Ancient seismites / Древние сейсмические события

Most studies of the geologic records of prehistoric earthquakes are driven by the need of seismic-hazard analyses for estimates of the locations, ages, and magnitudes of individual large earthquakes. In North America, most such studies analyze surface ruptures and earthquake-induced sand blows, dikes, and sills. In contrast, small, softsediment structures in one or a few beds, possibly induced by seismic shaking, are little used in North American hazard analyses. The reason is that present methods for studying such structures often cannot demonstrate an earthquake origin, rule out alternatives, or estimate location, age, and magnitude as well as can methods developed for the study of surface ruptures and sand blows, dikes, and sills. This chapter proposes six tests to distinguish seismic from nonseismic origins of small, soft-sediment structures in one or a few beds. The tests utilize evidence for sudden formation, synchroneity and zoned map distribution over many exposures, size of the structures, and tectonic and depositional settings. The main barriers to more rigorous utilization of these soft-sediment structures in hazard analysis are (1) few observations of their formation during historical earthquakes, and (2) few or no measurements of the threshold earthquake magnitudes and threshold horizontal accelerations that are required to form the structures. <...>