A new interpretive slow-varying (long-wavelength) static estimation method is introduced to remove the effects of static anomalies caused by lateral variations in near-surface velocity. The application becomes critical where the wavelength of the variation of statics is larger than the maximum offset between source and receiver (spreadlength) used during data acquisition. The method used in this study utilizes the reflection and refraction arrival times from the shallowest reflector or refractor to determine the statics variations. The study include reprocessing of 12 seismic reflection data sets from the Savannah River Site area, near Aiken, South Carolina. The same data sets were also used to extract the refracted arrivals by the refraction stack processing. Application of the estimated slow-varying statics enhanced the S/N ratio, lateral continuity, and coherency for deep as well as shallow data and allowed to better determine the geometry of faults in the Coastal Plain sediments, which penetrate from the basement. Interpretation of the enhanced seismic reflection and generated seismic refraction sections helped to constrain the depth of upward penetration of the faults imaged in the seismic data.

Refraction stack sections were used to obtain better definition of the delineation of the upward penetration of the faults at shallower depths. Despite the smoothing effect that is incorporated in the refraction stacks due to long refracted paths they exhibit clear-cut termination and offset on some of the lines in spatial zones where the Pen Branch fault can be projected in the shallow sediments.

The seismic data indicate that the Coastal Plain sediments dip and thicken toward the southeast in the area. The basement top provides a high acoustic impedence contrast, and has a regional dip towards the southeast. The Pen Branch fault is one of the longest faults in the area, that acts as a basin bounding fault separating the Paleozoic crystalline basement from the Triassic basin fill. Other faults such as the Steel Creek and A TT A have also been discerned by the seismic data in the area. Small antithetic faults appear to join the Pen Branch and the A TT A fault. The offset of the Pen Branch fault (15 ms; 32 m) is relatively higher then the offsets observed for the ATTA (11.5 ms; 24.5 m) and Steel Creek (13 ms; 27.5 m) faults. The delineation of the upward depth of penetration of the Pen Branch fault is imaged best on lines 28 and 2EXP where the reflections at 0.18 to 0.2 s exhibit termination with amplitude changes, thereby suggesting the presence of the fault at that level. The offset associated with the A TT A fault can be traced up to 0.16 son line 27. The expression associated with the Steel Creek fault does not seem to go above 0.2 s. On the basis of the result from the interpretation of line 27, the upward depth of penetration of the A TT A fault in the Coastal Plain sediments reaches to a higher level then that of the Pen Branch fault. On the basis of the reflection and refraction data it is interpreted that the reactivation of the Pen Branch and the A TT A fault is as young as the age of the shallow reflector at 200 ms (top of Cretaceous?).