Environmental Engineering Reference
In-Depth Information
TABLE 6.8
Surface Evidence of Faulting
Feature
Characteristics
Fault Type
Figure
Lineations
Strong rectilinear features of
All types
6.28
significant extent are indicative but
6.29
not proof. Can also represent dikes,
6.63
joints, foliations, bedding planes, etc.
6.4
Landforms
Scarps
Long, relatively smooth-faced,
Normal
6.53a
steep-sided cliffs
Truncated ridges
Lateral displacement of ridges and
Wrench
other geomorphic features
Faceted spurs
Erosion-dissected slopes form a
Normal
6.53c
series of triangular-shaped faces on
the foot wall
Horst and graben
Block faulting. A sunken block
Normal
6.53d
caused by downfaulting or uplifting
of adjacent areas forms a rift valley
(graben). An uplifted block between
two faults forms a horst. Soils
forming in the valley are more
recent than those on the uplands.
Examples: Lake George, New York;
Dead Sea; Gulf of Suez; Rhine
Valley, West Germany; Great Rift
Valley of Kenya; parts of Paraiba
River, Sao Paulo, Brazil
Drainage
Rejuvenated streams
Direction of flow reversed by tilting
Normal
6.53a
Blocked or truncated
Flow path blocked by scarp and
Normal
6.53a
takes new direction
Offset
Flow path offset laterally
Wrench
6.53e
Sag pond
Lakes formed by blocked drainage
Normal
6.53a
Secondary features
Practically disappear within less
than 10 years in moist climates, but
may last longer in dry (Oakeshott, 1973)
Mole tracks
En-echelon mounds of heaved
Thrust, wrench
6.61a
ground near base of thrust fault or
along wrench fault
Step-scarps
En-echelon fractures form behind
Normal
6.61b
the scarp crest in a reverse fault
(tension cracks)
Seismological
Alignment of epicenters
All types
11.25
The fault is represented by a complex zone of crushed and broken rock ranging gener-
ally from about 300 to 500 ft in width at the surface. It provides substantial evidence of
faulting including linear valleys in hilly terrain
(Figure 6.64),
offset stream drainage, and
offset geologic formations.
6.5.4
Engineering Significance
Earthquake Engineering
Relationship
As discussed in
Section 11.3.1,
it is generally accepted that large earthquakes are caused
by the rupture of one or more faults. The dominant fault is termed the causative fault.
