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Central U.S. Seismic Observatory (CUSSO)

The University of Kentucky operates a strong-motion network of nine stations in the remote area of the central and northern New Madrid Seismic Zone. All the strong-motion stations are accessed through dial-up telephone lines and equipped with 3- to 12-channel Kinemetrics K2’s.  The unique feature of the strong-motion network is the vertical strong-motion arrays which consist of one to two downhole accelerometers. The first vertical strong-motion recordings in the central and eastern United States were recorded at station VSAP from the February 5, 1994, southern Illinois earthquake. The deepest borehole is 260 m below the surface at station VSAS in Fulton County, Ky.  The vertical accelerometer array at VSAS consists of three 3-component accelerometers, recorded on a 24-bit, 9-component accelerograph equipped with GPS timing. The deep borehole accelerometer (FBA-23DH) is placed at the bottom of the hole. The second borehole accelerometer (ES-152DH) is placed at the bottom of a 30 m geotechnical hole. The third accelerometer (Episensor) is a free-field installation placed in a surface vault between the two wells. The installation of the vertical strong-motion array at VSAS was completed in late 2003.

On October 21, 2004, a small earthquake (Md2.5) triggered the array at VSAS. The recordings are the first recorded from this deepest borehole in the New Madrid seismic zone. The acceleration time histories at the surface, 30 m, and 260 m depth, respectively, are shown. 

recording
Acceleration recordings from the October 21, 2004 earthquake (Md2.5) at the vertical strong motion array, VSAS. Top – surface, middle – 30 m deep, bottom – 260 m deep.


As the phase I of the Central United States Seismic Observatory (CUSSO) in the center of the New Madrid Seismic Zone (NMSZ) (following Figure), drilling and construction of a 2000-foot borehole is underway in Fulton County, Kentucky through a partnership of federal agencies (the United States Department of Energy and U.S. Geological Survey) and agencies at the University of Kentucky (the Kentucky Geological Survey, Department of Earth and Environmental Sciences, and  the Kentucky Research Consortium for Energy and Environment).  Following the borehole installation, a workshop will be convened to discuss what instruments should be installed. CUSSO will serve as a permanent observatory for earthquake studies as well as research for earthquake-resistant construction in the central U.S. 

Figure 1. New Madrid Seismic Zone and location of CUSSO.
Figure 1. New Madrid Seismic Zone and location of CUSSO.

Figure 2. Drilling rig at CUSSO 
Figure 2. Drilling rig at CUSSO

lowering drill string to begin drilling at CUSSo

Figure 2.  Lowering drill string to begin drilling at CUSSO

geophysical logging

Figure 4. Geophysical logging.

 

 

 

 

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Last modified January 9, 2008 .