High‐Resolution Interseismic Strain Mapping From InSAR Phase‐Gradient Stacking: Application to the North Anatolian Fault With Implications for the Non‐Uniform Strain Distribution Related to Coseismic Slip Distribution

• Published in: Geophysical research letters Vol. 50; no. 15
• Main Authors: Liu, Ziming, Wang, Teng
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.08.2023; Wiley
• Subjects: Budgets; Deformation; Distribution; Earthquakes; Echoes; Elastic deformation; Fault lines; Faults; Geological faults; Geological hazards; Hazard assessment; InSAR phase gradient stacking; inter seismic strain mapping; Interferometric synthetic aperture radar; Interferometry; Mapping; North Anatolian Fault; Phase unwrapping; Radar; Radar imaging; SAR (radar); Segments; Seismic activity; Seismic hazard; Seismic response; Shear; Shear strain; Slip; Solifluction; Spatial distribution; Stacking; Strain distribution; Strain rate; Synthetic aperture radar; Synthetic aperture radar interferometry; Velocity distribution; North Anatolian Fault
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL104168

High‐resolution interseismic strain mapping is important for studying faulting behavior and for assessing seismic hazards. Interferometric Synthetic Aperture Radar has been widely applied to measure interseismic deformation along active strike‐slip faults. However, phase unwrapping errors and over‐smoothing effects limit its ability to map the extremely‐high strain due to shallow creep. Here, without the involvement of ground‐based measurement, we perform phase‐gradient stacking on wrapped Sentinel‐1 interferograms to directly map the shear strain rates along the North Anatolian Fault (NAF) with unprecedented resolution. The derived high‐resolution strain‐rate map reveals five strain‐concentrated segments on the NAF, implying shallow creeps. We find that their spatial distribution coincides with the lower coseismic slip of previous earthquakes that occurred since 1939. The proposed method can be applied to other less‐studied strike‐slip faults to distinguish segments with shallow creep and strong coupling, and thus to better quantify the shallow strain budget and its associated seismic hazards. Plain Language Summary Surface deformation measurements along active faults are important for understanding the elastic energy, namely the strain that is accumulated and released during earthquake cycles. Interferometric Synthetic Aperture Radar (InSAR), is an imaging geodetic method that allows mapping millimeter‐scale deformation from phase differences of microwave echoes, has been applied for studying interseismic deformation across active strike‐slip faults worldwide. However, obtaining strain from InSAR‐derived velocity fields is challenged by the high computational burdens and the low resolution. Here, we propose a new phase‐gradient stacking method to obtain high‐resolution shear strain rates along the entire North Anatolian Fault (NAF) in Turkey. Our results show that the presented method can clearly reveal the spatial extents of the creeping segment, indicating the overall non‐uniform strain rate distribution and the close relation with the previous earthquake ruptures along the NAF. We propose to apply the presented phase‐gradient stacking approach to other active strike‐slip faults to better understand their strain budgets and associated seismic hazards. Key Points We map the shear strain rates along the North Anatolian Fault (NAF) with an unprecedented resolution by stacking phase gradients of Sentinel‐1 interferograms Distribution of shear strain rates indicates a tight relation between creeping segments and surface ruptures of NAF earthquakes since 1939 We identify two creeping segments previously undetected along the NAF from the high‐resolution shear strain map