The Role of Stress Transfer in Rupture Nucleation and Inhibition in the 2023 Kahramanmaraş, Türkiye, Sequence, and a One-Year Earthquake Forecast

We probe the interaction of large earthquakes on the East Anatolian fault zone, site of four Mw ≥ 6.8 events since 2020. We find that the 2023 Mw 7.8 Pazarcık shock promoted the Mw 7.7 Elbistan earthquake 9 hr later, largely through unclamping of the epicentral patch of the future rupture. Epicentral unclamping is also documented in the 1987 Superstition Hills, 1997 Kagoshima, and 2019 Ridgecrest sequences, so this may be common. The Mw 7.7 Elbistan earthquake, in turn, is calculated to have reduced the shear stress on the central Pazarcık rupture, producing a decrease in the aftershock rate along that section of the rupture. Nevertheless, the Mw 7.7 event ruptured through a Çardak fault section on which the shear stress was decreased by the Mw 7.8 rupture, and so rupture propagation was not halted by the static stress decrease. The 2020 Mw 6.8 Doğanyol–Sivrice earthquake, located beyond the northeast tip of the Mw 7.8 Pazarcık rupture, locally dropped the stress by ∼10 bars. The 2023 Mw 7.8 earthquake then increased the stress there by 1–2 bar, leaving a net stress drop, resulting in a hole in the 2023 Pazarcık aftershocks. We find that many lobes of calculated stress increase caused by the 2020–2023 Mw 6.8–7.8 earthquakes are sites of aftershocks, and we calculate 5–10 faults in several locations off the ruptures brought closer to failure. The earthquakes also cast broad stress shadows in which most faults were brought farther from failure, and we observe the beginnings of seismicity rate decreases in some of the deepest stress shadows. Some 41 Mw ≥ 5 aftershocks have struck since the Mw 7.8 mainshock. But based on these Coulomb interactions and on the rapid Kahramanmaraş aftershock decay, we forecast only about 1–3 Mw ≥ 5 earthquakes during the 12–month period beginning 1 December 2023, which is fortunately quite low.