Stress-field evolution during the 26 November 2019 Durrës (Albania) earthquake sequence: Co-seismic, early post-seismic, and tectonic-region inversions

We resolve the stress field associated with the 26 November 2019 Mw 6.3 Durrës earthquake sequence through three windows: the co-seismic mainshock, the early post-seismic phase (mainshock plus the 36 largest aftershocks recorded between 26 November and 2 December 2019), and a regional tectonic subset of 27 moderate-magnitude events. The co-seismic stress tensor is obtained by inverting the moment-tensor solutions reported by the contributing agencies for the mainshock. In contrast, the regional and immediate post-seismic stress fields are derived from previously published focal-mechanism and moment-tensor solutions, both from the existing report and from the continuously updated archive of mechanisms for the sequence, using the StressInverse methodology and assuming both nodal planes where required. Regional inversions define a persistent WSW-ENE compressional regime with a shallowly plunging ai axis and a steeply plunging σ3 axis. The early sequence preserves this compression orientation but shifts to lower ϕ and μ values (ϕ ≈ 0.546; u ≈ 0.45), indicating transient coseismic relaxation and short-lived stress redistribution following the mainshock. These changes imply a temporary reduction in deviatoric stress and a more oblate post-seismic configuration without rotation of the principal-stress axes. The TENSOR solution confirms reverse-faulting kinematics for the mainshock, and the recovered σ1 azimuth (≈239–248°) is consistent with present-day Adria–Eurasia convergence and the mapped thrust architecture of the Outer Albanides. Transient changes in ϕ and μ are consistent with short-lived coseismic relaxation and apparent weakening during rupture.