Plate tectonics theory is that the earth's lithosphere is not continuous but is broken into about a dozen large plates that move over the earth's asthenosphere which is almost mostly all liquid molten lava. The plates move a few centimeters per year, and each plate acts as a distinct, rigid unit that rides on the asthenosphere, which is also moving. The plates push on each other and pull on each other; they are empowered to do this by a process called convection. Convection is a mechanism of mass and energy transfer where hotter materials rise and cooler materials fall. The Plates push and pull when they are in the convection cycle; this is when mountain building, volcanism, and earthquakes occur.

The places where plates rupture each other are called faults. There are several kinds of faults: dip-slip fault, or normal faults, which cause a tension that extends the earth; Dip-slip fault, or reverse fault, which shortens the earth by compression; and last but not least there is a strike slip fault which has shearing plus tension, so the strike slip fault is also know as a transform fault. The famous San Andreas Fault is a transform fault and causes massive earthquakes.

Plate boundaries are where earthquakes happen; there are three major boundaries. The first of the plate boundaries are called Divergent Boundaries. At Divergent Plate Boundaries seafloor spreading occurs, and we have normal faulting with small earthquakes. The second type of the plate boundaries are called Transform-Fault Boundaries, which usually cause earthquake activity that is very great, which happens when the plates slide by each other in opposite directions, just like how the San Andreas Fault plates slide by one another. The last of the boundaries are called Convergent Boundaries, which is where the world&'s largest earthquakes occur. Convergent Boundaries occur by horizontal compression along huge thrust faults, called megathrusts. An example of this would be The Great Earthquake of Chile in 1960. The Great Earthquake of Chile had a magnitude of a whopping 9.5, the biggest earthquake ever recorded according to the book Understanding Earth. The crust of the Nazca Plate slipped an average of ten meters beneath the crust of the South American plate on a fault rupture which was the rough size of Kentucky.

There are also earthquakes that do not happen on plate boundaries. These earthquakes are called Interplate Earthquakes. Most earthquakes occur at plate boundaries, but not all of them do. Some of the worst earthquakes in America’s history have not happened at a plate boundary.

Boston, Massachusetts had one in 1755, New Madrid, Missouri, had a bad earthquake in 1811, and Charleston, South Carolina, had a big earthquake in 1886.

Many of the interplate earthquakes occur on old faults that used to be on ancient plat boundaries. The faults are not plate boundaries any more but are still spots of crustal weakness. The most recent and probably most deadly of the interplate earthquakes happened only a few years ago. In Gujarat State, in western India, a massive interplate earthquake killed more than 20,000 people in 2001.

Here is a list of recent earthquakes.

• 2002 Denali, Alaska 7.9 magnitude, very little property or human life lost was in the wilderness.
  
  
• 2001 Gujarat, India 8.0 magnitude, 20,000 people lost their lives.
  
  
• 1999 Izmit, Turkey 7.4 magnitude, 15,600 killed and thousands missing.
  
  
• 1998 Papua, New Guinea 7.0 magnitude, 3,000 killed and several villages destroyed
  
  
• 1997 Northern Iran 7.3 magnitude, 1567 people killed, 2,300 injured, 50,000 homeless.
  
  
• 1995 Kobe, Japan 6.9 magnitude, 5,502 killed, 36,896 injured, and 310,000 homeless.
  
  
• 1994 Northridge, California 6.9 magnitude, 58 people killed, 7,000 injured, and 20,000 homeless, $20 million in damages.
  
  
• 1992 Landers, California 7.3 magnitude, 1 killed, 400 people injured, and substantial damage.
  
  
• 1989 Loma Prieta, California 7.1 magnitude, 60 killed, 3757 injured, and $7 billion in damages according to Understanding Earth.

Earthquakes are going to continue to happen till the end of time, but with what we know and learn from earthquakes we can better prepare ourselves for them. We can prepare by making buildings that are more likely to stand up to a terrible shaking, and we can make new building codes to existing and proposed structures in earthquake-prone areas.