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Show These data will be presented and discussed in subsequent statements on the various Bonneville Unit systems previously defined. Each statement would be prepared and processed prior to making any decision to proceed with construction of the system or feature. Seismicity of the Bonneville Unit Area Utah is divided into three physiographic provinces: ( 1) The block- faulted Basin and Range, ( 2) The Colorado Plateau, and ( 3) The Middle Rocky Mountains which include the Uinta Mountain range. A belt of active seismicity extends along the boundary zone between the Basin and Range province and the Colorado Plateau- Middle Rocky Mountain provinces, which are part of a belt of seismicity extending northward from the East Pacific rise, along the Gulf of California through western Arizona, central Utah, southeast Idaho, western Wyoming, western Montana, and into British Columbia. This zone of active seismicity lies between or along the boundary of two distinctly different geologic crustal masses, and is a zone of extensive faulting. The seismicity of this belt is related to the faults. Bonneville Unit of Central Utah Project would have segments located on both of these crustal masses, and cross from one to the other. Strawberry Aqueduct would be located on the seismically inactive middle Rocky Mountain province while the Wasatch Aqueduct, Jordanelle Reservoir and their related storage and distribution features would lie upon the Basin and Range province, and generally within the belt of active seismicity. The large Wasatch Fault Zone presents the greatest earthquake potential to existing and proposed unit features. The fault lies parallel to the Wasatch Mountains and is situated along the eastern edge of Bonneville Basin. Fresh fault scarps ( probably occurring within 300 years) are found at the mouths of Big and Little Cottonwood Canyons and along the Wasatch Front north of Nephi. These show displacements of 10 to 20 feet and represent earthquakes having Richter magnitudes of about 7.0 to 7.2. A report published by the Seismological Society of America states: " At least 609 earthquakes occurred in Utah from 1850 to 1965. At least 38 of these caused some damage. More than 90 percent occurred along or in association with known fault zones. At least 15 earthquakes had an estimated Richter magnitude of 6.0 or greater. From 1950 to 1965 Utah experience 13 damaging earthquakes." 15 Figure B- 2 shows the occurrence and magnitude of earthquake activity for the State of Utah for the 1850- 1965 period. Data 121 |
