Integrating DInSAR and detailed mapping for characterizing ground displacement in the Cardona salt extrusion related to diapiric uplift, disolutional lowering, landsliding and sinkholes

Abstract

Salt diapirs, despite their inherent instability related to salt flow and dissolution (terra infirma), are often the focus of significant economic activities and sensitive facilities (e.g., salt mining, hydrocarbon production, geostorage). Nonetheless, Differential Interferometry SAR (DInSAR) studies on active diapirs are relatively scarce and frequently lack field-based characterization and independent validation of displacement rates. This work analyses the complex spatial and temporal patterns of ground displacement at the Cardona salt extrusion (NE Spain) combining detailed mapping and DInSAR LoS (Line of Sight) and vertical displacement data obtained by both coherence-based (i.e. Small BAseline Subset – SBAS) and Persistent Scatterers-like (PS) approaches. Overall, the salt extrusion is affected by steady diapiric uplift driven by differential loading and increasing towards the axis of the salt wall to vertical rates of 2–3.5 cm/yr. The obtained rates are in agreement with long-term rates previously calculated using radiocarbon dated uplifted terraces and are comparable with those obtained at vigorously rising salt extrusions in the Zagros Mountains. DInSAR data reveal other local ground displacement processes substantiated by field mapping and damage on human structures, including: (1) rapid dissolutional lowering at salt exposures, showing a tight temporal correlation with rainfall data (>5 cm/yr); (2) widespread dissolution-induced subsidence in valley-floor alluvium underlain by salt bedrock; (3) landsliding favored by diapiric rise and slope oversteepening; and (4) some large active sinkholes. This case study illustrates the practicality of integrating complementary DInSAR and field-based approaches for the comprehensive characterization of ground instability in salt diapirs, providing an objective basis for assessing the associated hazards.