Types and Causes of Induced Seismicity - Induced Seismicity Potential in Energy Technologies - page 23

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60˚

40˚

Method:
focal mechanism
breakouts
drill. induced frac.
borehole slotter
overcoring
hydro. fractures
geol. indicators
Regime:

NF SS TF U

Quality:
A
B
C
¹ (2008) World Stress Map

20˚

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World Stress Map Rel. 2008
Heidelberg Academy of Sciences and Humanities
Geophysical Institute, University of Karlsruhe

Projection: Mercator

Figure 4 North America stress map. The stress map displays the orientations of the maximum horizontal
compressive stress ( σ H ). The length of the stress symbols represents the data quality, with A being the best
quality. Quality A data are assumed to record the orientation of σ H to within 10°-15°, quality B data to
within 15°-20°, and quality C data to within 25°. As can be seen from this global dataset, stress measure-
ments are absent in many parts of North America and the offshore regions. Because stress measurements
are important in the consideration of induced seismicity, their measurement, particularly in areas where data
are sparse, could usefully contribute to understanding the potential for induced seismicity related to energy
development. The tectonic regimes are NF for normal faulting, SS for strike-slip faulting, TF for thrust faulting,
and U for an unknown regime. Topographic relief is indicated by green (lower elevations) to brown (higher
elevations) shading. SOURCE: Data used to plot this map were accessed from www.world-stress-map.org/
(see Heidbach et al., 2008).

small earthquakes. Thus, for fluid injection to trigger a significant earthquake, a fault or
faults of substantial size must be present that are properly oriented relative to the existing
state of crustal stress, and these faults must be sufficiently close to points of fluid injection
to have the rocks surrounding them experience a net pore pressure increase.