Despite their likely global importance, the large areas where transform faults and fracture zones occur are still underexplored, as are the coupling mechanisms between seismic activity, fluid flow, and life. Moreover, up- or downwelling of fluids within the complex system of fractures and seismogenic faults along MTFFZs could modify earthquake cycles and/or serve as “detectors” for changes in the stress state during interseismic phases. Chemicals transported upward in MTFFZs include energy substrates, such as H 2 and volatile hydrocarbons, which then sustain chemosynthetic, microbial ecosystems at and below the seafloor. In fact, they may act as conduits mediating vertical fluid flow and leading to elemental exchanges between Earth’s mantle and overlying sediments. Earthquakes at MTFFZs furthermore open and sustain pathways for fluid flow triggering reactions with the host rocks that may permanently change the rheological properties of the oceanic lithosphere. Historical examples are the Sumatra-Wharton Basin Earthquake in 2012 (M8.6) and the Atlantic Gloria Fault Earthquake in 1941 (M8.4). Together with the continental counterparts of MTFFZs, these structures also pose a risk to human societies as they can generate high magnitude earthquakes and trigger tsunamis. Marine transform faults and associated fracture zones (MTFFZs) cover vast stretches of the ocean floor, where they play a key role in plate tectonics, accommodating the lateral movement of tectonic plates and allowing connections between ridges and trenches.

21Integrated Geochemical Interpretation Ltd., The Granary, Hallsannery, Bideford, United Kingdom.

20LOCEAN, UPMC, Sorbonne Université, Paris, France.

19Hellenic Centre for Marine Research, Institute of Oceanography, Anavyssos, Greece.

18MARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany.

17EMCOL and Faculty of Mining, Department of Geological Engineering, İstanbul Technical University, Istanbul, Turkey.

16Department of Earth Sciences, University of Geneva, Geneva, Switzerland.

15Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Trieste, Italy.

14CNR, Institute of Marine Sciences (ISMAR), Bologna, Italy.

13Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.

12Barcelona-CSI, Institut de Ciències del Mar (CSIC), Barcelona, Spain.

11CNRS, IUEM, Laboratoire Géosciences Océan, University of Western Brittany, Brest, France.

10Department of Geosciences, University of Bremen, Bremen, Germany.9Aix Marseille Univ, CNRS, IRD, INRA, Coll France, CEREGE, Aix-en-Provence, France.8Institut Français de Recherche pour l’Exploitation de la Mer (IFREMER), Département Ressources Physiques et Ecosystèmes de Fond de Mer, Unité des Géosciences Marines, Plouzané, France.7IPMA- Portuguese Institute for Atmosphere and Ocean, Lisbon, Portugal.6Department of Environmental Systems Science, ETH Zürich, Zurich, Switzerland.5Centre for Earth Evolution and Dynamics (CEED), University of Oslo, Oslo, Norway.4Dipartimento di Scienze della Terra, Università di Firenze, Firenze, Italy.3Earth Sciences Department, Royal Holloway, University of London, Egham, United Kingdom.2Instituto Dom Luiz (IDL), Faculdade de Ciências da Universidade de Lisboa, Lisbon, Portugal.1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.Karageorgis 19, Livio Ruffine 8, Volker Liebetrau 1, Catherine Pierre 20, Christopher Schmidt 1, Luis Batista 2,7, Luca Gasperini 14, Ewa Burwicz 1, Marta Neres 2,7 and Marianne Nuzzo 21

Namık Çağatay 17, Marcus Elvert 18, Dimitris Sakellariou 19, Luis Matias 2, Rolf Kipfer 13, Aristomenis P. Lever 6, Pedro Terrinha 2,7, Louis Géli 8, Pierre Henry 9, Heinrich Villinger 10, Jason Morgan 3, Mark Schmidt 1, Marc-André Gutscher 11, Rafael Bartolome 12, Yama Tomonaga 13, Alina Polonia 14, Eulàlia Gràcia 12, Umberta Tinivella 15, Matteo Lupi 16, M.

Duarte 2, Paola Vannucchi 3,4, Adriano Mazzini 5, Mark A.

Transform fault