This document provides an overview of earthquakes including what they are, how they are measured, the damage and effects they can cause, the different types of seismic waves, and details about the 2011 Tohoku earthquake in Japan. Some key points covered include that earthquakes are caused by the abrupt movement of rocks along faults, they are measured by the Richter scale and Mercalli scale, can destroy infrastructure and harm populations, and the Tohoku quake was a 9.0 magnitude event that shifted Japan's coastline and caused a devastating tsunami.