To address the outlined challenges, this session aims to bring together seismologists, volcano and geothermal seismologists, wave propagation and source modellers, working on different aspects of volcano seismology including (i) seismicity catalogues, statistics and spatio-temporal evolution of seismicity, (ii) seismic wave propagation and scattering, (iii) new developments in volcano imagery, (iii) seismic source inversions, and (iv) seismic time-lapse monitoring. Contributions on controlled geothermal systems in volcanic environments are also welcome. Contributions on developments in instrumentation and new methodologies (e.g. Machine Learning) are particularly welcome.
By considering interrelationships in these complementary seismological areas, we aim to build up a coherent picture of the latest advances and outstanding challenges in volcano seismology.
This study addresses the challenge of reliably constraining non-double couple components (NDCCs) in moment tensor solutions for volcano-tectonic earthquakes in Iceland. While double-couple models adequately describe most global seismicity, Iceland's complex tectonic setting, featuring rifting and a hotspot, produces diverse seismic sources, some exhibiting significant NDCCs. These components, often dismissed as artifacts, may reflect actual source complexity. We analyze two recent volcanic events: seismicity related to the 2014-2015 Bárðarbunga caldera collapse and subsequent uplift, and the ongoing Reykjanes Peninsula unrest that started in 2021. Both events featured intense seismic swarms, with numerous moment tensors exhibiting pronounced NDCCs. However, the origin and interpretation of these components differ. At Bárðarbunga, CLVD components likely arise from inverting ring-fault geometries as point sources, while in Reykjanes, isotropic components may indicate magma intrusions. To assess the reliability of NDCCs, we conduct a rigorous uncertainty analysis of moment tensor solutions for both regions. This approach examines the stability of NDCCs under different inversion parameters and explores the pitfalls of constraining these components based on their potential causes. Our findings provide criteria for identifying reliable NDCCs and contribute to a better understanding of the limitations of tectonic interpretations based on moment tensor solutions in volcanic environments.
How to cite: Rodriguez Cardozo, F. R., Braunmiller, J., Hjörleifsdóttir, V., and Jónsdóttir, K.: On the challenge of constraining non-double couple moment tensor components, a case study of volcano-tectonic earthquakes in Iceland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13910, https://doi.org/10.5194/egusphere-egu25-13910, 2025.
Magmatic unrest within the Reykjanes Peninsula oblique rift zone, SW Iceland, ongoing since December 2019, has been closely monitored by a dense network of seismic and geodetic stations. A total of 12 dyke intrusions and 10 fissure eruptions have occurred near Fagradalsfjall and Svartsengi-Grindavík. The 2021-2023 Fagradalsfjall volcano-tectonic event consisted of 4 dyke intrusions, 3 of which surfaced in fissure eruptions. On 24 February 2021, intense seismicity along a 10 km long dyke path, fed a 6-months long eruption, the first in around 780 years on the Peninsula. The three subsequent dyke intrusions were shorter in time and space, propagating for around 5 days, along 5-7 km long paths, each illuminating a section of the February-March 2021 dyke’s path. Out of the subsequent dykes, the December 2021 dyke was most intense seismically, propagating to the SW, but not breaching the surface. The July-August 2022 dyke seismicity was more diffuse, illuminating the central to NE part, whereas the July 2023 dyke intrusion almost exclusively propagated NE. The 2022 and 2023 dyke intrusions both fed short lived eruptions. Our data show that all the Fagradalsfjall dyke intrusions were governed by N-S strike-slip faulting. Using high-resolution relative relocations of the dyke-induced seismicity, we find that the December 2021, the 2022 and 2023 intrusions all initiated at 6-8 km depth within an area of about 1 km2. All three dykes then propagated laterally at depths of 2 - 6 km. The December 2021 dyke was associated with seismicity at 4-6 km, the 2022 dyke at 1.5 - 3 km and the 2023 dyke at 2.5 - 5.5 km depth. The dykes initiated directly above a zone of deep long-period events (DLPs) at 8-14 km depth (Greenfield et al., 2022), between the 2022 and 2023 eruption sites, suggesting that the dykes were fed from near Moho magma levels.
Greenfield, T., Winder, T., Rawlinson, N., Maclennan, J., White, R.S., Ágústsdóttir, T., Bacon, C.A., Brandsdóttir, B., Eibl, E.P.S., Glastonbury-Southern, E., Gudnason, E.Á., Hersir, G.P. and Horálek, J. (2022). Deep long period seismicity preceding and during the 2021 Fagradalsfjall Eruption, Iceland. Bulletin of Volcanology, 84,101. https://doi.org/10.1007/s00445-022-01603-2.
How to cite: Ágústsdóttir, T., Glastonbury-Southern, E., Líndal Magnússon, R., Winder, T., Gudnason, E. Á., Brandsdóttir, B., Dubravová, J., Burjánek, J., Fischer, T., Hrubcova, P., Vlček, J., Eibl, E. P. S., and Hersir, G. P.: Common initiation point of repeated dyke intrusions during the 2021-2023 Fagradalsfjall volcano-tectonic rifting event, Reykjanes Peninsula, Iceland., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13890, https://doi.org/10.5194/egusphere-egu25-13890, 2025.
Similar to volcanoes, regularly erupting geothermal features such as geysers are based on a delicate balance between a heat source, fluid and geometry. This balance can be easily disturbed by various internal or external factors such as landslides, earthquakes or the weather. However, due to a lack of long-term studies, these relationships remain unclear in most cases. Here we examine the effect of the weather in detail in a long-term study. We include 4.5 years of seismic and weather data in our study and compile a water fountain catalogue containing 650 000 events. We find a strong relationship between the wind speed and waiting time after eruptions and discuss this in the context of a heat loss model. This effect is not limited to the surface water pool but affects the system down to at least 24 m depth. Additionally, we observe a weak inverse correlation between temperature and waiting time after eruption. Finally, we quantify this correlation to correct for these external weather effects in future studies. This will allow us to study further internal or external drivers.
How to cite: Eibl, E. P. S., Hamzaliyev, S., Hersir, G. P., and Petersen, G. N.: Illuminating the Meteorological Modulation of Eruptions of Strokkur Geyser, Iceland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-63, https://doi.org/10.5194/egusphere-egu25-63, 2025.
Understanding volcanic activity, especially unrest, is a challenging task. This complexity is magnified in Napoli (Southern Italy), where the presence of nearly a million people living on the Campi Flegrei (CF) caldera makes invasive monitoring activities impossible to be performed. Yet, the analysis of coda-waves from continuous ambient-noise recordings (Shapiro & Campillo, 2004) provides highly resolved in-time measurements of mechanical and structural variations in the crust without the need to be invasive, as also exploited in the geothermal field (Hillers et al., 2015; Sánchez-Pastor et al., 2023).
The CF caldera is one of the active hydrothermal systems of the Mediterranean region experiencing notable unrest episodes. Since 2005 a monotonic uplift phenomenon started with unsteadily accelerating seismicity (Bevilacqua et al., 2022). Subsurface rocks withstand a large strain and have high shear and tensile strength (Vanorio & Kanitpanyacharoen, 2015). As a consequence, seismicity reaches magnitude ~ 4.0 only upon relatively large uplifts (~70-80 cm in the previous unrest (’80 years) and > 1 m in the recent one) contrary to what is generally observed for calderas exhibiting much lower deformation levels (Hill et al., 2003). The caprock above the seismogenic area has a pozzolanic composition and a fibril-rich matrix contributing to its ductility and increased resistance to fracture (Vanorio & Kanitpanyacharoen, 2015). However, specific conditions, e.g., an increase in pore pressure or/and chemical alterations, may lead to mechanical failure over time of the caprock and a change in the structural properties of subsurface rocks. In addition, magma pressure in the reservoir can weaken the volcanic edifice, causing decreases in Elastic moduli (Carrier et al., 2015; Olivier et al., 2019). In recent years, a quasi-elastic behavior and a stress memory effect of the upper crust of the CF caldera under increasing stress suggest a progressive mechanical weakening (Bevilacqua et al., 2024; Kilburn et al., 2017, 2023).
Elastic models used to describe volcanic surface deformation would assume that accelerations in surface deformation are due to increases in reservoir pressure. Another possible cause for these accelerations is magma pressure in the reservoir weakening the volcanic edifice. Weakening models imagine crustal shear modulus to decrease with damage and therefore with time (Carrier et al., 2015; Olivier et al., 2019). In analogy to these models, we fixed the source of deformation (location and size) to values from the literature, and we inverted the observed deformation searching for changes in the crustal rigidity, modeling for the sill by Fialko et al. (2001).
We performed a continuous analysis at CF between 2016 and 2024 to investigate the recent unrest characterized by a significant uplift and increased seismicity. We compared seismic-waves velocity variations δv/v in relation to the deformation and other sources of changes controlling the mechanical and structural variations of crustal rocks, such as rain and temperature. For this purpose, we employ seismic ambient-noise interferometry to estimate δv/v (Shapiro & Campillo, 2004) at various local seismic stations from single-station autocorrelations and we quantify surface geodetic strain using data from a local GPS network (De Martino et al., 2021).
How to cite: Tarantino, S., Poli, P., Vassallo, M., D'Agostino, N., Garambois, S., and De Martino, P.: A multiparametric analysis of the recent unrest at Campi Flegrei, Italy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12985, https://doi.org/10.5194/egusphere-egu25-12985, 2025.
Submarine volcanoes pose considerable challenges in monitoring their activity. Kavachi, situated in the Western Province of the Solomon Islands, is a highly active submarine volcano that presents potential risks to nearby communities, as well as to air and marine traffic in the region. In this study, we employ onshore seismic stations to observe Kavachi's eruptive activity by analyzing volcano-seismic signals. Based on recordings from seismic array stations installed on Nggatokae Island, approximately 27 km and 36 km away from the volcanic edifice, we detected and quantified the eruptive activity of Kavachi between February and November 2023.
We first employed a dual-station approach, using recordings from stations separated by 9 km, to identify and quantify characteristic seismo-volcanic signals. This method is based on station-specific band-limited spectral-amplitude ratios, inspired by techniques originally developed in bioacoustics for detecting whale sounds in seismograms. Using this approach, we detected significant variability in volcanic activity, ranging from quiescent periods with no detected events to phases of intense activity with more than 2,500 seismo-volcanic events per day, associated with episodic volcanic tremors and short-duration explosive signals.
Additionally, array analysis was conducted using data from four closely spaced seismic stations (average spacing of 190 m) on the southern coast of Nggatokae. Cross-correlation techniques were applied to determine the back-azimuth and apparent velocity of the seismic wavefield associated with volcanic activity. Results indicated a consistent mean back-azimuth of 222.6°, closely aligning with the theoretical value of 225° for Kavachi.
Interpretation of these signals was further supported by waveform modeling to provide insights into the source mechanisms and path effects. The findings show that onshore seismic arrays can effectively monitor submarine volcanic eruptions. This methodology not only offers insights into the eruptive activity of Kavachi volcano but presents potential applications for monitoring other submarine volcanoes globally.
How to cite: Rümpker, G., Roga, C., Kaviani, A., Limberger, F., Bitzan, L., Laumann, P., Tatapu, C., Gwali, J., Manker, T., and Vehe, C.: Onshore Seismic Monitoring of Submarine Kavachi Volcano Reveals Vigorous Eruptive Activity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6692, https://doi.org/10.5194/egusphere-egu25-6692, 2025.
This study presents a seismic tomography analysis of the magmatic plumbing system beneath the Hachijojima Island, a populated volcanic island in Japan. The island hosts two volcanoes, Nishiyama and Higashiyama, with Nishiyama considered to be the active volcano. The seismic data were collected from seismic observation which was conducted over two separate 7-month periods in 2019 and 2021, utilizing a dense network of 55 seismic stations installed on the island. During the observation period, a total of 179 local earthquakes were recorded, with 119 occurring in 2019 and 60 in 2021. The earthquake events were predominantly located approximately 20-30 km northwest of the island, rather than directly beneath it. These recorded earthquakes provided 4642 P-wave arrival times and 3927 S-wave arrival times, which were subsequently analyzed using the Double Difference (DD) Tomography method to derive the subsurface velocity structure.
The seismic tomography analysis employed a two-step DD Tomography approach. It aims to construct a robust initial reference velocity model and obtain a better resolution at shallower region beneath Nishiyama. The first step utilized a coarser and uniform grid size to generate a 3D velocity model, which was then utilized as the initial model for the second step of DD tomography inversion with finer grid size beneath Nishiyama.
The 3-D tomography results revealed a high-velocity anomaly region at approximately 4 km depth, extending vertically from the deeper area beneath Nishiyama. This suggests the presence of a potential pathway through which magma from past volcanic activity may have migrated. This high-velocity region is characterized by high P-wave velocities, low S-wave velocities, and high Vp/Vs ratios, potentially indicative of the existence of fluid in this area. Furthermore, the Vp perturbation image clearly visualized a magmatic plumbing system to a depth of approximately 20 km in the deeper, northwestern region of the island. The hypocenters which are predominantly located in this zone appear to be associated with the long-distance lateral magma transport. This region, situated in the middle to lower crust at depths of 10-20 km, is driven by the regional tectonic conditions within the deeper crust.
How to cite: Kusumo, A. W., Azuma, H., Watanabe, T., and Oda, Y.: Imaging the Magmatic Plumbing System Using Seismic Tomography Beneath Hachijojima Volcanic Island, Izu-Bonin Arc, Japan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13877, https://doi.org/10.5194/egusphere-egu25-13877, 2025.
Seismic imaging in volcanic settings continues to be an extremely challenging task due to the significant effect of seismic wavefield scattering from sharp, high amplitude seismic impedance changes in the subsurface. The combined effect of these along-path effects with highly rugous surface topography and complex earthquake source mechanisms results in significant codas in recorded seismograms. One of the main challenges in seismic tomography and inversion is harnessing these information-rich codas at the upper end of their frequency content, in order to resolve seismic velocity models on length scales of the smallest significant heterogeneities.
Fourier Neural Operator (FNO) machine learning models have been applied to make predictions of physical systems including flow in porous media but there are only a few examples of their use in seismology. Recent studies have demonstrated that geologically feasible velocity models can be recovered by FNOs from forward-modelled seismograms when trained on generalised model:seismogram populations, in a simulation-to-simulation (sim-to-sim) paradigm. However, an outstanding challenge for FNO research is to progress the successful performance of sim-to-sim FNOs to make robust velocity model predictions from field-gathered seismic data.
Here we generate a large population of velocity models (order 104) with statistically-generated perturbations designed to represent the scale lengths of heterogeneity observed for volcanic rocks, informed by field measurements such as petrophysical logs. Full waveform modelling is used to produce a seismogram set for each velocity model, accounting for viscoelastic attenuation. We then train an FNO neural network to predict a velocity model from input seismic records. We discuss the resolution limits of the FNO-predicted velocity models, as well as the ability to recover geometric features likely to occur in volcanic settings, from unseen data.
How to cite: Totten, E., Bean, C. J., and O'Brien, G. S.: Seismic Imaging in Highly Scattering Environments using Fourier Neural Operators, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4995, https://doi.org/10.5194/egusphere-egu25-4995, 2025.
Basaltic and basaltic-andesite open-conduit volcanoes offer valuable opportunities to explore the mechanisms governing transitions from Strombolian activity to more intense paroxysmal events, such as lava fountains. Strombolian explosions can escalate into lava fountaining, a process characterized by surface fragmentation under choked-flow conditions, requiring low-viscosity, rapidly ascending basaltic magma. While strongly cyclic behaviour is common in Strombolian and lava-fountaining activity, it is rarely captured in geophysical datasets.
Beginning on November 12, 2023, the South-East Crater of Etna volcano exhibited cyclic Strombolian activity that culminated in paroxysmal events on December 2, 2023. This study exploits geophysical signals recorded by the monitoring network of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) to investigate the processes and timescales driving this eruptive sequence. The activity featured cyclic clusters of Strombolian explosions lasting 15–20 minutes, recurring every 50–70 minutes. Analysis of seismo-acoustic data reveals continuous, repetitive, and highly regular energy and volume emissions. Within each cycle, a systematic increase in both explosion frequency and amplitude was observed.
This behaviour is interpreted through a model involving foam collapse in the shallow conduit of the South-East Crater, which regulates degassing processes. The transition to paroxysmal activity occurs when the barrier trapping gas bubbles dissipates, enabling the choked flow conditions and driving the eruption. This study provides critical insights into the cyclic eruptive behaviour of basaltic volcanoes and contributes to a broader understanding of volcanic degassing dynamics and paroxysmal transitions.
How to cite: Gheri, D., Zuccarello, L., De Angelis, S., and Sciotto, M.: From Cyclic to Paroxysm: the cryptic paroxysmal eruption of Etna, December 2023, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5662, https://doi.org/10.5194/egusphere-egu25-5662, 2025.
Seismic tremor plays a crucial role in eruption forecasting and is therefore monitored extensively on volcanoes around the world. However, the use of volcanic tremor for eruption forecasting purposes requires improving our present understanding of its source processes. This has proven a challenging task.
Traditionally, the generation of volcanic tremor is attributed to processes associated with magma transport or linked to fluid-induced resonance (e.g. gases or hydrothermal systems) within the volcano plumbing system. In contrast, other studies suggest that fluids may not be required to generate tremor but the weak, unconsolidated, materials that make up volcanic edifices can experience diffusive failure patterns causing non-localised, low-amplitude seismic events merging into tremor. Small departures from the background stress levels would be sufficient to generate low-amplitude, small-stress-drop events for materials near the brittle-ductile boundary that still support seismicity, as demonstrated by numerical models and laboratory experiments. Changes in stress could be caused by variable magma flow or gas influx or simply linked to gravity impact on the edifice. Even if magma flow or gas influx drive stress level changes the subsequent failure of material would be dry mechanically.
Here, we investigate high-frequency tremor, in the frequency band 10-20 Hz, from data recorded on the summit of Mount Etna during a large seismo-acoustic deployment during the summer of 2022. High-frequency seismic signals, with energy at frequencies >10 Hz, experience rapid attenuation and are affected by extensive scattering making their analysis particularly challenging. We show how insights into the driving mechanisms of the episodic, high-frequency, tremor at Etna can be gained from the analysis of the seismo-acoustic energy ratio, which shows significant variations across different tremor episodes; this suggests different conditions for tremor generation. Additionally, we are able to locate the high-frequency tremor using multi-array beamforming and 3D grid-search algorithms; our results reveal the presence of different source regions from where tremor is radiated, including areas associated with extensive degassing. We also carry out synthetic tests to assess the reliability of the localisation results. Finally, frequency-magnitude distribution of tremor episodes is explored to investigate the hypothesis that tremor may result from sequences of multiple small-magnitude, very small-stress-drop, individual seismic events.
How to cite: Weber, M., Bean, C., De Angelis, S., Soubestre, J., Tary, J.-B., Zuccarello, L., Lokmer, I., and Smith, P.: Insights into driving mechanisms of volcanic seismic high frequency tremor above 10 Hz on Mount Etna, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9436, https://doi.org/10.5194/egusphere-egu25-9436, 2025.
The South Aegean Volcanic Arc remains active, presenting not only primary volcanic hazards such as ashfall and lava flows but also secondary hazards from active submarine and coastal volcanoes with the potential to trigger tsunamis. These tsunamis pose a threat even to far-distant coastlines, as shown by the destructive history of large-scale eruptions in the Mediterranean, including the Thera/Santorini explosion (~1600 BCE). With growing population density, expanding infrastructure development, and seasonal tourism, both primary and secondary volcanic risks along the Aegean coasts are increasing, even with respect to smaller, more frequent eruptions.
This study focuses on the western Saronic Gulf region within the Aegean Sea, as possible impacts may even extend into the greater Athens metropolitan area. In this region, the dormant volcanoes of the Methana volcanic system, which last erupted in 230 BCE, and the submarine Pausanias Volcanic Field represent underappreciated hazards. To address this, we search for evidence of possibly yet undetected magmatic activity through the identification of related microseismic events.
Since 2019, the National Observatory of Athens and the University of Patras operate six seismic stations on Methana and the nearby Peloponnese mainland. In March 2024, an additional 15 seismic recording stations were deployed across Methana, Aegina, Agistri, Kyra, and Poros islands and the mainland Peloponnese for a two-year period.
This expanded network configuration provides a dense and robust azimuthal coverage of seismic ray paths for earthquake location and structural analysis. The continuous recordings enhance the observational capacities for earthquake detection, e.g. first results indicate low noise levels at the recording sites and that low magnitude events to ML ca. 0 can be recorded with very good signal-to-noise ratios. This geophysical experiment is part of the DAM mission ‘mareXtreme’ under the MULTI-MAREX project.
How to cite: Föst, J.-P., Ritter, J. R. R., Evangelidis, C. P., Sokos, E., Richter, N., and Reicherter, K. R.: Insights from the Methana Magmatic Observational Experiment (MeMaX): Seismological Monitoring of Magmatic and Tectonic Activity in the Western Saronic Gulf Region, Greece, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16294, https://doi.org/10.5194/egusphere-egu25-16294, 2025.
The upper volcanic edifice is important in influencing the final leg of the migration pathway of magma to the earth’s surface. The expectation is that such migration will have a clear seismic response, which will allow it to be tracked through the shallow subsurface. Consequently, shallow Long Period (LP) seismicity and volcanic tremor are viewed with considerable interest in hazard estimation. However, a detailed analysis of LP seismicity and tremor signals demonstrates that it is possible to generate them in ways that do not require the presence of migrating fluids. Furthermore, it has long been recognised that a short interval of quiescence often precedes eruptions, which is puzzling if seismicity-generating fluids are approaching the surface. Here we look at the role played by compliant and weak rocks, the norm in upper volcanic settings, on the seismic & seismicity response. We find that many of the observed characteristics associated with pre-eruptive seismicity can be explained by considering upper edifice rheology. This analysis also points to exceptionally weak structures, at the scale of the whole edifice.
How to cite: Bean, C. and Lokmer, I.: Is the seismic response of the upper volcanic edifice dominated by the rheological properties of compliant weak rocks? , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17652, https://doi.org/10.5194/egusphere-egu25-17652, 2025.
During the summer of 2024, a large-scale deployment of 340 SmartSolo IGU-16 3C 5Hz nodal seismometers took place across 116 locations within the the East Rift Zone (ERZ) of Kīlauea volcano, on the Island of Hawaiʻi. Each site housed three instruments to overcome the limited battery capacity of approximately 30 days, allowing the array to operate continously for three months. The array is designed to push developments in high-resolution mantle-to-crust seismic imaging, temporal monitoring, seismicity characterization and fault loading response caused by ascending magma in the ERZ. The recent eruptive events in 2018 and 2020 caused significant changes to Kīlauea’s internal structure, raising new questions about its eruptive processes and the pathways through which magma is transported. During the array's recording period, three magma intrusions accompanied by swarm seismicity and deformation were observed, culminating in an eruption near the Nāpau Crater in the Middle East Rift Zone in September 2024. These events provide compelling evidence that magma has begun re-entering the ERZ after years of absence. Here we provide an overview of the deployment, evaluate the quality of the collected data, and explore the dataset's potential for seismic imaging.We also show first results, including the development of a seismicity catalog generated using state-of-the-art machine learning techniques, setting the stage for velocity inversion studies and other in-depth analyses. The 2-D nodal array offers new, independent constraints that complement previous geophysical investigations in the region, such as magnetotelluric surveys. The combined insights from these datasets are expected to contribute to a broader understanding of Kīlauea’s magmatic system and the changes occurring within its subsurface structure.
How to cite: Lanza, F., Rohnacher, A., Janiszweski, H., and Wiemer, S.: A large-N nodal array to study the structure and magmatic-tectonic processes of Kīlauea Volcanic System, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18464, https://doi.org/10.5194/egusphere-egu25-18464, 2025.
The emplacement of magmatic bodies within the crust induces significant changes in chemical and physical properties of the bedrock, which can be remotely measured to monitor the state of volcanoes and assess potential eruptions. In addition to geodetic (Dzurisin, 2003, 2007; Bruno et al., 2022) and geochemical (Aiuppa et al., 2007; Paonita et al., 2021) methods, seismology is widely used for volcano monitoring, as magma movement within the conduits and storages produces low-frequency vibrations of the volcanic edifice (i.e., volcanic tremor and long-period events; Eaton et al., 1987; Sciotto et al., 2022), while intruding magma loads the bedrock triggering volcano-tectonic earthquakes due to fracturing processes or the reactivation of pre-existing faults (McNutt et al., 2005; Firetto Carlino et al., 2022).
Magma movement along volcanic plumbing systems has been shown to also modify the rheology of the crust, influencing the attitude of a crustal volume at storing and releasing elastic energy (Firetto Carlino et al., 2022 and references therein). This aspect can be investigated by detecting changes in the slope b of the Gutenberg & Richter Frequency-Magnitude Distribution of earthquakes (Gutenberg and Richter, 1944; FMD; logN = a − bM, where N is the cumulative number of seismic events with magnitude above or equal to M and a represents the productivity), commonly referred to as the b-value.
The b-value expresses the proportion of small to large earthquakes, and time changes of this parameter should be considered a proxy for crustal stress variation (Scholz, 1973; Goebel et al., 2013). To examine whether the b-value can track magma movement from deep crustal sectors to the surface and potentially serve as an eruption precursor, we use Mount Etna (southern Italy) as a test site. Variation of the b-value over time has been computed on the 1 January 2005 - 31 December 2024seismic catalogue, but we restricted the period of observation from mid-2016 to December 2024, to ensure a significant number of earthquakes to be considered.
Our results show significant variations along the Etna plumbing system, which can be attributed to magma recharge from depth, increased fluid pressure within the magma storage and dike propagation, leading to eruptive activity.
How to cite: Firetto Carlino, M., Lo Bue, R., Cannavò, F., Taroni, M., Cocina, O., Barberi, G., Scarfì, L., and Coltelli, M.: Can changes in the frequency-magnitude distribution of earthquakes be used as an eruption precursor?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19845, https://doi.org/10.5194/egusphere-egu25-19845, 2025.
In volcanic systems, seismic anisotropy is a common phenomenon, typically attributed to the presence of eruptive fissure, dikes, sills and microcracks/pores, whose preferential orientation depends on the local stress field. A common tool for observing seismic anisotropy is the measurement of shear wave splitting (SWS), the splitting of shear waves into two quasi shear waves with orthogonal polarization directions and different propagation speeds when entering an anisotropic medium. The relationship between seismic anisotropy and the density and orientation of fluid-filled cracks makes SWS an excellent tool for studying the volcanic stress field and associated volcano dynamics (Savage et al. 2010; Araragi et al. 2015; Johnson et al. 2015; Mroczek et al. 2020; Nardone et al. 2020). However, SWS observations only provide path-integrated information, so the interpretation of anisotropic features from these observations is limited. In contrast, body wave tomography studies that have the potential to give insights into the 3D distribution of anisotropy are often conducted assuming isotropy as this simplifies the seismic inversion strategy. However, P-wave (Bezada et al. 2016; VanderBeek and Faccenda 2021) and S-wave (VanderBeek et al. 2023) tomography experiments have shown that the assumption of isotropy in the presence of anisotropic structure can generate significant velocity imaging artifacts, potentially resulting in misinterpretation of true thermal and compositional heterogeneities.
Here we present a study of seismic anisotropy beneath Mt. Etna, one of the best monitored active basaltic volcanoes in the world. Our preliminary SWS measurements of local earthquakes between 2006 and 2016 (following the automated method of Hudson et al. (2023)) provide evidence for strong anisotropy at Mt. Etna. This is supported by previous SWS studies (Bianco et al. 2006; Nardone et al. 2020), as well as by P-wave anisotropic tomography (Lo Bue et al. 2024). The well-established sensitivity of S waves to fluids suggests that in volcanic environments S waves should be particularly sensitive to anisotropy due to preferentially aligned fluid-filled cracks. To quantify the potential bias in seismic imaging caused by the neglection of anisotropy, we have performed seismological synthetic experiments and compared synthetic isotropic tomography results from an isotropic and an anisotropic model (based on prior imaging of Mt. Etna by Del Piccolo et al. (in review)). Our results give new insights into the importance of incorporating seismic anisotropy in the study of the subsurface structure and dynamics of active volcanoes with S wave tomography.
How to cite: van Helden, K., Vanderbeek, B., Del Piccolo, G., Faccenda, M., Lo Bue, R., Giampiccolo, E., Cocina, O., and Carlino, M. F.: Shear wave splitting and synthetic S wave tomography at Mt. Etna volcano, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18819, https://doi.org/10.5194/egusphere-egu25-18819, 2025.
