查看更多>>摘要：The glaciers of Mexico are very small ice bodies located on top of the highest mountains of Mexico. They represent a natural gauge for the climatic changes at the 19 degrees N latitude where no other ice bodies are located around the world. Glaciar Norte glacier on Citlaltepetl Volcano, Mexico, has been retreating in a huge scale, just like other glaciers close to the tropics. Following the current trend of the small glaciers around the world, this glacier will probably disappear before mid-century and with its disappearance an important climatic gauge at this latitude will be gone. Therefore, it is important to identify the factors influencing the retreat and eventual demise of the glaciers. This study focuses on the analysis of the energy fluxes of Glaciar Norte's surface on the northern flank of Citlaltepetl Volcano, Mexico. From this, it was calculated the energy balance for a single point on the glacier surface. Here, the glacio-meteorological study is described using data from automatic weather stations installed at >5100 masl with the energy balance model developed from this data. The results suggest that net radiation is the main component responsible for the retreat of Mexican glaciers since this parameter controls the energy balance variability. This situation was compared to the energy balance regime present on other tropical and mid-latitude glaciers and it was possible to establish a first approximation of the energy balance regime on glaciers near 19N latitude based on energy balance variability.
Alicia Miranda, SilviaHector Herrada, AlfredoCristina Pacino, Maria
315-322页
查看更多>>摘要：Gravity anomalies are often strongly influenced by topography, which effect is mitigated through appropriate reductions. Usually, a standard value of 2670 kg/m(3) is used for the density of topography in the absence of specific information. However, various methods have been implemented to obtain density of topography estimates directly from the gravity data. A particularly suitable technique for regional scale studies is based on analyzing the fractal nature of gravity anomalies for a particular region.
Alatorre-Zamora, Miguel AngelCampos-Enriquez, Jose OscarRosas-Elguera, Jose GuadalupePena-Garcia, Laura...
323-342页
查看更多>>摘要：Many geologic and tectonic-structural studies refer to the Chapala lake structure in general terms as a graben (or more generally as rift). However, no formal study has addressed its structure. The Chapala Lake is located in a major topographic depression surrounded by broad middle to late Miocene volcanic-capped plateaus. We conducted a magnetic survey comprising five S-N lines crossing the Chapala Lake. One profile comprises a land extension (southwards along roads). Magnetic anomalies obtained are mainly smooth and large scale features associated to the sedimentary infill, local and high amplitude anomalies are due to shallow basaltic and andesitic tilted blocks, and highest amplitudes due to the outcropped basaltic flows of the Los Alacranes and Mezcala islands. The models obtained point to a large structural high located at the central depression portion that separates two structural lows. The structural lows correspond to half-graben type structures. Through the faults delimiting it were emplaced the basaltic flows of the Mezcala and Los Alacranes islands. The presence of half-graben type structures indicates that the crust has been subject to an extensional tectonic.
Bayowa, Gabriel OyelowoFalebita, Dele EbenezerAdegboyesga, Raheem Olajide
343-352页
查看更多>>摘要：Surface DC resistivity techniques have been used to investigate the subsoil characteristics around an abandoned dumpsite in Ido Osun, Southwestern Nigeria. The aim was to delineate groundwater contamination, identify lithologic layers, locate possible leachate plumes, and assess the risk of groundwater pollution. Schlumberger vertical electrical sounding (VES) and Dipole-dipole resistivity profiling data were acquired at 20 m and 10 m intervals respectively along three northwest-southeast geophysical traverses. The geoelectric sections revealed four probable subsurface geoelectric layers which were considered to be topsoil, laterite, weathered/fractured bedrock and competent/fresh bedrock based on previous works. The weathered/fractured bedrock forms the groundwater reservoir in the area as interpreted from the over 98% occurrence of H, KH geoelectric curve types. The dipole-dipole sections showed several distinct low resistivity zones which extends into the weathered/fractured bedrock. These were interpreted as probable contamination plumes beneath the dumpsite.
Moreira, Cesar AugustoMunhoz, ThaisCavallari, FernandaInnocenti Helene, Livia Portes...
353-362页
查看更多>>摘要：Biogas produced in sanitary landfills consists in a potential source, formed by degradation of organic matter, this gas is constituted by CH4, CO2 and water vapor. Sanitary landfills represent important depository of organic matter with great energetic potential in Brazil, although presently with inexpressive use. Estimates for production or maintenance of productive rates of CH4 represent one of the main difficulties of technical order to the planning and continuity of collection systems for rational consumption of this resource. Electrical resistivity measurements are routinuously used in profiling oil wells for the determination of levels with accumulations of oil and gas, facing the contrast among fluids and rocks. This paper aims to evaluate eventual relationship among biogas flow quantified in surface drains of a waste cell in landfill, with characteristic patterns of in depth electrical resistivity. The integration of Electrical Resistivity Tomography (ERT) lines allowed for the generation of 3D blocks and a clear distinction among zones of high biogas production, quantified in surface drains, with areas of high resistivity in depth. The results suggest the possibility of use of the method in studies to place drains in areas promising to the collection of biogas for energetic generation in sanitary landfill.
查看更多>>摘要：Papanoa earthquake broke the plate interface NW of the Guerrero seismic gap. In this region, previous large earthquakes occurred in 1943 (M-S 7.4), 1979 (M(w)7.4) and 1985 (M(w)7.5). The earthquake was recorded in the near-source region by several accelerographs. Severe damage was reported in Papanoa (where PGA of similar to 0.9 g was recorded on one of the horizontal components at a soft site) and other nearby coastal towns. It was also felt strongly in Mexico City where the ground motions were comparable to those recorded during the 1979 and 1985 events.
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