Structural geometry, strain distribution, and mechanical evolution of eastern Umtanum Ridge and a comparison with other selected localities within Yakima fold structures, south-central Washington

Technical Report · Fri Jan 01 04:00:00 EST 1982

OSTI ID:5291503

Price, E H

The Yakima fold system of south-central Washington and north-central Oregon is a series of megascopic anticlinal ridge of multilayered basalt. Cross-sectional strain analyses were performed at five localities within three anticlines. The analyses show that the strain is consistent both laterally along a fold and within different folds. Folding strain is localized layer-internal faulting, extensive shattering, and limited layer-parallel faulting. Most strain is cataclastic, but glassy flow tops appear to have been more ductile. The strain distributions and structural geometries accord well with a flexural flow buckle model; however, the internal cataclastic flow is not inherently penetrative and limited flexural slip has occurred. This fold model suggests that most strain in the fold is by simple shear and it took place above the topographic surface of adjacent synclinal valleys. Large reverse faults associated with the anticlines are interpreted to be folding strain required by the concentric folding and their displacement is interpreted to have reached the surface late in the folding process. Therefore, the observed strain and its distribution are interpreted to be not directly the result of regional plateau shortening, but of local stresses and resultant strains related to fold geometry. A mechanical analysis of the Umtanum structure termination geometry, combined with slickenside striae movement directions from the study areas suggests that the Palouse slope has behaved as a rigid buttress around which the basalt has rotated clockwise into the folds from the southeast. Compression-box clay modeling of the Yakima fold system within the Pasco Basin shows that the buttress edge orientations control the localization and orientations of buckle folds. Fold orientations and three-dimensional shapes remarkably resembling the Yakima fold system in the Pasco Basin were produced under north-south compression.

• Research Organization: Atomics International Div., Richland, WA (USA). Rockwell Hanford Operations
• DOE Contract Number: AC06-77RL01030
• OSTI ID: 5291503
• Report Number(s): RHO-BWI-SA-138; ON: DE82012483
• Country of Publication: United States
• Language: English

Related Subjects

052002 -- Nuclear Fuels-- Waste Disposal & Storage
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
58 GEOSCIENCES
580100 -- Geology & Hydrology-- (-1989)
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
ANTICLINES
BASALT
FEDERAL REGION X
GEOLOGIC DEPOSITS
GEOLOGIC FAULTS
GEOLOGIC STRUCTURES
GEOMETRY
IGNEOUS ROCKS
MANAGEMENT
MATHEMATICS
MECHANICS
NORTH AMERICA
OREGON
ORIGIN
RADIOACTIVE WASTE DISPOSAL
ROCK MECHANICS
ROCKS
SITE SELECTION
STRAINS
USA
VOLCANIC ROCKS
WASHINGTON
WASTE DISPOSAL
WASTE MANAGEMENT