Improved coseismic deformation detection via SBAS InSAR-Hyperbolic tangent step model integration

• • SBAS-InSAR + tanh method detects cm-level coseismic deformation more accurately. • • Applied to 2021 Yangbi earthquake, it cuts deformation residuals by 18–61%. • • New method can separates coseismic and tectonic signals in low-coherence zones. The centimeter level deformation generated by small and medium-sized earthquakes contains rich information on tectonic activity, which is of great value for improving the coseismic deformation database and fault dynamics models. InSAR is an important means of observing coseismic deformation, but there is a problem of insufficient observation accuracy for centimeter level coseismic deformation in complex environments. Time-series InSAR advances achieve millimeter-scale deformation monitoring, yet detecting subtle coseismic signals from Mw 5.0–6.5 earthquakes remains challenging in complex environments by computational limits and step-like model discontinuities. We develop a method incorporating SBAS-InSAR and a hyperbolic tangent (tanh) step function to overcome these barriers. Simulations based on Sentinel-1 and MintPy demonstrate 15–55 % RMSE reductions (0.08–0.45 cm) in coseismic fields versus conventional DInSAR/Stacking methods. Applied to the 2021 Yangbi Mw5.9 event, our approach reveals: (1) The tanh-based model maintains phase continuity during abrupt deformation and decouples linear tectonic motion. (2) It enhances displacement field accuracy with 18–61 % noise suppression and the reliability of finite fault inversion. The model enables seconds deformation estimation for single earthquakes on standard hardware, advancing detection thresholds to sub-centimeter levels in high-coherence region. These breakthroughs expand InSAR’s capability in small-magnitude earthquake mechanics analysis. Future integration with advanced InSAR methodologies promises enhancements in seismic hazard system assessments.