THE GEOARCHAEOLOGY AND SOIL MICROMORPHOLOGY OF SEISMICALLY TRIGGERED SOFT SEDIMENT DEFORMATION STRUCTURES (SSDS)

Factors of earthquakes in the development of ancient cultures and societies and on site formation have been concerns of archaeologists since some of the earliest excavations in the Mediterranean. The geoarchaeological subfield of archaeoseismology grew out of these concerns to establish deeper time perspectives on past earthquake events and their role in sociocultural developments. Archaeoseismology focuses on types of seismic destruction and antiseismic reconstruction in architectural remains to identify and interpret past earthquake events and their consequences. However, factors other than earthquakes can also cause these types of destruction and reconstruction. The approach of this paper combines subfields of geoarchaeology, namely archaeoseismology and soil micromorphology, to overcome this critical difficulty. New applications of soil micromorphology allow for the analysis of geological residues of earthquakes in direct association with architectural remains in archaeological excavations. This combinatory geoarchaeological approach is applied to the archaeological case of Helike in the northwest Peloponnese of Greece for occupation phases spanning the third millennium BCE to fifth century CE. Earthquakes of magnitude (Mw) 5.5 or greater can cause the formation of soft sediment deformation structures (SSDS) in ground surface sediments. Seismically triggered SSDS vary in size from the macro-, meso-, and micro- scales, ranging from several meters to micrometers. The study of SSDS at Helike are interpreted as seismically triggered based on the vertical and horizontal formation patterns of water-escape structures, load structures, and convoluted and deformed cross-bedding, extending below and up to ancient occupation surfaces. In addition, the soil micromorphology investigation of SSDS reveals the past effects of other geological hazards, including flooding and rapid coastal change. The discovery of seismically triggered SSDS at Helike demonstrates for the first time the validity and efficacy of using techniques of soil micromorphology to accurately identify and interpret geological residues of earthquakes and other environmental hazards in archaeology.