SEISMIC SURVEYING OF QUATERNARY FAULTS:
Satsuma Road, Livingston Parish, LA
Environs of Satsuma Road
The location of shallow growth faults, their geophysical characterization and the natural moderators that control their rates of movement in the southern Gulf Coast region are poorly known. Traditionally, land-loss in the southern Gulf Coast region is assumed to result from a combination of growth faulting (slow faults of no earthquake hazard), natural sediment compaction, and salt-water incursion related human activities such as oil exploration and production. Movement of these faults may be related to reactivation of ancient deep-seated faults whose surface locations are unknown.
The upper 500-1000 m below the surface are critical to land-use and management but are virtually unknown. The characterization of faults is important to fault-hazard risk assessment and damage reduction. Southern Louisiana is traversed by a multitude of, active but aseismic faults of at least Tertiary age whose movement has been detected by the cumulative damage caused to adjacent buildings, roads and public utilities. Extensive oil-related geophysical studies have been performed in southern Louisiana and hundreds of faults have been mapped within deep oil-producing intervals. However, there is almost no understanding of where these faults exist in the shallow sub-surface. Existing oil well seismic data do not record the upper few hundred feet with sufficient resolution for us to interpret accurately the most recent fault movement activity. Until now, faults have been interpreted by their surface expression which is often difficult to distinguish from other geomorphological features such as river terraces.
By using seismic reflection we will locate and characterize buried and previously inferred faults along the Livingstone Fault Zone in the vicinity of Satsuma Road LA.
SEISMIC SURVEY I
The seismic reflection profiling system will be provided by the Department of Geology and Geophysics and consists of a 24-channel Geomterics seismograph, 48 geophones with roll-along switch box, a downhole seisgun as well as differential GPS (+-1.5 m horizontal resolution) and a total station (+/- 10 cm resolution) for accurately locating shotpoints and receivers. I estimate a vertical seismic resolution of 2 m (at 100-Hz, 2 000 m/s) and a penetration of about 500 - 1000 m will permit us to encounter reach the top of the Pleistocene (Fisk, 1944). Other shallow-penetration geophysical techniques such as ground-penetrating radar work poorly in the local clay-rich soils and do not provide as highly resolvable lateral correlation of stratigraphic units.
All processing will be conducted in the state-of-the-art subsurface laboratory of the Department of Geology and Geophysics at Louisiana State University, using industry-donated Schlumberger software.
Available 2D and 3D seismic facilities
The Department of Geology and Geophysics at Louisiana State University owns and houses two new geophysics facilities. The Subsurface laboratory has been designed for the analysis and interpretation of 3D and 2D seismic geophysical and stratigraphic information and comprises a modern, state-of-the-art hardware and software system comparable to any major oil-company seismic research facility. This $6 million lab was made possible largely by industry donations and has a guaranteed 6-year commitment for upgrade and maintenance from premier software providers. Comprehensive software permits interactive 3D visualization and GIS-mode data management. The facility also acts as a repository and retrieval center for 3D data sets provided by industry for research and teaching in the Department. Principal hardware includes two Pentium 4 linux processors, one dual-screen with 500 Mbyte and 1Gbyte and of RAM , and a combined hardisk capacity of 200 Gbytes, a DDDS-4 format DAT drive, an Exabyte drive, and four dual-screen Sun Ultra workstations, one fileservers with ~100 Gigagbyte capacity connected internally via a 150 Mbit/second network as well as large-format color hardcopy devices.
Second, the Department of Geology and Geophysics has a 24-channel high-resolution seismic reflection profiling system with an extended 48-channel roll-along capability while in production mode and can use both seisgun and .22 caliber gun energy sources. The seismic system is adaptable to 3D-seismic acquisition. Two gravity meters (Lacoste-Romberg, Worden) six GPS units and a total station theodolite system are used to locate major structures and optimize planning prior to seismic surveys.
Yuvancic, B., Latham, H., Lorenzo, J.M. van Heerden, I. 2000. Neotectonics in the lower Mississppi Valley: High-resolution gravity and seismic characterization of active shallow-subsurface normal faults. Official Program of 2000 AAPG Annual Convention, Vol. 9, A84
Lorenzo, J. M., Yuvancic, B*, Latham, H.*, Bouillon, A.* and Cazes, C.* 2000 Neotectonics in the lower Mississippi Valley: High-resolution gravity and seismic characterization of active shallow-subsurface normal faults. Geological Society of America Meeting Abstracts with Program.
Fisk, H. N. (1944). Geological investigation of the alluvial valley of the lower Mississippi River. Vicksburg, Mississippi, War Dept.