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  • Posted June 16, 2010 by
    Atlanta, Georgia
    This iReport is part of an assignment:
    Oil disaster views and solutions

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    Oil Spill and Earthquakes - Some Questions Answered


    Recently I was posed a few questions by a fellow iReporter, anne48503. After replying to her, I decided to make my responses public in the hope of clearing up some questions others might have as well:


    Q: Yesterday we had many small earthquakes or strong aftershocks in California. When I read ireports they said the first one was rolling like feeling and the second was like a thud. When I heard it I thought it sounded like it was rolling over and over again. Is that how they think California will fall in the sea?


    A: The rolling motions of the recent quakes in California can be easily explained. Rock rupture occurs at the epicenter focus, typically at the fault line between two plates. The San Andreas Fault in California is a Sliding Fault.

    The initial rupture releases huge amounts of energy, creating seismic body waves in two forms. First are P-waves, which take the form of longitudinal compressions across the Earth's upper crust (think of a slinky being stretched out, and an area of compression translating from one side to the other).

    S-waves, or Shear waves,  travel at approximately half the speed of P waves and are characterized by a wave of sinusoidal geometry (as opposed to just sinusoidal waveform). S-waves can only propagate through solids, meaning the Earth's crust and mantle.

    Quakes also cause a third type of wave: Surface waves. There are two main types - Rayleigh and Love waves. These waves generate the sensation of "rolling." The secondary shock felt was very likely the aftershock, a small quake following the main shock that is always of a smaller magnitude.


    Q: I heard that California has small earthquakes everyday and a lot of them but is this normal for the area?


    A: It is very normal for California to face frequent, if not daily earthquakes. California is right at the convergent plate boundary between the North American and Pacific Plates, making it the epicenter of much seismic activity.


    As a side note, both California and Guatemala fall within the Pacific Ring of Fire, a horseshoe region traced by plate boundaries marked by frequent and violent volcanic activity.


    Q:  I also want to know about the oil water displacement in the Gulf.  The water pressure, down by the oil spew, I heard was stronger psi than the oil and since oil is lighter than water wouldn't theoretically that water be able to sink down in the well the oil is gushing out of?


    A: It is true that water has a greater density than crude oil (petroleum), which explains why oil tends to float on the surface of water. Salt water also has a higher density than pure water (because it is a saline solution).

    Fluid pressure is a function of depth and density, so yes, there is a differential pressure in the system of the oil and water at the location of the leak. At that depth, there is a water pressure of approximately 15000000 Pascals, or 2220 PSI. If we assume the depth of the well is not as great as the distance from the ocean surface to the opening to the well, it's easy to see how there is a large differential pressure. This differential pressure creates flow. Physically speaking, because of the greater pressure of the water, the oil is displaced by the water. So yes, water would be replacing the oil in the well from which the oil is leaking. This would have no significant impact on the integrity of the crust surrounding the well, as there is not a significant enough difference in the properties (specifically density and viscosity) of water and oil.


    Q: One more thing:  There is a section of our earth that is between the crust and the mantel called the mohorovicic discontinuity.  I have another theory with this. A transmission has moving parts and it need transmission fluid to protect the metal parts that are turning quickly I think of a transmission kinda like the earth and oil is the fluid that allows the earth to turn smoothly. If the earth moves smoothly by oil and water is seeping down into the earths moho section could that cause things like earthquakes? Water completely destroys a transmission and a motor.

    A: The Mohorovičić discontinuity is found between 5 and 10 kilometers (5000-10000 m) beneath the Ocean Floor, separating the crust and upper mantle, likely representing a phase change in the material components of the Earth due to a temperature gradient. The leak is 5000 feet (about 1500 m) below Sea Level. It is extraordinarily improbably that the drilling ruptured the Moho.

    In regards to your transmission fluid analogy: Recall that petroleum is a fossil fuel, created by the decomposition of organic material. The only prevailing alternative theory is the Abiogenic Petroleum Hypothesis, which would suggest that petrol was formed from deep carbon deposits dating back to the formation of the Earth.

    The best way to explain the flaw in your analogy is to describe the Earth thusly: chaotic. The geological systems of the world do not subscribe to the same rules as are used to keep an engine running or a transmission working. Basically, there is no system to keep the Earth turning efficiently. In the Earth's mantle, there is a constant process of motion created by the temperature gradient. Deeper in the mantle, which consists mostly of Silicone Oxide and Magnesium Oxide by weight percentage, material becomes hotter. Nearer the surface, the substance of the mantle is cooler. Hotter material rises, and cooler material sinks. As the hot material rises, it cools, and vice versa, creating a constant circular flow in the mantle.

    Downward motion of cooler material occurs most frequently at subduction zones, at convergent plate boundaries (such as the San Andreas Fault in California). This convection is a dynamically chaotic system. This is what causes the motion of tectonic plates, not a lack of friction between the crust and mantle due to any material in the Moho.


    In fact, if there were no friction, there would be no earthquakes, and earthquakes have been occurring since the creation of the world (recall that the original arrangement of the continents as a supercontinent, Pangaea). This points to there being no correlation between the earthquakes and the oil leak.

    Hope this helps.

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