Dike-Induced Earthquakes as Probes of the Local Stress Field Prior to the 1998 Eruption of the Piton de la Fournaise Volcano, La Reunion

Volcano-tectonic (VT) earthquakes can occur during the movement of magma when it exerts pressure on surrounding rock. During the 1998 dike-fed eruption at Piton de la Fournaise (PdF), over 500 VT events were documented, offering a rare chance to analyze the volcano's stress conditions. We derived double-couple fault plane solutions (FPS) for these events. The main orientation of the compressional (P) axes varied with depth: between approximately 2 and 6 km below sea level, the P-axes were vertical, while above 2 km BSL, they became horizontal. This horizontal orientation is perpendicular to regional compression at depths of 0–2 km BSL, then aligns with regional compression between 0–2 km above sea level. By integrating edifice loading with stress alterations from dike activity through an innovative damage-based model for dike propagation, we examined various factors influencing the stress field at PdF, including rock strength, density, and magma viscosity, thereby enhancing our understanding of the volcano's stress state before an eruption.