When an earthquake strikes, seismologists use diagrams called focal mechanism plots to determine what type of faults moved. Each type generates a different pattern, with both black and white regions. Earthquake faults of different configurations, such as strike-slip or thrust faults, yield distinctive plot patterns when earthquakes occur along them. However, all regions of the diagram go dark if the jolt is caused by an explosion. Credit: Mikenorton, CC BY-SA 3.0, cropped from the original.