanced by acid brines, appears above the fracture, and another zone of calcite precipitation builds up between the cavity and the surrounding rock. Sulfide forms near the fracture and occupies a volume smaller than the cavity. A decline of the fluid flux in the fracture would cause the precipitation of calcite within the previously formed cavities. Therefore, dissolution of carbonate host rock, sulfide precipitation within the forming cavity, and later filling by carbonates may be part of the same overall process of mixing of fluids in the carbonate host rock.Editorial handling: C. Everett  相似文献   

The use of the marine biotic index AMBI in the assessment of the ecological status of the Obidos lagoon (Portugal)     

Carvalho S  Gaspar MB  Moura A  Vale C  Antunes P  Gil O  da Fonseca LC  Falcão M 《Marine pollution bulletin》2006,52(11):1414-1424

This study reports the longitudinal distribution of sediment properties, including inorganic and organic contaminants, and the structure of the benthic community in Obidos lagoon, a coastal system permanently connected to the sea and with negligible freshwater sources. Sediments from the upper to central lagoon consist of fine particles (91%) and from the lower lagoon of sands (94%). Chemical composition is strongly correlated to the percentage of fine particles. Contamination is relatively low in those sediments suggesting the effect of diffuse sources. The increase in organic matter content from down- to upstream areas was associated with the dominance of opportunistic species, while sensitive and indifferent species to organic enrichment were mainly associated to the clean sandy downstream area. The marine biotic index (AMBI) was suitable for the discrimination of the biological and environmental gradients in the Obidos lagoon and was highly related with the gradient of organic matter content in this system.  相似文献   

Syntectonic emplacement of the Middle Jurassic Concón Mafic Dike Swarm, Coastal Range, central Chile (33° S)     

Christian Creixell  Miguel ngel Parada  Pierrick Roperch  Diego Morata  Csar Arriagada  Carlos Prez de Arce 《Tectonophysics》2006,425(1-4):101-122

The Concón Mafic Dike Swarm (CMDS) consists of basaltic to andesitic dikes emplaced into deformed Late Paleozoic granitoids during the development of the Jurassic arc of central Chile. The dikes are divided into an early group of thick dikes (5–12 m) and a late group of thin dikes (0.5–3 m). Two new amphibole ⁴⁰Ar/³⁹Ar dates obtained from undeformed and deformed dikes, constrain the age of emplacement and deformation of the CMDS between 163 and 157 Ma. Based on radiometric ages, field observations, AMS studies and petrographic data, we conclude that the emplacement of the CMDS was syntectonic with the Jurassic arc extension and associated with sinistral displacements along the NW-trending structures that host the CMDS. The common occurrence of already deformed and rotated xenoliths in the dikes indicates that deformation in the granitoids started previously.The early thick dikes and country rocks appear to have been remagnetized during the exhumation of deep-seated coastal rocks in the Early Cretaceous (around 100 Ma). The remanent magnetization in late thin dikes is mainly retained by small amounts of low-Ti magnetite at high temperature and pyrrhotite at low temperature. The magnetization in these dikes appears to be primary in origin. Paleomagnetic results from the thin dikes also indicate that the whole area was tilted  23° to the NNW during cooling of the CMDS.The NNW–SSE extension vectors deduced from the paleomagnetic data and internal fabric of dikes are different with respect to extension direction deduced for the Middle–Late Jurassic of northern Chile, pointing to major heterogeneities along the margin of the overriding plate during the Mesozoic or differences in the mechanisms driving extension during such period.  相似文献   

利用遥感技术建立墨西哥热带地上生物量模型(英文)     

AGUIRRE-SALADO Carlos Arturo  TREVIO-GARZA Eduardo Javier  AGUIRRE-CALDERóN Oscar Alberto  JIMéNEZ-PéREZ Javier  GONZáLEZ-TAGLE Marco Aurelio  VALDEZ-LAZALDE José René  MIRANDA-ARAGóN Liliana  AGUIRRE-SALADO Alejandro Iván 《地理学报(英文版)》2012,22(4):669-680

Spatially-explicit estimation of aboveground biomass(AGB) plays an important role to generate action policies focused in climate change mitigation,since carbon(C) retained in the biomass is vital for regulating Earth’s temperature.This work estimates AGB using both chlorophyll(red,near infrared) and moisture(middle infrared) based normalized vegetation indices constructed with MCD43A4 MODerate-resolution Imaging Spectroradiometer(MODIS) and MOD44B vegetation continuous fields(VCF) data.The study area is located in San Luis Potosí,Mexico,a region that comprises a part of the upper limit of the intertropical zone.AGB estimations were made using both individual tree data from the National Forest Inventory of Mexico and allometric equations reported in scientific literature.Linear and nonlinear(expo-nential) models were fitted to find their predictive potential when using satellite spectral data as explanatory variables.Highly-significant correlations(p = 0.01) were found between all the explaining variables tested.NDVI62,linked to chlorophyll content and moisture stress,showed the highest correlation.The best model(nonlinear) showed an index of fit(Pseudo-r2) equal to 0.77 and a root mean square error equal to 26.00 Mg/ha using NDVI62 and VCF as explanatory variables.Validation correlation coefficients were similar for both models:lin-ear(r = 0.87**) and nonlinear(r = 0.86**).  相似文献   

Cities on edge: Smuggling and neoliberal policies at the Iguazú triangle     

José Carlos G. Aguiar 《Singapore journal of tropical geography》2012,33(2):171-183

The vision of a borderless world, of people, ideas and products freely circulating within a self‐regulating market, is one that clashes with the emerging legal regime based on the punitive force of the state. After a period of liberalization, seen in the opening of national economies and the promotion of regional trade projects and free‐trade zones, the ambivalence of neoliberalism is manifest in a borderless capitalism that ambiguously depends on the securitization of national borders. Such a changing regime of state intervention is clearly seen at the Iguazú triangle – the tri‐border urban conglomerate that straddles Brazil, Paraguay and Argentina – where the illegality of informal cross‐border trading has been tolerated for decades. Recently stepped up police raids and controls hinder the passage of people and goods, while a new fiscal regime introduced in 2009 in Brazil attempts to regularize cross‐border trafficking by turning petty smugglers into micro entrepreneurs. Petty smugglers – dubbed sacoleiros– can hardly be defined as entrepreneurs and do not constitute an identifiable category of entrepreneurship but, as typical in the informal sector, act on opportunity and need. Drawing on ethnographic research, this paper contextualizes the programmes for border controls and regularizing smuggling inspired by neoliberal ideology in South America.  相似文献   

Introduction – Neoliberalism and urban space in Latin America and the Caribbean     

Rivke Jaffe  José Carlos G. Aguiar 《Singapore journal of tropical geography》2012,33(2):153-156

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The new national climate change documents of Mexico: what do the regional climate change scenarios represent?     

Francisco Estrada  Benjamín Martínez-López  Cecilia Conde  Carlos Gay-García 《Climatic change》2012,110(3-4):1029-1046

This paper presents a review of the methodology applied for generating the regional climate change scenarios utilized in important National Documents of Mexico, such as the Fourth National Communication to the United Nations Framework Convention on Climate Change, the Fourth National Report to the Convention on Biological Diversity and The Economics of Climate Change in Mexico. It is shown that these regional climate change scenarios, which are one of the main inputs to support the assessments presented in these documents, are an example of the erroneous use of statistical downscaling techniques. The arguments presented here imply that the work based on such scenarios should be revised and therefore, these documents are inadequate for supporting national decision- making.  相似文献   

Extreme climatic events in the Amazon basin   总被引：1，自引：0，他引：1  

Jose Antonio Marengo  Javier Tomasella  Wagner R. Soares  Lincoln M. Alves  Carlos A. Nobre 《Theoretical and Applied Climatology》2012,107(1-2):73-85

During 2009 the Amazon basin was hit by a heavy flooding with a magnitude and duration few times observed in several decades. Torrential rain in northern and eastern Amazonia during the austral summer of 2008–2009 swelled the Amazon River and its tributaries. By July 2009, water levels of the Rio Negro, a major Amazon tributary, reached at Manaus harbor a new record, the highest mark of the last 107?years. During the 2008–2009 hydrological year, the rainy season on northern and northwestern Amazonia started prematurely, and was followed by a longer-than-normal rainy season. An anomalously southward migration of the ITCZ during May–June 2009, due to the warmer than normal surface waters in the tropical South Atlantic, was responsible for abundant rainfall in large regions of eastern Amazonia and Northeast Brazil from May to July 2009. We also compared the flood of 2009 with other major events recorded in 1989 and 1999. The hydrological consequences of this pattern were earlier than normal floods in Amazon northern tributaries, which peak discharges at their confluences with the main stem almost coincided with the peaks of southern tributaries. Since the time displacement of the contribution to the main stem of northern and southern Amazon tributaries is fundamental for damping flood waves in the main stem, the simultaneous combinations of peak discharges of tributaries resulted in an extreme flood.  相似文献   

Evolution and modulation of tropical heating from the last glacial maximum through the twenty-first century   总被引：1，自引：1，他引：0  

Carlos D. Hoyos  Peter J. Webster 《Climate Dynamics》2012,38(7-8):1501-1519

Twentieth century observations show that during the last 50?years the sea-surface temperature (SST) of the tropical oceans has increased by ~0.5°C and the area of SST >26.5 and 28°C (arbitrarily referred to as the oceanic warm pool: OWP) by 15 and 50% respectively in association with an increase in green house gas concentrations, with non-understood natural variability or a combination of both. Based on CMIP3 projections the OWP is projected to double during twenty-first century in a moderate CO₂ forcing scenario (IPCC A1B scenario). However, during the observational period the area of positive atmospheric heating (referred to as the dynamic warm pool, DWP), has remained constant. The threshold SST (T _H ), which demarks the region of net heating and cooling, has increased from 26.6°C in the 1950s to 27.1°C in the last decade and it is projected to increase to ~28.5°C by 2100. Based on climate model simulations, the area of the DWP is projected to remain constant during the twenty-first century. Analysis of the paleoclimate model intercomparison project (PMIP I and II) simulations for the Last Glacial maximum and the Mid-Holocene periods show a very similar behaviour, with a larger OWP in periods of elevated tropical SST, and an almost constant DWP associated with a varying T _H . The constancy of the DWP area, despite shifts in the background SST, is shown to be the result of a near exact matching between increases in the integrated convective heating within the DWP and the integrated radiative cooling outside the DWP as SST changes. Although the area of the DWP remains constant, the total tropical atmospheric heating is a strong function of the SST. For example the net heating has increased by about 10% from 1950 to 2000 and it is projected to increase by a further 20% by 2100. Such changes must be compensated by a more vigorous atmospheric circulation, with growth in convective heating within the warm pool, and an increase of subsiding air and stability outside the convective warm pool and an increase of vertical shear at the DWP boundaries. This finding is contrary to some conclusions from other studies but in accord with others. We discuss the similarities and differences at length.  相似文献