1 January 2008 Restless Kansas: Evidence of Structural Development in the Flatlands
Daniel F. Merriam
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The Phanerozoic structural development of Kansas is recorded by the stratigraphic and sedimentological evidence. The early Paleozoic was relatively quiet, but a major change in the structural regimen took place in the late Paleozoic as a result of events in adjacent areas. Structural development was mainly by vertical differential movement along faults defining rigid Precambrian basement blocks as they adjusted to the stress. These movements are recorded in the changes of sediment thickness over the fault blocks. Concurrently, as the basement blocks adjusted, seismites were triggered by paleoearthquakes. By mapping the occurrence of seismites vertically and laterally, conclusions can be made on the frequency and intensity of the paleoquakes. The occurrence of seismites formed by paleoquakes seemingly diminish with time, but this may be a function of suitable conditions for their formation and preservation.

Subsequent structural movement in the Mesozoic and Tertiary was mainly regional tilting, however, some convolute sedimentary structures and small intraformational faults in the Cretaceous indicate vertical movement was continuing. Paleoliquefaction features also have been reported in Holocene sediments in Edwards, Wabaunsee, and Woodson counties, Kansas. Historical recorded earthquakes and microseisms are evidence that the strain and structural movement is continuing today. Other than shallow man-made quakes, earthquake foci, in general seem to concentrate at two depths: 7.5 to 13.5km (Conrad discontinuity) and 35 to 50 km (Mohorovičić or Moho boundary). The major disturbances, for the most part, occur along the seismic active Nemaha Anticline from Nebraska to Oklahoma and the east-bounding Humboldt fault zone. From the available evidence, it is inferred that the structural development of Kansas is not and was not spectacular, but is and has been gradually continuous and intermittent.

Daniel F. Merriam "Restless Kansas: Evidence of Structural Development in the Flatlands," Transactions of the Kansas Academy of Science 111(1), 93-104, (1 January 2008). https://doi.org/10.1660/0022-8443(2008)111[93:RKEOSD]2.0.CO;2
Published: 1 January 2008
Conrad discontinuity
Mohorovičić (Moho) discontinuity
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