HR: 0800h
AN: T11A-0353    [Abstracts]
TI: A High-Precision, 3-Dimensional Fracture Characterization Study in the Bandelier Tuff, Pajarito Plateau, Northern New Mexico
AU: * Schultz-Fellenz, E S
EM: eschultz@lanl.gov
AF: Earth and Environmental Sciences, MS D452, Los Alamos National Laboratory, Los Alamos, NM 87545, United States
AU: Gardner, J N
EM: jgardner@lanl.gov
AF: Earth and Environmental Sciences, MS D452, Los Alamos National Laboratory, Los Alamos, NM 87545, United States
AU: Caporuscio, F A
EM: floriec@lanl.gov
AF: Earth and Environmental Sciences, MS D452, Los Alamos National Laboratory, Los Alamos, NM 87545, United States
AU: Kelley, R E
EM: rekelley@lanl.gov
AF: Earth and Environmental Sciences, MS D452, Los Alamos National Laboratory, Los Alamos, NM 87545, United States
AU: Greene, M K
EM: mgreene@lanl.gov
AF: Earth and Environmental Sciences, MS D452, Los Alamos National Laboratory, Los Alamos, NM 87545, United States
AB: For certain proposed new facilities at Los Alamos National Laboratory, located on the Pajarito Plateau of northern New Mexico, completion of seismic hazards studies must precede any construction to ensure appropriate engineering for damaging earthquakes is included in building design. For one such study, a two-phase excavation exposed approximately 4000 sq. m (42,000 sq. ft) of the two uppermost subunits of the 1.22 Ma Tshirege Member of the Bandelier Tuff (Qbt3 and Qbt4) and interbedded pyroclastic surge in excavation walls for detailed geologic investigations. Using traditional paleoseismic trenching techniques in an unconventionally large setting, we obtained detailed data on exposed geologic features, including contacts, fractures, and faults. Geologic mapping at an approximate scale of 1:36 on digital photographs, coupled with high-precision geodetic surveys of identified features, place the data within a geospatial reference frame and provide an unparalleled 3- dimensional composite dataset of localized contact relationships and structure within Qbt3 and Qbt4. The majority of fracture orientations trend east-northeast, with an overwhelming predominance of vertical or near- vertical dips. The pyroclastic surge exhibits radical thickness changes over short distances. Qbt3 and Qbt4 are intensely fractured in places, with the fractures exhibiting variable amounts of vertical continuity and displacement across the pyroclastic surge in particular. Fractures are commonly curvilinear and terminate at the contact with the pyroclastic surge. Minor faults with less than 0.6 m (2 ft) of vertical displacement across the pyroclastic surge are present. Many of these small faults exhibit displacement only on the upper or lower contact of the surge deposit. In several locations, these small faults bound funnel-shaped, fines-depleted zones in Qbt3 with significant overlying shattering in Qbt4. Thus, very little of the observed deformation is apparently tectonic in origin; rather, most deformation probably occurred during cooling and compaction of the thick tuff deposit, and some pronounced deformation is associated with zones of localized paleo-fumarolic activity.
DE: 5104 Fracture and flow
DE: 8010 Fractures and faults
DE: 8031 Rheology: crust and lithosphere (8159)
DE: 8175 Tectonics and landscape evolution
DE: 8428 Explosive volcanism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting