Faulting of rocks at three-dimensional stress field by micro-anticracks

Using 9-sets of different laboratory earthquake tests, we examined the nature of cracking under true triaxial stress conditions in the lithosphere . We found that 3D stress state can induce oblique nucleation of many fractures, forming final plane of complex polymodal faults. Our fully 3D experiments indicate unconventional fault nucleation with 2-3 times faster slip phase, implying a new slip-weakening mechanism for earthquakes in upper crust. In addition, We compared our observations of irregular cracks with typical anti-cracks signals in multi-anvil High Pressure and Temperature test. For the first time, we showed oblique faulting can change slip-weakening rate and accelerate the rate of energy release. This implicates a sharper source time function for further modeling of our experiments. Indeed, our results can be assumed as an ex tension to detachment fronts in micro-faults to a general concept of quasi-anti rupture fronts. We showed events from deep-focus earthquakes can share some similarity to shallow earthquakes, promoting recent approach on similarity of deep earthquakes to their shallow counterparts .