Earthquakes?

Question

How can they tell how deep an earthquake is if it happened under ground? And how big it was?

Answer 1

All earthquakes happen underground, more or less.

The Richter scale is a rating based on the amount of energy released by the EQ. Its logarithmic.

Seismographs and other instruments record the energy waves from the quakes. Seismologists and geophysicists use these measurements to find the focus and intensity of the quake.

Go to http://www.usgs.gov for scads of info on EQs and the science behind them.

Answer 2

An Earthquakes is what happens when two blocks of the earth suddenly slip past one another.

The size of an earthquake depends on the size of the fault and the amount of slip on the fault.
They use the seismogram recordings made on the seismographs at the surface of the earth to determine how large the earthquake was. A short wiggly line that doesn't wiggle very much means a small earthquake, and a long wiggly line that wiggles a lot means a large earthquake. The length of the wiggle depends on the size of the fault, and the size of the wiggle depends on the amount of slip.
The size of the earthquake is called its magnitude. There is one magnitude for each earthquake.

Answer 3

You can find the following data's from a seismograph. The arrival time of different waves,the amplitude of different waves,and frequency at different times. By knowing the arrival time of s wave minus p wave in seconds multiplied by 8 will give you the distance of epicenter in k/m.Three reading from different station can be used to locate the focal point,The distance together with maximum amplitude recorded will be used to find the magnitude of earthquake in Richter scale. To gain better knowledge on earthquake and Tsunami visit my web. Be patient to down load it.You can also hear my voice by clicking the speaker symbol.
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Answer 4

Triangulate the time it takes for the waves to arrive at given seismic sensors. I did it years ago but I forget how they come up with the circumference at these points. Anyways where these circles cross is the epicenter.