scholarly journals Fault rock heterogeneity produces fault weakness and promotes unstable slip

2021 ◽  
Author(s):  
John Bedford ◽  
Daniel Faulkner ◽  
Nadia Lapusta
Keyword(s):  
Small Scale ◽  
Slow Slip ◽  
Stress Concentrations ◽  
Fault Rock ◽  
Geological Heterogeneity ◽  
Friction Laws ◽  
Rock Heterogeneity ◽  
Fault Strength ◽  
Significant Strength ◽  
Earthquake Ruptures

Geological heterogeneity is abundant in crustal fault zones; however, its role in controlling the mechanical behaviour of faults is poorly constrained. Here, we present laboratory friction experiments on laterally heterogeneous faults, with patches of strong, rate-weakening quartz gouge and weak, rate-strengthening clay gouge. The experiments show that the heterogeneity leads to a significant strength reduction and decrease in frictional stability in comparison to compositionally identical faults with homogeneously mixed gouges typically used in the lab. We identify a combination of weakening effects, including smearing of the weak clay; differential compaction of the two gouges redistributing normal stress; and shear localization producing stress concentrations in the strong quartz patches. The results demonstrate that small-scale geological heterogeneity has pronounced effects on fault strength and stability, and by extension on the occurrence of slow-slip transients versus earthquake ruptures and the characteristics of the resulting events, and should be incorporated in lab experiments, fault friction laws, and earthquake source modelling.

scholarly journals Surface toughening – An industrial approach to increase the robustness of pure adhesive joints with film adhesives

2020 ◽  
Vol 234 (13) ◽  
pp. 1980-1987
Author(s):  
MJ Schollerer ◽  
J Kosmann ◽  
D Holzhüter ◽  
C Bello-Larroche ◽  
C Hühne
Keyword(s):  
Large Scale ◽  
Adhesive Bonding ◽  
Bolted Joints ◽  
Small Scale ◽  
Bonded Joints ◽  
Fiber Reinforced ◽  
Load Path ◽  
Stress Concentrations ◽  
Manufacturing Defects ◽  
Wide Range

Bonding is known for its wide range of advantages over bolted joints when joining different materials together. However, the advantages e.g. of homogeneous load distribution can quickly be lost in case of overload. For this reason, the load occurring in the adhesive is reduced by constructive measures far below the yield stress of the adhesive, which leads to a conservative joint design. And to be on the safe side, a few “chicken rivets” are then placed again. This problem is particularly well known in aviation. Highly loaded components are structurally bonded by a combination of rivets and adhesive in order to underline the advantages of structural adhesive bonding with the safety of the well-known bolted joints. Known as fail-safe design, this concept is damage tolerant and more robust against manufacturing defects through a secured double load path.  Especially when joining fiber-reinforced composites, bolts weaken the adherends of the joint and only contribute to load transfer when the brittle adhesive fails. With the help of Surface Toughening, a boltless technique for reducing stress concentrations and arresting cracks in adhesive bonded joints is available. This work describes the industrial application of this technique. Starting with coupon tests and a small scale demonstrator to ensure the compatibility with industrial manufacturing processes, such as infusion and prepreg manufacturing, a large scale demonstrator of a 2 m carbon fiber reinforced plastic (CFRP) - HTP leading edge with hybrid laminar flow control is manufactured by the industrial partner AERnnova. Verifying a simple and cost-effective application of the technology, Surface Toughening enables robust bonded joints with a minimum impact on today's process of adhesive bonding.

Modeling the Interaction between Slow Slip Events and Earthquake Ruptures in the Nicoya Peninsula, Costa Rica. 

2021 ◽  
Author(s):  
Lise Alalouf ◽  
Yajing Liu
Keyword(s):  
Costa Rica ◽  
Subduction Zones ◽  
Computation Time ◽  
Seismogenic Zone ◽  
Model Parameters ◽  
Slow Slip ◽  
Coseismic Slip ◽  
Slow Slip Events ◽  
Megathrust Earthquakes ◽  
Earthquake Ruptures

<p>Subduction zones are where the largest earthquakes occur. In the past few decades, scientists have also discovered the presence of episodic aseismic slip, including slow slip events (SSEs), along most of the subduction zones. However, it is still unclear how these SSEs can influence megathrust earthquake ruptures. The Costa Rica subduction zone is a particularly interesting area because a SSE was recorded 6 months before the 2012 Mw7.6 earthquake in the Nicoya Peninsula, suggesting a potential stress transfer from the SSE to the earthquake slip zone. SSEs beneath the Nicoya Peninsula were also recorded both updip and downdip the seismogenic zone, making it a unique area to study the complex interaction between SSEs and earthquakes.</p><p>As most of the shallow SSEs were recorded around the Nicoya Peninsula, we chose to start using a 1D planar fault embedded in a homogeneous elastic half-space, with different dipping angles following several geometric profiles of the subduction fault beneath the Nicoya Peninsula section of the Costa Rica margin. This 1D modelling study allows us to better investigate the interaction between shallow and deep SSEs and megathrust earthquakes with high numerical resolution and relatively short computation time. The model provides information on the long-term seismic history by reproducing the different stages of the seismic cycle (interseismic slip, shallow and deep episodic slow slip, and coseismic slip).</p><p>We study the influence of the variation of numerical parameters and frictional properties on the recurrence interval, maximum slip velocity and cumulative slip of SSEs (both shallow and deep) and earthquakes and their interaction with each other. We then compare our results with GPS and seismic observations (i.e. cumulative slip, characteristic duration, moment rate, depth and size of the rupture, equivalent magnitude) to identify an optimal set of model parameters to understand the interaction between various modes of subduction fault deformation.</p>

3D geometry of outcrop-scale normal faults from Taranaki, New Zealand

2020 ◽  
Author(s):  
Inbar Vaknin ◽  
Andy Nicol ◽  
Conrad Childs
Keyword(s):  
New Zealand ◽  
Fault Zone ◽  
Slip Surface ◽  
Geometric Model ◽  
Fault Zones ◽  
Normal Faults ◽  
Small Scale ◽  
Fault Geometry ◽  
Fault Rock ◽  
Fault Surface

<p>Fault surfaces and fault zones have been shown to have complex geometries comprising a range of morphologies including, segmentation, tip-line splays and slip-surface corrugations (e.g., Childs et al., 2009*). The three-dimensional (3D) geometries of faults (and fault zones) is difficult to determine from outcrop data which are typically 2D and limited in size. In this poster we examine the small-scale geometries of faults from normal faults cropping out in well bedded parts of the Mount Messenger and Mahakatino formations in Taranaki, New Zealand. We present two main datasets; i) measurements and maps of 2D vertical and horizontal sections for in excess of 200 faults and, ii) 3D fault model of a small-fault (vertical displacement ~1 cm) produced by serial fault-perpendicular sections of a block 10x10x13 cm. The sectioned block contains a single fault that offsets sand and silt layers, and comprises two main dilational bends; in the 3D model we map displacement, bedding and fault geometry for the sectioned fault zone. Faults in the 2D dataset comprise a range of geometries including, vertical segmentation, bends, splays and fault-surface corrugations. Although we have little information on the local magnitudes and orientations of stresses during faulting, geometric analysis of the fault zones provides information on the relationships between bed characteristics (e.g., thickness, induration and composition) and fault-surface orientations. The available data supports the view that the strike and dip of fault surfaces vary by up to 25° producing undulations or corrugations on fault surfaces over a range of scales from millimetres to metres and in both horizontal and vertical directions. Preliminary analysis of the available data suggests that these corrugations appear to reflect fault refractions due to changing bed lithologies (unexpectedly the steepest sections of faults are in mudstone beds), breaching of relays and development of conjugate fault sets. The relative importance of these factors and their importance for fault geometry will be explored further in the poster.</p><p> </p><p>*Childs, C., Walsh, J.J., Manzocchi, T., Bonson, C., Nicol A., Schöpfer, M.P.J. 2009. A geometric model of fault zone and fault rock thickness variations. Journal of Structural Geology 31, 117-127.</p>

scholarly journals Small scale contractional-extensional structures and morphotectonics along the fault traces of Izmit-Cocaeli (Turkey) 1999 earthquake

2001 ◽  
Vol 34 (1) ◽  
pp. 345 ◽  
Author(s):  
Z. TUTKUN ◽  
S. PAVLIDES
Keyword(s):  
Strike Slip ◽  
Small Scale ◽  
North Anatolian Fault Zone ◽  
Epicentral Area ◽  
The North ◽  
Digital Elevation ◽  
Earthquake Ruptures ◽  
Recent Sediments ◽  
Elevation Model ◽  
Extensional Structures

The Mw=7.4 Izmit (Kocaeli) earthquake of August 17, 1999 (Turkey) ruptured 100 km at least surface faults on land along the northwestern branch of the North Anatolian Fault Zone (NAFZ). Although the preexisting structures of NAFZ has been divided into segments, showing stepover and pull apart geometry, the earthquake ruptures are generally linear, E-W striking (N80°-100°), right-lateral. In small scale and on the recent sediments they show very typical strike-slip displacements (2 to 5m), pop-ups and pressure ridges (N 40- 70°), Ρ (N80°), R (N100-1100) and R' (~N350°) Riedel shears, extensional cracks (N115°-135°), restraining and releasing bends and small pull apart structures. In the epicentral area (Gölcük-Tepetarla) the seismic ruptures did not follow any known or previously mapped fault, but the morphology and the Digital Elevation Model (DEM) show typical and recognizable paleo-earthquake features. That is elongated valleys, shutter ridges, high angle slopes, scarplets, stream offset; while trenching tectonostratigraphy indicate palaeo sag-ponds (clayly deposits) and palaeo liquefaction (C14 dating-Holocene-historical deposits 200 to 11,000 yr. BP).

Strength of silicon containing nanoscale flaws

2004 ◽  
Vol 19 (2) ◽  
pp. 657-660 ◽  
Author(s):  
Antonia Pajares ◽  
Marina Chumakov ◽  
Brian R. Lawn
Keyword(s):  
Silicate Glass ◽  
Test Procedure ◽  
Local Stress ◽  
Silicon Surfaces ◽  
Small Scale ◽  
Stress Concentrations ◽  
Subthreshold Region ◽  
Fundamental Nature ◽  
Glass Surfaces ◽  
Small Scale Damage

Silicon is a principal material in submicrometer-scale devices. Components in such devices are subject to intense local stress concentrations from nanoscale contacts during function. Questions arise as to the fundamental nature and extent of any strength-degrading damage incurred at such contacts on otherwise pristine surfaces. Here, a simple bilayer test procedure is adapted to probe the strengths of selected areas of silicon surfaces after nanoindentation with a Berkovich diamond. Analogous tests on silicate glass surfaces are used as a control. The strengths increase with diminishing contact penetration in both materials, even below thresholds for visible cracking at the impression corners. However, the strength levels in the subthreshold region are much lower in the silicon, indicating exceptionally high brittleness and vulnerability to small-scale damage in this material. The results have important implications in the design of devices with silicon components.

Assessment of Steels for Nuclear Reactor Pressure Vessels

1964 ◽  
Vol 86 (4) ◽  
pp. 393-401 ◽  
Author(s):  
A. Cowan ◽  
R. W. Nichols
Keyword(s):  
Large Body ◽  
Stress Rupture ◽  
Crack Arrest ◽  
Pressure Vessels ◽  
Small Scale ◽  
Specimen Thickness ◽  
Stress Concentrations ◽  
Flat Plates ◽  
Reactor Pressure ◽  
Arrest Temperature

Some of the materials problems associated with the use of mild steels in large gas-cooled reactor pressure vessels are discussed. Tests to failure of 5-ft-dia 0.36 percent carbon-steel vessels with through-thickness longitudinal slots, supported by tests on 7-ft-wide centrally slotted flat plates, have indicated that rapid failure at working-stress levels can only initiate from very long cracks, feet rather than inches in length. Of the mechanisms whereby realistic defects can grow to these sizes, brittle-crack propagation is considered the most important and this can be prevented by the maintenance of a minimum pressurization temperature, based on the crack-arrest temperature. The tests used to assess the crack arrest temperature of plates up to 4 in. thick are described; compared with tests on thinner specimens the thick plate gives arrest temperatures higher by approximately 10 deg C per in. of test-specimen thickness. A comparison is made of crack-arrest temperature and data given by small-scale tests, particularly the Charpy V-notch test. Mechanical limitations of creep deformation in some current designs have been more restrictive on design stress than the values allowed by the existing BS.1500. The test data quoted for stress-rupture and fatigue indicate that these modes of crack extension are not important in current designs. Possible magnitudes and effects of stress concentrations are quoted but, other than a large body of satisfactory service operation, there is little direct evidence of the effect of operating in the creep range on these stress concentrations. The importance of work of this type in justifying higher design stresses and more economic use of material is emphasized.

scholarly journals Syncing fault rock clocks: Direct comparison of U-Pb carbonate and K-Ar illite fault dating methods

Geology ◽  
2020 ◽  
Vol 48 (12) ◽  
pp. 1179-1183
Author(s):  
C.M. Mottram ◽  
D.A. Kellett ◽  
T. Barresi ◽  
H. Zwingmann ◽  
M. Friend ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Fault Slip ◽  
Yukon Territory ◽  
Fault Reactivation ◽  
Radiometric Dating ◽  
Fault System ◽  
Fault Rock ◽  
Fault Strength ◽  
Dextral Strike Slip Fault ◽  
Fault Valve

Abstract The timing of slip on brittle faults in Earth’s upper crust is difficult to constrain, and direct radiometric dating of fault-generated materials is the most explicit approach. Here we make a direct comparison between K-Ar dating of fault gouge clay (authigenic illite) and U-Pb dating of carbonate slickenfibers and veins from the same fault. We have dated fault generated materials from the Big Creek fault, a northwest-striking, dextral strike-slip fault system in Yukon Territory, Canadian Cordillera. Both methods yielded dates at ca. 73 Ma and ca. 60–57 Ma, representing at least two periods of fault slip that form part of a complex fault and fluid-flow history. The Cretaceous result lies within previous indirect estimates for major slip on the fault. The Paleocene–Eocene result coincides with the estimated timing of slip of the nearby Tintina and Denali faults, which are crustal-scale, northwest-striking dextral faults, indicating Big Creek fault reactivation during regional faulting. The coincidence of periods of carbonate-crystallizing fracturing and fluid flow with intervals of seismic, gouge-generating slip supports the fault valve model, where fault strength is mediated by fluid pressures, and fluid emplacement requires seismic pumping in otherwise impermeable aseismic fault zones. The reproducibility of slip periods for distinct fault-generated materials using different decay systems indicates that these methods provide complimentary results and can be reliably applied to date brittle fault slip, opening new opportunities for investigating fault conditions with associated mineralizing fluid events.

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