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

Abstract

The seismically active Pajarito fault system (PFS) of northern New Mexico, UnitedStates, 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 throwlength profi les 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 profi les and throw defi cits 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. on 23 July 2009 geosphere.gsapubs.org Downloaded from Fault interaction and variation in throw in the Pajarito fault systemGeosphere,

Fumarolic pipes in the Tshirege Member of the Bandelier Tuff on the Pajarito Plateau, Jemez Mountains, New Mexico

“…The Pajarito fault system includes faults and monoclines of the Pajarito (PF), Rendija Canyon (RCF), Guaje Mountain (GMF) and Sawyer Canyon (SCF) faults. Map modified from Lewis et al (2009) pointed to three gradational stages of fumarolic activity as cooling proceeded: (1) high-temperature vapor phase degassing, (2) fumarolic gases interacting with water to create acids at the surface resulting in concentrated argillic alteration, and (3) present-day residual near-neutral steam emanations. Papike et al (1991) studied several fumarolic pipes at the Valley of Ten Thousand Smokes to determine chemical gains and losses, and mineralogic evolution.…”

Pliocene–Holocene deformation in the southern Rio Grande rift as inferred from topography and uplifted terraces of the Franklin Mountains, southern New Mexico and western Texas

“…Previous studies indicate that fault propagation and linkage may be an important process governing rift development. For example, in the Española Basin in northern New Mexico, multiple studies have been undertaken to decipher fault displacement profiles along the Pajarito fault system (Carter and Winter, 1995;Lewis et al, 2009;Goteti et al, 2013). Carter and Winter (1995) suggested that individual fault segments are generally bell shaped in the direction of dip, although they are asymmetric and displacement abruptly decreases at fault tips.…”

“…Carter and Winter (1995) suggested that individual fault segments are generally bell shaped in the direction of dip, although they are asymmetric and displacement abruptly decreases at fault tips. Lewis et al (2009) built upon these previous results and used the 1.25 Ma (Phillips, 2004) Tshirege Member of the Bandelier Tuff as a datum to construct a fault throw profile for the Pajarito fault system. Their results indicate that the Pajarito fault system is composed of multiple shorter segments.…”

“…Along some of these fault segments, the maximum fault throw is near the center of the fault trace, while in others it is shifted to one side, producing an asymmetrical fault throw profile. In addition, each of these shorter fault segments merges and overlaps with other segments in a series of monoclinal folds and distributed small-offset faults (Lewis et al, 2009). These observations are consistent with the results of three-dimensional finite-element modeling of the evolution of the Pajarito fault system, which predicts the development of overlapping fault segments and relay ramps (Goteti et al, 2013).…”

“…Their current elevations are therefore a valuable record of the recent evolution of these fault networks. These observations are used to compare results from the southern rift to fault profiles that have been studied to the north (Carter and Winter, 1995;Lewis et al, 2009) and to discuss fault propagation and linkage of these faults through time during continued development of the southern Rio Grande rift.…”