Artículos científicos

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Volcano hazard and surveillance in Costa Rica
(Volcanica, 2021-03-04) Avard, Geoffroy; Mora, Mauricio; Bakkar, Henriette; Alvarado, Guillermo; Angarita, Mario; Cascante, Monserrat; Maarten de Moor, J.; Martínez, María; Muller, Cyril; Pacheco, Javier; Ruiz, Paulo; Soto, Gerardo
Costa Rica hosts ten volcanic complexes and is highly tectonically active due to its location at the interaction between the Cocos, Nazca, and Caribbean plates and the Panama microplate. Three of the five historically active volcanoes had frequent eruptions in 2019. The institutions in charge of monitoring the volcanoes of Costa Rica are the Observatorio Vulcanológico y Sismológico de Costa Rica from Universidad Nacional (OVSICORI-UNA) and the Red Sismológica Nacional (RSN: UCR-ICE that groups the Escuela Centroamericana de Geología from the Universidad de Costa Rica, and the Observatorio Sismológico y Vulcanológico de Arenal y Miravalles from the Instituto Costarricense de Electricidad; acronyms ECG, UCR, OSIVAM, and ICE). These institutions are focused on the most dangerous volcanoes, i.e. those closest to the Great Metropolitan Area (2.2 million inhabitants), which includes San José (the capital), and those near hydroelectrical and geothermal plants. In 2020, those institutions operated a network of. 59 seismic stations on volcanoes, 5 infrasound stations, 25 permanent GPS sites, 2 permanent DOAS, 3 permanent MultiGAS, 13 webcams, and performed systematic analyses in geochemistry and petrology laboratories. Those institutes routinely communicate results with the authorities in charge of crisis management nationally and internationally (Comisión Nacional de Prevención de Riesgos y Atención de Emergencias and Volcanic Ash Advisory Centre, respectively) and are always looking for more scientific collaborations.
Changing tectonic regimes in the central Costa Rica forearc between the Paleogene and the present: Insights from structural analysis and focal mechanisms
(Elsevier, 2021-01-04) Porras, Hernán; Mescua, José; Durán, Patrick; Cascante, Monserrat; Giambiagi, Laura; Muller, Cyril
We discuss the Cenozoic history of the Central Costa Rica forearc, between 10° and 9°30′N, based on geological mapping, fault slip data and seismological records.The temporal variability in the regional stress-field suggests a variable and complex deformation pattern. The first stage of deformation, from the Paleogene to early Miocene, was controlled by an extensional regime in the forearc. Afterwards, a change to orthogonal convergence triggered a contractional deformation and subsequent inversion of the sedimentary extensional basins in the middle-upper Miocene. Finally, a transpressive regime has been developed since the Pliocene.
Shallow slow slip events identified offshore the Osa Peninsula in southern Costa Rica from GNSS time series
(AGU, 2023-08-21) Perry, Mason; Muller, Cyril; Protti, Marino; Feng, Lujia; Hill, Emma M.
Using new continuous geodetic time series, we identify five shallow slow slip events (SSEs) offshore and beneath the Osa peninsula in southern Costa Rica. An early event was detected by one station in 2013, and two events occurring in close succession in both 2018 and 2022 were detected by multiple stations, indicating a preliminary recurrence interval of ∼4–5 years. While SSEs have been observed to the northwest at Nicoya, this is their first documentation in southern Costa Rica. Modeled slip distributions of the 2018 and 2022 events indicate they likely ruptured the same or overlapping patches of the plate interface, near the trench, updip of the 1983 Mw 7.4 Osa event. Immediately offshore, estimated cumulative slip from the 2018 and 2022 events is sufficient to close the slip deficit from tectonic loading over the recurrence interval, potentially limiting the magnitude and spatial slip distribution of future large ruptures.
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.
Interseismic Megathrust Coupling at the Osa Peninsula, Costa Rica
(AGU, 2025-06-21) Perry, Mason; Muller, Cyril; Protti, Marino; Feng, Lujia; Hill, Emma
At the Osa Peninsula in southern Costa Rica, magnitude >7 earthquakes have been generated along the Middle American trench in 1904, 1941, and 1983 following a ∼40-year recurrence interval, suggesting a rupture may be impending. However, regional interseismic coupling remains poorly constrained, largely due to sparse observations that are likely contaminated by aliasing effects of repeating shallow slow slip events (SSEs) that occur roughly every 4 years, but were only discovered recently. These SSEs, while likely reducing megathrust coupling near the trench, may load or trigger the next rupture of the 1983 asperity. Using new continuous Global Navigation Satellite System (GNSS) data from an updated and densified regional network, we derive inter-SSE rates of deformation and invert for slip deficit and megathrust coupling along the Middle American Trench, implementing block modeling to correct for the motion of the Panama microplate. We invert for slow slip and remove a time-averaged estimate of cumulative slow slip from our models. Our results indicate that the region of highest inter-SSE coupling (>0.8) corresponds with the spatial extent of SSE slip. We also find that SSEs are sufficient to release nearly all the elastic strain accumulated over their 4-year recurrence interval in localized regions. Accounting for this, in the region immediately downdip of the slow slip patch—the same region thought to have ruptured in the 1983 Mw 7.4 event—we estimate an interseismic coupling ratio of ∼0.5–0.7 corresponding to ∼1.75–2 m of accumulated slip deficit since 1983, sufficient to generate a similar magnitude rupture in the future.
Temporarily Increased Recurrence Rate of Shallow Slow Slip Events Driven by Significant Afterslip Following the 2012 Mw 7.6 Nicoya Earthquake.
(AGU, 2025-09-01) Li, Guoli; Xie, Surui; Protti, Marino; Muller, Cyril
Slow slip events (SSEs) release tectonic strain without causing sudden ground shaking. SSEs have been observed at many subduction zones, some dynamically triggered by stress changes due to the passage of seismic waves. However, there are limited observations of SSEs induced by post-seismic deformation. Here, we report a significant increase in the recurrence rate of SSEs in the shallow portion of the Nicoya megathrust following the 2012 Mw 7.6 earthquake. These shallow SSEs occurred immediately updip of the large afterslip zone and their recurrence rate returned to pre-earthquake level 1.5 years after the earthquake. In contrast, deeper SSE recurrence rate remained unchanged. Coulomb Failure Stress modeling indicates the shallow SSE area experienced substantial stress perturbation during afterslip, while the deeper megathrust did not. We interpret this temporarily increased shallow SSE recurrence rate to be driven by static stress loading from large afterslip.
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 Events in the Early Part of the Earthquake Cycle
(Advancing Earth and Space Sciences, 2017-07-07) Voss, Nicholas; Malservisi, Rocco; Dixon, Timothy H.; Protti, Marino
In February 2014 a Mw = 7.0 slow slip event (SSE) took place beneath the Nicoya Peninsula, Costa Rica. This event occurred 17 months after the 5 September 2012, Mw = 7.6, earthquake and along the same subduction zone segment, during a period when significant postseismic deformation was ongoing. A second SSE occurred in the middle of 2015, 21 months after the 2014 SSE and 38 months after the earthquake. The recurrence interval for Nicoya SSEs was unchanged by the earthquake. However, the spatial distribution of slip for the 2014 event differed significantly from previous events, having only deep (~40 km) slip, compared to previous events, which had both deep and shallow slip. The 2015 SSE marked a return to the combination of deep plus shallow slip of preearthquake SSEs. However, slip magnitude in 2015 was nearly twice as large (Mw=7.2) as preearthquake SSEs.WeemployCoulomb Failure Stress change modeling in order to explain these changes. Stress changes associated with the earthquake and afterslip were highest near the shallow portion of the megathrust, where preearthquake SSEs had significant slip. Lower stress change occurred on the deeper parts of the plate interface, perhaps explaining why the deep (~40 km) region for SSEs remained unchanged. The large amount of shallow slip in the 2015 SSE may reflect lack of shallow slip in the prior SSE. These observations highlight the variability of aseismic strain release rates throughout the earthquake cycle.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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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