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Ítem Precursory seismic signals before two catastrophic landslides at Irazú Volcano, Costa Rica(Latin American and Caribbean Seismological Comission, 2024) Chaves Sibaja, Esteban; Pacheco, Javier; Schwartz, Susan; Chavarría, Nathalie; Noah, Finnegan; Higman, BretwoodMassive rock landslides impose a continuous impact on the socio-economic growth of developing cities, public infrastructure and telecommunications. Every year, millions of dollars are invested in reverting the negative effects associated with their occurrence all over the world. At volcanoes, complex landslide instabilities triggered in some cases by nearby earthquakes, rainfall, local deformation, or a combination of all, may induce changes in the lithostatic pressure of the edifice, suddenly affecting their internal dynamics and increasing the risk of catastrophic eruptions as occurred during the 80’s in Mt. San Helens. Near field geodynamic monitoring, including broadband seismic, GNSS stations and other techniques, is then essential to better characterize ground failure and to improve landslide hazards assessments. The southwest flank of the Irazú volcano in central Costa Rica has been recognized to host massive rock landslides in the past. Just in December 2014 and August 2020, a total combined of 53 million m3 of mass wasting were deposited along the basement of “Río Sucio”, one of the main tributaries of the Sarapiquí river. Using the near field and geodynamic monitoring network that OVSICORI-UNA operates at Irazú and Turrialba volcanos since 2011, we show unique seismological observations that shed light about the rupture initiation and dynamic evolution of the mass movement. Our results demonstrate that during the 2014 and 2020 events, the nucleation phase initiate weeks prior to the catastrophic collapse with the generation of low frequency earthquakes (LFEs), events dominated by velocity weakening frictional properties that likely represent the stick-slip failure of small asperities localized along the basement. Among the observed LFEs, we report the occurrence of 10 repeating earthquake families, each formed by multiple LFEs that rupture approximately the same asperity at different times, generating identical waveforms. Our observations show that as the mass accelerate with time 1) the number of repeating families increases progressively and 2) the inter-event time between LFEs decreases linearly until they merge forming a tremor signal that initiate 30 min prior to the collapse. Near-field seismic data exhibits an exponential increase in tremor amplitude, and thus, seismic moment, that suddenly reduces and become quiescent for 20 seconds before the impulsive mass detachment and failure. We posit that transient embrittlement is the mechanism responsible for such a unique observation. As the slip rate increases, faulting regions with predominantly stable-sliding (aseismic) frictional properties become unstable (seismic), as previously observed in subduction zones and laboratory experiments. As a result, the number of unstable asperities and/or the total effective area of contact between the sliding mass and the basement increases dramatically, modulating tremor amplitude with time. The shear strength from the elastically couple asperities is enough to provide temporal (~20 s) stability to the entire mass, inducing the seismic quiescence. However, the accrued shear stresses imposed by the slow slip episode on the weak asperities overcomes the frictional strength, inducing the catastrophic failure. Our results provide direct evidence of the mechanics that controlled landslide nucleation and resemble those from laboratory experiments and fault zones during tectonic earthquakes.Ítem OKSP: a novel deep learning automatic event detection pipeline for seismic monitoring in Costa Rica(Instituto de Ingenieros Eléctricos y Electrónicos (IEEE), 2021) Van der Laat, Leonardo; Baldares, Ronald; Chaves, Esteban; Meneses, EstebanSmall magnitude earthquakes are the most abundant but the most difficult to locate robustly and well due to their low amplitudes and high frequencies usually obscured by heterogeneous noise sources. They highlight crucial information about the stress state and the spatio-temporal behavior of fault systems during the earthquake cycle, therefore, its full characterization is then crucial for improving earthquake hazard assessment. Modern deep learning algorithms along with the increasing computational power and efficiency are exploiting the continuously growing seismological databases, worldwide, allowing scientists to improve the completeness for earthquake catalogs, systematically detecting and locating smaller magnitude earthquakes and reducing the errors introduced mainly by human intervention through traditional approaches in seismological observatories. In this work, we introduce OKSP, a novel deep learning automatic earthquake detection pipeline for seismic monitoring in Costa Rica. Using Kabre supercomputer from the Costa Rica High Technology Center, we applied OKSP to the day before and the first 5 days following the Puerto Armuelles, M6.5, earthquake that occurred on 26 June, 2019, along the Costa Rica-Panama border and found 1100 more earthquakes previously unidentified by the Volcanological and Seismological Observatory of Costa Rica. From these events, a total of 23 earthquakes with magnitudes below 1.0 occurred a day to hours prior to the mainshock, shedding light about the rupture initiation and earthquake interaction leading to the occurrence of this productive seismic sequence. Our observations show that for the study period, the model was 100% exhaustive and 82% precise, resulting in an F1 score of 0.90. This effort represents the very first attempt for automatically detecting earthquakes in Costa Rica using deep learning methods and demonstrates that, in the near future, earthquake monitoring routines will be carried out entirely by AI algorithms.Ítem Coda wave attenuation in Mara Rosa seismic zone(Sociedade Brasileira de Geofísica, 2013-08-26) schmidt, kellin; Ferreira, Vinicius; Vieira Barros, Lucas; Quintero, RonnieSmall local earthquakes from aftershock sequence in Mara Rosa, Goiás state, Brazil were used to estimate the coda wave attenuation in the frequency band of 1 to 20 Hz. The time-domain coda-decay method of a single backscattering model is employed to estimate frequency dependence of quality factor (Qc) of coda waves modeled using Qc = Q0fη, Q0 is the coda quality factor at a frequency of 1 Hz and η is the frequency parameter. Qc values have been computed at central frequencies and (band) of 1.5 (1-2), 3.0 (2-4), 6.0 (4-8), 9.0 (6-12), 12 (8-16) and 18 (12-24) Hz in the lapse time ranging from 5 to 25 sec in step of 5 seconds. It was determined the functional form Qc = (10.78) f(1.84)) .Ítem Parâmetros de fonte de sismos locais por inversão de formas de ondas(Sociedade Brasileira de Geofísica, 2010-11) Zahradnik, Jiri; Vieira Barros, Lucas; Quintero, RonnieThe main purpose of this work is to invert seismic waveforms in order to obtain moment tensor for two medium size earthquakes detected by OVSICORI-UNA Costa Rica permanent seismic network, occurred in 2004, following the mainshock of November 20 at 08:07 UTC (Mw=6.4 GCMT). The inversion for the focal mechanism is made using the package ISOLA (Zahradnik et al., 2005, Sokos & Zahradnik, 2008) and the seismicity are associated with a fault system that delineates the upper plate between the Caribbean plate and Panama Block. The obtained focal mechanisms are in agreement with results obtained by Pacheco et al. (2006) for this seismicity.Ítem Connections between hyper-acid crater lakes and ank springs: New evidence from Rincón de la Vieja Volcano (Costa Rica) and implications for lahar hazard assessment(2014-09) Martínez Cruz, María; Van Bergen, M. J.; Avard, Geoffroy; De Moor, J. Maarten; Saénz, W.Ítem What´s causing asymmetric deformation at Tungurahua volcano, Ecuador?(2017) Hickey, James; Lloyd, Ryan; Biggs, Juliet; Arnold, David; Mothes, Patricia A.; Muller, CyrilÍtem Combined GPS, EDM and triangulation surveys of the rapid downslope motion of the western flank of Arenal Volcano, Costa Rica(2011) Muller, Cyril; Del Potro, R.; Biggs, Juliet; Gottsmann, Joachim; Van der Laat, R.; Ebmeier, S. K.Here we present initial conclusions of a one year-long combined geodesy campaign on Arenal Volcano, in Costa Rica (2008-2009). Our data shows evidence for an active local tectonic surrounding, and a 7cm/yr displacement field of the western flank of the volcano edifice that is in general agreement with recent INSAR studies. The study shows that a rigorous combination of simultaneous GPS, EDM (Electronic Distance Measurements) and triangulation measurements provide a time-cost effective approach to volcanic monitoring.Ítem Turrialba volcano: plumbing system and magma budget(2017) Muller, CyrilÍtem The Nicoya segment of Middle American Trench: an Excellent Target for Drilling and Monitoring the Shallow Portion of the Seismogenic Zone(2011-06-28) Protti, Marino; González, Victor; Kaneda, Yoshiyuki; Brown, KevinThe Nicoya segment of Middle America Trench has generated large earthquakes in 1883, 1900 and 1950. Since the Nicoya peninsula sits right over the seismogenic zone, it has proved to be a unique site for near field monitoring of interplate interactions. Crustal deformation data indicates that locking on this plate boundary starts 30 km from the trench where the plate interface is around 6 km below the ocean floor. These results make this subduction segment an attractive target for drilling the plate interface and seismogenic zone at several different depths (all within Chikyu drilling capabilities) in a margin where collected data suggests it is close to rupture. This temporal proximity to failure gives a chance to monitor several parameters (such as fluid flow, geochemistry, strain, temperature, tilt, among others) in holes at several distances from the trench prior. The Nicoya segment of the Middle American Trench was one of the target regions of both, the Seismogenic Zone Experiment (SEIZE) and the Subduction Factory (SUBFAC) initiatives of MARGINS. As part of those initiatives and even earlier, this region has been studied for many years with different techniques (high resolution marine seismics, refraction profiles, broad band land and ocean seismic stations, scan mapping, an ALVIN cruise, ODP legs, CGPS, electronic tiltmeters). Therefore, there is already sufficient information to start an IODP proposal.Ítem Crustal Thickness of the Central American Arc(2007-06-18) Auger, Laura; Abers, Geoff; Syracuse, Ellen; Fischer, Karen; Strauch, Wilfried; Protti, Marino; González, VictorÍtem Slow Slip and Tremor Detected at the Northern Costa Rica Seismogenic Zone(2008) Schwartz, Susan; Walter, J.; Dixon, T.; Psencik, K.; Protti, Marino; González, V.; Rabbel, WolfgangÍtem Active Subduction on Both Coasts of Costa Rica Does not Represent an Important Tsunami Hazard(2007-05-22) Protti, Marino; González, V.Ítem Nicoya, Costa Rica: an IOPD target where the seismogenic zone or large earthquake can be drilled and instrumented(2009-09-23) Protti, Marino; González, Victor; Yoshiyuki, Kaneda; Brown, KevinÍtem Seismic and Geodetic Monitoring of the Nicoya, Costa Rica, Seismic Gap(2007-05-22) Protti, Marino; González, Victor; Schwartz, Susan; Timothy, Dixon; Kato, Teruyuki; Yoshiyuki, Kaneda; Simila, Gerald; SAMPSON, DANIELÍtem Shear-wave Splitting Tomography in the Central American Subduction Zone: Implications for Flow and Melt in the Mantle Wedge(2006) Abt, D. L.; Fischer, K. M.; Martin, L.; Abers, G. A.; Protti, Marino; González, V.; Strauch, WilfriedÍtem Imaging the Subduction Factory: The TUCAN Broadband Seismic Experiment in Central America(2002-04) Abers, G.; Fischer, K.; Syracuse, E.; Mackenzie, L.; Rychert, C.; Protti, Marino; González, V.; Strauch, WilfriedÍtem Constraining Upper Plate Deformation in Nicaragua Through Delineation of the August 3, 2005 Mw 6.3 Strike Slip Earthquake Fault Plane(2006) French, S. W.; Warren, L. M.; Fischer, K. M.; Abers, G. A.; Strauch, Wilfried; Protti, Marino; González, V.Ítem Crustal Thickness Variations Beneath the Central American Arc(2006) Auger, L. S.; Abers, G.; Fischer, K.; Protti, Marino; González, Victor; Strauch, WilfriedÍtem Seismic Velocities and Earthquake Locations in the Central America Upper Mantle: results from the TUCAN Experiment(2006) Syracuse, E. M.; Abers, G. A.; Auger, L.; Fischer, K.; Protti, Marino; González, Victor; Strauch, Wilfried; Brewer, J.Ítem Rayleigh Wave Tomography in the Nicaragua-Costa Rica Subduction Zone(2006) Salas de la Cruz, M.; Fischer, K. M.; Forsyth, D. W.; Abers, G. A.; Strauch, Wilfried; Protti, Marino; González, Victor
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