Earthquakes are some of the most devastating natural events known to man. They can destroy buildings, kill people, and even cause fires. These occurrences have happened often enough so that we have created different scales for them. To make judging the magnitude of earthquakes much easier, scientists have developed scales of measurement. Of the many different scales, the Richter Scale is one of the most commonly used.
An earthquake takes place when two plates rub against each other at a fault. Different types of faults cause earthquakes of different magnitudes. Click here to find out about the different types of faults. The deepest earthquakes, and the ones with the greatest magnitude occur at compressional boundaries. These earthquakes can go as deep as 700 km and their magnitudes can be more than a 9 on the Richter scale. The earthquakes with the next greatest magnitude happen at Transform boundaries. These earthquakes are usually less than an 8.5 on the Richter scale and are very shallow. They are rarely more than 25 km deep. The least powerful earthquakes happen at extensional boundaries. These shallow earthquakes are usually less than an eight on the Richter scale.
The earthquakes are so powerful because they produce certain waves. These waves are called, the P(rimary), the S(econdary), the Love, and the Rayleigh waves.
The P and S waves are both body waves, meaning that they travel in and below the crust. The P waves, also known as compressional waves, move at the average speed of 6.8 km (4.2 mi) per second, and the S waves, also known as shear waves, travel at the approximate speed of 3.8 km ( 2.4 mi) per second. The P waves are known as the Primary waves, because they travel at fast speeds, and S waves are known as Secondary waves because they travel at a slower rate than the P waves.
The other waves are the Love and Rayleigh waves, after the scientists who discovered them, Augusts E. H. Love and Lord Rayleigh in 1911 and 1885, respectively. Love waves travel 4.4 km (2 3/4 mi) per second. Rayleigh waves, the slowest of the four types, travel at the average rate of 3.7 km (2 1/4 mi) per second. These two types of waves are called surface waves, because they travel on the surface of the crust.
The shaking of the ground can cause major damage during an earthquake because the support systems of most buildings, especially private homes, are not designed to handle violent shaking. The homes can crumble and crack, crushing people and belongings.