Earthquake Nucleation Size: Evidence of Loading Rate Dependence in Laboratory Faults

Area of Science:

• Geophysics
• Earthquake Science
• Rock Mechanics

Background:

• Recent earthquake observations show slow preslip phases preceding dynamic rupture.
• Theoretical models and laboratory experiments have advanced understanding of earthquake nucleation.
• However, factors controlling preslip prevalence and slip amount remain unclear.

Purpose of the Study:

• To investigate the influence of loading rate and fault surface properties on earthquake nucleation.
• To observe slow slip preceding dynamic rupture in a laboratory setting.
• To determine how loading rate affects nucleation size and position.

Main Methods:

• Utilized a laboratory setup with two polycarbonate plates under direct shear.
• Simulated earthquake nucleation processes on a 30-cm long slip interface.
• Varied the shear loading rate from 10⁻² to 6 MPa/s.

Main Results:

• Observed slow slip preceding dynamic rupture, consistent with existing models.
• Demonstrated that increased loading rate significantly reduces nucleation length (by a factor of 3).
• Found that ruptures consistently nucleate in areas of higher shear stress.

Conclusions:

• Loading rate is a critical factor controlling earthquake nucleation size and position.
• Laboratory results align with theoretical predictions for rate-and-state friction laws.
• Further research is needed to incorporate fault inhomogeneities and their effect on rupture nucleation.