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Digital Elevation Models Used to Map Tectonic Setting

Analyses of tectonic processes in the central Basin and Range Province of the western United States are being conducted to better understand the regional tectonic setting of the proposed high-level radioactive waste repository site at Yucca Mountain, Nevada. Institute scientists are investigating the regional tectonic setting in order to assess the potential risk of geologic hazards such as volcanic eruptions and earthquakes.

Shaded relief digital elevation models (DEM) are used as information rich backgrounds for two-dimensional and three-dimensional visualizations of geologic and geophysical data such as earthquake hypocenters, faults, ground rupture, and horizontal stress data. In addition to using DEMs as backgrounds for visualizations of scientific data, investigators are assessing the suitability of using synthetically illuminated DEMs to discover previously unmapped faults.

Identification and analysis of faults is crucial in determining the risk of future volcanic and seismic events in the region. In the past, low sun-angle aerial photographs (taken in the early morning or late afternoon) have been used for detecting linear illuminations and shadows on the photographs, indicating the locations of potential faults.

High resolution digital elevation models can be illuminated from any angle, in contrast to aerial photographs, which are limited to naturally occurring illumination angles that follow the east-west solar illumination path. Previously unmapped surface faults may be discovered by exploring synthetically illuminated topographic surfaces.

Using previously mapped surface faults plotted over synthetically illuminated DEM surfaces, investigators select illumination angles with high potential for indicating surface lineaments created by faults. Investigators then scan the shaded relief images for linear illuminations and shadows that might indicate fault locations. Verification that these are indeed surface faults requires field investigation.

Higher resolution DEMs, such as those created from stereo-pairs of aerial photographs, can greatly increase the potential for effectively using DEMs for fault exploration.

Published in the Summer 1995 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.