Revealing the Tectonic-Driven Nature From the InSAR Surface Deformation Background Signals in Xiamen–Kinmen Coasts, China

Quantifying the characteristics of surface deformation is essential for monitoring geohazards like landslides and earthquakes. InSAR (Interferometric Synthetic Aperture Radar) technique provides high-resolution land deformation data, and becomes popular in studying multi-factor-driven coastal geomorphological changes. However, the “widespread” and “slow” InSAR deformation is often treated as a “non-significant background signal”, thus missing smaller signals, such as regional tectonic movements. This study aims to quantify and understand the characteristics of “background signal” of the InSAR deformation in the Xiamen-Kinmen coasts, and reveal its possible driving mechanisms. The multi-temporal InSAR method is used to extract regional surface deformation and separate the background deformation signal by threshold. We then analyze the spatial pattern of this background deformation using the spatial structure function and correlate it with geological and geophysical observations. Our results indicate a nearly uniform spatial distribution of background deformation rates ranging from -2 to 2 mm/year, with distinct northwest and northeast patterns observed over distances of 40-60 km. This spatial variation closely aligns with major regional fault zones. Additionally, the InSAR displacement rates correspond with tectonic-driven rates reconstructed from geological and geophysical records. The above results reveal the tectonic-driven nature of the InSAR background deformation, which can be explained by a simplified crustal movement model of the region. This study highlights the potential of InSAR data to provide a detailed quantitative understanding of small surface deformation driven by regional tectonics, which is crucial for the quantitative study of structural geology and the prediction of potential geohazards.