Investigation Methods and Procedures - Geotechnical Engineering Investigation - page 20

“Folios of the Geologic Atlas of the United States” was produced by the USGS until 1945.
Detailed maps of bedrock geology, structural geology, and surficial geology for many
cities in the United States and other areas of major geologic importance were included.
Soil survey maps , produced by the Soil Conservation Service (SCS) of the U.S. Department of
Agriculture, are usually plotted as overlays on aerial photographs at relatively large scales.
Prepared on a county basis they show the soil cover to a depth of about 6 ft (2 m), based on
pedological soil classifications (Section 7.8). They are often combined with symbology describ-
ing slopes, shallow groundwater, and soil drainage conditions. Recent maps contain engi-
neering-oriented data prepared by the Bureau of Public Roads in conjunction with the SCS.
However, the shallow depth depicted limits their usefulness in many engineering studies.
Flood insurance maps identify 100- and 500-year-old floodplains adjacent to water bodies.
These are available from the Federal Emergency Management Agency (FEMA), the USGS,
and State Agencies.
Tectonic maps give regional lineations often indicative of faulting.
Earthquake data may be presented as intensity maps (Figure 11.9), isoseismal maps
(Figure 11.15), various forms of seismic risk maps ( Figure 11.3), or as microzonation maps
(Section 11.4.3).
Other useful maps published by the Geological Society of America include the glacial map
of the United States and the loessial soils or wind-blown deposits of the United States.

Topographic Maps and Charts
Topographic maps , such as quadrangle sheets, show landforms, drainage patterns, stream
shapes, and surface water conditions, all indicators of geologic conditions. Because of their
availability and usefulness they should be procured as a first step in any study. They are
available from a number of sources and in a variety of scales as follows:

USGS provides maps covering a quadrangle area bounded by lines of latitude
and longitude available in 7.5° series (1:24,000) ( Figure 2.3) , 15° series (1:62,500),
30° series (1:125,000), and 1° series (1:250,000) for most of the United States,
although many of the larger scales are out of print.

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Other countries use scales ranging from 1:10,000 to 1:1,000,000 but coverage is
often incomplete. 1:50,000 is a common scale available for many areas, even in
countries not fully developed.

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Coastline charts , available from the National Ocean Service (NOAA-NOS), provide infor-
mation on water depths and near-shore topography.

Remotely Sensed Imagery
Remote-sensing platforms now include satellite-borne digital imagery and radar systems,
airborne imagery including digital and radar imagery, and aerial photography. In recent
years, many new sources of remotely sensed imagery have been, and continue to be,
developed. The relationship between the various forms and the electromagnetic spectrum
is given in Figure 2.4. Remotely sensed imagery is discussed in the following section.

2.2.3 Remotely Sensed Imagery

Satellite Imagery (Digital Sensors)
Satellite-borne systems obtain images of the Earth's entire surface every 16 days but
images are affected by cloud cover:

LANDSAT (USA-NASA): Landsat satellites have been launched periodically
since the first satellite (ERTS) was launched in 1972. Landsat 7, launched in 1999,

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