The prospect of natural hydrogen, also known as geologic or gold hydrogen that is produced in the sub-surface, is rapidly gaining interest as a potentially cheap, clean, and renewable energy source for the future. However, no standardised approach to natural hydrogen exploration yet exists. Traditional exploration activities in sedimentary basins do not easily translate to natural hydrogen, which is often linked instead to non-sedimentary cratonic settings.
Here we present a study of ambient noise tomography within the natural hydrogen exploration licence area (PEL 691) of H2EX Ltd. This area of exploration is focused on the eastern Eyre Peninsula in South Australia, beneath which lies the crystalline basement rocks of the Gawler Craton. A regional passive-seismic survey of 150 nodal seismometers was conducted over an area of 2500 km2 with average site spacing of 3-4 km. The area encompasses several major known faults as well as a zone of heightened intra-plate seismicity. The quality of the noise cross-correlations was found to be excellent, resulting in a 3D shear-wave velocity model that is well resolved down to 15 km depth. Prominently fast crustal velocities are found typical of Proterozoic crystalline crust, with average velocities of 3.17-3.43 km/s at 0-3 km depth and large lateral variations of up to 8%. At shallow depths (~1 km) alternating fast and slow anomalies are found to correlate with gravity indicating local variations in density and the sub-surface geology. Low velocity regions likely correspond to sedimentary/meta-sedimentary units, while high velocities reflect where the underlying crystalline basement is closer to the surface. These velocity variations are thus interpreted as reflecting the depth of the unconformity between the basement and the meta-sediments above. At deeper crustal depths lateral velocity variations beneath the major fault zones are assessed and considered for their potential as migration pathways for natural hydrogen. Overall ambient noise tomography is found to be helpful in detailing the sub-surface structures relevant to the natural hydrogen exploration system.
How to cite: Eakin, C. M., Jiang, C., Dong, S., Wallenius, S., Miller, M. S., Moresi, L., and Heinson, G. and the H2EX Ltd team: Ambient Noise Tomography for Natural Hydrogen Exploration: A Case Study from the Gawler Craton, South Australia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3359, https://doi.org/10.5194/egusphere-egu25-3359, 2025.
With the accelerating global climate crisis and the ratification of the Paris Agreement in 2015, reducing our carbon footprint has become crucial, particularly in the energy sector. Geothermal energy is becoming an attractive green energy since it is baseload-capable, and highly suitable for the supply of district heating in Europe. Identifying optimal locations for deep geothermal wells is essential, but such exploration typically depends on conventional active seismic surveys, which are logistically complex and costly. The high upfront costs associated with geothermal resource exploration remain a significant barrier to the large-scale development of deep geothermal energy across Europe. This is where passive seismic methods based on ambient noise, combined with large, dense seismic nodal arrays, offer a promising solution. In Austria, the central Vienna Basin is the primary target for deep geothermal production serving the city of Vienna. Meanwhile, the southern Vienna Basin also shows potential for geothermal production for smaller cities like Wiener Neustadt in lower Austria. In Spring 2024, we deployed 181 seismic nodal sensors in two temporary deployments over an area of 400 km2. We measured fundamental-mode Rayleigh and Love-wave group velocity dispersion from seismic noise correlations and employed transdimensional Bayesian tomography to invert for isotropic Rayleigh and Love group velocity maps at periods ranging from 0.8 to 3.5 s and 0.8 to 5.5 s, respectively. We then extracted Rayleigh and Love group velocity dispersion curves from the maps at all locations and jointly inverted them for shear-wave velocity and radial anisotropy as a function of depth using a transdimensional Bayesian framework. The 3-D VSV model highlights the seismic characteristics of the Neogene basin in the southern Vienna Basin. Additionally, the 3-D shear-wave radial anisotropy model reveals several features at depth. Combined, these findings hold significant implications for early-stage geothermal exploration in the southern Vienna Basin.
How to cite: Estève, C., Lu, Y., Bokelmann, G., and Götzl, G.: 3-D shear-wave velocity and radial anisotropy structure of the southern Vienna Basin, Austria from transdimensional ambient noise tomography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8766, https://doi.org/10.5194/egusphere-egu25-8766, 2025.
Deep geothermal energy is expected to play a key role as a baseload resource within the Net Zero climate initiatives of the European Union and Switzerland. In Switzerland, the Haute Sorne project, led by Geo-Energie Suisse, represents the first Enhanced Geothermal System (EGS) initiative since the suspension of the Basel project in 2010. Approved by the Canton of Jura in January 2022, this project aims to develop and validate advanced exploration and monitoring technologies to harness the geothermal potential of Switzerland while minimising seismic risk.To reduce subsurface uncertainty, particularly at basement depths, we deployed a seismic network comprising 700 3C nodal sensors around the Haute Sorne area, with a radius of 12 kilometres. Starting in February 2024, these sensors continuously recorded 3-component ambient noise data for one month.
In this study, we applied the classical Ambient Noise Tomography (ANT) technique and the Ambient Noise Attenuation Tomography (ANAT) method and compared the resulting 3D shear-wave velocity and intrinsic attenuation models. Standard data processing techniques were employed to retrieve Empirical Green's Functions (EGFs) from ambient noise cross-correlations for Rayleigh and Love waves. The methodology was then divided into two ways: ANT and ANAT.
For ANT, dispersion curves were extracted using the FTAN (Frequency Time Analysis) technique. Group velocity maps for various periods were obtained for both Rayleigh and Love waves through a linearized inversion approach. A joint inversion of Rayleigh and Love dispersion curves was then conducted using a transdimensional Bayesian formulation to obtain a 3D shear-wave velocity model.
For ANAT we used the methodology described by Cabrera-Pérez et al. (2024). The intrinsic attenuation for each EGF was calculated across multiple frequencies for Rayleigh and Love waves using the lapse-time dependence method, which evaluates attenuation based on the coda window length at different onsets of the ambient noise cross-correlation coda. Next, 2D intrinsic attenuation maps for various frequencies were derived via linear inversion using sensitivity kernels. Finally, a joint inversion of Rayleigh and Love attenuation data was performed to obtain a 3D intrinsic attenuation model.
Our research seeks to map regional geological features at depths of up to 5 kilometres to improve seismic hazard assessments and gain a more comprehensive understanding of the local seismotectonic context. Particular attention is being focused on basement formations, including a suspected Permo-Carboniferous trough. By identifying variations in shear-wave velocity and attenuation, we aim to characterise the subsurface structure of this region. We find that these passive seismic exploration methods are particularly valuable when surveying regions with significant lateral variations in subsurface structure and topography and where classical seismic reflection campaigns may be logistically challenging and cost prohibitive.
References:
Cabrera-Pérez, I., D’Auria, L., Soubestre, J., Del Pezzo, E., Prudencio, J., Ibáñez, J. M., ... & Pérez, N. M. (2024). 3-D intrinsic attenuation tomography using ambient seismic noise applied to La Palma Island (Canary Islands). Scientific Reports, 14(1), 27354.
How to cite: Cabrera Pérez, I., Savard, G., Riahi, A., and Lupi, M.: Geothermal Exploration of Jura Canton (Switzerland) using Ambient Noise Tomography: Velocity and Attenuation models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11040, https://doi.org/10.5194/egusphere-egu25-11040, 2025.
Passive seismic monitoring is an effective tool to assess seismic activity and analyze subsurface structures in and around well sites because it does not require an active source and, thus, is cheap, non-intrusive, and environmentally friendly. The on-campus shallow monitoring well at King Abdullah University of Science and Technology (KAUST) was drilled from February to April 2024, reaching a target depth of ~392 meters, and subsequently cased and cemented along its entire length to total depth. The main challenge for seismic monitoring at the site is the unconsolidated topmost layer of sand and construction debris that strongly weakens the seismic wave energy. At this site, we deployed various types of seismic sensors targeting different spatial and frequency-resolution scales to monitor seismic energy during drilling and from other random surface sources (e.g., vehicular traffic). The seismic monitoring system includes four three-component broadband stations deployed over a period of 5 to 18 months before drilling and a dense array of autonomous STRYDE nodes (measuring the vertical component of the particle acceleration field), which acquired data for about one month during drilling. The array was composed of 89 nodes with a spacing of 2 m and a total offset of 176 m. Seismic interferometry was applied on a portion of the data acquired while drilling operations were stopped (about 7 days) to synthesize surface waves and extract their dispersive behavior (i.e., dispersion curves) between 5 and 15 Hz. The resulting dispersion curves were then used to estimate a 2D near-surface shear wave velocity model down to 20 m depth. The horizontal-to-vertical spectral ratio (HVSR) was instead used on the recordings from the broadband seismic stations to estimate the site response transfer functions from which we extracted four 1D shallow shear wave velocity profiles. We first computed the HVSR for 14 days each month, then stacked the HVSR for 5 months to obtain the final HVSR of each station. The HVSR curves show two main peak frequencies ~2 Hz and 6 Hz. 1D shear wave velocity profiles down to 150 were finally obtained by joint inversion of the HVSR and dispersion curves. The velocity profiles from the broadband seismic stations and the closest profile from the nodes are consistent in the depth range where they overlap. Moreover, the shear wave profiles agree with the lithology interpreted from drilling cuttings. Our project demonstrates that a multi-scale seismic monitoring system can effectively reveal the subsurface structure of a specific site.
How to cite: Li, C., Deheuvels, M., Wang, N., Ravasi, M., Chambers, K., Finkbeiner, T., and Mai, P. M.: Passive subsurface imaging around the KAUST shallow well site using a multi-scale seismic acquisition system, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7217, https://doi.org/10.5194/egusphere-egu25-7217, 2025.
Geothermal energy is an essential low-carbon energy resource for the energy transition. The subsurface characterization of geothermal fields is vital for the expansion of this resource. Often, faults and fractures provide the secondary permeability required for hydrothermal circulation. Anisotropy in the ambient seismic noise wavefield is a novel method for constraining these faults and fractures within geothermal settings at an inexpensive cost.
We use the code package B3AM to perform three-component (3C) beamforming of ambient noise. It is an array-based method which extracts the polarisation, azimuths and phase velocities of coherent waves as a function of frequency from ambient seismic noise, providing a comprehensive understanding of the seismic wavefield. B3AM can be used to determine surface waves and their corresponding velocities as a function of depth and the direction of propagation of waves. Through previous studies, from real and numerical examples, a relationship between anisotropic velocities and present faults has been inferred from real and numerical examples, conveying the depth of permeability necessary for hydrothermal flow within a geothermal field.
The St Austell granite in Cornwall is one of the hottest granite plutons in the UK and, thus, has become a promising source of geothermal energy; the Eden Geothermal Project aims to utilise this naturally occurring heat using the fractures within this radiogenic granite. As part of the growing geothermal research in the area, a seismic node array of 450 STRYDE nodes was deployed from November to December 2022 to provide insight into this complex geological area. Utilizing a sub-array of three-component nodal stations, we investigate the anisotropy of the St Austell granite at depth.
Using 3C beamforming on the ambient noise data, we characterize the wavefield and assess Rayleigh wave velocities as a function of azimuth. To get an accurate representation of anisotropy within the geothermal field, anisotropy was corrected for any array effects. Rayleigh wave velocities were calculated based on wavenumbers, and anisotropy estimates were compared to numerical estimations and shear wave splitting results. Preliminary results indicate fast directions of Rayleigh waves, potentially indicating fractures, in the NNW – SSE orientation. Similarly, shear wave splitting analysis found that the fast S-wave polarisation is dominantly North-South, corresponding to fracture orientation from borehole imagery. This work shows that Rayleigh wave anisotropy is promising for characterising geothermal systems during the exploration process
How to cite: Kennedy, H., Löer, K., Gilligan, A., Finger, C., Hudson, T., and Kettlety, T.: Analysing Seismic Anisotropy in a Geothermal Field from a Three-Component Nodal Array using Beamforming, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8994, https://doi.org/10.5194/egusphere-egu25-8994, 2025.
A Seismic While Drilling (SWD) experiment, using a diamond impregnated drill bit has been conducted within the framework of the ICDP expedition 5071, Drilling the Ivrea-Verbano zonE (DIVE), during the drilling of borehole 507_1_A into the lower continental crust of the Ivrea zone (Megolo, Piedmont, Italy). The rotational grinding action of the diamond drill bit on the rock acts as a seismic source within the borehole. Ideally, this would enable real-time imaging of the subsurface directly around the drill bit without the need for separate active seismic surveys. This vibrational signal is known to be weak and the SWD experiment aims to evaluate the potential and limitations of the SWD method for such diamond core drilling commonly used in scientific drilling projects. The study focuses on fundamental developments of the methodology and data processing techniques. For the experiment, 45 three-component sensors were deployed at a 10-m-spacing along a straight line at the surface. The drill rig is located on top of a ca. 60-m-thick sedimentary wedge overlying the hard rocks of interest. The sensor line is approximately 50 m offset from the drill rig and runs entirely on bedrock. Passive seismic data were recorded from mid-November 2023 to late March 2024 at a sampling rate of 1 ms, with the drilling operation reaching a depth of almost 910 m. The seismic data are heavily contaminated by coherent and random noise generated at the drill site, including rig engines, mud-pumps, vehicles, and the handling of equipment. As a first step, we aim to spatially detect the (known) drill bit position using seismic interferometry and migration (back-projection). Cross-coherence interferograms were computed in 30-second time windows and then stacked to enhance the signal-to-noise ratio. Instead of summing the migrated signals, we use the semblance of the signals. The major noise sources that are imaged with the passive seismic data are the vibrations of the drill rig, which appear to mask the weaker signal from the drill bit. For comparison, we also conducted a reverse vertical seismic profile (RVSP) experiment with a borehole sparker source deployed in a depth range between 65 and 305 m. For this depth range, the RVSP data provide velocity constraints required for the imaging. The velocity model derived from the RVSP data likely improves the localization of the drill bit. Since seismic wave propagation is sensitive to velocity variations, having more accurate velocity constraints reduces ambiguity in the migration and interferometry steps. The clear signals from the sparker also help to validate the method under more controlled and favourable conditions. The detection of the (known) sparker position was done using the same method as for the drill bit, with the advantage that the sparker signal is not contaminated by noise sources from the drilling operation.
How to cite: Trabi, B., Bleibinhaus, F., and Greenwood, A.: Seismic While Drilling with a Diamond Core Drill Bit during ICDP Expedition 5071_1_A (DIVE) in the Ivrea-Verbano Zone (Western Alps, Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10925, https://doi.org/10.5194/egusphere-egu25-10925, 2025.
Volcanoes generate complex seismic wavefields due to their heterogeneous geological structure, making it challenging to obtain accurate reflection images of their interiors. However, understanding the internal structure and dynamics of volcanoes is essential for enhancing monitoring capabilities and improving eruption forecasting. In this study, we apply controlled-source seismic techniques to passive reflection imaging at Krafla volcano, NE Iceland. Krafla is globally recognised as one of the few sites where magma was directly encountered during drilling at the IDDP-1 borehole at a depth of 2.1 km. Using the known magma location as a reference, we employ common-depth-point binning and stacking for preconditioned seismic data from over 300 earthquakes recorded by more than 100 short-period (5 Hz) seismic nodes. At first, we computed theoretical arrival times for various P- and S-wave reflections, including both primary and multiple reflections, using a ray-tracing algorithm and local 1D velocity models. The computational domain was discretized between the surface and a depth of 6 km, using a grid of 80x80x20 m cells. For each grid cell, common-depth-point gathers were generated, and amplitudes were stacked along the reflection trajectories. We further use synthetic waveforms to systematically evaluate the challenges and limitations of this approach in our study area. We observe that the specific distribution of earthquakes and stations causes direct waves (e.g., P- and S-waves) to constructively interfere, creating spurious reflectors in the imaging results. To mitigate this effect, we exclude time windows corresponding to the arrival of direct waves. We also investigate the effect of various waveform attributes—such as absolute amplitudes, envelopes, and their derivatives—on the stacking process and the final imaging results. Preliminary results indicate that the second derivative of seismic trace envelopes might be particularly useful in complex environments characterized by a high degree of incoherent scattering and diverse earthquake source mechanisms. This approach has successfully revealed several discontinuities at shallow depths, offering new insights into the local structure of the Krafla geothermal system.
How to cite: Maaß, R., Li, K. L., Bean, C. J., Schwarz, B., and Lokmer, I.: Adapting Controlled-Source Seismic Techniques for Earthquake Reflection Imaging in Complex Environments: Insights from Krafla Volcano, NE Iceland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13493, https://doi.org/10.5194/egusphere-egu25-13493, 2025.
How to cite: Bordes, C., Gaubert-Bastide, T., Garambois, S., Collet, O., Voisin, C., and Brito, D.: Monitoring water content variations from seismic noise in a controlled laboratory experiment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15586, https://doi.org/10.5194/egusphere-egu25-15586, 2025.
