Characterization of the Kinematics of the Cordillera Blanca Normal Fault from InSAR

The Cordillera Blanca Normal fault (CBNF), located along the western margin of the Cordillera Blanca batholith in northern Peru, is a major extensional structure of the central Andes. Geological and geomorphological evidence indicates sustained slip over the past ~4 Ma, yet its present-day kinematics have not been quantified geodetically. Here, we use Sentinel-1 InSAR (Interferometric synthetic-aperture radar) data acquired between 2015 and 2021 to provide the first geodetic characterization CNBF. Fault-perpendicular line-of-sight (LOS) velocity profiles were extracted at regular intervals along the ~150 km-long fault and modeled using a Bayesian framework to explore a wide range of kinematic scenarios and associated uncertainties. Assuming a freely creeping fault, we infer a slip rate of ~2-2.5 mm/yr along the well-defined central segment of the mapped trace, consistent with independent geological and geomorphological estimates. When left unconstrained, fault dip and rake remain poorly resolved due to the limited signal-to-noise ratio to the InSAR data. However, imposing a purely dip-slip mechanism, in agreement with geological observations, significantly tightens parameter uncertainty and reveals a northward decrease in dip from ~45° to ~20° in the central segment. Southward, deformation appears more diffuse and model parameters less constrained, reflecting distributed strain and structural complexity. Although current uncertainties (~0.7 mm/yr) limit our ability to robustly assess fault locking, our results establish a first quantitative geodetic picture of the CNBF kinematics. Those constraints can be further refined in future work through longer InSAR time series and complementary GNSS observations, enabling a more reliable evaluation of the fault’s seismogenic potential.