Abstract
The Delaware Basin, Texas is currently a hot-spot of induced seismicity
and ground deformation due to fluid extraction and injection associated
with horizontal drilling techniques; however, the driving mechanism
behind the seismicity and deformation remains under debate. Using
vertical and east-west horizontal surface deformation measurements
derived from Sentinel-1 InSAR, we show that the subsurface responds
differently to oil and gas activity in the northern and southeastern
portions of the basin. In the north, where there is little seismicity,
deformation patterns display long-wavelengths and equidimensional
patterns. In contrast, the southeast region hosts most of the seismicity
and displays spatial deformation patterns with narrow linear features
that strike parallel to the maximum principal horizontal stress and to
trends in seismicity, suggesting movement along normal faults. We model
a linear deformation feature using edge dislocations and show that the
InSAR observations can be reproduced by slip on normal faults contained
within the Delaware Mountain Group (DMG), the formation that hosts local
wastewater injection and the majority of earthquakes. Our model consists
of three parallel, high-angle normal faults, with two dipping toward one
another in a graben structure. Slip magnitudes reach up to 27.5 cm and
are spatially correlated with injection wells. Measured seismicity can
only explain ~2% of the fault motion predicted by our
fault model, suggesting that slip leading to the deformation is
predominantly aseismic. We conclude that seismic and aseismic fault
motion in the southeastern Delaware Basin is likely driven by wastewater
injection near critically-stressed normal faults within the DMG.