Math Is Fun Forum

Colleges Quotes - I

1. And I think it's that time. And I think if you just step aside and Mr. Romney can kind of take over. You can maybe still use a plane. Though maybe a smaller one. Not that big gas guzzler you are going around to colleges and talking about student loans and stuff like that. - Clint Eastwood

2. Let reverence for the laws be breathed by every American mother to the lisping babe that prattles on her lap - let it be taught in schools, in seminaries, and in colleges; let it be written in primers, spelling books, and in almanacs; let it be preached from the pulpit, proclaimed in legislative halls, and enforced in courts of justice. - Abraham Lincoln

3. There's a level of service that we could provide when we're just at Harvard that we can't provide for all of the colleges, and there's a level of service that we can provide when we're a college network that we wouldn't be able to provide if we went to other types of things. - Mark Zuckerberg

4. With the changing economy, no one has lifetime employment. But community colleges provide lifetime employability. - Barack Obama

5. I've fought against transnational gangs. I took on the biggest banks and helped take down one of the biggest for-profit colleges. I know a predator when I see one. - Kamala Harris

6. I think, my own personal view is there should be higher and higher levels of autonomy; government should not interfere in setting up colleges, in running colleges. The market, the society will decide which is a good university, which is not a good university, rather than government mandating. - N. R. Narayana Murthy

7. Community colleges play an important role in helping people transition between careers by providing the retooling they need to take on a new career. - Barack Obama

8. There's a reasonable amount of traction in college education, particularly engineering, because quite a lot of that is privatized, so there is an incentive to set up new colleges of reasonably high quality. - Azim Premji.

Nauru

Gist

Nauru is a tiny, independent island republic in the South Pacific, known as the world's smallest republic, once rich from phosphate mining but now facing economic and environmental challenges from the mining's devastation, with high rates of obesity, yet possessing a resilient culture and unique language, relying on foreign aid and seeking sustainable development solutions.

Nauru is known for being the world's smallest republic, its history of immense wealth from phosphate mining (leading to extreme prosperity then economic collapse), severe environmental damage, hosting Australian offshore detention centers, and its struggles with obesity and economic sustainability, all while being a unique Pacific island nation with distinct culture and resilience.

Summary

Nauru, officially the Republic of Nauru, formerly known as Pleasant Island, is an island country and microstate in the South Pacific Ocean. It lies within the Micronesia subregion of Oceania, with its nearest neighbour being Banaba (part of Kiribati) about 300 kilometres (190 mi) to the east. Nauru is also known to have one of the highest obesity rates in the world, with around 70% of all adults over 18 being over 100kg (220 lb).

With an area of only 21 square kilometres (8.1 {mi}^{2}; 2,100 ha; 5,200 acres), Nauru is the third-smallest country in the world, larger than only Vatican City and Monaco, making it the smallest republic and island state, as well as the smallest member state of the Commonwealth of Nations by both area and population. Its population of about 10,800 is the world's third-smallest (not including colonies or overseas territories). Nauru is a member of the United Nations, the Commonwealth of Nations, and the Organisation of African, Caribbean and Pacific States.

Settled by Micronesians circa 1000 BCE, Nauru was annexed and claimed as a colony by the German Empire in the late 19th century. After World War I, Nauru became a League of Nations mandate administered by Australia, New Zealand, and the United Kingdom. During World War II, Nauru was occupied by Japanese troops and was bypassed by the Allied advance across the Pacific. After the war ended, the country entered into United Nations trusteeship. Nauru gained its independence in 1968. At various points since 2001, it has accepted aid from the Australian Government in exchange for hosting the Nauru Regional Processing Centre, a controversial offshore Australian immigration detention facility. As a result of heavy dependence on Australia, some sources have identified Nauru as a client state of Australia.

Nauru is a phosphate-rock island with rich deposits near the surface, which allowed easy strip mining operations for over a century. However, this has seriously harmed the country's environment, causing it to suffer from what is often referred to as the "resource curse". The phosphate was exhausted in the 1990s, and the remaining reserves are not economically viable for extraction. A trust established to manage the island's accumulated mining wealth, set up for the day the reserves would be exhausted, has diminished in value. To earn income, Nauru briefly became a tax haven and illegal money laundering centre.

Details

Nauru, island country in the southwestern Pacific Ocean. It consists of a raised coral island located in southeastern Micronesia, 25 miles (40 km) south of the Equator.

The island is about 800 miles (1,300 km) northeast of the Solomon Islands; its closest neighbor is the island of Banaba, in Kiribati, some 200 miles (300 km) to the east. Nauru has no official capital, but government offices are located in the district of Yaren.

Most of Nauru rises somewhat abruptly from the ocean, and there are no harbors or protected anchorages. A fairly fertile but relatively narrow belt encircles the island and surrounds the shallow inland Buada Lagoon. Farther inland, coral cliffs rise to a plateau 100 feet (30 meters) above sea level, with the highest point at about 213 feet (65 meters). The plateau is largely composed of rock phosphate, leached from guano, or bird droppings. The mineral deposit covers more than two-thirds of the island, and its extraction has left irregular, pinnacle-shaped outcrops of limestone that give the landscape a forbidding, otherworldly appearance.

Nauru is the third smallest country in the world.

Nauru’s climate is tropical, with daytime temperatures in the low 80s F (about 28 °C), tempered by ocean breezes. Rainfall, averaging about 80 inches (2,000 mm) annually, is extremely variable, and prolonged droughts occur. The only locally available water is collected from roof catchment systems, and water is imported as ballast on ships returning to Nauru for loads of phosphate. There are no rivers or streams.

Soils are generally poor and highly porous, and the irregular rainfall limits cultivation to the coastal belt and the lagoon’s fringe. Phosphate mining has ravaged the interior of the island, leaving about four-fifths of it uninhabitable and uncultivable. Subsistence crops, consisting mainly of coconut palms, pandanus, bananas, pineapple, and some vegetables, are not adequate to support the population; the land does yield a great variety of plants and trees, however. Nauru is a favorite stopover point for migratory birds, and chickens have been introduced. There was an absence of mammals until rats, mice, cats, dogs, and pigs were also imported.

People

Most of the island’s residents are indigenous Nauruans. There are small numbers of I-Kiribati (Gilbertese), Australians, New Zealanders, Chinese, and Tuvaluans; many members of the latter two groups were recruited as workers by the phosphate industry. Nauruan is the national language. No adequate written grammar of the language has been compiled, and its relationships to other Micronesian languages are not well understood. English is widely spoken. Nauru is considered one of the most Westernized countries in the South Pacific.

Missionization came later to Nauru than to many other Pacific islands. The first Protestant evangelist arrived in 1899 and was followed three years later by the first Roman Catholic missionary. Today more than four-fifths of Nauruans are Christians; more than half the total population is Protestant (mostly members of the Nauru Congregational Church), and one-third is Roman Catholic.

The settlement pattern on the island is dispersed. People are scattered along the coastal zone, and there is one small village, Buada, inland near the lagoon.

Economy

Agriculture (with the exception of coffee and copra plantations along the coastal and lagoon perimeters), fishing, manufacturing, and tourism are of minor value to the overall economy. However, Nauru has an exclusive economic zone extending 200 miles (320 km) offshore. The sale of commercial fishing licenses began to bring in a steady revenue during the 1990s.

Phosphate has been mined on Nauru since 1907. For decades it was Nauru’s main resource and sole export, dominating the island’s economy, and its quality was the highest in the world. The phosphate industry and government services together provided almost all of the island’s salaried employment. For much of the 20th century the phosphate industry was owned and operated by a corporation jointly managed by the British, Australian, and New Zealand governments. The government of independent Nauru gained control of phosphate operations in 1970, and in the 1980s Nauru was for a time one of the wealthiest countries in the world in terms of gross domestic product per capita. Landowners received royalties from the phosphate earnings, and many Nauruans were unemployed by choice. By the late 20th century, however, the phosphate deposits were quickly becoming exhausted, and Nauru experienced a severe drop-off in earnings, leading to the country’s near bankruptcy by the early years of the 21st century. Nauru struggled to develop other resources and find alternative sources of income. However, the country experienced some economic respite late in the first decade of the 2000s when repairs and improvements to mining-related infrastructure expedited the extraction and export of the remaining primary phosphate deposits and allowed the more difficult extraction of secondary phosphate deposits.

In the early 21st century Nauru agreed to temporarily house hundreds of Australia-bound asylum seekers while they awaited the processing of their applications. In exchange, the Australian government provided millions of dollars in aid to Nauru.

Virtually all food, water, and manufactured goods are imported. Australia supplies nine-tenths of Nauru’s imports; far smaller amounts come from New Zealand, Fiji, and Japan. Nigeria receives almost half of Nauru’s exports, and South Korea and Australia combined take another one-third. With the exception of those levied on alcohol and tobacco, there are no import duties. There is no income tax.

Nauru has its own banking system; the Bank of Nauru is wholly owned and operated by the government. The financial sector grew in importance after the 1980s as the island became known as an offshore banking center and tax haven. Beginning in 1999, amid allegations that it was a money-laundering conduit for organized crime and terrorist organizations, the financial sector underwent a series of reforms to increase its transparency. As one consequence of its colonial history, Nauru is within the Australian monetary system, and Australian currency is the country’s legal tender.

Transportation on the island is good. A paved road system links all villages. Surface transportation to other destinations is difficult. Because there are no wharves or natural harbors, passengers and cargo are shuttled by barge between oceangoing vessels and a small artificial anchorage. Most regional and international travel is by air. Nauru’s sole airport is located in Yaren district. In 1970 the country launched its national airline, control of which was transferred in 1996 to a government-owned corporation.

Government and society

Nauru’s constitution, implemented with independence in 1968, calls for broadly phrased fundamental rights and freedoms for individuals and a government that combines parliamentary and presidential systems. The parliament, whose members are elected by Nauruan citizens age 20 and older, has a tenure of three years unless dissolved by a vote of no confidence. It elects the president, who is both head of state and head of government. The president appoints a cabinet from the parliament. In 1999 Nauru became a full member of both the Commonwealth and the United Nations.

The tripartite judicial system comprises a Supreme Court, a District Court, and a Family Court. The Supreme Court, presided over by a chief justice, has both original and appellate jurisdiction. At Nauru’s request, final appeals may be taken to the High Court of Australia.

Basic services in education and health are provided free to all citizens, though services have been reduced as a result of the country’s changing economic fortunes. There is no government social security system. Education is compulsory between ages 6 and 16. The government provides several kindergartens and elementary and secondary schools. The Roman Catholic mission has its own school system at the same three levels. Traditionally, students have gone abroad, mainly to Australia, for higher education.

Additional Information:

Overview

Nauru is an island republic in the Pacific Ocean, 42 kilometers south of the equator and 4,000 kilometers northeast of Sydney, with a total land area of 21 square kilometers. Nauru has a population of approximately 13,000 people.

Political overview

Nauru is one of the world's smallest independent states. Its constitution, adopted upon gaining independence in 1968, established it as a republic with a Westminster-style parliamentary system of government. The President is elected by, and responsible to, the unicameral parliament and is both head of government and head of state.

As there are no political parties in Nauru, all Members of Parliament (MPs) stand as independents. MPs are elected every three years by Nauruan citizens over the age of 20. At its first sitting, where possible, parliament chooses a Speaker, a Deputy Speaker and chairs of committees before proceeding to elect the President from among the remaining members. The President then appoints a minimum of four members of parliament to join him or her in forming a cabinet. On 30 October 2023, His Excellency, David Adeang was appointed as President. Nauru's elections are held every three years, its next elections are due in 2025.

Bilateral relations

Australia and Nauru have a deep, long-standing relationship, underpinned by a shared history and people-to-people links. Australia is Nauru’s largest trade, investment, security and development assistance partner.

In December 2024, Nauru and Australia signed the Nauru-Australia Treaty. The Treaty elevates our long-standing relationship to an integrated partnership which supports Nauru’s economic security and resilience. It underscores Australia and Nauru's shared commitment to delivering Pacific-led solutions to meet our region's challenges.

Under the Treaty, Australia will provide $100 million over five years in budget support and $40 million over five years to support Nauru’s policing and security. The Treaty officially entered into force on 19 September 2025.

In September 2017, Nauru and Australia signed a Memorandum of Understanding on security cooperation which affirmed Australia's position as Nauru's primary security partner. Australia works in close cooperation with Nauru to address domestic and transnational security challenges whilst always having regard to the sovereignty and best interests of Nauru.

In September 2012, Australia established a regional processing centre in Nauru for the purpose of processing asylum seekers' international protection claims. In October 2021, Australia and Nauru signed a Memorandum of Understanding on the Enduring Regional Processing Capability in Republic of Nauru.

People-to-people links

Every year, a number of Australia Award and Australia Award Pacific Scholarships are offered for Nauruans to study abroad at selected Australian and Pacific regional universities.

Nauru participates in Australia's Pacific Australia Labour Mobility (PALM) scheme, connecting workers from Nauru and other Pacific islands with Australian employers experiencing labour shortages, typically in rural and regional Australia.

Nauru participates in Australia’s Pacific Engagement Visa, which offers access to Australian schools, tertiary education, health care and employment market.

Australia and Nauru also enjoy strong diaspora, alumni and professional linkages.

Economic overview

Nauru's economy faces significant constraints common to other small island states. These include its small size, remoteness and limited natural resources outside of fisheries.

Pelagic fish abound in Nauruan waters, but Nauru has yet to establish a substantial fishing industry of its own. Fees from fishing licenses issued to distant water fishing nations are an important source of revenue for Nauru.

Australia contributes financially to, and takes a shared management role in, the Intergenerational Trust Fund for the People of Nauru. The fund aims to provide a future revenue stream for Nauru to supplement domestic revenue in anticipation of current revenue declining over the next 20 years.

Trade and investment

Australia is Nauru's principal import source. Major Australian merchandise exports to Nauru include meat, motor fuel and civil engineering equipment and parts. For more information see the Nauru economic fact sheet.

Skull

Gist

A skull is the bony structure forming the head, protecting the brain and supporting facial features, but it also symbolizes mortality, knowledge (the mind), or danger (skull and crossbones) across cultures, representing the fragility of life or a warning. It consists of cranial bones (braincase) and facial bones, connected by immobile sutures, with the movable jaw (mandible) being a key part.

The rounded brain case surrounds and protects the brain and houses the middle and inner ear structures. In the adult, the skull consists of 22 individual bones, 21 of which are immobile and united into a single unit. The 22nd bone is the mandible (lower jaw), which is the only moveable bone of the skull.

Summary

Skull is a skeletal framework of the head of vertebrates, composed of bones or cartilage, which form a unit that protects the brain and some sense organs. The upper jaw, but not the lower, is part of the skull. The human cranium, the part that contains the brain, is globular and relatively large in comparison with the face. In most other animals the facial portion of the skull, including the upper teeth and the nose, is larger than the cranium. In humans the skull is supported by the highest vertebra, called the atlas, permitting nodding motion. The atlas turns on the next-lower vertebra, the axis, to allow for side-to-side motion.

In humans the base of the cranium is the occipital bone, which has a central opening (foramen magnum) to admit the spinal cord. The parietal and temporal bones form the sides and uppermost portion of the dome of the cranium, and the frontal bone forms the forehead; the cranial floor consists of the sphenoid and ethmoid bones. The facial area includes the zygomatic, or malar, bones (cheekbones), which join with the temporal and maxillary bones to form the zygomatic arch below the eye socket; the palatine bone; and the maxillary, or upper jaw, bones. The nasal cavity is formed by the vomer and the nasal, lachrymal, and turbinate bones. In infants the sutures (joints) between the various skull elements are loose, but with age they fuse together. Many mammals, such as the dog, have a sagittal crest down the centre of the skull; this provides an extra attachment site for the temporal muscles, which close the jaws.

Details

The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate.

In a human, the skull comprises two prominent parts: the neurocranium and the facial skeleton, which evolved from the first pharyngeal arch. The skull forms the frontmost portion of the axial skeleton and is a product of cephalization and vesicular enlargement of the brain, with several special senses structures such as the eyes, ears, nose, tongue and, in fish, specialized tactile organs such as barbels near the mouth.

The skull is composed of three types of bone: cranial bones, facial bones and ossicles, which is made up of a number of fused flat and irregular bones. The cranial bones are joined at firm fibrous junctions called sutures and contains many foramina, fossae, processes, and sinuses. In zoology, the openings in the skull are called fenestrae, the most prominent of which is the foramen magnum, where the brainstem goes through to join the spinal cord.

In human anatomy, the neurocranium (or braincase), is further divided into the calvaria and the endocranium, together forming a cranial cavity that houses the brain. The interior periosteum forms part of the dura mater, the facial skeleton and splanchnocranium with the mandible being its largest bone. The mandible articulates with the temporal bones of the neurocranium at the paired temporomandibular joints. The skull itself articulates with the spinal column at the atlanto-occipital joint. The human skull fully develops two years after birth.

Functions of the skull include physical protection for the brain, providing attachments for neck muscles, facial muscles and muscles of mastication, providing fixed eye sockets and outer ears (ear canals and auricles) to enable stereoscopic vision and sound localisation, forming nasal and oral cavities that allow better olfaction, taste and digestion, and contributing to phonation by acoustic resonance within the cavities and sinuses. In some animals such as ungulates and elephants, the skull also has a function in anti-predator defense and sexual selection by providing the foundation for horns, antlers and tusks.

Additional Information:

Overview

What is the skull?

Your skull is the part of your skeleton that holds and protects your brain. It also holds or supports several of your main sensory organs, like your eyes, ears, nose, tongue and more. The skull’s medical name is the cranium.

When you’re born, your skull is mostly formed but not quite complete. Some parts of it, called fontanelles, are softer and more flexible. You can see an example of this in the soft spot at the top of an infant’s head. The fontanelles allow your brain and skull to grow and develop.

There are also places where the left and right sides of a bone (like the parietal bone) or multiple bones join. Those are called sutures. These can change throughout your lifetime, even well into adulthood. Some sutures fuse solid while you’re an infant. Others may not fuse until your 60s.

Function:

What does the skull do?

Your skull has two main jobs:

* Protection. The bony structure of your skull protects your brain and critical sensory organs like your eyes and ears.
* Structure. Your skull is what gives your face and head their shape. It has many attachment points for muscles to anchor to. It’s one of the most important things that determines what your face looks like.

Anatomy:

What are the parts of the skull?

Your skull sits at the top of your spinal column, inside your neck. While it might seem like your skull is just one structure, there are two distinct parts of it. They are the:

* Cranial vault (neurocranium or calvarium). This surrounds and protects your brain.
* Facial skeleton (viscerocranium). This supports and holds the various parts of your face.

Cranial vault anatomy

This part of your skull consists mainly of the calvarium. That includes the:

* Frontal bone. This is a single, seamless bone. It gives your forehead its structure.
* Sphenoid bone. This is a single bone below and in front of your brain, but behind the bones making up your face. It also forms part of the lower rear of your eye sockets.
* Ethmoid bone. This is a single bone that fills in a heart-shaped, hollow space in the sphenoid bone at the lower front of your brain.
* Temporal bones. There are two of these bones, one on each side. Each has a small opening where your ear canal passes through the skull.
* Parietal bones. These are a pair of bones that join together at a seam called the sagittal suture. They form the upper middle and upper back of your skull.
* Occipital bone. This is a single seamless bone at the lower back of your skull.

Facial skeletal anatomy

The facial skeleton is at the front of your skull. It’s a group of bones that support and give your face its structure. The bones of this part of your skull are:

* Nasal bones. These form the bridge of your nose. They overlap slightly with the maxilla and the forward part of the ethmoid bone.
* Vomer. This bone is like the floor of the nasal cavity space right behind your nose.
* Lacrimal bones. These form the central-lower inside portion of your eye socket.
* Palatine bones. These are a small section of the bottom of your eye socket’s interior.
* Zygomatic bones. These form the outer lower edge of your eye socket.
* Maxilla. This single bone forms the central part of your cheekbones on both sides. It also is what makes up the central-lower-forward part of your eye socket. It also makes up your upper jaw. It overlaps slightly with the forward part of the ethmoid bone.
* Mandible. This single bone makes up your lower jaw. It’s the only bone of your skull that moves.

Conditions and Disorders:

What are the common conditions and disorders that affect the skull?

Your skull is prone to a wide range of conditions, and many of them are congenital. That means you have the condition when you’re born. Examples of congenital skull conditions include:

* Anencephaly
* Apert syndrome
* Carpenter syndrome
* Cleidocranial dysplasia
* Craniosynostosis
* Crouzon syndrome
* Encephalocele
* Goldenhar syndrome
* Hemifacial microsmia
* Microcephaly
* Micrognathia
* Pfeiffer syndrome
* Prognathism
* Scaphocephaly

There are also several conditions and injuries that you can develop at any time in life that affect your skull. Examples include:

* Temporomandibular joint disorders
* Jaw cysts and tumors, some of which can be jaw cancer
* Dental trauma, including a dislocated jaw or broken jaw
* Skull fractures and/or related concussions and traumatic brain injuries (TBIs)

Common signs or symptoms of skull conditions

The common signs and symptoms of skull conditions vary widely. Congenital skull conditions usually cause differences in skull appearance and/or development. That can cause distinctive facial or head appearances.

Non-congenital skull conditions can cause the following:

* Head pain, especially headaches
* Jaw popping or jaw pain
* Brain symptoms, like confusion or coma
* Bruising, often with specific patterns like raccoon eyes (a key sign of a skull fracture)

Common tests to check the skull

Diagnostic imaging tests are the main way to diagnose skull conditions. These include:

* X-rays, including dental x-rays
* CT scans
* MRI

Providers who suspect congenital conditions that affect your skull often recommend genetic testing. It can detect specific genetic variations that could help providers find the right diagnosis.

Other tests are possible, depending on your symptoms, health history and other factors. Your healthcare provider is the best person to tell you what tests they recommend and why.

What are some common treatments for skull conditions?

The treatments for skull conditions depend on which condition you have. Your health, personal history and circumstances can also be factors. Ask your healthcare provider about the treatment options for your specific case.

College Quotes - V

1. My father was a trained accountant, a BCom from Sydenham College and a self-taught violinist. In the 1920s, when he was in his teens, he heard a great violinist, Jascha Heifetz, and he was so inspired listening to him that he bought himself a violin, and with a little help from an Italian teacher, he learned to play it. - Zubin Mehta

2. The goal of my University education was to get into a medical college and equip myself to run a hospital in Kumbakonam left behind by my father, M.K. Sambasivan, who died at a young age in 1936. - M. S. Swaminathan

3. I dropped out of college before graduation. I opted to begin work as an actress. - Sharmila Tagore

4. A coach, especially at a college level - much more at a college or high school level, than at a pro level - you're more of a teacher than an actual coach. - Matthew McConaughey

5. When I was in Class XI, I started preparing for medical college, and after that, the Miss India pageant. - Manushi Chhillar

6. I didn't play soccer; I played that other football in grade school through college. - Joe Biden

7. I was born in Harlem, raised in the South Bronx, went to public school, got out of public college, went into the Army, and then I just stuck with it. - Colin Powell

8. I went to Moorehouse College. There was no track and field there. - Edwin Moses

9. I wanted to go to medical school. But, I never got a college scholarship. - Edwin Moses.

Earthquake

Gist

What is an earthquake? An earthquake is the sudden release of strain energy in the Earth's crust, resulting in waves of shaking that radiate outwards from the earthquake source. When stresses in the crust exceed the strength of the rock, it breaks along lines of weakness, either a pre-existing or new fault plane.

Earthquakes are primarily caused by geological faults, but also by volcanism, landslides, and other seismic events. Significant historical earthquakes include the 1976 Tangshan earthquake in China, with over 300,000 fatalities, and the 1960 Valdivia earthquake in Chile, the largest ever recorded at 9.5 magnitude.

Summary

An earthquake is any sudden shaking of the ground caused by the passage of seismic waves through Earth’s rocks. Seismic waves are produced when some form of energy stored in Earth’s crust is suddenly released, usually when masses of rock straining against one another suddenly fracture and “slip.” Earthquakes occur most often along geologic faults, narrow zones where rock masses move in relation to one another. The major fault lines of the world are located at the fringes of the huge tectonic plates that make up Earth’s crust.

Little was understood about earthquakes until the emergence of seismology at the beginning of the 20th century. Seismology, which involves the scientific study of all aspects of earthquakes, has yielded answers to such long-standing questions as why and how earthquakes occur.

About 50,000 earthquakes large enough to be noticed without the aid of instruments occur annually over the entire Earth. Of these, approximately 100 are of sufficient size to produce substantial damage if their centres are near areas of habitation. Very great earthquakes occur on average about once per year. Over the centuries they have been responsible for millions of deaths and an incalculable amount of damage to property.

The nature of earthquakes:

Causes of earthquakes

Earth’s major earthquakes occur mainly in belts coinciding with the margins of tectonic plates. This has long been apparent from early catalogs of felt earthquakes and is even more readily discernible in modern seismicity maps, which show instrumentally determined epicentres. The most important earthquake belt is the Circum-Pacific Belt, which affects many populated coastal regions around the Pacific Ocean—for example, those of New Zealand, New Guinea, Japan, the Aleutian Islands, Alaska, and the western coasts of North and South America. It is estimated that 80 percent of the energy presently released in earthquakes comes from those whose epicentres are in this belt. The seismic activity is by no means uniform throughout the belt, and there are a number of branches at various points. Because at many places the Circum-Pacific Belt is associated with volcanic activity, it has been popularly dubbed the “Pacific Ring of Fire.”

A second belt, known as the Alpide Belt, passes through the Mediterranean region eastward through Asia and joins the Circum-Pacific Belt in the East Indies. The energy released in earthquakes from this belt is about 15 percent of the world total. There also are striking connected belts of seismic activity, mainly along oceanic ridges—including those in the Arctic Ocean, the Atlantic Ocean, and the western Indian Ocean—and along the rift valleys of East Africa. This global seismicity distribution is best understood in terms of its plate tectonic setting.

Natural forces

Earthquakes are caused by the sudden release of energy within some limited region of the rocks of the Earth. The energy can be released by elastic strain, gravity, chemical reactions, or even the motion of massive bodies. Of all these the release of elastic strain is the most important cause, because this form of energy is the only kind that can be stored in sufficient quantity in the Earth to produce major disturbances. Earthquakes associated with this type of energy release are called tectonic earthquakes.

Details

An earthquake, also called 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 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 weapons testing. The initial point of rupture 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 volcanism, landslides, and other seismic events.

Significant historical earthquakes include the 1976 Tangshan earthquake in China, with over 300,000 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 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 the universality of such events beyond Earth.

Additional Information:

What is an Earthquake?

An earthquake is an intense shaking of Earth’s surface. The shaking is caused by movements in Earth’s outermost layer.

Why Do Earthquakes Happen?

Although the Earth looks like a pretty solid place from the surface, it’s actually extremely active just below the surface. The Earth is made of four basic layers: a solid crust, a hot, nearly solid mantle, a liquid outer core and a solid inner core.

The solid crust and top, stiff layer of the mantle make up a region called the lithosphere. The lithosphere isn’t a continuous piece that wraps around the whole Earth like an eggshell. It’s actually made up of giant puzzle pieces called tectonic plates. Tectonic plates are constantly shifting as they drift around on the viscous, or slowly flowing, mantle layer below.

This non-stop movement causes stress on Earth’s crust. When the stresses get too large, it leads to cracks called faults. When tectonic plates move, it also causes movements at the faults. An earthquake is the sudden movement of Earth’s crust at a fault line.

The location where an earthquake begins is called the epicenter. An earthquake’s most intense shaking is often felt near the epicenter. However, the vibrations from an earthquake can still be felt and detected hundreds, or even thousands of miles away from the epicenter.

How Do We Measure Earthquakes?

The energy from an earthquake travels through Earth in vibrations called seismic waves. Scientists can measure these seismic waves on instruments called seismometer. A seismometer detects seismic waves below the instrument and records them as a series of zig-zags.

Scientists can determine the time, location and intensity of an earthquake from the information recorded by a seismometer. This record also provides information about the rocks the seismic waves traveled through.

Do Earthquakes Only Happen on Earth?

Earthquake is a name for seismic activity on Earth, but Earth isn’t the only place with seismic activity. Scientists have measured quakes on Earth's Moon, and see evidence for seismic activity on Mars, Venus and several moons of Jupiter, too!

NASA’s InSight mission took a seismometer to Mars to study seismic activity there, known as marsquakes. On Earth, we know that different materials vibrate in different ways. By studying the vibrations from marsquakes, scientists hope to figure out what materials are found on the inside of Mars.

InSight is collecting tons of information about what Mars is like under the surface. These new discoveries will help us understand more about how planets like Mars—and our home, Earth—came to be.