But for very large earthquakes, some magnitudes underestimate true earthquake size, and some underestimate the size. When initially developed, all magnitude scales based on measurements of the recorded waveform amplitudes were thought to be equivalent. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude as measured on a seismogram. For example, a magnitude 5.3 is a moderate earthquake, and a 6.3 is a strong earthquake. Magnitude is expressed in whole numbers and decimal fractions. See the Intensity section below for more details on shaking intensity measurements. The shaking that it causes has many values thatВ vary from place to place based on distance, type of surface material, and other factors. Magnitude isВ theВ size of the earthquake.В An earthquake has a single magnitude. Modern systems precisely amplify and record ground motion (typically at periods of between 0.1 and 100 seconds) as a function of time. Sensitive instruments, which greatly magnify these ground motions, can detect strong earthquakes from sources anywhere in the world. Each seismometer records the shaking of the ground directly beneath it. Seismometers record the vibrations from earthquakes that travel through the Earth. The time, location, and magnitude of an earthquake can be determined from the data recorded by seismometer.

Relative intensity chart