TABLE OF CONTENTS Geology is the study ofthe earth, which is a dynamic system covered by crustal plates that are constantly moving and changing in structure. The crustal plates are driven by deep-lying forces that are not yet completely understood. New crustal plates are being formed by magma rising from molten regions deep in the earth at mid-ocean rifts. Other crustal plates are being consumed as they are drawn downward into the mantle at subduction zones at the edges of some continents, such as the Pacific coasts of North and South America.
Detailed analyses of earthquake wave seismograms, waves that travel on the earth's surface, gravity and magnetic differences, heat flow from the interior, and electrical conductivity have been used to develop a composite picture of the globe. Four distinct zones have been identified:
the lithosphere, which includes the continental and ocean crusts;
the mantle underlying the lithosphere, which is readily recognized because the seismic (earthquake) waves increase in velocity at the boundary known as the Mohorovicic discontinuity in honor of its discoverer (generally called the Moho discontinuity);
a liquid outer core composed principally of nickel and iron; and
the solid inner core.
More than 100,000 detectable earthquakes occur each year around the globe, and most of these originate at specific focal points (a point of maximum intensity within the crust) [1-3]. Two types of waves emanate from the focal point of the earthquake: compression and shear waves. Compression waves travel through all materials by moving particles...
