What Causes Earthquakes
Natural earthquakes occur mostly from tectonic movements of the plates. Tectonic plates are large parts of the oceanic and continental lithosphere. The lithosphere is the solid outer section of Earth's crust. These sometimes shift into various positions both underwater and above. Such movements generally occur along fault lines. When two rocks slide against each other, they create fault lines. These fault lines can be both extremely narrow or miles wide. Fault lines are created mostly in mountainous regions where plate tectonic movements are more likely. Movement between the tectonic plates is rarely smooth. When the plates slide against each other, they create a tremendous amount of friction. This friction forms seismic energy that travels in waves through the surface of the Earth. This causes the earthquake. While normal energy travels above the surface of the Earth, seismic energy travels under the Earth's surface. This creates more tension between the land plates, causes more shifting, and creates more fault lines. The spot below the Earth's surface where the rocks break against each other is called the focus of the earthquake. The place exactly above the focus on the surface of the planet is called the epicenter of the earthquake. Sometimes, earthquakes can also be man-made instead of natural. These can sometimes be caused due to explosions underground. Explosions big enough to cause a shift in the surface of the Earth are generally caused in mining tunnels or during nuclear testing. But the seismic energy formed due to these explosions is rarely very strong. Therefore, the strength of the earthquakes caused is not very high.

1 In “What Causes Earthquakes," which detail supports the idea that natural earthquakes are more dangerous than man-made ones? A. Whereas normal energy travels above the surface of the Earth, seismic energy travels under the Earth’s surface. B. Explosions big enough to cause a shift in the surface of the Earth are generally caused in mining tunnels or during nuclear testing. C. When two rocks slide against each other, they create fault lines. D. But the seismic energy formed due to these explosions is rarely very strong.