LiDAR Differencing Reveals How Subsidence Is Tied to Basin Structure in Cedar and Parowan Valleys, Utah

ABSTRACT Topographic differencing using high-resolution elevation data is a powerful tool for investigating land surface change. Impacts from ground subsidence were first observed in southern Utah in 2005 after winter flooding eroded earth fissures near Beryl Junction. In 2009, ground cracks were discovered throughout a new development located in Cedar Valley. Subsequent investigations in Cedar and Parowan Valleys used field mapping, ground surveying, interferometric synthetic aperture radar, and groundwater budgets to demonstrate that subsidence due to groundwater overdraft and pore space compaction had been occurring for decades. This study examined topographic differences across both Cedar and Parowan Valleys based upon previously published 1 m light detection and ranging (LiDAR) digital elevation models collected in October 2011 and May 2020. Differencing, histogram analysis, threshold classification, profiling, and spatial statistics revealed that somewhere between ∼40 and ∼90 percent of the ∼740 km2area is experiencing subsidence with an average rate of 1.2 cm/yr. Three localized areas (Parowan, Enoch Graben, and Quichapa Lake), encompassing about 23 percent of the study area, are experiencing higher subsidence rates ranging from 2.3 to 5.4 cm/yr. Investigation of these subsidence features using LiDAR differencing demonstrated how detailed spatial variability in subsidence is directly linked to basin structure. Importantly, differential subsidence across basin faults can account for all the surface slip observed across some apparent Holocene fault scarps. In other cases, differential subsidence is decreasing the apparent offset across fault scarps. Topographic differencing results also revealed evidence of ongoing earth fissuring along the west side of Enoch Graben.