Soft sediment relay zones: a high resolution seismic survey Livingston Parish, Louisiana

Abstract

The southern coast of the United States, bordering the Gulf of Mexico, is home to several down-to-the-south, listric, normal fault systems striking parallel to the coast. One of these, the Baton Rouge–Tepetate Fault System located in southern Louisiana, consists of a series of near-surface, reactivated growth faults and relay ramps– a broad area of ductile strain, with contemporaneous sedimentation. Evidence of recent fault and relay ramp movement is seen in surficial fault line scarps and offset roads. This thesis utilizes two near-surface (<500>m), high-resolution (10 - 300 Hz), continuous seismic reflection profiles (360 m and 480 m long, 3 m geophone spacing; 24-channel) previously collected across a growth fault and a portion of a possible relay ramp in Livingston Parish, Louisiana to study this soft sediment system. The seismic source is a down-hole Betsy seisgun and source-to-receiver offsets range from 4 to 73 meters. One seismic line, seismic line LSU 4 (480 m) crosses near the tip of the fault at a point where there is no noticeable vertical offset. Seismic line LSU 1 (360 m) crosses the fault where a surficial scarp shows an offset of 1.5 m. The two seismic profiles are processed and analyzed for broken, offset reflectors indicating fault movement. This analysis, combined with well log data and gravity surveys across the fault and in the relay ramp area has shown that: (1) the near surface consists of numerous small faults distributed over a distance of ~40 m (2) fault movement is ~40 m since the early Pleistocene (3) a previously interpreted gravity high coincides with the faulted region (4) the characteristics of the imaged region are consistent with those of a relay ramp.