Assessing the Impact of Burst Overlap Interferogram of Sentinel-1 TOPS on Near-Fault 3D Displacement Modelling: A Case Study of the 6th February 2023 Mw7.8 and Mw7.5 Kahramanmara&#351; Earthquakes, T&#252;rkiye.
Authors: Nergizci Muhammet , Ou Qi , Lazecky Milan , Watson C. Scott , Fang Jin , Hooper Andrew , Wright Tim J. 
Published: March 2024

On February 6, 2023, two devastating earthquakes, Mw7.8 and Mw7.5, struck the area surrounding Kahramanmara&#351;, T&#252;rkiye, resulting in extensive and complex surface deformations. The Mw7.8 event created a surface rupture over 310 km along the East Anatolian Fault, while the Mw7.5 earthquake resulted in a 150 km rupture along the &#199;ardak-S&#252;rg&#252; Fault segment. Here we use Sentinel-1 Burst Overlap Interferometry (BOI) to improve 3D displacement mapping and in particular investigate near-fault deformation.In response to the earthquakes, previous studies have utilized various datasets, either separately or in combination. These include near and far-field seismic observations, continuous and campaign GNSS datasets, offset tracking from SAR satellites like Sentinel-1 and ALOS-2 and optical satellites such as Sentinel-2, and InSAR. These diverse data sources are vital for calculating the 3D displacement field. However, extracting information from standard interferograms, critical due to their high spatial resolution, is often challenging because of large phase gradients, particularly in the near field of fault ruptures.This issue frequently complicates the accurate determination of fault displacement and 3D decomposition in impacted areas. For Sentinel-1, with a range resolution of approximately 5 m, displacement in the range direction is usually determined with acceptable accuracy using range offset tracking. However, the azimuth resolution of about 20 m makes azimuth offset tracking less precise. This lower resolution frequently results in less reliable displacement constraints in the azimuth direction. To overcome this limitation, we produced Burst Overlap Interferograms (BOI) from four different tracks of Sentinel-1. These BOI results enabled more precise measurements of along-track displacement near the fault lines, which are theoretically proportional to the number of looks and the decorrelation noise.A key aspect of our methodology was the unwrapping process of the BOI, guided by azimuth offset tracking to handle large displacements exceeding ~1.5 m in the azimuth direction. For the 3D displacement field, we referenced all offset and BOI data to zero points away from the co-seismic ruptures and removed planar ramps. Uncertainties were empirically estimated as the mean absolute deviation in 4x4 pixel windows for offset data and 2x2 pixel windows for BOI. These uncertainties were then used to weight 3D motion inversion and decomposed displacements, providing a more reliable depiction of the earthquake impact. Our approach, combining east and north motion fields, allowed us to extract precise surface slip distributions and highlight surface ruptures through detailed strain analysis. In this study, we explored how to extract more accurate deformation in the north-south direction and reveal detailed deformation near faults by applying 3D decomposition with jointly inverted all datasets in together. We will discuss the implications of our findings for our understanding of earthquakes, and in particular for understanding distributed off-fault deformation that occurs near the fault rupture.