Martitia P. Tuttle

The Earthquake Potential of the New Madrid Seismic Zone

The fault system responsible for New Madrid seismicity has generated temporally clustered very large earthquakes in A.D. 900 100 years and A.D. 1450 150 years as well as in 1811-1812. Given the uncertainties in dating liquefaction features, the time between the past three New Madrid events may be as short as 200 years and as long as 800 years, with an average of 500 years. This advance in understanding the Late Holocene history of the New Madrid seismic zone and thus, the contemporary tectonic behavior of the associated fault system was made through studies of hundreds of earthquake-induced liquefaction features at more than 250 sites across the New Madrid region. We have found evidence that prehistoric sand blows, like those that formed during the 1811-1812 earthquakes, are probably com- pound structures resulting from multiple earthquakes closely clustered in time or earthquake sequences. From the spatial distribution and size of sand blows and their sedimentary units, we infer the source zones and estimate the magnitudes of earth- quakes within each sequence and thereby characterize the detailed behavior of the fault system. It appears that fault rupture was complex and that the central branch of the seismic zone produced very large earthquakes during the A.D. 900 and A.D. 1450 events as well as in 1811-1812. On the basis of a minimum recurrence rate of 200 years, we are now entering the period during which the next 1811-1812-type event could occur.

Archeological and pedological evidence for large prehistoric earthquakes in the New Madrid seismic zone, central United States

Prehistoric liquefaction features have been identified by careful observation of their structural and stratigraphic relations to Native American occupation horizons and their subtle soil characteristics. The ages of these liquefaction features have been estimated from radiocarbon dating of wood associated with the features and Native American artifacts found within bounding occupation horizons. At three sites near Blytheville, Arkansas, in the central part of the New Madrid seismic zone, one sand-blow crater formed between A.D. 800 and 1400, two sand-blow deposits formed between A.D. 800 and 1670, and three, possibly four, sand dikes formed since 4035 B.C. Where not found in association with Native American occupation horizons and artifacts, prehistoric liquefaction features can be difficult to distinguish from features that formed during the great New Madrid earthquakes of A.D. 1811 and 1812. This raises the possibility that prehistoric liquefaction features may have been misinterpreted during previous studies in the area. Nevertheless, a paleoearthquake chronology is beginning to emerge for the New Madrid seismic zone. Our findings are consistent with paleoseismological studies in the northern part of the seismic zone and suggest a recurrence interval of hundreds of years for earthquakes large enough to induce liquefaction in this region (M ≥ 6.4). By mapping the age distribution of liquefaction features, a more accurate assessment of the long-term earthquake potential of the region will be possible.

The use of liquefaction features in paleoseismology: Lessons learned in the New Madrid seismic zone, central United States

A recent study in the New Madrid seismic zone demonstrates that large uncertainties, often involved but rarely expressed, in paleoliquefaction studies can be reduced by conducting detailed investigations at the most promising sites for dating liquefaction features. During the site investigations, care must be taken to collect samples that will provide close maximum and minimum dates for liquefaction features. It is advisable to use two-sigma calibrated dates, rather than one-sigma calibrated dates or radiocarbon ages, when estimating ages of liquefaction features. Well-constrained ages of individual liquefaction features should provide the basis for estimating the timing of paleoearthquakes and correlating features across a region. As uncertainty in ages of liquefaction features decreases, confidence in estimates of timing, source areas and magnitudes of paleoearthquakes increases. The New Madrid study also shows that modern or historic earthquakes that induced liquefaction in the same region and whose locations and magnitudes are fairly well know can serve as calibration events for paleoearthquakes. Future efforts that could further improve the usefulness of liquefaction feature in paleoseismology include (1) the development of new techniques for dating liquefaction features directly, (2) case studies of modern earthquakes that focus on the site and spatial distributions of liquefaction feature as well as geotechnical properties of liquefaction sites and (3) more rigorous quantification of uncertainties associated with estimates of timing, source areas and magnitudes of paleoearthquakes.

Earthquake recurrence inferred from paleoseismology

Publisher Summary This chapter describes three North American examples of earthquake history inferred from Quaternary geology and discusses earthquakes in the interior of the North America plate––in the New Madrid seismic zone of Missouri, Arkansas, and Tennessee. The study of prehistoric earthquakes––paleoseismology––provides long-term rates of earthquake occurrence to improve confidence in such forecasts. These earthquakes suggest the rates and patterns of recurrence that help define earthquake hazards. The eastern California shear zone, centered about 150 km northeast of Los Angeles, exhibits geologic evidence for prehistoric surface ruptures during episodes thousands of years apart. Typical intervals between the earthquakes span hundreds of years in the New Madrid and Cascadia examples and thousands of years in the eastern California example. Apart from enabling such estimates of recurrence intervals, paleoseismology can provide evidence for the regional clustering of earthquakes in seismic zones and for aperiodic rupture along the same part of a fault. Such findings have made paleoseismology an essential part of earthquake-hazard assessment in the United States.

Recognizing and dating prehistoric liquefaction features: Lessons learned in the New Madrid seismic zone, central United States

The New Madrid seismic zone (NMSZ), which experienced severe liquefaction during the great New Madrid, Missouri, earthquakes of 1811 and 1812 as well as during several prehistoric earthquakes, is a superb laboratory for the study of world-class, earthquake-induced liquefaction features and their use in paleoseismology. In seismically active regions like the NMSZ, frequent large earthquakes can produce a complex record of liquefaction events that is difficult to interpret. Lessons learned studying liquefaction features in the NMSZ may help to unravel the paleoseismic record in other seismically active regions. Soil characteristics of liquefaction features, as well as their structural and stratigraphic relations to Native American occupation horizons and other cultural features, can help to distinguish prehistoric liquefaction features from historic features. In addition, analyses of artifact assemblages and botanical content of cultural horizons can help to narrow the age ranges of liquefaction features. Future research should focus on methods for defining source areas and estimating magnitudes of prehistoric earthquakes from liquefaction features. Also, new methods for dating liquefaction features are needed.

New evidence for a large earthquake in the New Madrid seismic zone between A.D. 1400 and 1670

In an integrated geological, archaeological, and geophysical study in the New Madrid seismic zone of the southeastern United States, we documented a prehistoric sand blow and related feeder dikes at an archaeological site near Steele, Missouri. Archaeological analysis combined with radiocarbon dating suggest that the earthquake-induced features formed between A.D. 1400 and 1670. This paleoseismic study provides the best evidence to date for a large earthquake occurring in the zone within ∼400 yr prior to the 1811–1812 New Madrid earthquake sequence. To determine an optimal location for excavating at the study site, we mapped surficial artifact density and conducted geophysical surveys. In doing so, we were able to reveal critical relationships for constraining the age of the prehistoric earthquake with minimal impact to the archaeological site.

Geophysical reconnaissance of earthquake-induced liquefaction features in the New Madrid seismic zone

Abstract Electrical resistivity and electromagnetic induction surveys performed at a site in the New Madrid seismic zone in the central United States demonstrate the ability of geophysical instrumentation to determine the location, size and orientation of earthquake-induced liquefaction features in the subsurface. Liquefaction features, including sand blows and sand dikes, are common within the Late Pleistocene and Holocene floodplain of the Mississippi River. These features and their relationship to host sediments provide important information about historic and prehistoric earthquakes and their source parameters, such as timing, epicentral location and magnitude. Following the geophysical surveys, two excavations were made and documented for a paleoseismic study. Sediment samples of soils, Native American occupation horizons, and liquefaction features within the trenches were collected for sedimentological and archeological analyses and compared with the geophysical observations. Measurements of the heights of cotton plants growing at the site were also taken, since growth appeared to reflect variations in the texture and thickness of soils developed on fluvial deposits and sand blows. The excavations, along with sedimentological and agricultural data, provided a means for calibrating sediment characteristics with the geophysical interpretations and for developing criteria to distinguish anomalies due to facies changes from anomalies related to liquefaction features. Disruption of the local sedimentological trends by an en echelon arrangement of sand dikes and related sand blows is seen in the combined geophysical and agricultural data. Results of the surveys indicate that constant-spread resistivity profiling (Wenner array) was an effective method for locating and mapping shallow sand dikes, some with widths of less than 50 cm. The electromagnetic induction method (EM-31), while less sensitive to dike locations, was useful in characterizing depositional facies changes by their differences in electrical conductivity. Data from the study site support the interpretation that the earthquake-induced liquefaction features occurred near the boundary of a facies change, which may have constituted a zone of weakness along which excess pore fluids and sand escaped.

Use of archaeology to date liquefaction features and seismic events in the New Madrid seismic zone, Central United States

Prehistoric earthquake-induced liquefaction features occur in association with Native American occupation horizons in the New Madrid seismic zone. Age control of these liquefaction features, including sand-blow deposits, sand-blow craters, and sand dikes, can be accomplished by extensive sampling and flotation processing of datable materials as well as archaeobotanical analysis of associated archaeological horizons and pits. This approach increases both the amount of carbon for radiocarbon dating and the precision dating of artifact assemblages. Using this approach, we dated liquefaction features at four sites northwest of Blytheville, Arkansas, and found that at least one significant earthquake occurred in the New Madrid seismic zone between A.D. 1180 and 1400, probably about A.D. 1300 f 100 yr. In addition, we found three buried sand blows that formed between 3340 B.C. and A.D. 780. In this region where very large to great earthquakes appear to be closely timed, archaeology is helping to develop a paleoearthquake chronology for the New Madrid seismic zone. 0 1996 John Wiley & Sons, Inc.

Observing earthquake‐related dewatering using MISR/Terra satellite data

On 26 January 2001, at 8:46 am, the Gujarat province of India (see Figure 1A) was hit by destructive earthquake.This earthquake, considered one of the two most damaging seismic events in Indian recorded history, caused the death of about 20,000 people and affected 16 million individuals. Both local residents and post-earthquake survey teams reported the fountaining of water and sediments on the ground, especially in the Rann of Kachchh, which formed deposits known as sand and silt blows [e.g., Bendick et al., 2001; Jain and Lettis, 2001; Tuttle et al., 2002]. The water flow was significant enough to reactivate ancient river channels and to form shallow lakes. (Extensive information concerning the Gujarat earthquake can be found on the following Web sites: http://geoinfo.usc.edu/, http://cires.colorado.edu/, http://www.ceri. memphis.edu/, http://home. hiroshima-u-ac.jp/.)

Geophysical surveys of earthquake-induced liquefaction deposits in the New Madrid seismic zone

We explore the effectiveness and limitations of electrical and electromagnetic methods in imaging buried, earthquake-induced liquefaction deposits. Geophysical surveys conducted at liquefaction sites in the New Madrid seismic zone (NMSZ) in the central United States demonstrate that these subsurface-imaging techniques can be useful tools in paleoseismology. Paleoseismological studies of liquefaction features provide one of the few means for estimating recurrence intervals of large earthquakes in the NMSZ, a region with widespread evidence of strong ground shaking but short instrumental record. Noninvasive geophysical methods minimize ground disturbance during these studies, an attribute of particular importance when the studies are conducted at federally protected archaeological sites. Surveys such as those described here can be used to locate buried liquefaction deposits and to site trenches for detailed geologic studies.