Paleoliquefaction Studies in Moderate Seismicity Regions with a History of Large Events (NUREG/CR-7257)
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Manuscript Completed: January 2019
Date Published: June 2019
M.P. Tuttle, L.W. Wolf, K. Dyer-Williams, P. Mayne,
R.H. Lafferty, K. Hess, M.E. Starr, M. Haynes,
J. Morrow, R. Scott, T. Busch, P. Villamor, J. Dunahue,
M. Rathgaber, K. Tucker, C. Karrenbauer, and C. Moseley
Rasool Anooshehpoor, NRC Project Manager
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001
This report covers a multi-faceted paleoliquefaction project conducted between 2011 and 2018. The main focus of the report is the research component of the project, including a paleoliquefaction study in the New Madrid seismic zone (NMSZ) and surrounding region as well as post-earthquake survey for liquefaction features in the Central Virginia seismic zone following the 2011, magnitude (M) 5.7 Mineral, Virginia, earthquake. The report also summarizes two other components of the project including a NUREG/CR document and a training workshop on paleoliquefaction studies. NUREG/CR-7238 entitled, "Guidance Document: Conducting Paleoliquefaction Studies for Earthquake Source Characterization," captures today's best practices for conducting paleoliquefaction studies and includes an extensive bibliography. The training workshop was organized and held in the NMSZ for U.S. Nuclear Regulatory Commission (NRC) staff members and other members of the nuclear regulatory community.
The aim of paleoliquefaction research conducted in the NMSZ was to gather additional paleoliquefaction data that would help to reduce epistemic uncertainty in the seismic source model in this region, where seismic hazard is the highest in all of the central and eastern United States, and to evaluate the earthquake potential of other structural elements of the Reelfoot Rift system, including the Commerce Geophysical Lineament, the eastern and western Reelfoot Rift margins, and the Marianna area at the southern end of the eastern Reelfoot Rift margin. The research project involved conducting surveys for paleoliquefaction features in key areas that had not yet been systematically searched and constraining age estimates of previously and newly discovered sand blows to improve completeness of the paleoearthquake record in the region. Major discoveries include (1) a possible fault zone in western TN, delineated by northeast-oriented lineaments and large linear sand blows that formed during the A.D. 1811-1812 and A.D. 1450 New Madrid events; (2) sand blows near Paragould, AR, that suggest a previously unrecognized New Madrid earthquake about A.D. 0 ± 200 yr; (3) a sand blow near Blytheville, AR, that supports a previously recognized New Madrid earthquake about B.C. 1050 ± 250 yr and as one of three large earthquakes in a sequence; and (4) two to three generations of liquefaction features on Coldwater River in northwestern MS that may have formed during an ERM-S event in B.C. 300 ± 250 yr and/or during the Marianna events in B.C. 2850 ± 150 yr, B.C. 3550 ± 150 yr, or B.C 4850 ± 150 yr. Overall, findings support prior interpretations that the NMSZ was the source of earthquake sequences in A.D. 1811-1812, A.D. 1450, and A.D. 900 and that the A.D. 1450 and A.D. 900 events included one or more earthquakes of M 7.5-7.8. With the addition of events in A.D. 0 ± 200 yr and B.C. 1050 ± 250 yr to the New Madrid earthquake chronology, an average recurrence time of ~1100 years is estimated for the period between 4400-1200 yr B.P. and of ~500 yr for the last 1200 years. However, given that sand blows that formed prior to the three most recent New Madrid events are still being found, it is likely that the paleoearthquake chronology is still incomplete prior to A.D. 900.
Following the 2011 M 5.7 Mineral, Virginia, earthquake, reconnaissance for liquefaction features was performed along 24 km of the South Anna River downstream from the epicenter. No modern liquefaction features were found either in the cutbanks or on the floodplains; however, possible paleoliquefaction features were found at eight sites along river. The dike sizes appeared to increase towards the east, suggesting that the paleoearthquake(s) responsible for their formation was larger, and/or located farther to the east, than the 2011 Mineral earthquake. This finding prompted a follow-on study supported by the National Earthquake Hazard Reduction Program managed by the U.S. Geological Survey. During that study, paleoliquefaction features were confirmed along the South Anna River and additional paleoliquefaction features found along other rivers in the region. The findings suggested that there were two paleoearthquakes in the iv region during the past 4,500 years and that the older of the two events was of M ≥ 6 and located farther to the east than the 2011 Mineral earthquake.
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