Cotopaxi Volcano showed an increased activity since April 2015 and evolved into its eventual mild eruption in August 2015. In this work we use records from a broadband seismic station located at less ...than 4 km from the vent that encompass data from April to December of 2015, to detect and study low-frequency seismic events. We applied unsupervised learning schemes to group and identify possible premonitory low-frequency seismic families. To find these families we applied a two-stage process in which the events were first separated by their frequency content by applying the k-means algorithm to the spectral density vector of the signals and then were further separated by their waveform by applying Correntropy and Dynamic Time Warping. As a result, we found a particular family related to the volcano’s state of activity by exploring its time distribution and estimating its events’ locations.
Monitoring the evolution of lava flows is a challenging task for volcano observatories, especially in remote volcanic areas. Here we present a near real-time (every 12 h) and free tool for producing ...interactive thermal maps of the advance of lava flows over time by taking advantage of the free thermal data provided by FIRMS and the open-source R software. To achieve this, we applied two filters on the FIRMS datasets, one on the satellite layout (track) and another on the fire radiative power (FRP). To determine the latter, we carried out a detailed statistical analysis of the FRP values of nine hotspot subaerial eruptions that included Cumbre Vieja-2021 (Spain), Fagradalsfjall-2021 (Iceland), LERZ Kilauea-2018 (USA), and six eruptions on the Galápagos Archipelago (Ecuador). We found that an FRP filter of 35 ± 17 MW/pixel worked well at the onset and during the first weeks of an eruption. Afterward, once the cumulative statistical parameters had stabilized, a filter that better fit the investigated case could be obtained by running our statistical code. Using the suggested filters, the thermal maps resulting from our mapping code have an accuracy higher than 75% on average when compared with the official lava flow maps of each eruption and an offset of only 3% regarding the maximum lava flow extension. Therefore, our easy-to-use codes constitute an additional, novel, and simple tool for rapid preliminary mapping of lava fields during crises, especially when regular overflights and/or unoccupied aerial vehicle campaigns are out of budget.
Autocorrelation Infrasound Interferometry Ortiz, Hugo D.; Matoza, Robin S.; Johnson, Jeffrey B. ...
Journal of geophysical research. Solid earth,
April 2021, 2021-04-00, 20210401, Letnik:
126, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Seismic and infrasound multistation ambient‐noise interferometry has been widely used to infer ground and atmospheric properties, and single‐station and autocorrelation seismic interferometry has ...also shown potential for characterizing Earth structure at multiple scales. We extend autocorrelation seismic interferometry to ambient atmospheric infrasound recordings that contain persistent local noise from waterfalls and rivers. Across a range of geographic settings, we retrieve relative sound‐speed changes that exhibit clear diurnal oscillations consistent with temperature and wind variations. We estimate ambient air temperatures from variations in relative sound speeds. The frequency band from 1 to 2 Hz appears most suitable to retrieve weather parameters as nearby waterfalls and rivers may act as continuous and vigorous sources of infrasound that help achieve convergence of coherent phases in the autocorrelation codas. This frequency band is also appropriate for local sound‐speed variations because it has infrasound with wavelengths of ∼170–340 m, corresponding to a typical atmospheric boundary layer height. After applying array analysis to autocorrelation functions derived from a three‐element infrasound array, we find that autocorrelation codas are composed of waves reflected off nearby topographic features, such as caldera walls. Lastly, we demonstrate that autocorrelation infrasound interferometry offers the potential to study the atmosphere over at least several months and with a fine time resolution.
Plain Language Summary
Atmospheric infrasound is sound waves with frequencies less than the 20 Hz human hearing threshold. Infrasound sensors are being increasingly deployed to monitor volcanoes, streams, ocean wave activity, thunder, snow avalanches, meteorites, and anthropogenic explosions. Here, we present a new technique to analyze background noise recorded by infrasonic sensors to extract atmospheric sound‐speed perturbations, which in turn can be used to infer air temperature and wind velocity variations. We show that the infrasound inferred temperature changes recovered by this method track closely with independently measured temperature cycles. This method may be useful for exploiting existing infrasound networks to provide long time series of atmospheric temperature fluctuations and increasing the spatial density of ground‐based thermometry.
Key Points
Relative velocity changes derived from infrasound autocorrelations can track independently observed temperature and wind variations
Autocorrelation infrasound interferometry can take advantage of high‐frequency persistent infrasound noise sources, such as waterfalls
We demonstrate the applicability of autocorrelation infrasound interferometry for a range of geographical locations and station designs
Hazard and risk communication requires the design and dissemination of clear messages that enhance people’s actions before, during, and after volcanic crises. To create effective messages, the ...communication components such as message format and content, must be considered. Changes in technology are changing the way people communicate at an ever-increasing pace; thus, we propose revising the basic components of the communication process to improve the dialogue between scientists and the public. We describe communication issues during and outside volcanic crises in Ecuador and assess possible causes and consequences. These ideas were discussed during the short-duration “Volcano Geophysical Principles and Hazards Communications” Workshop in Baños, Ecuador in 2019. We review and propose communication strategies for volcanic hazards and risks that resulted from the workshop discussions and experiences of experts from the Instituto Geofísico (IG-EPN), local and international professors involved in volcano research and communication, and students from universities across Ecuador.
Complete and precise volcano-seismic event catalogues are important not only for the statistical value that they possess for describing past volcanic activity, but also because they constitute the ...input for automated systems that help monitor volcanic activity in real time. Computer systems are valuable assets in the task of volcano-seismic event classification because in theory they can have improved performance compared to humans due to speed, consistency, and unbiasedness. However, such systems are trained with data from previously created catalogues of events, and as such, if catalogues have noise, the systems will learn incorrectly. In this work, we propose the implementation of a methodology that is relatively easy and fast to apply for the identification of potentially mislabeled events in a seismic event catalogue. We compare the results of applying the procedure to two open catalogues from Cotopaxi and Llaima volcanoes. The first catalogue is believed to have an unknown but potentially significant level of noise, while the other is assumed to be clean. We further validate our results for one of the datasets with volcano observatory scientists in a blind-review fashion to demonstrate some of the hypotheses that can arise in a catalogue with a presumably important level of noise. We conclude that the methodology is valid for identifying potentially mislabeled seismic events and can help in assessing the quality of a given catalogue.
Basaltic shield volcanoes of the western Galápagos islands are among the most rapidly deforming volcanoes worldwide, but little was known of the internal structure and brittle deformation processes ...accompanying inflation and deflation cycles. A 15-station broadband seismic array was deployed on and surrounding Sierra Negra volcano, Galápagos from July 2009 through June 2011 to characterize seismic strain patterns during an inter-eruption inflation period and to evaluate single and layered magma chamber models for ocean island volcanoes. We compare precise earthquake locations determined from a 3D velocity model and from a double difference cluster method. Using first-motion of P-arrivals, we determine focal mechanisms for 8 of the largest earthquakes (ML≤1.5) located within the array. Most of the 2382 earthquakes detected by the array occurred beneath the broad (∼9 km-wide) Sierra Negra caldera, at depths from surface to about 8 km below sea level. Although outside our array, frequent and larger magnitude (ML≤3.4) earthquakes occurred at Alcedo and Fernandina volcano, and in a spatial cluster beneath the shallow marine platform between Fernandina and Sierra Negra volcanoes. The time–space relations and focal mechanism solutions from a 4-day long period of intense seismicity June 4–9, 2010 along the southeastern flank of Sierra Negra suggests that the upward-migrating earthquake swarm occurred during a small volume intrusion at depths 5–8 km subsurface, but there was no detectable signal in InSAR data to further constrain geometry and volume. Focal mechanisms of earthquakes beneath the steep intra-caldera faults and along the ring fault system are reverse and strike-slip. These new seismicity data integrated with tomographic, geodetic, and petrological models indicate a stratified magmatic plumbing system: a shallow sill beneath the large caldera that is supplied by magma from a large volume deeper feeding system. The large amplitude inter-eruption inflation of the shallow sill beneath the Sierra Negra caldera is accompanied by only very small magnitude earthquakes, although historical records indicate that larger magnitude earthquakes (Mw <6) occur during eruptions, trapdoor faulting episodes without eruptions, and large volume flank intrusions.
•Seismicity analyses from first seismic array on the rapidly deforming Sierra Negra volcano, Galápagos.•Small magnitude (ML ≤1.2) earthquakes concentrate beneath the 9 km-wide caldera at depths of 0–6 km.•A migrating swarm of earthquakes in June 2010 suggests an intrusion at depths 5–8 km below sealevel.•New and existing data indicate a stratified magmatic plumbing system.
Rapunzel syndrome or gastrointestinal trichobezoar is caused by hair ingestion. The diagnosis may be suspected in young females with important weight loss, who deny hair eating. We report a 16 ...year-old female consulting in the emergency room for abdominal pain. She was subjected to an exploratory laparotomy and a big mass was palpated in the stomach. A gastrostomy and enterostomy were performed and a 17 x 6 x 5 cm trichobezoar was extracted. The patient had an uneventful postoperative outcome and was derived to Psychiatry.
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.
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