Exam 3: Physical Geography: Landforms

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Earthquakes are scaled using several different magnitude scales, which are designed to estimate the energy released by an earthquake. The most commonly known and widely used scale is the Richter scale, developed in 1935 by Charles F. Richter. However, the Richter scale has largely been superseded by the moment magnitude scale (Mw), which is now the standard scale used by seismologists to compare the size of earthquakes.

Here are the main scales used to measure earthquakes:

1. **Richter Scale**: The Richter scale measures the amplitude of seismic waves as recorded on seismographs. Each whole number increase on the Richter scale represents a tenfold increase in measured amplitude and roughly 31.6 times more energy release. The scale is logarithmic, meaning that each whole number step represents a tenfold increase in magnitude. However, the Richter scale is most accurate for small to medium-sized earthquakes (less than magnitude 7) and within 600 kilometers of the epicenter.

2. **Moment Magnitude Scale (Mw)**: The moment magnitude scale is based on the seismic moment of the earthquake, which is a measure of the total energy released by the earthquake. It is calculated from the area of the fault that slipped, the average amount of slip, and the force that was required to overcome the friction holding the rocks together. The moment magnitude scale is considered to provide a more accurate and consistent measure of earthquake size, especially for larger earthquakes, and is the scale most commonly used by seismologists today.

3. **Modified Mercalli Intensity Scale (MMI)**: The MMI scale measures the intensity of an earthquake, which is the effect of the earthquake on the Earth's surface, humans, buildings, and the natural environment. It is expressed in Roman numerals from I (not felt) to XII (total destruction) and is based on qualitative assessments and observations of people who experienced the earthquake.

4. **Body Wave Magnitude (Mb)**: This scale measures the magnitude of the primary (P) seismic waves.

5. **Surface Wave Magnitude (Ms)**: This scale measures the magnitude of the secondary (S) seismic waves that travel along the Earth's surface.

While the Richter scale is still frequently mentioned in the media and popular culture, it is important to note that the moment magnitude scale is the one most commonly used by the scientific community for reporting earthquake sizes. The moment magnitude scale provides a more uniform scale of measurement and is valid over a wider range of earthquake sizes and distances.