What do earthquake magnitudes mean

An earthquake releases energy at many frequencies, and in order to compute an accurate value, you have to include all frequencies of shaking for the entire event. While each whole number increase in magnitude represents a tenfold increase in the measured amplitude, it represents an 32 times more energy release.

The energy can be converted into yet another magnitude type called the Energy Magnitude M e. However, since the Energy Magnitude and Moment Magnitude measure two different properties of the earthquake, their values are not the same. Did You Feel It? The earthquake epicenter is shown as a star, and the geocoded intensities are shown as small colored squares.

The associated MMI value for each color is shown in the key at the bottom. Whereas the magnitude of an earthquake is one value that describes the size, there are many intensity values for each earthquake that are distributed across the geographic area around the earthquake epicenter. The intensity is the measure of shaking at each location, and this varies from place to place, depending mostly on the distance from the fault rupture area.

However, there are many more aspects of the earthquake and the ground it shakes that affect the intensity at each location, such as what direction the earthquake ruptured, and what type of surface geology is directly beneath you. Intensities are expressed in Roman numerals, for example, VI, X, etc. Traditionally the intensity is a subjective measure derived from human observations and reports of felt shaking and damage. The data used to be gathered from postal questionnaires, but with the advent of the internet, it's now collected using a web-based form.

However, instrumental data at each station location can be used to calculate an estimated intensity. The intensity scale that we use in the United States is called the Modified Mercalli Intensity Scale , but other countries use other scales.

These examples illustrate how locations and depth , magnitudes, intensity, and faults and rupture characteristics are dependent and related. This shows the shaking amplitude recorded on 3 different seismometers from the M6. All 3 stations are about the same distance from the earthquake to the south, but the type of local geology beneath the instrument influences the amount of shaking at that location. Bedrock shakes the least, and soft mud the most.

However, anything in the 6. What's seriously alarming, though, is that it's extremely rare to get earthquakes of that magnitude this far north and east in the US. In fact, the largest earthquake to ever hit Virginia before today as far back as we have records was also a 5. That was back in Of course, there was no MMS back in —hell, there was no Richter scale.

There weren't even seismometers; scientists used pendulums to measure the movement of the Earth. Other earthquake questions. Can earthquakes be predicted?

Earthquake weather? How long does an earthquake last? Why are aftershocks recorded? What is the difference between Magnitude and Intensity? What is the Modified Mercalli Intensity Scale? What is the Richter Magnitude Scale? Unstable objects overturned. Pendulum clocks may stop.

Intensity 4: Light — Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound.

Sensation like heavy truck striking building. Standing motor cars rocked noticeably. Intensity 3: Weak — Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake.

Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated. The USGS switched its definition of magnitude from the Richter scale to the moment magnitude scale in the late s, Jones said. The Richter scale, developed in the s, was named after American seismologist and physicist Charles Richter.

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