Name a scale that scientists use to evaluate earthquakes?

Answer 1

There are a number of differing scales used to rate earthquakes depending on whether you are interested in their magnitude (the amount of energy released when they occur) or their intensity (a measurement of the amount of damage caused and severity of ground shaking in a given area).

There are two primary magnitude scales currently in use, the Richter (or local) magnitude scale and the moment magnitude scale. The Richter magnitude scale estimates earthquake magnitude based on the amplitude of seismic waves as recorded by a seismometer. The Richter scale is logarithmic and each single increment relates to a ten times increase in detected seismic wave amplitude and a 31 times increase in energy.

The Richter magnitude scale was originally developed for deriving the magnitude of small and medium sized earthquakes (those with magnitudes less than 7) at epicentral distances relatively close to a seismometer station (less than 600 km). As such it is poor at resolving large earthquakes as it relies on the detection of high frequency seismic waves that have wavelengths which are shorter than the rupture lengths of large earthquakes.

To attempt to improve the Richter scale for use in larger earthquakes and at greater epicentral distances, Charles Richter and Beno Guttenberg developed the surface and body wave magnitude scales. The surface wave magnitude scale derives magnitudes from the measured amplitude of Rayleigh surface waves at long distances. The Body wave magnitude scale is intended to be used to derive the magnitude of deep-focus earthquakes. Both scales are designed so that they produce magnitude numbers that are consistent with those from the Richter Local magnitude scale, and these improvements extended it's validity to earthquakes with magnitudes up to 8, however to measure earthquakes with magnitudes beyond this a new magnitude scale was required.

This new scale was developed in the 1970s and is known as the moment magnitude scale and derives the magnitude based on an earthquakes seismic moment. This is a calculation based on the length of the fault zone which ruptured, the amplitude of the fault movement when the rupture occurred (the length and amplitude giving a rupture cross sectional area) and the elastic modulus of the rock mass around the fault zone. It was decided that the familiar logarithmic scale produced by the Richter methodology be maintained to allow direct comparisons to be made and so the moment magnitude is also reported on the familiar scale.

Although more accurate at treating larger earthquakes the seismic moment and hence moment magnitude of an earthquake is more difficult to derive than the Richter magnitude and so initial estimates are most commonly made using the Richter scale. The common range of magnitudes and their relative effects are described below:

Less than 2.0: Micro - not felt.

2.0-2.9: Minor - not felt, but recorded.

3.0-3.9: Minor - felt, but rarely causes damage.

4.0-4.9: Light - noticeable shaking of items, damage unlikely.

5.0-5.9: Moderate - damage to poorly constructed buildings, unlikely damage to specially designed buildings.

6.0-6.9: Strong - destructive for up to 100 miles across populated areas.

7.0-7.9: Major - serious damage over large areas.

8.0-8.9: Great - serious damage over areas of several hundred miles.

9.0-9.9: Great - devastating damage in areas thousands of miles across.

10.0+: Great - yet to be recorded.

The intensity of an earthquake is currently most commonly measured using the

Modified Mercalli Intensity scale.

The scale indicates the perceived intensity of ground shaking based on the damage caused by an earthquake to buildings and infrastructure and the opinions of witnesses as to the severity of the felt ground movement.

In order to attempt to quantify the Mercalli scale and decrease it's reliance on the subjective opinion of witnesses, the USGS also include data of measured ground accelerations taken from seismometers in the formulation of the Mercalli value. In Europe earthquake intensity is derived using the Macroseismic scale which is essentially a further modification to the Modified Mercalli scale but essentially works the same way and in Japan and Taiwan, the Japan Meteorological Agency seismic intensity scale is used. This again is similar in concept to the Mercalli scale although the values and descriptions of damage used are somewhat different.

For more information, please see the related questions and links.

Answer 2

There are a number of scales used to measure earthquakes depending on what is of interest.

Scales which measure the amount of energy released by an earthquake are known as magnitude scales, these include the widely known Richter scale which is calculated based on the amplitude of seismic waves as measured on a seismometer but can not be used for large earthquakes (those with magnitudes greater than 7.0) and the less well known moment magnitude scale whose value is calculated based on measurements of the length and amplitude of the fault slip and the stiffness of the ground. This scale is used for large earthquakes greater than magnitude 7.0.

If you are interested in the severity of the ground shaking at a specific point, then you would use an intensity scale such as the Modified Mercalli scale or the European Macroseismic scale which score earthquakes based on witness reports of the perceived violence of the ground shaking, the degree of damage done to buildings and other structures and also on measured ground accelerations at a given location as recorded by seismometers.

Answer 3

One is the Richter Scale. It measures magnitude at the epicenter, which is a point directly above the focus. The focus is where the slipping of plates begin. The Richter Scale rates earthquakes from weakest to strongest. The other is the Mercalli Scale. It measures what people felt and what happened to objects.

Answer 4

Mercalli scale,Richter scale, Moment magnitude scale.

Answer 5

The moment magnitude scale. For further information, please see the related links.

Answer 6

The Richter Scale.

Answer 7

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