Volcanic Tremor and its Relation to Volcano- and Glacier-related Processes

Author(s):  
Eva P. S. Eibl

<p>Volcanic eruptions can affect the climate system, the environment and society. On ice covered volcanoes this threat intensifies due to the increasing explosivity in contact with water. Monitoring and early-warning of such eruptions is closely linked to real-time, multidisciplinary data analysis. This builds on a good understanding and location of the recorded signals.</p><p>I will summarize my work on understanding and modelling volcanic tremor, a long-lasting seismic signal with emergent onset. This tremor accompanies various volcano- and glacier-related processes and has to be reliably detected and distinguished from other sources. My examples range from modelling pre-eruptive subglacial tremor and silent magma flow, to monitoring eruptive tremor, to early warning of subglacial flooding, to hydrothermal explosions and boiling and other sources such as helicopters. These results are based on array analysis, amplitude location techniques and single-station arrays but I will also risk a look into the future embracing the emerging field of rotational seismology which might solve some challenges we face in volcanic and glacial environments and advance our understanding and modelling of volcanic signals at remote sites.</p>

Author(s):  
Zahra Zali ◽  
Matthias Ohrnberger ◽  
Frank Scherbaum ◽  
Fabrice Cotton ◽  
Eva P. S. Eibl

Abstract Volcanic tremor signals are usually observed before or during volcanic eruptions and must be monitored to evaluate the volcanic activity. A challenge in studying seismic signals of volcanic origin is the coexistence of transient signal swarms and long-lasting volcanic tremor signals. Separating transient events from volcanic tremors can, therefore, contribute to improving upon our understanding of the underlying physical processes. Exploiting the idea of harmonic–percussive separation in musical signal processing, we develop a method to extract the harmonic volcanic tremor signals and to detect transient events from seismic recordings. Based on the similarity properties of spectrogram frames in the time–frequency domain, we decompose the signal into two separate spectrograms representing repeating (harmonic) and nonrepeating (transient) patterns, which correspond to volcanic tremor signals and earthquake signals, respectively. We reconstruct the harmonic tremor signal in the time domain from the complex spectrogram of the repeating pattern by only considering the phase components for the frequency range in which the tremor amplitude spectrum is significantly contributing to the energy of the signal. The reconstructed signal is, therefore, clean tremor signal without transient events. Furthermore, we derive a characteristic function suitable for the detection of transient events (e.g., earthquakes) by integrating amplitudes of the nonrepeating spectrogram over frequency at each time frame. Considering transient events like earthquakes, 78% of the events are detected for signal-to-noise ratio = 0.1 in our semisynthetic tests. In addition, we compared the number of detected earthquakes using our method for one month of continuous data recorded during the Holuhraun 2014–2015 eruption in Iceland with the bulletin presented in Ágústsdóttir et al. (2019). Our single station event detection algorithm identified 84% of the bulletin events. Moreover, we detected a total of 12,619 events, which is more than twice the number of the bulletin events.


Geosciences ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 115
Author(s):  
Tiziana Sgroi ◽  
Giuseppe Di Grazia ◽  
Paolo Favali

The NEMO-SN1 seafloor observatory, located 2100 m below sea level and about 40 km from Mt. Etna volcano, normally records a background seismic signal called oceanographic noise. This signal is characterized by high amplitude increases, lasting up to a few days, and by two typical 0.1 and 0.3 Hz frequencies in its spectrum. Particle motion analysis shows a strong E-W directivity, coinciding with the direction of sea waves; gravity waves induced by local winds are considered the main source of oceanographic noise. During the deployment of NEMO-SN1, the vigorous 2002–2003 Mt. Etna eruption occurred. High-amplitude background signals were recorded during the explosive episodes accompanying the eruption. The spectral content of this signal ranges from 0.1 to 4 Hz, with the most powerful signal in the 0.5–2 Hz band, typical of an Etna volcanic tremor. The tremor recorded by NEMO-SN1 shows a strong NW-SE directivity towards the volcano. Since the receiver is underwater, we inferred the presence of a circulation of magmatic fluids extended under the seafloor. This process is able to generate a signal strong enough to be recorded by the NEMO-SN1 seafloor observatory that hides frequencies linked to the oceanographic noise, permitting the offshore monitoring of the volcanic activity of Mt. Etna.


2021 ◽  
Vol 58 ◽  
pp. 177
Author(s):  
Ioannis Spingos ◽  
Filippos Vallianatos ◽  
George Kaviris

The main goal of an Earthquake Early Warning System (EEWS) is to estimate the expected peak ground motion of the destructive S-waves using the first few seconds of P-waves, thus becoming an operational tool for real-time seismic risk management in a short timescale. EEWSs are based on the use of scaling relations between parameters measured on the initial portion of the seismic signal, after the arrival of the first wave. Herein, using the abundant seismicity that followed the 3 March 2021 Mw=6.3 earthquake in Thessaly we propose scaling relations for PGA, from data recorded by local permanent stations, as a function of the integral of the squared velocity (IV2p). The IV2p parameter was estimated directly from the first few seconds-long signal window (tw) after the P-wave arrival. Scaling laws are extrapolated for both individual and across sites (i.e., between a near-source reference instrument and a station located close to a target). The latter approach is newly investigated, as local site effects could have a significant impact on recorded data. Considering that further study on the behavior of IV2p is necessary, there are indications that this parameter could be used in future on-site single‐station earthquake early warning operations for areas affected by earthquakes located in Thessaly, as itpresents significant stability.


Author(s):  
Masumi Yamada ◽  
Koji Tamaribuchi ◽  
Stephen Wu

ABSTRACT An earthquake early warning (EEW) system rapidly analyzes seismic data to report the occurrence of an earthquake before strong shaking is felt at a site. In Japan, the integrated particle filter (IPF) method, a new source-estimation algorithm, was recently incorporated into the EEW system to improve the source-estimation accuracy during active seismicity. The problem of the current IPF method is that it uses the trigger information computed at each station in a specific format as the input and is therefore applicable to only limited seismic networks. This study proposes the extended IPF (IPFx) method to deal with continuous waveforms and merge all Japanese real-time seismic networks into a single framework. The new source determination algorithm processes seismic waveforms in two stages. The first stage (single-station processing) extracts trigger and amplitude information from continuous waveforms. The second stage (network processing) accumulates information from multiple stations and estimates the location and magnitude of ongoing earthquakes based on Bayesian inference. In 10 months of continuous online experiments, the IPFx method showed good performance in detecting earthquakes with maximum seismic intensity ≥3 in the Japan Meteorological Agency (JMA) catalog. By merging multiple seismic networks into a single EEW system, the warning time of the current EEW system can be improved further. The IPFx method provides accurate shaking estimation even at the beginning of event detection and achieves seismic intensity error <0.25  s after detecting an event. This method correctly avoided two major false alarms on 5 January 2018 and 30 July 2020. The IPFx method offers the potential of expanding the JMA IPF method to global seismic networks.


2011 ◽  
Vol 18 (6) ◽  
pp. 925-940 ◽  
Author(s):  
E. De Lauro ◽  
S. De Martino ◽  
M. Falanga ◽  
M. Palo

Abstract. We investigate the physical processes associated with volcanic tremor and explosions. A volcano is a complex system where a fluid source interacts with the solid edifice so generating seismic waves in a regime of low turbulence. Although the complex behavior escapes a simple universal description, the phases of activity generate stable (self-sustained) oscillations that can be described as a non-linear dynamical system of low dimensionality. So, the system requires to be investigated with non-linear methods able to individuate, decompose, and extract the main characteristics of the phenomenon. Independent Component Analysis (ICA), an entropy-based technique is a good candidate for this purpose. Here, we review the results of ICA applied to seismic signals acquired in some volcanic areas. We emphasize analogies and differences among the self-oscillations individuated in three cases: Stromboli (Italy), Erebus (Antarctica) and Volcán de Colima (Mexico). The waveforms of the extracted independent components are specific for each volcano, whereas the similarity can be ascribed to a very general common source mechanism involving the interaction between gas/magma flow and solid structures (the volcanic edifice). Indeed, chocking phenomena or inhomogeneities in the volcanic cavity can play the same role in generating self-oscillations as the languid and the reed do in musical instruments. The understanding of these background oscillations is relevant not only for explaining the volcanic source process and to make a forecast into the future, but sheds light on the physics of complex systems developing low turbulence.


2020 ◽  
Author(s):  
Massimo Orazi ◽  
Flora Giudicepietro ◽  
Carmen López ◽  
Giovanni Macedonio ◽  
Salvatore Alparone ◽  
...  

<p>In summer 2019, two paroxysmal explosions occurred in Stromboli. The first one occurred on July 3, when the Strombolian ordinary eruptive activity did not show a significant intensification. The explosion formed an eruptive column more than 3 km high. A pyroclastic flow ran down the “Sciara del Fuoco” slope causing a victim and some injuries. Moreover, the pyroclastic flow spread over the sea surface for about one kilometer. On August 28, a second paroxysmal explosion occurred, similar to the previous one. Also in this case the eruption formed an eruptive column of more than 3 km and a pyroclastic flow that expanded along the “Sciara del Fuoco” slope and traveled about 1 km on the sea surface. In the period between the two paroxysms, effusive activity occurred from the summit crater area. The eruptive phase of summer 2019, which began with the paroxysm of 3 July, was not preceded by significant changes in the routinely monitored parameters, such as the hourly frequency (daily average) of the VLP events (typical of Stromboli) and the amplitude of the seismic signal (RSAM). For this reason, we have analyzed the seismic and dilatometric data, which were recorded by the INGV geophysical network in the period November 2018 - September 2019, focusing our attention on other parameters that can give indications on the activity state of the volcano. In particular, we analyzed the data of the broadband seismic stations, equipped with the Guralp CMG40T sensors, and the data of one Sacks-Evertson borehole strainmeter. We defined the "VLP size", which takes into account the waveform of the VLP events, in terms of both amplitude and duration. We also applied time varying Fractal Dimension (FD) analysis to the seismograms of a seismic station close to the crater area and we analyzed the polarization of the same signal. We carried out the polarization analysis both without applying a filter and by filtering the seismic signal in the typical frequency bands of the Stromboli volcanic tremor (1-3 Hz) and of the VLPs (0.5-0.05 Hz). We found that the "VLP size", the FD and the polarization parameters showed significant changes about one month before the paroxysm of July 3. In the short term, we applied an appropriately tuned STA/LTA algorithm to the data of the borehole strainmeter, which is installed on the island at about 2km from the craters, and we obtained an automatic detection of the paroxysmal events 10 and 7.5 minutes before the explosion of July 3 and August 28, respectively.</p>


2016 ◽  
Vol 11 (1) ◽  
pp. 60-71 ◽  
Author(s):  
Leslie Jamie Cobar ◽  
◽  
Djoko Legono ◽  
Kuniaki Miyamoto ◽  

Indonesia’s Mount Merapi is one of the world’s most active, dangerous volcanoes. Its 2010 eruption – the largest following the 20th century – and succeeding 2011 lahar events killed 389 persons and injured and displaced many more. One way to mitigate a disaster’s impact is the provision of reliable information to the public through a well-established early warning system (EWS). A well-managed information flow network is the key to delivering early warning information, however, there is a lack of understanding on the information transfer down to the citizens. In addition, implementing the 2007 disaster management law may have affected Merapi’s EWS. This study reinvestigates Merapi’s EWS information flow through the construction of an information flow network. A single information flow network was difficult to construct due to the inconsistency of structures per district. Different networks had to be constructed for volcanic eruptions and lahars in each district. Inconsistencies were also found in the roles of the agencies that determine when evacuation orders would be issued. The system also had data transfer gaps and vulnerabilities such as redundancies, mistransfers and bottlenecks. Its use of forecasting information as a basis for decision-making must be reviewed for lahar information flow networks. Improving Merapi’s EWS must involve handling these issues.


Author(s):  
М.Г. Бергер

За полные 17 лет прошедшие после Кармадонской катастрофы научное сообщество не пришло к единому мнению о причинах внезапного схода ледника Колка. В условиях практического забвения режима регулярных наблюдений за состоянием ледников в главных ледниковых очагах гряды вершин Казбек-Тепли-Уалпата восточной части Центрального Кавказа особенно актуально концентрировать инструментальные и камеральные исследования для мониторинга воздействия основных эндогенных и экзогенных факторов на ледники региона, присутствие которых в подготовке Кармадонского события все исследователи единодушны. Среди множества гипотез внезапного схода ледника Колка основными являются три концепции: ударное воздействие обрушившихся висячих масс льда, отрыв ледника сейсмическим воздействием и газодинамический выброс, детально рассмотренные в различных ракурсах. Цель данной статьи обоснование газодинамической взрывоподобной природы выброса ледника Колка из своего ложа на основе анализа результатов изучения других природных, природно-техногенных и техногенных явлений, характеризующихся в той или иной мере принципиально сходными с этой катастрофой особенностями. Используется метод теоретического обоснования невозможности механической абляции ледника за счет гляциальных процессов, логического отрицания причин, связанных с самим ледником, его водным потенциалом или обвальными массами нависающих льдов и аномальных климатических условий. Одновременно с отрицанием гляциологических факторов используется методика аналогий, в качестве которых рассматриваются взрывные или взрывоподобные эксплозивные вулканические извержения и их сейсмическое сопровождение, вулканическое дрожание при извержениях. Теоретическое отрицание гляциально-экзогенной причины выброса ледника и теоретическая модель подготовки, протекания взрывоподобного выброса и транзита ледово-каменной массы позволяют впервые выдвинуть в качестве основного результата газодинамический фактор эндогенного воздействия на ледник напорными флюидами, образующимися за счет остывающего субстрата камеры стратовулкана Казбек. Газодинамическая природа катастрофической пульсации ледника Колка убедительно объясняет все аномальные природные явления, проявившиеся в 2002г. в районе ледника Колка и смежной с ним территории на этапах подготовки, протекания и постпароксизмального завершения катастрофы, взаимосвязь между ними и их связь с катастрофой, открывает большие перспективы для дальнейшего изучения ледника Колка и в области газогляциодинамических исследований. Изложенное позволяет сделать вывод: осторожность в признание столь неординарного результата научным сообществом вызвана крайне редким проявлением взрывоподобных газодинамических выбросов ледников (неординарный результат впервые озвучен как определяющий фактор внезапного выброса ледника Колка), но это вопрос времени In the full 17 years that have passed since the Karmadon disaster, the scientific community has not come to a consensus on the reasons for the sudden collapse of the Kolka glacier. In the conditions of the practical oblivion of the regular monitoring regime of the state of glaciers in the main glacial sources in the ridge of the Kazbek-Tepli-Ulpat peaks in the eastern part of the Central Caucasus, it is especially relevant to concentrate instrumental and desk studies to monitor the impact of the main endogenous and exogenous factors on the glaciers of the region, the presence of which in the preparation of the Karmadon event all researchers are unanimous. Among the many hypotheses of the sudden collapse of the Kolka glacier, the main are three concepts: the impact of collapsing suspended masses of ice, separation of the glacier by seismic impact and gas-dynamic outburst, which were examined in detail from different angles. The purpose of the paper is to substantiate the gas-dynamic explosive nature of the Kolka glacier outburst from its bed based on the analysis of the studies results of other natural, natural-technogenic and technogenic phenomena, characterized in one way or another by fundamentally similar features to this catastrophe. The method of theoretical justification of the impossibility of mechanical ablation of the glacier due to glacial processes, the logical denial of the reasons associated with the glacier itself, its water potential or collapsing masses of overhanging ice and abnormal climatic conditions is used. Along with the negation of glaciological factors, a methodology of analogies is used, which are considered explosive or explosion-like volcanic eruptions and their seismic accompaniment, volcanic tremor during eruptions. The theoretical denial of the glacial-exogenous cause of the glacier outburst and the theoretical model of the preparation, the course of the explosive outburst and the transit of the ice-stone mass make it possible to put forward as a main result for the first time the gas-dynamic factor of the endogenous impact on the glacier with pressure fluids generated by the cooling substrate of the Kazbek stratovolcano chamber. The gas-dynamic nature of the catastrophic pulsation of the Kolka glacier convincingly explains all the anomalous natural phenomena that appeared in 2002 in the region of the Kolka glacier and its adjacent territory at the stages of preparation, course and post-paroxysmal completion of the catastrophe, the relationship between them and their relationship with the catastrophe opens up great prospects for further study of the Kolka glacier and in the field of gas-dynamic research. The foregoing allows us to conclude that caution in recognition of such an extraordinary result by the scientific community is caused by an extremely rare manifestation of explosive gas-dynamic emissions of glaciers (an extraordinary result was first voiced as a determining factor in the sudden ouburst of the Kolka glacier), but this is a matter of time


2022 ◽  
Author(s):  
Ingo Sonder ◽  
Alison Graettinger ◽  
Tracianne Neilsen ◽  
Robin Matoza ◽  
Jacopo Taddeucci ◽  
...  

Blasting experiments were performed that investigate multiple explosions that occur in quick succession in the ground and their effects on host material and atmosphere. Such processes are known to occur during volcanic eruptions at various depths, lateral locations, and energies. The experiments follow a multi-instrument approach in order to observe phenomena in the atmosphere and in the ground, and measure the respective energy partitioning. The experiments show significant coupling of atmospheric (acoustic)- and ground (seismic) signal over a large range of (scaled)distances (30--330\m, 1--10\(\m\J^{-1/3}\)). The distribution of ejected material strongly depends on the sequence of how the explosions occur. The overall crater sizes are in the expected range of a maximum size for many explosions and a minimum for one explosion at a given lateral location. The experiments also show that peak atmospheric over-pressure decays exponentially with scaled depth at a rate of \bar{d}_0 = 6.47x10^{-4} mJ^{-1/3}; at a scaled explosion depth of \(4x10^{-3} mJ^{-1/3} ca. 1% of the blast energy is responsible for the formation of the atmospheric pressure pulse; at a more shallow scaled depth of 2.75x10^{-3 \mJ^{-1/3} this ratio lies at ca. 5.5–7.5%. A first order consideration of seismic energy estimates the sum of radiated airborne and seismic energy to be up to 20\% of blast energy.


2021 ◽  
Author(s):  
Vincent Twomey ◽  
William McCarthy ◽  
Craig Magee

<p>Laccoliths play a significant role in the transport and storage of magma in sub-volcanic systems. The construction and geometry of laccoliths can influence host rock and surface deformation patterns that may precede and provide warning of active magmatism and impending eruptions. Yet how laccolith construction and internal magma dynamics controls the location and form of magma ascent conduits (e.g., dykes and inclined sheets), which facilitate magma evacuation and may feed volcanic eruptions, remains poorly documented in natural examples.</p><p>The excellently exposed silicic, sub-volcanic Miocene Reyðarártindur Laccolith in SE Iceland offers an opportunity to investigate how magma ascent within inclined sheets, which emanated from the laccolith, related to intrusion construction and deformation in the surrounding host rock. We combine detailed structural mapping with anisotropy of magnetic susceptibility (AMS) analyses, which allow us to map magnetic rock fabrics that reflect magma flow patterns, to show that the laccolith comprises of several distinct magma lobes that intruded laterally towards the south-west. Each lobe intruded, inflated, and coalesced along a NE-SW primary axis facilitated by doming (i.e., forced folding) of the host rock. We also shown that pre-existing NNE-striking, left-stepping, en-echelon fault/fractures, as well as those generated during intrusion-induced host rock uplift, host moderately to steeply inclined rhyolitic/granophyric sheets that emanate from the lateral terminations of some flow lobes.</p><p>Based on the observed geometrical relationships between AMS fabrics and the sheet margins where magnetic foliations subparallel sheet contacts, or characterize an imbrication fabric, we suggest that magma evacuated moderately to steeply upward via these fault/fracture-controlled sheets. As these inclined sheets dip towards the laccolith, any eruptions they may have fed would have been laterally offset from the laccolith and any overlying surface deformation driven by forced folding. Our study shows that magma evacuation and ascent from laccoliths can be facilitated by inclined sheets that form at the lateral terminations of magma lobes that are spatially controlled by laccolith construction (e.g., flow direction and doming of the host rock) and the presence of pre-existing structures.</p>


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