Lecture #7: Introduction to Earthquakes
(Abbott, pp. 86-99, 152-153)
Causes of Earthquakes and the Elastic Rebound Model
Most, but not all, earthquakes are associated with active plate boundaries and hot spots
(Figure 3.9, p. 56).
The worst earthquake in American history occurred in Anchorage,
Alaska in 1964 (Table 6.1, p. 133).
Surprisingly, though, some of the worst US
earthquakes occurred in 1811-1812 along the
New Madrid fault
(Table 7.1, p. 163),
which is not associated with any known modern plate boundary.
The fault is located in
western Kentucky, western Tennessee, northeastern Arkansas, and southeastern Missouri
(Figure 7.18, p. 174).
elastic rebound model
(Figure 6.32, p. 152) has been used to describe
the build up of energy and earthquake generation along faults, such as the San Andreas in
Slow movements along the fault cause deformation and the buildup of
(forces on the rocks; Lecture #6) along the fault (Figure 6.32a-b, p. 152). The stress
builds up to a point where the stress overcomes the friction between the rocks in the fault.
The fault ruptures and produces an earthquake.
During the earthquake, the movement of
the rocks on one or both sides of the fault releases some of the stress (Figure 6.32c, p.
Geologists now recognize that an earthquake may not release all of the stress on a
fault, but the stress is often relieved by a series of earthquakes (p. 153) involving
aftershocks (p. 95).
In some cases, the slow movements associated with the build up of
stress along a fault can be detected with
satellite global positioning system
stations (p. 157).
If the buildup of stress is detected, the information may be used to
evaluate the future probabilities of an earthquake in an area.
Elastic Rebound Model:
After an earthquake,
or displacements along the fault may be very noticeable,
especially on a strike-slip fault (Figure 4.2, p. 79).
That is, fences, roads, walls, and other
features may be separated on either side of the fault.