Examinando por Autor "González, Victor"

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Active Deformation near the Nicoya Peninsula, Northwestern Costa Rica, Between 1996 and 2010: Interseismic Megathrust Coupling
(Advancing Earth and Space Sciences, 2012-06-26) Feng, Lujia; Protti, Marino; González, Victor; Jiang, Yan; Dixon, Timothy; Newman, Andrew V.
We use campaign and continuous GPS measurements at 49 sites between 1996 and 2010 to describe the long-term active deformation in and near the Nicoya Peninsula, northwestern Costa Rica. The observed deformation reveals partial partitioning of the Cocos-Caribbean oblique convergence into trench-parallel forearc sliver motion and less oblique thrusting on the subduction interface. The northern Costa Rican forearc translates northwestward as a whole ridge block at 11 1 mm/yr relative to the stable Caribbean. The transition from the forearc to the stable Caribbean occurs in a narrow deforming zone of 16 km wide. Subduction thrust earthquakes take 2/3 of the trench-parallel component of the plate convergence; however, surface deformation caused by interseismic megathrust coupling is primarily trench-normal. Two fully coupled patches, one located offshore Nicoya centered at 15 km depth and the other located inland centered at 24 km depth, are identified in Nicoya with the potential to generate an Mw 7.8 1950-type earthquake. Another fully coupled patch SE of Nicoya coincides with the rupture region of the 1990 Nicoya Gulf earthquake. Interface microearthquakes, non-volcanic tremor, low-frequency earthquakes, and transient slow-slip events generally occur in the intermediately to weakly coupled regions.
Constraints on upper mantle anisotropy surrounding the Cocos slab from SK(K)S splitting
(Universidad Nacional, Costa Rica., 2010) Abt, David L; Fischer, Karen M.; Abers, Geoffrey A.; Protti, Marino; González, Victor; Strauch, Wilfried
SKS and SKKS splitting observations are used to constrain the pattern of mantle flow in the Central American subduction zone beneath Costa Rica and Nicaragua. After removing the effects of shallow wedge anisotropy on SK(K)S waveforms, a best fitting model of anisotropy beneath the Cocos Plate and in the deeper mantle wedge is determined. Fast polarization directions and model symmetry axis orientations in both regions (as well as the shallow wedge) are dominated by roughly arc-parallel azimuths and, therefore, are not consistent with sublithospheric mantle flow entrained by the subducting Cocos Plate or simple two-dimensional corner flow in the wedge. In conjunction with geochemical data and local S splitting tomography, the SK(K)S splitting observations and anisotropy models are consistent with flow to theWNW within the mantle wedge on the Caribbean side of the Cocos Plate, possibly drawn through a slab window beneath Panama and southern Costa Rica. Anisotropy in the Pacific mantle beneath the Cocos Plate is also best explained by flow with a component that is roughly parallel to the strike of the slab, although the absolute direction of this flow is not uniquely constrained. Copyright © 2010 by the American Geophysical Union.
Crustal Thickness of the Central American Arc
(2007-06-18) Auger, Laura; Abers, Geoff; Syracuse, Ellen; Fischer, Karen; Strauch, Wilfried; Protti, Marino; González, Victor
Crustal Thickness Variations Beneath the Central American Arc
(2006) Auger, L. S.; Abers, G.; Fischer, K.; Protti, Marino; González, Victor; Strauch, Wilfried
Fine-Tuning the Seismic Potential of the Nicoya Gap in NW Costa Rica
(American Geophysical Union, 2007-05-22) González, Victor; Protti, Marino
The Nicoya seismic gap is a subduction segment along the Middle American Trench where the Cocos plate subducts under the Caribbean plate. This seismic gap, located under the Nicoya Peninsula in northwestern Costa Rica, has ruptured with large earthquakes in 1853, 1900 and 1950. Its strong coupling contrasts with the immediately adjacent weak segments: Nicaragua to the NW and central Costa Rica to the SE. The Nicaragua segment has a very high level of background seismicity with several earthquakes per year with magnitudes above 5.0; its most recent large event was an abnormally slow earthquake (Mw=7.6) that generated a destructive tsunami in 1992. The central Costa Rica segment also has a high level of background seismicity with very frequent events with magnitudes above 4.5; its last large event (Mw=7.0) occurred in 1990 just at the boundary with the Nicoya seismic gap. The aftershock areas of the Costa Rica, 1990 and Nicaragua, 1992 earthquakes allowed the geographic extent of the Nicoya seismic gap to be clearly defined. Evidences that support a strong coupling for the Nicoya segment are: a) very low background seismicity; b) the sudden end of aftershocks of the 1990 and 1992 earthquakes at its boundaries; and c) the fast NE motion (parallel to convergence) of the Nicoya Peninsula (nearly 30mm/yr.) observed with GPS. Recent seismological and geodetic studies (Protti et al., 2001; Newman et al., 2002; Iinuma et al., 2004; Norabuena et al., 2004; DeShone et al., 2006) restrict the seismic coupling to 50 +/- 5% and the potential rupture area to 8000 +/- 1500 km2. These values, together with a convergence rate around 88mm/yr and no significant seismic slip since 1950, give the Nicoya seismic gap a potential, for the following 5 years, to generate a earthquake with Mw=7.8 +/- 0.1 magnitude.
Monitoreo geodésico de una Brecha Sísmica Madura: Nicoya, Costa Rica
(Universidad Nacional, Costa Rica, 2002-10) Protti, Marino; González, Victor
Una brecha sísmica existe bajo y frente a la Península de Nicoya en el noroeste de Costa Rica. Esta brecha es un segmento de la zona de subducción de Centroamérica donde la placa del Coco se introduce por debajo de la placa del Caribe. Grandes sismos han ocurrido en este segmento en 1853, 1900 y 1950. Sin deslizamiento significativo desde 1950, con una velocidad de convergencia cercana a los 90 mm/año y con un área de ruptura entre los 5000 y 10000 km2, la brecha sísmica de Nicoya tiene potencial para generar un terremoto de magnitud superior a los 7.5 grados. Dado su alto potencial sísmico, la disponibilidad de información y especialmente el hecho de que la Península de Nicoya se encuentra directamente sobre el área de ruptura, esta brecha sísmica ha sido seleccionada como uno de los dos sitios para el Experimento Mundial de las Zonas Sismogénicas (SEIZE). En un esfuerzo internacional por monitorear y documentar la deformación cortical, el OVSICORI-UNA ha venido trabajando con instituciones de los Estados Unidos y del Japón en la operación de estaciones sísmicas y en la ocupación de una red de GPS en y alrededor de la Península de Nicoya. Esta península está siendo desplazada hacia el continente y subsidiendo a velocidades de hasta 25 mm/año, consistente con la acumulación de deformación esperada a lo largo de una zona de subducción bloqueda. Durante el año 2002 estamos instalando 3 estaciones de registro continuo de GPS y re-ocuparemos la red total de GPS durante el 2003. Dado el estado de madurez de la brecha sísmica de Nicoya, estas mediciones podrían darnos la oportunidad de documentar la deformación co-sísmica y post-sísmica cuando este gran sismo ocurra.
Nicoya earthquake rupture anticipated by geodetic measurement of the locked plate interface
(Nature Research, 2013-12-22) Protti, Marino; González, Victor; Newman, Andrew; Dixon, Timothy H.; Schwartz, Susan; Marshall, Jeffrey S; Feng, Lujia; Walter, Jacob; Malservisi, Rocco; Owen, Susan E.
The Nicoya Peninsula in Costa Rica is one of the few places on Earth where the seismically active plate interface of a subduction zone is directly overlaid by land rather than ocean. At this plate interface, large megathrust earthquakes with magnitudes greater than 7 occur approximately every 50 years. Such quakes occurred in 1853, 1900 and 1950, so another large earthquake had been anticipated. Land-based Global Positioning System (GPS) and seismic measurements revealed a region where the plate interface was locked and hence accumulated seismic strain that could be released in future earthquakes. On 5 September 2012, the long-anticipated Nicoya earthquake occurred in the heart of the previously identified locked patch. Here we report observations of coseismic deformation from GPS and geomorphic data along the Nicoya Peninsula and show that the magnitude 7.6 Nicoya earthquake ruptured the lateral and down-dip extent of the previously locked region of the plate interface. We also identify a previously locked part of the plate interface, located immediately offshore, that may not have slipped during the 2012 earthquake, where monitoring should continue. By pairing observations of the spatial extent of interseismic locking and subsequent coseismic rupture, we demonstrate the use of detailed near-field geodetic investigations during the late interseismic period for identifying future earthquake potential.
NICOYA, COSTA RICA, TRANS-PENINSULA GPS EXPERIMENT AND INTER-PLATE COUPLING
(2003-06-30) Iinuma, Takeshi; Protti, Marino; Obana, Koichiro; Miyazaki, Shinichi; González, Victor; Van der Laat, Rodolfo; Kato, Teruyuki; Kaneda, Yoshiyuki; Hernández, Enrique
Since 2001, a GPS observation project has been carried out on the Nicoya Peninsula, Costa Rica. Costa Rica is located on the western margin of the Caribbean plate, and the Cocos plate is subducting under the Caribbean plate from the Mesoamerican Trench. The speed of convergence between the two plates has caused large earthquakes on the west coast of Costa Rica.
Nicoya, Costa Rica: an IOPD target where the seismogenic zone or large earthquake can be drilled and instrumented
(2009-09-23) Protti, Marino; González, Victor; Yoshiyuki, Kaneda; Brown, Kevin
Potential for the installation of a system in northern Costa Rica for early warning to the capital city of San Jose, from large subduction earthquakes under the Nicoya peninsula
(1998-09-09) Protti, Marino; González, Victor; Malavassi, Eduardo; Hernández, Enrique; Guendel, Federico
Rayleigh Wave Tomography in the Nicaragua-Costa Rica Subduction Zone
(2006) Salas de la Cruz, M.; Fischer, K. M.; Forsyth, D. W.; Abers, G. A.; Strauch, Wilfried; Protti, Marino; González, Victor
Recovering the Importance of Monitoring Networks of Natural Processes in the Concept of Early Warning Systems
(2003) Protti, Marino; González, Victor
Recovering the Importance of Monitoring Networks of Natural Processes in the Concept of Early Warning Systems
(2006) Protti, Marino; González, Victor
Seismic and Geodetic Monitoring of the Nicoya, Costa Rica, Seismic Gap
(2007-05-22) Protti, Marino; González, Victor; Schwartz, Susan; Timothy, Dixon; Kato, Teruyuki; Yoshiyuki, Kaneda; Simila, Gerald; SAMPSON, DANIEL
Seismic Velocities and Earthquake Locations in the Central America Upper Mantle: results from the TUCAN Experiment
(2006) Syracuse, E. M.; Abers, G. A.; Auger, L.; Fischer, K.; Protti, Marino; González, Victor; Strauch, Wilfried; Brewer, J.
Seismogenic zone structure along the Middle America Trench, Nicoya Peninsula, Costa Rica, from 3D local earthquake tomography
(American Geophysical Union, 2004) Deshon, Heather R.; Schwartz, Susan; Dorman, LeRoy; Newman, Andrew V.; Protti, Marino; González, Victor
Resumen de la ponencia "Estructura de la zona sismogénica a lo largo de la Fosa Mesoamericana, Nicoya Península, Costa Rica, a partir de tomografía sísmica local 3D"
Seismogenic zone structure beneath the Nicoya Peninsula, Costa Rica, from three-dimensional local earthquake P- and S-wave tomography
(Geophysical Journal International, 2006) Deshon, Heather R.; Schwartz, Susan; Newman, Andrew; González, Victor; Protti, Marino; Dorman, LeRoy; Dixon, Timothy; SAMPSON, DANIEL; Flueh, Ernst R.
The subduction plate interface along the Nicoya Peninsula, Costa Rica, generates damaging large (Mw > 7.5) earthquakes. We present hypocenters and 3-D seismic velocity models (VP and VP/VS) calculated using simultaneous inversion of P- and S-wave arrival time data recorded from small magnitude, local earthquakes to elucidate seismogenic zone structure. In this region, interseismic cycle microseismicity does not uniquely define the potential rupture extent of large earthquakes. Plate interface microseismicity extends from 12 to 26 and from 17 to 28 km below sea level beneath the southern and northern Nicoya Peninsula, respectively. Microseismicity offset across the plate suture of East Pacific Rise-derived and Cocos-Nazca Spreading Center derived oceanic lithosphere is ∼5 km, revising earlier estimates suggesting ∼10 km of offset. Interplate seismicity begins downdip of increased locking along the plate interface imaged using GPS and a region of low VP along the plate interface. The downdip edge of plate interface microseismicity occurs updip of the oceanic slab and continental Moho intersection, possibly due to the onset of ductile behaviour. Slow forearc mantle wedge Pwave velocities suggest 20–30 per cent serpentinization across the Nicoya Peninsula region while calculated VP/VS values suggest 0–10 per cent serpentinization. Interpretation of VP/VS resolution at depth is complicated however due to ray path distribution.We posit that the forearc mantle wedge is regionally serpentinized but may still be able to sustain rupture during the largest seismogenic zone earthquakes.
Seismogenic zone structure of the southern Middle America Trench, Costa Rica
(Journal of Geophysical Research, 2003-10) DeShon, H.R.; Schwartz, S.Y.; Bilek, S.L.; Dorman, LeRoy; González, Victor; Protti, Marino; Flueh, E.R.; Dixon, T.H.
The shallow seismogenic portion of subduction zones generates damaging large and great earthquakes. This study provides structural constraints on the seismogenic zone of the Middle America Trench offshore central Costa Rica and insights into the physical and mechanical characteristics controlling seismogenesis. We have located 300 events that occurred following the MW 6.9, 20 August 1999, Quepos, Costa Rica, underthrusting earthquake using a three-dimensional velocity model and arrival time data recorded by a temporary local network of land and ocean bottom seismometers. We use aftershock locations to define the geometry and characteristics of the seismogenic zone in this region. These events define a plane dipping at 19 that marks the interface between the Cocos Plate and the Panama Block. The majority of aftershocks occur below 10 km and above 30 km depth below sea level, corresponding to 30–35 km and 95 km from the trench axis, respectively. Relative event relocation produces a seismicity pattern similar to that obtained using absolute locations, increasing confidence in the geometry of the seismogenic zone. The aftershock locations spatially correlate with the downdip extension of the oceanic Quepos Plateau and reflect the structure of the main shock rupture asperity. This strengthens an earlier argument that the 1999 Quepos earthquake ruptured specific bathymetric highs on the downgoing plate. We believe that subduction of this highly disrupted seafloor has established a set of conditions which presently limit the seismogenic zone to be between 10 and 35 km below sea level.
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.
Sismicidad de Costa Rica, Evaluación y Monitoreo de la Brecha Sísmica de Nicoya
(2004-08-27) Protti, Marino; González, Victor
Eventos sísmicos superficiales se presentan en Costa Rica: a) asociados con la subducción de la Placa del Coco bajo la Placa del Caribe y el Bloque de Panamá; b) a lo largo de la zona de fracturas de Panamá; c) como fallamiento intraplaca de esas tres unidades tectónicas; d) como actividad interplaca entre la Placa del Caribe y el Bloque de Panamá, tanto a lo largo del Cinturón Deformado del Norte de Panamá como a lo largo de la zona de fallas que atraviesa la parte central de Costa Rica; y e) asociada al arco volcánico. Sismos de profundidad intermedia (40 a 220 Km.) ocurren como deformación interna de la Placa del Coco. La brecha sísmica de Nicoya es un segmento de la zona de subducción en el noroeste de Costa Rica. Las últimas tres rupturas produjeron grandes sismos en 1853, 1900 y 1950. Las evidencias que indican la existencia de un fuerte acople sísmico en el segmento de Nicoya son: a) un bajo nivel de sismicidad de fondo; b) el cese repentino de la propagación de las réplicas de los sismos de 1990 y de 1992 justo en los bordes de la brecha sísmica de Nicoya; y c) el rápido movimiento hacia el NE de la Península de Nicoya.