Induced Seismicity and Energy Technologies - Induced Seismicity Potential in Energy Technologies - page 7

Figure Histograms showing relation between volume of waste injected into the Rocky Mountain Arsenal well
and earthquake frequency. SOURCES: Adapted from Evans (1966); Healy et al. (1968); McClain (1970); Hsieh
and Bredehoeft (1981).
Rocky Mountain Arsenal earthquakes, which did not have details about the magnitude scale being used. After
November 1967 earthquake activity steadily declined and virtually ceased by the late 1980s.
Initial theories postulated that the Denver earthquakes were caused by fluids being pumped into the ground
by pressure injection in the disposal well; the fluids were suggested to have acted as a lubricant, allowing large
blocks of rock in the subsurface to shift more easily. However, further analysis showed earthquakes triggered by
fluid injection are not caused by lubrication of a fracture system but suggested instead that the earthquakes were
caused by increasing the pressure of the existing fluid in the formation through high-pressure injection, which
lowered the frictional resistance between rocks along an existing fault system; lowering the frictional resistance
allowed the rocks to slide relative to each other.
a Note: Throughout the report we cite the units presented in the original reference followed by a conversion in parentheses
to U.S. measures, metric, or units that might be more familiar to the general reader.