Civil Engineering Reference
In-Depth Information
grabens, and sand boils. By comparing older aerial photographs with newer ones, the
engineering geologist can also observe any artificial or natural changes that have
occurred at the site.
Geologic reports and maps can be especially useful to the geotechnical engineer and
engineering geologist because they often indicate seismic hazards such as faults and land-
slides. Geologic reports and maps may indicate the geometry of the fault systems, the sub-
soil profile, and the amplification of seismic waves due to local conditions, which are
important factors in the evaluation of seismic risk. For example, Fig. 5.1 presents a portion
of a geologic map, and Fig. 5.2 shows cross sections through the area shown in Fig. 5.1
(from Kennedy 1975). Note that the geologic map and cross sections indicate the location
of several faults and the width of the faults, and often state whether the faults are active or
inactive. For example, Fig. 5.2 shows the Rose Canyon fault zone, an active fault having a
ground shear zone about 300 m (1000 ft) wide. The cross sections in Fig. 5.2 also show
fault-related displacement of various rock layers.
FIGURE 5.1
Geologic map. (
From Kennedy 1975.
)
