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An earthquake is the shaking of the surface of the Earth resulting from a 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 propel objects and people into the air, and wreak destruction across entire 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.
In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics. It occurs both naturally and artificially. As an example of the latter, a "major commercial application of liquefaction is the liquefaction of air to allow separation of the constituents, such as oxygen, nitrogen, and the noble gases." Another is the conversion of solid coal into a liquid form usable as a substitute for liquid fuels.
A seismic hazard is the probability that an earthquake will occur in a given geographic area, within a given window of time, and with ground motion intensity exceeding a given threshold. With a hazard thus estimated, risk can be assessed and included in such areas as building codes for standard buildings, designing larger buildings and infrastructure projects, land use planning and determining insurance rates. The seismic hazard studies also may generate two standard measures of anticipated ground motion, both confusingly abbreviated MCE; the simpler probabilistic Maximum Considered Earthquake, used in standard building codes, and the more detailed and deterministic Maximum Credible Earthquake incorporated in the design of larger buildings and civil infrastructure like dams or bridges. It is important to clarify which MCE is being discussed.
A slump is a form of mass wasting that occurs when a coherent mass of loosely consolidated materials or a rock layer moves a short distance down a slope. Movement is characterized by sliding along a concave-upward or planar surface. Causes of slumping include earthquake shocks, thorough wetting, freezing and thawing, undercutting, and loading of a slope.
Quicksand is a colloid consisting of fine granular material and water.
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. 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:
If the pressure of the water in the pores is great enough to carry all the load, it will have the effect of holding the particles apart and of producing a condition that is practically equivalent to that of quicksand… the initial movement of some part of the material might result in accumulating pressure, first on one point, and then on another, successively, as the early points of concentration were liquefied.
The New Madrid Seismic Zone, sometimes called the New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes in the Southern and Midwestern United States, stretching to the southwest from New Madrid, Missouri.
Earthquake engineering is an interdisciplinary branch of engineering that designs and analyzes structures, such as buildings and bridges, with earthquakes in mind. Its overall goal is to make such structures more resistant to earthquakes. An earthquake engineer aims to construct structures that will not be damaged in minor shaking and will avoid serious damage or collapse in a major earthquake. Earthquake engineering is the scientific field concerned with protecting society, the natural environment, and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels. Traditionally, it has been narrowly defined as the study of the behavior of structures and geo-structures subject to seismic loading; it is considered as a subset of structural engineering, geotechnical engineering, mechanical engineering, chemical engineering, applied physics, etc. However, the tremendous costs experienced in recent earthquakes have led to an expansion of its scope to encompass disciplines from the wider field of civil engineering, mechanical engineering, nuclear engineering, and from the social sciences, especially sociology, political science, economics, and finance.
A clastic dike is a seam of sedimentary material that fills an open fracture in and cuts across sedimentary rock strata or layering in other rock types. Clastic dikes form rapidly by fluidized injection or passively by water, wind, and gravity. Diagenesis may play a role in the formation of some dikes. Clastic dikes are commonly vertical or near-vertical. Centimeter-scale widths are common, but thicknesses range from millimetres to metres. Length is usually many times width.
A glacial cryoseism is a non-tectonic seismic event of the glacial cryosphere. A large variety of seismogenic glacial processes arising from internal, ocean calving, or basal processes have been identified and studied. Very large calving events in Greenland and Antarctica have been observed to generate seismic events of magnitude 5 or larger. Extremely large icebergs can also generate seismic signals that are observable at distances up to thousands of kilometers when they collide or grind across the ocean floor. Basal glacial motion be enhanced due to water accumulation underneath a glacier sourced from surface or basal ice melt. Hydraulic pressure of subglacial water can reduce the friction at the bed, allowing the glacier to suddenly shift and generate seismic waves. This type of cryoseism can be very brief, or may last for many minutes.
Sand boils or sand volcanoes occur when water under pressure wells up through a bed of sand. The water looks like it is boiling up from the bed of sand, hence the name.
Seismic microzonation is defined as the process of subdividing a potential seismic or earthquake prone area into zones with respect to some geological and geophysical characteristics of the sites such as ground shaking, liquefaction susceptibility, landslide and rock fall hazard, earthquake-related flooding, so that seismic hazards at different locations within the area can correctly be identified. Microzonation provides the basis for site-specific risk analysis, which can assist in the mitigation of earthquake damage. In most general terms, seismic microzonation is the process of estimating the response of soil layers under earthquake excitations and thus the variation of earthquake characteristics on the ground surface.
Ground–structure interaction (SSI) consists of the interaction between soil (ground) and a structure built upon it. It is primarily an exchange of mutual stress, whereby the movement of the ground-structure system is influenced by both the type of ground and the type of structure. This is especially applicable to areas of seismic activity. Various combinations of soil and structure can either amplify or diminish movement and subsequent damage. A building on stiff ground rather than deformable ground will tend to suffer greater damage. A second interaction effect, tied to mechanical properties of soil, is the sinking of foundations, worsened by a seismic event. This phenomenon is called soil liquefaction.
A sand geyser,sand fountain or sand blow is a geologic phenomena which occurs in association with earthquakes and other seismic events. In the geologic record, these are seen as clastic dikes. It is described as "a geyser of sand and water that shoots from the ground during a major earthquake." A quake can cause underlying sand to liquefy while pressure forces the eruption of the sand mixture to the surface. The mixture of sand and water can also contain dissolved gases such as methane and carbon dioxide.
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.
The 1979 Imperial Valley earthquake occurred at 16:16 Pacific Daylight Time on 15 October just south of the Mexico–United States border. It affected Imperial Valley in Southern California and Mexicali Valley in northern Baja California. The earthquake had a relatively shallow hypocenter and caused property damage in the United States estimated at US$30 million. The irrigation systems in the Imperial Valley were badly affected, but no deaths occurred. It was the largest earthquake to occur in the contiguous United States since the 1971 San Fernando earthquake eight years earlier.
River bank failure can be caused when the gravitational forces acting on a bank exceed the forces which hold the sediment together. Failure depends on sediment type, layering, and moisture content.
Earthquake environmental effects are the effects caused by an earthquake, including surface faulting, tsunamis, soil liquefactions, ground resonance, landslides and ground failure, either directly linked to the earthquake source or provoked by the ground shaking. These are common features produced both in the near and far fields, routinely recorded and surveyed in recent events, very often remembered in historical accounts and preserved in the stratigraphic record (paleoearthquakes). Both surface deformation and faulting and shaking-related geological effects not only leave permanent imprints in the environment, but also dramatically affect human structures. Moreover, underwater fault ruptures and seismically-triggered landslides can generate tsunami waves.
Seismic intensity scales categorize the intensity or severity of ground shaking (quaking) at a given location, such as resulting from an earthquake. They are distinguished from seismic magnitude scales, which measure the magnitude or overall strength of an earthquake, which may, or perhaps not, cause perceptible shaking.
The Olancha Earthquake Sequence (2009) was a consecutive series of three earthquakes, with magnitudes of 5.2, 5.0 and 4.9 respectively, with a number of small shocks between each, to accompany the main "triple shock".
References
- ↑ "Paleoliquefaction". EarthScope Voyager. University Corporation for Atmospheric Research. Archived from the original on 26 May 2015. Retrieved 15 July 2016.
- ↑ Wolf, Dr. Lorraine W. "Earthquake-Induced Liquefaction in the New Madrid Seismic Zone". Auburn University. Archived from the original on 19 August 2016. Retrieved 15 July 2016.
- ↑ Munson, Patrick J.; Munson, Cheryl Ann; Pond, Eric C. "Paleoliquefaction evidence for a strong Holocene earthquake in south-central Indiana (abstract)". Geology. Geological Society of America. Archived from the original on 15 July 2016. Retrieved 15 July 2016.
- ↑ Bell, F.G. (2016). Fundamentals of Engineering Geology (Revised ed.). Elsevier. p. 157. ISBN 9781483102306 . Retrieved 15 July 2016.
- ↑ Obermeier, Stephen F.; Pond, Eric C.; Olson, Scott M. (January 29, 2001). "Paleoliquefaction Studies In Continental Settings: Geologic and Geotechnical Factors In Interpretations And Back-Analysis" (PDF). U.S. Geological Survey Open-File Report. Open-File Report. doi:10.3133/ofr0129. Archived from the original (PDF) on 18 February 2017.
- ↑ Obermeier, Stephen F. (November 24, 1998). "Seismic Liquefaction Features: Examples From Paleoseismic Investigations In The Continental United States". U.S. Geological Survey Open-File Report 98-488. Archived from the original on 18 August 2016. Retrieved 15 July 2016.