23.04.2013 Views

Management of Commercially Generated Radioactive Waste - U.S. ...

Management of Commercially Generated Radioactive Waste - U.S. ...

Management of Commercially Generated Radioactive Waste - U.S. ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

B.8<br />

B.3 SEISMIC, TECTONIC AND MAGNETIC CONSIDERATIONS<br />

The tectonic stability <strong>of</strong> the repository site must be sufficient to assure geologic<br />

isolation (Office <strong>of</strong> <strong>Waste</strong> Isolation 1977). Tectonics refers to the deformation <strong>of</strong> the<br />

lithosphere (the solid, near-earth-surface materials) caused by large-scale and local<br />

dynamic earth processes.<br />

Tectonics, seismicity and volcanism relate to the stability <strong>of</strong> an area and reflect the<br />

past geological activity. Active or capable faults, a history <strong>of</strong> earthquakes and volcanism<br />

should not condemn an area if investigation can show that the activity was in the remote<br />

past (million to hundreds <strong>of</strong> million years ago) and has not occurred since. For preliminary<br />

selection <strong>of</strong> areas, crustal plate boundaries, areas <strong>of</strong> known active faults, and zones <strong>of</strong><br />

recent earthquake and volcanic activity would be avoided.<br />

Deformation <strong>of</strong> the lithosphere (tectonism) and the upward intrusion (or extrusion) <strong>of</strong><br />

molten rock (magma) are important in site selection. Deformation <strong>of</strong> the crust may consist<br />

<strong>of</strong> folding, faulting, uplift, depression or diapirism. (A diapir is a fold in which the<br />

mobile core is injected into the overlying materials.) These processes, even though they<br />

may not directly disturb a repository site by fault displacement or venting <strong>of</strong> volcanic<br />

material, can significantly affect the regional hydrology over a hundred thousand years or<br />

more by altering the topography and the subsurface fluid flow. In this respect, magmatism<br />

and tectonism rank with climatic change as important factors in determining the evolution<br />

<strong>of</strong> the hydrologic environment. In selecting a site, optimal conditions <strong>of</strong> tectonic sta-<br />

bility should be realized so that magmatism and tectonism will not adversely affect the<br />

hydrologic conditions at the site. To determine that only the site itself would not be<br />

directly disrupted by faulting or volcanism is not sufficient; the general region must be<br />

considered. In general, the tectonic constraints on site selection will generally be more<br />

difficult to satisfy for sites in the western U.S. than for sites east <strong>of</strong> the Rocky<br />

Mountains.<br />

The theory <strong>of</strong> plate tectonics on a continental scale is believed appropriate for iden-<br />

tifying areas <strong>of</strong> optimum tectonic stability in order to assess the constraints on site<br />

selection imposed by volcanic activity, tectonism, and seismicity. The plate tectonics<br />

theory explains in general the present global distribution <strong>of</strong> lithospheric deformation,<br />

magmatic activity and seismic activity, and also the geologic record <strong>of</strong> lithospheric defor-<br />

mation and magmatism over at least the past several hundred million years. Because vol-<br />

canism has in general occurred in regions <strong>of</strong> crustal plate boundaries, some aspects <strong>of</strong> the<br />

evolution <strong>of</strong> the lithosphere during the next million years can be forecast quantitatively<br />

from plate tectonics; for example, it is possible to forecast, within a factor <strong>of</strong> about two,<br />

an increase <strong>of</strong> 50 km in the horizontal displacement across the San Andreas fault system in<br />

California. However, many important aspects <strong>of</strong> the evolution <strong>of</strong> the lithosphere can be<br />

forecast only in qualitative terms, if at all; for example, the effects <strong>of</strong> tectonism on the<br />

physiography <strong>of</strong> the Rio Grande Rift in New Mexico are difficult, if not impossible to<br />

forecast.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!