4 coal (Greb and others, 2001) and Springfield (W. Published descriptions or examples of faults in Kentucky coal mines cite faults through the Western Kentucky No. Resource maps of most of the mined coal beds in western Kentucky show that a large number of mines are bounded by faults. Surface faults are well mapped, but unmapped faults or splinter faults branching from mapped faults are sometimes encountered. In western Kentucky, however, faulting is common. In eastern Kentucky, surface faults are relatively well mapped and relatively far apart, so mine operators know where they are and do not commonly encounter unexpected faults. Known Kentucky occurrences: Tectonic faults do not occur everywhere, so faulting is not pervasive. Many surface-fault traces are mapped on 7.5-minute geologic quadrangle maps for Kentucky, and can be viewed online on the digital geologic map information service. Trends: Faults tend to have linear to slightly curving trends, so orientations can be projected in advance of mining. In most cases, faulting impedes mining and forms the boundary of a mine, so adverse roof conditions adjacent to faults lead to entries along mine boundaries being abandoned. Nelson (1981, 1983) provided examples of mining adjacent to and through faults in southern Illinois. Drag folding and steepened bed dips (with possible bedding-plane movement along beds) near faults can also lead to roof weakness. Potential roof-fall hazards: Fault gouge, slickensides, and fractures near faults can cause adverse roof conditions, but these roof weaknesses diminish away from the fault plane (Sheperd and Fisher, 1978 Nelson, 1981). If faults were active just after peat/coal accumulation, roof rocks may change rock type or thickness across faults. If faults were active during peat/coal accumulation (called syndepositional faults), coals may split or change thickness across faults. Potential mining problems near tectonic faults. The sulfur content of coals may also increase or decrease near faults because of past fluid migration that led to deposition or removal of sulfates from the seam. In some cases, coals become mineralized (calcite veins, etc.) near faults. Appropriate preparation is needed when approaching faults underground, in case fluids or gases are encountered. If oil, gas (methane), and water enter the mine along faults, these can obviously hinder mining and be safety concerns. Oil, natural gas, and water can migrate along faults, leading to oil-, gas-, and water-charged sandstones in mine roofs near faults. Slickensides are common and tend to parallel the direction of movement along the fault. Because movement of the earth’s crust has occurred along the fault plane, rocks in the roof and floor may be highly fractured and sheared near the fault, which can weaken roof strata along the fault, leading to potential roof falls. 11) coal bed in an underground mine, western Kentucky.ĭiscontinuities and obstacles: Where a fault intersects a mined coal seam, the coal seam will be offset, generally causing an abrupt end to the seam into rock on the other side of the fault plane. Small nontectonic faults offsetting coal beds (A) beneath a paleochannel in eastern Kentucky and (B) along a clay vein (green dashes) in the Herrin (W. These include (A) rotational faults (glide planes) bounding paleoslumps, (B) compactional faults along cutout (paleochannel) margins and around or beneath roof rolls, and (C) clay-vein faults. Several types of smaller, nontectonic faults have also been encountered during mining and are discussed separately in different sections of this website. Moderate to steep coal dips are common in surface mines near faults around Middlesboro, Kentucky in eastern Kentucky. No 9) coal mine near Sebree in western Kentucky. Steep coal and rock bed dips near faults in a Springfield (W. Fault gouge formed from movement along the fault. Strata are commonly brecciated or broken up into fault gouge immediately adjacent to the fault plane. Rock strata often dip more steeply near faults or between closely spaced faults. General types of tectonic faulting, defined by the direction of movement. Offset along faults may be measured in inches to thousands of feet. Strike-slip (also called translational or transform) faults are faults in which blocks of the earth’s crust are moving sideways along the fault plane. Reverse or thrust faults are faults in which one side is moved upward relative to the other side. Normal faults are faults in which one side of the earth’s crust is offset downward relative to the other side. The relative direction or motion of movement defines the type of fault. Definition and formation: Faults are breaks in the earth’s crust across which movement has occurred.
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