Related Research Articles
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 based 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 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.
The 1703 Apennine earthquakes were a sequence of three earthquakes of magnitude ≥6 that occurred in the central Apennines of Italy, over a period of 19 days. The epicenters were near Norcia, Montereale and L'Aquila, showing a southwards progression over about 36 kilometres (22 mi). These events involved all of the known active faults between Norcia and L'Aquila. A total of about 10,000 people are estimated to have died as a result of these earthquakes, although because of the overlap in areas affected by the three events, casualty numbers remain highly uncertain.
In seismology, an isoseismal map is used to show countour lines of equally felt seismic intensity, generally measured on the Modified Mercalli scale. Such maps help to identify earthquake epicenters, particularly where no instrumental records exist, such as for historical earthquakes. They also contain important information on ground conditions at particular locations, the underlying geology, radiation pattern of the seismic waves, and the response of different types of buildings. They form an important part of the macroseismic approach, i.e. that part of seismology dealing with noninstrumental data. The shape and size of the isoseismal regions can be used to help determine the magnitude, focal depth, and focal mechanism of an earthquake.
The 1783 Calabrian earthquakes were a sequence of five strong earthquakes that hit the region of Calabria in southern Italy, the first two of which produced significant tsunamis. The epicenters form a clear alignment extending nearly 100 km from the Straits of Messina to about 18 km SSW of Catanzaro. The epicenter of the first earthquake occurred in the plain of Palmi. The earthquakes occurred over a period of nearly two months, all with estimated magnitudes of 5.9 or greater. Estimates of the total number of deaths lie in the range 32,000 to 50,000.
The 2010 Eureka earthquake occurred on January 9 at 4:27:38 pm PST offshore of Humboldt County, California, United States. The magnitude was measured 6.5 on the Mw scale, and its epicenter was located offshore in the Pacific Ocean 33 miles (53 km) west of the nearest major city, Eureka. Additionally, there was a separate earthquake further offshore of Eureka on February 4 with a slightly lower magnitude of 5.9. It was also the most significant earthquake in the Eureka area in terms of magnitude since the 1992 Cape Mendocino earthquakes. It was felt from Santa Cruz County, California in the south, to Eugene, Oregon in the north and to the east as far as Reno, Nevada.
The 2017 Chiapas earthquake struck at 23:49 CDT on 7 September in the Gulf of Tehuantepec off the southern coast of Mexico near the state of Chiapas, approximately 87 kilometres (54 mi) southwest of Pijijiapan, with a Mercalli intensity of IX (Violent). The moment magnitude was estimated to be Mw8.2.
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.
References
- (in Spanish) Instituto Nacional de Prevención Sísmica. Listado de Terremotos Históricos.