Emily S. Schultz-Fellenz

Fault interaction and along-strike variation in throw in the Pajarito fault system, Rio Grande rift, New Mexico

The seismically active Pajarito fault system (PFS) of northern New Mexico, United States, is a complex zone of deformation made up of many laterally discontinuous faults and associated folds and fractures that interact in ways that have important implications for seismic hazards. Mapping and drilling projects in the PFS provide new insights into the structural geometry and paleoseismic history of the fault system. A 1.25 Ma old datum (the Bandelier Tuff) and high-resolution digital elevation data allow construction of throw-length profiles along the entire length of the PFS, revealing primary geometric features previously unrecognized. The fault system as a whole consists of numerous closely spaced overlapping sections ~8–14 km long. Slip maxima in some cases occur near the centers of these sections, and in others they are shifted toward one end. Along-strike asymmetrical throw profiles and throw deficits indicate fault branching, merging, and strain transfer. This pattern results from processes of fault linkage and conservation of strain on diverse structures of a large fault system. New mapping reveals that the northern end of the Pajarito fault terminates in a wide zone of extensional monoclines and discontinuous, small-displacement faults, and interacts with nearby antithetic faults. New paleoseismic data from a normal fault splay, interpreted in light of previous paleoseismic work, argue for three Holocene surface-rupturing earthquakes; one ca. 1.4 thousand calendar years ago (1.4 cal ka) on the Pajarito fault, a second 6.5–5.2 ka ago on the Pajarito fault that is consistent with an event 6.5–4.2 ka ago on the Guaje Mountain fault, and a third ca. 9 ka ago on both the Pajarito and the Rendija Canyon faults. This paleoseismic event chronology demonstrates that the Pajarito fault often ruptures alone, but sometimes ruptures either with the Rendija Canyon or the Guaje Mountain fault. When this occurs, the resultant seismic moment and therefore the earthquake magnitude are larger than when the main Pajarito fault ruptures alone. Evidence for fault interaction, and the presence of prominent bends in the Pajarito fault system, imply structural control of paleoseismicity and neoseismicity and suggest the potential for stress concentrations and earthquake triggering in complex linking fault systems.

Paleomagnetism of the Quaternary Bandelier Tuff: Implications for the tectonic evolution of the Española Basin, Rio Grande rift

We present newly acquired paleomagnetic data from Bandelier Tuff exposures in the Jemez Mountains (New Mexico) that show no statistically significant tectonic rotation over Quaternary time. Cooling units of the tuff were mapped in detail and correlated using new geochemical data, allowing us to confidently sample isochronous units for paleomagnetic remanence directions. In total, 410 specimens were subjected to step-wise thermal and alternating field demagnetization. Of the 40 accepted site means, 30 have α 95 values ≤5°. Analysis of the geographic distribution of the site-mean declinations of the data set reveals no statistically significant tectonic rotation either across (northwest/southeast) the northeast-striking Jemez fault or across (east/west) the north-striking Pajarito fault zone. Similarly, our data do not record any measurable relative change in declination difference (−1.1° ± 1.6°) that could be interpreted as a rotation over the ∼0.36 m.y. time duration between deposition of the two principal stratigraphic members of the Bandelier Tuff. The step-over discussed in this paper is an area of exceptional structural complexity and, as such, meets the definition of “accommodation zone.” We propose the name “Jemez-Embudo accommodation zone” for this composite of structural and volcanic features in recognition of its regional importance in the evolution of the Rio Grande rift. In this part of the rift, where Proterozoic- and Laramide-age faults have preconditioned the crust, idealized relay ramps, prevalent locally, do not occur at the regional scale. Instead, transfer fault zones have developed between half grabens dominated by preexisting faults. The pattern of faulting and accommodation of strain in the right-relayed step-over of the rift has been more or less invariant since the onset of rifting. From a global perspective, the difference between areas of modest crustal extension dominated by distributed deformation and those regions that develop transfer fault zones may ultimately be diagnostic of crustal conditioning and fault strength, such that weak fault systems focus strain within narrow zones.

Preliminary volcanic hazards evaluation for Los Alamos National Laboratory Facilities and Operations : current state of knowledge and proposed path forward

The integration of available information on the volcanic history of the region surrounding Los Alamos National Laboratory indicates that the Laboratory is at risk from volcanic hazards. Volcanism in the vicinity of the Laboratory is unlikely within the lifetime of the facility (ca. 50–100 years) but cannot be ruled out. This evaluation provides a preliminary estimate of recurrence rates for volcanic activity. If further assessment of the hazard is deemed beneficial to reduce risk uncertainty, the next step would be to convene a formal probabilistic volcanic hazards assessment.

Using unmanned aerial systems to collect hyperspectral imagery and digital elevation models at a legacy underground nuclear explosion test site

Hyperspectral and multispectral imagers have been developed and deployed on satellite and manned aerial platforms for decades and have been used to produce spectrally resolved reflectance and other radiometric products. Similarly, light detection and ranging, or LIDAR, systems are regularly deployed from manned aerial platforms to produce a variety of products, including digital elevation models. While both types of systems have demonstrated impressive capabilities from these conventional platforms, for some applications it is desirable to have higher spatial resolution and more deployment flexibility than satellite or manned aerial platforms can offer. Commercially available unmanned aerial systems, or UAS, have recently emerged as an alternative platform for deploying optical imaging and detection systems, including spectral imagers and high resolution cameras. By enabling deployments in rugged terrain, collections at low altitudes, and flight durations of several hours, UAS offer the opportunity to obtain high spatial resolution products over multiple square kilometers in remote locations. Taking advantage of this emerging capability, our team recently deployed a commercial UAS to collect hyperspectral imagery, RGB imagery, and photogrammetry products at a legacy underground nuclear explosion test site and its surrounds. Ground based point spectrometer data collected over the same area serves as ground truth for the airborne results. The collected data is being used to map the site and evaluate the utility of optical remote sensing techniques for measuring signatures of interest, such as the mineralogy, anthropogenic objects, and vegetative health. This work will overview our test campaign, our results to date, and our plans for future work.

SPE-5 Pre- and Post-Shot UAS Photogrammetry Quick Look

This is a powerpoint presentation with a collection of SPE-5 pre- and post-shot UAS photogrammetry images performed in April 2016.

CORRTEX Diagnostic Deployment for the SPE-III experiment, 24 July 2012: Fielding Report and Preliminary Data Analysis

The Continuous Reflectometry for Radius vs Time Experiments (CORRTEX) diagnostic system was deployed for the third explosives test in the Source Physics Experiment (SPE) sequence to monitor and verify several conditions of the experiment including the detonation velocity of the explosive package and functioning of explosive initiators. Six distance-marked coaxial cables were installed on the SPE-III explosives canister, and key locations documented through along-cable length measurements and photography. CORRTEX uses electrical-pulse time-domain reflectometry to continuously record the two-way transit time (TWTT) of the cables. As the shock front of the detonation advances, the coaxial cable is shorted or destroyed, and the resulting TWTT also decreases. Interpretation of these changes as a function of TWTT can be converted to positional measurements using known parameters of the cables.

Review of the geological and structural setting near the site of the proposed Transuranic Waste Facility (TRUWF) Technical Area 52 (TA-52), Los Alamos National Laboratory

Because of Los Alamos National Laboratory’s proximal location to active geologic structures, assessment of seismic hazards, including the potential for seismic surface rupture, must occur before construction of any facilities housing nuclear or other hazardous materials. A transuranic waste facility (TRUWF) planned for construction at Technical Area 52 (TA-52) provides the impetus for this report. Although no single seismic hazards field investigation has focused specifically on TA-52, numerous studies at technical areas surrounding TA-52 have shown no significant, laterally continuous faults exhibiting activity in the last 10 ka within 3,000 ft of the proposed facility. A site-specific field study at the footprint of the proposed TRUWF would not yield further high-precision data on possible Holocene faulting at the site because post-Bandelier Tuff sediments are lacking and the shallowest subunit contacts of the Bandelier Tuff are gradational. Given the distal location of the proposed TRUWF to any mapped structures with demonstrable Holocene displacement, surface rupture potential appears minimal at TA-52.