Foreshock-induced slip transients set mainshock nucleation timing

Area of Science:

• Geophysics
• Seismology
• Earthquake Science

Background:

• Foreshocks preceding earthquakes are observed but their role in rupture nucleation is unclear.
• Classical earthquake models often overlook impulsive precursory events, focusing on slow slip and fault weakening.

Purpose of the Study:

• To investigate how foreshocks regulate earthquake initiation and rupture nucleation.
• To establish a link between foreshock characteristics and subsequent earthquake behavior.

Main Methods:

• Laboratory experiments simulating fault slip.
• Development of a rate-and-state-based Griffith-like rupture framework.
• Theoretical extension to tectonic faults and analysis of natural earthquake data.

Main Results:

• Foreshocks, occurring during nucleation, fundamentally regulate earthquake initiation.
• Foreshock-induced slip bursts generate a transient velocity (Vmin) that predicts nucleation duration and spatial length.
• Larger foreshocks lead to higher Vmin and faster dynamic rupture; smaller ones cause slower growth or arrest.
• Foreshock scaling observed in laboratory experiments aligns with natural earthquake sequences.
• Constrained realistic nucleation slip distances (0.3-3.0 mm), significantly smaller than dynamic rupture scales.

Conclusions:

• Foreshock-induced transients are critical in setting the timing and detectability of earthquake nucleation.
• The magnitude of foreshock slip directly influences the transition from slow nucleation to dynamic rupture.
• This study refines our understanding of earthquake initiation processes and the role of precursory seismic activity.