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Revealing Fracture Planes with a High-Resolution Catalog of Induced Microearthquakes
  • +7
  • Chengping Chai,
  • Monica Maceira,
  • Hector Santos-Villalobos,
  • Singanallur Venkatakrishnan,
  • Martin Schoenball,
  • Pengcheng Fu,
  • Clifford Thurber,
  • Paul Schwering,
  • Timothy Johnson,
  • Hunter Knox
Chengping Chai
Oak Ridge National Laboratory

Corresponding Author:[email protected]

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Monica Maceira
Oak Ridge National Laboratory
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Hector Santos-Villalobos
Oak Ridge National Laboratory
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Singanallur Venkatakrishnan
Oak Ridge National Laboratory
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Martin Schoenball
Lawrence Berkeley National Laboratory
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Pengcheng Fu
Lawrence Livermore National Laboratory
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Clifford Thurber
University of Wisconsin-Madison
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Paul Schwering
Sandia National Laboratories
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Timothy Johnson
Pacific Northwest National Laboratory
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Hunter Knox
Pacific Northwest National Laboratory
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Abstract

Seismic sensors and seismic imaging have been widely used to monitor the geophysical properties of the subsurface. As subsurface engineering techniques advance, more precise monitoring systems are required. Seismic event catalogs and seismic velocity structures are two of the major outputs of seismic monitoring systems. Although seismic event catalogs and velocity structure are often studied separately, published reports suggest constraining them simultaneously can lead to better results. We conducted a double-difference seismic tomography analysis to constrain both the seismic event locations and the 3D seismic velocity structure. Passive seismic data collected from a geothermal research project in Lead, South Dakota were used to image a 3D volume on the scale of tens of meters. Specifically, around 18,500 P-wave and 8,900 S-wave arrival times from 1,874 seismic events were used. Checkerboard tests showed that the observed data can image the seismically active region well. We compared tomography results with fixed seismic event locations against those with updated event locations. Tomography results with updated event locations showed better fits to the observations and improved the seismic event catalog, showing sharper patterns compared to the original one. These patterns helped us monitor the seismically active fractures since the seismic events were mostly due to hydraulic stimulations. Two parallel fractures revealed by the updated seismic event catalog spatially correlated with independent borehole temperature observations. The average seismic velocity values of the well-constrained volume agreed to the first order with core sample measurements and active-source seismic surveys.