InSAR Analysis of Induced Seismicity: Examples From Southern Colorado

Abstract:

We present interferormetric synthetic aperture radar (InSAR) analysis of human-induced ground deformation in the Raton Basin of southern Colorado and northern New Mexico, including displacements from a wastewater injection-induced earthquake. Geodetic observations of both seismic and aseismic surface displacements provide an additional tool to further constrain spatially and temporally variable deformation within these basins. Using Envisat observations, we image co-seismic surface displacements of the 2011 Trinidad earthquake and find that the earthquake slipped within the crystalline basement underlying basin sedimentary rocks and in the vicinity of high-volume wastewater injection wells. The spatial and temporal separation between the earthquake and the wastewater wells suggests a pore pressure migration triggering mechanism is present. The finite slip distributions further highlight the location and orientation of previously unmapped, seismogenic faults. Lastly, the precise earthquake location afforded by InSAR observations provides a well-located earthquake source that can be used to calibrate other regional earthquakes locations.

Additionally, we derive InSAR time series observations from ALOS imagery acquired from 2007-2011. These results highlight ongoing regions of surface subsidence within the basin, presumably caused by extraction of coal-bed methane and water that is later reinjected. While it is not clear if there is a causative relationship between regions of co-located surface subsidence and recorded earthquakes, the time series permits us to exclude several other hypotheses for the causes of increased seismicity in the Raton Basin, including volcanic activity related to the Rio Grande Rift. Furthermore, the InSAR time series analysis provides a calibration source for hydrological models that assess subsurface stress changes from the removal and injection of fluids. Forthcoming work will provide a detailed time series of surface deformation occurring prior to and following the onset of methane withdrawal and wastewater injection in the Raton Basin.