Unveiling Tectonic Deformation in El Salvador Through GNSS and InSAR Kinematic Modelling

Abstract. The El Salvador Fault Zone (ESFZ) accommodates most of the differential motion between the Central America Volcanic Forearc and the Chortís block in Central America. By combining recent Global Navigation Satellite System (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) observations, we develop the first kinematic block model for El Salvador that jointly inverts both data types. The model refines previous regional studies by resolving slip partitioning within the ESFZ and its continuations in Guatemala and the Gulf of Fonseca. Our preferred model predicts total slip rates of about 14 mm yr⁻¹ across the central ESFZ, distributed between a northern branch (5–8 mm yr⁻¹ dextral, 3–7 mm yr⁻¹ normal) and a southern branch (2–6 mm yr⁻¹ dextral). Dextral motion decreases toward the Jalpatagua Fault in Guatemala and toward the San Miguel Fault in eastern El Salvador, increasing again along the Marrabios Fault in Nicaragua. Subduction coupling beneath El Salvador appears weak (Φ≈0.2) and confined to shallow depths, strengthening westward into Guatemala. These results highlight a strongly coupled volcanic arc and a weakly coupled subduction interface. Future seafloor geodetic measurements and new radar satellite missions could improve constraints on slab coupling and crustal deformation processes in this seismically active region.