Quantitative analysis of the structural controls of faults on induced seismicity magnitude

Informations projet

FINSEIS

N° de convention de subvention: 884931

DOI

10.3030/884931

Projet clôturé

Date de signature de la CE 4 Mars 2020

Date de début 1 Janvier 2021

Date de fin 31 Decembre 2023

Financé au titre de

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Coût total

€ 244 326,72

Contribution de l’UE

€ 244 326,72

Coordonné par

UNIVERSITY COLLEGE DUBLIN, NATIONAL UNIVERSITY OF IRELAND, DUBLIN
Ireland

Periodic Reporting for period 2 - FINSEIS (Quantitative analysis of the structural controls of faults on induced seismicity magnitude)

Période du rapport: 2023-01-01 au 2023-12-31

Résumé du contexte et des objectifs généraux du projet

Induced seismicity refers to earthquakes related to human activity and can be caused by a range of industrial activities involving underground fluid injection operations such as Enhanced Geothermal System (EGS), Carbon Capture and Storage (CCS), Hydraulic Fracturing (HF) and Waste Water Disposal (WWD). Often, it involves a large number of low-moment magnitude earthquakes (Mw<2), but larger earthquakes (Mw>3) also occur. While the low-magnitude earthquakes typically cause limited societal concerns and risks, the larger ones can have a negative impact on the conduct and development of industrial operations. Specifically, hazards due to large magnitude induced seismicity are critical in the context of EGS and CCS operations, which are strategic activities in Europe designed to help diversify energy sources and minimize carbon emissions.

Previous studies aiming at understanding the controls on induced seismicity have been mainly focused on seismological, mechanical and engineering factors. By contrast, our understanding of structural factors, such as fault zone internal geometry, remains limited. In particular, previous forecasting methods typically considered faults as simple planar geometries, disregarding the segmented nature of faults and its potential impact on earthquake magnitude. This project aims to provide a fundamental understanding of fault structural controls on fluid-related seismicity and help integrate realistic fault zone geometry into seismic studies and forecasting methods.

During its three-year duration, the project has focussed on the following specific research objectives: (i) Identify the role of fault segmentation on spatio-temporal event migration. (ii) Quantify the structural control on earthquake rupture dynamic. (iii) Formalize an algorithm for risking IS magnitude integrating realistic fault zone geometry. (iv) Verify and test the role of fault geometry on induced seismicity magnitude for a range of field examples.

By adopting an alternative structural approach, the project provides an empirical, theoretical and numerical basis of fault structural controls on seismicity beyond state-of-the-art and helps improve algorithms for induced seismicity prediction. The findings are policy-relevant and impact the European economy and society because they inform geo-energy field developments, improve risk assessment and reduce investment risk. The project also produces fundamental scientific outcomes and informs research on the links between fault zone processes and earthquakes.

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 three-year duration, we first secured and collated multiple seismicity datasets (>30 datasets), including natural seismicity due to tectonic and volcanic activity and induced seismicity associated with EGS, WWD, CCS and HF, thus providing a range of behaviour and geological settings. Next, we analyzed the datasets, testing multiple advanced approaches, such as automatic clustering, events filtering, point cloud mapping (e.g. Fig. 1), M-T and R-T diagrams, and b-values analysis. In particular, we developed a new approach analyzing swarm's spatio-temporal development based on detailed mapping of isochrone contours on reactivated fault surface (e.g. Fig. 1) and measured fundamental parameters such as step size and maximum magnitude to investigate the conditions for step blocking or transferring deformation quantitatively. Finally, we developed a numerical modelling approach to incorporate realistic fault geometry into IS magnitude prediction. The chosen method relies on a stochastic approach based on quantitative fault zone parameterization and permits the simulation of rupture dynamics based on structural controls. Finally, this method has been tested and validated through best-in-class case studies (i.e. Harrison County, Ohio; Yushu-Ganzi, central-eastern Tibet; and NAF fault, Türkiye) and a sensitivity analysis.

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 project observations support the influence of fault segmentation on event migration and distribution. In particular, we provide new constraints on the role of fault connectivity inherited from 3D segmentation in channelling seismicity and producing 'along-step' and 'across-step' events migration. In addition, we show that such mechanisms depend on event magnitude and migration rate, with around-step migration that is predominant for seismicity development during fluid injection operations. These results, therefore, highlight the requirement to integrate more realistic fault geometries into ongoing analyses to improve our understanding and forecasting of induced seismicity.

In addition to the observational constraints above, the numerical modelling approach developed in this project supports the role of fault segmentation on earthquake magnitude distribution. In particular, modelling results suggest that fault geometry determines the seismic pattern, with rupture length controlled by internal geometry rather than fault lengths. Furthermore, testing the approach on the field cases demonstrates the potential of integrating realistic fault geometry into earthquake studies and seismicity prediction strategies. Overall, the stochastic method helps to tackle imaging issues associated with induced seismicity, and the structural geological perspective complements previous studies using seismology and fracture mechanics approaches.

The project results and findings above have fundamental implications and inform research on the links between fault zone processes and earthquakes, including the factors controlling the location, initiation and arrest of earthquake events. In addition, the project findings directly impact seismic hazard and risk analysis by providing a new basis for establishing potential maximum magnitudes for a wide range of contexts. In particular, the numerical modelling approach permits testing the role of hidden and mapped faults and can inform pre-drilling forecasting methods for fluid-injections operations, including during EGS or CCS projects in Europe.

Figure 1: Example of analysis of seismicity distribution (a) and migration (b).