120-6 Sinking Ground, Rising Concerns—A Century of Land Subsidence in California

Session: Land Surface Subsidence: Processes, Impacts, and Ongoing Challenges

Presenting Author:

Authors:

Abstract:

Over the past 100 years, California’s Central Valley has experienced some of the most significant land subsidence ever recorded, with vertical displacements exceeding 30 feet in certain regions. Subsidence associated with groundwater extraction can threaten the operation of critical infrastructure leading to economic damages and impacts to beneficial uses/users of groundwater. Using a century’s worth of water level and subsidence data, this talk explores the historical progression of subsidence, identifying key hydrologic factors such as critical head that are responsible for compaction of aquifer-systems.

At 50 benchmark locations distributed across California’s Central Valley, we leverage historical and current water level and subsidence to construct a long-term time series spanning 1901 to the present. Groundwater observations from state, federal, and local sources within a 2.5-mile radius of each benchmark are grouped by aquifer depth sampling, assessed for data quality and similarity, and joined together to create a long record of water-levels. The long-term subsidence time series relies primarily on leveling conducted at the benchmarks, with higher frequency measurements from nearby GPS, InSAR, and extensometer data registered to the late-time leveling observations. The results show highly differing patters of subsidence across the Central Valley that have not previously been compiled on a valley-wide scale to date. These results indicate much greater subsidence than is probably known in some areas, and rapidly increasing subsidence in other areas.

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

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