Richter seismic scale
The Richter seismic scale, also known as the local magnitude scale (ML ), is an arbitrary logarithmic scale that assigns a number to quantify the energy released by an earthquake, named after American seismologist Charles Francis Richter.
Global seismology uses this scale to determine the forces of earthquakes of a magnitude between 2.0 and 6.9 and from 0 to 400 kilometers in depth. Although the media often confuse the scales, when referring to current telluric events it is considered incorrect to say that an earthquake "had a magnitude greater than 7.0 on the Richter scale", since earthquakes with a magnitude greater than 6.9 are They have been measured since 1978 with the seismological scale of moment magnitude, since the latter is a scale that better discriminates in extreme values.
Development
It was developed by Charles Francis Richter with the collaboration of Beno Gutenberg in 1935, both researchers at the California Institute of Technology, with the original purpose of separating the large number of small earthquakes from the less frequent larger earthquakes observed in California in its time. The scale was developed to study only those earthquakes occurring within a particular area of Southern California whose seismograms would have been exclusively collected by the seismometer. Richter initially reported values accurate to quarter of a unit, however he later used decimal numbers.
M=log10 A+3log10 (8Δ Δ t)− − 2.92=log10 (A⋅ ⋅ Δ Δ t31.62){displaystyle M=log _{10}A+3log _{10}(8Delta t)-2.92=log _{10}left({Acdot Delta t^{3} over 1.62}right),!}
where:
- A{displaystyle A,} = width of waves in millimeters, taken directly into the sismogram.
- Δ Δ t{displaystyle Delta t,} = time in seconds from the start of the waves P (Primary) to the wave S (Secundarias).
- M{displaystyle M,} = arbitrary but constant magnitude to earthquakes that release the same amount of energy.
The use of the logarithm on the scale is to reflect the energy released in an earthquake. The logarithm built into the scale causes the values assigned to each level to increase logarithmically, rather than linearly. Richter got the idea from using logarithms on the stellar magnitude scale, used in astronomy to describe the brightness of stars and other celestial objects. Richter arbitrarily chose a magnitude 0 tremor to describe an earthquake that would produce a maximum horizontal displacement of 1 μm on a seismogram plotted by a Wood-Anderson torsion seismometer located 100 km from the epicenter. This decision was intended to prevent the assignment of negative magnitudes. However, the Richter scale had no upper or lower limit, and today, with more sensitive modern seismographs, they commonly detect movements with negative magnitudes.
Due to limitations of the Wood-Anderson torsion seismometer used to develop the scale, the original magnitude ML cannot be calculated for tremors larger than 6.8. Several researchers have proposed extensions to the local magnitude scale, the most popular being the surface wave magnitude MS and the body wave magnitude M i>b.
Richter seismological scale problems
The biggest problem with the local magnitude ML or Richter magnitude is that it is difficult to relate it to the physical characteristics of the origin of the earthquake. In addition, there is a saturation effect for magnitudes close to 8.3-8.5, due to the Gutenberg-Richter law of seismic spectrum scaling that causes traditional magnitude methods (ML, Mb, MS) produce estimates of similar magnitudes for tremors that they are clearly of different intensity. At the beginning of the 21st century, most seismologists considered the traditional magnitude scales obsolete, being replaced by a more physically significant measurement called the seismic moment, which is more suitable for relating physical parameters, such as the dimension of the seismic rupture. and the energy released by the earthquake.
In 1979, seismologists Thomas C. Hanks and Hiroo Kanamori, researchers at the California Institute of Technology, proposed the seismic scale of moment magnitude (MW), which provides a way of expressing seismic moments that can be roughly related to traditional measurements of seismic magnitudes.
Table of magnitudes
The greatest release of energy that could be measured was during the earthquake that occurred in the city of Valdivia (Chile), on May 22, 1960, which reached a moment magnitude (M W) of 9.5.
The following describes the typical effects of earthquakes of various magnitudes, near the epicenter. The values are estimates and must be taken with extreme caution, since the intensity and the effects on the ground will not only depend on the magnitude of the earthquake, but also on the distance from the epicenter, the depth, the focus of the epicenter and the geological conditions (some terrain can amplify seismic signals).
Typical effects of earthquakes of various magnitudes
| Magnitude (MW= 6.9 ML= 2.0 to 6.9) | Description | Effects of a earthquake | Frequency of occurrence |
|---|---|---|---|
| Less than 2.0 | Micro | Microsisms are not perceptible. | About 8,000 a day. |
| 2.0-2.9 | Minor | They are generally not perceptible. | About 1000 per day. |
| 3.0-3.9 | Perceptible often, but rarely cause damage. | 49 000 per year. | |
| 4.0-4.9 | Ligero | Movement of objects in the rooms that generates noise. Significant, but with unlikely damage. | 6200 a year. |
| 5,0-5,9 | Moderate | It can cause major damage to weak or poorly constructed buildings. In well-designed buildings the damage is mild. | 800 a year. |
| 6.0-6.9 | Strong. | They can destroy populated areas, up to 160 kilometres round. | 120 a year. |
| 7.0-7.9 | Major | It can cause serious damage to extensive areas. | 18 a year. |
| 8,0-8,9 | Epic or Catastrophic | It can cause serious damage to areas of several hundred kilometres. | 1-3 per year. |
| 9,0-9,9 | Devastators in areas of several thousand kilometers. | 1-2 in 20 years. | |
| 10,0+ | Legendary or apocalyptic | Never registered. | In the history of humanity (and since the historical records of the earthquakes) there has never been a earthquake of this magnitude. |
Scale equivalent to the energy released
Below is a table with the magnitudes of the scale and their equivalent in energy released.
| Magnitude Richter (ML{displaystyle M_{L}} or MS{displaystyle M_{S}}) | Magnitude moment | Equivalence of TNT energy | References |
|---|---|---|---|
| -1,5 | 1 g | Rotation of a rock at a lab table. | |
| 1.0 | 170 g | Small explosion at a building site. | |
| 1.5 | 910 g | Conventional World War II Pump. | |
| 2.0 | 6 kg | Explosion of a butane gas tank. | |
| 2.2 | 10 kg | Some of the daily earthquakes in the San Andrés Falla. | |
| 2.5 | 29 kg | Bombing the city of London. | |
| 2.7 | 64 kg | ||
| 3.0 | 181 kg | Explosion of a gas plant. If we think they happen daily inside the Tarapacá Region in Chile, they are generally not sensitive to their magnitude. | |
| 3.5 | 455 kg | Explosion of a mine. | |
| 4.0 | 6 t | Low-power atomic bomb. We believe that they occur daily in the border area of Chile-Argentina (Region of Antofagasta-Provincia de Jujuy-Provincia de Salta) at great depth and are generally not sensitive. | |
| 5,0 | 199 t | Albolote Earthquake, 1956 (Granada, Spain). Berja Earthquake 1993 (Almería, Spain). Earthquake of Lorca 2011 (Murcia, Spain). | |
| 5.1 | Earthquake caused by a North Korean nuclear test January 2016. | ||
| 5.3 | Earthquake caused by a nuclear test from North Korea of September 2016. | ||
| 5.5 | 500 t | El Calvario (Colombia) Earthquake, 2008. Popayán Earthquake 1983 (Colombia). Earthquake of the Rio de la Plata of 1888 (Buenos Aires, Argentina - Uruguay). | |
| 6.0 | 1270 t | 1994 Double Spring Flat Earthquake (Nevada, United States). Sismo de Mala of 2021 (Peru). | |
| 6.2 | 1 900 t | Costa Rica Earthquake 2009. Carabobo State Earthquake 2009 (Venezuela). Managua Earthquake 1972 (Nicaragua). Earthquake of the Coffee Axis of 1999 (Colombia). 2020 Petrinja Earthquake (Croatia). Sullana Earthquake 2021. | |
| 6.3 | 2 300 t | Alboran Sea Earthquake 2016 (Almería, Spain). Terremoto Amatrice (Lacio, Italy). | |
| 6.4 | 10 000 t | Salta Earthquake 2010 (Argentina). Taiwan Earthquake 2018. San Juan Earthquake of 2021 (Argentina). | |
| 6.5 | 31 550 t | Northridge Earthquake, 1994 (California, United States). Warrior Earthquake 2011 (Mexico). Earthquake of the coast of Tarapacá of 2009 (Iquique, Chile). | |
| 6.6 | 50 000 t | Los Santos Earthquake 2015 (Los Santos, Colombia). | |
| 6.7 | 98 300 t | Mendoza Earthquake 1985 (Argentina). L'Aquila Earthquake 2009 (Italy). Peruvian Earthquake 2011 (Loreto, Peru). Veracruz Earthquake 2011 (Veracruz, Mexico). Tecpan Earthquake 2014 (Guerrero, Mexico). Hokkaido Earthquake 2018 (Japan). Coquimbo Earthquake of 2019 (Coquimbo, Chile). | |
| 6.8 | 129 900 t | Bolivian Earthquake 1998 (Aiquile, Bolivia). | |
| 6.9 | 158 000 t | Loma Prieta Earthquake 1989 (San Francisco, United States). Hanshin-Awaji Earthquake 1995 (Kobe, Japan). Peaceful zone earthquake in Colombia (Departments of Nariño, Valle del Cauca and Cauca) in 2013. Guatemala Earthquake 2017. | |
| 7.0 | 199 000 t | Almeria Earthquake of 1522 (Spain). Cariac Earthquake 1997 (Venezuela). 2020 Aegean Sea Earthquake. | |
| 7.1 | 236 000 t | Biobio-Araucanian Earthquake 2010 (Chile). Punitaqui Earthquake 1997 (Chile). Alaska Earthquake 2016 (United States). Puebla Earthquake 2017 (Mexico). Southern Peru Earthquake 2018. Warrior Earthquake of 2021 (Mexico) | |
| 7.2 | 250 000 t | Spitak Earthquake 1988 (Armenia). Baja California Earthquake 2010 (Mexicali, Baja California). Equator Earthquake 2010 (180 kilometers from Ambato). Warrior Earthquake 2014 (Mexico). Oaxaca Earthquake 2018 (Mexico). Haiti Earthquake of 2021. | |
| 7.3 | 419 700 t | Veracruz Earthquake 1973 (Mexico). Honduras Earthquake 2009. Xinjiang Earthquake 2014 (China). Kermanshah Earthquake 2017 (Iran). Venezuelan Earthquake 2018. Fukushima Earthquake of 2022 (Japan). | |
| 7.4 | 550 000 t | Earthquake of La Ligua of 1965 (Chile). Guatemalan Earthquake 2012. Warrior-Oaxaca Earthquakes 2012 (Oaxaca, Mexico). | |
| 7.5 | 750 000 t | Guatemalan Earthquake of 1976. Earthquake of Caucete 1977 (San Juan, Argentina). Oaxaca Earthquake 1999 (Mexico). Afghanistan Earthquake 2015. Célebes Earthquake 2018 (Indonesia). San Salvador Earthquake 1986. | |
| 7.6 | 820 000 t | Colima Earthquake 2003 (Mexico). Costa Rica Earthquake 2012. De Chiloé Island Earthquake 2016 (Chile). | |
| 7.7 7.7 | 997 000 t | Earthquake of Limon of 1991 (Limon, Costa Rica and Bocas del Toro, Panama). Orizaba Earthquake of 1937 (Veracruz, Mexico). Tocopilla Earthquake 2007 (Tocopilla, Chile). Mexico Earthquake of 1957 (Mexico). Replica of the 2014 Iquique Earthquake (Chile). Earthquake of El Salvador 2001 (El Salvador). Michoacán Earthquake of 2022 (Mexico). | |
| 7.8 | 1 250 000 t | Earthquake of San Juan de 1944 (San Juan, Argentina) Sichuan Earthquake 2008 (China). Tarapacá Earthquake 2005 (Iquique, Chile). Nepal Earthquake April 2015. Ecuadorian Earthquake 2016 (Manta, Esmeraldas, Ecuador). Christchurch Earthquake 2016 (New Zealand). Sumatra Earthquake 2016. Turkey and Syria Earthquakes of 2023. | |
| 7.9 | 5 850 000 t | Earthquake of Áncash of 1970 (Peru). | |
| 8,0 | 10 120 000 t | Peruvian Earthquake 2007 (Pisco, Peru). Algarrobo Earthquake 1985 (Chile). | |
| 8.1 | 16 460 000 t | Mexico Earthquake 1985 (Michoacán, Mexico). | |
| 8.2 | 21 000 000 t | Chiapas Earthquake 2017 (Mexico). Arica and Iquique Earthquake 2014 (Chile) Valparaiso Earthquake of 1906 (Chile). | |
| 8.3 | 50 190 000 t | Storm Pump (Soviet Union). Guatemalan Earthquake of 1942. | |
| 8.4 | 50 190 000 t | Coquimbo Earthquake 2015 (Chile). Jalisco-Colima Earthquake of 1932 (Mexico). | |
| 8.5 | 119 500 000 t | Sumatra Earthquake in 2007. Southern Peru Earthquake 2001 (Arequipa, Peru). Valdivia Earthquake of 1575 (Chile). | |
| 8.6 | 119 500 000 t | Earthquake of San Juan de 1894 (San Juan, Argentina). Sumatra Earthquake 2012. Vallenar Earthquake of 1922 (Chile). San Francisco Earthquake 1906 (United States). New Spain Earthquake of 1787 (Mexico). | |
| 8.7 | 171 000 t | Valparaiso Earthquake of 1730 (Chile). Lisbon Earthquake of 1755 (Lisbon, Portugal). | |
| 8.8 | 210 000 t | Cobquecura Earthquake 2010 (Chile). Earthquake of Ecuador and Colombia of 1906. | |
| 9.0 | 240 000 t | Japan Earthquake 2011. Kamchatka Earthquake of 1952 (Soviet Union). Arica Earthquake 1868 (Chile). Lima Earthquake of 1746 (Peru). Cascadia Earthquake of 1700. | |
| 9,1 | 260 000 t | 2004 Indian Ocean Earthquake (Sumatra, Indonesia). | |
| 9,2 | 260 000 t | Anchorage Earthquake of 1964 (Alaska, United States). | |
| 9,5 | 290 000 t | Valdivia Earthquake of 1960 (Chile). The most powerful recorded in the history of humanity, since the invention of the seismographer. | |
| 10,0 | 630 000 t | Estimated for the crash of a 2 km diameter rocky meteorite that impacts 25 km/s (90 000 km/h). | |
| 12,0 | 1012t 106megatons 1 teraton | Earth fracture through the center. Number of solar energy received daily on Earth. | |
| 13.0 | 108megatons 100 teratons | Impact on the Yucatan peninsula that caused the crater of Chicxulub 65 million years ago. | |
| 25,0 | 1.2 Hiroshima atomic bomb quadrillions | Impact of Theia 4.530 million years ago. There is no precise place of impact due to the size of the planetoid. | |
| 32,0 | 1.5×1043t | Gamma-ray burst of the Magnetar SGR 1806-20, registered on December 27, 2004. Earthquake similar to the solar surface. |
Use of units in the media
In the media, in Spain and Latin America, it is common to combine the terms proper to the measurement of magnitude (energy) and intensity (effects), and even to confuse both concepts. It can be heard that "the earthquake was 3.7 degrees", using the term degree to express the magnitude, when that unit or term is typical of the measurement of intensities on the Mercalli scale, in for which there are no decimal values.
Another way that is also used to falsely resolve this way of indicating the importance of the earthquake is to publish that the earthquake had "a magnitude of 3.7 degrees", which is equally confusing, since it amounts to saying that "the marathon runner covered a distance of 2 hours and 15 minutes."
These forms should be avoided, saying that "the earthquake had a magnitude of 3.7", or reached 3.7 on the Richter scale, although this second expression is not entirely correct, since for some time the Earthquake magnitude is measured on the moment magnitude scale, matching the Richter scale only for earthquakes of magnitude less than 6.9.
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