Experimental study on the rupture behaviours of orthogonal faults: Effects of stress state and rupture initiation location

SUMMARY Fault rupture dynamics is expected to be significantly affected by the geometry of fault system, especially for orthogonal faults. However, the rupture behaviours of orthogonal faults, especially the coseismic interactions, are far from fully understood. Here, we present experimental results from a series of laboratory earthquakes to elucidate the effect of the stress state and initiation location on the rupture behaviours of orthogonal faults. Our results reveal a phase diagram of rupture behaviours of orthogonal faults, which is collectively controlled by stress state and rupture initiation location. For events initiating from the main fault, the rupture cannot jump to the branch, which may be due to the clamping effect or the inhibited shear stress accumulation on the branch. On the contrary, events initiating from the branch can persistently trigger ruptures of the main fault. This difference highlights the directional effect associated with the rupture of orthogonal faults. Further, the rupture length of triggered ruptures on the main fault is controlled by the stress state of the fault system. With the increase of the ratio between the shear stress and normal stress, the rupture length of the main fault increases. Our results reproduce the rupture behaviours of orthogonal faults, which may provide insights into the rupture characteristics of natural earthquakes.