Overview
Accurate and consistent analysis of seismic data is essential for understanding both natural and potential injection-induced seismicity in the North Sea. However, current approaches vary between countries and institutions, leading to differences in detection capability, event characterisation and reported earthquake catalogues.
SAFE-C addresses these challenges by developing advanced, harmonised workflows for the analysis of seismological data, combining established techniques with new approaches in machine learning and uncertainty quantification.
Seismic data integration
Seismic data used in SAFE-C originate from a variety of sources, including:
- National onshore seismic networks
- Offshore sensors and ocean-bottom instruments
- Fibre-optic Distributed Acoustic Sensing (DAS) systems
A key task is to integrate these heterogeneous data streams into a unified framework. This enables consistent processing and improves the overall quality and completeness of seismic observations across the North Sea.
Event Detection and Characterisation
Detecting small seismic events in offshore environments is challenging due to noise and limited station coverage. SAFE-C develops improved workflows that:
- Enhance the detection of weak seismic signals
- Automatically identify seismic phases in continuous data
- Improve the estimation of earthquake parameters such as location, magnitude and depth
These advances contribute to more complete and reliable earthquake catalogues.
Machine Learning Approaches
SAFE-C applies modern machine learning methods to support seismic data analysis, including:
- Automated event detection in continuous waveform data
- Phase picking to identify key seismic signals
- Classification of seismic events to distinguish natural earthquakes from other sources
These methods are adapted specifically to the conditions of the North Sea, where noise characteristics and signal properties differ from typical onshore environments.
Harmonisation of Earthquake Catalogues
Seismological agencies around the North Sea currently use different methodologies for detecting and reporting earthquakes. This can lead to inconsistencies in:
- Event locations
- Magnitude estimates
- Catalogue completeness
The harmonisation of these catalogues is one of the core tasks of SAFE-C, resulting in a consistent and unified North Sea earthquake catalogue. This is essential for reliable interpretation of seismicity and for communication with stakeholders.
Uncertainty and Reliability
Understanding the uncertainty of seismic observations is critical, particularly when assessing potential risks related to CO₂ storage. SAFE-C focuses on:
- Quantifying uncertainties in earthquake locations and magnitudes
- Evaluating the influence of velocity models and data quality
- Providing probabilistic descriptions of seismic parameters
This allows for more robust interpretation and supports risk-informed decision-making.
Monitoring Subsurface Changes
In addition to detecting earthquakes, SAFE-C explores methods to monitor changes in the offshore subsurface, for example, related to pressure variations or fluid movement. This includes:
- Analysis of ambient seismic noise from OBS and DAS cables
- Tracking temporal changes in seismic velocities
These approaches provide complementary information for assessing reservoir behaviour and integrity.
Case Studies
The monitoring technologies and strategies developed in SAFE-C are tested and validated at selected CO₂ storage sites in the North Sea.