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    Why So Many Earthquakes Recently? It's Physics
    By News Staff | April 14th 2010 02:00 AM | 15 comments | Print | E-mail | Track Comments
    The earth has four major layers: the inner core, outer core, mantle and crust.  The crust is what we need to think about here and the earth's crust is divided into 'plates' that are like puzzle pieces but are up to 50 miles thick and they are in constant motion in the earth's interior.   These puzzle pieces are tectonic plates and the edges of the plates are called the plate boundaries. The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults.  Most earthquakes are due to pressure that builds up over time and that pressure causes the ground to 'slip' along a geological fault plane on or near a plate boundary. The vibrations that occur when that slip happens create ground motion at the surface that vibrates 

    Here are some terms to understand.

    Focus/Hypocenter - The point where the fault first slips.
    Epicenter - a theoretical point on the earth's surface directly above the focus.
    Fault - a fracture across which slippage (or displacement) has occurred during an earthquake, which may be less than an inch or more than 10 yards in a severe earthquake.
    Magnitude - the energy released during an earthquake, computed from the amplitude of the seismic waves.   We commonly call it the Richter Scale and each whole number on the scale represents an increase of about 30 times more energy released than the previous whole number represents. Therefore, an earthquake measuring 6.0 is about 30 times more powerful than one measuring 5.0.    
    Aftershock - an earthquake of lesser intensity that follows the main earthquake.

    why so many earthquakes

    How do scientists measure magnitude?   In the easiest way imaginable - a simple device called a seismograph.    A seismograph has a base in the ground and a heavy weight that hangs free. When an earthquake causes the ground to shake, the base of the seismograph shakes too, but the hanging weight does not. Instead the spring or string that it hangs from absorbs all the movement and the difference in position between the shaking part of the seismograph and the motionless part is what is recorded.

    seismograph
    A short wiggly line 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.

    Lots of things can cause an earthquake that is not natural at all.   Underground nuclear bomb testing restrictions are easy to enforce, for example, because a nuclear bomb produces seismic waves that can easily be detected, like any large earthquake.

    Dr. Pat Abbott explains an earthquake in action:

    Comments

    Sums it up? What?! The title should just be "The Basic Physics of an Earthquake." The article says nothing about the recent string of activity around the world.

    I'm with anonymous on this one.

    it's the earth fighting back!

    Ummmm....actually it has five major layers. You forgot the lower and upper mantles. It is the consensus among geophysicists that there is no actual mixing going on between the upper and lower mantles but only a thermal exchange. They are, for all intensive purposes, distinct and separate layers.
    Hank
    The USGS disagrees with your assessment that there are five major layers instead.  Obviously I am no expert but, if I am wrong, it is because they are making everyone else in America wrong too.
    I have to confess that the division of the mantle is still controversial among scholars. The problem is we have no way of going down there and directly making measurements. So we extrapolate from seismic data, which admittedly, is open to interpretation.

    But, I'm not disagreeing with the USGS. This is still very much a theory, and I should have stated that. I'm just used to thinking of the upper mantle and lower mantle as being separate because of the area I worked in. But you're right; it hasn't been officially established. So for now, I will concede, that there are just four major layers. : )
    "for all intensive purposes", you mean, "for all intents and purposes". Not to be a grammar troll, but get it right brotha!

    I think what this article tried to say, I could be wrong; was that when force is released in an earthquake there very well could be an equal opposite reaction, for example on the other side of the fault that got "pushed" by the area that slipped. If you move one piece in a tight system it should move other pieces.

    this is a stupid article. It has nothing to do with the title of it! This does not explain why the numbers of earthquakes have inreased.

    The title should just be "The Basic Physics of an Earthquake."

    Hank
    This does not explain why the numbers of earthquakes have inreased.
    Because the number of earthquakes have not increased any more than two-sided coins suddenly have just tails on one side if you get a bunch of tails throws all at once.   You're seeing more of them in a shorter period of time because that's how physics and probability work.   If you take 2010 as your scale, you may want to believe the world is doomed.  If you take the last 10 years, earthquakes have gone down and the last 100, no difference.
    Hank, this is nonsense, and I think you know so. The question is "why so many earthquakes recently?". The article doesn't attempt to explain the recent surge in seismic activity. Neither does your response. You can't shrug yor shoulders and say probability, or physics. There has been a notable increase and there must be a reason. You stretch the reporting period to fit with your notion that things are normal, but they are far from that. Perhaps you can enlighten us as to the specific causes of the RECENT (2010) increases without resorting to mass historical generalisation?

    NB, I do not accept the argument that earthquakes are as random and independent as the toss of the coin, therefore rebuffing your argument. In contrast, evidence shows that seismic activity is inextricably linked to activity of the earth and solar system, much as weighting a coin will make it more likely to return a certain result.

    Hank
    therefore rebuffing your argument.
    It is not an argument, it is science.  You accept science or you do not.   Judging by your name, I think you do not.  You instead choose to believe whatever you want and find supporting evidence to match your beliefs.
    well, sorta shows why the byline was 'news staff' and had no name.
    i think someone was so tired and exhausted they just tossed in 'earthquakes 101' from
    a 'for dummies' book.

    nice drawing, though, don't you think?

    :-)

    logicman
    nice drawing, though, don't you think?
    Circa 1940s unless I miss my guess.

    A short wiggly line means a small earthquake and a long wiggly line that wiggles a lot means a large earthquake.

    If the pen goes off the chart, don't worry.  That's just Big Boy delivering the goods: