The USGS National Center site straddles the boundary of the eastern edge of the Triassic lowland and the margin of the Piedmont crystalline rock province. The Piedmont upland at the east side of the site is underlain by the Peters Creek Schist, a foliated metamorphic rock that is probably 550 to 650 million years old.
The schist is overlain at an erosion unconformity by a layered sequence of conglomerate, sandstone, siltstone, and shale. These sedimentary rocks of Late Triassic age are typically dark red. The sedimentary sequence was intruded by 195-million-year-old diabase, some of which lies 500 meters west of the site. The rocks in contact with the diabase intrusion were thermally meta-morphosed into hornfels, a brittle gray and mauve rock containing abundant green epidote crystals.
USGS scientists continuously monitor the groundwater level at several observation wells on the National Center site. Between 1976 and 1980, the wells were drilled or cored to depths of 63 meters to 184 meters . An observation well containing a continuous water-level recorder is northeast of the main building in a small enclosed hut. Display panels explain the hydrograph's operation and provide additional information on the local and regional hydrogeology.
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New USGS-FEMA study highlights economic earthquake risk in the United StatesSAN JUAN, Puerto Rico — Earthquakes cost the nation an estimated $14.7 billion annually in building damage and associated losses according to a new report released jointly today by the U.S. Geological Survey and the Federal Emergency Management Agency at the annual Seismological Society of America meeting.
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