High-resolution tomographic imaging of the subsurface structures beneath volcanic systems is fundamental to better assess their hazard and potentially estimate the amount of eruptive materials. However, obtaining such images represents a major challenge for multiple reasons. The significant velocity contrasts commonly present within volcanic systems require accurate wave simulations or traveltime modeling to correctly account for wavefield triplications and ray bending. Moreover, station coverage and temporary deployments usually cannot achieve the requirements needed to meet high-resolution imaging targets.

We demonstrate how distributed acoustic sensing (DAS) data recorded on existing telecommunication fiber cables and employed within an accurate and efficient matrix-free Eikonal tomography workflow can overcome these limitations. Specifically, we produce high-resolution tomographic images of the Long Valley caldera system in California, which in recent years has been undergoing significant inflation and seismic unrest. Our results reveal a distinct separation between the large magma chamber at approximately 10 km depth and the shallow crust. We interpret this separation as an upper-crust lid confining the pressurized volcanic fluid released through the crystallization of the magma reservoir over time. 

Our study highlights the potential of DAS for advancing volcano science; from providing insights into subsurface structures to monitoring dynamic processing due to fluid and magma movements through these complex systems.

How to cite: Biondi, E., Zhu, W., Li, J., Williams, E., and Zhan, Z.: Fiber seismic tomography of the Long Valley volcanic system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4185, https://doi.org/10.5194/egusphere-egu24-4185, 2024.

Ischia Island is the westernmost, active volcanic complex of the Campanian plain (Southern Italy, Civetta et al., 1991). A long-term depressurization (Sepe et al., 2007) in the local hydrothermal system is causing deflation and contraction (Trasatti et al., 2019) of the surrounding volcanic edifice. In 2017 a Mw 3.9 shallow earthquake occurred in Casamicciola, in the northern part of the island, causing landslides and several collapses (Nappi et al., 2018). Here we present seismic velocity variation measurements δv/v over 8 years (2016-2023) for variable coda waves time lapse using empirical Green's functions reconstructed by autocorrelation of seismic noise recorded at local velocimeters. We compared velocity variations time series with the temporal evolution of the strain, obtained from displacements measured at the GPS network deployed on the island.  We focused on short-term velocity variations caused by the earthquake and on the long-term trend of δv/v measurements. This latter shows to be related to the deformation mechanism affecting the volcanic edifice. We found high values in both dynamic and static strain sensitivity of velocity variations with appreciable differences on the island, reflecting the anisotropic pattern of depressurization. This also proves a significant non-linearity in the elastic properties of the local volcanic materials. The joint use of geodetic methods and ambient noise monitoring revealed a remarkable sensitivity of δv/v to depressurization processes and its potential to enhance our understanding of the dynamics of the magmatic system.

References

Civetta, L., Gallo, G., & Orsi, G. (1991). Sr- and Nd-isotope and trace-element constraints on the chemical evolution of the magmatic system of Ischia (Italy) in the last 55 ka. Journal of Volcanology and Geothermal Research, 46(3–4), 213–230. https://doi.org/10.1016/0377-0273(91)90084-D

Nappi, R., Alessio, G., Gaudiosi, G., Nave, R., Marotta, E., Siniscalchi, V., Civico, R., Pizzimenti, L., Peluso, R., Belviso, P., & Porfido, S. (2018). The 21 August 2017 Md 4.0 Casamicciola Earthquake: First Evidence of Coseismic Normal Surface Faulting at the Ischia Volcanic Island. Seismological Research Letters, 89(4), 1323–1334. https://doi.org/10.1785/0220180063

Sepe, V., Atzori, S., & Ventura, G. (2007). Subsidence due to crack closure and depressurization of hydrothermal systems: a case study from Mt Epomeo (Ischia Island, Italy). Terra Nova, 19(2), 127–132. https://doi.org/10.1111/j.1365-3121.2006.00727.x

Trasatti, E., Acocella, V., Di Vito, M. A., Del Gaudio, C., Weber, G., Aquino, I., Caliro, S., Chiodini, G., de Vita, S., Ricco, C., & Caricchi, L. (2019). Magma Degassing as a Source of Long‐Term Seismicity at Volcanoes: The Ischia Island (Italy) Case. Geophysical Research Letters, 46(24), 14421–14429. https://doi.org/10.1029/2019GL085371

How to cite: Tarantino, S., Poli, P., Vassallo, M., and D'Agostino, N.: Dynamic and static strain sensitivity of seismic velocity variations at Ischia Island, southern Italy , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6321, https://doi.org/10.5194/egusphere-egu24-6321, 2024.

In 1978, seven seismic reflection profiles were acquired through a joint venture between Agip and Enel to explore geothermal resources in the Campi Flegrei caldera. These vintage profiles reflect the technological limitations of that era: sparse shot points, limited channels, low bandwidth and dynamic range, resulting in a low signal-to-noise ratio, especially near volcanic structures. Despite these limitations, they can offer invaluable insights in Campi Flegrei, where obtaining new seismic data is impractical due to urbanization, environmental concerns, and intensified volcanic hazards.

This presentation shares the outcomes of a reprocessing aimed at enhancing profile signal-to-noise ratio. Given acquisition geometry and data quality, contemporary seismic processing methods like pre-stack depth imaging, reflection tomography, and full-waveform inversion are impractical. The reprocessing adapted to data quality limitations, utilizing time-domain algorithms. It involved assigning a crooked line geometry, conventional common-midpoint (CMP) processing, and less conventional common reflection surface (CRS) processing. CRS stacking, not reliant on stacking velocity estimation, improves seismic imaging quality. P-wave velocity models were reconstructed along the profiles through tomography algorithms applied to picked first arrivals. Post-stack time migration and depth conversions with vertical stretching were applied to CDP/CRS stacks.

Despite limitations, these depth images, tied to exploration wells and geophysical logs, can significantly contribute to understanding the near-surface structure of this dynamic region and its structural and stratigraphic relations with the sedimentary Volturno Plain to the North.

How to cite: Bruno, P. P. G. and Cardillo, C.: Results from reprocessing the vintage 1978 ENI-ENEL seismic reflection profiles acquired on the onshore of Campi Flegrei, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11650, https://doi.org/10.5194/egusphere-egu24-11650, 2024.

The interplay between volcanism and tectonics gives rise to a spectrum of geological phenomena, including eruptions, earthquakes, mass failures, and tsunamis, posing significant threats to both local and global environments. Seismic data interpretation serves as a crucial tool for reconstructing past volcanic-tectonic interactions, offering insights into potential precursors and triggers for future events. However, the inherent complexity of volcanic-tectonic regions often poses challenges for seismic imaging and interpretation, particularly regarding the delineation of faults, as well as the identification of volcanic structures, volcanic products, and mass transport events.

In this study, we explore the frequently overlooked diffracted wavefield as a tool to aid seismic interpretation of volcano-tectonic structures. Wave diffraction occurs at geodynamically important features like faults, erosional surfaces or other small-scale scattering objects and encodes information on a sub-wavelength resolution. Our approach models and adaptively subtracts the reflected wavefield from the un-migrated seismic data before we focus the separated diffractions to generate diffraction-energy images. We will present two seismic profiles from the Christiana-Santorini-Kolumbo volcanic field, one of the most active volcano-tectonic fields in Europe. These profiles cross major rift basins, complex fault zones, volcanic edifices, and mass-transport deposits. Our derived diffraction images provide a unique window into the subsurface, highlighting important small-scale heterogeneities. We observe that diffractions cluster at geodynamically important subsurface structures, such as faults, volcanic cones, as well as distinct unconformities within the rift basins. Diffractions also cluster at seismic subunits previously interpreted as eruptive products such as ignimbrites and lava flows, as well as mass-wasting deposits. In contrast, we observe that little diffraction occurs in sedimentary strata interpreted to be the result of hemipelagic background sedimentation. Thus, this study strongly advocates for the integration of diffraction energy images into the standard practice of seismic data analysis and interpretation in the context of volcano-tectonic interactions.

How to cite: Ischebeck, L., Preine, J., and Hübscher, C.: Utilizing Diffractions as a Tool to Study the Volcano-Tectonic Processes at the Christiana-Santorini-Kolumbo Volcanic Field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9403, https://doi.org/10.5194/egusphere-egu24-9403, 2024.

There is an ongoing debate about the water depths to which explosive submarine volcanism is possible. In this study, we present high-resolution reflection seismic data from cone-shaped intraplate volcanoes on the southeastern Azores Plateau that indicate explosive submarine volcanism at water depths greater than 2 km. In addition, the data illustrate the early stages of volcanic ridge evolution at similar water depths, which were mainly formed by fissure eruptions. The volcanic cones are ca. 4 km wide and 500 m high above the ocean floor. They are characterised by stratified flanks that are onlapped by sub-horizontal, hummocky high-amplitude reflections. We interpret the layered flanks as evidence of rather unconsolidated volcanic deposits from submarine explosive eruptions, where the magma emerging from the seafloor was fragmented by expanding volatiles. Guided by diffraction imaging, we interpret the high-amplitude reflections as the top of lava flows from effusive eruptions, that postdated the explosive eruptions. Distinct upward-bent reflections beneath the volcanic cones are interpreted to be velocity pull-ups caused by the presence of dense, high p-wave velocity material in the central part of the volcanic cones. We apply depth-stretching to correct for these artefacts and to access the true geometry of the volcanic cones and the underlying features. Upward concave reflections within the basaltic basement might represent funnel shaped conduits or diatremes. The seismic signature of a volcanic ridge between two of the volcanic cones suggests that stacked effusive eruptions dominated its evolution. Both the cones and ridges superimpose hemipelagic sediments, which in turn overlie the basaltic basement. Hence, the evolution of the volcanic features postdated the main magmatic evolution of the western part of the eastern Azores Plateau that started in the middle Miocene. Generally, our study sheds new light on the complex volcanic evolution of the southeastern Azores Plateau and highlights the potential of seismic imaging as a tool for submarine volcanology.

How to cite: Friedrich, A., Hübscher, C., Preine, J., Beier, C., Hildenbrand, A., Nomikou, P., and Terinha, P.: Seismic Imaging of Submarine Volcanoes and Volcanic Ridges at the Southeastern Azores Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9449, https://doi.org/10.5194/egusphere-egu24-9449, 2024.

Seismic attenuation plays a vital role in geothermal exploration due to its direct association with the fluid content of reservoirs. In this study, we obtained the first attenuation model of La Palma island (Canary Islands) for geothermal exploration, applying a novel local-scale ambient noise attenuation tomography technique. Data from 44 seismic stations underwent meticulous processing. The initial stages involved preprocessing ambient noise data via standard normalization techniques, bandpass filtering and cross-correlation to retrieve the Empirical Green's functions (EGFs). For each EGF we retrieve the intrinsic attenuation  across various frequencies using the lapse-time dependence method, in which intrinsic attenuation is measured as a function of the coda window length for different onsets of the ambient-noise cross-correlation coda (Calvet and Margerin, 2013). Subsequently, 2-D spatial intrinsic attenuation maps for different frequencies were generated through linear inversion using sensitivity kernels (Del Pezzo and Ibáñez, 2020). Finally, we inverted the 2-D spatial intrinsic attenuation maps to derive 1-D depth profiles of intrinsic attenuation. The results unveiled distinct high-attenuation anomalies which releveled a possible hydrothermal zone  beneath the southern part of La Palma island. Comparative analyses with previous resistivity studies (Di Paolo et al., 2020), S-wave velocity research (Cabrera-Pérez et al., 2023), and density models (Montesinos et al., 2023) further corroborated these findings, underscoring the significance of ambient noise attenuation tomography in geothermal exploration.

References:

Cabrera-Pérez, I. et al. Geothermal and structural features of La Palma island (Canary Islands) imaged by ambient noise tomography. Sci. Reports 13, 12892 (2023)

Calvet, M. & Margerin, L. Lapse-time dependence of coda q: Anisotropic multiple scattering models and application to the pyrenees. Bull. Seismol. Soc. Am. 103, 1993–2010 (2013).

Del Pezzo, E. & Ibáñez, J. M. Seismic coda-waves imaging based on sensitivity kernels calculated using an heuristic approach. Geosciences 10, 304 (2020).

Di Paolo, F. et al. La Palma island (Spain) geothermal system revealed by 3D magnetotelluric data inversion. Sci. reports 10, 1–8, DOI: 10.1038/s41598-020-75001-z (2020).

Montesinos, F. G. et al. Insights into the magmatic feeding system of the 2021 eruption at Cumbre Vieja (La Palma, Canary Islands) inferred from gravity data modeling. Remote. Sens. 15, 1936 (2023)

How to cite: Cabrera-Pérez, I., D'Auria, L., Soubestre, J., del Pezzo, E., Prudencio, J., Ibáñez, J. M., Jiménez, M., Padilla, G. D., Barrancos, J., and Pérez, N. M.: 3-D Intrinsic Attenuation Tomography of La Palma island (Canary Islands) using Ambient Seismic Noise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3069, https://doi.org/10.5194/egusphere-egu24-3069, 2024.

The origin of the Canary Islands has been under debate for the last decades. The hotspot hypothesis as the origin of the islands was abandoned long ago, however, there are still theories that partially incorporate this idea. The scientific community widely accepts none of these models and the recent volcanic eruptions of El Hierro and La Palma once again question these theories. 

In order to confirm the structure and to explain the diversity of the eruptive processes observed in the Canarian archipelago, we return to El Hierro island to obtain a high-resolution seismic attenuation tomography, as it has proven to be more sensitive to the presence of magma as shown in Mt. Etna (Castro-melgar et al., 2021). Thus, we have analyzed the same database that García-Yeguas et al. (2014) used in the velocity tomography and we have obtained a new tomographic model of El Hierro island that confirms the existence of an intermediate chamber as observed in Tenerife and La Palma which could feed the 2011 eruption.

The lack of high attenuation anomalies in the central part of the island is already observed in the velocity tomography results obtained by García-Yeguas et al. (2014). In addition, Montesinos et al. (2005) identified high-density anomalies in the same zone, where Sainz-Maza et al. (2017) also observed high gravity values. These results could demonstrate the existence of a dense core in the center of the island related to the oldest volcanism of El Hierro and diverting the magma intrusions to the outer zone of the island as the 2011 Tagoro eruption.

How to cite: Prudencio, J., Díaz-Suárez, E. A., Cid, A., Dominguez-Cerdeña, I., Cabrera, I., Del Fresno, C., and Ibáñez, J. M.: Seismic attenuation structure of the lower crust upper mantle under El Hierro island (Spain), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16182, https://doi.org/10.5194/egusphere-egu24-16182, 2024.

Rift volcanoes worldwide present significant hazards to people from eruptions but also provide resources such as geothermal energy. Aluto volcano in the Ethiopian rift is a hotspot for geothermal power exploitations, despite significant periods of deformation in the last 15 years.

Various geophysical imaging methods have been applied to Aluto to obtain a detailed 3D image of the hydrothermal reservoir and the location, geometry, and size of possible magma bodies. However, the models give a single or narrow range of answers without the possibility for the exploration of uncertainties arising from the data and assumptions.

Here we address this current limitation for the seismic data by performing a fully nonlinearized joint inversion of local seismic P- and S-wave travel times, and surface wave dispersion data between 0.5 Hz and 2 Hz from empirical Green's functions, for the location of earthquakes and the velocity of the subsurface. The combination of data types helps reduce the range of permitted models.

We use a reversible-jump Markov chain Monte Carlo approach to incorporate prior information and, from our data, retrieve the posterior probability of earthquake parameters and seismic velocity in a Bayesian sense. This provides rigorous distributions of the covariance of the earthquake and velocity parameters.

Our 3D seismic models display areas of elevated V_p/V_s ratio at 2-6 km depth under the caldera, interpreted as areas of partial melt. The hydrothermal reservoir shows in our results as lower V_p/V_s. This is in good agreement with the previous resistivity models from the magnetotelluric study of Samrock et al. 2020. However, while Samrock et al. observed two zones of partial melt, our model suggests that the lower and upper melt zones are connected.

To go one step further, we developed a workflow to link seismic velocities to melt fraction estimates by combining the posterior distributions of seismic velocity and thermodynamic modeling. We conclude that the melt fraction under Aluto is between 3 and 7 % at 5 km depths, and the melt volume is approximately 0.37 km³.

How to cite: Roy, C., Nowacki, A., Curtis, A., and Baptie, B.: Magma storage quantified under Aluto volcano, Ethiopia, using probabilistic tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17405, https://doi.org/10.5194/egusphere-egu24-17405, 2024.

The volcano Askja in the Northern Volcanic Zone (NVZ) of Iceland last erupted in 1961 and has been steadily deflating from the 1970s until August 2021 when GPS and InSAR measurements confirmed that it had begun re-inflating. The NVZ has hosted a network of seismic stations operated by the University of Cambridge Volcano Seismology group since 2006. In the summer of 2023, this network has been augmented by 12 three component nodes that will record for ~2 months in addition to 10 broadband instruments that will be left for a year in or around the caldera of Askja with an average station spacing of ~1-2 km. The combination of the long-term recordings from the backbone network during deflation and the more recent short-term dense recordings will provide a unique dataset to examine how this switch from deflation to inflation may effect the seismic velocity structure beneath the volcano, thereby providing new insight into the underlying magmatic system. In this study, we present preliminary results from the application of ambient noise tomography to this dataset to try and image any changes in the magmatic system, which will involve stacking different periods of ambient noise cross-correlations to obtain two sets of dispersion curves that are sensitive to the subsurface velocity structure beneath Askja prior to and following the switch to reinflation in August 2021. This allows us to produce 3D models of shear wave velocity that can be compared to help elucidate changes in the plumbing system that occurred due to this switch. The dense deployments in the caldera have the advantage of allowing us to measure dispersion curves to high frequencies due to the short interstation distances, which is expected to yield more information on shallow subsurface structure where GPS and InSAR measurements appear to indicate that the source of the inflation is concentrated.

How to cite: Fone, J., Winder, T., Rawlinson, N., White, R., and Brandsdóttir, B.: A detailed view of the magmatic plumbing system beneath Askja Volcano, Iceland, from ambient noise tomography , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17692, https://doi.org/10.5194/egusphere-egu24-17692, 2024.

Popocatépetl volcano is among Mexico’s most risky due to its proximity to populated areas. Since its reactivation in 1994, several geophysical studies have been performed to understand the eruptive history, volcanic activity, and associated hazards. Although several seismic studies were carried out using permanent and temporal seismic network records, the internal structure of Popocatépetl volcano is still unclear.

In this work, we propose the first 3D velocity model of Popocatépetl volcano, describing the whole edifice inverting group velocity dispersion curves. We used data recorded at 39 broadband seismic stations installed in different epochs. We computed ambient noise cross-correlations, which were computed using two methods to increase the information for the modeling. Our results suggest the presence of a mushroom-shaped Popocatépetl’s system composed of two high shear wave velocity regions, the first one located at 5-0 km a.s.l., the second one located at 4-7 km b.s.l., and a narrow ‘pipe-like’ conduit connects both. The shallow high velocities are related to old and young volcanic structures due to mixed magmatic materials, which are affected by an intense degassing process that increases the magma viscosity and crystal content. The deepest reservoir is interpreted as a magmatic body that is confined due to the lithostatic pressure. The intermediate region is considered a narrow pipe conduit, where there is a low-velocity layer at the same depth. Moreover, our model reveals evidence of buried volcanic paleo-structures and the remains of ancient collapses generated by previous eruptions.

How to cite: Esquivel-Mendiola, L. I., Calò, M., Iglesias, A., Tago, J., and Macías, J. L.: Ambient noise tomography of Popocatépetl volcano, México, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-358, https://doi.org/10.5194/egusphere-egu24-358, 2024.

La Soufrière is an active andesitic stratovolcano lava dome at 1467 m elevation. It is the most recently eruptive centre of the Guadeloupe archipelago in the eastern Caribbean Sea. Previous activity has consisted of effusive, explosive magmatic, and phreatic eruptions. Many hazards are associated with La Soufrière volcano, including explosive blasts, pyroclastic flows, acid degassing and contamination of groundwater sources. Since 1992, increased seismic and fumarolic activity at La Soufrière has raised the alert level to yellow, peaking with a volcanically triggered ML 3.7 earthquake in 2018.  

In the framework of the MEGaMu project, innovative geophysical subsurface imaging methods are deployed at La Soufrière to produce a high-resolution model of the volcanic edifice at up to ~1 km depth to improve our understanding of the volcano’s shallow structure. In October 2023, we deployed an array of 48 3-component 5 Hz nodal geophones around the base of the volcanic massif and the summit crater, recording continuous passive seismic data at a sampling of 250 Hz for one month. An electrical resistivity campaign was conducted at the same time, providing an outstanding opportunity to compare the derived 3D seismic velocity model with a 3D electrical resistivity model on a similar scale. In this study, we apply seismic ambient noise tomography using data from our temporary nodal network and nearby existing broadband stations to produce Rayleigh wave group velocity maps and a 3D model of shear wave velocity. This model is interpreted with the 3D resistivity model to determine the extent of the shallow hydrothermal system and known fault zones crossing the volcanic massif. Such a multi-scale and multi-physics geophysical prospection approach greatly helps in reducing subsurface uncertainty in the interpretation of geophysical datasets.

We use new nodal technologies and up-to-date applications of seismic passive noise tomography to analyse Rayleigh wave shear-velocity dispersion data from a nodal seismic network of 48 3-component units, and generated 2D group velocity maps at different periods, and 3D depth insertion of shear wave velocities. We compare this to a 3D electrical resistivity, carried out simultaneously with seismic deployment, to better constrain the subsurface plumbing system based on comprehensive geophysical methodologies.

How to cite: Jiwani-Brown, E. A., Savard, G., Barsuglia, F., Rosselli, A., Fischanger, F., Truffert, C., and Lupi, M.: Nodal Local Earthquake Tomography of La Soufrière Volcano, Guadeloupe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18404, https://doi.org/10.5194/egusphere-egu24-18404, 2024.

The Tengchong volcano is the most famous active intraplate volcano in Southwest China, which has been dormant for hundreds. The significant seismicity, active geothermal activities and gas emissions are all indicate that the volcanoes still have potential for future eruptions. However, the origin of the Tengchong volcano is still on debate, which is strongly depend on the structure underneath. Here we employ a recently developed H-κ-c method to characterize the crustal structure with its thickness and the Vp/Vs ratio of the Tengchong volcanic area. A total of 4,040 receiver functions are obtained from 9 permanent seismic stations, providing an overall good coverage in both distance and azimuth of the analyzed data. After removing the back azimuthal effects of dipping Moho and/or crustal anisotropy, our results are more robust and highlight local variations. The crustal thickness increases from south to north, ranging from 33.5 to 41.9 km with an average of 37.6 km. The crustal thickness beneath stations RHT is thicker than the surrounding stations, suggesting a possible local crustal depression beneath this station. The Vp/Vs ratios vary from 1.75 to 1.79 and the average value is 1.76 with a standard deviation of 0.015. Stations with high Vp/Vs values indicate partial melting magma chambers in the crust beneath those stations.

How to cite: Zhang, Y. and An, Y.: Crustal structure in the Tengchong Volcanic Area based on the H-κ-c method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13907, https://doi.org/10.5194/egusphere-egu24-13907, 2024.