MAPPING PRECAMBRIAN FAULTS USING AEROMAGNETICS IN SOUTH-CENTRAL KANSAS AND NORTHERN OKLAHOMA

Recent earthquake activity in south-central Kansas and northern Oklahoma has raised many questions about distribution of structural features in Precambrian basement rocks. These rocks are known to be fractured and faulted, but the extent of these structural features are unknown. This study is being conducted to identify the orthogonally fractured nature of the Precambrian basement and to create maps of fault distributions across south central Kansas and northern Oklahoma. Inactive and active faults are being identified from timing of past seismic events, their magnitudes, and epicenters. Structure maps of post-Pennsylvanian sediments, records of salt water disposal volumes, and detailed residual aeromagnetic maps will further help identify fault locations in south-central Kansas and northern Oklahoma.

Residual aeromagnetics is proving to be particularly useful in recognizing basement structural features by measuring the magnetic susceptibility of Precambrian rock. Magnetic highs and lows show that areas surrounding individual Precambrian basement blocks can be interpreted as fault or shear zones due to the truncating nature of the fault blocks. Four terrains containing individual fault blocks are identified in south central Kansas, whose truncations and linear trends underlie major recent seismic events in the area. Earthquake locations are located along these zones of structural weakness. Using overlays and the structural history of the area, movement of fault blocks over geologic time can be interpreted. This study will produce (1) an updated map of faults in Precambrian rocks in south central Kansas and northern Oklahoma and (2) a map of corresponding earthquake migratory paths.