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by parita98
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Earth Sciences

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Most earthquakes occur along the edge of the oceanic and continental plates.

When the rocks break, the earthquake occurs. During the earthquake and afterward, the plates or blocks of rock start moving, and they continue to move until they get stuck again.

Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves that make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little. They don't just slide smoothly; the rocks catch on each other. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that's built up.


The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs.

So, why is it hazardous to us humans? First is the effect of the ground shaking. Buildings can be damaged by the shaking itself or by the ground beneath them settling to a different level than it was before the earthquake. Second is the effect of flooding which may occur because of ruptures in dams or levees. Third is the effect of fire which can be started by broken gas lines or power lines.

This earthquake was in San Francisco, California on April 18, 1906 at 13:12:21 UTC with a magnitude of 7.8. This earthquake is one of the most devastating in the history of California. The earthquake and resulting fires caused an estimated 3,000 deaths and $524 million in property loss. Damage in San Francisco resulting only from the earthquake was estimated at $20 million; outside the city, it was estimated at $4 million. The sensible duration of the shaking in San Francisco was about 1 minute.

This was the 1964 Great Alaska Earthquake. It happenend on March 28th 03:36 UTC with a magnitude of 9.2. This great earthquake and ensuing tsunami took 131 lives (tsunami 122, earthquake 9), and caused about $2.3 billion in property loss (in 2013 dollars; equivalent to $311 million in 1964).



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