85-536: The Bi-State Vietnam Gold Star Twin Bridges , (usually referred to as simply The Twin Bridges , despite differences in their widths), are located in Henderson County, Kentucky and connect Henderson, Kentucky , and Evansville, Indiana , along U.S. Route 41 (US 41), two miles (3.2 km) south of the current southern terminus of Interstate 69 (I-69). The two bridges average more than 40,000 vehicles crossings
170-485: 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
255-729: 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
340-513: A day across the Ohio River . The northbound bridge opened to traffic on July 4, 1932. The southbound bridge opened on December 16, 1965, but will be decommissioned after the completion of the Interstate 69 Ohio River Bridge about 1.6 miles (2.6 km) east, which is scheduled to be completed in 2031. The more historic northbound bridge will remain in service for US-41 as a two way bridge. Both of
425-571: 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
510-488: 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
595-475: 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
680-530: A household in the county was $ 35,892, and the median income for a family was $ 44,703. Males had a median income of $ 33,838 versus $ 22,572 for females. The per capita income for the county was $ 18,470. About 9.70% of families and 12.30% of the population were below the poverty line , including 17.20% of those under age 18 and 10.10% of those age 65 or over. 37°48′N 87°34′W / 37.80°N 87.57°W / 37.80; -87.57 Earthquake An earthquake – also called
765-474: A nickel for pedestrians. The toll was removed on March 20, 1941. By the mid-1950s, it became apparent that the single two-lane bridge was outmoded. With it came plans for a second span to address congestion. This span opened to traffic in July 1965; at this point, the original span was closed for much needed repairs. It reopened to northbound-only traffic in 1966. On May 31, 1969, the bridges were officially renamed as
850-603: 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,
935-650: A portion of northern Tennessee . Their intention was to establish a 14th colony to be called Transylvania Colony . To help attract people to purchase land and populate the region, Henderson & Co. hired pioneer, explorer, woodsman, and frontiersman Daniel Boone to lead settlers through Cumberland Gap and direct woodsmen to cut the Wilderness Road through the Kentucky forest. However, the Continental Congress declined to act on Transylvania Co.'s petition without
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#17328523249631020-730: 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
1105-499: A sixth, before taking his own life. The mass murder is the worst in the history of Henderson County, surpassing the triple homicides that took place in 1799 and 1955. According to the United States Census Bureau , the county has a total area of 466 square miles (1,210 km ), of which 437 square miles (1,130 km ) is land and 30 square miles (78 km ) (6.4%) is water. The county's northern border with Indiana
1190-592: A visitor. Moses Stegall later tracked down the brothers, and killed Micajah Harpe, cutting off his head and hanging it in a tree as a warning to other outlaws. Wiley Harpe was captured and hanged four years later in Mississippi. During the 19th century, a cultivar of dark tobacco raised in Henderson County became very popular in Great Britain and continental Europe. Henderson became the largest dark-tobacco market in
1275-515: Is a county in the U.S. state of Kentucky . The county is located in western Kentucky on the Ohio River across from Evansville, Indiana . As of the 2020 census , the population was 44,793. Its county seat is Henderson . The county was formed in 1798 and named for Richard Henderson who purchased 17,000,000 acres (69,000 km ) of land from the Cherokee , part of which would later make up
1360-515: 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
1445-410: 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
1530-473: 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
1615-400: 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
1700-625: Is mostly formed by the Ohio River , though some of the county lies north of the river. As of the census of 2000, there were 44,829 people, 18,095 households, and 12,576 families residing in the county. The population density was 102 per square mile (39/km ). There were 19,466 housing units at an average density of 44 per square mile (17/km ). The racial makeup of the county was 91.16% White , 7.10% Black or African American , 0.16% Native American , 0.33% Asian , 0.01% Pacific Islander , 0.39% from other races , and 0.86% from two or more races. Hispanic or Latino people of any race were 0.97% of
1785-532: 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
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#17328523249631870-423: 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,
1955-410: 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
2040-467: 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
2125-501: 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
2210-400: 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
2295-587: 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
2380-630: The Bi-State Vietnam Gold Star Bridges in remembrance to the men who died in the Vietnam War . In 1983, the northbound span was renovated. In 1990, the southbound span was repainted. In 2007, the Bi-State Vietnam Gold Star Bridges underwent $ 22 million in renovations involving maintenance and painting. Kentucky Governor Ernie Fletcher directed that at least two lanes in each direction should remain open during
2465-490: 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
2550-426: 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
2635-413: 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
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2720-541: 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,
2805-433: 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
2890-547: The 5.2 earthquake hit, Kentucky Transportation Cabinet spokesman Keith Todd said that such a quake "would not be expected to cause damage to well-engineered structures." However, both bridges were inspected as a precaution. Aside from earthquakes, another particular concern is the presence of the two piers holding the three central spans on each bridge inside the river transit lanes. The bridges have been struck at least once every 5 years on average. The bridges are located at 37°54'15" N, 87°33'02" W. Although they are not currently on
2975-407: The Bi-State Vietnam Gold Star Bridges are cantilever bridges. The northbound bridge stands 100 feet (30 m) over the Ohio River with a main span of 720 feet (220 m), with the steel gridwork extending 100 feet (30 m) above the driving surface. The southbound span has a main span of 600 feet (180 m). An unusual fact about the bridges is that they are entirely within Kentucky. Although
3060-631: The Bi-State Vietnam Gold Star Bridges was the second of three bridges built in Henderson County in 1932, a building novelty during the Great Depression . It was originally named the John James Audubon Bridge , or Audubon Memorial Bridge , after John James Audubon , who lived in Henderson in the 1810s. It was built by notable bridge designer Ralph Modjeski . The 5,395-foot (1,644 m) long cantilever bridge cost $ 2.4 million to build, with
3145-399: 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
3230-481: 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,
3315-556: The Henderson Grant land to lay out a town and mark off land for the respective investors. The location they selected for the town was the site of an existing settlement that sat high above the Ohio River called Red Banks. The new town was subsequently named Henderson . Henderson County was created out of Christian County in December 1798, and was officially established in May 1799. Henderson
3400-719: The I-69 ORX is built. Like with the Clark Memorial Bridge and the Ohio River Bridges Project upriver in Louisville , Indiana and Kentucky also want to avoid a situation where the US ;41 bridges become a toll free alternative for long-distance traffic. 37°54′15″N 87°33′2″W / 37.90417°N 87.55056°W / 37.90417; -87.55056 Henderson County, Kentucky Henderson County
3485-486: The Ohio River forms most of the border between Kentucky and Indiana , the state border is based on the course of the river as it existed when Kentucky became a state in 1792, when what would be Indiana was part of the unorganized Northwest Territory . Due to the New Madrid earthquake of 1812, the river changed course to the south, leaving the land where the bridges cross the river within Kentucky. The northbound span of
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3570-715: The Ohio from Henderson, which now forms Union Township, Vanderburgh County, Indiana , was the subject of Handly's Lessee v. Anthony , a U.S. Supreme Court case in 1820. An area known as "Green River Island" is part of Kentucky, even though it is on the Indiana side of the Ohio River. The Ellis Park Race Course is located there. A workplace shooting occurred at an Atlantis Plastics factory in Henderson , Kentucky , United States on June 25, 2008. The gunman, 25-year-old Wesley Neal Higdon, shot and killed five people and critically injured
3655-558: 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
3740-463: 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
3825-416: The bridge, taking 40 minutes to do so and a two-mile (3.2 km) parade lasting two hours also celebrated the occasion. More than 100,000 visitors attended the celebration and 111,091 vehicles crossed the bridge in its first two days of operation, creating delays of up to two hours to go from Henderson to Evansville. Originally, crossing the bridge required paying a toll, usually 30 to 35 cents for cars, and
3910-404: 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
3995-555: 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
4080-458: The consent of Virginia and North Carolina , which laid claim to the disputed lands. In December 1778, Virginia's Assembly declared the Transylvania claim void. In compensation, Henderson and his partners received a grant of 200,000 acres on the Ohio River below the mouth of Green River . In 1797, the surviving Transylvania Company investors and heirs sent Samuel Hopkins and Thomas Allin to
4165-591: The construction. The maintenance ended in the middle of 2008. The last time the northbound bridge was rehabbed was in 1983. After the I-35W Mississippi River bridge collapsed in Minneapolis, Minnesota, in August 2007, officials stated that the main threat to the safety of the Bi-State Vietnam Gold Star Bridges would be a "catastrophic earthquake ". This statement was made before the 2008 Illinois earthquake . After
4250-645: The county. Henderson County lies within the West Kentucky Coal Field area. It is also part of the Evansville , IN -KY Metropolitan Statistical Area . The Transylvania Co., also known as Richard Henderson & Co., in 1775 purchased from the Cherokees a large swath of wilderness between the Kentucky River and Cumberland River , encompassing approximately half of what would become Kentucky as well as
4335-521: 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
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#17328523249634420-678: 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
4505-439: 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
4590-543: 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
4675-403: 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
4760-426: 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
4845-498: 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,
4930-458: 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
5015-462: 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
5100-411: 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
5185-418: 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
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#17328523249635270-536: 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,
5355-424: The federal government paying half, with the states of Kentucky and Indiana paying the remainder. The dedication ceremony featured Kentucky Governor Ruby Laffoon and Indiana Governor Harry G. Leslie shaking hands with one another, as 22 military planes under the command of Jimmy Doolittle flew overhead with cannon fire and boat whistles in the distance celebrating the occasion. A flotilla of boats passed under
5440-417: 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
5525-406: 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
5610-410: 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
5695-471: 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
5780-622: The list, they have been ruled eligible for inclusion in the National Register of Historic Places . The Kentucky Transportation Cabinet (KYTC) plans to reduce the US 41 bridges from two to one, which would be toll-free for local traffic, once the Interstate 69 Ohio River Crossing (I-69 ORX) project is complete. Residents and local officials in Henderson and Evansville favor keeping both US 41 bridges without tolls, but state officials have stated that it would not be financially viable to maintain both US 41 bridges without tolls after
5865-402: 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
5950-414: 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
6035-403: The population. There were 18,095 households, out of which 32.40% had children under the age of 18 living with them, 54.40% were married couples living together, 11.60% had a female householder with no husband present, and 30.50% were non-families. 26.40% of all households were made up of individuals, and 10.60% had someone living alone who was 65 years of age or older. The average household size
6120-518: 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
6205-437: 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
6290-522: 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
6375-464: 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
6460-422: 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
6545-490: 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
6630-443: 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
6715-461: 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
6800-505: 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
6885-436: 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
6970-404: The world, generating considerable wealth in Henderson County. Around 1880, Henderson had 17 stemmeries in the city and 18 in the county. Stemmeries were where tobacco was stripped from its stem and made ready for use. However, tobacco production in Henderson County declined through the 20th century and early 21st century, with few farmers still raising the labor-intensive crop. A peninsula across
7055-401: Was 2.43 and the average family size was 2.93. In the county, the population was spread out, with 24.60% under the age of 18, 8.40% from 18 to 24, 30.00% from 25 to 44, 23.90% from 45 to 64, and 13.10% who were 65 years of age or older. The median age was 37 years. For every 100 females, there were 93.60 males. For every 100 females age 18 and over, there were 90.60 males. The median income for
7140-493: Was designed as its county seat. The county initially encompassed a larger area than it does today. It was reduced in size when Hopkins County was formed in 1806, when Union County was established in 1811, and when Webster County was established in 1860. In August 1799, serial killers Micajah and Wiley Harpe came to the house of Moses Stegall, near what is now Dixon in Webster County, and murdered his wife, child, and
7225-626: 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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