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1.
N. Segovia S. de la Cruz-Reyna M. Mena E. Ramos M. Monnin J. L. Seidel 《Natural Hazards》1989,1(4):319-329
A radon anomaly in a nuclear track detector placed on a fault was detected prior to the destructive (Ms = 8.1) Mexican earthquake of 19 September 1985. The fault is a structural feature of the geothermal field Los Azufres, 260 km NE of the epicentral area. Since no other phenomenon can be found as a possible cause for the radon anomaly, it is proposed that preseismic regional stress perturbations may produce changes in the fluid transport patterns at the fault, suggesting that radon measurements in similar conditions could provide a good precursor in high seismic risk areas. 相似文献
2.
Carolina Boix‐Fayos Joris de Vente María Martínez‐Mena Gonzalo G. Barberá Víctor Castillo 《水文研究》2008,22(25):4922-4935
Extensive land use changes have occurred in many areas of SE Spain as a result of reforestation and the abandonment of agricultural activities. Parallel to this the Spanish Administration spends large funds on hydrological control works to reduce erosion and sediment transport. However, it remains untested how these large land use changes affect the erosion processes at the catchment scale and if the hydrological control works efficiently reduce sediment export. A combination of field work, mapping and modelling was used to test the influence of land use scenarios with and without sediment control structures (check‐dams) on sediment yield at the catchment scale. The study catchment is located in SE Spain and suffered important land use changes, increasing the forest cover 3‐fold and decreasing the agricultural land 2·5‐fold from 1956 to 1997. In addition 58 check‐dams were constructed in the catchment in the 1970s accompanying reforestation works. The erosion model WATEM‐SEDEM was applied using six land use scenarios: land use in 1956, 1981 and 1997, each with and without check‐dams. Calibration of the model provided a model efficiency of 0·84 for absolute sediment yield. Model application showed that in a scenario without check dams, the land use changes between 1956 and 1997 caused a progressive decrease in sediment yield of 54%. In a scenario without land use changes but with check‐dams, about 77% of the sediment yield was retained behind the dams. Check‐dams can be efficient sediment control measures, but with a short‐lived effect. They have important side‐effects, such as inducing channel erosion downstream. While also having side‐effects, land use changes can have important long‐term effects on sediment yield. The application of either land use changes (i.e. reforestation) or check‐dams to control sediment yield depends on the objective of the management and the specific environmental conditions of each area. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
3.
Mabel Mena Avto Goguitchaichvili Miguel Cervantes Solano Juan Francisco Vilas 《Studia Geophysica et Geodaetica》2011,55(2):279-309
The Early Cretaceous may be considered a key period for understanding the evolution of the Earth’s magnetic field. Some still
unsolved problems are related to the mode of paleosecular variation (PSV) of the Earth’s magnetic field before and during
the Cretaceous Normal Superchron. We report here a detailed rock-magnetic, paleomagnetic and paleointensity investigation
from 28 lava flows (331 standard paleomagnetic cores) collected in the Argentinean part of the Parana Flood Basalts (Formation
Posadas) in order to contribute to the study of PSV during the early Cretaceous and to obtain precise Cretaceous paleomagnetic
pole positions for stable South America. The average paleofield direction is precisely determined from 26 sites, which show
small within-site dispersion and high directional stability. Five sites show evidences for the self-reversal of thermoremanent
magnetization. 23 sites yielded normal polarity magnetization and only 3 are reversely magnetized. Moving windows averages
were used to analyze the sequential variation of virtual geomagnetic pole’s (VGP) axial positions. Interestingly, the axial
average VGP path traces an almost complete cycle around the geographical pole and passes near the location of all previously
published Paraná Magmatic Province poles. Both paleomagnetic poles and average VGP paths are significantly different from
the pole position suggested by fixed hotspot reconstructions, which may be due to true polar wander or the hotspot motion
itself. Only 15 samples from 5 individual basaltic lava flows, yielded acceptable paleointensity estimates. The site mean
paleointensities range from 25.2 ± 2.2 to 44.0 ± 2.2 μT. The virtual dipole moments (VDMs) range from 4.8 to 9.9 × 1022 Am2. This correspond to a mean value of 7.7 ± 2.1 × 1022 Am2 which is 96% of the present day geomagnetic field strength. These intensities agree with the relatively high values already
reported for Early Cretaceous, which are consistent with some inferences from computer simulations previously published. 相似文献
4.
The elongated distribution of virtual geomagnetic poles (VGPs) of South American Jurassic units has been interpreted as reflecting: 1) the behavior of the Earth's magnetic field (EMF), and 2) apparent polar shift of the South American plate before the breakup of Gondwana. New paleomagnetic data do not support the latter. We analyze these Jurassic VGPs together with those of other Pangean continents, considering a model based on the following assumptions: 1) Pangea was assembled over the present African-Atlantic geoid high; 2) the hotspot framework has not been significantly deformed over the last 200 Ma; 3) the present geoid matches the present topography of the core mantle boundary (CMB); 4) the overall topography of the CMB remains unchanged for long periods of time. We plotted Jurassic VGPs of Pangean continents, previously returned to a fixed-hotspot framework, on a map of the present topography of the CMB. The VGPs seem to follow the trend of regions of increased CMB seismic velocities. When a polarity reversal was registered by a Jurassic unit, the path of the VGPs was channeled on zones that have been observed in translational paths for the last 10 Ma. 相似文献
5.
A better knowledge of soil erosion by water is essential for planning effective soil and water conservation practices in semi‐arid Mediterranean environments. The special climatic and hydrological characteristics of these areas, however, make accurate soil loss predictions difficult, particularly in the absence of minimal data. Two zero‐order experimental microcatchments (328–759 m2), representative of an extensive semi‐arid watershed with a high potential erosion risk in the south‐east of Spain, were selected and monitored for 3 years (1991–93) in order to provide information on the hydrological and erosional response. A pluviogram and hydrograph recorded data at 1‐min intervals during each storm, after which the soil loss was collected and the particle size of the sediment was analysed. Runoff coefficients of about 9% and soil losses of between 84·83 and 298·9 g m?2 year?1 were observed in the area. Rapid response times (geometric mean values lower than 2 h) and low runoff thresholds (mean values between 3·5 to 5·9 mm) were the norm in the experimental areas. A rain intensity of over 15 mm h?1 was considered as ‘erosive rainfall’ in these areas because of the total soil loss and the transport capacity of the overland flow. Differences in pore‐size distribution explained the different hydrological responses observed between areas. The erosional response was more complex and basically seemed to be determined by soil aggregate stability and topographical properties. A greater proportion of finer particles in the eroded material than in the soil matrix indicated selective erosion and the transport of finer material. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
6.
Castro-Correa Carmen-Paz Aldunce Ide Paulina Wyndham Vásquez Katherine Mena Maldonado Dania Pérez Tello Sonia 《Natural Hazards》2020,103(2):2427-2440
Natural Hazards - This article analyzes the impact of socio-natural disasters on social capital at a local level, studying the cases of the communities of Chañaral and Diego de Almagro after... 相似文献
7.
Francisco Javier Hern��ndez-Molina Dorrik A. V. Stow Estefan��a Llave Michele Rebesco Gemma Ercilla David Van Rooij Anxo Mena Juan-Tom��s V��zquez Antje H. L. Voelker 《Geo-Marine Letters》2011,31(5-6):285-300
Deep-water circulation is a critical part of the global conveyor belt that regulates Earth??s climate. The bottom (contour)-current component of this circulation is of key significance in shaping the deep seafloor through erosion, transport, and deposition. As a result, there exists a high variety of large-scale erosional and depositional features (drifts) that together form more complex contourite depositional systems on continental slopes and rises as well as in ocean basins, generated by different water masses flowing at different depths and at different speeds either in the same or in opposite directions. Yet, the nature of these deep-water processes and the deposited contourites is still poorly understood in detail. Their ultimate decoding will undoubtedly yield information of fundamental importance to the earth and ocean sciences. The international congress Deep-water Circulation: Processes & Products was held from 16?C18 June 2010 in Baiona, Spain, hosted by the University of Vigo. Volume 31(5/6) of Geo-Marine Letters is a special double issue containing 17 selected contributions from the congress, guest edited by F.J. Hernández-Molina, D.A.V. Stow, E. Llave, M. Rebesco, G. Ercilla, D. Van Rooij, A. Mena, J.-T. Vázquez and A.H.L. Voelker. The papers and discussions at the congress and the articles in this special issue provide a truly multidisciplinary perspective of interest to both academic and industrial participants, contributing to the advancement of knowledge on deep-water bottom circulation and related processes, as well as contourite sedimentation. The multidisciplinary contributions (including geomorphology, tectonics, stratigraphy, sedimentology, paleoceanography, physical oceanography, and deep-water ecology) have demonstrated that advances in paleoceanographic reconstructions and our understanding of the ocean??s role in the global climate system depend largely on the feedbacks among disciplines. New insights into the link between the biota of deep-water ecosystems and bottom currents confirm the need for this field to be investigated and mapped in detail. Likewise, it is confirmed that deep-water contourites are not only of academic interest but also potential resources of economic value. Cumulatively, both the congress and the present volume serve to demonstrate that the role of bottom currents in shaping the seafloor has to date been generally underestimated, and that our understanding of such systems is still in its infancy. Future research on contourites, using new and more advanced techniques, should focus on a more detailed visualization of water-mass circulation and its variability, in order to decipher the physical processes involved and the associations between drifts and other common bedforms. Moreover, contourite facies models should be better established, including their associations with other deep-water sedimentary environments both in modern and ancient submarine domains. The rapid increase in deep-water exploration and the new deep-water technologies available to the oil industry and academic institutions will undoubtedly lead to spectacular advances in contourite research in terms of processes, morphology, sediment stacking patterns, facies, and their relationships with other deep-marine depositional systems. 相似文献
8.
Stylized environments and ABMs: educational tools for examining the causes and consequences of land use/land cover change 总被引：1，自引：0，他引：1
A challenge in land change science is to assess the causes and consequences of LULC change and associated pattern–process relations. Increasingly, land change organizations are examining land use at local to global scales for historical, contemporary and future periods through scenarios that assess population–environment interactions. Spatial analytical tools in GIScience are being used to link people and environment and to search for the distal and proximate factors that affect local to global land use patterns. Spatial simulation models that rely upon complexity theory as the framework and agent-based models as the analytical approach offer the capability to inform through experimentation about land issues important to science and society. Using a stylized landscape where a selected set of key social, geographical and ecological elements are spatially organized, we describe how land dynamics can be examined through agent-based models as educational tools that are useful in the classroom, boardroom and public forums. 相似文献
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