Artículos científicos

URI permanente para esta colecciónhttp://10.0.96.45:4000/handle/11056/17882

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Central American subduction system
(GEOPHYSICISTS, 2007-10) Protti, Marino; Gonzalez, Victor; Alvarado, Guillermo; Hoernle, Kaj; Plank, Terry; Silver, Eli
The driving force for great earthquakes and the cycling of water and climate-influencing volatiles (carbon dioxide, sulfur, halogens) across the convergent margin of Central America have been a focus of international efforts for over 8 years, as part of the MARGINS pro gram of the U.S. National Science Foundation, the Collaborative Research Center (SFB 574) of the German Science Foundation, and the Cen tral American science community. Over 120 scientists and students from 10 countries met in Costa Rica to synthesize this intense effort spanning from land to marine geological and geophysical studies.
Constraints on upper plate deformation in the Nicaraguan subduction zone from earthquake relocation and directivity analysis
(American Geophysical Union, 2010-03-12) French, S. W.; Warren, L. M.; Fischer, K. M.; Abers, G. A.; Strauch, W.; Protti, J. M.; Gonzalez, V.
In the Nicaraguan segment of the Central American subduction zone, bookshelf faulting has been proposed as the dominant style of Caribbean plate deformation in response to oblique subduction of the Cocos plate. A key element of this model is left‐lateral motion on arc‐normal strike‐slip faults. On 3 August 2005, a Mw 6.3 earthquake and its extensive foreshock and aftershock sequence occurred near Ometepe Island in Lake Nicaragua. To determine the fault plane that ruptured in the main shock, we relocated main shock, foreshock, and aftershock hypocenters and analyzed main shock source directivity using waveforms from the TUCAN Broadband Seismic Experiment. The relocation analysis was carried out by applying the hypoDD double‐difference method to P and S onset times and differential traveltimes for event pairs determined by waveform cross correlation. The relocated hypocenters define a roughly vertical plane of seismicity with an N60°E strike. This plane aligns with one of the two nodal planes of the main shock source mechanism. The directivity analysis was based on waveforms from 16 TUCAN stations and indicates that rupture on the N60°E striking main shock nodal plane provides the best fit to the data. The relocation and directivity analyses identify the N60°E vertical nodal plane as the main shock fault plane, consistent with the style of faulting required by the bookshelf model. Relocated hypocenters also define a second fault plane that lies to the south of the main shock fault plane with a strike of N350°E– N355°E. This fault plane became seismically active 5 h after the main shock, suggesting the influence of stresses transferred from the main shock fault plane. The August 2005 earthquake sequence was preceded by a small eruption of a nearby volcano, Concepción, on 28 July 2005. However, the local seismicity does not provide evidence for earthquake triggering of the eruption or eruption triggering of the main shock through crustal stress transfer.
Fore-arc motion and Cocos Ridge collision in Central America
(American Geophysical Union, 2009-05-07) LaFemina, Peter; Dixon, Timothy H.; Govers, Rob; Norabuena, Edmundo; Turner, Henry; Saballos, Armando; Mattioli, Glen; Protti, Marino; Strauch, Wilfried
We present the first regional surface velocity field for Central America, showing crustal response to interaction of the Cocos and Caribbean plates. Elastic half-space models for interseismic strain accumulation on the dipping subduction plate boundary fit the GPS data well and show strain accumulation offshore and beneath the Nicoya and Osa peninsulas in Costa Rica but not in Nicaragua. Since large subduction zone earthquakes occur in Nicaragua, we suggest that interseismic locking in Nicaragua and some other parts of Central America occurs but is mainly shallow, <20 km depth, too far offshore to be detected by our on-land GPS measurements. Our data also show significant trench-parallel motion for most of the region, generally interpreted as due to oblique convergence and strong mechanical coupling between subducting and overriding plates. However, trench-parallel motion is also observed in central Costa Rica, where plate convergence is normal to the trench, and in the Nicaraguan fore arc, where trench-parallel motion is fast, up to 9 mm a 1, but mechanical coupling is low. A finite element model of collision (as opposed to subduction) involving the aseismic Cocos Ridge also fits the GPS surface velocity field, most significantly reproducing the pattern of trench-parallel motion. We infer that buoyant, thickened CNS-2-Cocos Ridge crust resists normal subduction and instead acts as an indenter to the Caribbean plate, driving crustal shortening in southern Costa Rica and contributing to trench-parallel fore-arc motion in Costa Rica and perhaps Nicaragua as a type of tectonic escape.
Seismic tomography and earthquake locations in the Nicaraguan and Costa Rican upper mantle
(American Geophysical Union, 2008-07-30) Syracuse, Ellen M.; Abers, Geoffrey A.; Fischer, Karen; MacKenzie, Laura; Rychert, Catherine; Protti, Marino; González, Víctor; Strauch, Wilfried
The Central American subduction zone exhibits large variations in geochemistry, downgoing plate roughness and dip, and volcano locations over a short distance along the arc. Results from joint inversions for Vp, Vp/Vs, and hypocenters from the Tomography Under Costa Rica and Nicaragua (TUCAN) experiment give insight into its geometry and structure. In both Costa Rica and Nicaragua, the intermediate-depth seismic zone is a single layer no more than 10 to 20 km thick. Tomographic images show that throughout Nicaragua and Costa Rica the slowest mantle P wave velocities appear below and behind the volcanic front, indicating likely zones of highest temperature extending 80 to 120 km depth. A sheet of high Vp/Vs, thought to be caused by melt, is imaged directly beneath the Nicaraguan volcanoes, whereas a weaker, broader anomaly is imaged beneath the Costa Rican volcanoes, potentially indicating a greater extent of melting beneath Nicaragua. Within the downgoing plate, anomalously low velocities occur at least 20–30 km below Wadati-Benioff zone seismicity, to depths of 140 km beneath Nicaragua and to 60 km depth beneath Costa Rica. They indicate 10–20% serpentinized upper mantle of the downgoing plate beneath Nicaragua, similar to that inferred from refraction seaward of the trench, but continuing to subarc depths. This unusually hydrated lithosphere may introduce more water into the Nicaraguan mantle, initiating increased amount of melting and fluid flux to the arc.
Shear wave anisotropy beneath Nicaragua and Costa Rica: Implications for flow in the mantle wedge
(American Geophysical Union, 2009-05-27) Abt, David L.; Fischer, Karen M.; Abers, Geoffrey A.; Strauch, Wilfried; Protti, J. Marino; González, Victor
We present new shear wave splitting data from local events in Costa Rica and Nicaragua recorded by the temporary (July 2004 to March 2006) 48-station TUCAN broadband seismic array. Observed fast polarization directions in the fore arc, arc, and back arc range from arc-parallel to arc-normal over very short distances (<5 km when plotted at raypath midpoints) making the direct interpretation of individual splitting measurements in terms of flow tenuous, even when considering variations in the relationship between lattice-preferred orientation and deformation (e.g., B-type dislocation creep in olivine). Therefore, we tomographically invert the splitting measurements to find a three-dimensional model of crystallographic orientation in the wedge. We assume the elastic constants of olivine and orthopyroxene with hexagonal symmetry and use a damped, iterative least squares approach to account for the nonlinear behavior of splitting when considering three-dimensional ray propagation and distributions of anisotropy. The best fitting model contains roughly horizontal, arc-parallel olivine [100] axes in the mantle wedge down to at least 125 km beneath the back arc and arc, which we interpret to indicate along-arc flow in the mantle wedge. Pb and Nd isotopic ratios in arc lavas provide additional evidence for arc-parallel flow and also constrain the direction (northwest, from Costa Rica to Nicaragua) and minimum flow rate (63–190 mm/a). With only slightly oblique subduction at 85 mm/a of the relatively planar Cocos Plate, the most likely mechanism for driving along-arc transport is toroidal flow around the edge of the slab in southern Costa Rica, generated by greater slab rollback in Nicaragua. Two important implications of this arc-parallel flow are the progressive depletion of the mantle source for arc lavas from Costa Rica to Nicaragua and the possible need for significant decoupling between the wedge and downgoing plate.
Strong along-arc variations in attenuation in the mantle wedge beneath Costa Rica and Nicaragua
(American Geophysical Union, 2008-10-09) Rychert, C. A.; Fischer, K .M.; Abers, G. A.; Plank, T.; Syracuse, E.; Protti, J. M.; Gonzalez, V.; Strauch, W.
La estructura de atenuación en la zona de subducción de Centroamérica se visualizó utilizando eventos locales registrados por el conjunto Tomography Under Costa Rica and Nicaragua, un despliegue de 20 meses (julio de 2004 a marzo de 2006) de 48 sismómetros que abarcaron las regiones de antearco, arco y trasarco de Nicaragua y Costa Rica. Las formas de onda P y S se invirtieron por separado para la frecuencia de esquina y el momento de cada evento y para el operador de atenuación promediado por trayectoria (t*) de cada par evento-estación, asumiendo que la atenuación depende ligeramente de la frecuencia (/ = 0,27). Luego, se realizaron inversiones tomográficas para la atenuación S y P (QS1 y QP1). Dado que las amplitudes de la onda P reflejan tanto el módulo de cizallamiento como el de volumen, también se realizaron inversiones tomográficas para determinar la atenuación de cizallamiento y volumen (QS1 y Qk1), la pérdida de energía por ciclo debido al cizallamiento y la compresión uniforme, respectivamente. El amortiguamiento y otros parámetros tomográficos de inversión se variaron sistemáticamente. Como es típico en los estudios de atenuación de la zona de subducción, se obtuvieron imágenes de una losa, placa superior y esquina de cuña menos atenuantes y una cuña del manto más atenuante. Además, se observaron diferencias de primer orden entre los mantos debajo de Nicaragua y Costa Rica. La losa en Nicaragua es más atenuante que la losa en Costa Rica. Una zona más grande de mayor atenuación por cizalladura también caracteriza la cuña del manto nicaragüense. Dentro de la cuña, los valores máximos de atenuación a 1 Hz corresponden a Qs = 38-73 debajo de Nicaragua y Qs = 62-84 debajo de Costa Rica, y los valores promedio son Qs = 76-78 y Qs = 84-88, respectivamente. Las variaciones de atenuación se correlacionan con las tendencias a lo largo del arco en los indicadores geoquímicos que sugieren que la fusión debajo de Nicaragua ocurre en condiciones más hidratadas, y posiblemente a mayores extensiones y profundidades, en relación con el norte de Costa Rica.

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Examinando Artículos científicos por Materia "AMÉRICA CENTRAL"