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11.
Peter Luger M. Gröschke M. Bussmann A. Dina W. Mette A. Uhmann H. Kallenbach 《International Journal of Earth Sciences》1994,83(4):711-727
The Jurassic and Cretaceous sedimentary history of northern Somalia and the Morondava Basin of south-western Madagascar have been studied. Both regions display an independent facial development; however, a comparison of the sequential evolution of the Mesozoic sedimentary successions in these two presently widely separated areas reveals a surprisingly high level of similarity, which probably reflects major events during the disintegration of Eastern Gondwana during the Jurassic and Cretaceous. Although in Jurassic times the onset of transgressions and regressions in both areas compares well with eustatic development, major deviations in combination with the tectonic activities of different degrees are observed in the Early and Late Cretaceous synchronously in both regions. Transgressions are observed in Toarcian, Bajocian (not dated in northern Somalia), Callovian, Valanginian (Madagascar only), Aptian and Campanian times. Tectonism is noted before the Aptian and Campanian transgressions in northern Somalia and the Morondava Basin of south-western Madagascar. 相似文献
12.
Dina Vaiou 《Geoforum》2004,35(5):529-531
In this comment, I discuss the dominance of Anglophone geographical literature in Greece, arguing that it is a recent and still contested phenomenon, to do with broader historical/political circumstances, as well as with the development of geographical studies at university level. In the context of the power-knowledge system, in which Anglophone debates, theory production and spaces of academic communication and exchange dominate, radical academics in Greece are caught in a complex web of contradictions, have to negotiate their/our paths across languages, plural voices, local and international communities. 相似文献
13.
Anomalous Emissions of SO2 During the Recent Eruption of Santa Ana Volcano, El Salvador, Central America 总被引:1,自引:0,他引:1
Rodolfo Olmos José Barrancos Claudia Rivera Francisco Barahona Dina L. López Benancio Henriquez Agustín Hernández Efrain Benitez Pedro A. Hernández Nemesio M. Pérez Bo Galle 《Pure and Applied Geophysics》2007,164(12):2489-2506
Santa Ana volcano in western El Salvador, Central America, had a phreatic eruption at 8:05 am (local time) on October 1, 2005,
101 years after its last eruption. However, during the last one hundred years this volcano has presented periods of quiet
degassing with fumarolic activity and an acidic lake within its crater. This paper presents results of frequent measurements
of SO2 degassing using the MiniDOAS (Differential Optical Absorption Spectroscopy) system and a comparison with the volcanic seismicity
prior to the eruption, during, and after the eruption. Vehicle measurements of SO2 flux were taken every hour during the first nine days of the eruption and daily after that. The period of time reported here
is from August to December, 2005. Three periods of degassing are distinguished: pre-eruptive, eruptive, and post-eruptive
periods. The intense activity at Santa Ana volcano started in July 2005. During the pre-eruptive period up to 4306 and 5154
ton/day of SO2 flux were recorded on October 24 and September 9, 2005, respectively. These values were of the same order of magnitude as
the recorded values just after the October 1st eruption (2925 ton/day at 10:01 am). Hourly measurements of SO2 flux taken during the first nine days after the main eruptive event indicate that explosions are preceded by an increase
in SO2 flux and that this parameter reaches a peak after the explosion took place. This behavior suggests that increasing accumulation
of exsolved magmatic gases occurs within the magmatic chamber before the explosions, increasing the pressure until the point
of explosion. A correlation between SO2 fluxes and RSAM (Real Time Seismic Amplitude Measurements) is observed during the complete sampling period. Periodic fluctuations
in the SO2 and RSAM values during the entire study period are observed. One possible mechanism explaining these fluctuations it that
convective circulation within the magmatic chamber can bring fresh magma periodically to shallow levels, allowing increasing
degasification and then decreasing degasification as the batch of magma lowers its gas content, becomes denser, and sinks
to give space to a new magma pulse. These results illustrate that the measurements of SO2 flux can provide important warning signals for incoming explosive activity in active volcanoes. 相似文献
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Luis Cumbal Paulina Vallejo Brigida Rodriguez Dina Lopez 《Environmental Earth Sciences》2010,61(2):299-310
The arsenic content of geothermal hot springs and their sediments in the north-central Andean region of Ecuador has been investigated.
The area of study is located between parallels 1°11′N and 1°30′S and includes five provinces. The area is rich in geothermal
surface manifestations that are mainly used for medicinal baths in recreational complexes. Unfortunately, water residuals
without treatment are released from the recreational facilities to surrounding water bodies. The results indicate that total
arsenic in geothermal waters in this region has a range of 2–969 μg As/L, and sediments contain arsenic ranging from 1.6 to
717.6 mg/kg. Chemical analyses of sediment samples show the presence of sulfur, iron, aluminum and calcium. A high concentration
of natural organic matter was also found in some samples (20–29.5%); thus sorption and coprecipitation can be the main mechanisms
of As immobilization on mineral phases and natural organic matter. 相似文献
20.
Lateral force, response spectrum and step‐by‐step pushover analyses are performed and compared with the post‐earthquake survey of two Dieh‐Dou buildings seriously affected in the 1999 Chi‐Chi earthquake in Taiwan. The results show that the proposed FE model with finite translational and rotational stiffness can successfully be employed to assess the vulnerability of the frames. The fundamental period of Dieh‐Dou structures is about 1.0 s higher than that calculated by the simplified approach of the codes for regular frames; a modal analysis is, therefore, essential for this typology of structure. The elastic analysis, either lateral force or response spectrum, is shown to be reliable to assess Dieh‐Dou frames when quick results are desired. However, a non‐linear step‐by‐step pushover analysis has the advantage of greater accuracy, as it allows mapping the failure trend and indicating the critical elements. The lateral drifts are compared with the actual observed damage pattern and when the damage level is related to the peak ground acceleration on a vulnerability curve plot, it is shown that the joint failure combined with the lateral drift gives an indication of the global structural behaviour of this historic construction typology. Owing to the unique construction features of the Dieh‐Dou, the joint failure represents also a critical criterion in terms of maximum retention for conservation. Based on a damage level approach, an assessment methodology is suggested that would allow optimizing a strengthening strategy, for protection of these precious structures from future earthquakes while avoiding unnecessary interventions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献