Originally designed specifically for California, the Richter magnitude scale becomes an approximation in other states and countries. Also, the type of wave whose amplitude is to be measured is not specified, and it does not distinguish between deep and shallow foci. Below is a chart that shows how to measure Richter magnitude by an "eyeball" fit.
First, the amplitude of the surface wave is measured on a seismogram produced by a Wood-Anderson seismometer a specfic type of seismometer and then it is compared with distance from the earthquake or the S-P time which is the amount of time between the P-wave and S-wave arrival to yield a magnitude.
Click on the image to see a larger version. There are many other magnitude measurements. In addition to Richter magnitude, there is also body wave magnitude and surface wave magnitude.
These magnitude scales differ by the type of wave amplitude that is measured from the seismogram and the mathematical formula used to determine the magnitude.
They are all, however, logarithmic scales. A third type of measurement is called the seismic moment. Using the seismic waves and field measurements that describe the fault area, the moment, a parameter related to the angular leverage of the forces that produce slip on a fault, can be measured.
Whenever a major earthquake is in the news, you'll probably hear about its Richter scale rating. You might also hear about its Mercalli Scale rating, though this isn't discussed as often. These two ratings describe the power of the earthquake from two different perspectives. The most common standard of measurement for an earthquake is the Richter scale , developed in by Charles F.
Richter of the California Institute of Technology. The Richter scale is used to rate the magnitude of an earthquake -- the amount of energy it released. This is calculated using information gathered by a seismograph. The Richter scale is logarithmic , meaning that whole-number jumps indicate a tenfold increase. In this case, the increase is in wave amplitude.
That is, the wave amplitude in a level 6 earthquake is 10 times greater than in a level 5 earthquake, and the amplitude increases times between a level 7 earthquake and a level 9 earthquake. The amount of energy released increases As we previously noted, most earthquakes are extremely small. A majority of quakes register less than 3 on the Richter scale; these tremors, called microquakes , aren't even felt by humans.
Only a tiny portion -- 15 or so of the 1. See the Magnitude Types Table below for a summary of types, magnitude ranges, distance ranges, equations, and a brief description of each.
Earthquake magnitudes and energy release, and comparison with other natural and man-made events. Another way to measure the size of an earthquake is to compute how much energy it released. The amount of energy radiated by an earthquake is a measure of the potential for damage to man-made structures. 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. Maps showing the shaking intensity from two different earthquakes with about the same magnitude. The shaking from the M6.
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