Fracture characterizatioin of the Bandelier tuff in OU-1098 (TA-2 and TA-41)
Rock fracture characterization documents a total of 1496 fractures in unit 2 of the Tshirege Member of the Bandelier Tuff along 6013 feet of Los Alamos Canyon`s north wall adjacent to Operational Unit 1098. Geologically termed joints, these fractures likely owe their primary origin to brittle failure during the cooling contraction of the tuff after its emplacement nearly 1 million years ago. Subsequent tectonic movement along the Pajarito Fault system has modified fracture strikes, dips, apertures, and linear density. From a background linear density of approximately 20 fractures per 100-foot interval along the canyon wall, fracture density increases to values in excess of 50 fractures per 100-foot interval in a zone at and immediately east of the Omega West reactor building TA-2-1. This increase in fracture density is coincident with the mapped trace of the Guaje Mountain Fault (GMFZ) that apparently bifurcates with a branch running through the canyon at Building TA-2-1 and another about 200 feet east of the Omega site east gate. With it occurs notable slump failure of the canyon wall, increased cumulative fracture aperture, and slight rotation of fracture orientations. Fractures show average strikes of either N35W or N47E, average dips between 75N and 82N, and average apertures of 0.7 cm. Calculations, based on the assumption that fracture apertures are produced by vertical movement along each fracture, suggest approximately 3 m of westward downdrop has occurred over the GMFZ is this area. While fracture character is not documented for Bandelier Tuff units above and below unit 2, observations indicate that inferred tectonic movement has likely influenced fracture permeability in the Bandelier Tuff in Los Alamos Canyon along the trace of the Guaje Mountain Fault. Because of increased fracture permeability, groundwater movement is expected to show greater penetration into bedrock units in that area just east of the Omega West reactor.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 402250
- Report Number(s):
- LA-13194-MF; ON: DE96015348
- Resource Relation:
- Other Information: PBD: [1996]
- Country of Publication:
- United States
- Language:
- English
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