U.S. Geological Survey




Stephen F. Obermeier

U.S. Geological Survey
Reston, VA 20191

This text and the accompanying slides concentrate on the manifestations of seismically induced liquefaction features that are most commonly encountered in paleoliquefaction searches. The liquefaction features shown in this presentation are mainly from field studies in the continental United States in which I was a principal investigator. These studies began in the 1980's, when searching for evidence of paleoliquefaction over a large geographic region was first used to determine the paleoseismic record. Since then, paleoliquefaction evidence has determined the timing and likely magnitude of many prehistoric earthquakes in the central and eastern United States, through much of the Holocene. Also, paleoliquefaction features first showed that seismic shaking accompanied subduction earthquake downdropping in prehistoric time along coastal Washington and Oregon. (References documenting these studies are listed at the end of this text.)

Clastic intrusions (dikes and sills) in sediments of fluvial, deltaic, estuarine, or aeolian origin (i.e., nonmarine origin) are the effects of seismic liquefaction that are the focus of this presentation. Such intrusions develop when water and sediment (typically sand) flow from depth into fissures along the base of an overlying fine-grained cap. A seismic origin is often easy to prove by using recently developed, stringent criteria.

Only rarely have searches been made for evidence of paleoseismicity in the form of soft-sediment deformations that plastically deform the ground, such as warped beds of very soft clay, load casts, ball-and-pillow features, etc. Even though seismic shaking often forms all these features, they also commonly (even typically) develop without shaking, and a seismic origin is difficult to verify in most field settings. An in-depth discussion of such deformations is not in the scope of this presentation, although a few examples are shown.

Background information is first given about the process of liquefaction in this presentation, especially as that process relates to the effects of liquefaction in vertical section. Concentration is on the vertical view because liquefaction features from earthquakes as recent as 500 to 1,000 years ago are rarely available for examination at the ground surface (in plan view), even when aerial photographs or remote sensing imagery are used.

Next, many field examples of various manifestations of liquefaction are shown. The discussion notes geologic and engineering techniques for analysis of prehistoric earthquake magnitude by means of using data from sites of paleoliquefaction. Finally, some examples of features that are not of seismic origin are shown, because they can closely mimic those of seismic origin.

Nearly all the material in this presentation is discussed in state-of-the-art compendia by Obermeier (1996a, b), which mainly concern the factors that control the formation and morphology of seismically induced liquefaction features and the methodology for verification of origin. These and other relevant articles are listed at the end of this presentation. The state of the art for analyzing the strength of prehistoric shaking by using paleoliquefaction studies is discussed by Obermeier and Pond (1999). If an article is especially relevant to the slide being shown in the presentation following, that article is noted in the text.

The numbers below are keyed to the slide numbers, and the discussions that follow relate to those slides. Values of earthquake magnitudes given below are in terms of moment magnitude (M).


Selected References

Li, Y., Craven, J., Schweig, E.S., and Obermeier, S.F., 1996, Sand boils induced by the 1993 Mississippi River flood - Could they one day be misinterpreted as earthquake-induced liquefaction?: Geology, vol. 24, no. 2, p. 171-174.

Obermeier, S.F., 1996a, Use of liquefaction-induced features for seismic analysis - An overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of Holocene paleo-earthquakes: Engineering Geology, vol. 44, p. 1-76.

Obermeier, S.F., 1996b, Using liquefaction-induced features for paleoseismic analysis, Ch. 7 in Paleoseismology, J.P. McCalpin, ed., San Diego, California , Academic Press,. p. 331-396.

Obermeier, S.F., and Pond, E.C., 1999, Issues in using liquefaction features for paleoseismic analysis: Seismological Research Letters, vol. 70, no. 1.

Pond, E.C., 1996, Seismic parameters fot the central United States based on paleoliquefaction evidence in the Wabash Valley, Ph. D. Thesis, Virginia Polytechnic Institute, Blacksburg, Virginia, 580 p.

This page is <http://pubs.usgs.gov/openfile/of98-488/>
Last revised November 24, 1998

For more information, contact Stephen F. Obermeier