Seismic noise interferometry for stress analysis

Informations projet

SIRENS

N° de convention de subvention: 101209608

DOI

10.3030/101209608

Date de signature de la CE 12 Mars 2025

Date de début 1 Avril 2025

Date de fin 31 Mars 2027

Financé au titre de

• Marie Skłodowska-Curie Actions (MSCA)

Coût total

Aucune donnée

Contribution de l’UE

€ 194 074,56

Coordonné par

AGENCIA ESTATAL CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS
Spain

Periodic Reporting for period 1 - SIRENS (Seismic noise interferometry for stress analysis)

Période du rapport: 2025-04-01 au 2027-03-31

Résumé du contexte et des objectifs généraux du projet

Many key challenges linked to the energy transition and environmental safety involve the subsurface. These include geothermal energy, carbon storage, mining, and the assessment of geological hazards. In all these cases, understanding how rocks are stressed underground is essential, because stress influences how fractures open or close, how faults may reactivate, and how the subsurface responds to natural or human-induced changes.

One particularly important parameter is the orientation of the maximum horizontal stress (SHmax). This information is commonly obtained from boreholes or other local measurements, which can be expensive, invasive, and spatially limited. As a result, there is a strong need for alternative methods that are less intrusive and can potentially be applied over broader areas.

The SIRENS project explored a passive seismic approach to this problem. The idea behind the project was to investigate whether very small changes in seismic wave velocity, driven by solid Earth tides and measured through ambient seismic noise correlations, could be used to infer stress orientation in the Earth’s crust. Ambient seismic noise is continuously generated by natural and human activity, while solid Earth tides produce small but regular stress variations caused by the gravitational pull of the Moon and the Sun. Together, these signals offer a promising way to probe the mechanical behaviour of the subsurface without active sources or drilling.

The project focused on the Iberian Peninsula, a region with diverse tectonic settings, abundant seismic data, and high relevance for georesources and geohazards. Its overall objectives were to refine the methodological framework required for this type of analysis, test its applicability at regional scale, and explore its potential at smaller spatial scales.

In the longer term, this research line could contribute to the development of new non-invasive tools for subsurface monitoring. Such approaches are relevant to European priorities linked to sustainable resource use, low-impact monitoring, and a better understanding of geological processes affecting environmental safety and the energy transition.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

During the project, a methodological framework was developed to analyse very small seismic velocity variations associated with tidal stresses using ambient seismic noise recordings. This involved compiling and preparing a large dataset of seismic stations across the Iberian Peninsula and developing computational workflows to process continuous seismic data and retrieve correlations between stations.

Several signal-processing strategies were tested in order to obtain stable measurements of seismic velocity variations. In particular, different correlation approaches and stacking techniques were evaluated to determine which methods provide the most reliable results when analysing long time series of ambient seismic noise.

The methodology was then applied to seismic networks across the Iberian Peninsula to investigate whether tidal-induced velocity variations could reveal the orientation of the maximum horizontal stress. These analyses provided important insights into the practical challenges of applying this approach at large spatial scales.

The results showed that the distribution of seismic noise sources can introduce directional biases in the measurements obtained from ambient noise correlations. In addition, seismic wave paths often cross geological regions with different mechanical properties, which can also influence the observed velocity variations. These factors can produce azimuthal patterns that may mask the stress-related signal that the method aims to detect.

Although these effects complicate the direct estimation of stress orientation at regional scale, the project significantly improved the understanding of the methodological conditions required for this type of analysis. The results highlight the importance of selecting geomechanically homogeneous areas and well-distributed seismic station geometries when applying this approach.

Overall, the work carried out during the project established a computational and methodological basis for future developments of passive seismic approaches aimed at imaging the stress field direction in the Earth’s crust.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

The SIRENS project contributed to advancing the understanding of how tidal-induced seismic velocity variations derived from ambient noise correlations can be used to investigate stress conditions in the Earth’s crust. While previous studies had demonstrated that tidal stresses can produce measurable velocity variations in seismic waves, the project explored the feasibility of using these observations to infer stress orientation at regional scales.

The analyses carried out during the project provided new insights into the methodological constraints affecting this approach. In particular, the results highlight the strong influence of the distribution of seismic noise sources on the measurements obtained from ambient noise correlations. Anisotropic noise source distributions can introduce directional biases in the estimated velocity variations, potentially masking the stress-related signal that the method aims to detect.

In addition, the study showed that geological heterogeneity along seismic wave propagation paths can significantly affect the observed velocity variations. When seismic correlations involve stations located in geologically different regions, the resulting measurements may reflect structural contrasts rather than regional stress conditions. These findings refine the current understanding of the requirements to apply this methodology successfully.

Further research is needed to improve the robustness of the methodology, including the development of strategies to mitigate the influence of anisotropic noise sources and to better constrain the spatial sensitivity of the measurements. Continued methodological development and testing in suitable geological settings will be important to fully evaluate the potential of this passive seismic approach for monitoring stress variations in the subsurface.