Seismicity and tectonic relationships of the Nemaha uplift in Oklahoma

Technical Report · Tue Nov 01 04:00:00 EST 1977

OSTI ID:6816249

Luza, K V

Geologic and seismologic investigations of the Nemaha uplift began on October 1, 1976. The geological studies have focused, thus far, on the construction of a series of structure-contour maps on key stratigraphic horizons: the top of the Viola Formation, the base of the Pennsylvanian, and the top of the Oswego Formation. The contour-mapping phase of the program is approximately two-thirds completed. Our initial mapping program reveals a complex fault pattern and geologic history of the Nemaha ridge. It appears that the uplift and associated faults began in Early Pennsylvanian time and that tectonic activity ceased in Middle Pennsylvanian time, at least in central Oklahoma. A discussion of basement rocks in central Oklahoma is included. The most systematic basement-rock study that includes the Nemaha ridge area was done by Denison (1966), who classified the central Oklahoma basement rocks into the following four units: (1) Washington County Volcanic Group, (2) Spavinaw Granite Group, (3) Osage County Microgranite, and (4) Central Oklahoma Granite Group. The isotopic ages range from 1,150 to 1,270 million years, and these ages, when considered with analytical variations, indicate a main period of thermal activity about 1,200 million years ago. The seismological studies have concentrated on the installation of eight seismometers in such a way as to include detailed coverage of the entire Nemaha ridge as well as most of the remaining area of Oklahoma. Work has begun on the installation of three high-frequency vertical seismometers radiolinked to the observatory for extended directional capability. Six computer programs were developed for storage and processing of all teleseismic and local-arrival-time and amplitude data. A catalogue of all known Oklahoma earthquakes was prepared.

• Research Organization: Oklahoma Geological Survey, Norman (USA)
• OSTI ID: 6816249
• Report Number(s): NUREG/CR-0050
• Country of Publication: United States
• Language: English

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USA