Longer Migration and Spontaneous Decay of Aseismic Slip Pulse by Fault Roughness

It has been known that natural faults possess rough profiles, which may play a vital role in earthquake dynamics. Here we examine the effect of fault roughness in the earthquake nucleation process using the rate and state friction law with the slip evolution law. The nucleation process on rough faults behaves as accelerating and migrating aseismic slip pulse, which is similar to previous studies for flat faults. However, the migration distance on rough faults is much larger than flat faults. The effect of fault roughness on the aseismic slip pulse migration is described by a single parameter known as the roughness drag, which depends on the amplitude, the minimum wavelength, and the Hurst exponent of the fault roughness profile. We also show that aseismic slip pulse cannot accelerate to dynamic rupture and ceases spontaneously if the roughness drag exceeds the static stress drop. Plain Language Summary Natural faults possess complex geometry. Even nominally flat segments of them are actually rough. We investigate how earthquakes prepare themselves on such rough faults using numerical simulation. We find that slow slip propagates longer distance on a rougher fault before the onset of an earthquake, implying that a larger energy is released during the preparation phase. We further show that a fault cannot slip fast enough to emit seismic waves if the fault roughness exceeds a critical level. This may be a possible mechanism of slow earthquakes.