Abstract E-4 is one of eight Geodynamics transects that cross the Atlantic margin of North America between Georgia and Newfoundland. Five of the transects are in the United States and three are in Canada. Transect E-4, which is 110 km wide and more than 1,100 km long, extends from the stable North American craton just west of the Grenville front near Lexington, Kentucky southeastward across Cape Fear, North Carolina, on the Atlantic coast to oceanic crust east of the Blake Spur magnetic anomaly. Like all of the other U.S. Atlantic coast transects, it crosses Cambrian and Jurassic continental margins of North America as well as the Appalachian orogen. The display, based upon published information, portrays the geology, tectonic style and geophysical expression of this segment of the eastern North American continental margin and interprets its Phanerozoic history. The Decade of North American Geology 1983 geologic time scale (Palmer, 1983) is used throughout the display and text.

Abstract The prehistoric Egiin Davaa earthquake rupture is well-preserved in late Quaternary deposits within the Hangay Mountains of central Mongolia. The rupture is expressed by a semi-continuous 80 km-long topographic scarp. Geomorphological reconstructions reveal a relatively constant scarp height of 4–4.5 m and a NW-directed slip vector. Previous researchers have suggested that the scarp’s exceptional geomorphological preservation indicates that it may correspond to an earthquake that occurred in the region c. 500 years ago. However, we constrain the last rupture to have been at least 4 ka ago from morphological dating and <7.4 ka ago based on radiocarbon dating from one of two palaeoseismic trenches. Our study shows that discrete earthquake ruptures, along with details such as the locations of partially infilled fissures, can be preserved for periods well in excess of 1000 years in the interior of Asia, providing an archive of fault movements that can be directly read from the Earth’s surface over a timescale appropriate for the study of slowly deforming continental interiors. The Egiin Davaa rupture involved c. 8 m of slip which, along with the observations that it is largely unsegmented along its length and that the ratio of cumulative slip ( c. 250 m) to fault length ( c. 80 km) is small, suggests relatively recent reactivation of a pre-existing geological structure. Supplementary material: All scarp profiles are available at http://www.geolsoc.org.uk/SUP18871