The most common way of detecting and measuring earthquakes is a seismometer (also known as a seismograph). A seismometer is any device used to detect vibration in the Earth's surface. A simple seismometer consists of a something suspended from springs that are allowed to swing as the Earth shakes. A pen attached the device records all vibrations (see Figure 3). Seismometers can be sensitive enough to detect earthquakes that people cannot even feel. Seismometers can detect a powerful earthquake anywhere in the world, but often seismometers are placed near fault lines to detect very small earthquakes. This information can help engineers predict when a large earthquake is due to occur. Faults are the boundaries between the tectonic plates that make up the surface of the Earth's crust. As the plates slide along each other, they slip and grind, causing earthquakes.