  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 .
