There Are Earthquakes Every Day
The Earth has been having earthquakes ever since it became solid and the crust was formed. Earthquakes have reportedly caused over 3.5 million known recorded deaths and have wreaked destruction throughout the world. Hundreds if not thousands of earthquakes happen each day around the world, but they are usually undetected.
I decided to do this lens on earthquakes because I wanted to learn more about them myself and making a lens is a great way to learn more about something. Thank you for reading this and I hope you enjoy my lens about earthquakes.
Earthquakes Bring Changes
Earthquakes have always been a threat to people, especially those who live in areas where earthquakes are common, and they will continue to be a threat Although earthquakes and other natural disasters often cause death, ruin people's property, and cause destruction to the the surface of the Earth, there are formations that probably wouldn't have been created had the earthquake not occurred. If it weren't for earthquakes and other natural disasters, the earth would always be the same. Earthquakes aid the making of ocean basins, mountains, and other formations and the Earth undergoes many positive changes due to these events.
US Geological Survey Website
- Welcome to the USGS - U.S. Geological Survey
Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment.
Why Do Earthquakes Happen
What causes seismicity (earthquake activity)? Why do earthquakes occur in the places that they do? How do they cause damage? Can earthquakes be predicted? Is it possible to prevent earthquakes from happening?
Earthquakes cannot be exactly predicted nor can they be prevented. Scientists know that certain areas on Earth are prone to earthquakes or seismic activity because the area has experienced seismicity in the past. But there is no way to predict exactly when an earthquake will happen. Rather than using the word "prediction", they use the word "probability" because in seismic areas there is a high probability that an earthquake will occur there since they have occurred in the past.
Long term earthquake predictions are based on the identification of seismic zones and the recurrence interval (average time in between earthquakes). The basic premise of a long-term earthquake prediction is that in an area where there have been earthquakes in the past will most likely experience earthquakes in the future. Seismic zones are therefore regions of higher seismic risk. Not to say that a disastrous earthquake cannot happen out of a seismic zone, but the likelihood is a lot less.
Likewise, there is no way to prevent earthquakes from occurring. There are clues, however, to imminent earthquakes and scientists continue to try and understand them so that people can be warned and preventative measures may be taken such as enacting building codes and other measures of protection.
Epicenter And Hypocenter
The hypocenter or focus of the earthquake is the location within the Earth where the rock ruptures and slips, or the place where an explosion takes place. The spot directly above the hypocenter or focus is the epicenter. The movement or formation of faults generally is the cause of most destructive earthquakes, so typically the hypocenter of an How do faults develop? A fault is a fracture on which slipping or sliding of rock occurs. The rock mass above a sloping fault plane is described as the hanging wall. This was first encountered by 19th century miners in mine tunnels because it hung over their heads. The mass of rock below the fault plane was described as the foot wall, as it was beneath their feet. The direction in which the rock masses slipped on these faults was specified by the direction in which the hanging wall moved in relation to the foot wall, and these terms are still used today.
Normal faults are formed in response to the extension or stretching of Earth's crust. Reverse faults form in response to squeezing or compression and shortening of the Earth's crust. Strike-slip faults form where one block of crust slides past another laterally. The measurement between the Earth's offset by a fault is called the displacement. That is the amount of slip on the fault.
The Earth Has Faults
Faults in the Earth are found almost everywhere, but most of them will not likely produce earthquakes. Faults that have recently moved or are likely to move are called active faults. If they generate earthquakes, they are usually called earthquake faults. Faults that have not moved in the distant past and will not likely move in the future are called inactive faults. Some faults have not had any activity for billions of years. The intersection between a fault and the ground surface is called a fault trace or fault line. In locations where an active normal fault or reverse fault intersects with the ground, movement on the fault displaces the surface and generates a step-like formation called a fault scarp.
A seismograph is the machine or an instrument that records that systematically records the ground motion from an earthquake happening anywhere on Earth. It is measured by using two basic configurations: one measures vertical or up and down motion, the other measures horizontal or back and forth motion. These machines are generally placed on bedrock in areas where they are sheltered, kept away from any noises or other types of motion. The read-out provided by this machine is called a seismogram.
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The Richter Scale was designed for measuring the magnitude of California earthquakes, not earthquakes in other locations.
Magnitude - What Does It Mean?
What does magnitude mean you ask? Magnitude is a number which indicates the relative size of an earthquake. Magnitude is determined by the measurement of the maximum amplitude of ground motion recorded by a seismograph. Amplitude of ground motion, simply put, just means the amount of up and down motion or back and forth motion by the ground. The Richter Scale only works well for shallow earthquakes that are near the seismograph so scientists now use another method for measuring earthquake intensity called the moment magnitude scale. The moment magnitude scale provides the most accurate representation of the size of an earthquake. The moment magnitude is calculated by measuring the amplitude of several seismic waves, determine the area of the fault that slipped as well as the amount of slippage that occurred. This method works very well for large scale earthquakes. Sometimes the magnitude may change of an earthquake after a few days because of certain variables.
All magnitude scales are said to be logarithmic which means that an increase of one unit of magnitude represents a tenfold increase in the maximum ground motion. Therefore, an earthquake that is a magnitude 8 will result in ground motion that is 10 times greater than a magnitude 7 earthquake and about 1000 times greater than an earthquake with a magnitude of 5. There has been terms put in place by scientists to make this much easier: great, major, strong, moderate, light, and minor.
Where Earthquakes Usually Happen
Earthquakes occur in places called seismic zones or seismic belts. Most of these are near plate boundaries. When an earthquake occurs away from a plate boundary it is called an intraplate earthquake. About 80% of all earthquakes happen at plate boundaries that surround the Pacific Ocean. Earthquakes also occur at different depths. They are distinguished as follows: shallow earthquakes occur at the top 20 km of the surface of Earth; intermediate earthquakes happen at about 20 to 300 km; deep earthquakes take place at about 660 km deep. It is not possible to occur any deeper than that because rock that deep cannot rupture or change in a way that will cause shock waves.
There is seismicity at divergent plate boundaries. A divergent plate boundary (mid-ocean ridge) is where two oceanic plates are moving away, spreading apart, diverging from each other. They are usually segmented by transform faults. Therefore two kinds of faults develop at divergent boundaries.
Convergent plate boundary seismicity is vary different. Several types of earthquakes can take place at convergent plate boundaries. A convergent plate boundary is where two continents are moving together, converging. One of the plates is subducting, or basically being sucked under or pushed down, underneath the other plate, into a trench.
Transform plate boundaries are where two plates are sliding past each other, such as California's San Andreas Fault. These earthquakes are generally fairly shallow in depth. The motion felt is called a strike-slip motion, and they are not smooth, but happen in jerking motions.
What They Used To Think
In ancient times, the cultures believed that earthquakes were caused by such things as a giant animal or God. Scientific study suggests rather that earthquakes or seismicity occurs because of several factors, including:
The sudden formation of a new fault (a fracture on earth where sliding occurs);
A sudden slip on an existing fault;
A sudden change in the arrangement of the atoms in the minerals of the rocks;
Movement of magma in a volcano;
A volcanic explosion;
A giant landslide;
An impact by a meteorite;
An underground nuclear bomb test.
Yet Even More...
- Take Me to the Earthquake Education Store
Books, videos, earthquake survival kits and more!
Being prepared for a natural disaster is important. I found this disaster preparedness kit for five people for under $200.00. This was the best deal.
Earh Points By Taking A Poll
Love your family, be prepared for a natural disaster. It is a good idea to have (at least) a 30-day supply of drinking water for each person.
Are you prepared for a natural disaster?
Have you ever been in an earthquake?
Some Earthquake PicturesClick thumbnail to view full-size
In conclusion, we know that earthquakes occur in seismic belts or seismic zones. Seismic zones are narrow areas of the Earth where earthquakes happen. Earthquakes don't occur at random depths in the Earth, they're distinguished in three categories: shallow, intermediate, and deep. Most earthquakes happen when rock breaks during faulting. A fault is a fracture on which sliding happens. The place where it occurs is called the hypocenter and the point directly above it is the epicenter. Active faults are faults on which movement is likely. Inactive faults are faults where activity has not happened for a long time, but can still be recognized due to the displacement that occurred. Displacements may yield a fault scarp. Displacement is the amount of movement. The elastic rebound theory tells us that during fault formation, rock elastically bends, then cracks. These cracks eventually touch to form a throughgoing rupture on which sliding occurs. At this point, the rock breaks, vibrates, and that generates an earthquake. Faults exhibit stick-slip behavior, moving in sudden increments. The deeper the earthquake, the more intense it is. There are different types of earthquakes, depending on where it happens, whether it is at a divergent plate boundary, a convergent plate boundary, a transform plate boundary, continental rifts, collision zones or intraplate earthquakes. Also that the ground can undergo liquefaction. This occurs in places where there is wet sediment. The sediment tries to settle together but because the spaces between them are filled with water, the pressure in the spaces increases and pushes them apart. This causes the wet silt or sand to turn to a slurry. This is liquefaction. Earthquakes can cause major damage, even tsunamis to happen, such as what happened in Japan recently. Earthquakes cannot be prevented, nor can they be predicted, although we know certain areas are prone to earthquakes so precautionary measures can be taken to prevent as much damage from occurring.
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