HR: 1330h
AN: G43A-02    [Abstracts]
TI: Determination of Recent Fault Activity in Southwestern Louisiana from Geodetic Leveling and LIDAR Data
AU: * Heltz, J O
EM: jheltz1@lsu.edu
AF: Center for Geoniformatics, Louisiana State University , Baton Rouge, LA 70803
AU: Dokka, R K
EM: rkdokka@c4g.lsu.edu
AF: Center for Geoniformatics, Louisiana State University , Baton Rouge, LA 70803
AB: An analysis of geodetic leveling data and LIDAR digital elevation models in southwestern Louisiana has led to the identification of several surface scarps in the area that exhibit measurable differential movement over the past half-century. Computation of relative benchmark velocities has shown that some of these faults had slip rates as much as 6 mm/yr during the 1960's and 70's. However, leveling data obtained as recently as January 2005 has revealed that these faults are currently moving at much slower rates. This study identifies the presence of several previously mapped fault-line scarps in addition to some unidentified surface features that exhibit similar characteristics. High-resolution mapping with LIDAR data has provided evidence of numerous linear topographic features that clearly offset and truncate alluvial ridges and terraces in the study area. Also, field observations have led to the discovery of significant damage to built structures due to differential movement across these scarps. These lines of evidence, combined with the leveling data, suggest that these faults are currently active and have moved episodically over the past fifty years on time scales of months to years. Previously mapped faults in this region of the state have been known to exhibit episodic motion since the late Tertiary and the driving force behind this movement is thought to be the enormous load of sediments along the Gulf Coast. This mechanism for fault movement acts on much longer time-scales, however, and an alternative source for the shorter wavelength fault activity is proposed. A possible cause for the accelerated slip rates that were calculated during the 60's and 70's could be the large amounts of fluid withdrawal that occurred in the southwestern part of the state during that time. From 1965 to 1980, groundwater withdrawals for the study area were the highest recorded in the state and petroleum production also peaked during that period. A reduction in pore pressure due to fluid withdrawal results in an increase in the effective stress in the subsurface and compaction of the underlying sediments. Differential compaction of sediments adjacent to faults accelerates fault activity and this motion is detected by the leveling data. Similar faults in the nearby Houston area also exhibit this spatial and temporal relationship of increased slip rates coinciding with increased subsurface fluid withdrawal. This suggests that in addition to the natural forces driving fault motion, anthropogenic activities may have also affected faulting in this area of Louisiana.
DE: 1208 Crustal movements--intraplate (8110)
DE: 8107 Continental neotectonics
SC: Geodesy [G]
MN: 2005 Joint Assembly