What are the Differences Between the Richter and Mercalli Scale?
The two scales differ on several aspects:
- Richter scale ratings are produced soon after an earthquake occurs as scientists only need to compare the data from various seismograph stations. Mercalli ratings take some time as investigators need to correspond with eyewitnesses to determine the occurrences witnessed during the earthquake. Once the researchers acquire an idea of the range of damage, they can then assign an appropriate rating by use of the Mercalli criteria.
- The Mercalli scale determines the intensity of a particular earthquake by its observed effects. The Richter scale determines the magnitude of the earthquake in question by measuring its seismic waves.
- While the Richter scale is logarithmic, the Mercalli scale is linear. The measuring tool used in a Richter scale is a seismograph while observation is used on the Mercalli scale. The Richter scale is absolute which means that wherever an earthquake is registered, it will have the same measurement on the Richter scale.
- The Mercalli scale is relative at it relies on people's feelings and reactions to an earthquake. People experience varying levels of shaking in various areas and the further away a person is located from the epicenter, the less shaking is felt.
An earthquake is the vibration of the Earth's surface which results from rocks of the Earth's crust breaking under stress. Earthquakes typically occur along fault lines that is where tectonic plates collide or slide past one another. The breaking of the rocks releases vibrational energy which radiates in all directions from the focus point. Seismologists use various methods to measure the exact intensity of a particular earthquake.
The Richter Scale
The Richter scale was unveiled in the 1930s, and it gives a magnitude number to quantify an earthquake's size. The Richter magnitude of a particular earthquake is deduced from the logarithm of the amplitude of the waves recorded by seismographs. Adjustments are made for the difference in distance between individual seismographs as well as the epicenter of the earthquakes. It is a base-10 logarithmic scale which means that every order of magnitude ranks ten times stronger than the previous one. An earthquake measuring 5.0, for example, possesses shaking amplitude ten times more intense than that of an earthquake which measures 4.0 at the same distance. Magnitudes on the scale are expressed in both whole numbers and decimals.
The Mercalli Scale
Giuseppe Mercalli, an Italian volcanologist, introduced the Mercalli Intensity Scale in 1885. The scale was expanded to accommodate 12 degrees of intensity by Adolfo Cancani in 1902. The scale was designed to determine the extent of damage in the aftermath of an earthquake. Mercalli ratings are assigned by Roman numerals. An earthquake which registers low intensity is addressed as an I. The highest rating is a XII, and it denotes an earthquake which devastates structures, triggers natural disasters such as tsunamis, and landslides.
Uses And Application
The Mercalli scale is only employed in inhabited regions and it is not regarded as particularly scientific as the accounts of witnesses may vary, and the occurring damage may not reflect the strength of an earthquake accurately. The scale is mostly used in comparing the devastation caused by earthquakes in different regions. The Richter scale is favored by scientists in measuring the magnitudes of many recent earthquakes as it allows them to correctly compare the intensity of earthquakes at varying locations and time.