Earthquake Processes Along Oceanic Transform Faults

This dissertation investigates the seismicity and rupture behavior of earthquakes occurring along oceanic transform faults (OTFs), with a particular focus on the integration of hydroacoustic observations (T-waves). Oceanic transform faults are a key plate boundary structure, yet their rupture processes and mechanical properties remain less understood than those of continental faults. This work aims to address these gaps by combining observations along different OTFs.

A central contribution of this thesis is the demonstration that hydroacoustic T-waves provide a robust and quantitative tool for the constraining of rupture parameters of earthquakes occurring along the OTFs. Analysis of 47 strike-slip events (Mw > 5.6) along OTFs in Atlantic Ocean reveals that rupture lengths are systematically larger than those observed in continental lithosphere for earthquakes with the same respective magnitude. This finding is further supported by the detailed study of the 2020 Mw 6.6 Vernadsky earthquake, where the aftershock distribution indicates a rupture propagation that exceeds the prediction from classical scaling relationships. These results suggest that the OTFs are mechanically weaker than continental faults, likely due to hydration and serpentinization processes within the oceanic lithosphere.

This thesis also provides new insights into the thermal and rheological structure of the OTFs. The analysis of seismicity along the St. Paul Transform System, Atlantic Ocean, demonstrates that nucleation of the earthquakes occurs to greater depths in the central area of the OTFs offsets, with temperatures reaching up to 600-900 °C. These observations contradict existing geodynamic models that predict warmer and weaker conditions at the central area of the OTFs, instead supporting the presence of locally cooler and hydrated area that promote enhanced brittle behavior.

Beyond the OTFs, this work highlights the broader application of the hydroacoustic methods. The study of the 2025 Mw 6.5 Jan Mayen earthquake shows that the longer ruptures lengths of the earthquakes along the OTFs can also trigger slope failures on land, which generates infrasound signals that can be used to identify and locate these secondary cryospheric processes, using the same approach applied on hydroacoustic observations.