Earthquakes
by
Twyla Race
All information and pictures for this book are obtained from the U.S. Geological Survey website.
What is an earthquake?
An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane.
The location below the earth's surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.
Sometimes an earthquake has foreshocks. These are smaller earthquaked that happen in the same place as the larger earthquake that follows. Scientists can't tell that an earthquake is a foreshock until the larger earthquake happens, which is called the mainshock. Mainshocks always have aftershocks that follow. These are smaller and occur in the same place as the mainshock. Aftershocks can continue for weeks, months, and even years after the mainshock.
What causes earthquakes and where do they happen?
The earth has four major layers: the inner core, outer core, mantle, and crust. The crust and the top of the mantle make up a skin on the surface of the planet. The skin is made up of many pieces that slowly move around, sliding past one another, and rubbing into each other. The pieces are called tectonic plates, and the edges of the plates are called plate boundaries. Most of the earthquakes around the world occur on the faults, which are on the plate boundaries. The earthquake is caused from the movement of the plates with each other, creating enormous energy that is released with occurance of the earthquake.
Why does the earth shake when there is an earthquake?
The movement of the earth is caused by earth moving. While the edges of the faults are stuck together, the rest of the block is moving, the energy that would normally cause the blocks to slide past one another is being stored up. When the force of the moving blocks overcomes the location that is stuck together, all that stored up energy is released. The energy than radiates outward from the fault in all directions in the pattern of rippled water, called seismic waves. The waves shake the ground and everything upon it.
How are earthquakes recorded?
Insturments call seismographs record earthquakes. The base sets firmly on the ground, and a heavy weight hangs freely from the center. When an earthquake causes the ground to shake, the base also shakes, but the weight does not. The difference in position between the shaking is what is recorded.
The magnitude of the earthquake depends on the size of the fault. The length of the wiggles that the seismograph creates during the earthquake helps scienctists determine the magnitude.
Energy that is released from an earthquake causes waves that are called P wave or S wave. They each skake the ground in a different pattern as they move through. P waves travel first, and the S waves follow. Scientists look at the amount of time between the two waves that are recorded on the seismogram to determine the distance waves traveled. They then determine the location of the earthquake by viewing the information from three relevant readings.
Can scientists predict earthquakes? No. Scienctists however can tell that there is activity along fault lines, but they can not determine when and where another earthquake will happen.