Civil Engineering Reference
In-Depth Information
2.
Length of shaking:
The length of shaking depends on how the fault breaks during
the earthquake. For example, the maximum shaking during the Loma Prieta earthquake
lasted only 10 to 15 s. But during other magnitude earthquakes in the San Francisco Bay
area, the shaking may last 30 to 40 s. The longer the ground shakes, the greater the poten-
tial for structural damage. In general, the higher the magnitude of an earthquake, the longer
the duration of the shaking ground (see Table 2.2).
3.
Type of subsurface conditions:
Ground shaking can be increased if the site has a
thick deposit of soil that is soft and submerged. Many other subsurface conditions can cause
or contribute to structural damage. For example, as discussed in Sec. 3.4, there could be
structural damage due to liquefaction of loose submerged sands.
4.
Type of building:
Certain types of buildings and other structures are especially sus-
ceptible to the side-to-side shaking common during earthquakes. For example, sites located
within approximately 10 mi (16 km) of the epicenter or location of fault rupture are gener-
ally subjected to rough, jerky, high-frequency seismic waves that are often more capable of
causing short buildings to vibrate vigorously. For sites located at greater distance, the seis-
mic waves often develop into longer-period waves that are more capable of causing high-
rise buildings and buildings with large floor areas to vibrate vigorously (Federal
Emergency Management Agency 1994).
Much as diseases will attack the weak and infirm, earthquakes damage those structures
that have inherent weaknesses or age-related deterioration. Those buildings that are not rein-
forced, poorly constructed, weakened from age or rot, or underlain by soft or unstable soil are
most susceptible to damage. This chapter discusses some of these susceptible structures.
4.2 EARTHQUAKE-INDUCED SETTLEMENT
Those buildings founded on solid rock are least likely to experience earthquake-induced
differential settlement. However, buildings on soil could be subjected to many different
types of earthquake-induced settlement. As discussed in Chap. 3, a structure could settle or
be subjected to differential movement from the following conditions:
Tectonic Surface Effects
●
Surface fault rupture, which can cause a structure that straddles the fault to be displaced
vertically and laterally.
●
Regional uplifting or subsidence associated with the tectonic movement.
Liquefaction
●
Liquefaction-induced settlement.
●
Liquefaction-induced ground loss below the structure, such as the loss of soil through the
development of ground surface sand boils.
●
Liquefaction-induced bearing capacity failure. Localized liquefaction could also cause
limited punching-type failure of individual footings.
●
Liquefaction-induced flow slides.
●
Liquefaction-induced localized or large-scale lateral spreading.
Seismic-Induced Slope Movement
●
Seismic-induced slope movement or failure (Tables 3.1 and 3.2).
