Map: Country Drained by the Mississippi, 1823, Stephen Long

New Madrid Seismic Zone (NMSZ)

Geology of the NMSZ

Earthquake-Induced Liquefaction of the NMSZ

Paleoseismology: Digging up the Past

Paleoseismology of the New Madrid Seismic Zone

Archeology and New Madrid Paleoseismology

Paleoseismology and Earthquake Hazard Mapping

Bibliography

Links

M. Tuttle & Associates Home




Background map courtesy Cartography Associates: Edwin James and Stephen Long, Country drained by the Mississippi, Eastern Section, 1822. Carey and Lea Philadelphia.

 


Paleoseismology is the study of the timing, location, and magnitude of prehistoric earthquakes preserved in the geologic record. Knowledge of the pattern of earthquakes in a region and over long periods of time helps to understand the long-term behavior of faults and seismic zones and is used to forecast the future likelihood of damaging earthquakes. Paleoseismology is proving especially useful in regions where of the time between large earthquakes is usually longer than the historical record. In western North America, paleoseismology usually focuses on faulting of near-surface sediment whose age can be determined. In eastern North America, where near-surface faulting is uncommon or difficult to identify, paleoseismology often employs liquefaction features to learn about prehistoric earthquakes. Earthquake-induced liquefaction features are distinctive and form as the result of strong ground shaking. Liquefaction features include sand blows, dikes, and sills. Sand blows are deposits that form on the ground surface as the result of venting of water and sand. Sand dikes are sediment-filled cracks through which water and sand flowed. Sand sills usually take the form of lenses intruded below clay layers and are connected to sand dikes. Most large earthquakes around the world have induced liquefaction.

Photograph of sand blow deposit and related feeder dike exposed in excavation. Sand blow buries soil that was at ground surface at time of event. Sand dike fills fissure that formed in soil. For scale, shovel blade is 20 cm wide. Photograph by Martitia Tuttle.

Photograph of large, 80-cm-wide sand dike exposed in cutbank of Hatchie River in western Tennessee. Note clasts of mottled silt in sand dike. Weathering is especially pronounced in upper 15 cm of sand dike and extends downward for another 70 cm, suggesting it is probably prehistoric in age. Hoe is 1 m long with each color band representing 25 cm. Photograph by Martitia Tuttle.

Photograph of sand dike and sill exposed in drainage ditch in southeastern Missouri. Sand dike intruded weathered sand; sill emplaced below weathered clay. Layering within the dike and sill indicate that they formed during two or more events. For scale, knife is 8 cm long. Photograph by Martitia Tuttle.



M. Tuttle & Associates: P.O. Box 345, Georgetown ME 04548•   mptuttle@earthlink.net