The Balmuccia fault, situated in Italy, is a thin line of glass formed during an earthquake which occured millions years ago, several kilometers underground and eventually surfaced during the formation of the Alps. This bearly visible line is studied by Alexandre Schubnel and his team from the Geology Laboratory of Paris Ecole Normale Supérieure (France). This series of images completed in 2015 is the result of the photographer’s collaboration with the scientists to produce a precise mapping of the fault, as well as proposing a personal, visual extension of the story. The Fault is the second chapter of a photographic trilogy on physical science, started in 2010 with astrophysics (A Black Matter, published in 2012 by Journal/F93). It will end in 2017 with a final chapter covering the field of glaciology.