Progressive failure on the North Anatolian fault since 1939 by earthquake stress triggering

TLDR

10 M ≥ 6.7 earthquakes ruptured 1 000 km of the North Anatolian fault (Turkey) during 1939–1992, providing an unsurpassed opportunity to study how one large shock sets up the next. Using mapped surface slip and fault geometry, the authors infer stress transfer across the sequence and translate the calculated Coulomb failure stress changes into earthquake probability gains via an earthquake‑nucleation constitutive relation that accounts for permanent and transient effects. Coulomb failure stress calculations show that nine of ten ruptures were brought closer to failure by preceding shocks (1–10 bar, 3–30 years of secular stressing), with transient effects dominating the mean 10‑year interval and producing an average three‑fold increase in net earthquake probability; today stress is high at isolated sites, yielding a 15 % chance of a M ≥ 6.7 event east of Ercinzan and 12 % south of Izmit over the next 30 years, indicating that stress‑based probability calculations can help update earthquake hazards.

Abstract

10 M ≥ 6.7 earthquakes ruptured 1000 km of the North Anatolian fault (Turkey) during 1939–1992, providing an unsurpassed opportunity to study how one large shock sets up the next. We use the mapped surface slip and fault geometry to infer the transfer of stress throughout the sequence. Calculations of the change in Coulomb failure stress reveal that nine out of 10 ruptures were brought closer to failure by the preceding shocks, typically by 1–10 bar, equivalent to 3–30 years of secular stressing. We translate the calculated stress changes into earthquake probability gains using an earthquake-nucleation constitutive relation, which includes both permanent and transient effects of the sudden stress changes. The transient effects of the stress changes dominate during the mean 10 yr period between triggering and subsequent rupturing shocks in the Anatolia sequence. The stress changes result in an average three-fold gain in the net earthquake probability during the decade after each event. Stress is calculated to be high today at several isolated sites along the fault. During the next 30 years, we estimate a 15 per cent probability of a M ≥ 6.7 earthquake east of the major eastern centre of Ercinzan, and a 12 per cent probability for a large event south of the major western port city of Izmit. Such stress-based probability calculations may thus be useful to assess and update earthquake hazards elsewhere.