Formation Of Fracture Zones Research Articles

Analysis of a Potential Correlation between Seismicity and Production in Kiruna Mine on a Mine-wide and an Extraction Block Scale

The creation of cavities in the underground results in stress redistributions and energy changes in the rock mass. Zones with increased stresses and zones with lower stresses develop. The energy changes manifest themselves amongst others in changes in potential energy, absorption of energy in the formation of fracture zones, and release of energy such as seismic energy. To prevent damage to infrastructure and personnel, it is important to understand the mechanisms of energy changes as a result of mining. As far as seismic energy release is concerned, it is important to understand to relationship between large scale mineral extraction and mining induced seismicity. One coarse way to do this is to correlate for specific areas the cumulated tons of mined rock multiplied by the depth of extraction and multiplied by the gravitational acceleration to get the unit of energy, which is a rough assessment of the mining-induced energy changes, with the cumulated released seismic energy, which is derived from the seismic monitoring system. This correlation is studied for Kiruna Mine on a mine-wide scale and on an extraction block scale for the years 2014 to 2020. The results show that there is a reasonable correlation between the mining-induced energy changes and the seismic energy release not only on a mine-wide scale but also on an extraction block scale. Periods of decreased seismic energy release are followed either by a period of increased seismic activity or by one or a series of large seismic event. Accordingly, periods of decreased seismic activity can be considered as an indicator for a likely increase in future seismic activities. More detailed investigations should be made to find out the cause for the lack of energy release. A disadvantage of this method is that it does not reveal the exact area and reason for the decrease in seismicity. Therefore, additional rock mechanics analysis is needed to understand the background of the change in energy release.

Detection of prefracture zones in structural materials by magnetic and optical methods

The study of the applicability of magnetic and optical methods to the detection of prefracture zones under fatigue degradation of structural materials is exemplified by the 09G2S steel. The regularities of changes in the signal of an attached fluxgate gradiometer with the increasing number of loading cycles have been revealed; namely, significant changes in the gradiometer readings on individual specimen surface areas prove to result from the formation of fracture zones. The change in the value of the coefficient of correlation among the speckle images is studied at different stages of cyclic testing. Speckle image heterogeneity is shown to appear due to fracture nucleation. Thus, the applicability of magnetic and speckle-interferometric methods to detecting prefracture zones in objects under cyclic loading is substantiated.

Influence of Precambrian shear zones on the formation of oceanic fracture zones along the continental margin of Brazil

Abstract Structural inheritance control of oceanic fracture zone formation by a large basement shear zone during continental breakup is still a matter of debate. In this research, we investigated the reactivation of Precambrian shear zones and their role in the formation of the Ascension and Fernando Poo fracture zones during the evolution of the South Atlantic Ocean. We used aeromagnetic and multichannel 2D seismic reflection data associated with previous geological and geophysical data to analyze how the Precambrian shear zones may have influenced the formation of oceanic fracture zones. Our results suggest that the fracture zones are extensions of the shear zones in the transition between continental and oceanic crust. The Sao Miguel do Aleixo and Pernambuco shear zones were reactivated during the Pangea breakup and acted as zones of weakness controlling the location of the Ascension and Fernando Poo fracture zones during the process of oceanic crust spreading. Our model suggests that the formation of these fracture zones influenced by the shear zones occurred in the early stages of ocean opening. It indicates that the fracture zones that formed in the late opening stages were related to the thermal subsidence stage, as suggested in previous studies.

Visualizing the blast-induced stress wave and blasting gas action effects using digital image correlation

Rock blasting fragmentation is a result of the combined action of a blast-induced stress wave and the blasting gas. Incorporating high-speed camera technology, an experimental system of high-speed digital image correlation is established and is extended to blasting research. Using two-dimensional model experiments, the action effects of a blast-induced stress wave and blasting gas on the formation of the crush and fracture zones are studied, and the blasting attenuation law in the elastic vibration zone is also analyzed. The results show that the blast-induced stress wave and the blasting gas are respectively the main driving forces for the crush zone and fracture zone formation. The effect of the blasting gas reduces the crush zone size and increases the crack propagation length as well as the medium's stress peak. In the elastic vibration zone, the radial and circumferential stress of the medium are both first compressive and then tensile. The radial and circumferential stress are respectively dominated by compressive and tensile stress, and the radial stress decays more rapidly. With increased distance from the borehole, the medium's stress state gradually turns from mainly circumferential tensile to mainly radial compressive. In addition, in decoupled charge blasting, the stress attenuation index shows a trend of initially increasing and then decreasing with the increase of the decoupling coefficient. Compared with the attenuation of the circumferential stress, the air filling in the decoupled charge blasting more significantly affects the radial stress attenuation.

Experimental-calculation study of ion-plasma thermal barrier coatings for turbine blades made of intermetallic nickel superalloys

The ion-plasma thermal barrier coatings deposited onto samples and blades made of intermetallic VKNA-1V and VKNA-25 alloys are tested in a laboratory. The external ceramic layer of the thermal barrier coatings (TBC) is formed by magnetron sputtering of zirconium alloy targets and has a columnar structure. The influence of NiCrAlY(Re, Ta, Hf) + AlNiY(Hf) + ZrYGdO TBC on the long-term strength at a test temperature of 1200°C and on the high-cycle fatigue at a temperature of 900°C is studied. Blades with TBC are subjected to thermal cycling tests in the temperature range 950 ↔ 400°C and 1050 ↔ 400°C during air cooling and in the range 950 ↔ 200°C during water cooling at 500 cycles. The temperature fields in the cross section of a blade airfoil during thermal cycling are calculated. The laws of formation of fracture zones and the development of thermal fatigue cracks under the conditions that are close to the operating conditions of nozzle TBC-containing blades are investigated.

Geometrical-statistical modelling of systems of fracture zones along oceanic ridges

SUMMARY A mechanical-statistical model is presented that aims to help to understand the history and geometry of the process of formation of fracture zones along oceanic ridges. It uses ideas of statistical fracture theory used in engineering, namely the Weibull fracture model. The approximate parallelism of the fracture zones along ridges makes it possible to use a onedimensional point process model with points along the ridge axes, which represent the transform faults. The ratios of the lengths of the corresponding fracture zones to the ocean width are used to obtain a rough estimate of the Weibull modulus, which is an important material parameter in fracture theory. The theory is refined by introducing a hard-core point process model. The corresponding positive minimum distance between subsequent fracture zones results from stress relaxation in the vicinity of a given fracture zone.

Shock and thermal history of Martian meteorite Allan Hills 84001 from transmission electron microscopy

Abstract— Microstructures in the Allan Hills 84001 meteorite were studied using optical and electron microscopy, putting emphasis on shock effects, which are widespread. Some orthopyroxene exhibits only (100) slip, but more typical grains suffered extensive slip, microfracturing, and frequently contain (100) clino‐inversion lamellae. In fracture zones, shock deformation of orthopyroxene has produced all three effects in profusion, together with intergranular pockets of orthopyroxene glass and intragranular glass lamellae, which were apparently created by shearing on low index planes, usually (100) or {110}. Both types of plane are loci that pseudo‐planar fractures tend to follow. Thus, the glass lamellae, which have not been observed in other meteorites, probably formed by frictional heating during the sliding of microscale corrugated surfaces, one over another, leading to local melting. We infer that the orthopyroxene glass and the fracture zones both formed from shear stresses created by strong shock. Ubiquitous undeformed micrometer and submicrometer euhedral chromites in orthopyroxene and plagioclase glasses and carbonate probably crystallized after shock heating and fracture zone formation. Nanocrystals of eskolaite (Cr2O3) coating silica glass grains are probably also a result of shock‐induced thermal decomposition of chromite. Iron sulfides (pyrite and pyrrhotite were identified) tended to be associated with plagioclase glass. A carbonate disk showing no evidence for shock deformation had a substructure of elongated, slightly misoriented subcells in the exterior; interior regions had more eqiaxed subcells. Both microstructures probably formed during growth, but the conditions are undetermined. Chemical composition varied on a micron scale, but the rim of the disk was more ferroan; oxide precipitates and voids were widely distributed as in fracture‐filling carbonates. If the fracture zones and opx glass are the result of strong shock, as we deduce, it is very unlikely that pores could have filled by carbonate long after the fracture zones formed. We infer that the carbonate, like the phosphate, olivine, pyrrhotite, eskolaite, and many euhedral, submicrometer chromites, crystallized during the final stages of the impact that created the fracture zones and glasses with compositions of plagioclase, silica, and orthopyroxene.

On the structure and formation of fracture zones

Studies of the oceanic fracture zones, as well as field observations of the on‐land parts of a fracture zone in Iceland, show that there are numerous tension fractures, normal faults, small‐scale grabens and dykes within, and trending subparallel with, the fracture zones. These structures indicate that, in addition to the shear displacement, there is considerable extension associated with the development of fracture zones and that many of them may be regarded as complex graben structures. The ridges surrounding the continents of Africa and Antarctica are examples of mid‐ocean ridges that are moving away from the continental margins where they originated and therefore expanding. Here it is suggested that as the perimeter of an expanding ridge increases, the tensile stresses associated with the ridge extension may contribute to the formation of fracture zones.

Three-dimensional secondary surface geomorphology of submarine landslides on northwest Pacific plate guyots

Slump and debris slides form on seamounts as they grow, age, and are transported across the sea floor. Slump scars, evident as amphitheater headwalls, are a good morphological indicator where a landslide has occurred. Radical changes in the lower flank slope angles are also good indicators. Debris flows can be surmised by hummocky topography, with the larger blocks being nearer the main edifice. A cursory inspection of the Pacific plate from younger to older shows: (1) the Hawaiian-Emperor Ridge from Loihi to Suiko at 65 Ma, where the lower flank slopes increase with age, (2) Mammerickx seamount in the Mapmakers on 140 Ma crust, out of the fractured region, still showing moats and having no sign of landslides, (3) Castor and Pollux guyots of the Michelson Ridge on 150 Ma crust, where the debris field size is added to or overprinted by later volcanics, to (4) Hunk, Jennings, and Jaybee guyots in the Marcus-Wake seamounts on 160 Ma crust, where later fracture zone formation may have helped form landslides. None of the older seamounts have been dated. Three-dimensional views aid in the location and description of landslides.

Structural geology and geochronology of subduction complexes along the margin of Gondwanaland: New data from the Antarctic Peninsula and southernmost Andes

Subduction complexes along the Andean margin in central and southern Chile yield mid-Paleozoic to lower Mesozoic ages, yet they crop out within 100 km of the modern trench that shows evidence of active accretion along much of its length. The scarcity of uplifted subduction-complex rocks younger than mid-Mesozoic along the Chilean margin and in parts of the Scotia Arc suggests to us that these old, crystalline rocks, uplifted in the Triassic and Jurassic, represent a boundary in the forearc beyond which tectonic erosion does not easily occur. Greenschist-, blueschist-, and amphibolite-facies subduction-complex rocks from the Scotia Arc were originally thought to be a simple continuation of the subduction complexes in Chile. Based on new 40 Ar/ 39 Ar ages, the Scotia Arc subduction complexes reveal a complex history related to distinct local tectonic events and are not a simple continuation of the old accretionary prism in Chile. Structural and metamorphic analysis indicates the earliest and most penetrative deformation in the subduction complexes around the Scotia Arc occurred at some depth in a subduction zone or zones, certainly below the brittle-ductile transition, and in some cases under blueschist-facies conditions. We believe that the early subduction-related deformation and metamorphism in the greenschist- and blueschist-facies rocks of the Scotia Arc to be overprinted by mid-Cretaceous transpression along the South America-Antarctica plate boundary in the case of Elephant Island, transpression and subsequent localized transtension in the earliest Cenozoic in the case of the Darwin Complex, a mid-Cenozoic spreading-rate change in the case of Smith Island, and early Neogene initiation of Drake Passage opening/Shackleton Fracture Zone formation in the case of the Gibbs Island subgroup.

The Marcus-Wake Seamounts and Guyots as paleofracture indicators and their relation to the Dutton Ridge

The Dutton Ridge is on the oldest extant oceanic crust (the Jurassic) in the northwestern Pacific and lies on the Pacific plate. Because of internal alignments and different summit plateau break depths in line on a secondary axis, the ridge was probably once more contiguous, in the form of a plateau. The direction of movement of the Pacific plate is known to have been northwesterly for the past 43 m.y. and almost due north from then into the Cretaceous. However, there is a southwesterly azimuth through the region from the Hawaiian Emperor elbow to the subduction zone where the Dutton Ridge presently resides. This portion of the Pacific plate is overprinted by the Marcus-Wake Seamounts which formed during the Cretaceous. Evidence of the SW-striking features including fracture zones, flank rift zones, ridge alignments, and tectonic spreading fabric is shown. The time frame of the change in spreading direction and consequent fracture zone formation is suggested to have been between the formation of the Dutton Plateau and the Marcus-Wake Group, possibly from Late Jurassic to Early Cretaceous. The breakup of the Dutton Plateau to form the Dutton Ridge is suggested to have been caused by fracturing.

Formation of geochemical fields of concentration in the thermal gradient fields of intrusive bodies

The concentration of metals and ores in thermal fields of intrusive bodies can be analyzed by numerical simulation (modelling) of the heat-mass transfer process. A knowledge of the dynamics and the movement of the temperature and crystallization fronts, as well as an understanding of the characteristics of the thermal gradients, heat flows, energy, and thermal stresses which result in the formation of fracture zones, are necessary for an estimation of the spacial and temporal aspects of the mass balance calculations and the ore concentration processes. The application of the method is illustrated by observing the changes in the rare earth element concentration in a vein-type apatite orebody in limestone which has been intruded by a post-ore dike. The method has potential value in exploring for hidden mineralization.