Conference Agenda

The East Anatolian Fault (EAF) forms a plate boundary (~800 km) between the Arabian and Anatolian plates. Its southern extension connects to the Dead Sea Fault (DSF) and creates a triple junction between Africa, Anatolia and Arabia plates at Kahramanmaraş. Its northern tip connects with the North Anatolian Fault Zone and creates another triple junction between Arabia, Anatolia and Eurasian plates at Karlıova. Numerous destructive earthquakes have taken place along the left-lateral East Anatolian Fault and left-lateral Dead Sea Transform fault as documented by historical records dating back to two millennia, the latest being the Mw 7.8 and Mw7.6, February 6, 2023 Kahramanmaras earthquake sequence that generated more than 50 thousand victims in southeastern Turkiye and northern Syria. Geodetic data (GNSS and Envisat and Sentinel time series) along with mapped fault ruptures not only depict the relative plate motions ranging from 6 to 10 mm/yr, but also reveal complex behavior of fault slip during the earthquake cycle. While the EAF creeps partially and fully along its ~150 km-long eastern sections, it is fully locked along its western sections where the 2023 Kahramanmaraş earthquakes. Mw 6.8 Elaziğ and 7.8 Kahramanmaraş earthquakes and related slip-rupture modeling show that fault creep plays an important role in rupture arrest and earthquake fault segmentation. Slip distribution of the Mw 7.8 Kahramanmaras earthquake is in agreement with the existence of a seismic gap and the interpretation of historical seismicity along the EAF and DSF as it is consistent with the accumulated slip during the last millenia along the fault segments that ruptured during the Mw 7.8 February 6, 2023 earthquake.

In this study we show preliminary results from the French CIEST² initiative (Cellule d’Intervention et d’Expertise Scientifique et Technique – second generation) related to the 2023 Turkey-Syria earthquakes sequence. CIEST² is a synergy of the French community belonging to the Solid Earth national Data and Services center “ForM@Ter” and the MDIS group (Measurement of Deformations by Spatial Imagery) aiming at the measurement, interpretation and understanding of geophysical phenomena from spaceborne data.

On 6 of February 2023, a Mw 7.8 earthquake struck Southern Turkey and North Syria with an epicenter located ~37km Northwest of the city of Gaziantep. It was followed by a Mw 7.7 earthquake centered 95 km North-Northeast from the first. These two earthquakes occurred in the transition between the Dead Sea fault and the East Anatolian fault. This earthquake sequence ruptured much of the southwestern third of the East Anatolian fault, as well as the northernmost portion of the Dead Sea fault. Here, we concentrate on the mapping of ground displacement and surface ruptures from both SAR (Synthetic Aperture Radar) and optical sensors. On the one hand, we used SAR data acquired by the European Copernicus Sentinel-1 C-band mission as well as the JAXA (Japanese Aerospace Administration) Alos2/Palsar2 L-band mission. On the other hand, we used very-high resolution optical data from the Pléiades (Airbus/CNES) and from the Copernicus Sentinel-2 platforms. Where possible, we used platform based processing, such as GEP (Geohazard Exploitation Platform, ESA – European Space Agency), the French FLATSIM service (LArge-scale multi-Temporal Sentinel-1 InterferoMetry processing chain) and the GDM-OPT-ETQ service (ForM@Ter) as well as tailored in-house processing.

Interferometric SAR shows large scale, far-field ground displacement, while subpixel offset applied to both SAR and optical data shows the near-field surface displacement. These data are used along with an inversion strategy to gain an understanding of the fault slip and geometry at depth. Moreover, we show that the surface rupture, produced by the first earthquake, measured more than 300 km while the second earthquake produced a surface rupture of more than 125 km. Spatial offsets in the range of 3 to near 10 m are identified with large spatial variability along the faults. This dataset is also used to better identify landslides triggered or accelerated by the earthquake sequences and study their controlling factors.

In this study, we used pixel-offset tracking and InSAR data from Sentinel-1 and ALOS-2 radar images to map the surface displacements of the 6 February 2023 Kahramanmaraş earthquake duplet. We first derived along-track (azimuth) and across-track (range) pixel offsets from multiple ascending and descending orbit images. We then inverted for the complete three-dimensional surface displacement field using these offset images along with InSAR data, yielding both near- and far-field displacements. The results clearly show the left-lateral motion across the two main faults, with relatively small vertical displacements, confirming the almost pure strike-slip mechanism of both events. Our results are accurate to within ~10 cm for the horizontal displacements when compared with GPS data. We mapped the main surface rupture of the first event along the East Anatolian Fault (EAF) for approximately 300 km and the surface rupture of the second mainshock for over 130 km, which is somewhat shorter than illuminated by the aftershocks. We found three slip maxima along the EAF, using multiple profiles across the faults of the fault-parallel displacements derived from the offset results. The largest slip of 6-7 m was found northeast of the epicenter, about 30 km east of the city of Kahramanmaraş. Another slip maximum of ~4 m was found further southwest, near Islahiye, with fault slip abruptly decreasing near Antakya at the southwestern end of the rupture. The maximum surface offset of the second fault was even larger than for the first rupture, reaching approximately 8 m and located near the epicenter. Our analysis also appears to reveal off-fault damage extending several km away from the surface ruptures, as evidenced by deformation gradients in profiles crossing the faults of the fault-parallel displacements. The off-fault damage is most evident near fault step-overs, whereas within relatively straight fault segments, the spatial scale and magnitude of off-fault deformation is smaller. We also used the derived coseismic 3D displacements and available GPS observations to invert for spatially variable fault slip. The results show that most of the fault slip occurred above 15 km, with maximum slip of both quakes reaching almost 10 m. The spatially variable slip model of the first mainshock has primarily three areas of high slip, consistent with what was seen at the surface. In summary, our results provide a comprehensive overview of the fault offsets, about which faults were activated, and of near-fault damage in the earthquakes. They also help assessing the influence of the Kahramanmaraş earthquakes on other faults in the region.

Two devastating earthquakes hit southeast Turkey on February 6, 2023. The first, M_w7.8, ruptured approximately 320 km of the south-western East Anatolian Fault. Nine hours later an M_w7.5 earthquake struck about 80 km north of the M_w7.8 epicentre and ruptured an approximately 150 km long segment of the Sürgü fault. The two earthquakes caused significant ground deformation and damage throughout southeast Turkey and north Syria, and over 50,000 fatalities.

We reconstruct the coseismic and early postseismic deformation field associated with these two events, using Sentinel-1 SAR and GNSS measurements. Due to the extensive ground disruption up to about 20 km away from the surface rupture, InSAR coherence is very low at the near-fault strip and is thus used primarily for the far-fault field. This limitation is compensated by the pixel offset tracking methodology (in azimuth and range) that allows mapping of the surface displacement near the fault trace at a high spatial resolution, but with a lower precision. To complement these measurements, we use the Sentinel-1 TOPS observation mode to perform Burst Overlap Interferometry (BOI) in strips across the main faults that provide surface displacement measurements in the satellite flight direction with much higher accuracy than the azimuth pixel offset tracking. The three radar datasets reveal left-lateral horizontal displacements ranging from zero to ~7.5 metres along both the East Anatolian and Sürgü faults. More than 1 metre of left-lateral offset is observed with the BOI along a minor ~N-S striking fault that has been interpreted as the site of initial nucleation of the M_w7.8 event and joins the East Anatolian fault further north.

We invert the radar and the available GNSS measurements for the co-seismic slip distributions along the East Anatolian and Sürgü faults. Our analysis has shown an average slip of 2.56 and 4.83 metres, with total geodetic moments of M_w7.76 and M_w7.46, in accordance with the reported M_w7.8 and M_w7.5 seismic moments, respectively. Furthermore, we have found that the modelled and measured displacement profiles across the faults and their along-strike variations are in excellent agreement. The inversion slip model shows twice as large average slip during the M_w7.5 earthquake compared to the earlier M_w7.8 earthquake yielding average stress drops of 3.9 and 0.9 MPa, respectively, and thus suggesting a relatively low stress drop along the East Anatolian Fault .

To reconstruct the early post-seismic deformation field, we use the Small Baseline Subset (SBAS) time-series approach. The analysis reveals a complex pattern of post-seismic deformation, highest near the hypocenter of the M_w7.8 earthquake off the East Anatolian Fault. It should be noted, however, that this result is very preliminary and that our post-seismic analysis is still ongoing. We aim to present a more comprehensive analysis of the February 6, 2023 earthquakes postseismic, as well as the interseismic deformation along this section of the fault, at Fringe 2023.