The Role of Normal Stress and Shear Stress Heterogeneity in the Inferred Depth-Independence of Stress Drop

Minghan Yang, Valere R. Lambert, & Emily E. Brodsky

Submitted September 7, 2025, SCEC Contribution #14915, 2025 SCEC Annual Meeting Poster #TBD

Earthquake stress drops are inferred to be independent of their source depth, contradicting standard linear scaling predictions for frictional stick-slip models of earthquakes, assuming increasing fault normal stress due to rock overburden. Here, we examine the scaling between averaged stress drops and increasing normal stress for simulated earthquakes sequences in continuum rate-and-state fault models. Our models exhibit a power-law-like scaling that is weaker than the linearity predicted by traditional friction models, and hence asymptotically approaches zero as the ratio of fault length to the nucleation scale increases. This result occurs as the fault dimension becomes increasingly larger than the earthquake nucleation scale with increasing normal stress. Consequently, the averaged behavior of ruptures becomes increasingly dominated by conditions for rupture propagation, reflecting more heterogeneous shear stress conditions. As natural faults can be considerably larger than the smallest earthquakes they host, such weaker scaling between averaged rupture conditions and normal stress may partially explain the lack of an inferred depth dependence of earthquake stress drops.

Key Words
Stress Drop; Normal Stress; Stress Heterogeneity; Numerical Modeling;

Citation
Yang, M., Lambert, V. R., & Brodsky, E. E. (2025, 09). The Role of Normal Stress and Shear Stress Heterogeneity in the Inferred Depth-Independence of Stress Drop. Poster Presentation at 2025 SCEC Annual Meeting.

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