February 11, 2013
What is an Earthquake?
Hi, I’m Emerald Robinson, and in this “What is” video, we’re going to examine earthquakes.
An earthquake is an event in which the earth suddenly shakes, trembles, or rocks. Earthquakes are very common; about 900,000 happen worldwide every year.
To understand how an earthquake happens, we need to review plate tectonics. Geologists think that the top layers of the earth, called the crust and the mantle, are broken into large pieces, or plates. The places where these plates meet are called “faults,” and are where most earthquakes occur.
This is because tectonic plates move very slowly, at a rate of about 1 to 2 inches per year. When one plate is pushed beneath another, or when two plates move along side of one another, friction can cause them to become stuck together. When the force that moves the plates is enough to overcome the force holding them together, the plates can break apart suddenly, sending shock waves through the earth.
The place where the earthquake is actually generated is often hundreds of feet below the surface, and is called the quake’s “focus.” The point on the surface of the earth directly above the focus is called its epicenter, and is usually where the earthquake is the strongest, and where most damage occurs.
Seismologists, scientists who study and try to predict earthquakes, used to use the Richter scale to compare the size of earthquakes. But since 1979, the more precise Moment Magnitude Scale has been used to measure the strength of the waves that move through the earth during an earthquake – the stronger the quake, the higher the number. The most severe earthquake on the MMS earned a 9.5.
Earthquakes are changing the face of our planet one shake, rattle, and quake at a time so engineers must create buildings able to withstand their force, while scientists become more accurate at predicting them.