High-Resolution Thermal Imaging of the Surface Rupture of the February 6 2023, Kahramanmaraş Earthquake (Mw 7.8), Türkiye

Large-magnitude strike-slip earthquakes can cause extensive surface ruptures that stretch hundreds of kilometres. High-resolution mapping of these ruptures provides insights into the location of the rupture strands, coseismic displacements and geometrical complexities that are vital to understanding earthquake rupture processes and fault zone hazards. The February 6, 2023, Kahramanmaraş Earthquake, the most destructive earthquake in Türkiye, reactivated the East Anatolian and Dead Sea Fault zones and created a 350 km long surface rupture with a maximum displacement of ~8 m.

In this study, we acquired optical and thermal imagery strips using an Unmanned Aerial Vehicle (UAV) system along 320 km of the surface rupture. The width of the strip is 300 m. The data were preprocessed (RJPG to TIFF conversion), the temperature anomalies in the thermal images obtained compared to the surroundings of the surface rupture were mapped, and the thermal-based surface rupture map was confirmed with high-resolution (10 cm) optical images.

Generally, optical or radar satellite imagery is widely used to map earthquake surface ruptures, but their resolutions are limited to a maximum of 0.5 m and 12 m, respectively. These resolutions can be increased ten times by the pixel offset tracking. However, there are still issues with locating rupture strands precisely and quantifying coseismic displacement accurately, especially on-fault displacements. The recent developments in Unmanned Aerial Vehicle (UAV) technologies allow for the mapping of earthquake surface ruptures with a very high resolution (e.g., <10 cm) along very long distances (e.g. 30 km per day). One of the issues with most UAV systems with only an optical camera is tracing surface rupture correctly under vegetation cover (e.g. forest, grassland) and rugged surfaces with different slope aspects.

A UAV equipped with a thermal and optical camera was deployed to address this issue, enabling comprehensive data collection and analysis. While surveying, we used real-time optical and thermal imaging to trace surface rupture and test the effectiveness of thermal imaging. This approach enabled the identification of surface fractures that are not visible in optical images because the thermal signature of the rupture is more vivid than in optical images. This signature is relative temperature differences compared to the surrounding area due to the changing humidity and micro-topography of the surface because of shearing. Using thermal imagery provides two advantages: incrementally improves the tracing of surface rupture while the UAV acquires the data in the field, especially under different vegetation covers. So, it provides extra guidance to UAV pilots to trace strands of the earthquake surface rupture. The second advantage is that it facilitates the mapping of surface rupture in the lab when optical imagery cannot be used to trace surface rupture for several reasons (e.g., vegetation, sunlight, ploughing, and topographic shadow). As the first application of thermal imaging on earthquake surface rupture mapping, our findings demonstrate the advantages of thermal imaging, especially in forested and agricultural areas where conventional optical methods fall short. Integrating thermal data with optical provides key insights for improving mapping accuracy in surface rupture areas, significantly advancing earthquake research.