We use Global Positioning System (GPS) observations and elastic half-space models to estimate the distribution of coseismic and postseismic slip along the Izmit earthquake rupture. Our results indicate that large coseismic slip (reaching 5.7 meters) is confined to the upper 10 kilometers of the crust, correlates with structurally distinct fault segments, and is relatively low near the hypocenter. Continued surface deformation during the first 75 days after the earthquake indicates an aseismic fault slip of as much as 0.43 meters on and below the coseismic rupture. These observations are consistent with a transition from unstable (episodic large earthquakes) to stable (fault creep) sliding at the base of the seismogenic zone.

Southern Türkiye faced widespread catastrophic destruction by two devastating earthquakes on the same day. As the earthquakes occurred at 04:17 (M _w = 7.7, Pazarcık, Kahramanmaraş) and 12:30 (M _w = 7.6, Elbistan, Kahramanmaraş) on 6 February 2023, neighbouring active fault systems were broken in succession between the Hatay and Malatya provinces in the region. The first earthquake, one of the largest earthquakes in this region during the last century, caused major fatalities and widespread damage to infrastructure and buildings, and produced large-scale seismo-gravitational surface deformation such as landslides, lateral spreading, liquefaction and extensional cracks. Here, we present the surface rupture geometry and coseismic displacement characteristics of the fault systems, determined by field observations immediately after the 6 February 2023 Pazarcık (Kahramanmaraş, Türkiye) earthquake (M _w = 7.7). Preliminary results show that the total rupture length ( L _max ) is 270 ± 10 km on the Karasu, Pazarcık and Erkenek segments of the East Anatolian Fault Zone. Left-lateral strike-slip faulting developed with a maximum horizontal displacement ( D _max ) of 7.30 m and an average displacement ( D _avg ) of 3.00 m. Although the surface rupture generally exhibits a narrow deformation zone width of 2–5 m, this expands to 50 m in some sections of the faults. The implications for rupture dynamics suggest that fracture development started on a secondary fault (Narlı Fault), transferred to the main fault and triggered the breaking of asperities on the Pazarcık segment, which exhibits a long period of accumulation of stress, to initiate the major rupturing. Supplementary material: Figures S1–S12 with details on coseismic displacement are available at https://doi.org/10.6084/m9.figshare.c.6487245

We reevaluate the 72 year history of surface slip on the North Anatolian Fault at Ismetpasa since the M_w = 7.4 1944 Bolu/Gerede earthquake. A revised analysis of published observations suggests that days after the earthquake the fault had been offset by 3.7 m and 6 years later by an additional 0.74 m. Creep was first recognized on the fault in 1969 as a 0.13 m offset of a wall constructed in 1957 that now (2016) has been offset by 0.52 m. A carbon rod creep meter operated across the fault in the past 2 years confirms results from an invar wire creep meter operated 1982–1991 that surface slip is episodic. Months of fault inactivity are interrupted by slow slip (≤10 µm/d) or multiple creep events with cumulative amplitudes of 2–10 mm, durations of several weeks, and with slip rates briefly exceeding >2.5 mm/h. Creep events accommodate 80% of the surface slip and individually release ≈ 10⁻⁶ shear strain on the flanks of the uppermost 3–7 km of the fault. GPS and interferometric synthetic aperture radar methods yield a current fault slip rate of 7.6 ± 1 mm/yr suggesting that creep meters incompletely sample the full width of the surface shear zone. The slip rate has slowed from >10 mm/yr in 1969 to 6.1 mm/yr at present, 4.65 mm/yr of which appears to be due to steady interseismic creep driven by plate boundary stressing rates. We calculate that a further 1 m of aseismic surface slip will precede the next major earthquake on the fault assuming an ≈ 260 year main shock recurrence interval on this segment.