Understanding the subtle differences between Tshirege Member cooling units and the nature of the contacts between cooling units is critical to identifying the presence or absence of faults associated with the Pajarito fault system on the Pajarito Plateau. The Tshirege Member cooling unit exposed at the surface at TA-63 is Qbt3. Commonly accepted stratigraphic nomenclature for the Tshirege Member is described in detail by Broxton and Reneau (1995), Gardner et al.
Several discrete cooling units comprise the Tshirege Member. 2007) and is widely exposed as the mesa-forming unit around Los Alamos. The younger member (Tshirege Member) of the Bandelier Tuff has been dated at 1.256 Ma (age from Phillips et al. The older member (Otowi Member) of the Bandelier Tuff has been dated at 1.61 Ma (Izett and Obradovich 1994). The local bedrock is the Quaternary Bandelier Tuff, formed in two eruptive pulses from nearby Valles caldera, the eastern edge of which is located approximately 6.5 miles west-northwest of the technical area. The proposed TWF area at TA-63 is situated on an unnamed mesa in the north-central part of LANL between Twomile Canyon to the south, Ten Site Canyon to the north, and the headwaters of Canada del Buey to the east (Figure 2). This fault system forms the local active western margin of the Rio Grande rift near Los Alamos, and is potentially seismogenic (e.g., Gardner et al., 2001 Reneau et al., 2002 Lewis et al., 2009). LANL and the Los Alamos townsite sit atop the Pajarito Plateau, which is bounded on its western edge by the Pajarito fault system, a 35-mile-long system locally comprised of the down-to-the-east more » Pajarito fault (the master fault) and subsidiary down-to-the-west Rendija Canyon, Guaje Mountain, and Sawyer Canyon faults (Figure 1). Any questions about the data presented herein, or about the Los Alamos Seismic Network, should be directed to the authors of this technical paper. This technical paper presents the most recent and updated catalog of earthquakes measured by the Los Alamos Seismic Network at and around Los Alamos National Laboratory (LANL), with specific focus on the site of the proposed transuranic waste facility (TWF) at Technical Area 63 (TA-63). The instrumental and historical seismicity and earthquake evidence from fault displacements consistently show the overall region to have moderate = ,
Almost no earthquakes are originating beneath the Valles Caldera, suggesting the presence of a hot shallow body where strain relief occurs by creep rather than by brittle fracture. The regional epicenter map for the period September 1973 through December 1975 shows earthquake concentrations (1) along the Nacimiento Uplift and its northward extension to Dulce, NM, (2) near Abiquiu, north of Los Alamos (3) beneath the western part of the Taos Plateau and (4) within the Rio Puerco fault zone, between Albuquerque and Grants. The seismic data thus obtained are used to study the contemporary tectonic activity near the Valles Caldera and the Rio Grande Rift between 35/sup 0/ and 37/sup 0/ north latitude.
These stations record most regional earthquakes having magnitudes (M/sub L/) greater than one. A network of twelve short period seismic stations within 150 kilometers of Los Alamos is telemetered to LASL, and recordings are mailed from a similar station at Lukachukai, Arizona. The Los Alamos Scientific Laboratory is located in north-central New Mexico within an area of geologically recent volcanic and tectonic activity.
0 kommentar(er)
