Earthquakes
Seismography
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 thehypocenter, and the location directly above it on the surface of the earth is called the epicenter.
Sometimes an earthquake has foreshocks. These are smaller earthquakes 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. The largest, main earthquake is called the mainshock. Mainshocks always haveaftershocks that follow. These are smaller earthquakes that occur afterwards in the same place as the mainshock. Depending on the size of the mainshock, aftershocks can continue for weeks, months, and even years after the mainshock!
(From The Science of Earthquakes)
A Diagram of an Earthquake
After the Earthquake
A Simple Seismograph
Seismography
The Steps of an Earthquake
- Stress caused by extreme heat inside the earth builds up between tectonic plates. This can happen over hundreds of years.
- The brittle part of the plates are found along fault lines. These brittle edges give way under the stress.
- Part of a stressed plate on the fault line pushes over another plate, and the earth buckles.
- After the earthquake, aftershocks or tremors that happen after the original tremor, can still shake the earth.
A Map of the World's Fault Lines (Where Earthquakes Occur)
The New Madrid Earthquake of 1811 and 1812
Let's go learn more about this earthquake at the U.S. Geological Society's website.