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

Sylvain MICHEL , Lea Pousse-Beltran, Laurence Audin, Juan Carlos Villegas-Lanza, Marie-Pierre Doin, Bertrand Lovery, Swann Zerathe, Mohamed Chlieh

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.