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In geography , regions , otherwise referred to as areas , zones , lands or territories , are portions of the Earth's surface that are broadly divided by physical characteristics ( physical geography ), human impact characteristics ( human geography ), and the interaction of humanity and the environment ( environmental geography ). Geographic regions and sub-regions are mostly described by their imprecisely defined, and sometimes transitory boundaries, except in human geography, where jurisdiction areas such as national borders are defined in law. More confined or well bounded portions are called locations or places .

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95-619: Ostwürttemberg ( East Württemberg ) is a region in eastern Baden-Württemberg , Germany , in the Stuttgart subdivision (Regierungsbezirk) . It is located in the southwestern part of Germany. It consists of the districts of Heidenheim and Ostalb . It borders the Stuttgart Region to the west, the Heilbronn-Franken Region to the north, western Middle Franconia ( Bavaria ) to the east, Bavarian Swabia to

190-785: A Field Marshal or General of the Army (US five stars), or Generalissimo (Soviet Union); and in the US Armed Forces an Admiral (typically four stars) may also command a region. Due to the large size of this formation, its use is rarely employed. Some of the very few examples of an Army Region are each of the Eastern, Western, and southern (mostly in Italy) fronts in Europe during World War II . The military map unit symbol for this echelon of formation (see Military organization and APP-6A )

285-489: A quake , tremor , or temblor  – is the shaking of the Earth 's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves . Earthquakes can range in intensity , from those so weak they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The seismic activity of an area

380-729: A tsunami . Earthquakes can trigger landslides . Earthquakes' occurrence is influenced by tectonic movements along faults, including normal, reverse (thrust), and strike-slip faults, with energy release and rupture dynamics governed by the elastic-rebound theory . Efforts to manage earthquake risks involve prediction, forecasting, and preparedness, including seismic retrofitting and earthquake engineering to design structures that withstand shaking. The cultural impact of earthquakes spans myths, religious beliefs, and modern media, reflecting their profound influence on human societies. Similar seismic phenomena, known as marsquakes and moonquakes , have been observed on other celestial bodies, indicating

475-404: A country or the world having definable characteristics but not always fixed boundaries. In the fields of physical geography , ecology , biogeography , zoogeography , and environmental geography , regions tend to be based on natural features such as ecosystems or biotopes , biomes , drainage basins , natural regions , mountain ranges , soil types . Where human geography is concerned,

570-665: A cultural region. Examples of natural resource regions are the Rumaila Field , the oil field that lies along the border or Iraq and Kuwait and played a role in the Gulf War ; the Coal Region of Pennsylvania, which is a historical region as well as a cultural, physical, and natural resource region; the South Wales Coalfield , which like Pennsylvania's coal region is a historical, cultural, and natural region;

665-571: A depth of less than 70 km (43 mi) are classified as "shallow-focus" earthquakes, while those with a focal depth between 70 and 300 km (43 and 186 mi) are commonly termed "mid-focus" or "intermediate-depth" earthquakes. In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, deep-focus earthquakes may occur at much greater depths (ranging from 300 to 700 km (190 to 430 mi)). These seismically active areas of subduction are known as Wadati–Benioff zones . Deep-focus earthquakes occur at

760-488: A depth where the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure. Earthquakes often occur in volcanic regions and are caused there, both by tectonic faults and the movement of magma in volcanoes . Such earthquakes can serve as an early warning of volcanic eruptions, as during

855-475: A few exceptions to this: Supershear earthquake ruptures are known to have propagated at speeds greater than the S wave velocity. These have so far all been observed during large strike-slip events. The unusually wide zone of damage caused by the 2001 Kunlun earthquake has been attributed to the effects of the sonic boom developed in such earthquakes. Slow earthquake ruptures travel at unusually low velocities. A particularly dangerous form of slow earthquake

950-416: A functional region. Nodal regions, functional urban regions, daily urban systems, local labour-market areas (LLMAs), or travel-to-work areas (TTWAs) are considered to be special instances of a general functional region that need to fulfil some specific conditions regarding, for instance, the character of the region-organising interaction or the presence of urban cores, (Halas et al., 2015 ). In military usage,

1045-536: A lesser degree, regions in the sphere of influence of Greater New England, "Acadia" (Nova Scotia), "Newfoundland and The Fishery/The Banks". Other examples of historical regions are Iroquoia, Ohio Country , Illinois Country , and Rupert's Land . In Russia , historical regions include Siberia and the Russian North , as well as the Ural Mountains . These regions had an identity that developed from

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1140-508: A number of countries have borrowed the term as the formal name for a type of subnational entity (e.g., the región , used in Chile ). In English, the word is also used as the conventional translation for equivalent terms in other languages (e.g., the область ( oblast ), used in Russia alongside a broader term регион ). The following countries use the term "region" (or its cognate ) as

1235-612: A particular location in the Earth is the average rate of seismic energy release per unit volume. One of the most devastating earthquakes in recorded history was the 1556 Shaanxi earthquake , which occurred on 23 January 1556 in Shaanxi , China. More than 830,000 people died. Most houses in the area were yaodongs —dwellings carved out of loess hillsides—and many victims were killed when these structures collapsed. The 1976 Tangshan earthquake , which killed between 240,000 and 655,000 people,

1330-418: A region is shorthand for the name of a military formation larger than an Army Group and smaller than a Theater . The full name of the military formation is Army Region. The size of an Army Region can vary widely but is generally somewhere between about 1 million and 3 million soldiers. Two or more Army Regions could make up a Theater. An Army Region is typically commanded by a full General (US four stars),

1425-529: A significant percentage of their respective continental land area. To a large extent, major continental regions are mental constructs created by considering an efficient way to define large areas of the continents. For the most part, the images of the world are derived as much from academic studies, from all types of media, or from personal experience of global exploration . They are a matter of collective human knowledge of their own planet and are attempts to better understand their environments. Regional geography

1520-658: A similar way, as does Romania and Venezuela . The government of Singapore makes use of the term " region " for its own administrative purposes. The following countries use an administrative subdivision conventionally referred to as a region in English: China has five 自治区 ( zìzhìqū ) and two 特別行政區 (or 特别行政区; tèbiéxíngzhèngqū ), which are translated as " autonomous region " and " special administrative region ", respectively. There are many relatively small regions based on local government agencies such as districts, agencies, or regions. In general, they are all regions in

1615-765: A single rupture) are approximately 1,000 km (620 mi). Examples are the earthquakes in Alaska (1957) , Chile (1960) , and Sumatra (2004) , all in subduction zones. The longest earthquake ruptures on strike-slip faults, like the San Andreas Fault ( 1857 , 1906 ), the North Anatolian Fault in Turkey ( 1939 ), and the Denali Fault in Alaska ( 2002 ), are about half to one third as long as

1710-625: A sort of social and political polity . The term Muslim world is sometimes used to refer to the region of the world where Islam is dominant. These broad terms are somewhat vague when used to describe regions. Within some religions there are clearly defined regions. The Roman Catholic Church , the Church of England , the Eastern Orthodox Church , and others, define ecclesiastical regions with names such as diocese , eparchy , ecclesiastical provinces , and parish . For example,

1805-403: Is a branch of geography that studies regions of all sizes across the Earth . It has a prevailing descriptive character. The main aim is to understand or define the uniqueness or character of a particular region, which consists of natural as well as human elements. Attention is paid also to regionalization, which covers the proper techniques of space delimitation into regions. Regional geography

1900-525: Is a theory that earthquakes can recur in a regular pattern. Earthquake clustering has been observed, for example, in Parkfield, California where a long-term research study is being conducted around the Parkfield earthquake cluster. An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. Rapid changes of stress between rocks, and the stress from the original earthquake are

1995-477: Is also considered as a certain approach to study in geographical sciences (similar to quantitative or critical geographies ; for more information, see history of geography ). Human geography is a branch of geography that focuses on the study of patterns and processes that shape human interaction with various discrete environments. It encompasses human , political , cultural , social , and economic aspects among others that are often clearly delineated. While

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2090-410: Is called the hypocenter or focus, while the ground level directly above it is the epicenter . Earthquakes are primarily caused by geological faults , but also by volcanic activity , landslides, and other seismic events. The frequency, type, and size of earthquakes in an area define its seismic activity, reflecting the average rate of seismic energy release. Significant historical earthquakes include

2185-473: Is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior. There are three main types of fault, all of which may cause an interplate earthquake : normal, reverse (thrust), and strike-slip. Normal and reverse faulting are examples of dip-slip, where

2280-714: Is currently a controversial proposal to divide the rest of Sweden into large regions , replacing the current counties. The government of the Philippines uses the term "region" (in Filipino , rehiyon ) when it is necessary to group provinces, the primary administrative subdivision of the country. This is also the case in Brazil , which groups its primary administrative divisions ( estados ; "states") into grandes regiões ( greater regions ) for statistical purposes, while Russia uses экономические районы ( economic regions ) in

2375-400: Is divided into 754 Flinn–Engdahl regions (F-E regions), which are based on political and geographical boundaries as well as seismic activity. More active zones are divided into smaller F-E regions whereas less active zones belong to larger F-E regions. Standard reporting of earthquakes includes its magnitude , date and time of occurrence, geographic coordinates of its epicenter , depth of

2470-483: Is giving spatial understanding of mediated image. [REDACTED] Africa [REDACTED] Antarctica [REDACTED] Asia [REDACTED] Australia [REDACTED] Europe [REDACTED] North America [REDACTED] South America [REDACTED] Afro-Eurasia [REDACTED] Americas [REDACTED] Eurasia [REDACTED] Oceania Earthquake An earthquake  – also called

2565-421: Is identified with six Xs. Media geography is a spatio-temporal understanding, brought through different gadgets of media, nowadays, media became inevitable at different proportions and everyone supposed to consumed at different gravity. The spatial attributes are studied with the help of media outputs in shape of images which are contested in nature and pattern as well where politics is inseparable. Media geography

2660-432: Is not an abstract spatial concept, but to a certain extent it can be regarded as a reflection of the spatial behaviour of individuals in a geographic space. The functional region is conceived as a general concept while its inner structure, inner spatial flows, and interactions need not necessarily show any regular pattern, only selfcontainment. The concept of self-containment remains the only crucial defining characteristic of

2755-545: Is probably a statistical fluctuation rather than a systematic trend. More detailed statistics on the size and frequency of earthquakes is available from the United States Geological Survey. A recent increase in the number of major earthquakes has been noted, which could be explained by a cyclical pattern of periods of intense tectonic activity, interspersed with longer periods of low intensity. However, accurate recordings of earthquakes only began in

2850-423: Is proportional to the area of the fault that ruptures and the stress drop. Therefore, the longer the length and the wider the width of the faulted area, the larger the resulting magnitude. The most important parameter controlling the maximum earthquake magnitude on a fault, however, is not the maximum available length, but the available width because the latter varies by a factor of 20. Along converging plate margins,

2945-410: Is the tsunami earthquake , observed where the relatively low felt intensities, caused by the slow propagation speed of some great earthquakes, fail to alert the population of the neighboring coast, as in the 1896 Sanriku earthquake . During an earthquake, high temperatures can develop at the fault plane, increasing pore pressure and consequently vaporization of the groundwater already contained within

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3040-467: Is the frequency, type, and size of earthquakes experienced over a particular time. The seismicity at a particular location in the Earth is the average rate of seismic energy release per unit volume. In its most general sense, the word earthquake is used to describe any seismic event that generates seismic waves. Earthquakes can occur naturally or be induced by human activities, such as mining , fracking , and nuclear tests . The initial point of rupture

3135-509: The 1556 Shaanxi earthquake in China, with over 830,000 fatalities, and the 1960 Valdivia earthquake in Chile, the largest ever recorded at 9.5 magnitude. Earthquakes result in various effects, such as ground shaking and soil liquefaction , leading to significant damage and loss of life. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause

3230-400: The 1980 eruption of Mount St. Helens . Earthquake swarms can serve as markers for the location of the flowing magma throughout the volcanoes. These swarms can be recorded by seismometers and tiltmeters (a device that measures ground slope) and used as sensors to predict imminent or upcoming eruptions. A tectonic earthquake begins as an area of initial slip on the fault surface that forms

3325-587: The 2004 Indian Ocean earthquake is simultaneously one of the deadliest earthquakes in history. Earthquakes that caused the greatest loss of life, while powerful, were deadly because of their proximity to either heavily populated areas or the ocean, where earthquakes often create tsunamis that can devastate communities thousands of kilometers away. Regions most at risk for great loss of life include those where earthquakes are relatively rare but powerful, and poor regions with lax, unenforced, or nonexistent seismic building codes. Tectonic earthquakes occur anywhere on

3420-826: The Grand Banks . He rejects regions traditionally used in describing American history, like New France , "West Indies", the Middle Colonies , and the individual colonies themselves ( Province of Maryland , for example). Instead he writes of "discrete colonization areas", which may be named after colonies but rarely adhere strictly to political boundaries. Among other historic regions of this type, he writes about "Greater New England" and its major sub-regions of "Plymouth", "New Haven shores" (including parts of Long Island), "Rhode Island" (or "Narragansett Bay"), "the Piscataqua", "Massachusetts Bay", "Connecticut Valley", and to

3515-499: The Himalayan Mountains . With the rapid growth of mega-cities such as Mexico City, Tokyo, and Tehran in areas of high seismic risk , some seismologists are warning that a single earthquake may claim the lives of up to three million people. While most earthquakes are caused by the movement of the Earth's tectonic plates , human activity can also produce earthquakes. Activities both above ground and below may change

3610-554: The Kuznetsk Basin , a similarly important coal mining region in Russia; Kryvbas , the economic and iron ore mining region of Ukraine; and the James Bay Project , a large region of Quebec where one of the largest hydroelectric systems in the world has been developed. Sometimes a region associated with a religion is given a name, like Christendom , a term with medieval and renaissance connotations of Christianity as

3705-1057: The Metropolitan Water Reclamation District of Greater Chicago , the Las Vegas-Clark County Library District , the Metropolitan Police Service of Greater London , as well as other local districts like the York Rural Sanitary District , the Delaware River Port Authority , the Nassau County Soil and Water Conservation District , and C-TRAN . The traditional territorial divisions of some countries are also commonly rendered in English as "regions". These informal divisions do not form

3800-579: The Northwest European Atlantic Protestant Region , which includes sub-regions such as the "Western Channel Community", which itself is made of sub-regions such as the English West Country of Cornwall , Devon , Somerset , and Dorset . In describing historic regions of America, Meinig writes of "The Great Fishery" off the coast of Newfoundland and New England, an oceanic region that includes

3895-515: The United Kingdom 's Lake District and California's Wine Country . great plains region Natural resources often occur in distinct regions. Natural resource regions can be a topic of physical geography or environmental geography, but also have a strong element of human geography and economic geography. A coal region, for example, is a physical or geomorphological region, but its development and exploitation can make it into an economic and

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3990-426: The brittle-ductile transition zone and upwards by the ground surface. The mechanics of this process are poorly understood because it is difficult either to recreate such rapid movements in a laboratory or to record seismic waves close to a nucleation zone due to strong ground motion. In most cases, the rupture speed approaches, but does not exceed, the shear wave (S wave) velocity of the surrounding rock. There are

4085-416: The global continental regions, there are also hydrospheric and atmospheric regions that cover the oceans , and discrete climates above the land and water masses of the planet. The land and water global regions are divided into subregions geographically bounded by large geological features that influence large-scale ecologies, such as plains and features. As a way of describing spatial areas,

4180-413: The least principal stress. Strike-slip faulting is intermediate between the other two types described above. This difference in stress regime in the three faulting environments can contribute to differences in stress drop during faulting, which contributes to differences in the radiated energy, regardless of fault dimensions. For every unit increase in magnitude, there is a roughly thirty-fold increase in

4275-553: The 20th century and has been inferred for older anomalous clusters of large earthquakes in the Middle East. It is estimated that around 500,000 earthquakes occur each year, detectable with current instrumentation. About 100,000 of these can be felt. Minor earthquakes occur very frequently around the world in places like California and Alaska in the U.S., as well as in El Salvador, Mexico, Guatemala, Chile, Peru, Indonesia,

4370-433: The 21st century. Seismic waves travel through the Earth's interior and can be recorded by seismometers at great distances. The surface-wave magnitude was developed in the 1950s as a means to measure remote earthquakes and to improve the accuracy for larger events. The moment magnitude scale not only measures the amplitude of the shock but also takes into account the seismic moment (total rupture area, average slip of

4465-399: The Earth's core was located in 1913 by Beno Gutenberg . S waves and later arriving surface waves do most of the damage compared to P waves. P waves squeeze and expand the material in the same direction they are traveling, whereas S waves shake the ground up and down and back and forth. Earthquakes are not only categorized by their magnitude but also by the place where they occur. The world

4560-484: The Earth. Also, the depth of the hypocenter can be computed roughly. P wave speed S waves speed As a consequence, the first waves of a distant earthquake arrive at an observatory via the Earth's mantle. On average, the kilometer distance to the earthquake is the number of seconds between the P- and S wave times 8. Slight deviations are caused by inhomogeneities of subsurface structure. By such analysis of seismograms,

4655-573: The Philippines, Iran, Pakistan, the Azores in Portugal, Turkey, New Zealand, Greece, Italy, India, Nepal, and Japan. Larger earthquakes occur less frequently, the relationship being exponential ; for example, roughly ten times as many earthquakes larger than magnitude 4 occur than earthquakes larger than magnitude 5. In the (low seismicity) United Kingdom, for example, it has been calculated that

4750-706: The United States is divided into 32 Roman Catholic ecclesiastical provinces . The Lutheran Church–Missouri Synod is organized into 33 geographic districts , which are subdivided into circuits (the Atlantic District (LCMS) , for example). The Church of Jesus Christ of Latter-day Saints uses regions similar to dioceses and parishes, but uses terms like ward and stake . In the field of political geography , regions tend to be based on political units such as sovereign states ; subnational units such as administrative regions, provinces , states (in

4845-709: The United States) , counties , townships , territories , etc.; and multinational groupings, including formally defined units such as the European Union , the Association of Southeast Asian Nations , and NATO , as well as informally defined regions such as the Third World , Western Europe , and the Middle East. The word "region" is taken from the Latin regio (derived from regere , 'to rule'), and

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4940-534: The area and suggest a coherent tourism experience to visitors. Countries, states, provinces, and other administrative regions are often carved up into tourism regions to facilitate attracting visitors. Some of the more famous tourism regions based on historical or current administrative regions include Tuscany in Italy and Yucatán in Mexico. Famous examples of regions created by a government or tourism bureau include

5035-463: The average recurrences are: an earthquake of 3.7–4.6 every year, an earthquake of 4.7–5.5 every 10 years, and an earthquake of 5.6 or larger every 100 years. This is an example of the Gutenberg–Richter law . The number of seismic stations has increased from about 350 in 1931 to many thousands today. As a result, many more earthquakes are reported than in the past, but this is because of

5130-578: The basis of the modern administrative divisions of these countries, but still define and delimit local regional identity and sense of belonging. Examples are: Functional regions are usually understood to be the areas organised by the horizontal functional relations (flows, interactions) that are maximised within a region and minimised across its borders so that the principles of internal cohesiveness and external separation regarding spatial interactions are met (see, for instance, Farmer and Fotheringham, 2011; Klapka, Halas, 2016; Smart, 1974 ). A functional region

5225-404: The brittle crust. Thus, earthquakes with magnitudes much larger than 8 are not possible. In addition, there exists a hierarchy of stress levels in the three fault types. Thrust faults are generated by the highest, strike-slip by intermediate, and normal faults by the lowest stress levels. This can easily be understood by considering the direction of the greatest principal stress, the direction of

5320-566: The cause of other earthquakes in the past century. A Columbia University paper suggested that the 8.0 magnitude 2008 Sichuan earthquake was induced by loading from the Zipingpu Dam , though the link has not been conclusively proved. The instrumental scales used to describe the size of an earthquake began with the Richter scale in the 1930s. It is a relatively simple measurement of an event's amplitude, and its use has become minimal in

5415-431: The concept of regions is important and widely used among the many branches of geography, each of which can describe areas in regional terms. For example, ecoregion is a term used in environmental geography , cultural region in cultural geography , bioregion in biogeography , and so on. The field of geography that studies regions themselves is called regional geography . Regions are an area or division, especially part of

5510-529: The dip angle of the rupture plane is very shallow, typically about 10 degrees. Thus, the width of the plane within the top brittle crust of the Earth can reach 50–100 km (31–62 mi) (such as in Japan, 2011 , or in Alaska, 1964 ), making the most powerful earthquakes possible. The majority of tectonic earthquakes originate in the Ring of Fire at depths not exceeding tens of kilometers. Earthquakes occurring at

5605-678: The displacement along the fault is in the direction of dip and where movement on them involves a vertical component. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip. The topmost, brittle part of the Earth's crust, and the cool slabs of the tectonic plates that are descending into the hot mantle, are the only parts of our planet that can store elastic energy and release it in fault ruptures. Rocks hotter than about 300 °C (572 °F) flow in response to stress; they do not rupture in earthquakes. The maximum observed lengths of ruptures and mapped faults (which may break in

5700-439: The distance from the earthquake and the underlying rock or soil makeup. The first scale for measuring earthquake magnitudes was developed by Charles Francis Richter in 1935. Subsequent scales ( seismic magnitude scales ) have retained a key feature, where each unit represents a ten-fold difference in the amplitude of the ground shaking and a 32-fold difference in energy. Subsequent scales are also adjusted to have approximately

5795-554: The early 1900s, so it is too early to categorically state that this is the case. Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000-kilometre-long (25,000 mi), horseshoe-shaped zone called the circum-Pacific seismic belt, known as the Pacific Ring of Fire , which for the most part bounds the Pacific plate . Massive earthquakes tend to occur along other plate boundaries too, such as along

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5890-435: The early modern period and led to Siberian regionalism . A tourism region is a geographical region that has been designated by a governmental organization or tourism bureau as having common cultural or environmental characteristics. These regions are often named after a geographical, former, or current administrative region or may have a name created for tourism purposes. The names often evoke certain positive qualities of

5985-403: The earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane . The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the fault surface that increases the frictional resistance. Most fault surfaces do have such asperities, which leads to a form of stick-slip behavior . Once

6080-426: The earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to aftershocks but on adjacent segments of fault, these storms occur over the course of years, with some of the later earthquakes as damaging as the early ones. Such a pattern was observed in the sequence of about a dozen earthquakes that struck the North Anatolian Fault in Turkey in

6175-504: The energy released. For instance, an earthquake of magnitude 6.0 releases approximately 32 times more energy than a 5.0 magnitude earthquake and a 7.0 magnitude earthquake releases 1,000 times more energy than a 5.0 magnitude earthquake. An 8.6-magnitude earthquake releases the same amount of energy as 10,000 atomic bombs of the size used in World War II . This is so because the energy released in an earthquake, and thus its magnitude,

6270-458: The fact that no single earthquake in the sequence is the main shock, so none has a notably higher magnitude than another. An example of an earthquake swarm is the 2004 activity at Yellowstone National Park . In August 2012, a swarm of earthquakes shook Southern California 's Imperial Valley , showing the most recorded activity in the area since the 1970s. Sometimes a series of earthquakes occur in what has been called an earthquake storm , where

6365-462: The fault has locked, continued relative motion between the plates leads to increasing stress and, therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy . This energy is released as a combination of radiated elastic strain seismic waves , frictional heating of

6460-411: The fault plane that holds it in place, and fluids can exert a lubricating effect. As thermal overpressurization may provide positive feedback between slip and strength fall at the fault plane, a common opinion is that it may enhance the faulting process instability. After the mainshock, the pressure gradient between the fault plane and the neighboring rock causes a fluid flow that increases pore pressure in

6555-418: The fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory . It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or

6650-541: The fault, and rigidity of the rock). The Japan Meteorological Agency seismic intensity scale , the Medvedev–Sponheuer–Karnik scale , and the Mercalli intensity scale are based on the observed effects and are related to the intensity of shaking. The shaking of the earth is a common phenomenon that has been experienced by humans from the earliest of times. Before the development of strong-motion accelerometers,

6745-417: The focus. Once the rupture has been initiated, it begins to propagate away from the focus, spreading out along the fault surface. Lateral propagation will continue until either the rupture reaches a barrier, such as the end of a fault segment, or a region on the fault where there is insufficient stress to allow continued rupture. For larger earthquakes, the depth extent of rupture will be constrained downwards by

6840-406: The force that "pushes" the rock mass during the faulting. In the case of normal faults, the rock mass is pushed down in a vertical direction, thus the pushing force ( greatest principal stress) equals the weight of the rock mass itself. In the case of thrusting, the rock mass "escapes" in the direction of the least principal stress, namely upward, lifting the rock mass, and thus, the overburden equals

6935-580: The general sense of being bounded spatial units. Examples include electoral districts such as Washington's 6th congressional district and Tennessee's 1st congressional district ; school districts such as Granite School District and Los Angeles Unified School District ; economic districts such as the Reedy Creek Improvement District ; metropolitan areas such as the Seattle metropolitan area , and metropolitan districts such as

7030-410: The intensity of a seismic event was estimated based on the observed effects. Magnitude and intensity are not directly related and calculated using different methods. The magnitude of an earthquake is a single value that describes the size of the earthquake at its source. Intensity is the measure of shaking at different locations around the earthquake. Intensity values vary from place to place, depending on

7125-399: The largest of water regions known as oceans . There are also significant regions that do not belong to either classification, such as archipelago regions that are littoral regions, or earthquake regions that are defined in geology . Continental regions are usually based on broad experiences in human history and attempt to reduce very large areas to more manageable regionalization for

7220-476: The lengths along subducting plate margins, and those along normal faults are even shorter. Normal faults occur mainly in areas where the crust is being extended such as a divergent boundary . Earthquakes associated with normal faults are generally less than magnitude 7. Maximum magnitudes along many normal faults are even more limited because many of them are located along spreading centers, as in Iceland, where

7315-402: The main causes of these aftershocks, along with the crust around the ruptured fault plane as it adjusts to the effects of the mainshock. An aftershock is in the same region as the main shock but always of a smaller magnitude, however, they can still be powerful enough to cause even more damage to buildings that were already previously damaged from the mainshock. If an aftershock is larger than

7410-414: The mainshock, the aftershock is redesignated as the mainshock and the original main shock is redesignated as a foreshock . Aftershocks are formed as the crust around the displaced fault plane adjusts to the effects of the mainshock. Earthquake swarms are sequences of earthquakes striking in a specific area within a short period. They are different from earthquakes followed by a series of aftershocks by

7505-432: The major focus of human geography is not the physical landscape of the Earth (see physical geography ), it is hardly possible to discuss human geography without referring to the physical landscape on which human activities are being played out, and environmental geography is emerging as a link between the two. Regions of human geography can be divided into many broad categories: The field of historical geography involves

7600-604: The name of a type of subnational administrative unit: The Canadian province of Québec also uses the "administrative region" ( région administrative ). Scotland had local government regions from 1975 to 1996. In Spain the official name of the autonomous community of Murcia is Región de Murcia . Also, some single-province autonomous communities such as Madrid use the term región interchangeably with comunidad autónoma . Two län (counties) in Sweden are officially called 'regions': Skåne and Västra Götaland , and there

7695-521: The purpose of the study. As such they are conceptual constructs, usually lacking distinct boundaries. The oceanic division into maritime regions is used in conjunction with the relationship to the central area of the continent, using directions of the compass . Some continental regions are defined by the major continental feature of their identity, such as the Amazon basin , or the Sahara , which both occupy

7790-442: The regions and subregions are described by the discipline of ethnography . Global regions are distinguishable from space, and are therefore clearly distinguished by the two basic terrestrial environments, land and water . However, they have been generally recognized as such much earlier by terrestrial cartography because of their impact on human geography. They are divided into the largest of land regions, known as continents and

7885-530: The rock. In the coseismic phase, such an increase can significantly affect slip evolution and speed, in the post-seismic phase it can control the Aftershock sequence because, after the main event, pore pressure increase slowly propagates into the surrounding fracture network. From the point of view of the Mohr-Coulomb strength theory , an increase in fluid pressure reduces the normal stress acting on

7980-437: The rupture of geological faults but also by other events such as volcanic activity, landslides, mine blasts, fracking and nuclear tests . An earthquake's point of initial rupture is called its hypocenter or focus. The epicenter is the point at ground level directly above the hypocenter. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The seismicity at

8075-522: The same numeric value within the limits of the scale. Although the mass media commonly reports earthquake magnitudes as "Richter magnitude" or "Richter scale", standard practice by most seismological authorities is to express an earthquake's strength on the moment magnitude scale, which is based on the actual energy released by an earthquake, the static seismic moment. Every earthquake produces different types of seismic waves, which travel through rock with different velocities: Propagation velocity of

8170-464: The seismic waves through solid rock ranges from approx. 3 km/s (1.9 mi/s) up to 13 km/s (8.1 mi/s), depending on the density and elasticity of the medium. In the Earth's interior, the shock- or P waves travel much faster than the S waves (approx. relation 1.7:1). The differences in travel time from the epicenter to the observatory are a measure of the distance and can be used to image both sources of earthquakes and structures within

8265-687: The southeast, and the Alb-Danube district to the south. The area of Ostwürttemberg covers 2139 km², with a population of 446 349 people. The administrative seat is Schwäbisch Gmünd . The region is mainly rural, encompassing most of the eastern parts of the Swabian Alb and parts of the valleys of the rivers Brenz , Jagst , Kocher and Rems . The main towns are Aalen , Ellwangen , Heidenheim and Schwäbisch Gmünd. 48°45′36″N 10°08′17″E  /  48.760°N 10.138°E  / 48.760; 10.138 Region Apart from

8360-422: The stresses and strains on the crust, including building reservoirs, extracting resources such as coal or oil, and injecting fluids underground for waste disposal or fracking . Most of these earthquakes have small magnitudes. The 5.7 magnitude 2011 Oklahoma earthquake is thought to have been caused by disposing wastewater from oil production into injection wells , and studies point to the state's oil industry as

8455-425: The study of human history as it relates to places and regions , or the study of how places and regions have changed over time. D. W. Meinig , a historical geographer of America, describes many historical regions in his book The Shaping of America: A Geographical Perspective on 500 Years of History . For example, in identifying European "source regions" in early American colonization efforts, he defines and describes

8550-490: The surrounding fracture networks; such an increase may trigger new faulting processes by reactivating adjacent faults, giving rise to aftershocks. Analogously, artificial pore pressure increase, by fluid injection in Earth's crust, may induce seismicity . Tides may trigger some seismicity . Most earthquakes form part of a sequence, related to each other in terms of location and time. Most earthquake clusters consist of small tremors that cause little to no damage, but there

8645-443: The thickness of the brittle layer is only about six kilometres (3.7 mi). Reverse faults occur in areas where the crust is being shortened such as at a convergent boundary . Reverse faults, particularly those along convergent boundaries, are associated with the most powerful earthquakes (called megathrust earthquakes ) including almost all of those of magnitude 8 or more. Megathrust earthquakes are responsible for about 90% of

8740-461: The total seismic moment released worldwide. Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Strike-slip faults, particularly continental transforms , can produce major earthquakes up to about magnitude 8. Strike-slip faults tend to be oriented near vertically, resulting in an approximate width of 10 km (6.2 mi) within

8835-505: The universality of such events beyond Earth. An earthquake is the shaking of the surface of Earth resulting from a sudden release of energy in the lithosphere that creates seismic waves . Earthquakes may also be referred to as quakes , tremors , or temblors . The word tremor is also used for non-earthquake seismic rumbling . In its most general sense, an earthquake is any seismic event—whether natural or caused by humans—that generates seismic waves. Earthquakes are caused mostly by

8930-436: The vast improvement in instrumentation, rather than an increase in the number of earthquakes. The United States Geological Survey (USGS) estimates that, since 1900, there have been an average of 18 major earthquakes (magnitude 7.0–7.9) and one great earthquake (magnitude 8.0 or greater) per year, and that this average has been relatively stable. In recent years, the number of major earthquakes per year has decreased, though this

9025-641: Was the deadliest of the 20th century. The 1960 Chilean earthquake is the largest earthquake that has been measured on a seismograph, reaching 9.5 magnitude on 22 May 1960. Its epicenter was near Cañete, Chile. The energy released was approximately twice that of the next most powerful earthquake, the Good Friday earthquake (27 March 1964), which was centered in Prince William Sound , Alaska. The ten largest recorded earthquakes have all been megathrust earthquakes ; however, of these ten, only

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