GPS Constraints on Drought-Induced Groundwater Loss Around Great Salt
Lake, Utah, with Implications for Seismicity Modulation
Abstract
Great Salt Lake (GSL), Utah, lost 1.89 +/- 0.04 meters of water during
the 2012 to 2016 drought. During this timeframe, data from the GRACE
mission do not detect anomalous mass loss, but nearby Global Positioning
System (GPS) stations show significant shifts in position. We find that
crustal deformation, from unloading the Earth’s crust with the observed
GSL water loss alone, does not explain the GPS displacements, suggesting
contributions from additional water storage loss surrounding GSL. This
study applies a damped least squares inversion to the 3D GPS
displacements to test a range of distributions of radial mass load rings
to fit the observations. When considering the horizontal and vertical
displacements simultaneously, we find the most realistic distribution of
water loss while also resolving the observed water loss of the lake. Our
preferred model identifies radially decreasing mass loss up to 64 km
from the lake. The contribution of exterior groundwater loss is
substantial (10.9 +/- 2.8 km^3 vs. 5.5 +/- 1.0 km^3 on the lake),
and greatly improves the fit to the observations. Nearby groundwater
wells exhibit significant water loss during the drought, which
substantiates the presence of significant water loss outside of the
lake, but also highlights greater spatial variation than our model can
resolve. We observe seismicity modulation within the inferred load
region, while the region outside the (un)loading reveals no significant
modulation. Drier periods exhibit higher quantities of events than
wetter periods and changes in trend of the earthquake rate are
correlated with regional mass trends.