Interseismic deformation and 3D kinematic reconstruction of the Balapur Fault, NW Himalaya: Insights from InSAR and gravity data

Abstract

The Balapur Fault is one of the most studied faults within the Kashmir Basin due to its possible role in future seismicity and its proximity to the population center in the NW Himalaya. This study utilizes the multidisciplinary approach of Persistent Scatterer InSAR and gravity analysis to study the surface kinematics and subsurface characteristics of the fault structure. Over 200 Sentinel-1 scenes acquired in ascending and descending geometries between 2014 and 2023 were analyzed to derive interseismic deformation patterns, yielding mean Line-of-Sight rates ranging from 1 ± 0.3 mm/yr to 2 ± 0.4 mm/yr. LOS data were decomposed into east-west and vertical components, revealing uplift rates of approximately 2 mm/yr in agreement with the known shortening rates. Cross-sectional velocity analyses along the entire fault length (both mapped and inferred) indicate uniform fault activity, although a detailed fault-locking inversion reveals along-strike heterogeneities. Specifically, Monte Carlo simulations integrated within the inversion framework quantify uncertainties in fault parameters and indicate that while most segments lock at depths of 12–13 km, the northern Segment 1 appears to be locked at greater depths (∼16 km), consistent with a deepening décollement observed in the region. Continuous GPS station data from 3 nearby locations is further utilized to cross-validate and calibrate InSAR-derived displacement rates. Gravity data acquisition and processing, including Complete Bouguer anomaly and Total Horizontal Derivative mapping, provide further constraints on the subsurface structure, delineating fault strike and revealing contrasting density gradients. 3D model inversion of the gravity data uncovers three prominent zones of discontinuity corresponding to the main fault and its subsidiary branches, indicating a high dip angle (>60°) and the deep-rooted nature of the fault. This integrated approach enhances our understanding of fault kinematics and locking behavior in the Balapur Fault and demonstrates the utility of combining geodetic and gravimetric methods for comprehensive seismic hazard assessment.