Seismites are sedimentary beds disturbed by seismic shaking. The German paleontologist Adolf Seilacher

Adolf Seilacher

Adolf "Dolf" Seilacher is a German palaeontologist who has made major contributions to evolutionary and ecological palaeobiology in a career stretching over 60 years. He won the Crafoord Prize in 1992, the Paleontological Society Medal in 1994 and the Palaeontological Association's Lapworth Medal...

 first used the term in 1969 to describe a variety of post-depositional effects of seismic shocks on unconsolidated sediments. Today, the term describes both sedimentary beds deformed by seismic shaking and associated soft sediment deformation structures formed by shaking that may or may not remain confined to a stratigraphic layer (i.e., clastic dike

Clastic dike

A clastic dike is a seam of sedimentary material that fills a crack in and cuts across sedimentary strata. Clastic dikes form rapidly by fluidized injection or passively by water, wind, and gravity . Diagenesis may play a role in the formation of some dikes. Clastic dikes are commonly vertical or...

s or sand volcano

Sand volcano

A sand volcano or sand blow is a cone of sand formed by the ejection of sand onto a surface from a central point. The sand builds up as a cone with slopes at the sand's angle of repose. A crater is commonly seen at the summit...

s). Several informal classification systems have been developed to distinguish seismites from soft sediment deformation features formed by non-seismic processes, though a formal, standardized system has not. Geologists use seismites to better understand the earthquake history of an area. If age and distribution can be determined, then recurrence interval and seismic hazard risk can be assessed.