Is complex fault zone behaviour a reflection of rheological heterogeneity?

Fault slip speeds range from steady plate boundary creep through to earthquake slip. Geological descriptions of faults range from localized displacement on one or more discrete planes, through to distributed shearing flow in tabular zones of finite thickness, indicating a large range of possible strain rates in natural faults. We review geological observations and analyse numerical models of two-phase shear zones to discuss the degree and distribution of fault zone heterogeneity and effects on active fault slip style. There must be certain conditions that produce earthquakes, creep and slip at intermediate velocities. Because intermediate slip styles occur over large ranges in temperature, the controlling conditions must be effects of fault properties and/or other dynamic variables. We suggest that the ratio of bulk driving stress to frictional yield strength, and viscosity contrasts within the fault zone, are critical factors. While earthquake nucleation requires the frictional yield to be reached, steady viscous flow requires conditions far from the frictional yield. Intermediate slip speeds may arise when driving stress is sufficient to nucleate local frictional failure by stress amplification, or local frictional yield is lowered by fluid pressure, but such failure is spatially limited by surrounding shear zone stress heterogeneity

Low‐temperature frictional characteristics of chlorite‐epidote‐amphibole assemblages: implications for strength and seismic style of retrograde fault zones

In retrograde faults exhuming mafic rocks, shearing occurs in metamorphic and/or hydrothermally altered mineral assemblages whose frictional properties are not well known. Here, we present the results of laboratory shearing experiments on chlorite schist, epidotite, and hornblende‐dominated amphibolite and mixtures of these rocks and evaluate their frictional properties and microstructures. The experiments were conducted on powdered rock samples with starting grain size of <125 μm, at room temperature, under fluid‐saturated conditions and applied normal stress of 10 MPa. The results show that chlorite schist is relatively weak (friction coefficient of 0.36), whereas epidotite and amphibolite are strong (friction coefficients of 0.63 and 0.67, respectively). The friction of chlorite schist‐epidotite and chlorite schist‐amphibolite mixtures decreases nearly linearly with increasing chlorite content. Chlorite schist exhibits velocity‐strengthening behavior, epidotite is velocity‐weakening, and the amphibolite shows mostly velocity‐weakening friction. Mixtures show intermediate strength and velocity dependence of friction. Well‐developed striations formed on slip surfaces in samples with ≥50% chlorite schist. The epidotite slip surface exhibits a mixture of very fine particles and coarser crystals. Amphibolite slip surfaces have less very fine grains and are composed of subhedral to euheral needles. Few intragranular fractures are preserved, and we infer wear at contact asperities to be the likely cause of velocity‐weakening in our epidote gouges. Addition of chlorite to epidotite and amphibolite produces a striated slip surface and disrupts contacts between harder grains. Therefore, retrograde chlorite growth is expected to facilitate frictional weakening and stable slip in higher‐grade mineral assemblages exhumed to low‐temperature conditions

The role of coseismic Coulomb stress changes in shaping the hard-link between normal fault segments

The mechanism and evolution of fault linkage is important in the growth and development of large faults. Here we investigate the role of coseismic stress changes in shaping the hard-links between parallel normal fault segments (or faults), by comparing numerical models of the Coulomb stress change from simulated earthquakes on two en echelon fault segments to natural observations of hard-linked fault geometry. We consider three simplified linking fault geometries: 1) fault bend; 2) breached relay ramp; and 3) strike-slip transform fault. We consider scenarios where either one or both segments rupture and vary the distance between segment tips. Fault bends and breached relay ramps are favoured where segments underlap, or when the strike-perpendicular distance between overlapping segments is less than 20% of their total length, matching all documented examples. Transform fault linkage geometries are preferred when overlapping segments are laterally offset at larger distances. Few transform faults exist in continental extensional settings, and our model suggests that propagating faults or fault segments may first link through fault bends or breached ramps before reaching sufficient overlap for a transform fault to develop. Our results suggest that Coulomb stresses arising from multi-segment ruptures or repeated earthquakes are consistent with natural observations of the geometry of hard-links between parallel normal fault segment

Lean i Norge : opplever norske bedrifter som er mer lean, større økning i kundetilfredshet enn de som er mindre lean?

Vi ønsker å måle i hvor stor grad norske bedrifter har implementert lean, og for å måle grad av lean har vi utviklet et rammeverk basert på lean teori. Hovedformålet med lean er å øke kundeverdi med minst mulig ressursbruk, anstrengelse, energi, utstyr, tid, plass, material og kapital (Womack, Roos and Jones 2007). Vi vil utforske om høyere grad av lean fører til mer tilfredse kunder enn de som har lavere grad av lean. Altså om hovedformålet med lean blir oppnådd hvis man implementerer lean i større grad. Vi har derfor utformet følgende hypotese som utgangspunkt for vår oppgave: ”Norske bedrifter som er mer lean, opplever større økning i kundetilfredshet enn de som er mindre lean.” Våre funn indikerer at norske bedrifter har implementert lean i varierende grad og vi har i vår undersøkelse sett en klar sammenheng mellom grad av lean og økning i kundetilfredshet. Dette kan tyde på at hovedformålet med lean, økt kundeverdi, blir oppnådd ved å implementere lean i stor grad i norske bedrifte

Hydrous oceanic crust hosts megathrust creep at low shear stresses

The rheology of the metamorphosed oceanic crust may be a critical control on megathrust strength and deformation style. However, little is known about the strength and deformation style of metamorphosed basalt. Exhumed megathrust shear zones exposed on Kyushu, SW Japan, contain hydrous metabasalts deformed at temperatures between ~300° and ~500°C, spanning the inferred temperature-controlled seismic-aseismic transition. Field and microstructural observations of these shear zones, combined with quartz grain-size piezometry, indicate that metabasalts creep at shear stresses <100 MPa at ~370°C and at shear stresses <30 MPa at ~500°C. These values are much lower than those suggested by viscous flow laws for basalt. The implication is that relatively weak, hydrous, metamorphosed oceanic crust can creep at low viscosities over a wide shear zone and have a critical influence on plate interface strength and deformation style around the seismic-aseismic transition

Subduction megathrust creep governed by pressure solution and frictional-viscous flow

Subduction megathrust slip speeds range from slow creep at plate convergence rates (centimetres per year) to seismic slip rates (metres per second) in the largest earthquakes on Earth. The deformation mechanisms controlling whether fast slip or slow creep occurs, however, remain unclear. Here, we present evidence that pressure solution creep (fluid-assisted stress driven mass transfer) is an important deformation mechanism in megathrust faults. We quantify megathrust strength using a laboratory-constrained microphysical model for fault friction, involving viscous pressure solution and frictional sliding. We find that at plate-boundary deformation rates, aseismic, frictional–viscous flow is the preferred deformation mechanism at temperatures above 100 °C. The model thus predicts aseismic creep at temperatures much cooler than the onset of crystal plasticity, unless a boundary condition changes. Within this model framework, earthquakes may nucleate when a local increase in strain rate triggers velocity-weakening slip, and we speculate that slip area and event magnitude increase with increasing spacing of strong, topographically derived irregularities in the subduction interface

Mid-crustal shear zone development under retrograde conditions: pressure–temperature–fluid constraints from the Kuckaus Mylonite Zone, Namibia

The Kuckaus Mylonite Zone (KMZ) forms part of the larger Marshall Rocks–Pofadder shear zone system, a 550 km-long, crustal-scale strike-slip shear zone system that is localized in high-grade granitoid gneisses and migmatites of the Namaqua Metamorphic Complex. Shearing along the KMZ occurred ca. 40 Ma after peak granulite-facies metamorphism during a discrete tectonic event and affected the granulites that had remained at depth since peak metamorphism. Isolated lenses of metamafic rocks within the shear zone allow the P–T–fluid conditions under which shearing occurred to be quantified. These lenses consist of an unsheared core that preserves relict granulite-facies textures and is mantled by a schistose collar and mylonitic envelope that formed during shearing. All three metamafic textural varieties contain the same amphibolite-facies mineral assemblage, from which calculated pseudosections constrain the P–T conditions of deformation at 2.7–4.2 kbar and 450–480 °C, indicating that deformation occurred at mid-crustal depths through predominantly viscous flow. Calculated T–MH2O diagrams show that the mineral assemblages were fluid saturated and that lithologies within the KMZ must have been rehydrated from an external source and retrogressed during shearing. Given that the KMZ is localized in strongly dehydrated granulites, the fluid must have been derived from an external source, with fluid flow allowed by local dilation and increased permeability within the shear zone. The absence of pervasive hydrothermal fractures or precipitates indicates that, even though the KMZ was fluid bearing, the fluid/rock ratio and fluid pressure remained low. In addition, the fluid could not have contributed to shear zone initiation, as an existing zone of enhanced permeability is required for fluid infiltration. We propose that, following initiation, fluid infiltration caused a positive feedback that allowed weakening and continued strain localization. Therefore, the main contribution of the fluid was to produce retrograde mineral phases and facilitate grain-size reduction. Features such as tectonic tremor, which are observed on active faults under similar conditions as described here, may not require high fluid pressure, but could be explained by reaction weakening under hydrostatic fluid pressure conditions

Significant shortening by pressure solution creep in the Dwyka diamictite, Cape Fold Belt, South Africa

The Dwyka diamictite preserves a record of horizontal shortening related to the development of the Cape Fold Belt at subgreenschist conditions. This shortening was accommodated by folding and thrust faulting, but pressure solution may also have contributed significantly to bulk deformation. Cleavage within the Dwyka group is, in the studied part of the Karoo Basin, subvertical to moderately south dipping, and approximately axial planar to regional folds. The cleavage is anastomosing, leading to the development of ‘tombstone cleavage’, and defined microscopically by thin seams of fine grained dark material. X-ray diffraction analyses show that the diamictite matrix is made up of quartz, feldspars, muscovite and chlorite. Element maps further indicate that the cleavage is defined predominantly by phyllosilicates and minor oxides, implying that it is made up of relatively insoluble material and hydrothermal alteration products. Overall, the cleavage therefore formed by dissolution and removal of mobile elements. This indicates that pressure solution likely accommodated a significant component of shortening during the Cape Orogeny, and provides an example of low temperature cleavage development during orogenesis

Foreldresamarbeid i hentesituasjoner

Selv om tema for oppgaven var tidlig ferdigstilt, brukte jeg lang tid på å formulere min problemstilling. Ved oppstart av prosjektet fant jeg en artikkel på forskning.no. Artikkelen er basert på en masteroppgave som omhandler henting i norske barnehager, skrevet av Kjersti Lønning Velde. Masteroppgaven tar for seg hvordan foreldrene opplever hentesituasjonen. Resultatene viser at det er stor variasjon i måten foreldrene blir møtt, hvor mye informasjon som formidles og hvor mye tid de ansatte bruker på samarbeidet (Strand, 2017). Artikkelen ble en inspirasjonskilde til min problemstilling. Jeg ønsket derimot å vinkle oppgaven mot personalet sin opplevelse av hentesituasjoner, nærmere bestemt barnehagelæreren. Dette ble en naturlig vinkling for meg, siden jeg snart er ferdig utdannet barnehagelærer. Jeg ønsker selv å bidra til å skape et godt foreldresamarbeid i hentesituasjoner i fremtiden. For å avgrense oppgaven har jeg valgt å fokusere på storbarnsavdelinger. Problemstillingen min ble som følger: ”Hvordan kan barnehagelæreren ved storbarnsavdelinger oppleve hentesituasjoner som en arena for foreldresamarbeid”.publishedVersionBDBAC490