Variations in Subsidence along the Gulf of Mexico passive margin from
Airborne-LiDAR data and Time Series InSAR in Louisiana
Abstract
Coastal Louisiana is affected by sea level rates compounded by
subsidence rates, leading to flooding and land loss. Subsidence in the
region is caused by natural and anthropogenic processes that vary
spatially and temporally across the Gulf of Mexico. Here, we quantify
modern vertical and horizontal displacement using InSAR time-series and
LiDAR differencing with data spanning between 1999-2020. Our study area
is in Baton Rouge (BR), LA. It encompasses two Quaternary faults that
cut cemented Pleistocene sediments. We test the ability of these methods
to detect millimetric changes in an urban area with extraction and
injection wells. Both methods indicate that the footwall of the BR fault
has larger subsidence values (InSAR time series x̄=-0.552 to -0.732 mm/y)
than the hanging wall of the fault (x̄=1.94 mm/y). LiDAR differencing
accurately detects displacement trends, although it can overestimate the
displacements. There are areas of uplift that spatially correlate to the
locations of injection wells. Our results indicate that subsidence
follows the spatial pattern of groundwater level changes proposed by
previous studies, suggesting volumetric changes caused by fluid
extraction and injection. The correlation of the BR fault zone with the
boundary between blocks subsiding at different rates indicates that
creep occurs along some sectors of the fault zone at rates of
~3 mm/y, similar to estimates from displaced structures.
The creep may be accommodating changes in groundwater level rather than
gravity and salt dynamics. The fault zones may be more permeable than
surrounding areas, and more susceptible to hydrological and
anthropogenic processes.