Earthquakes in the American state of Utah, the Soultz-sous-Forêts region of France or in the Dutch province of Groningen should not be able to occur even if the subsurface has been exploited for decades. This is because the shallow subsurface behaves in such a way that faults there become stronger as soon as they start moving. At least that is what geology textbooks teach us. And so, in theory, it should not be possible for earthquakes to occur. So why do they still occur in such nominally stable subsurfaces?
