Performance assessments for radioactive waste repositories; the rate of movement of faults

Abstract

Performance assessments of mined repositories for radioactive waste require estimates of the likelihood of fault movements and earthquakes that may affect the repository and its surrounding ground water flow system. Some previous assessments have attempted to estimate the rate of formation of new faults; some have relied heavily on historic seismicity or the time of latest movement on faults. More appropriate emphasis is on the identification of faults that have been active or may have been active under the present teconic regime in a broad region and on estimates of the long-term rate of movement of such faults. Faults that have moved under the current stress field, even at low rates, are likely to move again during the time the wastes will remain toxic. A continuum exists for the present rate of movement of faults which ranges from 10 mm per year for obviously active faults along the western margin of the North American plate to as low as 10~4 mm per year for recently documented faults in the Atlantic Coast province. On the basis of regional consistency in movement rates and constraints imposed by geomorphology, I derive upper bounds for the rates of occurrence of fault offsets for various crustal stress provinces in the conterminous United States. These upper bounds are not meant to substitute for detailed studies of specific faults and seismicity at specific sites. They can help to reduce the considerable uncertainty that attaches to all estimates of future tectonic activity. The principal uncertainty in their estimation is the manner in which total slip across faults is distributed among discrete events especially in regions in which the rate of movement is very low.

Studies of geology and hydrology in the Basin and Range Province, Southwestern United States, for isolation of high-level radioactive waste - Basis of characterization and evaluation

“…However, engineering design can compensate for potential damage to structures caused by a certain degree of seismic activity. A fault or earthquake near a repository cannot be considered to be a "failure" of the system, and it need not result in a degradation of the isolation system (Trask, 1982). In some ground-water regimes, movement along faults may have no effect on the existing ground-water flow system (Davis, 1980).…”

“…Many lines of evidence support the conclusion that rates of tectonic activity are episodic. Such evidence includes occurrences of faulting (Trask, 1982), earthquakes, and rapid vertical changes documented by successive leveling surveys. Schumm (1963) may be greater or lesser than the short-term rates.…”

Geologic and hydrologic characterization and evaluation of the Basin and Range Province relative to the disposal of high-level radioactive waste: Part II, Geologic and hydrologic characterization

“…However, the apparent absence of Quaternary faults in some areas may be due to lack of detailed study; or Quaternary-fault movement may be masked by younger Quaternary deposits. Trask ( 1982) fault movement. Trask has suggested an upper unit on the rate of recurrence of major movements of 8 x 10 5 events per year on active faults within the Basin and Range Province other than those near Sierra Nevada and Wasatch fronts.…”