Lifeng Wang, State Key Laboratory of Earthquake Dynamics, China Earthquake Administration

Fault asperity is often deemed to be responsible for occurrences of seismic clusters, repeating earthquakes, or concentrated slip during large events. However, because of the inaccessible fault surface, its possible presence and relevant role in mechanical controls are still based on indirect inferences from fault activities, and a direct measure of the roles of fault asperity is still missing. Here, we take the advantage of a rock experiment about two half-meter granite plates with apparent asperity structures. Acoustic emission and fault slip measurements, assisted by numerical simulation, unveil asperity acting as a mechanical attractor to small events during the interseismic phase, while as a barrier to slow slip during the mainshock nucleation. The slip deficit long hosted by asperity is finally filled up, producing the largest coseismic slip there. The full scenario unfolds how fault asperity partitions stress in both temporal and spatial domains, constituting a physical link about the background seismicity, foreshocks, preseismic slow slip and the characteristic mainshock.