Seismographs are used to detect earthquakes and locate their epicenters. Scientists use seismograms from multiple seismographs to determine the time an earthquake's waves arrived using the S-P Time Method, locating the epicenter above the focus where it began. The Richter scale measures an earthquake's magnitude based on the ground motion recorded, adjusted for distance to the seismograph. The Modified Mercalli Intensity Scale further describes earthquake impacts from I (not felt) to XII (total damage), with higher intensities nearer the epicenter.