earthquakes?

Question

what do you guys know about them? please help me find some info for my science essay. ugh i needa do 5 pages!

Answer 1

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph. The moment magnitude of an earthquake is conventionally reported, or the related and mostly obsolete Richter magnitude, with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude 7 causing serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale.

At the Earth's surface, earthquakes manifest themselves by a shaking and sometimes displacement of the ground. When a large earthquake epicenter is located offshore, the seabed sometimes suffers sufficient displacement to cause a tsunami. The shaking in earthquakes can also trigger landslides and occasionally volcanic activity.

In its most generic sense, the word earthquake is used to describe any seismic event—whether a natural phenomenon or an event caused by humans—that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, but also by volcanic activity, landslides, mine blasts, and nuclear experiments.

An earthquake's point of initial rupture is called its focus or hypocenter. The term epicenter means the point at ground level directly above this.
Most naturally occurring earthquakes are related to the tectonic nature of the Earth. Such earthquakes are called tectonic earthquakes. The Earth's lithosphere is a patchwork of plates in slow but constant motion caused by the release to space of the heat in the Earth's mantle and core. The heat causes the rock in the Earth to flow on geological timescales, so that the plates move slowly but surely. Plate boundaries lock as the plates move past each other, creating frictional stress. When the frictional stress exceeds a critical value, called local strength, a sudden failure occurs. The boundary of tectonic plates along which failure occurs is called the fault plane. When the failure at the fault plane results in a violent displacement of the Earth's crust, energy is released as a combination of radiated elastic strain seismic waves, frictional heating of 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 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.[1]

The majority of tectonic earthquakes originate at depths not exceeding tens of kilometers. In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, Deep focus earthquakes may occur at much greater depths (up to seven hundred kilometers). These seismically active areas of subduction are known as Wadati-Benioff zones. These are earthquakes that occur at a depth at which 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.[2]

Earthquakes also often occur in volcanic regions and are caused there, both by tectonic faults and by the movement of magma in volcanoes. Such earthquakes can serve as an early warning of volcanic eruptions.

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 was observed in the sequence of about a dozen earthquakes that struck the North Anatolian Fault in Turkey in the 20th century, the half dozen large earthquakes in New Madrid in 1811-1812, and has been inferred for older anomalous clusters of large earthquakes in the Middle East and in the Mojave Desert.
Small earthquakes occur nearly constantly around the world in places like California and Alaska in the U.S., as well as in Chile, Peru, Indonesia, Iran, the Azores in Portugal, New Zealand, Greece and Japan.[3] Large earthquakes occur less frequently, the relationship being exponential; for example, roughly ten times as many earthquakes larger than magnitude 4 occur in a particular time period than earthquakes larger than magnitude 5. In the (low seismicity) United Kingdom, for example, it has been calculated that the average recurrences are:

an earthquake of 3.7 - 4.6 every year
an earthquake of 4.7 - 5.5 every 10 years
an earthquake of 5.6 or larger every 100 years.
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 because of the vast improvement in instrumentation (not because the number of earthquakes has increased). The 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.[4] In fact, in recent years, the number of major earthquakes per year has actually decreased, although this is likely a statistical fluctuation. More detailed statistics on the size and frequency of earthquakes is available from the USGS.[5]

Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000-km-long, horseshoe-shaped zone called the circum-Pacific seismic belt, also known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate.[6][7] Massive earthquakes tend to occur along other plate boundaries, too, such as along the Himalayan Mountains.

Shaking and ground rupture are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings or other rigid structures. The severity of the local effects depends on the complex combination of the earthquake magnitude, the distance from epicenter, and the local geological and geomorphological conditions, which may amplify or reduce wave propagation. The ground-shaking is measured by ground acceleration.

Specific local geological, geomorphological, and geostructural features can induce high levels of shaking on the ground surface even from low-intensity earthquakes. This effect is called site or local amplification. It is principally due to the transfer of the seismic motion from hard deep soils to soft superficial soils and to effects of seismic energy focalization owing to typical geometrical setting of the deposits.

Ground rupture is a visible breaking and displacement of the earth's surface along the trace of the fault, which may be of the order of few metres in the case of major earthquakes. Ground rupture is a major risk for large engineering structures such as dams, bridges and nuclear power stations and requires careful mapping of existing faults to identify any likely to break the ground surface within the life of the structure.

Earthquakes can cause landslides and avalanches, which may cause damage in hilly and mountainous areas.

Following an earthquake, fires can be generated by break of the electrical power or gas lines. In the event of water mains rupturing and a loss of pressure, it may also become difficult to stop the spread of a fire once it has started.

Soil liquefaction occurs when, because of the shaking, water-saturated granular material temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, as buildings or bridges, to tilt or sink into the liquefied deposits.

Undersea earthquakes and earthquake-triggered landslides into the sea, can cause Tsunamis. See, for example, the 2004 Indian Ocean earthquake.

Earthquakes may result in disease, lack of basic necessities, loss of life, higher insurance premiums, general property damage, road and bridge damage, and collapse of buildings or destabilization of the base of buildings which may lead to collapse in future earthquakes.

This can cause total devastation for those affected as the country may not have the funds for the regeneration of people lives and possessions. An earthquake can ruin someones life forever, only 3% of buildings in kobe, for instance, have earthquake insurance; therefore un-enabling them to get back ont their feet again.

Answer 2

I think it's the frequency with which they are happening, along with the death-toll, that is worrying. Haiti on January 14 (scale - 7); Chile on 27 February (scale - 6.2); Turkey on 8 March (scale 6.2) and Sumatra on 6 April (scale 7.8). Regardless of whether this is perceived as nothing abnormal, the effect on human lives has been devastating. It will only take an earthquake in a densely populated area such as the U.S.A. for some people to wake up. One of the many signs of the end of the age is "great earthquakes, famines and pestilences in various places, and fearful events and great signs from heaven" (Luke 21:11). Needless to say, there have been great earthquakes, famines and pestilences for the last 2,000 years. What demands our attention, from God's point of view, is that despite all the trials and tribulations that will culminate in the end of the age, those who have placed their faith in Christ Jesus as Lord and Saviour, and who stand firm, need not fear. "There will be signs in the sun, moon and stars. On the earth, nations will be in anguish and perplexity at the roaring and tossing of the sea. Men will faint from terror, apprehensive of what is coming on the world, for the heavenly bodies will be shaken. At that time they will see the Son of Man (Jesus Christ) coming in a cloud with power and great glory. When these things begin to take place, stand up and lift up your heads, because your redemption is drawing near" (Luke 21:25-28). I suspect things are going to get an awful lot worse before they start to get better.

Answer 3

They are scary..They come without warning..The higher on the scale the worse it is,,the stronger it is...BUT sometimes we get some that are not high on the scale that last a long time..they are just as bad..
You should not be in open spaces, or near windows, because glass and things can fall on you.
It is a myth to stand in a door way, because things can fall on you...You should go under a bed, table, or bathtub..
Its best to have a safety kit ready if you live in California..Flashlight, water, prescriptions..and a telephone number for the family to call if something happens in your state.

Answer 4

Dont know much but I have been through a few.
They can happen any time of the day. All different strengths. It could be a little shake you barely feel could be one. From what I remember in scholl its the earths plates moving.
Probly not helpful but I tried.
Maybe you can get some helpful infoprmation here at this site:
http://quake.usgs.gov/

Answer 5

you should talk about the northridge earthquake.. that was a pretty big one.. and we always have earthquakes but we don't feel all of them. look on yahoo or something

Answer 6

Hope our help helps you finish soon!

http://en.wikipedia.org/wiki/Earthquakes

Answer 7

Here's a site. (seriously, You could type this question but you can't do a goole search?)

Answer 8

earthquakes are like typhoonshat destroy earth

Answer 9

earthquake happens in california mostly.

Answer 10

http://www.alternativescentral.com/threedaysofdarkness.htm

http://www.alternativescentral.com/healthcrusade.htm