Artículos científicos

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A model of degassing and seismicity at Arenal Volcano, Costa Rica
(Universidad Nacional, Costa Rica, 2001-08) Williams Jones, G; Stix, J; Heiligmann, M; Barquero, J; Fernandez, E
Arenal volcano is the most active volcano in Costa Rica and has emitted at least 1.3 Mt of SO2 since its reactivation in July 1968. Gas emissions from the volcano have been both by passive degassing and explosive eruptions, with passive degassing being dominant. Based on correlation spectrometry (COSPEC) measurements made during 1982, 1995 and 1996, the minimum average daily output is 130 ± 60 t d-1 SO2 emitted from Arenal. Arenal is extremely active, with tremor fluctuations showing a distinct correlation with Earth tides; decreased explosive activity and increased tremor appear to coincide with the maximum rate of change in Earth tides. This suggests that a system such as Arenal may be extremely sensitive to small changes in the confining pressure or stress regime of the conduit. The cyclic nature of explosive activity also may be caused by corresponding fluctuations in the extrusion rate of lava. At high extrusion rates, lava from the non-explosive conduit may overflow into the explosive conduit, temporarily blocking it with a resulting pressurisation of the system. Arenal is likely tapping a deep to mid crustal magma chamber and, unlike many volcanoes, there is a comparatively small difference between petrological and COSPEC SO2 estimates (0.41 vs. 1.3 Mt, respectively, since 1968), suggesting that Arenal is being continuously supplied by fresh magma. © 2001 Elsevier Science B.V. All rights reserved.
A model of diffuse degassing at three subduction-related volcanoes
(Universidad Nacional, Costa Rica, 2000) Williams-Jones, G; Stix, J; Heiligmann, M; Charland, A; Sherwood Lollar, B; Arner, N; Gustavo Garzón, V; Barquero, J; Fernandez, E
Radon, CO2 and δ13C in soil gas were measured at three active subduction-related stratovolcanoes (Arenal and Poas, Costa Rica; Galeras, Colombia). In general, Rn, CO2 and δ13C values are higher on the lower flanks of the volcanoes, except near fumaroles in the active craters. The upper flanks of these volcanoes have low Rn concentrations and light δ13C values. These observations suggest that diffuse degassing of magmatic gas on the upper flanks of these volcanoes is negligible and that more magmatic degassing occurs on the lower flanks where major faults and greater fracturing in the older lavas can channel magmatic gases to the surface. These results are in contrast to findings for Mount Etna where a broad halo of magmatic CO2 has been postulated to exist over much of the edifice. Differences in radon levels among the three volcanoes studied here may result from differences in age, the degree of fracturing and faulting, regional structures or the level of hydrothermal activity. Volcanoes, such as those studied here, act as plugs in the continental crust, focusing magmatic degassing towards crater fumaroles, faults and the fractured lower flanks.
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 inner forearc deformation from balanced cross sections, Fila Costeña thrust belt, Costa Rica
(Universidad Nacional, Costa Rica, 2007) Sitchler, Jason C.; Fisher, Donald M.; Gardner, Thomas W.; Protti, Marino
The Fila Costeña thrust belt in the forearc of Costa Rica is accommodating a significant portion of the convergence of the Cocos plate and Panama microplate. Geologic mapping of the thrust belt depicts a duplex with three horses that incorporate Eocene limestones and Oligocene to early Miocene clastics inboard of the subducting Cocos Ridge axis. By constructing a cross section at this location along a NE-SW trending transect perpendicular to the thrust belt, we constrain a shortening rate of approximately 40 mm/a and propose that as much as 50% of the total plate convergence rate is taken up in the inner forearc. The Eocene limestones at the base of the thrust sheets pinch out in both directions away from the onland projection of the Cocos Ridge axis owing to decrease in slip on faults and a lateral ramp in the basal décollement. The thrust belt terminates near the Panama border at the onland projection of the subducting Panama Fracture Zone. These observations suggest that shortening is propagating to the east with the migration of the Panama triple junction and the onset of shallow subduction of the thickened edge of the Cocos plate. The absence of similar features in the Nicaraguan forearc, where the subducting crust is older, subducts more steeply, and lacks incoming ridges and seamounts, indicates that deformation of the forearc basin in Costa Rica reflects greater couplin between converging plates inboard of the Cocos Ridge. Copyright 2007 by the American Geophysical Union.
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 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.
Crustal Velocity Structure Beneath The Western Andes of Colombian Using Receiver-Function Inversion
(ELSEVIER, 2013-12-01) Monsalve, Hugo; Pacheco, Javier F.; Vargas, Carlos A.; Morales, Yorly A.
Analysis of teleseismic records obtained in two broadband seismic stations of three components located on the Andean region of Colombia is presented in this work. The two stations are located at the Western Cordillera (WC), station BOL, and at the Central Cordillera (CC), station PBLA. The analysis of seismograms was performed by inversion of the receiver functions (RF) in order to obtain the crustal velocity structure beneath the receivers. The receiver function is a spectral ratio obtained from teleseismic earthquakes recorded by broadband seismic stations, which allows the calculation of the velocity structure beneath the receiver by removing source effects in the horizontal components of the seismic traces. Data stacking was performed in order to improve signal to noise ratio and then the data was inverted by using two optimization algorithms: a genetic algorithm (GA), and a simulated annealing algorithm (SA). The present work calculates the receiver functions using teleseismic earthquakes at epicentral distances (Δ) ranging between 30° and 90° and recorded at the two stations within the years 2007 and 2009.
Detailed spatiotemporal evolution of microseismicity and repeating earthquakes following the 2012 Mw 7.6 Nicoya earthquake
(Universidad Nacional, Costa Rica., 2017) Yao, Dongdong; Walter, Jacob; Meng, Xiaofeng; Hobbs, Tiegan; Peng, Zhigang; Newman, Andrew V.; Schwartz, Susan Y.; Protti, Marino
We apply a waveform matching technique to obtain a detailed earthquake catalog around therupture zone of the 5 September 2012 moment magnitude 7.6 Nicoya earthquake, with emphasis on itsaftershock sequence. Starting from a preliminary catalog, we relocate ~7900 events using TomoDD to betterquantify their spatiotemporal behavior. Relocated aftershocks are mostly clustered in two groups. Thefirst isimmediately above the major coseismic slip patch, partially overlapping with shallow afterslip. The secondone is 50 km SE to the main shock nucleation point and near the terminus of coseismic rupture, in a zone thatexhibited 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 templateevents. Wefind 190 aftershocks in thefirst half hour following the main shock, mostly along the plateinterface. 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 withmean cross-correlation values larger than 0.9, and indistinguishably intracluster event locations, suggestingslip on the same fault patch. Most repeating clusters occurred within thefirst major aftershock group. Veryfew 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 afterslipalong the plate interface drives spatiotemporal evolution of aftershocks just above the main shock rupturepatch, while aftershocks in the SE group are to the SE of the observed updip afterslip and poorly constrained.
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 and Inter‐Transient Locking on the Nicoya Megathrust in the Late and Early Stages of an Earthquake Cycle
(Advancing Earth and Space Sciences, 2020-10-20) Xie, Surui; Dixon, Timothy H; Malservisi, Rocco; Jiang, Yan; Muller, Cyril; Protti, Marino
We analyzed continuous GPS data collected from 2002–2020 to characterize slow slip events (SSEs) in and near the Nicoya Peninsula, Costa Rica. These data are bisected by the 5 September 2012 Mw 7.6 earthquake. The displacement time series contain multiple signals, including plate convergence, plate interface locking, coseismic and postseismic deformation, seasonal oscillations, SSEs, and noise. GPS‐measured coseismic and postseismic displacements associated with the Mw 7.6 earthquake are modeled and removed by a step function plus multiple timescale relaxation processes with four characteristic times: 11, 94, 470, and 1,865 days. Seasonal oscillations are eliminated using a multichannel singular spectrum analysis (M‐SSA). Ten major SSEs (Mw > 6.6) are observed in the remaining time series, with a constant recurrence interval of 21.7 ± 2.6 months. SSEs occur in both shallow (~10 km) and deep (~35 km) portions of the plate interface, but the latter last longer and have larger magnitudes. There is minimum to no slow slip in theMw 7.6 seismic rupture area and a persistent slow slip patch beneath the Nicoya Gulf entrance. Despite strong earthquake‐related stress perturbations, the inter‐SSE locking status on the megathrust is very similar between the late and early stages of the earthquake cycle and includes locked patches that ruptured in the 2012 earthquake or continue to rupture via SSEs. Some locked patches offshore south of the Nicoya Peninsula did not rupture in 2012, do not participate in SSEs, and may be indicative of supercycle behavior, that is, strain accumulation over several seismic cycles. These areas warrant heightened monitoring.
Slow Slip and Inter‐transient Locking on the Nicoya Megathrust in the Late and Early Stages of an Earthquake Cycle
(Blackwell Publishing Ltd, 2020-11) Xie, Surui; Malservisi, Rocco; Protti, Marino; Dixon, Timothy; Jiang, Yan; Muller, Cyril
We analyzed continuous GPS data collected from 2002–2020 to characterize slow slipevents (SSEs) in and near the Nicoya Peninsula, Costa Rica. These data are bisected by the 5 September2012 Mw 7.6 earthquake. The displacement time series contain multiple signals, including plate convergence, plate interface locking, coseismic and postseismic deformation, seasonal oscillations, SSEs, and noise. GPS‐measured coseismic and postseismic displacements associated with the Mw 7.6 earthquake are modeled and removed by a step function plus multiple timescale relaxation processes with four characteristic times: 11, 94, 470, and 1,865 days. Seasonal oscillations are eliminated using a multichannel singular spectrum analysis (M‐SSA). Ten major SSEs (Mw > 6.6) are observed in the remaining time series, with a constant recurrence interval of 21.7 ± 2.6 months. SSEs occur in both shallow (~10 km) and deep (~35 km) portions of the plate interface, but the latter last longer and have larger magnitudes. There is minimum to no slow slip in the Mw 7.6 seismic rupture area and a persistent slow slip patch beneath the Nicoya Gulf entrance. Despite strong earthquake‐related stress perturbations, the inter‐SSE locking status on the megathrust is very similar between the late and early stages of the earthquake cycle and includes locked patches that ruptured in the 2012 earthquake or continue to rupture via SSEs. Some locked patches offshore south of the Nicoya Peninsula did not rupture in 2012, do not participate in SSEs, and may be indicative of supercycle behavior, that is, strain accumulation over several seismic cycles. These areas warrant heightened monitoring
Spatiotemporal deformation and activity distribution of Irazú and Turrialba volcanoes, Costa Rica: are these volcanoes interconnected?
(ELSEVIER, 2024-03-14) Muller, Cyril; Alvarado, Guillermo E.; Angarita, Mario; Avard, Geoffroy
The spatiotemporal distribution of volcanic activity poses a significant challenge to risk mitigation measures, as it is still largely unexplored in most of the volcanic systems. In this study, we re-assess the deformation observed by leveling surveys covering the nationwide tragedy 1963–1965 Irazú eruption in Costa Rica with a state-of-the-art analytical source inversion model. We combine the analytical model results with recent geophysical, geochemical, and petrology data to build a geological model of Irazú and its 10 km-distant Turrialba volcano. Based on the leveling survey, the source inversion model finds a reservoir between 5 and 7 km below the Irazú crater which is deeper than previously published. We also confirm that the source location is on top of the mid-crustal reservoir that was feeding Turrialba between the 2010–2022 eruptions. Using previous seismic tomography, gravity, petrology, and geochemistry study of Turrialba and Irazú, as well as other studies conducted on nearby volcanoes worldwide, we find that Irazú and Turrialba volcanoes likely share a mid-crustal plumbing system which could suggesting that their plumbing systems are interconnected with each other. These findings have important implications on the spatiotemporal distribution of the volcanic activity and for the 2.8 million inhabitants settled within a 50 km radius. Observations during recent episodes indicates that inflation beneath Irazú has the potential to trigger eruptive activity at either Irazú or Turrialba. While further analysis is required to assess the tectonic control on volcanic activity, tectonic processes may shape both short- and long-term volcanic activity. These results have global implications for risk mitigation measures for nearby volcanoes.
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.
Sulfur Degassing at Erta Ale (Ethiopia) and Masaya (Nicaragua) Volcanoes : Implications for Degassing Processes and Oxygen Fugacities of Basaltic Systems
(Advancing Earth ans Space Sciencess, 2013-10-02) De Moor, J. M.; Fischer, T. P.; Sharp, Z. D.; King, P. L.; Wilke, M.; Botcharnikov, R. E.; Cottrell, E.; Zelenski, M.; Marty, B.; Klimm, K.; Rivard, C.; Ayalew, D.; Ramirez, C.; Kelley, K. A.
We investigate the relationship between sulfur and oxygen fugacity at Erta Ale and Masaya volcanoes. Oxygen fugacity was assessed utilizing Fe3þ/ PFe and major element compositions measured in olivine-hosted melt inclusions and matrix glasses. Erta Ale melts have Fe3þ/ PFe of 0.15–0.16, reflecting fO2 of DQFM 0.0 6 0.3, which is indistinguishable from fO2 calculated from CO2/CO ratios in high-temperature gases. Masaya is more oxidized at DQFM þ1.7 6 0.4, typical of arc settings. Sulfur isotope compositions of gases and scoria at Erta Ale (34Sgas 0.5%; 34Sscoria þ 0.9%) and Masaya (34Sgas þ 4.8%; 34Sscoria þ 7.4%) reflect distinct sulfur sources, as well as isotopic fractionation during degassing (equilibrium and kinetic fractionation effects). Sulfur speciation in melts plays an important role in isotope fractionation during degassing and S6þ/ PS is <0.07 in Erta Ale melt inclusions compared to >0.67 in Masaya melt inclusions. No change is observed in Fe3þ/ PFe or S6þ/ PS with extent of S degassing at Erta Ale, indicating negligible effect on fO2, and further suggesting that H2S is the dominant gas species exsolved from the S2-rich melt (i.e., no redistribution of electrons). High SO2/H2S observed in Erta Ale gas emissions is due to gas re-equilibration at low pressure and fixed fO2. Sulfur budget considerations indicate that the majority of S injected into the systems is emitted as gas, which is therefore representative of the magmatic S isotope composition. The composition of the Masaya gas plume (þ4.8%) cannot be explained by fractionation effects but rather reflects recycling of high 34S oxidized sulfur through the subduction zone.
Using Drones and Miniaturized Instrumentation to Study Degassing at Turrialba and Masaya Volcanoes, Central America
(Advancing Earth and Space Sciences, 2018-07-05) Stix, John; de Moor, Joost Maarten; Rüdiger, Julian; Alan, Alfredo; Corrales, Ernesto; D´Arcy, Fiona; Diaz, Jorge Andres; Liotta, Marcello
Gas measurements using unmanned aerial vehicles, or drones, were undertaken at Turrialba volcano, Costa Rica, and Masaya volcano, Nicaragua, in 2016 and 2017. These two volcanoes are the largest time-integrated sources of gas in the Central American Volcanic Arc, and both systems are currently extremely active with potential for sudden destabilization. We employed a series of miniaturized drone-mounted instrumentation including a mini-DOAS, two MultiGAS instruments, and an optical particle counter, supplemented by ground-based measurements. Payloads were typically 1–1.5 kg and flight times were 10–15 min. The measurements were both accurate and precise due to the inherent sensitivity of the instrumentation and the high gas concentrations, which the drones were able to sample. The quality of data obtained by our drones was comparable to that obtained by our ground-based measurements. At Turrialba in April 2017, we measured an average SO2 flux of 1,380 ± 280 T/day, CO2/SO2 of 6.5, and H2O/SO2 of 27.8. Using these values, we calculated a CO2 flux of 6,170 T/day and an H2O flux of 10,790 T/day. At Masaya in May 2017, the average SO2 flux was 1,560 ± 180 T/day, with CO2/SO2 of 3.9 and H2O/SO2 of 62.3, giving a mean CO2 flux of 4,150 T/day and mean H2O flux of 27,330 T/day. The elevated carbon and water fluxes and ratios are indicative of underlying magmas that are enriched in these components, resulting in the high levelsof activity observed.

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