Student Seth Berman
Shallow Seismic Studies of the Big Creek Fault Zone, Arkansas and Mississippi

Seth A. Berman and James B. Harris, Millsaps College, Jackson, Mississippi, 39210

A recent study of the Big Creek fault zone (BCFZ), mapped at the surface in southeast Arkansas, suggests that the fault zone projects to the northeast, beneath the Delta region of northwest Mississippi, and may show Holocene movement. In order to investigate this possible extension of the BCFZ, shear (S-) wave seismic reflection tests were performed in order to design acquisition parameters for future seismic profiling. Results of S-wave expanding spread tests, executed south of Helena, AR and east of Tunica, MS (along the trend of the BCFZ), indicate that data quality is sufficient to image the near-surface geology. Following correlation with local well data, a strong reflection from an approximate depth of 33 m was interpreted to represent the Quaternary/Tertiary unconformity at the base of the Mississippi River alluvium. Test data also indicated possible reflections from within the Quaternary section. S-wave techniques were chosen for this investigation because of their ability to provide increased seismic resolution in unconsolidated, water saturated sediments, such as those present in the study area. Analysis of S-wave seismic frequencies and velocities indicate a minimum resolvable limit of 1.3 m in the alluvium; a suitable value to image displacements (reported to range from 3 -10 m) on the BCFZ. Determining the presence and style of Holocene deformation along the BCFZ is key to understanding potential earthquake hazards that exist for the area.