Lecture%20#4%20notes%20Geol%203950%202010%20CR%20Stern

Lecture%20#4%20notes%20Geol%203950%202010%20CR%20Stern -...

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Lecture #4 notes Geology 3950, Spring 2010; CR Stern Seismic waves, earthquake magnitudes and location, and internal earth structure Earthquakes result from building up of stress along a fault in the brittle lithosphere (see table 1 and figure 1 below) of the earth until the stress becomes large enough to overcome the friction along the fault and it ruptures. The stress results from convection inside the deeper plastic asthenosphere of the earth. This is caused by build up of heat generated by decay of radioactive elements. The pattern of convection focuses stress on the boundaries of large areas of lithosphere called plated. The process of the movement of the lithosphere plates above the convecting asthenosphere, which causes earthquakes along the boundaries of plates, is called plate tectonics. Convection may occur throughout the mantle, but most probably only occurs in the upper part of the mantle asthenosphere. Internal Layers of the Earth Lithologic or compositional layers Crust (20-60 km thick) – rock (density of about 2.8 gms/cm 3 ) Mantle – rocks (density of about 3.4 gms/ cm 3 – peridotites) Core – iron metal (density of >9 gms/cm 3 ) Rheologic layers Lithosphere (100-200 km thick; crust and upper mantle) – brittle rocks – they rupture to produce earthquakes Asthenosphere – plastic rocks – they flow and convect Outer core – liquid iron metal Inner core – solid iron metal
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Figure 1 Seismic waves - An earthquake generates many different types of seismic waves,
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Lecture%20#4%20notes%20Geol%203950%202010%20CR%20Stern -...

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