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,

alshukri@seismo.ualr.edu

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.