Paths Forward to Understanding and Managing Induced Seismicity in Energy Technology Development - Induced Seismicity Potential in Energy Technologies - page 123

FIGURE 5.4 Example of relative probability distribution of maximum shaking at the ground surface
from induced seismicity caused by one well. The relative probability increases upward on the vertical axis.
The horizontal axis shows several kinds of measurements or effects of ground shaking: the upper scale
indicates the amount of shaking (slight through moderate+); the second scale indicates ground accelera-
tion, which increases from left to right; the next scale indicates MMI or the Modified Mercalli Intensity scale,
which indicates the level of ground shaking at a particular location and has units designated by Roman
numerals, also increasing from left to right in the level of ground shaking (see also Chapter 1); and the
lower scale is the “felt” effect, ranging from “felt only” on the left through minor to moderate or greater
(“moderate+”) damage. The probability of very slight shaking is much higher than for moderate+ shaking
(or damage) for one well that causes an induced seismic event of any magnitude.
A more general distribution of ground motion from a range of earthquakes with
ground motions quantified by the largest horizontal acceleration 1 that occurs shows that
the majority of shaking will be in the category of “felt only” (Figure 5.4). A small per-
centage (~25 percent) may have the potential to cause minor damage, and a very small
percentage (~1 percent) may have the potential to cause moderate+ damage (Figure 5.4).
The important conclusion is that, while the risk of minor, moderate, or heavy damage
from induced earthquake shaking may be small for each individual well, a large, spatially
distributed operation leads to a higher probability of such damage. If we define P M as the
probability of moderate+ damage given surface ground motion from one well, then the prob-
1 The peak horizontal acceleration of the ground is a common measure of ground shaking because the maximum force
on objects sitting on the ground is proportional to the peak horizontal acceleration through Newton's second law. Acceleration
is measured in units of gravity, “ g ,” which is the acceleration of a falling object. For comparative purposes, a modern, high-
powered sports car can accelerate at about 50%g.