|Meeting||2012 Fall Meeting|
|Session||Understanding Recent and Historical Seismicity in the Central and Eastern U.S. I Posters|
|Authors||Ellsworth, W L*, Earthquake Science Center, U. S. Geological Survey, Menlo Park, CA, USA Horton, S, CERI, University of Memphis, Memphis, TN, USA Benz, H M, National Earthquake Information Center, U. S. Geological Survey, Golden, CO, USA Hickman, S H, Earthquake Science Center, U. S. Geological Survey, Menlo Park, CA, USA Leeds, A, National Earthquake Information Center, U. S. Geological Survey, Golden, CO, USA Leith, W S, U. S. Geological Survey, Reston, VA, USA Meremonte, M, National Earthquake Information Center, U. S. Geological Survey, Golden, CO, USA Rubinstein, J L, Earthquake Science Center, U. S. Geological Survey, Menlo Park, CA, USA Withers, M, CERI, University of Memphis, Memphis, TN, USA Herrmann, R B, Earth and Atmospheric Sciences, Saint Louis University, Saint Louis, MO, USA|
|Index Terms||Monitoring, forecasting, prediction  Emergency management  Earthquake source observations  Seismic instruments and networks |
Beginning in early June, 2012, an extended series of earth tremors were reported by residents of Bayou Corne in Assumption Parish, Louisiana, and at well control facilities on the nearby Napoleonville salt dome. The salt dome contains numerous caverns resulting from solution mining; some are used to store LPG and natural gas while others produce saltwater brine. Residents also reported natural gas bubbling at nearby locations in Bayou Corne and Grand Bayou. Some of the tremors were large enough to produce “cracks in sheet rock and foundations” (The Advocate, Baton Rouge, July 5, 2012). It was thus quite surprising to find that no earthquakes were detected in this region by either the USGS NEIC or the USArray Array Network Facility despite the presence of Transportable Array station 544A only 10 km from Bayou Corne. Careful inspection of the seismograms at 544A did reveal multiple events characterized by virtually no body wave energy and strong surface waves at the times of reported tremors. In response to a request for assistance from the State of Louisiana six temporary seismic stations with Trillium broad band sensors were deployed in the immediate epicentral region by the USGS and University of Memphis starting on July 12. Seismograms recorded by the temporary stations revealed a variable rate of tremor activity, with several hundred events registered on active days. Even at very close distance (S-P < 0.5 s) the body waves are weak and surface waves prominent, indicating a very shallow source depth. Precise location of the events is complicated by the presence of the high-seismic velocity and steep-sided Napoleonville salt dome that reaches to within 220 m of the surface and is overlain and surrounded by very low velocity sediments. Following several repositionings of the seismic network we have determined that the source region lies on the western edge of the salt dome top at very shallow depth and in the vicinity of an abandoned brine supply cavern. Tremor activity abruptly decreased on August 2nd, contemporaneously with the formation of a large sink hole on the margin of the dome immediately adjacent to the abandoned cavern. Efforts are ongoing to determine the origin of the tremors and relationship, if any to the industrial facilities on the dome.
Cite as: Author(s) (2012), Title, Abstract S51E-2453 presented at 2012 Fall Meeting, AGU, San Francisco, Calif., 3-7 Dec.