Time filter

Source Type

Davi R.,University College Dublin | O'Brien G.S.,University College Dublin | De Barros L.,University College Dublin | Lokmer I.,University College Dublin | And 4 more authors.
Journal of Volcanology and Geothermal Research | Year: 2012

Moment 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. © 2011 Elsevier B.V.


Cordero-Leiton J.,Instituto Costarricense Of Electricidad
Proceedings of the 2014 IEEE Central America and Panama Convention, CONCAPAN 2014 | Year: 2014

The article discusses two very specific study cases where reliability errors occurred at protective relaying functions. The cases took place under fault conditions at the Costa Rican electric power grid. The study cases occurred between 2004 and 2011 in different elements of the transmission system owned by ICE, and they are representative cases in which it was necessary to perform a thorough analysis and laboratory tests. In each case was perform the following tasks: an explanation of the event, a failure categorization under the context of reliability fault type, a relay behavior analysis through its events and disturbance records, laboratory tests conducted to evaluate the behavior of the functions involved, and finally, a description of the corrective actions implemented to solve the detected problem. As a result, was achieved a sample of some of the most interesting experiences in the field of protective relaying maintenance, related to the costarrican electric power transmission network. © 2014 IEEE.


The analysis of salinity data collected during three campaigns of monitoring (2002-2004, 2005-2008 and 2011-2012) in the estuarine sector of Terraba Sierpe National Wetlands (HNTS) was performed. The information collected allows to separate a northern zone with a strong influence of the Rio Grande de Terraba, which during the period of low flow (December-April) shows characteristics of a partially mixed estuary, while it resembles a salt-wedge estuary during intermediate and high flows rates (May-November). A central area with greater marine influence features a vertically homogeneous or well mixed estuary, while the south of the estuary has a balanced (intermediate) condition, through the contributions of the Sierpe river and the tidal regime, which confers characteristics of a partially mixed estuary. The statistical analysis model confirms variations in the salinity values in relation to tides, time of year (season) and the distance along a longitudinal profile of 24km away from the town of Ciudad Cortes to the sea opening at Coronado mouth (F1,47=2.5, p<0.001). The first 7km downstream from Ciudad Cortes have a very well-defined fluvial condition with salinities below 1psu, in the sector of Viuda island, located 8km towards the sea, there is a range of variation in salinity values higher than 5psu; a final section that starts 14km towards the Coronado mouth shows a gradual increase in the salinity values up to 30psu reflecting a greater influence of the tides. The eventual development of the El Diquis hydroelectric project could cause an increase in the contribution of freshwater between an 82-66% of the minimum and maximum average flow values over the northern part of the estuarine sector of the HNTS during the low flow periods, which would create similar conditions to those recorded during the intermediate flow rates. The provided analysis constitutes a first approach to the understanding of the estuarine dynamics of the HNTS. Analysis and monitoring of the relationships between the physical, chemical and biological aspects are essential for future discern between possible sources of changes in the estuarine sector of the HNTS and must be considered to be a firm commitment by the institutions involved in the management and conservation of this ecosystem. © 2015, Universidad de Costa Rica. All rights reserved.


The Térraba-Sierpe Reserve has the largest mangrove in Costa Rica but has suffered from changes in sea level. I used published data to analyze the area and found that sea level rise, generated by coast subsidence or global warming, created a new platform for waves and changed the beach profile and sediment type. Increased sediment deposition on the north maintains the balance of this system, with a sediment gain on the island in front of the Térraba river mouth. A lower sediment output from the Sierpe river is generating a landward delta migration, especially in the southern part, a symptom of local sea level rise. Future scenarios of greater wave energy and additional sea level rise will not allow a dynamic sediment balance, especially on the southern part of the delta, and will generate a loss mangrove cover. © 2015, Universidad de Costa Rica. All rights reserved.


Dzierma Y.,University of Kiel | Rabbel W.,University of Kiel | Thorwart M.M.,University of Kiel | Flueh E.R.,University of Kiel | And 2 more authors.
Geochemistry, Geophysics, Geosystems | Year: 2011

The deep structure of the south-central Costa Rican subduction zone has not been studied in great detail so far because large parts of the area are virtually inaccessible. We present a receiver function study along a transect of broadband seismometers through the northern flank of the Cordillera de Talamanca (south Costa Rica). Below Moho depths, the receiver functions image a dipping positive conversion signal. This is interpreted as the subducting Cocos Plate slab, compatible with the conversions in the individual receiver functions. In finite difference modeling, a dipping signal such as the one imaged can only be reproduced by a steeply (80) dipping structure present at least until a depth of about 70-100 km; below this depth, the length of the slab cannot be determined because of possible scattering effects. The proposed position of the slab agrees with previous results from local seismicity, local earthquake tomography, and active seismic studies, while extending the slab location to greater depths and steeper dip angle. Along the trench, no marked change is observed in the receiver functions, suggesting that the steeply dipping slab continues until the northern flank of the Cordillera de Talamanca, in the transition region between the incoming seamount segment and Cocos Ridge. Considering the time predicted for the establishment of shallow angle underthrusting after the onset of ridge collision, the southern Costa Rican subduction zone may at present be undergoing a reconfiguration of subduction style, where the transition to shallow underthrusting may be underway but still incomplete. Copyright © 2011 by the American Geophysical Union.


Arias A.M.,Instituto Costarricense Of Electricidad
Revista de Biologia Tropical | Year: 2011

The cichlid Hypsophrys nicaraguensis is a popular fish known as butterfly, and despite its widespread use as pets, little is known about its reproductive biology. In order to contribute to this knowledge, the study describes the relevant larval development characteristics, from adult and larval cultures in captivity. Every 12h, samples of larvae were collected and observed under the microscope for larval stage development, and every 24h morphometric measurements were taken. Observations showed that at 120h, some larvae had swimming activity and the pectoral fins development was visible; at 144h, the dorsal fin appear and all larvae started food intake; at 168h, the formation of anal fins begins, small rudiments of pelvic fins emerge, the separation of caudal fin from anal and dorsal fins starts, and the yolk sac is reabsorbed almost completely; at 288h, the pelvic fins starts to form; at 432h, the rays and spines of dorsal and anal fins can be distinguished, both the anal and the dorsal fins have the same number of spines and rays as in adults. After 480h larvae have the first scales, ending the larval stages and starting the transformation to fingerlings. Larvae were successfully fed with commercial diet.


The aquatic insects have been used to evaluate water quality of aquatic environments.The population of aquatic insects and the water quality of the area were characterized according to the natural and human alterations present in the study site. During the monthly-survey, pH, DO, temperature, water level, DBO, PO4 and NO3 were measured. Biological indexes (abundance, species richness and the BMWP-CR) were used to evaluate the water quality. No relation between environmental and aquatic insects was detected. Temporal and spatial differences attributed to the flow events (temporal) and the presence of Peñas Blancas reservoir (spatial). In the future, the investigations in Peñas Blancas watershed need to be focused on determining the real influence of the flows, sediment release and the possible water quality degradation because of agriculture activities.


Vega D.C.,Instituto Costarricense Of Electricidad | Alpizar F.,Tropical Agriculture Research and Higher Education Center
Impact Assessment and Project Appraisal | Year: 2011

Choice experiments, a stated preference valuation method, are proposed as a tool to assign monetary values to environmental externalities during the ex ante stages of environmental impact assessment. This case study looks at the impacts of the Costa Rican Institute of Electricity's Toro 3 hydroelectric project and its impacts on the Recreo Verde tourism center in San Carlos, Costa Rica. Compared to other valuation methods (e.g., travel cost and contingent valuation), choice experiments can create hypothetical but realistic scenarios for consumers and generate restoration alternatives for the affected good. Although they have limitations that must be taken into account in environmental impact assessment, incorporating economic parameters (especially resource constraints and tradeoffs) can substantially enrich the assessment process. © IAIA 2011.


Dinc A.N.,University of Kiel | Dinc A.N.,ExxonMobil | Rabbel W.,University of Kiel | Flueh E.R.,Leibniz Institute of Marine Science | Taylor W.,Instituto Costarricense Of Electricidad
Geophysical Journal International | Year: 2011

The continental margin of Nicaragua and Costa Rica is characterized by significant lateral changes from north to south such as a decreasing dip of the slab, a decreasing magma production and a shift in the volcanic front. To investigate this transition, a joint on- and offshore local earthquake tomography was performed. LowP-wave velocities and highVp/Vsratios, indicative for hydration, were found in the upper-mantle and lowermost crust beneath the Sandino Basin. The mantle wedge hydration can be estimated to 2.5 wt. per cent beneath south Nicaragua. In contrast, the mantle wedge beneath north Costa Rica is weakly or not hydrated. The hydration leads to a local gap in the seismicity in Nicaragua. The lateral transition between the hydrated and non-hydrated areas occurs within a distance of about 10 km. This transition coincides with a change in the crustal thickness in the order of 5-10 km, thickening to the south, and in the tectonic regimes. The change in the tectonic regimes towards a stronger extension along the margin of Nicaragua could be the key for understanding the observations: the extension may support the opening of pathways for a wide zone of fluid migration and hydration through the overriding plate which are identified with areas of lowVp, highVp/Vsand low seismicity. © 2011 The Authors. Geophysical Journal International © 2011 RAS.


Worzewski T.,University of Kiel | Jegen M.,University of Kiel | Kopp H.,University of Kiel | Brasse H.,Free University of Berlin | Taylor Castillo W.,Instituto Costarricense Of Electricidad
Nature Geoscience | Year: 2011

Fluids entering the subduction zone play a key role in the subduction process. They cause changes in the dynamics and thermal structure of the subduction zone1, and trigger earthquakes when released from the subducting plate during metamorphism2,3. Fluids are delivered to the subduction zone by the oceanic crust and also enter the oceanic plate as it bends downwards at the plate boundary. However, the amount of fluids entering subduction zones is not matched by that leaving through volcanic emissions 4 or transfer to the deep mantle2, implying possible storage of fluids in the crust. Here we use magnetotelluric data to map the entire hydration and dehydration cycle of the Costa Rican subduction zone to 120 km depth. Along the incoming plate bend, we detect a conductivity anomaly that we interpret as sea water penetrating down extensional faults and cracks into the upper mantle. Along the subducting plate interface we document the dehydration of sediments, the crust and mantle. We identify an accumulation of fluids at ∼20-30 km depth at a distance of 30 km seaward from the volcanic arc. Comparison with other subduction zones5-14 indicates that such fluid accumulation is a global phenomenon. Although we are unable to test whether these fluid reservoirs grow with time, we suggest that they can account for some of the missing outflow of fluid at subduction zones. © 2011 Macmillan Publishers Limited. All rights reserved.

Loading Instituto Costarricense Of Electricidad collaborators
Loading Instituto Costarricense Of Electricidad collaborators