|
Paleoliquefaction
Paleoliquefaction is any liquefaction features attributed to seismic events occurring before measurements or written records were kept of earthquakes. The study of these features can reveal a great deal about the seismicity of regions where large earthquakes happen infrequently. This is a subset of the broader field of paleoseismology. Paleoliquefaction studies in areas like the New Madrid Seismic Zone, and the Wabash Valley have helped scientists and engineers determine the severity of ground shaking to expect when planning for future earthquakes. Paleoliquefaction features The phenomenon of paleoliquefaction causes a soil to lose its shear strength and behave like a fluid. This liquefied soil (most often sand) flows like water, leaving several kinds of evidence behind in the geologic record. Dikes Dikes are intrusions of a lower liquefied sand that penetrate strata of an upper, non-liquefied soil. This penetration can occur due to hydraulic fracturing, where the non-liquefied ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Soil Liquefaction
Soil liquefaction occurs when a cohesionless saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in which material that is ordinarily a solid behaves like a liquid. In soil mechanics, the term "liquefied" was first used by Allen Hazen in reference to the 1918 failure of the Calaveras Dam in California. He described the mechanism of flow liquefaction of the embankment dam as: The phenomenon is most often observed in saturated, loose (low density or uncompacted), sandy soils. This is because a loose sand has a tendency to compress when a load is applied. Dense sands, by contrast, tend to expand in volume or ' dilate'. If the soil is saturated by water, a condition that often exists when the soil is below the water table or sea level, then water fills the gaps between soil grains ('pore spaces'). In response to soil compressing, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paleoseismology
Paleoseismology looks at geologic sediments and rocks, for signs of ancient earthquakes. It is used to supplement seismic monitoring, for the calculation of seismic hazard. Paleoseismology is usually restricted to geologic regimes that have undergone continuous sediment creation for the last few thousand years, such as swamps, lakes, river beds and shorelines. In this typical example, a trench is dug in an active sedimentation regime. Evidence of thrust faulting can be seen in the walls of the trench. It becomes a matter of deducting the relative age of each fault, by cross-cutting patterns. The faults can be dated in absolute terms, if there is dateable carbon, or human artifacts. Many notable discoveries have been made using the techniques of paleoseismology. For example, there is a common misconception that having many smaller earthquakes can somehow 'relieve' a major fault such as the San Andreas Fault, and reduce the chance of a major earthquake. It is now known ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
New Madrid Seismic Zone
The New Madrid Seismic Zone (), sometimes called the New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes (earthquakes within a tectonic plate) in the Southern and Midwestern United States, stretching to the southwest from New Madrid, Missouri. The New Madrid fault system was responsible for the 1811–12 New Madrid earthquakes, and has the potential to produce large earthquakes in the future. Since 1812, frequent smaller earthquakes have been recorded in the area. Earthquakes that occur in the New Madrid Seismic Zone potentially threaten parts of seven American states: Illinois, Indiana, Missouri, Arkansas, Kentucky, Tennessee, and Mississippi. Location The -long seismic zone, which extends into five states, stretches southward from Cairo, Illinois; through Hayti, Caruthersville, and New Madrid in Missouri; through Blytheville into Marked Tree in Arkansas. It also covers a part of West Tennessee, near Reelfoot Lake, extending south ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wabash Valley
The Wabash Valley is a region located in sections of both Illinois and Indiana. It is named for the Wabash River and, as the name is typically used, spans the middle to the middle-lower portion of the river's valley and is centered at Terre Haute, Indiana. The term Wabash Valley is frequently used in local media in Clinton, Lafayette, Mount Carmel, Princeton, Terre Haute, and Vincennes all of which are either on or near the Lower Wabash River. Counties Counties in the Wabash Valley include Posey, Gibson, Vigo, Clay, Sullivan, Vermillion, Parke, Greene, Putnam, Owen, Knox, Daviess, Martin, Fountain, Tippecanoe and Warren counties in Indiana. The Illinois portion consists of Clark, Edgar, Crawford, Jasper, Cumberland, Coles, Douglas, Gallatin, Edwards, Wabash, and White counties. It also may or may not include, depending on the source, Montgomery county in Indiana, and Lawrence, Richland, Vermillion, Champaign, Clay, and Effingham counties in Illinois due to th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydraulic Fracturing
Fracking (also known as hydraulic fracturing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of bedrock formations by a pressurized liquid. The process involves the high-pressure injection of "fracking fluid" (primarily water, containing sand or other proppants suspended with the aid of thickening agents) into a wellbore to create cracks in the deep-rock formations through which natural gas, petroleum, and brine will flow more freely. When the hydraulic pressure is removed from the well, small grains of hydraulic fracturing proppants (either sand or aluminium oxide) hold the fractures open. Hydraulic fracturing began as an experiment in 1947, and the first commercially successful application followed in 1950. As of 2012, 2.5 million "frac jobs" had been performed worldwide on oil and gas wells, over one million of those within the U.S. Such treatment is generally necessary to achieve adequate flow rates in shale gas, tight ga ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Seismite
{{Earthquakes Seismites are sedimentary beds and structures deformed by seismic shaking. The German paleontologist Adolf Seilacher first used the term in 1969 to describe earthquake-deformed layers. Today, the term is applied to both sedimentary ''layers'' and soft sediment deformation ''structures'' formed by shaking. This subtle change in usage accommodates structures that may not remain within a layer (i.e., clastic dikes or sand volcanos). Caution is urged when applying the term to features observed in the field, as similar-looking features may be products of either seismic or non-seismic perturbation. Several informal classification systems exist to help geologists distinguish seismites from other soft-sediment deformation features, though a formal, standardized system has not been developed. Geologists use seismites, in combination with other evidence, to better understand the earthquake history of an area. If age and distribution of seismically-generated features can b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
