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

• Published in: Geophysical research letters Vol. 46; no. 2; pp. 636 - 643
• Main Authors: Ozawa, So W., Hatano, Takahiro, Kame, Nobuki
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28-01-2019
• Subjects: Computer simulation; Distance; Drag; Dynamics; earthquake nucleation; Earthquakes; Evolution; Fault lines; fault roughness; Faults; Geological faults; Mathematical models; Migration; Nucleation; Numerical simulations; P-waves; Profiles; Roughness; Seismic activity; Seismic waves; Slip; Wavelength
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL081465

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.
Key Points
On rough faults, the nucleation sizes of earthquakes are several times larger than flat faults
Dynamic rupture is suppressed if the extent of roughness exceeds a threshold
The effects of roughness are described by a single parameter that depends on the amplitude and the minimum wavelength of the fault profile