Observatorio Vulcanológico y Sismológico de Costa Rica

URI permanente para esta comunidadhttp://10.0.96.45:4000/handle/11056/14933

El Observatorio Vulcanológico y Sismológico de Costa Rica (OVSICORI) de la Universidad Nacional, es un instituto de investigación universitaria dedicado a la investigación de los volcanes, los sismos y otros procesos tectónicos, con el propósito de encontrar aplicaciones útiles a la sociedad que ayuden a mitigar los efectos adversos de esos fenómenos al desarrollo económico y social. Se trata de un observatorio, por cuanto una cantidad considerable de su esfuerzo va orientada a documentar la actividad sísmica, volcánica y la deformación cortical que, a su vez, retroalimenta a las actividades investigativas propias de un instituto de investigación universitaria.

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Página web: www.ovsicori.una.ac.cr

Correo: ovsicori@una.cr

Teléfono: (506) 2562 4001 / (506) 2261 0611 / (506) 2261 0781

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Compendio de Boletines Sismológicos Mensuales publicados en el año 2024
(Universidad Nacional, Costa Rica, 2025) Protti, Marino
El presente documento corresponde a uno de los productos comprometidos como parte de la Actividad Continua “Red de Monitoreo Geodinámico del OVSICORI-UNA 2024-2028” registrado con el Código SIA “0426-24”, bajo la cual se desarrollan muchas de las más importantes tareas y obligaciones del OVSICORI-UNA. Se trata de un compromiso de emitir boletines mensuales con el resumen de la actividad sísmica al final de cada mes. Dichos boletines se publican en las redes sociales del OVSICORI-UNA y representan una oportunidad no solo de mantener al público informado, sino también de interactuar con las personas que nos siguen en esos medios. Con el fin de cumplir con los requerimientos de los informes de avance, hemos compilado aquí todos los boletines mensuales correspondientes al 2024. En ocasiones anteriores, la actividad del mes de diciembre se incluye en el reporte anual; sin embargo, para el 2024 decidimos describir la actividad de diciembre en un boletín específico para ese mes.
Compendio de Reportes de Sismos Sentidos por la Población durante el año 2024
(Universidad Nacional, Costa Rica, 2025) Protti, Marino
El presente documento corresponde a uno de los productos comprometidos como parte de la Actividad Continua “Red de Monitoreo Geodinámico del OVSICORI-UNA 2024-2028” registrado con el Código SIA “0426-24”, bajo la cual se desarrollan muchas de las más importantes tareas y obligaciones del OVSICORI-UNA. Se trata de un compromiso de brindar informes oportunos inmediatamente después de ocurridos sismos que hayan sido sentidos por la población. Dichos informes se envían a todos los medios de comunicación y se comparten en las redes sociales del OVSICORI-UNA. Además, se mantiene un registro en la página web del OVSICORI-UNA para la consulta pública, por mes y año. Con el fin de cumplir con los requerimientos de los informes de avance, hemos compilado aquí todos los reportes de sismos sentidos correspondientes al 2024. Para facilidad del lector, los hemos tabulado en registros por mes.
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.
Detailed spatiotemporal evolution of microseismicity and repeating earthquakes following the 2012Mw 7.6 Nicoya earthquake
(Universidad Nacional de Costa Rica, 2017-01-04) Yao, Dongong; Walter, Jacob l.; Meng, Xiaofeng; Hobbs, Teigan E.; Peng, Zhigang; Newman, Andrew V.; Schawartz, Susan Y.; Protti, Marino
We apply a waveform matching technique to obtain a detailed earthquake catalog around the rupture zone of the 5 September 2012 moment magnitude 7.6 Nicoya earthquake, with emphasis on its aftershock sequence. Starting from a preliminary catalog, we relocate ~7900 events using TomoDD to better quantify their spatiotemporal behavior. Relocated aftershocks are mostly clustered in two groups. The first is immediately above the major coseismic slip patch, partially overlapping with shallow afterslip. The second one is 50 km SE to the main shock nucleation point and near the terminus of coseismic rupture, in a zone that exhibited little resolvable afterslip. Using the relocated events as templates, we scan through the continuousrecording from 29 June 2012 to 30 December 2012, detecting approximately 17 times more than template events. We find 190 aftershocks in the first half hour following the main shock, mostly along the plate interface. Later events become more scattered in location, showing moderate expansion in both along- trench and downdip directions. From the detected catalog we identify 53 repeating aftershock clusters with mean cross-correlation values larger than 0.9, and indistinguishably intracluster event locations, suggesting slip on the same fault patch. Most repeating clusters occurred within the first major aftershock group. Very few repeating clusters were found in the aftershock grouping along the southern edge of the Peninsula, which is not associated with substantial afterslip. Our observations suggest that loading from nearby afterslip along the plate interface drives spatiotemporal evolution of aftershocks just above the main shock rupture patch, while aftershocks in the SE group are to the SE of the observed updip afterslip and poorly constrained.
Earth's Magnetic Field Strength and the Cretaceous Normal Superchron: New Data From Costa Rica
(American Geophysical Union, 2021-03-12) Di Chiara, A.; Tauxe, L.; Staudigel, H.; Florindo, F.; Protti, M.; Yu, Y.; Wartho, J. A.; Van den Bogaard, P.; Hoernle, K.
Limitar la variabilidad a largo plazo y el promedio de la intensidad del campo magnético terrestre es fundamental para comprender las características y el comportamiento del campo geomagnético. Persisten interrogantes sobre la intensidad del campo promedio y la relación entre esta y la frecuencia de inversión, debido a la dispersión de los datos de intervalos de tiempo clave. En este estudio, nos centramos en el Supercrón Normal Cretácico (CNS; 121-84 Ma), durante el cual no se observaron inversiones. Presentamos nuevos resultados de intensidad de 41 sitios de vidrio basáltico submarino (SBG) recolectados en la Península de Nicoya y las Islas Murciélago, Costa Rica. Las nuevas y revisadas restricciones de edad 40Ar/39Ar y bioestratigráficas de estudios previos indican edades de 141 a 65 Ma. Un sitio con una edad de 135,1 ± 1,5 Ma (2σ) arrojó un resultado de intensidad confiable de 34 ± 8 µT (equivalente a un momento dipolar axial virtual, VADM, valor de 88 ± 20 ZAm2), tres sitios de 121 a 112 Ma, que abarcan el inicio del CNS, varían de 21 ± 1 a 34 ± 4 µT (53 ± 3 a 87 ± 10 ZAm2). Estos resultados del CNS son todos superiores al promedio a largo plazo de ∼42 ZAm2 y los datos de Suhongtu, Mongolia (46–53 ZAm2) y son similares a la ofiolita de Troodos, Chipre (81 ZAm2, reinterpretada en este estudio). Junto con los datos reinterpretados, los nuevos resultados de Costa Rica sugieren que la intensidad del campo geomagnético fue aproximadamente la misma antes y después del inicio del SNC. Por lo tanto, los datos no respaldan una correlación estricta entre la longitud del intervalo de polaridad y la intensidad del campo magnético.
Effect of subducting sea-floor roughness on fore-arc kinematics, Pacific coast, Costa Rica
(Geological Society of America, 1998-05-01) Fisher, Donald M.; Gardner, Thomas W.; Marshall, Jeffrey S.; Sak, Peter B.; Protti, Marino
Fault kinematics and uplift in the Costa Rican fore arc of the Middle America convergent margin are controlled to a large extent by roughness on the subducting Cocos plate. Along the northwest flank of the incoming Cocos Ridge, seafloor is characterized by short wavelength roughness related to northeast-trending seamount chains. Onland projection of the rough subducting crust coincides with a system of active faults oriented at high angles to the margin that segment the fore-arc thrust belt and separate blocks with contrasting uplift rates. Trunk segments of Pacific slope fluvial systems typically follow these margin-perpendicular faults. Regionally developed marine and fluvial terraces are correlated between drainages and acrossfaults along the Costa Rican Pacific coast. Terrace separations across block-bounding faults reveal a pattern of fore-arc uplift that coincides roughly with the distribution of incoming seamounts. Magnitude and distribution of Quaternary uplift along the Costa Rican Pacific coast suggests that, despite a thin incoming sediment pile, the inner fore arc shows an accumulation of mass—a characteristic that may be due to underplating of seamounts beneath the fore-arc high.
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.
High-resolution gravity survey: Investigation of subsurface structures at Poás volcano, Costa Rica
(Universidad Nacional, Costa Rica, 2003-08-03) Fournier, Nicolas; Rymer, Hazel; Williams-Jones, Glyn; Brenes, Jorge
Bouguer gravity surveys have long been used to investigate sub-surface density contrasts. The main sources of error in previous surveys have been the determination of relative elevations of stations and the effect of topography (removed via the terrain correction). The availability of high precision Kinematic GPS data now facilitates generation of high-resolution Digital Elevation Models that can help to improve the accuracy of relative elevation determination and the terrain correction. Here we describe a highresolution gravity survey at Poás volcano, Costa Rica. Our gravity modelling identifies small pockets of magma at shallow depths which relate to successive magma intrusion through time and shows that the persistent degassing in the eastern part of the crater is related to local deformation at the top of the volcano and changes in the fracture network, rather than to the presence of a shallow magma intrusion.
Horizontal subduction and truncation of the Cocos Plate beneath central Mexico
(American Geophysical Union, 2008-09-27) Pérez-Campos, Xyoli; Kim, YoungHee; Husker, Allen; Davis, Paul M.; Clayton, Robert W.; Iglesias, Arturo; Pacheco, Javier F.; Singh, Shri K.; Manea, Vlad Constantin; Gurnis, Michael
Based on analysis of data from a trans-Mexico temporary broadband seismic network centered on Mexico City, we report that the subducting Cocos Plate beneath central Mexico is horizontal, and tectonically underplates the base of the crust for a distance of 250 km from the trench. It is decoupled from the crust by a very thin low viscosity zone. The plate plunges into the mantle near Mexico City but is truncated at a depth of 500 km, probably due to an E-W propagating tear in the Cocos slab. Unlike the shallow slab subduction in Peru and Chile, there is active volcanism along the Trans Mexican Volcanic Belt (TMVB) that lies much further inland than regions to either side where subduction dip is not horizontal. Geodynamical modeling indicates that a thin weak layer such as imaged by the seismic experiment can explain the flat subduction geometry.
Informe preliminar Terremoto 22 de abril 1991, Ms: 7.4 Valle de La Estrella, Limón, Costa Rica
(Universidad Nacional, Costa Rica, 1991-05) Montero, C; Segura, J; Malavasi, F; Güendel, V; Gonzáles, V; Fernández, E; De Obaldia, F; Rojas, D; Rodriguez, H; Mata, A; Van Der Laat, R; Barboza,V; Barranrtes, O; Marino, T
El sismo del 22 de abril de 1991, Ms=7.4, se ubicó con epicentro 39.5 kms al sur de puerto Limón, Costa Rica, una latitud de 80 kms y una longitud de 60 km a una profundidad de 17 kms. Este sismo de magnitud elevada para eventos de intraplaca (ubicados cerca de la superficie), produjo daños de gran envergadura en la infraestructura de puerto Limón y la región del Caribe de Costa Rica. La falla responsable del terremoto del Valle de la Estrella, es una falla inversa, con ángulo de buzamiento variable en dirección del continente.
La percepción del riesgo volcánico por la actividad del Turrialba (2010-2017) en las comunidades de la pastora y el Tapojo, Costa Rica
(Geo UERJ, 2019-09-17) Campos, D. D.; Alvarado, G. E.
El 5 de enero de 2010, el volcán Turrialba inició su periodo eruptivo asociado a la caída de ceniza, actividad que se mantiene hasta el presente (mayo de 2019), destacando las erupciones del 29 de octubre de 2014, del 12 de marzo de 2015 y del 19 de setiembre de 2016, que afectaron las actividades productivas de las comunidades localizadas en el flanco sur del volcán, en los sectores pecuario (producción de leche y queso) y agrícola (cultivo de papa, repollo, cebolla y zanahoria), por lo que presentaron condiciones de vulnerabilidad ante la actividad volcánica con pérdidas económicas entre el 2010 y el 2017. El presente artículo analiza la percepción de la población de La Pastora y El Tapojo en relación con los peligros volcánicos asociados al Turrialba y su nivel de vulnerabilidad. Para ello, se realizaron grupos focales con líderes comunales con el objetivo de conocer su percepción sobre las condiciones de riesgo, lo cual se contrastó con información científica existente sobre los peligros volcánicos. El análisis demostró que existe una importante coincidencia entre los datos científicos de los peligros volcánicas del Turrialba y la percepción de la población, ya que señalan que la caída de ceniza, los gases, la sismicidad, la lluvia ácida y los lahares representan una amenaza para elementos que podrían verse afectados en la comunidad, principalmente en las actividades agropecuarias, viviendas y puentes.
Magma plumbing processes for persistent activity at Poás volcano, Costa Rica
(American Geophysical Union Advancing Earth, 2005-04-21) Rymer, Hazel; Locke, Corinne A.; Brenes, jorge; Williams-Jones, Glyn
New microgravity data from the active crater of Poás volcano, Costa Rica, collected in 2002 – 2004 extends the existing dataset to provide a unique 20-year time series. These data show that gravity has decreased monotonically in the north and east of the crater over the last 5 years, whilst it has increased to the west and remained approximately constant in the south. These changes are interpreted in terms of convective recharge within dendritic intrusions beneath the crater, with overall down-welling in the north and up-welling in the west. The data reveal a 5 –10 year periodicity in sub-crater mass movement, but overall, the upper part of the conduit system appears to have maintained a state of mass equilibrium.
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.
Plant Responses to Volcanically Elevated CO2 in Two Costa Rican Forests
(Copernicus Publications, 2019-04-01) Bogue, Robert R.; Schwandner, Florian M.; Fisher, Joshua B.; Pavlick, Ryan; Magney, Troy S.; Famiglietti, Caroline A.; Cawse-Nicholson, Kerry; Yadav, Vineet; Linick, Justin P.; North, Gretchen B.; Duarte, Eliecer
We explore the use of active volcanoes to determine the short- and long-term effects of elevated CO2 on tropical trees. Active volcanoes continuously but variably emit CO2 through diffuse emissions on their flanks, exposing the overlying ecosystems to elevated levels of atmospheric CO2. We found tight correlations (r2=0.86 and r2=0.74) between wood stable carbon isotopic composition and co-located volcanogenic CO2 emissions for two of three investigated species (Oreopanax xalapensis and Buddleja nitida), which documents the long-term photosynthetic incorporation of isotopically heavy volcanogenic carbon into wood biomass. Measurements of leaf fluorescence and chlorophyll concentration suggest that volcanic CO2 also has measurable short-term functional impacts on select species of tropical trees. Our findings indicate significant potential for future studies to utilize ecosystems located on active volcanoes as natural experiments to examine the ecological impacts of elevated atmospheric CO2 in the tropics and elsewhere. Results also point the way toward a possible future utilization of ecosystems exposed to volcanically elevated CO2 to detect changes in deep volcanic degassing by using selected species of trees as sensors.
Precursory seismic signals before two catastrophic landslides at Irazú Volcano, Costa Rica
(Latin American and Caribbean Seismological Comission, 2024) Chaves Sibaja, Esteban; Pacheco, Javier; Schwartz, Susan; Chavarría, Nathalie; Noah, Finnegan; Higman, Bretwood
Massive rock landslides impose a continuous impact on the socio-economic growth of developing cities, public infrastructure and telecommunications. Every year, millions of dollars are invested in reverting the negative effects associated with their occurrence all over the world. At volcanoes, complex landslide instabilities triggered in some cases by nearby earthquakes, rainfall, local deformation, or a combination of all, may induce changes in the lithostatic pressure of the edifice, suddenly affecting their internal dynamics and increasing the risk of catastrophic eruptions as occurred during the 80’s in Mt. San Helens. Near field geodynamic monitoring, including broadband seismic, GNSS stations and other techniques, is then essential to better characterize ground failure and to improve landslide hazards assessments. The southwest flank of the Irazú volcano in central Costa Rica has been recognized to host massive rock landslides in the past. Just in December 2014 and August 2020, a total combined of 53 million m3 of mass wasting were deposited along the basement of “Río Sucio”, one of the main tributaries of the Sarapiquí river. Using the near field and geodynamic monitoring network that OVSICORI-UNA operates at Irazú and Turrialba volcanos since 2011, we show unique seismological observations that shed light about the rupture initiation and dynamic evolution of the mass movement. Our results demonstrate that during the 2014 and 2020 events, the nucleation phase initiate weeks prior to the catastrophic collapse with the generation of low frequency earthquakes (LFEs), events dominated by velocity weakening frictional properties that likely represent the stick-slip failure of small asperities localized along the basement. Among the observed LFEs, we report the occurrence of 10 repeating earthquake families, each formed by multiple LFEs that rupture approximately the same asperity at different times, generating identical waveforms. Our observations show that as the mass accelerate with time 1) the number of repeating families increases progressively and 2) the inter-event time between LFEs decreases linearly until they merge forming a tremor signal that initiate 30 min prior to the collapse. Near-field seismic data exhibits an exponential increase in tremor amplitude, and thus, seismic moment, that suddenly reduces and become quiescent for 20 seconds before the impulsive mass detachment and failure. We posit that transient embrittlement is the mechanism responsible for such a unique observation. As the slip rate increases, faulting regions with predominantly stable-sliding (aseismic) frictional properties become unstable (seismic), as previously observed in subduction zones and laboratory experiments. As a result, the number of unstable asperities and/or the total effective area of contact between the sliding mass and the basement increases dramatically, modulating tremor amplitude with time. The shear strength from the elastically couple asperities is enough to provide temporal (~20 s) stability to the entire mass, inducing the seismic quiescence. However, the accrued shear stresses imposed by the slow slip episode on the weak asperities overcomes the frictional strength, inducing the catastrophic failure. Our results provide direct evidence of the mechanics that controlled landslide nucleation and resemble those from laboratory experiments and fault zones during tectonic earthquakes.
Quantifying recent pyroclastic and lava flows at Arenal Volcano, Costa Rica, using medium-footprint lidar
(American Geophysical Union Advancing Earth and Space Sciences, 2006-11-03) Hofton, M. A.; Malavassi, E.; Blair, J. B.
Arenal volcano is a small, active stratovolcano in Costa Rica. In 1998 and 2005, NASA’s Laser Vegetation Imaging Sensor (LVIS) was used to collect wide-swath 3- dimensional topographic images of the volcano. The LVIS is a full-waveform, scanning, medium-sized footprint, airborne laser altimeter system. By digitally recording the shape of the returning laser pulse (waveform), the LVIS provides a precise and accurate view of both the sub-canopy and canopy-top topographies as well as the vertical and horizontal structure of vegetation at 15– 25 m horizontal resolution. By comparing georeferenced waveform data collected in 1998 and 2005, we mapped lava and pyroclastic flows deposited during this period. The active crater grew by 3.82 m yr 1. A flow volume estimate of 2.19 107 m3 (Dense Rock Equivalent of 1.89 107 m3 or 0.085 m3s 1) Nwas obtained for the period 1998 to 2005. Precise elevation and elevation change data such as those provided by the LVIS are essential to calculate eruption volume and to study magma-supply dynamics, as well as assess the danger posed by the volcano to the local population from hazards such as pyroclastic flows.
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.
The 5 September 2012 Nicoya, Costa Rica Mw 7.6 earthquake rupture process from joint inversion of high-rate GPS, strong-motion, and teleseismic P wave data and its relationship to adjacent plate boundary interface properties
(Universidad Nacional de Costa Rica, 2013-10-03) Yue, Han; Lay, Thorne; Schwartz, Susan; Rivera Pérez, Luis; Protti, Marino; Dixon, Timothy; Owen, Susan E.; Newman, Andrew V.
On 5 September 2012, a large thrust earthquake (Mw 7.6) ruptured a densely instrumented seismic gap on the shallow-dipping plate boundary beneath the Nicoya Peninsula, Costa Rica. Ground motion recordings directly above the rupture zone provide a unique opportunity to study the detailed source process of a large shallow megathrust earthquake using very nearby land observations. Hypocenter relocation using local seismic network data indicates that the event initiated with small emergent seismic waves from a hypocenter ~10 km offshore, 13 km deep on the megathrust. A joint finite-fault inversion using high-rate GPS, strong-motion ground velocity recordings, GPS static offsets, and teleseismic P waves reveals that the primary slip zone (slip>1 m) is located beneath the peninsula. The rupture propagated downdip from the hypocenter with a rupture velocity of ~3.0 km/s. The primary slip zone extends ~70 km along strike and ~30 km along dip, with an average slip of ~2 m. The associated static stress drop is ~3 MPa. The seismic moment is 3.5 × 1020 Nm, giving Mw = 7.6. The coseismic large-slip patch directly overlaps an onshore interseismic locked region indicated by geodetic observations and extends downdip to the intersection with the upper plate Moho. At deeper depths, below the upper plate Moho, seismic tremor and low-frequency earthquakes have been observed. Most tremor locates in adjacent areas of the megathrust that have little coseismic slip; a region of prior slow slip deformation to the southeast also has no significant coseismic slip or aftershocks. An offshore locked patch indicated by geodetic observations does not appear to have experienced coseismic slip, and aftershocks do not overlap this region, allowing the potential for a comparable size rupture offshore in the future.
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.
Tracking Formation of a Lava Lake From Ground and Space: Masaya Volcano (Nicaragua), 2014–2017
(American Geophysical Union, 2018-02-22) AIUPPA, Alessandro; de Moor, J. Marteen; Arellano, Santiago; Coppola, Diego; Francofonte, Vincenzo; Galle, Bo; Giudice, Gaetano; Liuzzo, Marco; Mendoza, Elvis; Saballos, Armando; Tamburello, Giancarlo; Battaglia, Angelo; Bitetto, Marcello; Gurrieri, Sergio; Laiolo, Marco; Mastrolia, Andrea; Moretti, Robertto
A vigorously degassing lava lake appeared inside the Santiago pit crater of Masaya volcano (Nicaragua) in December 2015, after years of degassing with no (or minor) incandescence. Here we present an unprecedented-long (3 years) and continuous volcanic gas record that instrumentally characterizes the (re)activation of the lava lake. Our results show that, before appearance of the lake, the volcanic gas plume composition became unusually CO2 rich, as testified by high CO2/SO2 ratios (mean: 12.2 6 6.3) and low H2O/CO2 ratios (mean: 2.3 6 1.3). The volcanic CO2 flux also peaked in November 2015 (mean: 81.3 6 40.6 kg/s; maximum: 247 kg/s). Using results of magma degassing models and budgets, we interpret this elevated CO2 degassing as sourced by degassing of a volatile-rich fast-overturning (3.6–5.2 m3 s21) magma, supplying CO2-rich gas bubbles from minimum equivalent depths of 0.36–1.4 km. We propose this elevated gas bubble supply destabilized the shallow (<1 km) Masaya magma reservoir, leading to upward migration of vesicular (buoyant) resident magma, and ultimately to (re)formation of the lava lake. At onset of lava lake activity on 11 December 2015 (constrained by satellite-based MODIS thermal observations), the gas emissions transitioned to more SO2-rich composition, and the SO2 flux increased by a factor 40% (11.4 6 5.2 kg/s) relative to background degassing (8.0 kg/s), confirming faster than normal (4.4 versus 3 m3 s21) shallow magma convection. Based on thermal energy records, we estimate that only 0.8 of the 4.4 m3 s21 of magma actually reached the surface to manifest into a convecting lava lake, suggesting inefficient transport of magma in the near-surface plumbing system.

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