Abrupt lateral or vertical changes in soil or rock materials may indicate faults (active or inactive) or bedrock structures, such as tight folds, shear zones, and vertical bedding. Seismic zones 3 and 4, as defined in TR-60, Earth Dams and Reservoirs, and locally delineated, typically require special considerations in design of embankments including embankment slopes, cut slopes, zoned fill, or internal drainage. A foundation consisting of loose, saturated, fine-grained, relatively clean sand is most susceptible to seismic activity. Most well compacted embankments and those foundations and embankments consisting of finegrained soil with plasticity are inherently resistant to seismic shocks.
Determine the seismic zone of a site using the map in TR-60. Identify other geologic hazards from information as may be listed in section I of the Field Office Technical Guide (FOTG) and in geology reports, geologic maps, or other local technical resources.
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