An earthquake is a sudden shaking of the ground. Most earthquakes are very small — so small you wouldn’t even feel them. But some quakes can be very violent and dangerous. They can collapse buildings and open seams in the earth. Earthquakes that shake the ocean can sometimes cause huge waves called tsunamis.
Many earthquakes are caused by the movement of massive slabs called tectonic plates that make up the Earth’s surface. These slabs move slowly against each other. They collide, pull apart and slide over each other. In the process, continents and oceans expand, shrink and move. But massive plates don’t slip and slide without making themselves felt. The shifts can spark earthquakes. Some of the plate movement shoves up mountains or sets off volcanoes. Those volcanoes can also produce earthquakes when they erupt.
Scientists used to measure earthquakes using the Richter scale. Now, though, they use a more accurate measurement called moment magnitude.
In a sentence
Wastewater from the oil extraction process called fracking gets pumped into the ground — and can cause earthquakes where none are normally occur.