Re: dose depleating the oil from under the surface eventualy cause friction?

First, we should review the basics of Earth's structure. The crust is the outermost shell. There are two types: ocean crust and continental crust, which have thicknesses of about 5 and 35 km, respectively. Below the crust there is the solid mantle (2885 km thick), the liquid outer core (2270 km thick) and the solid inner core (1216 km thick). Now here's where things get a little complicated: the lithosphere is made of the outermost 100 or so km of Earth and includes the crust and a thin layer at the top of the mantle. The lithosphere is cold and brittle, and is broken up into the tectonic plates. Earthquakes occur only in the lithosphere because it is brittle and can crack under the stresses of plate tectonics.

Before we go on, remember that the mantle is solid rock, but it's a visco-elastic material that can be deformed, or flow, like silly putty when put under slow acting stresses over very long periods of time. The stress is caused by very, very slow churning motions in the solid mantle, which in turn is caused by the continuous release of heat from deep inside the planet. The lithospheric plates float on top of the asthenosphere, where the viscous flow takes place. So the plates ride along on top of this solid, flowing rock at a speed about as fast as your fingernails grow, and scrape and jostle against one another, causing earthquakes and volcanoes. Check this webpage for graphics and an alternative explanation.

Oil and coal are resources that we remove from the shallow crust. They are formed out of formerly living things like plants and animals that have died and been buried by natural erosional and depositional processes occuring at Earth's surface. In fact, for the most part we don't go very deep to get our oil from under the ground because it's too difficult and expensive; the deepest oil wells bottom at about 8 to 10 km. There is no oil to be found in oceanic crust because it does not provide the hosting environment of continental crust (offshore oil rigs drill into the continental shelf), but there have been some attempts to drill through oceanic crust to the mantle. This drilling is done in ocean crust because it is very much thinner than continental crust and intended to find out more about the physical and chemical properties of the upper mantle.