“Water is clearly vital for life. What is perhaps more surprising is that water plays a crucial role in lubricating the motion of plates – without it there would be no plate techtonics. So water quickens life and the Earth itself.” – David Singleton
Source: Earth Story: The Shaping of Our World
The earth’s crust is not one piece. There are plates, called tectonic plates, that sit next to one another like pieces in a puzzle. These plates bump against each other, sometimes causing cracks we call faults. Faults and mountain ranges are often found together, as the mountains were formed by edges of faults slipping past one another. There are also faults beneath the oceans.
A fault is a fracture (crack or break) in the earth’s outer layer (crust) in which the edges have moved up, down, or sideways. It is like two puzzle pieces that no longer fit together smoothly. As the broken edges press against one another energy is stored up. When the edges finally move, that energy is released as an earthquake.
Think of moving a heavy chest of drawers across a floor. You push harder and harder, storing energy, until the dresser finally slides over the floor, then stops as the energy is used up. Then you have to push a gain to cause more movement.
On a dip-slip fault, the rock planes move against one another mostly vertically. The two types of dip-slip faults are the normal (also called normal-slip fault, tensional fault or gravity fault) and the reverse (also called thrust fault, reverse-slip fault or compressional fault.) In a normal fault, the footwall of crust moves up over the hanging wall. In the reverse fault, the footwall moves down.
Along a strike-slip fault, the rock planes move mostly horizontally (laterally or sideways.) One plate moves right or left, rubbing against the other plate. The San Andreas Fault in California and the Anatolian Fault in Turkey are two well-known examples of this type of fault. Other names for this type of fault are: transcurrent fault, lateral fault, tear fault or wrench fault.
The oblique fault has both horizontal (strike-slip) and vertical (dip-slip) movements that are measurable. Most faults have both types of movement, but one is much greater than the other. The oblique fault has significant movement in both directions.
“Shake It Up” Engineering Design Challenge: You are a groovy earthquake engineer who has been contracted by the city of Los Angeles. Using only the materials from your Groovy Lab in a Box, can you design and build the tallest skyscraper that can withstand the next BIG quake?
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