Repeated Large-Magnitude Earthquakes in the Marianna Area of East-Central Arkansas During the Middle-Early Holocene and Possibly the Late Pleistocene

Abstract Very large, weathered sand blows and related sand dikes in the Marianna area indicate that large earthquakes were centered there in the past. Radiocarbon (C14) and optically stimulated luminescence dating suggest that the liquefaction features formed during paleoearthquakes about 4.7, 5.4, 6.8, and 9.8 thousand years ago (ka) and possibly during two earlier events about <19.5 and <24.3 ka. Many sand blows occur along or near a northwest-oriented tonal lineament—known as the Daytona Beach lineament (DBL)—located southwest of Marianna. Supported by an independent seismic reflection study that identified a fault zone beneath the lineament, the DBL and spatially associated sand blows may be the surface expression of an active fault zone. Sand blows along the lineament at sites DB1, DBSE2, DBNW2, DBNW3, and DBNW5 are elongated in a northwest–southeast direction and have sand dikes with northwest trends. At sites DBSE2 and DBNW2, soft-sediment faults, also with northwest trends, crosscut sand dikes, displacing soil lamellae within the dikes. At one of the sites, small sand dikes were injected along the faults. Northeast of Marianna at site SF500, a compound sand blow composed of multiple depositional units formed about 6.8 ka. Located near the intersection of the White River fault zone and Eastern Reelfoot Rift Margin fault zone, the compound sand blow likely formed as the result of a sequence of large earthquakes, perhaps produced by these fault zones. Liquefaction potential analysis suggests that moment magnitude (M) 6.0–6.5 earthquakes generated by the fault zone beneath the DBL could have induced liquefaction in the Marianna area. However, larger Marianna earthquakes ranging up to M 7.5 would be required to induce liquefaction at distal sites near Blytheville and Marked Tree, Arkansas, and Tunica, Mississippi, where relatively small liquefaction features may have formed during the 4.7, 5.4, and 6.8 ka events.