SSA '01: Abstracts Online
SPATIAL AND TEMPORAL CHARACTERISTICS OF
PALEOSEISMIC FEATURES IN THE SOUTHERN TERMINUS OF
THE NEW MADRID SEISMIC ZONE IN EASTERN ARKANSAS
AL-SHUKRI, H.J., LEMMER, R.E., MAHDI, H.H., and CONNELLY, J.B.,
Department of Earth Sciences, University of Arkansas at Little
Rock, 2801 South University Avenue, Little Rock, AR 72204,
In the past 25 years our understanding of earthquake hazards in the New Madrid seismic
zone (NMSZ) has been profoundly changed by results of paleoseismic investigations.
Hundreds of earthquake-related features have been systematically surveyed and examined.
However, most investigations have been concentrated within the area of enhanced seismicity
terminating near Marked Tree, Arkansas. Numerous large (up to 107m X 55m) liquefaction
features resembling those within the NMSZ have been discovered 90 to 100 km
south-southwest of Marked Tree, Arkansas. Following an aerial reconnaissance survey of
east central Arkansas, a detailed subsurface investigation was conducted at three sites, two
near Marianna, Arkansas (Nancy 1 and Nancy 2) and one near Parkin, Arkansas (Parkin
1). One trench was excavated at Nancy 1 and two trenches were excavated at Nancy 2.
Each of the excavations exposed a fine-medium grained sand blow deposit overlying a thick,
plastic clay layer. The sand blows are fed by numerous vertical to shallow dipping sand dikes
<1cm to 20cm thick. Forty-five near vertical dikes were logged at Nancy 1 whereas only
3-5 dikes were exposed in the trenches at Nancy 2. Parkin 1 was also trenched to
investigate a 1.5 km long linear feature. The lineament trends N56°E and has a ground
surface that is 2.75 meters higher to the southeast. No fault was seen in the trench; however,
sand and clay layers tilted to the northwest were exposed suggesting possible faulting. A
seismic survey is planned to investigate this possibility. The size of the liquefaction features
and the distance of 100 km from the active NMSZ require either a major New Madrid
earthquake or a more local seismogenic source. In either case, the seismic hazard in the
region may be underestimated.