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Attempts to determine the age of faulting recorded by fault rocks have been made using K–Ar, fission‐track, electron spin resonance, and luminescence dating methods. Here we report the unambiguous reduction (resetting) of optically stimulated luminescence (OSL) signals of quartz gouge after friction experiments and estimate the seismological and geological conditions required for OSL signal resetting in natural fault zones. In the experiments, we used quartz sand with a particle size of <150 μm and equivalent dose of 31.5 ± 16.6 Gy. Friction experiments were conducted with a rotary‐shear, high‐velocity friction apparatus at slip rates (V) of 200 μm s−1 to 1.3 m s−1, normal stress of 1.0 MPa, and displacement of 10 m. In the experiments conducted under dry conditions, the OSL signal starts to decrease from V = 0.25 m s−1 and becomes near zero at V ≥ 0.65 m s−1. OSL signal resetting is also observed in the experiment sheared at 1.3 m s−1 under water‐added conditions. At V = 0.25 and 0.40 m s−1, partial resetting occurs, which is characterized by coexistence of particles with and without an OSL signal. OSL signal intensity shows a strong correlation with applied power density and frictional heat during high‐velocity friction, and the signal exponentially decreases with increasing power density and temperature. The power density required for partial and complete OSL signal resetting is ~0.17 and 0.6 MW m−2, respectively. Assuming a co‐seismic fault slip rate of 0.6 m s−1, the depths required for partial and complete resetting are expected to be ≥11 and ≥42 m. Key Points: Optically stimulated luminescence of quartz loses its signal as the velocity approaches a co‐seismic slip rate of 1 m s−1Remnant signal intensity after friction experiments shows a clearly reverse correlation with fault zone temperatureThe depths required for partial and complete resetting of optically stimulated luminescence ages are ≥11 and ≥42 m, respectively [ABSTRACT FROM AUTHOR]

The subduction of bathymetric anomalies at convergent margins can profoundly affect subduction dynamics, magmatism, and the structural and geomorphic evolution of the overriding plate. The Northern Patagonian Icefield (NPI) is located east of the Chile Triple Junction at ~47°S, where the Chile Rise spreading center collides with South America. This region is characterized by an abrupt increase in summit elevations and relief that has been controversially debated in the context of geodynamic versus glacial erosion effects on topography. Here we present geomorphic, thermochronological, and structural data that document neotectonic activity along hitherto unrecognized faults along the flanks of the NPI. New apatite (U-Th)/He bedrock cooling ages suggest faulting since 2-3 Ma. We infer the northward translation of an ~140 km long fore-arc sliver-the NPI block-results from enhanced partitioning of oblique plate convergence due to the closely spaced collision of three successive segments of the Chile Rise. In this model, greater uplift occurs in the hanging wall of the Exploradores thrust at the northern leading edge of the NPI block, whereas the Cachet and Liquiñe-Ofqui dextral faults decouple the NPI block along its eastern and western flanks, respectively. Localized extension possibly occurs at its southern trailing edge along normal faults associated with margin-parallel extension, tectonic subsidence, and lower elevations along the Andean crest line. Our neotectonic model provides a novel explanation for the abrupt topographic variations inland of the Chile Triple Junction and emphasizes the fundamental effects of local tectonics on exhumation and topographic patterns in this glaciated landscape. [ABSTRACT FROM AUTHOR]

Recent works documented Neogene to Quaternary dextral strike-slip tectonics along the Kuh-e-Sarhangi and Kuh-e-Faghan intraplate strike-slip faults at the northern edge of the Lut Block of Central Iran, previously thought to be dominated by sinistral strike-slip deformation. This work focuses on the evidence of Quaternary activity of one of these fault systems, in order to provide new spatiotemporal constraints on their role in the active regional kinematic scenario. Through geomorphological and structural investigation, integrated with optically stimulated luminescence dating of three generations of alluvial fans and fluvial terraces (at ~53, ~25, and ~6 ka), this study documents (i) the topographic inheritance of the long-term (Myr) punctuated history of fault nucleation, propagation, and exhumation along the northern edge of Lut Block; (ii) the tectonic control on drainage network evolution, pediment formation, fluvial terraces, and alluvial fan architecture; (iii) the minimum Holocene age of Quaternary dextral strike-slip faulting; and (iv) the evidence of Late Quaternary fault-related uplift localized along the different fault strands. The documented spatial and temporal constraints on the active dextral strike-slip tectonics at the northern edge of Lut Block provide new insights on the kinematic model for active faulting in Central Iran, which has been reinterpreted in an escape tectonic scenario. [ABSTRACT FROM AUTHOR]

Deciphering deformation mechanisms within Quaternary sediments in a highly dynamic environment such as the southeast European Alps is often a challenging task that requires the use of a variety of methods. Due to the geohazards involved, the interpretation of deformation mechanisms can have a major impact on society and may enable the preparation of appropriate engineering solutions. We present an example of how deformation structures can be studied by integrating geomorphological, sedimentological and structural geological mapping using photogrammetric and leveling surveys, paleoseismological techniques, optically stimulated luminescence dating and ground penetrating radar surveys. Quaternary deposits on the slopes of the formerly glaciated Soča Valley near Most na Soči are tilted and dissected along numerous faults within the deformation zone of the Idrija Fault, a large, active, dextral strike-slip fault. Reconstruction of deformation history indicates that at least five deformation events occurred during deposition of the glaciofluvial succession interbedded with glaciolacustrine deposits, dated to Penultimate Glaciation. Ground penetrating radar profiles and outcrop observations reveal NE – SW striking faults, which are approximately perpendicular to the primary Idrija Fault. Based on the local geologic setting, we considered glaciotectonics, gravitational faulting due to ice-decay collapse or slope instability, and tectonic faulting as possible deformation mechanisms. Based on detailed documentation and analysis of the geometry and kinematics of the deformations, we interpret the observed deformations as secondary structures that result from paleoseismic activity of the Idrija Fault, and some structures resulting from glaciotectonics and gravitational faulting. The transtensional type of deformations at the studied site shows the local character of the main fault, which occurs here due to geometrical and kinematical changes of the Idrija Fault causing local transtension in the Most na Soči area. The complexity of the fault and the first paleoseismic evidence dating back to Penultimate Glaciation provide valuable new data for understanding the seismic hazard in the region. • Origin of deformations within Quaternary sediments in a highly dynamic environment unraveled. • Glaciofluvial and glaciolacustrine deposits record recurrent faulting and non-tectonic deformations. • First paleoseismological evidence on the major Idrija Fault extending back to Penultimate Glaciation. • Local scale fault complexities reflect fault geometric and kinematic changes. [ABSTRACT FROM AUTHOR]

Abstract: The Pajarito fault forms the western margin of the Rio Grande rift in north-central New Mexico, and lies adjacent to Los Alamos National Laboratory, a major Federal research facility. Vertical displacement on this normal fault over the past 1.2 Ma has created a 50- to 120-m-high fault scarp on Bandelier Tuff (1.2 Ma), yielding a long-term average slip rate of ca. 0.1 mm/yr. In support of a Laboratory-wide seismic hazards assessment, we excavated 14 trenches in the Pajarito fault zone to determine the age of the most recent displacement event, the recurrence interval between events, the displacement per event, and the variability in slip rate and recurrence through time. The large number of trenches was required by the large height of the fault scarp and the complexity of the fault zone. Only about half the trenches contained significant thicknesses of Holocene deposits, but in those trenches there was clear evidence for an early-to-mid-Holocene displacement event. The previous event was at least 20–40 ka, and the average recurrence interval over the past ca. 300 ka was about 20–40 kyr. We infer that much of the structural relief across this fault developed soon after eruption of the Bandelier Tuff between 1.0 and 1.2 Ma, and that slip rate slowed considerably after that time. [Copyright &y& Elsevier]