How a strong low-angle normal fault formed: The Whipple detachment, southeastern California

2019 ◽  
Vol 132 (9-10) ◽  
pp. 1817-1828 ◽  
Author(s):  
Gary J. Axen
Keyword(s):  
Principal Stress ◽  
Maximum Shear Stress ◽  
Fluid Pressure ◽  
Normal Fault ◽  
Maximum Principal Stress ◽  
Detachment Fault ◽  
Normal Faults ◽  
Small Scale ◽  
Tectonic Model ◽  
Stress Rotation

Abstract Many low-angle normal faults (dip ≤30°) accommodate tens of kilometers of crustal extension, but their mechanics remain contentious. Most models for low-angle normal fault slip assume vertical maximum principal stress σ1, leading many authors to conclude that low-angle normal faults are poorly oriented in the stress field (≥60° from σ1) and weak (low friction). In contrast, models for low-angle normal fault formation in isotropic rocks typically assume Coulomb failure and require inclined σ1 (no misorientation). Here, a data-based, mechanical-tectonic model is presented for formation of the Whipple detachment fault, southeastern California. The model honors local and regional geologic and tectonic history and laboratory friction measurements. The Whipple detachment fault formed progressively in the brittle-plastic transition by linking of “minidetachments,” which are small-scale analogs (meters to kilometers in length) in the upper footwall. Minidetachments followed mylonitic anisotropy along planes of maximum shear stress (45° from the maximum principal stress), not Coulomb fractures. They evolved from mylonitic flow to cataclasis and frictional slip at 300–400 °C and ∼9.5 km depth, while fluid pressure fell from lithostatic to hydrostatic levels. Minidetachment friction was presumably high (0.6–0.85), based upon formation of quartzofeldspathic cataclasite and pseudotachylyte. Similar mechanics are inferred for both the minidetachments and the Whipple detachment fault, driven by high differential stress (∼150–160 MPa). A Mohr construction is presented with the fault dip as the main free parameter. Using “Byerlee friction” (0.6–0.85) on the minidetachments and the Whipple detachment fault, and internal friction (1.0–1.7) on newly formed Reidel shears, the initial fault dips are calculated at 16°–26°, with σ1 plunging ∼61°–71° northeast. Linked minidetachments probably were not well aligned, and slip on the evolving Whipple detachment fault probably contributed to fault smoothing, by off-fault fracturing and cataclasis, and to formation of the fault core and fractured damage zone. Stress rotation may have occurred only within the mylonitic shear zone, but asymmetric tectonic forces applied to the brittle crust probably caused gradual rotation of σ1 above it as a result of: (1) the upward force applied to the base of marginal North America by buoyant asthenosphere upwelling into an opening slab-free window and/or (2) basal, top-to-the-NE shear traction due to midcrustal mylonitic flow during tectonic exhumation of the Orocopia Schist. The mechanical-tectonic model probably applies directly to low-angle normal faults of the lower Colorado River extensional corridor, and aspects of the model (e.g., significance of anisotropy, stress rotation) likely apply to formation of other strong low-angle normal faults.

scholarly journals Numerical Investigation of a Hydrosplitting Fracture and Weak Plane Interaction Using Discrete Element Modeling

Water ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 535
Author(s):  
Shuaiqi Liu ◽  
Fengshan Ma ◽  
Haijun Zhao ◽  
Jie Guo ◽  
Xueliang Duan ◽  
...  
Keyword(s):  
Shear Stress ◽  
Principal Stress ◽  
Stress Ratio ◽  
Water Pressure ◽  
Maximum Shear Stress ◽  
Water Inrush ◽  
Discrete Element ◽  
Maximum Principal Stress ◽  
In Situ Stress

Water inrush caused by hydrosplitting is an extremely common disaster in the engineering of underground tunnels. In this study, the propagation of fluid-driven fractures based on an improved discrete element fluid-solid coupling method was modeled. First, the interactions between hydrosplitting fractures (HFs) and preexisting weak planes (WPs) with different angles were simulated considering water pressure in the initial fracture. Second, the influence of the in situ stress ratio and the property of WPs were analyzed, and corresponding critical pressure values of different interactions were calculated. Lastly, the maximum principal stress and maximum shear stress variation inside the pieces were reproduced. The following conclusions can be drawn: (1) Five different types of interaction modes between HFs and natural WPs were obtained, prone to crossing the WPs under inclination of 90°. (2) The initiation pressure value decreased with an increased in situ stress ratio, and the confining stress status had an effect on the internal principal stress. (3) During HFs stretching in WPs with a high elastic modulus, the value of the maximum principal stress was low and rose slowly, and the maximum shear stress value was smaller. Through comprehensive analysis, the diversity of the principal stress curves is fundamentally determined by the interaction mode between HFs and WPs, which are influenced by the variants mentioned in the paper. The analysis provides a better guideline for understanding the failure mechanism of water gushing out of deep buried tunnel construction and cracking seepage of high head tunnels.

Mechanics of Cell Mechanosensing on Patterned Substrate

2016 ◽  
Vol 83 (5) ◽  
Author(s):  
Chenglin Liu ◽  
Shijie He ◽  
Xiaojun Li ◽  
Bo Huo ◽  
Baohua Ji
Keyword(s):  
Shear Stress ◽  
Principal Stress ◽  
Maximum Shear Stress ◽  
Cell Monolayer ◽  
Maximum Principal Stress ◽  
Mechanical Force ◽  
Shear Stresses ◽  
Plane Shear ◽  
Cell Behaviors ◽  
Mechanical Signals

It has been recognized that cells are able to actively sense and respond to the mechanical signals through an orchestration of many subcellular processes, such as cytoskeleton remodeling, nucleus reorientation, and polarization. However, the underlying mechanisms that regulate these behaviors are largely elusive; in particular, the quantitative understanding of these mechanical responses is lacking. In this study, combining experimental measurement and theoretical modeling, we studied the effects of rigidity and pattern geometry of substrate on collective cell behaviors. We showed that the mechanical force took pivotal roles in regulating the alignment and polarization of cells and subcellular structures. The cell, cytoskeleton, and nucleus preferred to align and polarize along the direction of maximum principal stress in cell monolayer, and the driving force is the in-plane maximum shear stress. The higher the maximum shear stress, the more the cells and their subcellular structures preferred to align and polarize along the direction of maximum principal stress. In addition, we proved that in response to the change of in-plane shear stresses, the actin cytoskeleton is more sensitive than the nucleus. This work provides important insights into the mechanisms of cellular and subcellular responses to mechanical signals. And it also suggests that the mechanical force does matter in cell behaviors, and quantitative studies through mechanical modeling are indispensable in biomedical and tissue engineering applications.

The influence of loading path on fault reactivation: a laboratory perspective

2020 ◽  
Author(s):  
Carolina Giorgetti ◽  
Marie Violay
Keyword(s):  
Shear Stress ◽  
Stress Field ◽  
Mechanical Behavior ◽  
Normal Stress ◽  
Principal Stress ◽  
Maximum Principal Stress ◽  
Fault Reactivation ◽  
Loading Path ◽  
Normal Faults ◽  
Loading Paths

<p>Despite natural faults are variably oriented to the Earth's surface and to the local stress field, the mechanics of fault reactivation and slip under variable loading paths (sensu Sibson, 1993) is still poorly understood. Nonetheless, different loading paths commonly occur in natural faults, from load-strengthening when the increase in shear stress is coupled with an increase in normal stress (e.g., reverse faults in absence of the fluid pressure increase) to load-weakening when the increase in shear stress is coupled with a decrease in normal stress (e.g., normal faults). According to the Mohr-Coulomb theory, the reactivation of pre-existing faults is only influenced by the fault orientation to the stress field, the fault friction, and the principal stresses magnitude. Therefore, the stress path the fault experienced is often neglected when evaluating the potential for reactivation. Yet, in natural faults characterized by thick, incohesive fault zone and highly fractured damage zone, the loading path could not be ruled out. Here we propose a laboratory approach aimed at reproducing the typical tectonic loading paths for reverse and normal faults. We performed triaxial saw-cut experiments, simulating the reactivation of well-oriented (i.e., 30° to the maximum principal stress) and misoriented (i.e., 50° to the maximum principal stress), normal and reverse gouge-bearing faults under dry and water-saturated conditions. We find that load-strengthening versus load-weakening path results in clearly different hydro-mechanical behavior. Particularly, prior to reactivation, reverse faults undergo <em>compaction</em> even at differential stresses well below the value required for reactivation. Contrarily, normal faults experience <em>dilation</em>, most of which occurs only near the differential stress values required for reactivation. Moreover, when reactivating at comparable normal stress, normal faults (load-weakening path) are more prone to slip seismically than reverse fault (load-strengthening path). Indeed, the higher mean stress that normal fault experienced before reactivation compacts more efficiently the gouge layer, thus increasing the fault stiffness and favoring seismic slip. This contrasting fault zone compaction and dilation prior to reactivation may occur in different natural tectonic settings, affecting the fault hydro-mechanical behavior. Thus, to take into account the loading path the fault experienced is fundamental in evaluating both natural and induced fault reactivation and the related seismic risk assessment.</p>

scholarly journals THE GEOLOGICAL STRUCTURE OF THE ALLOCHTHONOUS "ATHENS SCHISTS"

2004 ◽  
Vol 36 (4) ◽  
pp. 1550 ◽  
Author(s):  
Δ. I. Παπανικολάου ◽  
Σ. Γ. Λόζιος ◽  
K. Ι. Σούκης ◽  
Εμ. Ν. Σκούρτσος
Keyword(s):  
Internal Structure ◽  
Upper Cretaceous ◽  
Normal Fault ◽  
Accretionary Prism ◽  
Geological Structure ◽  
Detachment Fault ◽  
Metamorphic Rocks ◽  
Normal Faults ◽  
Low Grade

Based on lithological fades, deformation and metamorphic degree the alpine tectonostratigraphic complex known in the literature as "Athens Schists" is divided into two units: the non-metamorphosed overlying Athens Unit and the very low grade metamorphosed underlying Alepovouni Unit. Athens Unit crops out in several hills of the western and central part of the Athens Basin emerging through the post-alpine sediments. It comprises several lithologies that constitute two lithologie groups: the first one of neritic white massive-to thick-bedded carbonates that bear rudist fragments and Upper Cretaceous foraminifera. These limestones are olistholites within the second pelagic formation comprising marly limestones with Globotruncana sp., shales, sandstones, tuffs and ophiolithic blocks. Due to tectonic intercalating of these two lithological groups Athens Unit shows a complex internal structure. It represents an Upper Cretaceous mélange formed in an accretionary prism. Alepovouni Unit is observed at the eastern part of the Athens Basin along the foothills of Mt. Hymettos, wedged between Athens Unit and the metamorphic rocks of Mt. Hymettos. It comprises two lithological groups, in which remnants of Thassic fossils were reported. Alepovouni Unit is correlated to the allochthonous Lavhon Unit that tectonically overlies the autochthonous Attica Unit in SE Attica. At the eastern part of the Athens Basin, Alepovouni Unit is bounded by two west-dipping lowangle normal faults. Along these contacts the formations of both Athens and Alepovouni Units exhibit microstructures indicating top-to NW sense of shear. The contact between the Athens Unit and Alepovouni Unit in western Hymettos is probably a major extensional detachment separating the metamorphic units of Attica autochthon and Alepovouni at the footwall to the SE from the nonmetamorphic units of the Sub-Pelagonian and the Athens unit at the hangingwall to the NW. This major detachment fault accommodated the uplift of the metamorphic rocks and juxtaposed these two units. At the western part Athens Unit overlies tectonically the Paleozoic - Mesozoic formations of the Sub-Pelagonian unit. The contact is an east-dipping normal fault, antithetic to the major detachment of western Hymettos.

scholarly journals The Mechanism of Rock Mass Crack Propagation of Principal Stress Rotation in the Process of Tunnel Excavation

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Guanfeng Chang ◽  
Xinzhu Hua ◽  
Jie Zhang ◽  
Peng Li
Keyword(s):  
Rock Mass ◽  
Crack Propagation ◽  
Principal Stress ◽  
Maximum Principal Stress ◽  
Surrounding Rock ◽  
Shear Load ◽  
Principal Stress Rotation ◽  
Principal Stress Direction ◽  
Stress Rotation ◽  
Crack Angle

Rock excavation has experienced complex stress paths. The development of the original crack under the path of principal stress magnitude and principal stress direction is a key scientific problem that needs to be solved in rock underground engineering. The principal stress magnitude dominates the initiation and propagation of the crack and increases rock damage under the action of principal stress rotation. In this study, the theoretical calculation and numerical analysis method have been combined with the crack propagation conditions to study the stress-driven mechanism of brittle rock crack propagation under principal stress rotation. The results show that the “relative initial angle” of crack angle is being updated in time during the principal stress rotation process; once the stress is rotated, it will become the next initial crack angle; the crack propagation direction is deviated under the applied shear load, and it is always in the direction of minimum shear load, leading to a certain degree of inhibition of crack propagation depth in the initial direction. According to the results of numerical simulation, the effect of principal stress rotation caused by mining excavation is obvious and has a certain range of influence depth, the stress of surrounding rock of roadway is the highest within the depth range of 1∼2 m, and the maximum principal stress is as high as 26.89 MPa. The rotation of principal stress direction on the roadway surrounding rock surface is the strongest, which makes the surrounding rock more fragmented, and the middle principal stress and the maximum principal stress rotate about 90° counterclockwise along the Ox axis. Studying the action mechanism of principal stress rotation on fractured rock masses can provide scientific basis for geotechnical engineering design and rock mass surrounding support.

Progressive development of the Büyük Menderes Graben based on new data, western Turkey

2009 ◽  
Vol 146 (5) ◽  
pp. 652-673 ◽  
Author(s):  
ÖMER FEYZİ GÜRER ◽  
NURAN SARICA-FILOREAU ◽  
MUZAFFER ÖZBURAN ◽  
ERCAN SANGU ◽  
BÜLENT DOĞAN
Keyword(s):  
Middle Miocene ◽  
Normal Fault ◽  
Structural Data ◽  
Detachment Fault ◽  
Normal Faults ◽  
Tectonic Event ◽  
Alluvial Deposits ◽  
Western Turkey ◽  
Northern Margin ◽  
The North

AbstractOblique and normal fault systems exposed in the Büyük Menderes Graben (BMG) region record two successive and independent complex tectonic events. The first group tectonic event is defined by an E–W extension related to N–S contraction and transpression. This group is responsible for the development of NW- and NE-trending conjugate pairs of oblique faults which controlled Early–Middle Miocene basin formation. Between the Early–Middle Miocene and Plio-Quaternary strata exists an unconformity, indicating a period of folding, uplift and severe erosion associated with N–S shortening. The second group of events was the change in tectonic regime from E–W extension to N–S extension which controlled the formation of the Büyük Menderes Graben by three progressive pulses of deformation. The first pulse of extensional deformation was initially recorded in the region by the exhumation of the deep part of the Menderes Massif (MM) with the development of the E-trending Büyük Menderes Detachment Fault (BMDF). The minimum age of this pulse is constrained by the older Plio-Quaternary fluviatile deposits of the Büyük Menderes Graben that range in age from the Plio-Pleistocene boundary interval to Late Pleistocene. The second pulse, which is marked by the rapid deposition of alluvial deposits, initiated the formation of approximately E–W-trending high-angle normal faults synthetic and antithetic to the Büyük Menderes Detachment Fault, on the northern margin during Holocene times. These faults are interpreted as secondary steeper listric faults that merge with the main Büyük Menderes Detachment Fault at depth. The third pulse was the migration of the Büyük Menderes Graben depocentre to the present day position by diachronous activity of secondary steeper listric faults. These steeper faults are the most seismically active tectonic elements in western Turkey. According to the stratigraphic and structural data, the N–S extension in the Büyük Menderes Graben region produced a progressive deformation phase with different pulses during its Plio-Quaternary evolution, with migration of deformation from the master fault to the hangingwall. The formation of diachronous secondary synthetic and antithetic steeper faults on the upper plate of the Büyük Menderes Detachment Fault, hence the southward migration of the deformation and of the Büyük Menderes Graben depocentre, should be related to the evolution of detachment in the region. The presence of the seismically active splays of secondary faults implies an active detachment system in the region. This young Plio-Quaternary N–S extension in the Büyük Menderes Graben may be attributed to the combined effects of the two continuing processes in Aegean region. The first process is back-arc spreading or probably the roll-back of African slab below the south Aegean Arc, which seems to be responsible for the change in the stress tensor from E–W extension to N–S extension. The second and later event is the southwestward escape of the Anatolian block along its boundary fault, that is, the North Anatolian fault (NAF).

Vein geometry and hydrostatics during Yellowknife mineralisation

1978 ◽  
Vol 15 (10) ◽  
pp. 1653-1660 ◽  
Author(s):  
R. Kerrich ◽  
I. Allison
Keyword(s):  
Principal Stress ◽  
Shear Zone ◽  
Fluid Pressure ◽  
Shear Zones ◽  
Horizontal Stress ◽  
Maximum Principal Stress ◽  
Ambient Conditions ◽  
Stress Regime ◽  
Quartz Veins ◽  
Vertical Arrays

Three vein systems with distinct geometry and time relations are located within major ductile shear zones at Yellowknife. En échelon arrays of centimetre width quartz veins initiated at ~45° to the shear zone boundaries and normal to the schistosity during initial translation on the structures. These geometrical relations conform to the simple shear model of Ramsay and Graham. Orientation of the maximum principal stress was ~45° to the 70° dipping shear zone boundaries, implying that the horizontal stress in the crust was greater than the vertical stress.Gold-bearing quartz veins of metre dimensions are disposed parallel to the schistosity, cross cutting early veins. This geometry requires the stress regime to switch from the former orientation such that the maximum principal stress is parallel to the schistosity, and the effective stress normal to the schistosity is tensile. The change of stress orientation is attributed to transient high fluid pressure which generated hydraulic fracturing and correspondingly high values of permeability. Under these conditions the shear zones act as conduits for massive fluid discharge; quartz and gold were precipitated from solutions cooling along a temperature–pressure (TP) gradient. Crustal vertical stress was greater than horizontal stress.Late stage lenticular gold-bearing quartz veins of metre dimensions were emplaced as vertical arrays within the shear zones, oriented normal to schistosity. These tension fractures formed when the stress regime reverted to the ambient conditions for stage 1 veining during a second episode of displacement on the shear zones. Consideration of the kinetics of intergranular diffusion, with reference to the required transport distances of gold into a lode deposit, implies that long-range diffusive transport of gold into veins was not significant.

scholarly journals Modelling of orbital deformation using finite-element analysis

2005 ◽  
Vol 3 (7) ◽  
pp. 255-262 ◽  
Author(s):  
Jehad Al-Sukhun ◽  
Christian Lindqvist ◽  
Risto Kontio
Keyword(s):  
Finite Element ◽  
Ct Scan ◽  
Principal Stress ◽  
Maximum Shear Stress ◽  
Element Model ◽  
Maximum Principal Stress ◽  
Blunt Injury ◽  
Shear Stresses ◽  
Element Analysis ◽  
Finite Element Software

The purpose of this study was to develop a three-dimensional finite-element model (FEM) of the human orbit, containing the globe, to predict orbital deformation in subjects following a blunt injury. This study investigated the hypothesis that such deformation could be modelled using finite-element techniques. One patient who had CT-scan examination to the maxillofacial skeleton including the orbits, as part of her treatment, was selected for this study. A FEM of one of the orbits containing the globe was constructed, based on CT-scan images. Simulations were performed with a computer using the finite-element software NISA (EMRC, Troy, USA). The orbit was subjected to a blunt injury of a 0.5 kg missile with 30 m s −1 velocity. The FEM was then used to predict principal and shear stresses or strains at each node position. Two types of orbital deformation were predicted during different impact simulations: (i) horizontal distortion and (ii) rotational distortion. Stress values ranged from 213.4 to 363.3 MPa for the maximum principal stress, from −327.8 to −653.1 MPa for the minimum principal stress, and from 212.3 to 444.3 MPa for the maximum shear stress. This is the first finite-element study, which demonstrates different and concurrent patterns of orbital deformation in a subject following a blunt injury. Finite element modelling is a powerful and invaluable tool to study the multifaceted phenomenon of orbital deformation.

scholarly journals Design of Tapered Flatted End Tube for Tension and Compression Loading

2019 ◽  
Vol 8 (6) ◽  
pp. 1047-1057
Keyword(s):  
Shear Stress ◽  
Principal Stress ◽  
Circular Tube ◽  
Maximum Shear Stress ◽  
Maximum Principal Stress ◽  
Space Structure ◽  
Bolted Joints ◽  
Space Structures ◽  
Bolted Connection ◽  
Tension And Compression

Hollow circular tube has the most efficient section in space structure. Hollow circular tube joint either welding or bolting but welding aluminum structural alloys lead to unavoidable annealing which can reduce efficiency to the order of only 50%. The efficiency of riveted and bolted joints is usually assumed to be around 75% in both aluminum and steel construction. Welded connections give the maximum strength in steel space structures and used for large spans. Hollow circular tube flatted at the end for single bolted connection and at flatted end increase this thickness for reducing stresses and this thicker plate make a hole for single bolted connection. Study this performance for varies the tapered flattened angle tube. Apply vertically upward and downward incremental load on the tapered flatted end tube at fixed bolted joint in ANSYS. Run this model for maximum shear stress and maximum principal stress. Find out the allowable tensile and compression stress in simple hollow circular tube in SAP2000 as per IS800-2007.. Find out the design load as per maximum shear stress theories and maximum principal stress theories

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