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The energy budget and the interplay between stable friction evolution and dynamic stick‐slips are tested here under continuous slip along rough faults. We conducted 34 direct‐shear experiments coupled with precise roughness measurements on diabase and limestone fault samples. The faults broad roughness ranges from highly rough and interlocked fractured interfaces to smooth polished surfaces. The analysis focuses on two slip phases: (a) the evolution of the shear strength of rough sample under stable, cumulative displacement; and (b) the dynamic of unstable stick‐slip sliding. We found that the breakdown work during frictional strength evolution increases with roughness increase across multiple scales. The diabase samples are more sensitive to roughness increase than limestone samples in terms of the breakdown work implied by frictional evolution. We attribute this increased diabase sensitivity with fault roughness to its higher bulk elasticity and not to the fault shear stiffness. The diabase faults displayed multiple periodic system‐size stick‐slips, and the measured stored energy during the preparatory stage were surprisingly independent of the fault roughness. This finding suggests that during the preparatory stage a balance between the intracycle fault stiffness and stress drop govern the stored energy magnitude. Further, this energy balance suggests that some interface conditioning occurs before the spontaneous slip overcomes a sticking barrier. Plain Language Summary: The breakdown energy dissipated as work during friction evolution along laboratory faults can be determined by integration of the shear stress versus shear displacement. In this study, we quantitatively analyze the relationship between the roughness of laboratory faults and the dissipated energy during sliding. The experiments with rough diabase and limestone faults show an increase of breakdown work implied by the frictional strength with increasing fault roughness, and breakdown work increase with increasing host rock rigidity. We also find that the energy dissipated during frictional evolution of rough faults is four orders of magnitude larger than the energy dissipated during system size stick‐slip cycles in the same experimental setting. We attribute this observed discrepancy to the difference in contact area between interlocked, and sheared, surfaces. Surprisingly, our examination of breakdown work during stick‐slip cycles reveals a roughness‐independent behavior. We ultimately show that the energy components of both stick‐slip and friction evolution follow the same power law relationship when scaled to the sliding displacement. Key Points: The breakdown work implied by the evolution of frictional strength scales with roughness (RMS) height and elasticity of intact rockThe stored energy within stick‐slip cycles is four orders of magnitude lower than the energy accommodated during friction evolutionThe stored energy at the onset of breakdown during stick‐slip cycles is generally independent of fault roughness [ABSTRACT FROM AUTHOR]

Principal slip surfaces in fault zones accommodate most of the displacement during earthquakes. The topography of these surfaces is integral to earthquake and fault mechanics, but is practically unknown at the scale of earthquake slip. We use new laser-based methods to map exposed fault surfaces over scales of 10 pm to 120 m. These data provide the first quantitative evidence that fault-surface roughness evolves with increasing slip. Thousands of profiles ranging from 10/[micro]m to >100 m in length show that small-slip faults (slip Keywords: faults, earthquakes, bumps, asperities, fault slip, slip surfaces, fault-surface roughness.

A newly discovered active small-scale pull-apart (Mor structure), located in the western part of the Dead Sea Basin, shows recent basin-parallel extension and strike-slip faulting, and offers a rare view of pull-apart internal structure. The Mor structure is bounded by N-S-trending strike-slip faults. and cross-cut by low-angle, E-W-trending normal faults. The geometry of this pull-apart suggests that displacement between the two stepped N-S strike-slip faults of the Mor structure is transferred by the extension associated with the normal faults. The continuing deformation in this structure is evident by the observation of at least three deformation episodes between 50 ka and present. The calculated sinistral slip-rate is 3.5 mm/yr over the last 30 000 years. This slip rate indicates that the Mor structure overlies the currently most active strike-slip fault within the western border of the Dead Sea pull-apart. The Mor structure is an example of a small pull-apart basin developed within a larger pull-apart. This type of hierarchy in pull-apart structures is an indication for their ongoing evolution. Keywords: Dead Sea, strike-slip faults, pull-apart basins, Late Pleistocene.

[1] Rifled basins are bounded by marginal belts with fault networks and flexures. We analyze the internal structure of such a belt, the western margins of the Dead Sea basin. This basin is 150 km long, 15-20 km wide with more than 10 km of sediment fill; and it is currently subsiding due to slip of the Dead Sea pull-apart. The western margin of the Dead Sea basin is an elongated N-S belt with an intricate three-dimensional (3-D) pattern of zigzag faults, flexures and joints. The dominant structures are four sets of oblique-normal faults, arranged in orthorhombic symmetry. The faults are steep with prevalent strike directions of NNW and NNE. Large flexures developed along and above these faults, forming tilted blocks and localized asymmetric folds. Two sets of subvertical joints that dominate the area trend NNE and NNW, subparallel to the strikes of the dominant fault sets. The parallel relations between these structures at all scales suggest that they formed during a single tectonic phase. Three-dimensional fault modeling reveals a 3-D strain field with a large vertical shortening, a minor horizontal shortening in N-S direction (belt-parallel) and a large horizontal E-W extension (basinward). The calculated stress fields associated with the zigzag fault segments are compatible with the observed fault-parallel flexures. Further, the calculations predict the formation of local tensile belts above the faults, and these tensile belts could explain the penecontemporaneous development of the two joint sets. Architecture similar to the western margins of the Dead Sea basin is likely to develop on rifled margins wherever 3-D deformation is required by the tiffing kinematics. INDEX TERMS: 8105 Tectonophysics: Continental margins and sedimentary basins; 8109 Tectonophysics: Continental tectonics--extensional (0905); 8010 Structural Geology: Fractures and faults; 8020 Structural Geology: Mechanics; KEYWORDS: faults, slip partitioning, three-dimensional, pull-apart, joints, zigzag.

Author(s): Amir Sagy [1]; Ze'ev Reches [1]; Jay Fineberg (corresponding author) [2] A large impact by a comet or meteorite releases an enormous amount of energy, which evaporates, melts and [...]

We present a methodology for mapping faults that constitute a potential hazard to structures, with an emphasis on special facilities such as dams and nuclear power plants. The methodology categorises faults by hierarchical seismo-tectonic criteria, which are designed according to the degree of certainty for recent activity and the accessibility of the information within a given region. First, the instrumental seismicity is statistically processed to obtain the gridded seismicity of the earthquake density and the seismic moment density parameters. Their spatial distribution reveals the zones of the seismic sources, within the examined period. We combine these results with geodetic slip rates, historical earthquake data, geological maps and other sources to define and categorise faults that are likely to generate significant earthquakes (M ≥ 6.0). Their mapping is fundamental for seismo-tectonic modelling and for PSHA analyses. In addition, for surface rupture hazard, we create a database and a map of capable faults, by developing criteria according to the regional stratigraphy and the seismotectonic configuration. The relationship between seismicity slip dynamics and fault activity through time is an intrinsic result of our analysis that allows revealing the tectonic evolution of a given region. The presented methodology expands the ability to differentiate between subgroups for planning or maintenance of different constructions or for research aims, and can be applied in other regions. [ABSTRACT FROM AUTHOR]