Seismic signatures: Small-scale features and ground fractures
Published:January 01, 2013
Ronald Counts, Stephen F. Obermeier, 2013. "Seismic signatures: Small-scale features and ground fractures", Recent Advances in North American Paleoseismology and Neotectonics East of the Rockies, Randel Tom Cox, Martitia P. Tuttle, Oliver S. Boyd, Jacques Locat
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Paleoseismic investigations in fluvial deposits frequently use large-scale (many centimeters to decimeters wide) ground-failure features of liquefaction origin as indicators of larger earthquakes (i.e., exceeding M ~6). Such large features are not the only signature of seismicity, however. Seismic shaking often produces an abundance of small-scale features (millimeter to centimeter in size) such as sills, small clastic dikes, and ground fractures, which can vary widely in height and range from paper-thin to a few centimeters wide. These small-scale seismic signatures commonly form in field settings where large liquefaction features are absent, such as regions with a reduced susceptibility for liquefaction or sites far from earthquake meizoseismal regions where shaking levels were lower. Thus, these small signatures have the potential to significantly expand the geographic area useful for paleoseismic studies, yet they are not typically sought in most paleoseismic field studies because many can develop nonseismically, and interpreting their formative origin can be challenging.
We examined small-scale features that occur in association with large liquefaction features at a variety of field sites across the United States. We present new criteria, with many photographic examples, to evaluate whether small-scale features and ground fractures were seismically generated. Although this research was done primarily in fluvial settings in the United States, these criteria should be applicable worldwide in many field settings with clastic sediments, potentially giving the study of small-scale seismic features and fractures a significant role in future paleoseismic investigations.