Regional tectonics and seismicity of eastern Nebraska. Annual report, June 1977--May 1978

This report presents and interprets the information obtained by the Conservation and Survey Division (Nebraska Geological Survey) during the year June 1, 1977, to May 30, 1978. The information pertains to the geology, structure, tectonics, and seismicity of eastern Nebraska with emphasis on the vicinity of the Humboldt Fault Zone in western Richardson and eastern Pawnee counties. The scope of the studies is summarized as follows: rock outcrops in western Richardson and eastern Pawnee counties were reexamined and reevaluated, and 64 test holes were drilled to determine the altitude of the upper surface of the Tarkio Limestone of Pennsylvanian age; the possible relation of earthquakes in eastern Nebraska to Pleistocene glaciation was evaluated; three new seismograph installations were established in southeastern Nebraska; gravity surveys of western Richardson and eastern Pawnee counties were extended to the northern end of the Humboldt Fault Zone and were evaluated; ground magnetic surveys in western Richardson and eastern Pawnee counties were made and evaluated; gravity and ground magnetic surveys of the Elk Creek Anomaly were made and evaluated. 30 figures, 1 table