|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
,1,1,1,2
1 U.S. Geological Survey, Denver Federal Center, Denver, Colorado 80225-0046, USA
2 S.M. Stoller Corporation, 990 South Public Road, Suite A, Lafayette, Colorado 80026, USA
Geologic mapping and fracture studies have documented the fundamental patterns of joints and faults in the thick sequence of rhyolite tuffs at Yucca Mountain, Nevada, the proposed site of an underground repository for high-level radioactive waste. The largest structures are north-striking, block-bounding normal faults (with a subordinate left-lateral component) that divide the mountain into numerous 1–4-km-wide panels of gently east-dipping strata. Block-bounding faults, which underwent Quaternary movement as well as earlier Neogene movement, are linked by dominantly northwest-striking relay faults, especially in the more extended southern part of Yucca Mountain. Intrablock faults are commonly short and discontinuous, except those on the more intensely deformed margins of the blocks. Lithologic properties of the local tuff stratigraphy strongly control the mesoscale fracture network, and locally the fracture network has a strong influence on the nature of intrablock faulting.
The least faulted part of Yucca Mountain is the north-central part, the site of the proposed repository. Although bounded by complex normal-fault systems, the 4-km-wide central block contains only sparse intrablock faults. Locally intense jointing appears to be strata-bound. The complexity of deformation and the magnitude of extension increase in all directions away from the proposed repository volume, especially in the southern part of the mountain where the intensity of deformation and the amount of vertical-axis rotation increase markedly.
Block-bounding faults were active at Yucca Mountain during and after eruption of the 12.8–12.7 Ma Paintbrush Group, and significant motion on these faults postdated the 11.6 Ma Rainier Mesa Tuff. Diminished fault activity continued into Quaternary time. Roughly half of the stratal tilting in the site area occurred after 11.6 Ma, probably synchronous with the main pulse of vertical-axis rotation, which occurred between 11.6 and 11.45 Ma. Studies of sequential formation of tectonic joints, in the context of regional paleo-stress studies, indicate that north- and northwest-striking joint sets formed coevally with the main faulting episode during regional east-northeast–west-southwest extension and that a prominent northeast-striking joint set formed later, probably after 9 Ma.
These structural analyses contribute to the understanding of several important issues at Yucca Mountain, including potential hydrologic pathways, seismic hazards, and fault-displacement hazards.
Key Words: structural geology • Yucca Mountain • Nevada • faults • joints
This article has been cited by other articles:
|
|
 |
|
  D. J. Andrews, T. C. Hanks, and J. W. Whitney Physical Limits on Ground Motion at Yucca Mountain Bulletin of the Seismological Society of America, December 1, 2007; 97(6): 1771 - 1792. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. S. Stuckless and D. W. O'Leary Geology of the Yucca Mountain region Geological Society of America Memoirs, January 1, 2007; 199(0): 9 - 50. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. R. Keefer, J. W. Whitney, and D. C. Buesch Geology of the Yucca Mountain site area, southwestern Nevada Geological Society of America Memoirs, January 1, 2007; 199(0): 53 - 103. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. Parsons, G. A. Thompson, and A. H. Cogbill Earthquake and volcano clustering via stress transfer at Yucca Mountain, Nevada Geology, September 1, 2006; 34(9): 785 - 788. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
