Mainshock and aftershock sequence simulations in a nonplanar fault network
So Ozawa, University of Tokyo

Aftershocks seem to be located along the trace of the mainshock fault; however, due to the location error, we do not know their exact location relative to the mainshock fault. Here, we hypothesize that most aftershocks occur on small subsidiary faults instead of the mainshock fault, and they are triggered by the local increase of stress due to the rough geometry of the mainshock fault. To explore this scenario, we perform 2-D earthquake sequence simulations considering a rough main fault and numerous subsidiary faults that obey the rate and state friction law. We show that many aftershocks occur at the side of the main fault, delineating the main fault trace. We also show that the roughness of the main fault decreases the concentration of aftershocks around the tip of the mainshock fault. Our numerical simulation reproduces the Omori-Utsu law for the temporal decay of aftershocks and the log-time expansion of the aftershock zone. This is one of the first earthquake sequence simulations based on the continuum mechanics framework that reproduces realistic spatiotemporal aftershock activities.

Rupture styles and recurrence patterns in seismic cycles linked to physical properties of the fault zone
Shiying Nie, University of Southern California

Rupture styles emerge in a broad range of rupture styles, from slow-slip events collocated with or without tremors to pulse-like earthquake sequences. Meanwhile, Earthquake catalogs exhibit various recurrence patterns, from periodic and characteristic earthquakes to chaotic sequences with super-cycles, aftershocks and dissimilar ruptures. The underlying physical mechanisms of these phenomena are usually documented separately and the potential connection between them is poorly understood. Here, we explore a wide range of frictional properties using quasi-dynamic models of seismic cycles in two dimension to assess the link between rupture style and recurrence patterns. We obtain a broad spectrum of rupture behaviors controlled by several non-dimensional parameters, including the Dieterich-Ruina-Rice number R_u, which is the ratio of asperity to a characteristic nucleation size, and R_b, which reflects the relative amplitude of weakening and strengthening effects. Seismogenic slow-slip events are the natural behavior of near-velocity neutral condition (low R_b) with a small characteristic nucleation size (high R_u), which is commonly found below the seismogenic zone. The deviation from periodic and characteristic recurrence behaviors are responses of homogeneous or compliant fault-zone models with high R_u numbers. The presence of a compliant zone can be incorporated into the Ru number in quasi-dynamic simulations. Observations of rupture characteristics and recurrence patterns can bring useful constraints on the physical properties of fault zones.