What Happens When Two Ruptures Collide?

We investigate the interaction between two rupture fronts as they propagate toward each other and ultimately collide. This phenomenon was observed during laboratory experiments conducted on poly methyl methacrylate. Subsequently, we used numerical simulations to elucidate key aspects of these observations and draw broader conclusions. Our findings indicate that the collision of the rupture fronts generates interface waves that propagate along the sliding interface at the Rayleigh wave speed. Additionally, the rupture fronts interact with the starting and stopping S‐wave phases radiated by the opposite rupture fronts, which can locally change their velocity and generate additional interface waves. We discuss the implications of these results for understanding earthquake source phenomena. Plain Language Summary: Earthquakes are caused by sudden and rapid sliding along tectonic faults. Sliding generally begins at a specific location, the hypocenter, and then expands over the fault. The manner in which this expansion occurs determines the properties and severity of the shaking generated by the earthquake. The edge of the slipping zone is called the rupture front. If the rupture front becomes very distorted, it might arrive in an area of the fault from two different sides and coalesce. In this study, we conducted experiments and numerical simulations to understand what happens when two rupture fronts propagate toward each other and collide. We show that the two rupture fronts disappear upon collision, and produce a specific type of wave that propagates along the sliding surface, called interface waves. Both the rupture front and the waves emitted by the opposing rupture front interact, which can alter the rupture front's speed and create additional interface waves. If similar waves were observed during real earthquakes, they could provide valuable information about the friction between fault rocks. Key Points: We present a unique experimental observation of the collision of two mode II rupture frontsThe collision radiates interface waves that propagate at the Rayleigh wave speed along the sliding interfaceInterface waves are also generated when stopping waves enter the sliding area of the opposite rupture [ABSTRACT FROM AUTHOR]