TITLE: Imaging the ambient permeability field and active fracture fault fairways in the brittle crust using Passive Seismic Emission Tomography (PSET™)

Auth1: Peter Geiser; STRM LLC, Boulder, CO * pete@geologicsystems.com
Auth2: Peter Duncan; MicroSeismic Inc., Houston, TX
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We present recently obtained data on the successful use of PSET™ for the imaging of kilometer scale fracture/fault fairways in the brittle crust as well as for the direct imaging of the geometry of the ambient permeability field using a method developed by STRM LLC. Initial results have resolution varying from 100 to 60 meters however resolutions as high as 30 meters may be reasonably expected. PSET™ is a tomographic method for imaging patterns of earthquake activity too small to be pinpointed as individual discrete events. These creep related emissions are imaged and mapped using a dense network of micro-array stations employing beam-forming to enhance low level seismic energy flux. Interpretation of the PSET™ image for the permeability field uses a simple mechanical model developed by STRM LLC for the response of the ambient permeability field to changes in fluid pressure. The method allows those fairways comprising the permeability field associated with the point of fluid pressure change, to be identified. This information is likewise at the kilometer scale. Among other things the work has shown that even in regions of low seismicity, the crust is apparently in continuous state of weak tectonic activity primarily in the form of what is inferred to be micro-cracking. The ability to image these fairways, invisible to active seismic imaging and which are potential zones of failure or flooding, opens new opportunities both for the engineering of large underground structures as well as monitoring any changes that may be induced during construction activities. It is proposed to use these techniques to monitor the construction of the DUSEL facility both prior to and during construction.