Continuous subsidence associated to the long lasting eruption of Arenal volcano (Costa Rica) observed by dry tilt stations

International audienceArenal Volcano is a small (~1750 m above sea level, ~10 km3) stratovolcano that continuously erupted between July 1968 and October 2010. During this longlasting eruption (over 42 yr), a large volume of material--~5.6 × 108 m3 of dense rock equivalent--has been extruded and has produced a thick and extended lava fi eld, mainly on the western fl ank of the edifi ce. Measurements of ground deformation obtained using a network of dry-tilt stations are presented for the period 1986-2000. They show a continuous subsidence of the volcano with maximal amplitude on the western side. The load effect of the lava fi eld is calculated and explains the largest part of the observed tilts. Once the data are corrected by this load effect, pressure source models are not supported by the observations and by quality criteria on the models. Although the dry-tilt data from Arenal Volcano give limited constraints on the deformation models, they are representative of a long period of activity that cannot be recovered by other means. Moreover, the corresponding interpretative model is consistent with results obtained by geotechnical studies and modern ground deformation methods like interferometric synthetic aperture radar (InSAR)

Seismic source mechanisms of tremor recorded on Arenal volcano, Costa Rica, retrieved by waveform inversion

International audienceMoment tensor inversions of volcanic tremor are synthetically tested and subsequently applied to a dataset recorded on Arenal volcano in 2005. We selected 15 harmonic tremor events showing an emergent but very clear onset with a fundamental frequency range of 0.8-1.5 Hz. These events constitute an excellent opportunity to broaden our knowledge of tremor generation models. The inversions were performed for a common source location, the position of which was retrieved through the evaluation of the joint probability density function of the misfit values obtained by the moment tensor inversion of all the events and all predefined source locations (grid search). Events are located beneath the summit crater, in a shallow position. The inversion procedure was tested through the use of synthetic tremor, generated using full wavefield numerical simulations. The maximum amplitude decomposition method is used to analyse the solutions of the synthetic tests. The results highlight the stability of the moment tensor solution when the whole length of the signal is used in the inversion procedure. Hence the whole length of the tremor is utilised to retrieve the source mechanism generating the 15 tremor events. A sliding window is utilised to investigate the time variability of our solution. A crack dipping 20° to the North-Northeast is reconcilable with all 15 tremor events. This mechanism is found to be constant for the entire length of each tremor and for different events

Recombination reduction on lead halide perovskite solar cells based on low temperature synthesized hierarchical TiO2 nanorods

Intensive research on the electron transport material (ETM) has been pursued to improve the efficiency of perovskite solar cells (PSCs) and decrease their cost. More importantly, the role of the ETM layer is not yet fully understood, and research on new device architectures is still needed. Here, we report the use of three-dimensional (3D) TiO2 with a hierarchical architecture based on rutile nanorods (NR) as photoanode material for PSCs. The proposed hierarchical nanorod (HNR) films were synthesized by a two-step low temperature (180 °C) hydrothermal method, and consist of TiO2 nanorod trunks with optimal lengths of 540 nm and TiO2 nanobranches with lengths of 45 nm. Different device configurations were fabricated with TiO2 structures (compact layer, NR and HNR) and CH3NH3PbI3, using different synthetic routes, as the active material. PSCs based on HNR-CH3NH3PbI3 achieved the highest power conversion efficiency compared to PSCs with other TiO2 structures. This result can be ascribed mainly to lower charge recombination as determined by impedance spectroscopy. Furthermore, we have observed that the CH3NH3PbI3 perovskite deposited by the two-step route shows higher efficiency, surface coverage and infiltration within the structure of 3D HNR than the one-step CH3NH3PbI3−xClx perovskite.This work was supported by the Universitat Jaume I (project 12I361.01/1), the Spanish MINECO (project MAT2013-47192- C3-1-R), CONACYT-México (project CB-2010/153270) and UNAM (PAPIIT-IN1030

Testimonios sobre la activación social y la radicalización política de las décadas del 60' y el 70' : Los primeros pasos en la constitución de un archivo oral

En las últimos años en nuestro país, en el marco de la notable expansión que han tenido los estudios sobre el pasado reciente en el campo de las ciencias sociales, se han puesto en marcha diversos proyectos destinados a la constitución de archivos orales, tanto dentro como fuera del ámbito académico. Estas iniciativas apuntan centralmente a la producción, conservación y accesibilidad de fuentes orales bajo métodos, problemas y perspectivas teóricas determinadas por la investigación socio-histórica. Su rasgo central es la utilización de fuentes orales como medio fundamental para reconstruir acontecimientos y procesos históricos, así como estudiar y analizar las representaciones, imaginarios y discursos de los actores. Este trabajo se propone presentar algunos lineamientos que guiaron la constitución del Archivo Oral que hemos empezado a construir en el marco del Proyecto de Investigación “Sociedad y política en la Argentina post-peronista (1955-1976): acontecimientos, actores y discursos de la Nueva Izquierda”, dirigido por Cristina Tortti y radicado en el Dpto. de Sociología de la FaHCE, UNLP. El mismo se propone la reconstrucción y el análisis de procesos, acontecimientos, actores y discursos, de corte renovador y revolucionario, que pueden ser considerados típicos o representativos de ese amplio movimiento de carácter contestatario, que genéricamente se alude como “nueva izquierda”. En esta breve comunicación nos proponemos presentar algunas de las principales características y contenido que guían la conformación del Archivo Oral. En segundo término, realizaremos algunas consideraciones tomando como base unas pocas entrevistas realizadas en el marco del Proyecto.Encuentro realizado junto con el III Congreso Internacional de Historia OralFacultad de Humanidades y Ciencias de la Educació

Sociedad y política en argentina (1955-1976) : La 'nueva izquierda' entre la protesta social y la política revolucionaria

El presente proyecto de investigación analiza la relación entre sociedad y política en la Argentina entre 1955 y 1976. Se trata de un período signado por una aguda crisis socio-política, una profunda pérdida de legitimidad de las instituciones y el Estado y en que la acelerada modernización socio-cultural posterior a 1955 se combinó rápidamente con una tendencia a la radicalización política. Uno de los primeros efectos de este proceso fue la recomposición de la izquierda. Del seno de sus partidos "tradicionales" (el Partido Comunista y Socialista) surgieron diversas formaciones de la "nueva izquierda", mientras que rupturas y transformaciones similares se verificaban en sectores nacionalistas, peronistas y cristianos. Estos nuevos actores sociales y políticos solieron orientarse hacia objetivos que proclamaron la "liberación nacional" y el "socialismo" y hacia estrategias revolucionarias. Nuestro trabajo se interesa centralmente en reconstruir los orígenes de las nuevas prácticas y organizaciones surgidas por entonces así como las formas de articulación entre demandas sociales y propuestas políticas, y entre elencos dirigentes y sectores populares. A su vez, examina una multiplicidad de "casos" que formaron parte de este social y políticamente variado campo, sin subsumirlo exclusivamente al accionar de las organizaciones armadas.This research project analyzes the relationship between society and politics in Argentina between 1955 and 1976. This is a period marked by an acute socio-political crisis, a profound loss of legitimacy of the institutions and the state and that the accelerated socio-cultural modernization after 1955 was quickly combined with a tendency to political radicalization. One of the first effects of this process was the restructuring of the left. From their "traditional" parties (the Communist Party and Socialist) emerged various formations of the "new left", while ruptures and similar transformations were verified in "peronistas", nationalist, and christians sectors. These new social and political actors tended to move towards objectives that proclaimed "national liberation" and "socialism" and to revolutionary strategies. Our work is centrally interested in reconstructing the origins of the new practices and organizations emerged and forms of articulation between social demands and policy proposals, and between leadership groupsand and popular sectors. In turn, examines a multiplicity of "cases" that were part of this process, without subsuming exclusively to the actions of the armed organizations.Facultad de Humanidades y Ciencias de la Educació

Prevalencia de anormalidades de células epiteliales y factores asociados en mujeres de un municipio rural colombiano

Introduction. In spite of implementation of cytology-based cervical cancer screening in Colombia, mortality rates remain stable. The description of factors associated to cervical pre-neoplasic lesions is needed to establish strategies for mortality prevention.Objective. The prevalence of epithelial squamous cell abnormalities was determined to explore the association of cytology abnormalities with described risk factors. Materials and methods. This population-based, cross-sectional study included 739 women randomly selected by age. A validated face-to-face questionnaire and conventional cervical cytology were used to collect the information. To establish the association between cervical abnormalities and some qualitative variables, the independent chi squared test was used. We also calculated prevalence ratio with their 95% confidence intervals. A logistic regression model was used to explore variables that potentially explain cytology abnormalities.Results. The prevalence of squamous cell abnormality was 15.8%. Among women with abnormal cytology, 10% presented atypical squamous cells of undetermined significance, 3.9% low grade squamous intra-epithelial lesion and 1.9% high grade squamous intra-epithelial lesion. The adjusted logistical regression analysis showed that history of sexual transmitted disease, two or more sexual partners during entire life and previous abnormal cytology were associated with cytology abnormalities.Conclusion. The relation of epithelial squamous cell abnormalities with sexual behavior history reflexes the link between human papiloma virus infection and cervical cancer pre-neoplasic lesions. The frequency of use and knowledge about the purpose of cytology were factors that suggested other diagnostic limitations such as quality of cervical cytology or barriers to access health care. These latter factors may be the underlying basis for the high cervical cancer mortality rates.Introducción. A pesar de la existencia de los programas de tamización basados en la citología, las tasas de cáncer de cuello uterino permanecen estables en Colombia. La descripción de los factores asociados a las lesiones precursoras de cáncer de cuello uterino es necesaria para establecer estrategias para su prevención.Objetivo. Determinar la prevalencia de las anormalidades de células epiteliales escamosasy su asociación con los factores de riesgo descritos.Materiales y métodos. Estudio transversal de población en 739 mujeres, seleccionadas en forma aleatoria. La información se recolectó mediante la citología y un cuestionario previamente validado. La medida de asociación fue la razón de prevalencia con su respectivo intervalo de confianza del 95%. Las variables de confusión fueron controladas en un modelo de regresión logística multivariado.Resultados.La prevalencia del evento fue de 15,8%. Entre las mujeres con citología anormal, 10% presentó células escamosas atípicas de significado indeterminado; 3,9%, lesión escamosa intraepitelial de bajo grado, y 1,9%, lesión escamosa intraepitelial de alto grado.La regresión logística ajustada sugiere que los antecedentes de enfermedades de transmisión sexual, una citología anormal y tener dos o más parejas regulares/ocasionales durante la vida se asocian con la presencia del evento.Conclusiones. La relación de anormalidades de células escamosas con conducta sexual refleja la asociación entre el virus del papiloma humano y lesiones preneoplásicas de cáncer de cuello uterino. El uso frecuente y el adecuado conocimiento sobre la citología, sugiere que aspectos tales como las dificultades con la calidad de la citología o el acceso al diagnóstico y tratamiento, pudieran explicar las altas tasas de cáncer de cuello uterino

Crustal structure across the Costa Rican Volcanic Arc

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 1087–1103, doi:10.1002/ggge.20079.Island arcs are proposed to be essential building blocks for the crustal growth of continents; however, island arcs and continents are fundamentally different in bulk composition: mafic and felsic, respectively. The substrate upon which arcs are built (oceanic crust versus large igneous province) may have a strong influence on crustal genesis. We present results from an across-arc wide-angle seismic survey of the Costa Rican volcanic front which test the hypothesis that juvenile continental crust is actively forming at this location. Travel-time tomography constrains velocities in the upper arc to a depth of ~15 km where average velocities are <6.5 km/s. The upper 5 km of crust is constrained by velocities between 4.0 and 5.5 km/s, which likely represent sediments, volcaniclastics, flows, and small intrusions. Between 5 and 15 km depth, velocities increase slowly from 5.5 to 6.5 km/s. Crustal thickness and lower crustal velocities are roughly constrained by reflections from an inferred crust-mantle transition zone. Crustal thickness beneath the volcanic front in Costa Rica is ~40 km with best-fit average lower-crustal velocities between 6.8 and 7.1 km/s. Overall, velocities across the arc in central Costa Rica are at the high-velocity extreme of bulk continental crust velocities and are lower than modern island arc velocities, suggesting that continental compositions are created at this location. These data suggest that preexisting thick crust of the Caribbean Large Igneous Province has a measurable effect on bulk composition. This thickened arc crust may be a density filter for mafic material and thereby support differentiation toward continental compositions.Funding was provided by the NSF-MARGINS and ODP programs, under NSF grant OCE-0405654 and project Nº 113- A4-408 from the University of Costa Rica.2013-10-2

Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO

Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principle calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI. Supplemental material in the ancillary file

Seismic evidence for fluids in fault zones on top of the subducting Cocos Plate beneath Costa Rica

Author Posting. © The Authors, 2010. This article is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 181 (2010): 997-1016, doi:10.1111/j.1365-246X.2010.04552.x.In the 2005 TICOCAVA explosion seismology study in Costa Rica we observed crustal turning waves with a dominant frequency of ~10 Hz on a linear array of short-period seismometers from the Pacific Ocean to the Caribbean Sea. On one of the shot records, from Shot 21 in the backarc of the Cordillera Central, we also observed two seismic phases with an unusually high dominant frequency (~20 Hz). These two phases were recorded in the forearc region of central Costa Rica and arrived ~7 s apart and 30 to 40 s after the detonation of Shot 21. We considered the possibility that these secondary arrivals were produced by a local earthquake that may have happened during the active-source seismic experiment. Such high-frequency phases following Shot 21 were not recorded after Shots 22, 23, and 24, all in the backarc of Costa Rica, which might suggest that they were produced by some other source. However, earthquake dislocation models cannot produce seismic waves of such high frequency with significant amplitude. In addition, we would have expected to see more arrivals from such an earthquake on other seismic stations in central Costa Rica. We therefore investigate whether the high-frequency arrivals may be the result of a deep seismic reflection from the subducting Cocos plate. The timing of these phases is consistent with a shear wave from Shot 21 that was reflected as a compressional (SxP) and a shear (SxS) wave at the top of the subducting Cocos slab between 35 and 55 km depth. The shift in dominant frequency from ~10 Hz in the downgoing seismic wave to ~20 Hz in the reflected waves requires a particular seismic structure at the interface between the subducting slab and the forearc mantle in order to produce a substantial increase in reflection coefficients with frequency. The spectral amplitude characteristics of the SxP and SxS phases from Shot 21 are consistent with a very high Vp/Vs ratio of 6 in ~5 m thick, slab-parallel layers. This result suggests that a system of thin shear zones near the plate interface beneath the forearc is occupied by hydrous fluids under near-lithostatic conditions. The overpressured shear zone probably takes up fluids from the downgoing slab, and it may control the lower limit of the seismogenic zone.This work was funded by the US National Science Foundation MARGINS programme