Wave Aamplitude, Mistake Size, Corporeality of Slip

There are a number of ways to mensurate the magnitude of an earthquake. About scales are based on the amplitude of seismic waves recorded on seismometers. These scales account for the distance between the earthquake and the recording seismometer so that the calculated magnitude should be about the aforementioned no thing where information technology is measured. Another calibration is based on the physical size of the convulsion fault and the corporeality of slip that occurred. And then in that location are also measures of earthquake shaking intensity. The intensity from i earthquake varies profoundly from identify to place.

What'due south the divergence betwixt magnitude and intensity? This 8 minute video uses the analogy of a lightbulb to explain the how an earthquake tin can take different intensities at different places.

Earthquake Intensity

What Controls the Shaking You Feel?

A few of these scales are described in more detail below.

Charles Richter examines a seismogram on a table.
Charles Richter studying a seismogram.

The Richter Scale

The first widely-used method, the Richter calibration, was developed by Charles F. Richter in 1934. Information technology used a formula based on the aamplitude of the largest moving ridge recorded on a specific type of seismometer and the altitude between the earthquake and the seismometer. That scale was specific to California earthquakes and crust; other scales, based on wave amplitudes and full convulsion elapsing, were developed for use in other situations and they were designed to be consistent with Richter's scale.

The Moment Magnitude Scale

Unfortunately, many scales, such as the Richter scale, do non provide accurate estimates for large magnitude earthquakes. Today the moment magnitude scale, abbreviated MW , is preferred because information technology works over a wider range of convulsion sizes and is applicable globally. The moment magnitude scale is based on the total moment release of the earthquake. Moment is a production of the distance a fault moved and the force required to move information technology. Information technology is derived from modeling recordings of the earthquake at multiple stations. Moment magnitude estimates are nearly the same equally Richter magnitudes for small to big earthquakes. But only the moment magnitude scale is capable of measuring M8 (read "magnitude 8") and greater events accurately.

Magnitudes are based on a logarithmic scale (base x). What this means is that for each whole number you go up on the magnitude scale, the amplitude of the footing motion recorded by a seismograph goes up 10 times. Using this scale, a magnitude 5 convulsion would outcome in x times the level of ground shaking every bit a magnitude four earthquake (and about 32 times equally much free energy would be released). To requite yous an thought how these numbers tin add up, think of it in terms of the free energy released by explosives: a magnitude one seismic moving ridge releases as much free energy every bit bravado up 6 ounces of TNT. A magnitude eight earthquake releases every bit much energy as detonating six million tons of TNT. Pretty impressive, huh? Fortunately, most of the earthquakes that occur each yr are much too small to exist felt by near people.

Magnitude scales can be used to draw earthquakes so small that they are expressed in negative numbers. The scale also has no upper limit. The largest recorded convulsion occurred along the subduction zone in Chile in 1960. It was a magnitude 9.5 simply larger earthquakes may be possible.

Fortunately, large earthquakes are much less common than modest ones. Here'due south a tabular array describing the magnitudes of earthquakes, their effects, and the estimated number of those earthquakes that occur each yr.

The Mercalli Scale

Another way to measure the strength of an earthquake is to utilize the observations of the people who experienced the earthquake, and the amount of damage that occurred, to judge its intensity. The Mercalli scale was designed to do just that The original scale was invented by Giuseppe Mercalli in 1902 and was modified by Harry Wood and Frank Neumann in 1931 to get what is now known as the Modified Mercalli Intensity Scale. To help distinguish it from magnitude scales, the MMI scale uses roman numerals.

Although the Mercalli scale does not utilise scientific equipment to measure seismic waves, it has been very useful for understanding the damage acquired by big earthquakes. It has besides been used extensively to investigate earthquakes that occurred before there were seismometers.

Some factors that touch the amount of damage that occurs are:

  • the size (magnitude) of the earthquake
  • the distance from the epicenter,
  • the depth of the earthquake,
  • the edifice (or other structure) design,
  • and the type of surface material (rock or dirt) the buildings rest on.

Dissimilar edifice designs concur up differently in an earthquake and the further you are from the convulsion, the less damage you'll ordinarily encounter. Whether a building is built on solid rock or sand makes a large divergence in how much damage it sustains. Solid rock usually shakes less than sand, and then a building congenital on top of solid stone shouldn't be equally damaged as it might if it was sitting on a sandy lot.

Earthquake Magnitude Scale