With the development of several CO₂ storage operations in the North Sea, there is a clear need to better characterise the seismic hazard and stress state in the region. Faults and associated fracture sets can act as hydraulic pathways for unintended CO₂ migration, ill-defined stress states can lead to numerous operational difficulties, and induced seismicity will be a clear risk as CO₂ is injected into subsurface reservoirs. Seismicity can reveal the location and extent of faults and fractures, and can be used to invert for the state of stress. Both operators and regulators therefore need a clear understanding of the rate of natural seismicity, to identify and distinguish induced events from natural, and to assess the likelihood of induced fault reactivation. This requires a dedicated, site specific background monitoring programme, as well as a high-quality seismic catalogue for the region around any CO₂ storage operation. Our study has produced the first dedicated seismic catalogue of the North Sea, based on all available data from each of the relevant seismological agencies. This dataset fosters further studies into seismic hazard, leakage risk, and stress state in a region that will be vital for European CO₂ storage efforts in the coming decades.

Continental rupture processes under mantle plume influence are still poorly known although extensively studied. The Gulf of Aden presents volcanic margins to the west, where they are influenced by the Afar hotspot, and non volcanic margins east of longitude 46° E. We imaged the crustal structure of the Gulf of Aden continental margins from Afar to Oman to evaluate the role of the Afar plume on the evolution of the passive margin and its extent towards the East. We use Ambient Noise Seismic Tomography to better understand the architecture and processes along the Gulf of Aden. This recent method, developed in the last decade, allows us to study the seismic signal propagating between two seismic stations. Ambient Noise Seismic Tomography is thus free from artifacts related to the distribution of earthquakes. We collected continuous records from about 200 permanent or temporary stations since 1999 to compute Rayleigh phase velocity maps over the Gulf of Aden.