Examinando por Autor "Gonzalez, Victor"

Mostrando 1 - 8 de 8

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.
Crustal structure along the southern Central American volcanic front
(Universidad Nacional, Costa Rica., 2018-08-20) MacKenzie, Laura; Abers, Geoffrey A.; Fischer, Karen M.; Syracuse, Ellen; Protti, Marino; Gonzalez, Victor; Strauch, Wilfried
Subduction alters continents several ways, including accretion, magmatic addition, mantle wedge serpentinization, and crustal differentiation. These changes affect seismic velocities, so characterizing upper plate crust establishes a baseline for composition and continental growth. Teleseismic P and PP arrivals from a temporary deployment of broadband seismometers in Central America have been used to estimate crustal thickness and Vp/Vs ratio from receiver functions and to image crust across the active arc. Crustal thickness ranges from 25 to 44 km with formal errors of 1.6–9.2 km. The thinnest crust (24.6 ±3.5 km) lies directly beneath the Nicaraguan arc, whereas the thickest crust lies in the Nicaraguan back arc (43.5 ± 2.5 km) and beneath the Costa Rican arc (37.9 ± 5.2 km). Crustal structure and Vp/Vs show sharp transitions at terrane boundaries. The Moho exhibits strong velocity contrasts throughout the study area of 0.5–1.0 km/s, even beneath arc and fore arc, precluding extensive serpentinization or ponded melt below the Moho. Crust is thicker beneath the Costa Rican arc, consistent with 10–23 km3/km/Ma crustal growth. The crust is thinner by 11–18 km beneath the large depression in central Nicaragua, with the thinnest crust beneath the arc. There, the relationship between thin crust, arc location, and deeper seismic velocities suggests that upper plate structure plays a critical role in focusing magma to the surface.
Detailed data available for recent Costa Rica earthquake.
(University of South Florida, 2013) Dixon, Timothy H.; Schwartz, Susan; Protti, Marino; Gonzalez, Victor; Newman, Andrew; Marshall, Jeff; Spotila, Jim
On 5 September 2012 a magnitude 7.6 earthquake occurred beneath the Nicoya Peninsula of northwestern Costa Rica, rupturing the subduction zone between the Cocos and Caribbean plates. In most subduction zones the locus of seismic slip lies far offshore, making it difficult to infer interface seismogenic processes from on-shore observations. In contrast, the Nicoya Peninsula lies close to the trench (within 70 kilometers), allowing observations directly over the earthquake rupture zone.
Earthquake and tsunami forecasts: Relation of slow slip events to subsequent earthquake rupture
(National Academy of Sciences, 2014-11-17) Dixon, Timothy H.; Jiang, Yan; Malservisi, Rocco; McCaffrey, Robert; Voss, Nicholas; Protti, Marino; Gonzalez, Victor
The 5 September 2012 Mw 7.6 earthquake on the Costa Rica subduction plate boundary followed a 62-y interseismic period. Highprecision GPS recorded numerous slow slip events (SSEs) in the decade leading up to the earthquake, both up-dip and down-dip of seismic rupture. Deeper SSEs were larger than shallower ones, if characteristic of the interseismic period, release most locking down-dip of the earthquake, limiting down-dip rupture and earthquake magnitude. Shallower SSEs were smaller, accounting for some but not all interseismic locking. One SSE occurred several months before the earthquake, but changes in Mohr-Coulomb failure stress were probably too small to trigger the earthquake. Because many SSEs have occurred without subsequent rupture, their individual predictive value is limited, but taken together they released a significant amount of accumulated interseismic strain before the earthquake, effectively defining the area of subsequent seismic rupture (rupture did not occur where slow slip was common). Because earthquake magnitude depends on rupture area, this has important implications for earthquake hazard assessment. Specifically, if this behavior is representative of future earthquake cycles and other subduction zones, it implies that monitoring SSEs, including shallow up-dip events that lie offshore, could lead to accurate forecasts of earthquake magnitude and tsunami potential.
Multiscale postseismic behavior on a megathrust: the 2012 Nicoya earthquake, Costa Rica
(American Geophysical Union, 2015-06-17) Malservisi, Rocco; Schwartz, Susan Y.; Voss, Nicholas; Protti, Marino; Gonzalez, Victor; Dixon, Timothy H.; Jiang, Yan; Newman, Andy V.; Richardson, Jacob; Walter, Jacob I.; Voyenko, Denis
La Península de Nicoya, en el noroeste de Costa Rica, se encuentra sobre una sección del megaembotamiento de subducción a lo largo de la Fosa Mesoamericana. El 5 de septiembre de 2012, un megaembotamiento de magnitud de momento 7,6 se produjo bajo una densa red de estaciones GPS y sísmicas continuas. Muchas de las estaciones GPS registraron el evento a alta frecuencia, 1 Hz o mejor. Analizamos la evolución temporal y espacial de la deformación superficial tras el terremoto. Nuestros resultados muestran que la ruptura principal fue seguida por un deslizamiento posterior significativo dentro de las primeras 3 h posteriores al evento principal. El comportamiento del desplazamiento superficial puede representarse mediante procesos de relajación con tres tiempos característicos: 7, 70 y más de 400 días. Suponemos que el tiempo de relajación largo corresponde a la relajación viscoelástica y el tiempo de relajación intermedio corresponde al deslizamiento posterior en la falla principal. El tiempo de relajación corto puede representar una combinación de deslizamiento posterior rápido, ajuste poroelástico en la corteza superior u otros procesos. Durante los primeros meses posteriores al terremoto, el deslizamiento posterior probablemente liberó una cantidad significativa del déficit de deslizamiento aún presente tras la ruptura cosímica, en particular el buzamiento ascendente de la ruptura. El deslizamiento posterior parece estar limitado por el buzamiento ascendente de las regiones afectadas por deslizamientos lentos previos al terremoto, lo que sugiere que ambos procesos se ven influenciados por diferentes propiedades de fricción.
Persistent tremor within the northern Costa Rica seismogenic zone
(American Geophysical Union Advancing Earth and Space Sciences, 2011-01-13) Walter, Jacob I.; Schwartz, Susan Y.; Protti, Marino; Gonzalez, Victor
We identify tremor using a spectral detection method and characterize its occurrence over a period of four years (2006–2009) in the vicinity of the Nicoya Peninsula, Costa Rica. Although a few major tremor events accompanied by geodetic slow slip occur, much of the tremor record consists of minor episodes with short duration and no detectable geodetic slip. Its persistent occurrence suggests that some portion of the interface is experiencing slow slip nearly continuously driving small patches to fail in accelerated slip. Locations indicate that much of the tremor occurs at shallow depth, in freely slipping regions of the seismogenic zone. This result is significant in that locations of slow slip and tremor at other subduction zones are largely limited to the downdip frictional transition. Tremor locations may help to refine the heterogeneous distribution of locked and freely slipping patches within the Costa Rica seismogenic zone.
Slow slip events in Costa Rica detected by continuous GPS observations, 2002–2011
(American Geophysical Union, 2012-04-18) Jiang, Yan; Wdowinski, Shimon; Dixon, Timothy H.; Hackl, Matthias; Protti, Marino; Gonzalez, Victor
Una red de estaciones GPS de registro continuo ha operado en la Península de Nicoya en el norte de Costa Rica desde 2002. Procesamos todos los datos disponibles de esta red para el período 2002-2011 para investigar la ocurrencia de Eventos de Deslizamiento Lento (SSE) en la interfaz de subducción entre las placas de Cocos y Caribe. Con el fin de superar el enmascaramiento de la señal por los altos niveles de ruido troposférico, desarrollamos una nueva técnica que facilita la detección de eventos transitorios en presencia de ruido. Identificamos cinco SSE significativos durante el período 2002-2011, con tiempos medios de evento en 2003, 2005, 2007, 2009 y 2011, con un intervalo de recurrencia promedio de 216 meses. El análisis de series de tiempo muestra que la deformación transitoria imparte una firma similar a la caminata aleatoria. La eliminación de los SSE y los errores regionales de modo común de la serie de tiempo redujo la incertidumbre de la velocidad en casi un orden de magnitud. Los datos limitados disponibles para los eventos de 2003, 2005 y 2011 impiden la caracterización detallada de estos eventos. Sin embargo, una buena cobertura espaciotemporal de los eventos de 2007 y 2009 sugiere que ambos eventos tuvieron una duración y distribución irregulares. En el evento de 2007, el deslizamiento lento comenzó en el área costera del noroeste y migró hacia el sureste durante un período de 1 mes. El evento de 2009 tuvo una duración significativamente mayor y un mayor desplazamiento en la superficie. Las estaciones en el área noroeste observaron dos SSE separados en 2008.6 y 2009.4, correlacionándose bien con los episodios de temblores en alta mar, lo que indica un parche de deslizamiento SSE poco profundo con un intervalo de recurrencia más corto. Las diferencias significativas entre los eventos de 2009 y 2007 nos llevan a cuestionar el modelo simple de intervalo de recurrencia para el SSE en Nicoya.
The synchronous occurrence of shallow tremor and very low frequency earthquakes offshore of the Nicoya Peninsula, Costa Rica
(American Geophysical Union, 2013-03-05) Walter, Jacob I.; Schwartz, Susan Y.; Protti, Marino; Gonzalez, Victor
The occurrence of transient, shallow slow slip at seismogenic zones has important implications for earthquake and tsunami hazards. Here we provide evidence that a tremor and slow slip event occurred at shallow depth offshore of the Nicoya Peninsula, Costa Rica, in August 2008. The temporal coincidence of offshore tremor, very low frequency earthquakes (VLFEs), motions consistent with slow slip on the plate interface on western coastal GPS stations, and a pressure transient in an IODP borehole all indicate slow slip occurring at shallow depths. Large ocean loading stresses on the shallow plate interface modulate tremor activity, with the peak Coulomb stress forced by semi-diurnal ocean tides correlating with tremor productivity. Based on beamforming data, we constrain that the VLFE activity occurs in the same region as the tremor and slow slip. The presence of slow slip at shallow depth has important implications for the up-dip extent of earthquake rupture. The proximity of the 5 September 2012, Mw 7.6 megathrust earthquake to slow slip, tremor, and VLFE activity in the 2008 event suggests abrupt frictional transitions from locked to conditionally stable behavior on the plate interface offshore of the Nicoya Peninsula.