The record of seismically induced liquefaction on late quaternary terraces in northwestern Tennessee

Abstract

Between December 1811 and February 1812, the four largest historical earthquakes (mb > 7.0) in eastern North America occurred in the New Madrid (Missouri) seismic zone (NMSZ). Although this area has been the focus of considerable seismological and geological research, estimates of the repeat time of large-magnitude seismic events remain poorly constrained. The available estimates are based primarily on earthquake-frequency statistics and limited paleoseismology studies. Johnston and Nava (1985) analyzed about 180 yr of historical seismicity data and 10 yr of instrumental data and concluded that the repeat time for largemagnitude events ( m b > 7.0) is between 550 and 1100 yr. This estimate assumes that the data set is representative of the seismicity in the NMSZ and that the slope of the line relating earthquake frequency to magnitude (b value) is constant from smallto large-magnitude earthquakes (Johnston and Nava, 1985). However, Pacheco et al. (1992) reported that b values may not be constant in earthquake frequency-magnitude distributions and, thus, the estimated recurrence interval of Johnston and Nava (1985) must be considered tentative. Two geological studies suggest that the recurrence interval of large-magnitude earthquakes in the NMSZ is on the order of 450 to 600 yr. Two exploratory trenches across the Reelfoot scarp in northwestern Tennessee (Fig. 1) revealed the only unequivocal example of Holocene surface faulting in the upper Mississippi embayment (Russ et al., 1978; Russ, 1979; Kelson et al., 1993). Stratigraphic relations across the northern part of the scarp indicate at least two episodes of faulting had occurred after about 2250 yr B.P. and before the 1811 to 1812 seismic events (Russ, 1979). Based on these two prehistoric earthquakes, the dating error limits, and the 1811 to 1812 events, Russ (1979) estimated an average recurrence interval of 600 yr or less for large-magnitude earthquakes in the NMSZ. This estimated average recurrence interval is corroborated by a radiocarbon age estimate of A.D. 1310 to 1540 for fault-scarp colluvium along the central Reelfoot scarp (Kelson et al., 1993). However, inasmuch as Russ (1979) found no evidence that offset occurred on the Reelfoot scarp during the 1811 to 1812 earthquakes, the relation between surface ruptures on the Reelfoot scarp and large paleo-earthquakes in the NMSZ is not clear. The widespread development of liquefaction features during the 1811 to 1812 earthquake series (Obermeier, 1989; Obermeier et al., 1990), and the probable development of similar features during previous large-magnitude seismic events ( m b > 6.2, Nuttli, 1982) has been the basis for several efforts to identify paleoliquefaction features. Saucier (1991) estimated an average recurrence