Paths Forward to Understanding and Managing Induced Seismicity in Energy Technology Development - Induced Seismicity Potential in Energy Technologies - page 120

4. What are the shaking effects? If ground motions are strong enough to be felt, they

can be represented by three categories, depending on the maximum strength of
shaking. Ground motions fall into the following categories:

a. Very slight shaking. These are felt ground motions, typically with peak accel-

erations less than 4%g, and do not cause damage to structures. Isolated cracks
in plaster walls may be observed or items in houses may be knocked over, but
these motions cause no damage of consequence. Frequent occurrence of these
motions may be a nuisance to people.

b. Minor shaking. These are ground motions that frighten people and/or wake

them from sleep, typically with peak accelerations between about 4%g and
18%g. If structures are present, these ground motions may cause light property
damage (cracks in concrete, broken windows, or cosmetic damage) but do not
cause buildings to collapse.

c. Moderate-strong shaking. These are moderate, strong, or severe ground

motions with the potential of causing moderate or heavy damage, typically
with peak accelerations greater than about 18%g. If structures are present,
moderate to heavy damage may occur, including partial or complete collapse
of structures or structural elements (foundations, walls, roofs). These effects
on structures may cause human casualties (injuries and deaths, in severe cases).

Ground motions from induced seismicity generated at shallow depths can be more
troublesome compared to the ground motions from deeper events (Figures 5.2 and 5.3).
In a cross section of the Earth where a deep tectonic (natural) earthquake occurs at a
depth of 10 km (Figure 5.2), the semicircles illustrate the distance within which minor
shaking (or greater) occurs if the earthquake M is 3, 4, or 5. Because of the depth of the
earthquake, minor (or greater) shaking usually does not reach the Earth's surface for M 3
or 4. For M 5, minor (or greater) shaking may occur at the Earth's surface within about
15 km (9 miles) of the epicenter (Figure 5.2).
Figure 5.3 shows a similar cross section of the Earth where a shallow earthquake oc-
curs at the bottom of a 2-km-deep (1.2-mile-deep) well. Because of this shallow depth,
a M 4 earthquake can cause minor (or greater) shaking within about 8 km of the well, and a
M 3 earthquake may cause minor (or greater) shaking very close to the well.

Factors Affecting Risk

Risk from induced seismicity only occurs if structures are present that may be damaged.
Risk exists to those structures only if the shaking is minor, moderate, or larger. Factors that
should be considered for risk include location of faults, location of infrastructure that can be