InSAR Reveals Significant Ground Deformation in the Samail Ophiolite in Oman

Abstract:

The Samail Ophiolite comprises ultramafic rocks, which were thrust up by tectonic forces millions of years ago. When exposed to air and water, these rocks undergo serpentinization and carbonation, which chemically changes peridotite and as a byproduct, permanently binds and stores atmospheric CO₂ to stable carbonate minerals underground. After a significant rainfall event, serpentinization fractures the rock to increase pore space and allow CO₂ to mineralize underground, which produces observable uplift. While this process was thought to occur at very slow rates, recent carbon dating studies reveal that the mineralized carbon is only 26,000 years old, thus the carbonation rate is much faster than previously thought.

In this study, we use 100 Sentinel-1 SAR images, and therefore 4950 interferogram measurements to derive surface displacement history from May 2015 through February 2020 over the Samail Ophiolite. InSAR measures relative surface deformation with respect to a reference location, which are not sensitive to the region-wide tectonic deformation. Due to the absence of hydrologic and localized tectonic forcings, surface uplift should correspond to carbonation after major rainfall events. InSAR time series analysis shows a period of up to 8 cm of uplift, starting in early 2017 and peaking in August 2017. This uplift follows a significant 70 mm rainfall event in March 2016. The time lag between the rainfall event and initial uplift could be explained by kinetics of groundwater movement and initial fracturing of the rock but can be further explained with the future development of a reactive transport model. Initial tropospheric removal and comparison with the Generic Atmospheric Correction Online Service (GACOS) correction, indicates that this signal is not related to the atmosphere. These observations show promise that it is possible to improve the current estimates of the spatial extent, volume, and rate of CO₂ captured by the carbonation of ultramafic rocks. These estimates influence ongoing research related to accelerating this process as a means to help reduce our carbon footprint.