234-7 Squeezing hydrogeology from InSAR time series and Borehole Grain-Size distributions: Insights from Taiwan’s Changhua-Yunlin Plain

Session: Advance Ground Surface Modeling for Hydrological and Environmental Applications

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Authors:

Abstract:

The Changhua-Yunlin Plain represents Taiwan's most rapidly subsiding region. Extensive monitoring efforts address subsidence issues to mitigate disasters associated with surface deformation driven by groundwater withdrawal. Monitoring approaches include precise leveling, GNSS, and radar interferometry.

InSAR time series analysis exploits stable radar scatterers to extract coherent phase signals across extensive areas, enabling derivation of surface deformation velocities at high spatial resolution. Surface deformation originates from multiple geological processes including fault activities, climate variability, seasonal changes, and groundwater withdrawal. Understanding deformation drivers is crucial for deciphering how various factors interact to modify ground elevation.

This study analyzes Sentinel-1 InSAR time series (2018-2021) covering Taiwan's Changhua-Yunlin Plain, validated against comprehensive GNSS data (R²=0.952). We investigate surface deformation rates and seasonal signals (quarterly, semi-annual, annual, and multi-annual components) along with their spatial distribution. We examine how deformation patterns relate to underlying sediment compositions forming aquifer-aquitard systems governing groundwater storage and flow dynamics.

Our analysis reveals neighboring pixels with similar seasonal patterns cluster geographically, though spatial coherence remains moderate (R²=0.3-0.6 when comparing seasonal signals between nearby locations). Areas with high agricultural water demand show larger wet-dry seasonal oscillations (up to ±30 mm), while urban areas exhibit minimal seasonal variation (<5 mm), suggesting differential aquifer responses to pumping cycles.

While subsidence rates generally increase with higher fine-sediment content, certain areas maintain minimal subsidence despite high fine-sediment proportions, revealing significant spatial heterogeneity in sediment-subsidence relationships.

These findings highlight critical needs in InSAR time series interpretation: (1) further testing of decomposition methods to accurately separate true geological signals from artifacts, (2) subsidence patterns reflect complex spatial controls transcending simple grain-size relationships, and (3) historically compacted areas may exhibit reduced deformation sensitivity. The spatial clustering of subsidence rates and seasonal responses demonstrates that effective monitoring strategies must incorporate spatial heterogeneity in aquifer-system behavior. This spatially variable grain-size correlation suggests current subsidence patterns may represent residual compaction in systems approaching equilibrium under present-day stress conditions, bearing significant implications for future monitoring and mitigation strategies.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8012

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