Paper No. 2
Presentation Time: 8:00 AM-6:00 PM
PRELIMINARY RESULTS FROM SEISMIC IMAGING NEAR THE MARIANNA, ARKANSAS, SAND-BLOW TREND
DADA, Olamide, Geology and Geophysics, University of Oklahoma, 100 East Boyd Street Suite 710, Norman, OK 73019, WILLIAMS, R.a., Geologic Hazards, U.S. Geological Survey, Golden, CO 80401, STEPHENSON, W.J., U.S. Geological Survey, Denver Federal Center MS 966, Box 25046, Denver, CO 80225, ODUM, J.K., U.S. Geological Survey, Box 25046 MS-966, Denver, CO 80225 and MULLINS, C., Network for Earthquake Engineering Simulation (NEES), University of Texas, 301 E. Dean Keeton, Austin, TX 78712-1020, Olamide.Dada-1@ou.edu
A linear trend of mid-Holocene earthquake-induced sand blows near Marianna, Arkansas, prompted the USGS in June 2010 to look for possible related faults in this area using high-resolution P-wave seismic reflection profiles. The field area is located in east-central Arkansas about 75 km southwest of Memphis, Tennessee, and 80 km south of the southwestern end of the New Madrid seismicity trend. Previous studies of the sand blows indicate that they were produced 5000 to 7000 years ago by large earthquakes of similar magnitude (M7+) to the 1811 and 1812 New Madrid earthquakes. This site adds to a growing list of potentially-active faults discovered in the last 15 years that are within the Mississippi embayment but lie outside the main New Madrid seismicity trend.
Two parallel, 5-km-long profiles, with 5- and 10-m geophone and Minivibe source spacing, respectively, were acquired in an east-west direction across the northwest-southeast sand blow trend. Preliminary processing and interpretation of the data reveals several prominent and well known marker reflections imaging the top of the Paleozoic and overlying Cretaceous sections, as well as several coherent reflections within the Tertiary section. In one profile there are two west-up vertical discontinuities in the Paleozoic reflection at about 1100 m depth that are strongly suggestive of steeply dipping reverse faulting. The western-most fault displacement is larger and appears to have recurrent motion with about 40 m of uplift on the Paleozoic reflection and about 20 m of foldeing on Eocene reflections at 400 m depth. The magnitude of these fault and fold displacements are typical of those seen in many reflection profiles that image the Paleozoic and younger section in the Mississippi embayment region. Additional data processing and analysis are needed to clarify whether the apparent faults reach the base of the Quaternary section.
