Parts of this article (those related to Mexican earthquakes following significant land subsidence - see talk page) need to be updated.September 2017)(
Subsidence is the sudden sinking or gradual downward settling of the ground's surface with little or no horizontal motion. The definition of subsidence is not restricted by the rate, magnitude, or area involved in the downward movement. It may be caused by natural processes or by human activities. The former include various karst phenomena, thawing of permafrost, consolidation, oxidation of organic soils, slow crustal warping (isostatic adjustment), normal faulting, caldera subsidence, or withdrawal of fluid lava from beneath a solid crust. The human activities include sub-surface mining or extraction of underground fluids, e. g. petroleum, natural gas, or groundwater.Ground subsidence is of global concern to geologists, geotechnical engineers, surveyors, engineers, urban planners, landowners, and the public in general.
Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant rocks, such as quartzite, given the right conditions. Subterranean drainage may limit surface water, with few to no rivers or lakes. However, in regions where the dissolved bedrock is covered or confined by one or more superimposed non-soluble rock strata, distinctive karst features may occur only at subsurface levels and be totally missing above ground.
In geology, permafrost is ground, including rock or (cryotic) soil, at or below the freezing point of water 0 °C (32 °F) for two or more years. Most permafrost is located in high latitudes, but at lower latitudes alpine permafrost occurs at higher elevations. Ground ice is not always present, as may be in the case of non-porous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of the ground material. Permafrost accounts for 0.022% of total water on Earth and exists in 24% of exposed land in the Northern Hemisphere. It also occurs subsea on the continental shelves of the continents surrounding the Arctic Ocean, portions of which were exposed during the last glacial period, with global weather implications.
In soil mechanics, consolidation refers to the process by which soil changes volume gradually in response to a change in pressure. This happens because soil is a two-phase material, comprising soil grains and pore fluid, usually groundwater. When soil saturated with water is subject to an increase in pressure, the high volumetric stiffness of water compared to the soil matrix means that the water initially absorbs all the change in pressure without changing volume, creating excess pore water pressure. As water diffuses away from regions of high pressure due to seepage, the soil matrix gradually takes up the pressure change and shrinks in volume. The theoretical framework of consolidation is therefore closely related to the diffusion equation, the concept of effective stress, and hydraulic conductivity.
Subsidence frequently causes major problems in karst terrains, where dissolution of limestone by fluid flow in the subsurface creates voids (i.e., caves). If the roof of a void becomes too weak, it can collapse and the overlying rock and earth will fall into the space, causing subsidence at the surface. This type of subsidence can cause sinkholes which can be many hundreds of meters deep.
Limestone is a carbonate sedimentary rock that is often composed of the skeletal fragments of marine organisms such as coral, foraminifera, and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3). A closely related rock is dolostone, which contains a high percentage of the mineral dolomite, CaMg(CO3)2. In fact, in old USGS publications, dolostone was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolostones or magnesium-rich limestones.
A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word cave can also refer to much smaller openings such as sea caves, rock shelters, and grottos, though strictly speaking a cave is exogene, meaning it is deeper than its opening is wide, and a rock shelter is endogene.
A sinkhole, also known as a cenote, sink, sink-hole, swallet, swallow hole, or doline, is a depression or hole in the ground caused by some form of collapse of the surface layer. Most are caused by karst processes – for example, the chemical dissolution of carbonate rocks or suffosion processes. Sinkholes vary in size from 1 to 600 m both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Sinkholes may form gradually or suddenly, and are found worldwide.
Several types of sub-surface mining, and specifically methods which intentionally cause the extracted void to collapse (such as pillar extraction, longwall mining and any metalliferous mining method which uses "caving" such as "block caving" or "sub-level caving") will result in surface subsidence. Mining-induced subsidence is relatively predictable in its magnitude, manifestation and extent, except where a sudden pillar or near-surface underground tunnel collapse occurs (usually very old workings). Mining-induced subsidence is nearly always very localized to the surface above the mined area, plus a margin around the outside. The vertical magnitude of the subsidence itself typically does not cause problems, except in the case of drainage (including natural drainage)–rather, it is the associated surface compressive and tensile strains, curvature, tilts and horizontal displacement that are the cause of the worst damage to the natural environment, buildings and infrastructure.
Longwall mining is a form of underground coal mining where a long wall of coal is mined in a single slice. The longwall panel is typically 3 – 4 km long and 250 – 400 m wide.
Underground hard rock mining refers to various underground mining techniques used to excavate hard minerals, usually those containing metals such as ore containing gold, silver, iron, copper, zinc, nickel, tin and lead, but also involves using the same techniques for excavating ores of gems such as diamonds or rubies. Soft rock mining refers to excavation of softer minerals such as salt, coal, or oil sands.
Where mining activity is planned, mining-induced subsidence can be successfully managed if there is co-operation from all of the stakeholders. This is accomplished through a combination of careful mine planning, the taking of preventive measures, and the carrying out of repairs post-mining.
If natural gas is extracted from a natural gas field the initial pressure (up to 60 MPa (600 bar)) in the field will drop over the years. The pressure helps support the soil layers above the field. If the gas is extracted, the overburden pressure sediment compacts and may lead to subsidence at the ground level.
Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxide, nitrogen, hydrogen sulfide, or helium. It is formed when layers of decomposing plant and animal matter are exposed to intense heat and pressure under the surface of the Earth over millions of years. The energy that the plants originally obtained from the sun is stored in the form of chemical bonds in the gas.
The bar is a metric unit of pressure, but is not approved as part of the International System of Units (SI). It is defined as exactly equal to 100,000 Pa, which is slightly less than the current average atmospheric pressure on Earth at sea level.
Overburden pressure, also called lithostatic pressure, confining pressure or vertical stress, is the pressure or stress imposed on a layer of soil or rock by the weight of overlying material.
Since exploitation of the Slochteren (Netherlands) gas field started in the late 1960s the ground level over a 250 km² area has dropped by a current maximum of 30 cm.
Slochteren is a village and former municipality with a population of 15,546 in the province of Groningen in the northeast of the Netherlands. On January 1, 2018, Slochteren merged with Hoogezand-Sappemeer and Menterwolde, forming the municipality Midden-Groningen.
The Netherlands is a country located mainly in Northwestern Europe. The European portion of the Netherlands consists of twelve separate provinces that border Germany to the east, Belgium to the south, and the North Sea to the northwest, with maritime borders in the North Sea with Belgium, Germany and the United Kingdom. Including three island territories in the Caribbean Sea—Bonaire, Sint Eustatius and Saba— it forms a constituent country of the Kingdom of the Netherlands. The official language is Dutch, but a secondary official language in the province of Friesland is West Frisian.
Land subsidence can occur in various ways during an earthquake. Large areas of land can subside drastically during an earthquake because of offset along fault lines. Land subsidence can also occur as a result of settling and compacting of unconsolidated sediment from the shaking of an earthquake.
The Geospatial Information Authority of Japan reported immediate subsidence caused by the 2011 Tōhoku earthquake. m (1.64 ft) was observed on the coast of the Pacific Ocean in Miyako, Tōhoku, while Rikuzentakata, Iwate measured 0.84 m (2.75 ft). In the south at Sōma, Fukushima, 0.29 m (0.95 ft) was observed. The maximum amount of subsidence was 1.2 m (3.93 ft), coupled with horizontal diastrophism of up to 5.3 m (17.3 ft) on the Oshika Peninsula in Miyagi Prefecture.In Northern Japan, subsidence of 0.50
Groundwater-related subsidence is the subsidence (or the sinking) of land resulting from groundwater extraction. It is a growing problem in the developing world as cities increase in population and water use, without adequate pumping regulation and enforcement. One estimate has 80% of serious land subsidence problems associated with the excessive extraction of groundwater,making it a growing problem throughout the world.
Groundwater fluctuations can also indirectly affect the decay of organic material. The habitation of lowlands, such as coastal or delta plains, requires drainage. The resulting aeration of the soil leads to the oxidation of its organic components, such as peat, and this decomposition process may cause significant land subsidence. This applies especially when groundwater levels are periodically adapted to subsidence, in order to maintain desired unsaturated zone depths, exposing more and more peat to oxygen. In addition to this, drained soils consolidate as a result of increased effective stress. cm/yr. Water management used to be tuned primarily to factors such as crop optimization but, to varying extents, avoiding subsidence has come to be taken into account as well.In this way, land subsidence has the potential of becoming self-perpetuating, having rates up to 5
When differential stresses exist in the Earth, these can be accommodated either by geological faulting in the brittle crust, or by ductile flow in the hotter and more fluid mantle. Where faults occur, absolute subsidence may occur in the hanging wall of normal faults. In reverse, or thrust, faults, relative subsidence may be measured in the footwall.
The crust floats buoyantly in the asthenosphere, with a ratio of mass below the "surface" in proportion to its own density and the density of the asthenosphere. If mass is added to a local area of the crust (e.g., through deposition), the crust subsides to compensate and maintain isostatic balance.
The opposite of isostatic subsidence is known as isostatic rebound—the action of the crust returning (sometimes over periods of thousands of years) to a state of isostacy, such as after the melting of large ice sheets or the drying-up of large lakes after the last ice age. Lake Bonneville is a famous example of isostatic rebound. Due to the weight of the water once held in the lake, the earth's crust subsided nearly 200 feet (61 m) to maintain equilibrium. When the lake dried up, the crust rebounded. Today at Lake Bonneville, the center of the former lake is about 200 feet (61 m) higher than the former lake edges.
Many soils contain significant proportions of clay. Because of the very small particle size, they are affected by changes in soil moisture content. Seasonal drying of the soil results in a lowering of both the volume and the surface of the soil. If building foundations are above the level reached by seasonal drying, they move, possibly resulting in damage to the building in the form of tapering cracks.
Trees and other vegetation can have a significant local effect on seasonal drying of soils. Over a number of years, a cumulative drying occurs as the tree grows. That can lead to the opposite of subsidence, known as heave or swelling of the soil, when the tree declines or is felled. As the cumulative moisture deficit is reversed, which can last up to 25 years, the surface level around the tree will rise and expand laterally. That often damages buildings unless the foundations have been strengthened or designed to cope with the effect.
An earthquake is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to toss people around and destroy whole cities. The seismicity, or seismic activity, of an area is the frequency, type and size of earthquakes experienced over a period of time. The word tremor is also used for non-earthquake seismic rumbling.
Groundwater is the water present beneath Earth's surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table. Groundwater is recharged from and eventually flows to the surface naturally; natural discharge often occurs at springs and seeps, and can form oases or wetlands. Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology.
Soil liquefaction occurs when a 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.
Post-glacial rebound is the rise of land masses after the lifting of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound and isostatic depression are phases of glacial isostasy, the deformation of the Earth's crust in response to changes in ice mass distribution. The direct raising effects of post-glacial rebound are readily apparent in parts of Northern Eurasia, Northern America, Patagonia, and Antarctica. However, through the processes of ocean siphoning and continental levering, the effects of post-glacial rebound on sea level are felt globally far from the locations of current and former ice sheets.
Induced seismicity refers to typically minor earthquakes and tremors that are caused by human activity that alters the stresses and strains on the Earth's crust. Most induced seismicity is of a low magnitude. A few sites regularly have larger quakes, such as The Geysers geothermal plant in California which averaged two M4 events and 15 M3 events every year from 2004 to 2009.
Diastrophism refers to deformation of the Earth's crust, and more especially to folding and faulting. Diastrophism can be considered part of geotectonics. Diastrophism comes from the Greek word meaning a twisting.
Tectonic uplift is the portion of the total geologic uplift of the mean Earth surface that is not attributable to an isostatic response to unloading. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal thickening, changes in the density distribution of the crust and underlying mantle, and flexural support due to the bending of rigid lithosphere.
A depression in geology is a landform sunken or depressed below the surrounding area. Depressions form by various mechanisms.
In geomorphology, a knickpoint or nickpoint is part of a river or channel where there is a sharp change in channel slope, such as a waterfall or lake. Knickpoints reflect different conditions and processes on the river, often caused by previous erosion due to glaciation or variance in lithology. In the cycle of erosion model, knickpoints advance one cycle upstream, or inland, replacing an older cycle.
Houston, the most populous city in the Southern United States, is located along the upper Texas Gulf Coast, approximately 50 miles (80 km) northwest of the Gulf of Mexico at Galveston. The city, which is the ninth-largest in the United States by area, covers 601.7 square miles (1,558 km2), of which 579.4 square miles (1,501 km2), or 96.3%, is land and 22.3 square miles (58 km2), or 3.7%, is water.
Interferometric synthetic aperture radar, abbreviated InSAR, is a radar technique used in geodesy and remote sensing. This geodetic method uses two or more synthetic aperture radar (SAR) images to generate maps of surface deformation or digital elevation, using differences in the phase of the waves returning to the satellite or aircraft. The technique can potentially measure millimetre-scale changes in deformation over spans of days to years. It has applications for geophysical monitoring of natural hazards, for example earthquakes, volcanoes and landslides, and in structural engineering, in particular monitoring of subsidence and structural stability.
Overdrafting is the process of extracting groundwater beyond the equilibrium yield of the aquifer.
Groundwater-related subsidence is the subsidence of land resulting from groundwater extraction. It is a growing problem in the developing world as cities increase in population and water use, without adequate pumping regulation and enforcement. One estimate has 80% of serious U.S. land subsidence problems associated with the excessive extraction of groundwater, making it a growing problem throughout the world.
Deformation monitoring is the systematic measurement and tracking of the alteration in the shape or dimensions of an object as a result of stresses induced by applied loads. Deformation monitoring is a major component of logging measured values that may be used to for further computation, deformation analysis, predictive maintenance and alarming.
The interaction between erosion and tectonics has been a topic of debate since the early 1990s. While the tectonic effects on surface processes such as erosion have long been recognized, the opposite has only recently been addressed. The primary questions surrounding this topic are what types of interactions exist between erosion and tectonics and what are the implications of these interactions. While this is still a matter of debate, one thing is clear, the Earth's landscape is a product of two factors: tectonics, which can create topography and maintain relief through surface and rock uplift, and climate, which mediates the erosional processes that wear away upland areas over time. The interaction of these processes can form, modify, or destroy geomorphic features on the Earth’s surface.
The Goose Creek Oil Field is a large oil field in Baytown, Texas, on Galveston Bay. Discovered in 1903, and reaching maximum production in 1918 after a series of spectacular gushers, it was one of the fields that contributed to the Texas Oil Boom of the early 20th century. The field was also the location of the first offshore wells in Texas, and the second group of offshore wells in the United States. Consequences of the development of the Goose Creek field included an economic boom and associated influx of workers, the founding and fast growth of Baytown, and the building of the adjacent Baytown Refinery, which is now the 2nd largest oil refinery in the United States with a capacity of 584,000 barrels per day. The field remains active, having produced over 150 million barrels (24,000,000 m3) of oil in its 100-year history.
The 1964 Niigata earthquake struck at 13:01 local time on 16 June with a magnitude of 7.5 or 7.6. The epicenter was on the continental shelf off the northwest coast of Honshu, Japan in Niigata Prefecture, about 50 kilometres (31 mi) north of the city of Niigata. The earthquake caused liquefaction over large parts of the city.
The Teton fault is a normal fault located in northwestern Wyoming. The fault has a length of 44 miles (70 km) and runs along the eastern base of the Teton Range. Vertical movement on the fault has caused the dramatic topography of the Teton Range.
Tectonic subsidence is the sinking of the Earth's crust on a large scale, relative to crustal-scale features or the geoid. The movement of crustal plates and accommodation spaces created by faulting create subsidence on a large scale in a variety of environments, including passive margins, aulacogens, fore-arc basins, foreland basins, intercontinental basins and pull-apart basins. Three mechanisms are common in the tectonic environments in which subsidence occurs: extension, cooling and loading.
Madeira began to form more than 100 million years ago in the Early Cretaceous, although most of the island has formed in the last 66 million years of the Cenozoic, particularly in the Miocene and Pliocene. The island is an example of hotspot volcanism, with mainly mafic volcanic and igneous rocks, together with smaller deposits of limestone, lignite and other sediments that record its long-running uplift.
|Wikimedia Commons has media related to Subsidence .|
|Look up subsidence in Wiktionary, the free dictionary.|
This article needs additional citations for verification . (November 2007) (Learn how and when to remove this template message)