Artículos científicos

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El volcán Turrialba y Ovsicori en redes sociales
(Universidad Nacional de Costa Rica, 2015-06) Vega, Floribeth
Como instituto dedicado a la investigación sísmica y volcánica, la misión de Ovsicori (Observatorio Vulcanológico y Sismológico de Costa Rica) es documentar, analizar e interpretar los procesos sísmicos y volcánicos y divulgar el conocimiento resultante para contribuir con la prevención de riesgos y mitigación de los desastres que generan. En función de comunicar tal conocimiento a la población, y de aumentar el alcance de los contenidos informativos y educativos generados, en 2009 iniciamos nuestra aventura en las redes sociales, fundando, en setiembre de ese año, un perfil en la red social Twitter y, unos meses después, en abril de 2010, creamos un perfil en Facebook. Nuestro perfil en Twitter cuenta con más de 120.000 seguidores y en Facebook nos aproximamos a 300.000 “me gusta”. A través de esas dos redes, evacuamos dudas y proveemos documentos educativos, sencillos y atractivos, que facilitan al usuario entender nuestro trabajo y aprender sobre la actividad sísmica y volcánica en nuestro país y en el mundo.
Tomographic imaging of P- and S-wave velocity structure beneath Costa Rica
(Springer Nature, 1999) Yao, Z. S.; Quintero, Ronnie; Roberts, R. G.
45287 P-wave and 26813 S-wave arrival times from the data base of the Costa Rica network have been tomographically inverted to image the structure beneath Costa Rica. A regularized recursive least squares inverse method was used to produce the high resolution and minimum variance model parameter estimates. The first arrival times are calculated using a finite difference technique, which allows for flexible parameterization of the velocity model and easy inclusion of topography and source-receiver geometry. The P wave velocity structure and hypocenters are determined simultaneously, while the S wave velocity structure is determined using the relocated seismicity and an initial model derived from the P wave model assuming an average P to S wave velocity ratio of 1.78. The most prominent features in the inverted model are a low velocity structure under the volcanic chain in the center of the country, which is related to the hot material connected with the active volcanoes; and a high velocity zone in the mantle, which is related to the Cocos plate subducted under Costa Rica.
Animation Crustal Deformation in the Nicoya Peninsula Associated with the September 5th, 2012 Earthquake
(Universidad Nacional, Costa Rica, 2018) Hernandez Castro, F; Monge-Fallas, J; Mendez-Morales, M; Protti-Quesada, M
For the past fifteen years, the Volcanological and Seismological Observatory of Costa Rica (OVSICORI) in cooperation with American Universities, has been recording crustal defor mation data prior a potential earthquake in the Nicoya Peninsula, anticipation which came true on September 5th, 2012 with the occurrence of a 7.6 moment magnitude (Mw) earth quake. The historical importance of this earthquake is based on continuous monitoring of the Nicoya Peninsula before, during and after the earthquake, making it one of the best docu mented earthquake in history. The objective of this project is to visualize earthquake data in order to view displacement in two and three dimensions. Another goal is to make the method for showing the behavior of the crust during the earthquake, more intuitive. The target ques tion of the visualizations is only one: to show how the earths crust moved previous and dur ing the earthquake in each of the affected areas. We know of no other visualization that use a 3D environment to visualize one earthquake with actual data in this detail level
The Last Eighteen Years (1998–2014) of Fumarolic Degassing at the Poás Volcano (Costa Rica) and Renewal Activity
(Springer, 2019) Vaselli, Orlando; Tassi, Franco; Fischer, Tobias P; Tardani, Daniele; Fernández, Erick; Martínez, María del Mar; Moor, Marteen de; Bini, Giulio
This chapter reviews the geochemical and isotopic data from the fumarolic gas discharges collected in a discontinuous mode from 1998 to 2014 at Poás volcano. During this period, the “Tico” volcano experienced a renewed phreatic activity that started in 2006 after a couple of decades of relative quiescence. In January 2009, a 6.2 Mw earthquake hit the village of Cinchona, which is located a 4 km to the east of Poás. As the phreatic activity kept evolving, the hyperacidic lake (“Laguna Caliente”) dried out and the high-temperature fumaroles that previously were likely entering the lake were revealed, though not accessible. The pyroclastic dome that formed in the early fifties was destroyed at the beginning of 2017 by several relatively small phreatomagmatic (strombolian and vulcanian type) small-size eruptions. The risk of sudden phreatic and phreato-magmatic events prevented the direct sampling of the fumaroles and as a consequence, no geochemical data were sampled in the last three years. Nevertheless, interesting hints were recorded by the gas geochemistry before the 2006 phreatic activity and the 2009 Cinchona seismic events, mainly based on the temporal variations of the H2S/SO2, H2/H2O, H2/Ar, CO/CO2, CH4/CO2 and HCl/HF ratios. However, in most cases the geochemical record is not complete since the gas discharging vents migrated or stopped their activity and new fumaroles formed up to the recent visual observations.
Stress Field in Costa Rica, Central America
(2000) Quintero, Ronnie; Güendel, Federico
We have relocated 1658 earthquakes which occurred in Costa Rica, and its vicinity. These relocated earthquakes were then used to investigate the stress and orientation of fault planes within the study area. The analysis was made using the polarities of first motion P-waves. We found that the subduction zone for Costa Rica is mainly characterized by thrust faulting, with some areas also exhibiting a component of strike-slip motion. The intraplate Caribbean seismicity in central Costa Rica shows a predominant shallow left-lateral strike-slip faulting. In southern Costa Rica, the subduction of very young oceanic lithosphere beneath the Caribbean plate (i.e. Panama Block), enhanced by the collision and subduction of the Cocos Ridge, has produced a highly compressive stress regime. This highly compressive regime is characterized by strike-slip faults oriented in a NE-SW direction, extending all the way from the Pacific margin into the back-arc, connecting with the North Panama Deformed Belt.
Forearc carbon sink reduces long-term volatile recycling into the mantle
(Nature Publishing Group, 2019-04-25) Barry, Peter; Giovannelli, Donato; Schrenk, Matthew; Fattorini, Daniele; Manini, Elena; Nakagawa, Mayuko; Regoli, Francesco; smedile, francesco; Ballentine, Chris; Lloyd, Karen; Hummer, Daniel; Lopez, T.; Pratt, C. A.; Alpízar Segura, Y.; Battaglia, A.; Beaudry, P.; Bini, G.; Cascante, M.; d’ Errico, G.; di Carlo, M.; Fullerton, K.; Gazel, E.; González, G.; Halldórsson, Sæmundur Ari; Iacovino, K.; Kulongoski, J. T.; Martínez, M.; Miller, H.; Ono, S.; Patwardhan, S.; Ramírez, C. J.; Turner, S.; Vetriani, C.; Yücel, M.; Fischer, T. P.; Hilton, D. R.
Carbon and other volatiles in the form of gases, fluids or mineral phases are transported from Earth’s surface into the mantle at convergent margins, where the oceanic crust subducts beneath the continental crust. The efficiency of this transfer has profound implications for the nature and scale of geochemical heterogeneities in Earth’s deep mantle and shallow crustal reservoirs, as well as Earth’s oxidation state. However, the proportions of volatiles released from the forearc and backarc are not well constrained compared to fluxes from the volcanic arc front. Here we use helium and carbon isotope data from deeply sourced springs along two cross-arc transects to show that about 91 per cent of carbon released from the slab and mantle beneath the Costa Rican forearc is sequestered within the crust by calcite deposition. Around an additional three per cent is incorporated into the biomass through microbial chemolithoautotrophy, whereby microbes assimilate inorganic carbon into biomass. We estimate that between 1.2 × 108 and 1.3 × 1010 moles of carbon dioxide per year are released from the slab beneath the forearc, and thus up to about 19 per cent less carbon is being transferred into Earth’s deep mantle than previously estimated.
Terremoto del Valle de La Estrella: análisis sísmico, cascada de desastres y pérdidas económicas en valor presente (2020)
(Universidad Nacional, Costa Rica, 2021-04-21) Campos Durán, Daniela; Quintero Quintero, Ronnie; Abarca Rojas, Tatiana
Seismicity and focal mechanisms in the of North Panama Deformed Belt (NPDB) indicate a compressional environ-ment associated with the overthrusting of the Panama Block (PB) on the Caribbean plate; crustal PB strike-slip focal mechanisms are observed in the Talamanca and Central Volcanic Cordillera. The hypocenters reach maximum depths between 50-60 km at the foot of the Talamanca mountain range and are shallow near the Caribbean coast. The 1991, Valle de la Estrella earthquake (Mw 7.6) triggered aftershocks in an area of ~140x70 km; landslides and liquefaction were the secondary events that caused most damage and losses in infrastructure (housing, bridges, railroad network, road network and aqueducts); its effects were concentrated in coastal cities, such as Limón and Bocas del Toro. The economic losses in present 2020 value correspond to $3 433 266 937.41.
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.

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