|An earthquake is a trembling or shaking movement of the Earth's surface. The earth is like a cracked boiled egg with Tectonic Plates. The reason eathquakes happen is because those Tectonic Plates keep moving, hitting, crashing, and pushing each other.
Tectonic Plates are plates that are floating on the Earths crust. There are two tectonic plates in between California and Nevada. To be exact, the two plates are on San Anders Fault. A lot of earthquakes happen there because the two plates keep moving.
Scientests have discovered how to measure earthquakes. The measuring tool that they use is called a Seismograph. It is numbered from 1-10. This machine has a point, with ink at the tip, that is moving depending on how much vibration the plates give off.
Earthquakes occur every day on Earth, but the vast majority of them are minor and cause no damage. Large earthquakes can cause serious destruction and massive loss of life via a variety of agents of damage including fault rupture, vibratory ground motion (i.e., shaking), inundation (e.g., tsunami, seiche, dam failure), various kinds of permanent ground failure (e.g. liquefaction, landslide), and fire or hazardous materials release. In a particular earthquake, any of these agents of damage can dominate, and historically each has caused major damage and great loss of life, but for most earthquakes shaking is the dominant and most widespread cause of damage.
Most large earthquakes are accompanied by other, smaller ones, known as foreshocks when they occur before the principal or mainshock and aftershocks when they occur following it. The source of an earthquake is distributed over a significant area -- in the case of the very largest earthquakes, in excess of a thousand kilometres -- but it is usually possible to identify a point from which the earthquake waves appear to emanate. That point is called its "focus" and usually proves to be the point at which fault rupture was initiated. The position of the focus is known as the "hypocenter" and the location on the surface directly above it is the "epicenter."
Earthquakes, especially those that occur beneath sea- or ocean-covered areas, can give rise to tsunamis, either as a direct result of the deformation of the sea bed due to the earthquake, or as a result of submarine landslips or "slides" indirectly triggered by it.