A foreshock is an earthquake that occurs before a larger earthquake, called the mainshock.
An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. An aftershock is in the same region of the main shock but always of a smaller magnitude. Aftershocks are formed as the crust adjusts to the effects of the main shock.
Earthquake swarms are sequences of earthquakes striking in a specific area within a short period of time. They are different from earthquakes followed by a series of aftershocks by the fact that no single earthquake in the sequence is obviously the main shock, therefore none have notably higher magnitudes than the other. An example of an earthquake swarm is the 2004 activity at Yellowstone National Park.
Sometimes a series of earthquakes occur in a sort of earthquake storm, where 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, and with some of the later earthquakes as damaging as the early ones. Such a pattern occurred in the North Anatolian fault in Turkey in the 20th century.
Tsunami or a chain of fast moving waves in the ocean caused by powerful earthquakes is a very serious challenge for people's safety and for earthquake engineering. Those waves can inundate coastal areas, destroy houses and even swipe away whole towns. This is a danger for the whole mankind.
Unfortunately, tsunamis can not be prevented. However, there are warning systems which may warn the population before the big waves reach the land to let them enough time to rush to safety.we aware of this tsunami
Earthquake-proof buildings are constructed to withstand the destructive force of an earthquake. This depends upon its type of construction, shape, mass distribution, and rigidity. Different combinations are used. Square, rectangular, and shell-shaped buildings can withstand earthquakes better than skyscrapers. To reduce stress, a building's ground floor can be supported by extremely rigid, hollow columns, while the rest of the building is supported by flexible columns inside the hollow columns. Another method is to use rollers or rubber pads to separate the base columns from the ground, allowing the columns to shake parallel to each other during an earthquake.
To help prevent a roof from collapsing, builders make the roof out of light-weight materials. Outdoor walls are made with stronger and more reinforced materials such as steel or reinforced concrete. During an earthquake flexible windows may help hold the windows together so they don’t break.
Colour
Colour or color is a property of light as seen by people. In Commonwealth English, it is spelled “colour” (notice the U), while in American English it is “color” (no U).
The most common colour names are:
"Primary colours" can be mixed to make other colours. Red, yellow, and blue are the three traditional primary colours. The primary colours for television screens and computer monitors are red, green and blue. Printers and paints use magenta, yellow, and cyan as their primary colours; they may also use black. Sometimes this set of colours is simply called red, yellow, and blue.
People who can not see colours or have a distorted sense of colour are called colour blind. Most colour blind people are male.
Colours are sometimes added to food. Food colouring is used to colour food, but some foods have natural colourings, like beta carotene.
When something has no colour, it is transparent. An example is air.
The science of color is sometimes called chromatics, colorimetry, or simply color science.
A translucent material is not the same as a colourless material because it can still have a colour, like stained glass.
Scurvy
Scurvy is a disease (sickness). It is caused by not eating enough vitamin C. But scurvy can be prevented. It has many symptoms. People who have scurvy get spots on their skin, especially on their legs. Their teeth may loosen and/or fall out. They may bleed from the mouth, nose, and gums (mucus membranes). A person with scurvy will look pale and feel sad (see depression). They will not be able to move easily, because their joints hurt.
Scurvy can be easily cured. Oranges and other fruits can restore normal vitamin levels. In the past, sailors more commonly got scurvy due to being unable to access these foods. Fresh fruit could not be kept for long. The main cause of scurvy is lack of fresh fruits and vegetables. It is now uncommon.
At first, a person with scurvy may:
A bit later a person with scurvy may:
When a person gets help for scurvy, they usually get better very quickly. Babies start eating again after one or two days of help. The symptoms get better within seven days.
Eating vitamin C prevents scurvy. How much vitamin C a person needs changes with his or her age and is different for pregnant and lactating women. The following is the Food and Nutrition Board of the National Academy of Sciences, National Research Council's advice on how much vitamin C to eat every day:
Foods with a lot of vitamin C include the following:
Ion
An ion is an electrically charged atom or group of atoms.
It can be made from an atom, or from a group of atoms (molecule). It is "charged" so it will move near electricity. This is because atoms are made of three smaller parts:
An ion has unequal numbers of protons and electrons. Making an ion from an atom or molecule is called "ionization".
The charge on a proton is chosen as +1 (positively charged). The charge on an electron is opposite to the charge on the proton. The charge on the electron is -1 (negatively charged). An atom that is ionized makes two parts, one positive, and one negatively charged. For example, a neutral hydrogen atom has one proton and one electron. Ionizing the atom breaks it into two parts: (1) a positively charged hydrogen ion, H+ (2) a negatively charged electron.
A liquid with ions is called an electrolyte. A gas with lots of ions is called a plasma. When ions move, it is called electricity. For example, in a wire, the metal ions do not move, but the electrons move as electricity. A positive ion and a negative ion will move together. Two ions of the same charge will move apart. When ions move they also make "magnetic fields".
Many ions are colourless. Elements in the main groups in the Periodic Table form colourless ions. Some ions are coloured. The transition metals usually form coloured ions.
In physics, atomic nuclei that have been completely ionized are called charged particles. These are ones in alpha radiation.
Ionization happens by giving atoms high energy. This is done using electrical voltage or by high-energy ionizing radiation or high temperature.
A simple ion is formed from a single atom.
Polyatomic ions are formed from a number of atoms. Polyatomic ions usually consist of all non-metal atoms. But sometimes the polyatomic ion can have a metallic atom too.
Positive ions are called cations. They are attracted to cathodes (negatively charged electrodes). ("Cation" is pronounced "cat eye on", not "kay shun".) All simple metal ions are cations.
Negative ions are called anions. They are attracted to anodes (positively charged electrodes). All simple non-metal ions (except H, which is a proton) are anions.
Transition metals can form more than one simple cation with different charges.
Most ions have a charge of less than 4, but some can have higher charges.
Michael Faraday was the first person to write a theory about ions, in 1830. In his theory, he said what the portions of molecules were like that moved to anions or cations. Svante August Arrhenius showed how this happened. He wrote this in his doctoral dissertation in 1884 (University of Uppsala). The university did not accept his theory at first (he only just passed his degree). But in 1903, he won the Nobel Prize in Chemistry for the same idea.