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The Modified Mercalli intensity scale measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake.
Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at a given location. Magnitudes are usually determined from measurements of an earthquake's seismic waves as recorded on a seismogram. Magnitude scales vary on what aspect of the seismic waves are measured and how they are measured. Different magnitude scales are necessary because of differences in earthquakes, the information available, and the purposes for which the magnitudes are used.
The 1949 Tierra del Fuego earthquakes occurred slightly more than eight hours apart on 17 December. Their epicenters were located in the east of the Chilean Tierra del Fuego Province, close to the Argentine border on the island of Tierra del Fuego.
The 1952 San Juan earthquake took place on 11 June at 00:31:43 UTC in the province of San Juan, Argentina. It measured 6.8 on the moment magnitude scale with a depth of 30 kilometers (19 mi). The earthquake was felt in San Juan with a maximum of VIII (Severe) on the Mercalli intensity scale. It caused damage in some locations in the south and west of the province, and a small number of casualties.
The 1920 Mendoza earthquake took place in the province of Mendoza, Argentina, on 17 December at 6:59:49 p.m. It measured magnitude 6.0, and its epicenter was at 32°42′S68°24′W, with a depth of 40 km.
The 2006 Gulf of Mexico earthquake occurred in the eastern Gulf of Mexico on September 10 at 10:56 AM Eastern Daylight Time. The intraplate earthquake measured 5.9 on the moment magnitude scale and its epicenter was located about 250 miles (400 km) west-southwest of Anna Maria, Florida. The event was felt throughout much of the Gulf Coast of the United States and was the second earthquake of magnitude 5 or greater in the Gulf during 2006. Felt intensities, as measured on the Mercalli intensity scale, were as high as IV (Light) in Florida, with parts of Georgia at III (Weak).
The Richter scale, also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale, is a measure of the strength of earthquakes, developed by Charles Francis Richter in collaboration with Beno Gutenberg, and presented in Richter's landmark 1935 paper, where he called it the "magnitude scale". This was later revised and renamed the local magnitude scale, denoted as ML or ML .
The 2007 Alum Rock earthquake occurred on October 30 at 8:04 p.m. Pacific Daylight Time in Alum Rock Park in San Jose, in the U.S. state of California. It measured 5.6 on the moment magnitude scale and had a maximum Mercalli intensity of VI (Strong). The event was then the largest in the San Francisco Bay Area since the 1989 Loma Prieta earthquake, which measured 6.9 on the moment magnitude scale, but was later surpassed by the 2014 South Napa earthquake. Ground shaking from the Alum Rock quake reached San Francisco and Oakland and other points further north. Sixty thousand felt reports existed far beyond Santa Rosa, as far north as Eugene, Oregon.
The 1925 Charlevoix–Kamouraska earthquake struck northeastern North America on February 28, reaching 6.2 on the moment magnitude scale. It was one of the most powerful measured in Canada in the 20th century, with a maximum perceived intensity of VIII (Severe) on the Mercalli intensity scale at its epicentre in the area of Charlevoix-Kamouraska along the Saint Lawrence River near île aux Lièvres and not greater than VI (Strong) in the United States. The quake was felt in Quebec City, Shawinigan, Montreal, as far south as Virginia, and as far west as the Mississippi River.
The 1965 Puget Sound earthquake occurred at 08:28 AM PDT on April 29 within the Puget Sound region of Washington state. It had a magnitude of 6.7 on the moment magnitude scale and a maximum perceived intensity of VIII (Severe) on the Mercalli intensity scale. It caused the deaths of seven people and about $12.5–28 million in damage. There were no recorded aftershocks.
Striking central Romania on August 30 at 21:28 UTC, the 1986 Vrancea earthquake killed more than 150 people, injured over 500, and damaged over 50,000 homes. The second largest earthquake in the area since the modernization of earthquake monitoring devices, it was felt north to Poland and south to Italy and Greece. The death toll makes it the second deadliest earthquake to occur in 1986 worldwide, after major seism of San Salvador that took the lives of almost 1,500 people.
The 1974 Zhaotong earthquake occurred at 3:25 in the morning local time on 11 May 1974, with a Coordinated Universal Time (UTC) time of 19:25:16 on 10 May. It had a magnitude that was measured at 7.0 on the moment magnitude scale and 7.1 on the surface wave magnitude scale. It had a maximum perceived intensity of IX (Violent) on the Mercalli intensity scale. The epicenter was located in Zhaotong prefecture in Yunnan province and it caused between 1,641 and 20,000 deaths.
The 1954 Chlef earthquake struck Chlef Province in French Algeria on September 9 at 02:04:43 local time. The shock measured 6.7 on the moment magnitude scale and had a maximum Mercalli intensity of XI (Extreme). It destroyed Chlef, then named Orléansville, leaving over 1,243 people dead and 5,000 injured. Damage was estimated at $6 million. It was followed by multiple aftershocks. Algeria faces annual earthquakes and has undergone several changes to its earthquake building codes since its first earthquake engineering regulations from 1717.
The 1992 Murindó earthquake occurred on October 18 at 15:11 UTC with an epicenter in the Department of Chocó, northern Colombia. The shallow magnitude 7.2 earthquake struck northwest of the town of Murindó, killing ten and injured more than a hundred. Thirty-three municipalities were severely damaged.
Seismic intensity scales categorize the intensity or severity of ground shaking (quaking) at a given location, such as resulting from an earthquake. They are distinguished from seismic magnitude scales, which measure the magnitude or overall strength of an earthquake, which may, or perhaps may not, cause perceptible shaking.
The Nemuro-Oki earthquake in scientific literature, occurred on June 17 at 12:55 local time. It struck with an epicenter just off the Nemuro Peninsula in northern Hokkaidō, Japan. It measured 7.8–7.9 on the moment magnitude scale (Mw ), 8.1 on the tsunami magnitude scale (Mt ) and 7.4 on the Japan Meteorological Agency magnitude scale (MJMA ).
The 1984 Cachar earthquake rattled much of Southern Assam on December 31, 1984, at 5:03 a.m. (UTC+5:30) with an epicenter 20 kilometers southwest of Lakhipur. The quake measured with a magnitude of 6.0 on the moment magnitude scale and an estimated intensity of VIII (Severe) on the Modified Mercalli intensity scale. About 20 people died and 100 others sustained mild to severe injuries.
The 1983 Heze earthquake occurred near the administrative borders between the provinces of Shandong and Henan in the People's Republic of China on November 7, 1983, 05:09 local time and date. The earthquake had a body-wave magnitude of 5.7 and maximum intensity of VII on the Modified Mercalli intensity scale. The event caused 34 deaths and injured 2,200 people. More than 3,300 houses were destroyed.
The 2022 Guatemala earthquake occurred on the early morning of February 16, 2022 in the southern regions of Guatemala. The quake measured a moment magnitude of 6.2 and reached a peak intensity of VI (Strong) on the Modified Mercalli Intensity scale. Damage was widespread but light in and around the capital, Guatemala City, resulting mostly in cracked walls and rockslides.
References
- (in Spanish) Instituto Nacional de Prevención Sísmica. Listado de Terremotos Históricos.