The Planchón-Peteroa Volcanic Complex (PPVC) is located in the Central Andes, Argentina-Chile. Even though this active volcanic system is considered one of the most dangerous volcanoes in the region, ...with more than twenty modest (VEI < 4) Holocene eruptions, knowledge of its subsurface structures, internal processes, dynamics, and their relation, is still limited.
Seismic interferometry (SI) is a high-resolution technique based on analyses of the interference of the propagation seismic energy at one or many stations. SI can be used to characterize the subsurface properties of a target area. In particular, previous SI studies performed in the area of the PPVC describe specific ranges of depth; therefore, more information is required for a thorough description of the subsurface features in the area and for a better understanding of the PPVC dynamics.
We apply SI based on autocorrelations of selected regional and teleseismic events to image the subsurface structures below stations located in Argentina and Chile during 2012. The selection of the events is performed according to their location, magnitude, angle of incidence of P-wave seismic energy, and signal-to-noise ratio in the records. For each station, we extract time windows and we process them using two ranges of frequency, which are sensitive to different depth ranges.
This work describes depths and zones previously not analyzed in the area using SI methods. The results not only complement the available geological, geochemical, and geophysical information, but present new information for depths between 10 and ~750 km depth, increasing the general knowledge of the subsurface features in the PPVC. Finally, we also propose a model for the subsurface down to the Moho, which indicates the crustal structure and the likely distribution of magma bodies in depth.
•Closest-ever body-wave seismic characterization of the subsurface structure to the Peteroa volcano, Argentina-Chile.•Main subsurface reflecting boundaries below the stations down to ~750 km depth are imaged.•A model of magma emplacement in the subsurface down to the Moho is proposed.
Argentina is a country that presents a complex situation regarding volcanic risk, where a total of 38 volcanoes are considered active. Although Argentina has no major cities close to these volcanoes, ...the continuous increase in economic activity and infrastructure near the Andean Codillera will increase exposure to volcano hazards in the future. Further, volcanic activity on the border between Argentina and Chile poses a unique challenge in relation to volcano monitoring and the management of volcanic emergencies. Additionally, due to atmospheric circulation patterns in the region (from West to East), Argentina is exposed to ashfall and ash dispersion from frequent explosive eruptions from Chilean volcanoes. Considering this, the Servicio Geológico Minero Argentino (SEGEMAR) decided to create and implement a Volcanic Threat Assessment Program, which includes the creation of the the first permanent volcano observatory for the country, the Observatorio Argentino de Vigilancia Volcánica (OAVV). Previously the Decepcion Island volcano observatory was created as a collaboration between the Instituto Antártico Argentino (IAA) and the Museo Nacional de Ciencias Naturales (MNCN) from the Consejo Superior de Investigaciones Científicas (CSIC).
Argentina es un país que presenta una compleja situación con respecto al riesgo volcánico, donde un total de 38 volcanes son considerados activos. Aunque Argentina no tiene ciudades importantes cerca de estos volcanes, el continuo incremento de la actividad económica y la infraestructura cerca de la Cordillera de los Andes, generará en el futuro un aumento en la exposición a estos peligros. Además, la actividad volcánica en la frontera entre Argentina y Chile constituye un desafío único en relación con el monitoreo de volcanes y la gestión de emergencias volcánicas. Adicionalmente, debido a los patrones de circulación atmosférica en la región (desde el oeste hacia el este), Argentina está expuesta a la caída y dispersión de cenizas de las frecuentes erupciones explosivas de volcanes chilenos. Teniendo esto en cuenta, el Servicio Geológico Minero Argentino (SEGEMAR) decidió crear e implementar un programa de evaluación de amenazas volcánicas, que incluye, la creación del primer observatorio permanente de volcanes para el país, el Observatorio Argentino de Vigilancia Volcánica (OAVV). Previamente, el Observatorio Volcanológico de la Isla Decepción fue creado como una colaboración entre el Instituto Antártico Argentino (IAA) y el Museo Nacional de Ciencias Naturales (MNCN) del Consejo Superior de Investigaciones Científicas de España (CSIC).
The changes in physical properties leading up to a volcanic eruption provide clues to processes occurring within volcanoes and may reveal premonitory signals. The Sierra Negra shield volcano, located ...in the Galápagos Islands, erupted on 26 June 2018 after months of continued inflation and escalating earthquake activity. We applied ambient noise interferometry to five months of continuous seismic data from 12 broadband stations to calculate crustal shear‐wave velocity changes before and during the eruption. Using the Moving Window Cross‐Spectral technique and a pre‐eruption stack of ambient seismic data as reference, we found a −0.27% decrease in velocity 17 days before the eruption in station‐pairs that pass beneath the caldera's north‐eastern sector. Sensitivity kernels suggest that the velocity changes of this precursory signal are greatest at depths corresponding to the shallow sill (∼2 km) beneath the wide caldera. Our results, considered in light of geodetic, seismicity, and petrological results, suggest that this velocity decrease is in part caused by dilatation from a ML 4.8 earthquake, and degassing after a possible magma intrusion below or at the base of the sill. The precursory velocity decrease within the sill region offers an important tool for forecasting future eruptions at Sierra Negra.
Plain Language Summary
Geoscientists use seismic methods to detect changes in the characteristics of volcanoes that could indicate increasing risk of eruption. The Sierra Negra volcano, located in the Galápagos Islands, erupted on 26 June 2018. Using time variations in seismic signals mainly generated by the ocean's interaction with the shoreline, we found a decrease in the velocity of seismic waves about 2 weeks before the eruption. The decrease is largest when these waves travel through Sierra Negra's shallow magma reservoir. This velocity reduction started on June 9th, the same day as the second‐largest pre‐eruptive earthquake recorded since 2017, and ended one day before the eruption, on June 25th. A slight increase in velocity was observed on May 13th and lasted 4 days. We interpret this increase as a magma pulse that destabilizes the volcanic system. The combined effect of this magma intrusion and the magnitude 4.8 earthquake altered the volcano's state and favored the start of the eruption. The technique that we used could forecast future eruptions at Sierra Negra and other basaltic island volcanoes.
Key Points
A velocity variations analysis provides important evidence of pre‐eruptive physical processes inside the volcanic edifice
Using ambient noise interferometry we obtained a precursor signal for the 2018 Sierra Negra eruption, which offers a forecasting tool
The velocity anomaly is spatially constrained to station‐pairs near the initial eruptive fissures, and is caused by extensional stress
Electrical discharges are observed in many volcanic eruptions and they have often been used as indicators of such eruptions. Volcanic lightning is remarkably similar to those produced during ...thunderstorms and is called analogous to thunderstorm-like plume lightning. The WWLLN developed a program called “Ash Cloud Monitor” (ACM), in which alerts are issued for possible volcanic eruptions when lightning strokes are detected around a volcano. The ACM tool has demonstrated to be a very effective technique to be aware of volcanic eruptions. However, most of the alerts released by ACM belong to false alarms of volcanic activity, because, in general, the detected lightning is produced by thunderstorms near the volcano.
In order to assess and improve the ACM to detect volcanic eruptions, reducing false alert emissions and improving the quick interpretation of them, we develop a web platform called Georayos-VolcanoAr with a new structure and a modified algorithm, with respect to the algorithm used by ACM, for the classification of alerts. The new algorithm considers an alert system with 3 levels: Red - Yellow - Green, with the Red alert being the highest level and decreasing towards Green. The Red alert was assigned to those volcanoes where only recorded lightning within a radius of 20 km or the lightning detected within a radius of 20 km is at least twice as much as that detected up to 100 km from the vent.
The study focused on 32 volcanoes located in the Andes, close to the Argentine-Chilean border, and analyzed the results reported by the ACM network in terms of a climatological study of the lightning activity, thunderstorm days and predominant winds in that region. This analysis serves as a basis for a general recognition of the study zone in order to improve the interpretation of the distribution and generation of false alerts; as well as to help decision makers, among others, to have a reference that allows them to issue the warning.
•The electric discharges detection tool to detect volcanic events is more precise towards the Southern sector of the study area.•Georayos-VolcanoAr is a web platform that improves the alerts received by the decision maker for their quick interpretation.•We observed a decrease in the number of false alerts issued compared to the Ash Cloud Monitor.•Georayos-VolcanoAr helps to discriminates between meteorological and volcanic lightning with greater precision.
The Caviahue-Copahue Volcanic Complex (CCVC, 37° 51’ S-71° 05′ W) is located in the central segment of the South Volcanic Zone, ~30 km eastward from the main Andean volcanic arc. Within a complex ...tectonic setting, it has developed under the influence of the northern transtensional Liquiñe-Ofqui Fault Zone, to the south and the Copahue-Antiñir Fault Zone to the northeast. The onset of volcanic activity within Caviahue volcano-tectonic depression has been dated at Ar/Ar 125 ± 9 ka and it is represented by lava flows and ignimbrites of Las Mellizas Formation. Copahue volcano has a very well documented historical eruptive record, encompassing 13 eruptive cycles in the last 260 years. On the contrary, volcano stratigraphy during Late Pleistocene and pre-historic times is poorly constrained, mainly due to the lack of reliable radiometric data. Based on the peculiar morphology and cooling-fracture systems, lavas that crop out along Dulce, Jara and NE Agrio river valleys have been included in a new stratigraphic unit, here named as Río Dulce Formation. A subglacial emplacement is proposed taking into account the evidence of ice-confinement, provided by the flat-topped and steep-sided lava domes/flows and dammed lava flows. In addition, melt water-magma interaction is supported by conspicuous fine columnar-jointing and closely spaced curved bands with plumose structures, well-developed pseudopillow fracture systems, platy and hackly fractures and cube-jointed entablature-bearing lava flows. The basaltic andesites (SiO2= 55–57%) are porphyritic, with ~30–40% of sieved plagioclase, two pyroxenes and olivine, set in a glassy groundmass. Lava vent distribution and primary anisotropy planes orientation, in coincidence with WNW-ESE and NE-SW trending faults, lineaments and fault scarps, document a first-order structural control on the volcanic emplacement. Although undated, this study can contribute to understanding the timing of glacial fluctuations during Late Pleistocene. Furthermore, it has implications on hazard assessment since it highlights that the evolution of the CCVC has experienced alternating fissure and central eruptive style, likely related to the dynamics of the magma-plumbing system, as suggested by geophysical evidence of unrest.
•Río Dulce Formation is proposed as a new stratigraphic unit in the CCVC.•A subglacial emplacement is supported by the volcanic landforms and the several types of quenching-related fractures.•Late Pleistocene in age.•The CCVC includes a succession of alternating or even coeval fissure-related and central eruptive activity.
Advanced techniques in the recognition and classification of seismo-volcanic events are transcendental when studying active volcanoes, not only for their importance as an accurate real time seismic ...monitoring procedure but also for the use of their results in modeling the dynamics of the volcanic environment. It is well known that real time seismic monitoring deals with such a large amount of data that it would become an overwhelming job for an operator to do manually. Therefore the use of automatic detection and classification techniques based on the Machine Learning approach are suitable in meeting such a challenge.
The aim of this work is to test the capability of the Deep Neural Network (DNN) by using different event parametrization as a confident classifier tool that could permit a reliable seismic catalog to be built in a new and un-analyzed volcanic scenario. We tested different configurations in order to build an approach that was as simple as possible to use this classifier with a limited number of events. In this regard, the feature space was explored in order to select the most significant parameters of the seismic signals. The data used for this analysis corresponds to the Planchon Peteroa Volcanic Complex (PPVC) located in the Transitional Southern Volcanic Zone (TSVZ) between Chile and Argentina, South America. The most significant result of this work was not only that it provided an analysis in terms of performance of this algorithm, especially when the training, validation and test dataset is reliable although definitely reduced, but it also gave an insight of into how an optimal event parametrization can significantly improve the automatic detection and classification of seismo-volcanic events.
Fall Meeting 2019-American Geophysical Union, 8th International Symposium on Andean Geodynamics y al 1er Congreso de la Asociación Latinoamericana de Volcanología. Durante el taller "Community ...Network For Volcanic Eruption Response" realizado en Fairbanks, Alaska, se coordinó y conversó sobre los productos científicos del proyecto con Jeffrey Johnson y Juan Anzieta. 10. Los productos científicos del proyecto fueron presentados en el American Geophysical Union Fall Meeting 2019. Decisiones tomadas * Continuación con el mantenimiento y descarga de datos de los arreglos acústicos: CON, LAV y AZU. * Pruebas de campo en el volcán Reventador del sistema de digitalización y revisión del código. * Preparación de un trabajo científico sobre la diversa actividad acústica en el volcán, para la presentación en Fall Meeting 2019, American Geophyscal Union. * Entrega de certificados a los estudiantes que aprobaron el taller "Principios de Geofísica y Comunicación" * Reunión técnica en noviembre de 2019 con el doctor Johnson. * Elaboración de artículos científicos para Revista Geofísica del IPGH y Journal Geochemistry, Geophysics, Geosystems.
La Región de Nuevo Cuyo (RNC) ha sido calificada como la de más alta peligrosidad sísmica en la República Argentina (Giardini et al., 1999). Este es el primer trabajo de atenuación sísmica con datos ...digitales sobre ondas P, S y coda en la región de Nuevo Cuyo utilizando datos de estaciones permanentes argentinas. Es además, el resultado de la colaboración entre varias instituciones, del país y del exterior, ya que los datos han sido provistos por el INPRES (Instituto Nacional de Prevención Símica, San Juan) y parte del trabajo se ha realizado en colaboración con investigadores de España: del Instituto Andaluz de Geofísica (IAG), Univ. de Granada y de Italia: del Osservatorio Vesuviano, Istituto Nazionale di Geofisica e Vulcanologia, Nápoles y de la Universidad de Salerno. La caracterización del comportamiento de la región ante la acción de las ondas sísmicas es un dato indispensable para la prevención. La mayoría de los análisis sismológicos que extraen información de las formas de onda registradas requieren identificar las pérdidas y redistribuciones de energía en las ondas, que resumen el efecto de la atenuación, a lo largo de la trayectoria. Estos efectos se originan en la heterogeneidad y en la anelasticidad del medio y pueden estudiarse sobre distintos tipos de ondas sísmicas, en función de la frecuencia o independientemente de ella. Cada resultado por separado, sus variaciones y las relaciones que pueden establecerse entre los mismos dan una visión integrada de la interacción de las ondas con el medio dinámico donde se propagan. La caracterización de la atenuación relacionada a los parámetros reológicos que la definen, brinda además un mejor conocimiento de los procesos geodinámicos de la región. Mediante el estudio de las variaciones de la energía para ondas directas y dispersadas en los sismogramas se determinan los factores de calidad del medio, Q, cuya inversa permite cuantificar el efecto de la atenuación y efectuar regionalizaciones de acuerdo al modelo empleado. Vinculando los valores de Q de ondas directas y dispersadas mediante métodos numéricos y analíticos se separan la proporción anelástica, Qi, y de scattering, Qs, de la atenuación en la región. El valor de Qs se relaciona con la densidad de heterogeneidades y el de Qi con la anelasticidad del medio, vinculada a su vez a la temperatura, la presión, el grado de fluidez y el contenido de fluidos. Por lo anteriormente expuesto es que Q es más sensible a los parámetros reológicos que la velocidad de las ondas. Los valores de la atenuación obtenidos para la RNC son una clara manifestación de su estado de actividad tectónica. La RNC se caracteriza por una alta atenuación de ondas coda con variaciones laterales a profundidades corticales, estabilizándose su valor cuando los volúmenes de scattering alcanzan profundidades más allá de la zona sismogénica en la placa subducida. Las determinaciones de la atenuación de ondas directas, realizadas por los distintos métodos muestran cierta convergencia en frecuencia y profundidad. Los valores medios de atenuación de ondas P y S muestran los diferentes efectos de la atenuación de corteza y manto y mantienen una relación entre sí que ubica a la atenuación en la RNC dentro de los valores promedio para regiones de actividad tectónica similar. La separación de la atenuación intrínseca y de scattering ha mostrado que no son las heterogeneidades estructurales superficiales las que dominan la atenuación sino que la absorción anelástica es el efecto predominante, más aún cuanto mayor sea la profundidad de validez de los resultados
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