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### OPEN-FILE REPORT 98-488

## SEISMIC LIQUEFACTION FEATURES: 

EXAMPLES
FROM PALEOSEISMIC INVESTIGATIONS 

IN THE CONTINENTAL UNITED STATES



### 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).



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### 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.



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For more information, contact Stephen F. Obermeier