The April 1928 seismic sequence in the Maritsa River valley of southern Bulgaria, comprising the Chirpan (Mw 6.9) and Plovdiv (Mw 7.1) earthquakes, represents one of the most destructive events in southeastern Europe. Previous studies have constrained the overall fault geometry and kinematics using macroseismic data and geodetic measurements; however, the internal heterogeneity of the rupture remains poorly resolved. Contemporary models indicate that seismic rupture is an inherently heterogeneous process, characterized by localized zones of intense slip (asperities) that influence rupture propagation and energy release. Probabilistic slip models enable the reconstruction of such historical events under conditions of limited data and can be integrated with geological and geophysical information. Gravity and magnetic anomaly data from the Chirpan–Plovdiv region reveal significant lateral heterogeneity in the Earth’s crust, which likely governs the development and termination of rupture processes.