New Delhi: Over 50 people have been killed after a magnitude 7.1 earthquake hit Tibet, near the border of Nepal, on January 7. The tremors were felt in several parts of India, including Bihar, Assam, and West Bengal. According to the National Centre for Seismology (NCS), the earthquake was recorded at 6.35 am, and the data also revealed that two more earthquakes hit the region shortly after the first one.
Do you know how earthquakes are measured and recorded? Let us understand through this article.
Measuring Earthquakes: The Role of Seismometers
According to the United States Geological Survey (USGS), earthquakes are recorded using a global network of seismometers. Seismometers, also known as seismographs, are sensitive tools that detect tectonic plate movements. They have a mass suspended by springs or pendulums, which stays steady during calm periods. When tectonic plates move, and seismic waves reach the seismometer, the mass vibrates, and these vibrations are recorded.
When an earthquake happens, each seismic station measures ground movement at that location. Data is gathered and analysed by various scientific institutions, including India’s National Centre for Seismology and the European-Mediterranean Seismological Centre (EMSC).
According to the National Institute of Disaster Management, the size of an earthquake depends on the fault’s size and the amount of slip on the fault. Scientists cannot measure this directly because faults are deep underground. Instead, they analyse seismogram recordings from seismographs on the surface to determine the earthquake’s size.
A small earthquake produces a short, slight wiggle, while a large earthquake creates a long, pronounced wiggle. The wiggle length depends on the fault size, and the wiggle amplitude depends on the amount of slip.
What is Magnitude?
The severity of an earthquake is expressed in terms of intensity and magnitude, which are different concepts. Magnitude indicates the amount of seismic energy released at the earthquake’s hypocenter, while intensity describes the observed effects of shaking on people, buildings, and the environment. The intensity of shaking can vary depending on a person’s location during the earthquake.
Magnitude is a number that reflects the relative size of an earthquake. It is based on the maximum motion recorded by a seismograph. Several scales exist, but the most commonly used ones are:
1. Local magnitude (ML), often called “Richter magnitude”
2. Surface-wave magnitude (Ms)
3. Body-wave magnitude (Mb)
4. Moment magnitude (Mw)
The first three scales have limited use and do not effectively measure large earthquakes. The moment magnitude (Mw) scale is more broadly applicable to all sizes of earthquakes but is harder to calculate. All magnitude scales should give similar values for the same earthquake.
The Richter Scale and its Limitations
The Richter scale, created in 1935 by Charles F. Richter of the California Institute of Technology, compares earthquake sizes. The magnitude is determined by calculating the logarithm of the wave amplitude recorded by seismographs. The formula accounts for the distance between various seismographs and the earthquake’s epicentre. The Richter scale expresses magnitude in whole numbers and decimal fractions.
For example, a magnitude of 5.3 indicates a moderate earthquake, while a strong earthquake can have a magnitude of 6.3. Each whole number increase in magnitude means a tenfold increase in amplitude, and each increase corresponds to about 31 times more energy than the previous whole number.
Richter Magnitudes and Earthquake effects
Richter Magnitudes
Description
Earthquake Effects
Frequency of Occurrence
< 2.0
Micro
Microearthquakes, not felt.
About 8,000 per day
2.0-2.9
Minor
Generally not felt, but recorded.
About 1,000 per day
3.0-3.9
Minor
Often felt, but rarely causes damage.
49,000 per year (est.)
4.0-4.9
Light
Noticeable shaking of indoor items, rattling noises. Significant damage unlikely.
6,200 per year (est.)
5.0-5.9
Moderate
Can cause major damage to poorly constructed buildings over small regions. At most slight damage to well-designed buildings.
800 per year
6.0-6.9
Strong
Can be destructive in areas up to about 160 kilometers (100 mi) across in populated areas.
120 per year
7.0-7.9
Major
Can cause serious damage over larger areas.
18 per year
8.0-8.9
Great
Can cause serious damage in areas several hundred miles across.
1 per year
9.0-9.9
Great
Devastating in areas several thousand miles across.
1 per 20 years
10
Epic
Never recorded
Extremely rare (Unknown)
A recent magnitude 7.1 earthquake in Tibet highlighted the importance of understanding earthquake measurement. Seismometers, or seismographs, globally record ground motion caused by tectonic plate movements. Though superseded by the moment magnitude scale (Mw), the Richter scale remains a common way to express earthquake magnitude, with each whole number increase representing a tenfold increase in amplitude. knowledge Knowledge News, Photos and Videos on General Knowledge
