Source Characteristics of the Mw 4.3 and Mw 4.4 Central San José Earthquakes Derived from Empirical Green’s Functions, Costa Rica

We investigated the source characteristics of the August 22, 2025 (Mw 4.3) and January 19, 2026 (Mw 4.4) San José earthquakes in Costa Rica. Although moderate in magnitude, both events occurred at a shallow depth (~4.0 km) beneath the central urban area of the capital city. They produced strong ground shaking with peak ground accelerations reaching approximately 230 gal. Using small aftershocks as Empirical Green’s functions (EGFs), we estimated the size of the strong‑motion generation areas (SMGAs), rise time, rupture velocity, and associated stress drop for each event. Despite their similar magnitudes, the two earthquakes exhibit notable differences in SMGA size and stress drop, which appear to control the spatial distribution of observed acceleration.