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4438 . (3) Adjustment of crystalline structure of the rock caused by loading of the reservoir (Tizdel', 1972). (4) Changes in the properties of the rock under the effect of the water (Tizdel', 1972). It must be emphasized that the above are hypotheses only, since other conflicting conclusions have also been drawn. Active faults, as defined by the Atomic Energy Commission exhibit one or more of the following characteristics: (1) once past Movement at or near the ground surface at least in the past 35,000 years or more than once in the 500,000 years. (2) Instrumentally well-determined macro-seismicity for a fault located in the Continental United States west of the Rocky Mountain Front, or in Alaska, Hawaii, or Puerto Rico. . (3) A relationship to an active fault according to characteristics (1) or (2) such that movement on one could be reasonably expected to be accompanied by movement on the other. In addition to the above criteria, it must be emphasized that a great deal of geological judgment is also involved. Several active faults have been mapped within a 100-mile radius of Pueblo Dam, the closest being about 25 miles southwest of the dam. None of these active faults cross the reservoir although some inactive ones do. The Bureau of Reclamation has evaluated the feature for a maximum pro- bable earthquake and designed the structure accordingly. The Pueblo Dam and Reservoir falls in Zone 1 of the Seismic Zone Map of the United States (Figure 111-7). This is the zone where minor damage would occur ill an earthquake. The tunnels and canals will withstand minor tremors, but will not withstand a major shock. If a major earthquake should occur, tunnel collapse would be expected. In addition, if a tunnel should encounter a sheer, collapse could also occur. However, the Project is located in a seismically stable area with a low probability of earthquake occurrence. . IV-48