This volume addresses the tectonic complexity and diversity of strike-slip restraining and releasing bends with 18 contributions divided into four thematic sections: a topical review of fault bends and their global distribution; bends, sedimentary basins and earthquake hazards; restraining bends, transpressional deformation and basement controls on development; releasing bends, transtensional deformation and fluid flow.

Geometric complexities such as bends and stepovers along strike-slip faults impact the propagation of earthquake ruptures and can control the ultimate sizes of earthquakes. The ability of a rupture to propagate through a geometric complexity constitutes a fundamental predictor of seismic hazard, as the resulting length of a seismic fault rupture dictates the extent, intensity, and duration of damaging ground motion. Simulations of individual ruptures along a simple fault system indicate that bends of sufficient length or angle halt earthquake ruptures, yet simulations of rupture over multiple seismic cycles reveal that specific local geometry and the history of prior ruptures further modulate this behavior. Thus, assessing the proportion of ruptures that terminate at versus propagate through a geometric complexity requires specific geologic observations of fault geometry and seismic history. To investigate to what extent geometry alone controls rupture length, and validate the predictions of numerical models with observational data, I investigate the geomorphic record of multiple Quaternary earthquake cycles at the Aksay restraining double-bend on the Altyn Tagh fault (ATF) in western China. At the Aksay bend two overlapping subparallel strike-slip faults (the northern--NATF--and southern--SATF--Altyn Tagh faults) permit testing of model predictions for different fault bend angles. First I document the size and extent of the most recent earthquake (MRE) along the SATF, mapping 95 km of continuous fresh rupture as well as 70 measurements of small offsets that represent average coseismic slip of 5.6 m. Importantly, I constrain the eastward extent of this MRE and several before it at the most highly misoriented reach of the Aksay bend. Through Beryllium-10 exposure age dating of an undeformed Pleistocene alluvial deposit covering the fault, I demonstrate that no other Quaternary ruptures of the SATF have propagated farther through the bend than the MRE. Together with 270 km of fresh rupture previously mapped to the west, this minimum rupture length of 95 km, and average slip of 5.6 m, indicate a large magnitude M(w)>7.8) for this event. I measure Quaternary slip-rates at four locations spanning the bend on each of the two faults, in order to assess, using accumulated slip, how frequently and where prior ruptures have terminated within the bend. I present a new geomorphic interpretation of the controversial Huermo Bulak He slip rate site on the eastern NATF, at which prior studies reported contradictory slip rates based on conflicting mapping. The rate I determine of 6.3 (+2.1)/(-1.6) mm/yr−1 is substantially lower than some earlier estimates at this site, but agrees with rates determined here from both geodetic modeling and older offset geomorphic markers. At this site and the others I employ optically stimulated luminescence (OSL) burial-age dating of surface-capping loess deposits to interpret abandonment ages of geomorphic surfaces. Using cross-cutting relationships to interpret geomorphic history of deposition and incision at these sites, I relate these surface ages to offset piercing lines to obtain time-averaged slip rates. The resulting distribution of slip rates on each fault define opposing gradients on the west side of the Aksay bend, ranging from 6.3 (+2.1)/(-1.6) mm/yr−1 in the east to 2.1 ± 0.7 mm/yr−1 in the west on the NATF over a 150 km length of fault, but declining abruptly within 50 km on the SATF from 4.1 ± 0.4 mm/yr−1 in the west to effectively zero in the middle of the bend, with only a fraction of the fault-zone slip rate accommodated locally in the east (0.8 ± 0.3 mm/yr−1). This distribution of slip rates indicates that ruptures repeatedly stop at the bend on the SATF, but propagate through on the NATF. These slip gradients reveal persistence of a geometric barrier along the SATF through multiple earthquake cycles, and suggest the absence of a barrier on the NATF. These observed slip rates agree well with the synthetic slip rate distributions derived from numerical models of multiple rupture cycles along the Aksay bend fault system, validating the physics-based behavior in the models. These models, developed by collaborators in parallel with this observational study, provide the extents and distributions of individual earthquake ruptures that sum to produce the long-term slip rates, presenting the ensemble of possible ruptures that geology alone cannot distinguish. Together, the observational results presented here and the corresponding model results indicate that the vast majority of large ruptures halt along the most highly misoriented reach of the SATF, but that the less misoriented NATF remains favorable for occasional rupture. These results demonstrate that numerical modeling, tuned by field observations, may offer probabilistic estimates of the proportion of ruptures that violate expected barriers to propagation and thus generate larger, more damaging earthquakes.

The volume is organized into three sections entitled Overview, Extensional Settings and Contractional Settings together with a glossary of terms having to do with strike-slip deformation, basin formation and sedimentation.

The northwest part of the North America-Caribbean plate boundary zone is characterized by active, left-lateral strike-slip faults that are well constrained seismically and are corroborated by on- and offshore geologic mapping. The onshore plate boundary zone comprises the Motogua and Polochic fault systems of southern Guatemala which join and continue offshore as the Swan Islands fault zone along the southern edge of the Cayman trough. At the Mid-Cayman spreading center in the central Caribbean Sea, the fault motion is transferred at a 100 km wide left-step in the fault system to the Oriente fault zone. A third system, the Walton fault zone, continues east from the Mid-Cayman Spreading center to define the Gonave microplate. Seafloor features produced by strike-slip faulting along the Swan Islands and Walton fault zones have been imaged and mapped using the SeaMARC II side-scan sonar and swath bathymetric mapping system, single-channel seismic data, multichannel seismic data and 3.5 kHz depth profiles. Structures mapped along the Swan Islands and Walton fault zones include: 1) twenty-six restraining bends and five releasing bends ranging in size from several kilometers in area to several hundred kilometers in area; 2)en echelon folds which occur only within the restraining bends; 3) straight, continuous fault segments of up to several tens of kilometers in length; 4) restraining and releasing bends forming in "paired" configurations; and 5) a fault-parallel fold belt fold and thrust belt adjacent to a major restraining bend. The features observed along the Swan Islands and Walton fault systems are compared to other features observed along other strike-slip fault systems, from which empirical models have previously been derived. Based on the features observed in these strike-slip systems, a rigid plate scenario is envisioned where the geometry of the fault and the direction of plate motion have controlled the types of deformation that have occurred. In a related study, microtectonic features in an area of Neogene extension within the northwestern Caribbean plate were investigated in order to provide insight on the nature of intraplate deformation related to the motion along the plate boundary. Microtectonic features were measured in the Sula-Yojoa rift of northwestern Honduras with the intention of inverting the data to estimate stress states responsible for the observed strains. Data inversion for the estimation of stress states could not be undertaken with the available measurements, however, the observations made can be used to support several existing models for the intraplate deformation as well as to encourage the elimination of other models.

Assessment of seismic hazards in southern California may be improved with more accurate characterization of active geometry, stress state, and slip rates along the active San Andreas fault strands within the San Gorgonio Pass region. For example, on-going debate centers on the activity and geometry of the Mill Creek and Mission Creek strands. Calculated misfits of model slip rates to geologic slip rates for six alternative active fault configuration models through the San Gorgonio Pass reveal two best-fitting models, both of which fit many but not all available geologic slip rates. Disagreement between the model and geologic slip rates indicate where the model fault geometry is kinematically incompatible with the interpreted geologic slip rate, suggesting that our current knowledge of the fault configuration and/or slip rates may be inaccurate. Focal mechanism of microseismicity can estimate stress state; however, within the San Bernardino basin, some focal mechanisms show slip that is inconsistent with the interseismic strike-slip loading of the region. We show that deep creep along the nearby northern San Jacinto fault can account for this discrepancy. Consequently, if local stresses are estimated using these focal mechanisms, the resulting information about fault loading may be inaccurate. We also use another way to estimate the present-day, by calculating evolved fault tractions along a portion of the San Andreas fault using the time since last earthquake, fault stressing rates (which account for fault interaction), and co-seismic models of the impact of recent nearby earthquakes. Because this method considers the loading history of each fault, the evolved tractions differ significantly from the resolved regional tractions and can provide more accurate initial conditions for dynamic rupture models within regions of complex fault geometry. Numerical models of restraining bends in a viscoelastic material have implications for how we model the Earth's crust. Deforming the model at faster velocities decreases the amount of visco-relaxation, allowing the model to behave more elastically. Viscoelastic models allow for velocity-dependent deformation, which could improve our understanding of crustal deformation, especially within complex fault systems.

Faults are primary focuses of both fluid migration and deformation in the upper crust. The recognition that faults are typically heterogeneous zones of deformed material, not simple discrete fractures, has fundamental implications for the way geoscientists predict fluid migration in fault zones, as well as leading to new concepts in understanding seismic/aseismic strain accommodation. This book captures current research into understanding the complexities of fault-zone internal structure, and their control on mechanical and fluid-flow properties of the upper crust. A wide variety of approaches are presented, from geological field studies and laboratory analyses of fault-zone and fault-rock properties to numerical fluid-flow modelling, and from seismological data analyses to coupled hydraulic and rheological modelling. The publication aims to illustrate the importance of understanding fault-zone complexity by integrating such diverse approaches, and its impact on the rheological and fluid-flow behaviour of fault zones in different contexts.

Volcanism and tectonism are the dominant endogenic means by which planetary surfaces change. This book aims to encompass the broad range in character of volcanism, tectonism, faulting and associated interactions observed on planetary bodies across the inner solar system - a region that includes Mercury, Venus, Earth, the Moon, Mars and asteroids. The diversity and breadth of landforms produced by volcanic and tectonic processes is enormous, and varies across the inner solar system bodies. As a result, the selection of prevailing landforms and their underlying formational processes that are described and highlighted in this volume are but a primer to the expansive field of planetary volcanism and tectonism. This Special Publication features 22 research articles about volcanic and tectonic processes manifest across the inner solar system.

Strike-slip faults evolve to accommodate more fault slip, resulting in less off-fault deformation. In analog experiments, the measured fault slip to off-fault deformation ratios are similar to those measured in crustal strike-slip systems, such as the San Andreas fault system. Established planar faults have the largest fault slip to off-fault deformation ratio of ~0.98. In systems without a pre-existing fault surface, crustal thickness and basal detachment conditions affect shear zone width and roughness. However, once the applied plate displacement is 1-2 times the crustal thickness, partitioning of deformation between fault slip and off-fault distributed shear is >0.90, regardless of the basal boundary conditions. In addition, at any moment during the evolution of the analog fault system, the ratio of fault slip to off-fault deformation is larger than the cumulative ratio. We also find that the upward and lateral propagation of faults as an active shear zone developing early in the experiments has greater impact on the system's strike-slip efficiency than later interaction between non-collinear fault segments. For bends with stepover distance of twice the crustal thickness, the fault slip to off-fault deformation ratio increases up to ~0.80-0.90, after applied plate displacement exceeds twice the crustal thickness. Propagation of new oblique-slip faults around sharp restraining bends reduces the overall off-fault deformation within the fault system. In contrast, fault segments within gentle restraining bends continue to slip and the propagation of new oblique-slip faults have less effect on the system's efficiency than for sharp restraining bends.

Understanding Faults: Detecting, Dating, and Modeling offers a single resource for analyzing faults for a variety of applications, from hazard detection and earthquake processes, to geophysical exploration. The book presents the latest research, including fault dating using new mineral growth, fault reactivation, and fault modeling, and also helps bridge the gap between geologists and geophysicists working across fault-related disciplines. Using diagrams, formulae, and worldwide case studies to illustrate concepts, the book provides geoscientists and industry experts in oil and gas with a valuable reference for detecting, modeling, analyzing and dating faults. - Presents cutting-edge information relating to fault analysis, including mechanical, geometrical and numerical models, theory and methodologies - Includes calculations of fault sealing capabilities - Describes how faults are detected, what fault models predict, and techniques for dating fault movement - Utilizes worldwide case studies throughout the book to concretely illustrate key concepts