The generation of large and small earthquakes due to weak fault zone deformation

Peng Zhai, Yihe Huang, & Jean-Paul Ampuero

Submitted September 7, 2025, SCEC Contribution #14377, 2025 SCEC Annual Meeting Poster #TBD

Major faults can produce both large and small earthquakes. The variation in earthquake sizes is commonly linked to heterogeneities on the fault itself such as seismogenic asperities and rupture barriers that influence the ultimate size of an earthquake. Traditionally, earthquake mechanics is considered to occur principally on the localized main fault plane, with the surrounding rocks experiencing only elastic deformation. However, natural fault zones are structurally complex systems with fractures and faults of various length scales. Observations have shown that earthquakes are also associated with inelastic deformation and changes in the elastic properties of the distributed fault zone. The long-term interaction between the main fault slip and the characteristics of bulk fault zone deformation is still not well understood. In this study, we present a crustal-scale seismic cycle model that incorporates the spontaneous development of fault zone damage, which can produce both large and small earthquakes within a single framework. The dynamic interaction between the main fault slip and fault zone damage leads to a cascading sequence of seismic events, including foreshocks, mainshocks, and aftershocks. The simulated earthquakes reproduce several key features of real earthquakes, such as the power-law distribution of earthquake magnitudes, magnitude-invariant static stress drop, and scaling of breakdown energy (also known as fracture energy). Moreover, we discovered that low material strength within the fault zone is required for generating multiscale seismicity, indicating that many natural fault zones may be inherently weak. Overall, our findings suggest that the coevolution of earthquakes and fault zone deformation is a fundamental mechanism that governs the occurrence of both large and small earthquakes.

Key Words
Seismic cycle, Damage rheology, Magnitude frequency distribution, Stress drop, Fracture energy

Citation
Zhai, P., Huang, Y., & Ampuero, J. (2025, 09). The generation of large and small earthquakes due to weak fault zone deformation. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)