An earthquake is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from those that are so weak that they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The seismicity at a particular location in the Earth is the average rate of seismic energy release per unit volume. The word tremor is also used for non-earthquake seismic rumbling.
The modified Mercalli intensity scale, developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the effects of an earthquake at a given location, distinguished from the earthquake's inherent force or strength as measured by seismic magnitude scales. While shaking is caused by the seismic energy released by an earthquake, earthquakes differ in how much of their energy is radiated as seismic waves. Deeper earthquakes also have less interaction with the surface, and their energy is spread out across a larger volume. Shaking intensity is localized, generally diminishing with distance from the earthquake's epicenter, but can be amplified in sedimentary basins and certain kinds of unconsolidated soils.
Soil liquefaction occurs when a cohesionless saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in which material that is ordinarily a solid behaves like a liquid. In soil mechanics, the term "liquefied" was first used by Allen Hazen in reference to the 1918 failure of the Calaveras Dam in California. He described the mechanism of flow liquefaction of the embankment dam as:
If the pressure of the water in the pores is great enough to carry all the load, it will have the effect of holding the particles apart and of producing a condition that is practically equivalent to that of quicksand... the initial movement of some part of the material might result in accumulating pressure, first on one point, and then on another, successively, as the early points of concentration were liquefied.
Paleoseismology looks at geologic sediments and rocks, for signs of ancient earthquakes. It is used to supplement seismic monitoring, for the calculation of seismic hazard. Paleoseismology is usually restricted to geologic regimes that have undergone continuous sediment creation for the last few thousand years, such as swamps, lakes, river beds and shorelines.
The 1964 Niigata earthquake struck at 13:01 local time on 16 June with a magnitude of either 7.5 or 7.6. The epicenter was on the continental shelf off the northwest coast of Honshu, Japan in Niigata Prefecture, about 50 kilometres (31 mi) north of the city of Niigata. The earthquake caused liquefaction over large parts of the city.
The Environmental Seismic Intensity scale is a seismic scale used for measuring the intensity of an earthquake on the basis of the effects of the earthquake on the natural environment.
The 1983 Sea of Japan earthquake occurred on May 26, 1983 at 11:59:57 local time. It had a magnitude of 7.8 on the moment magnitude scale. It occurred in the Sea of Japan, about 100 km west of the coast of Noshiro in Akita Prefecture, Japan. Out of the 104 fatalities, all but four were killed by the resulting tsunami, which struck communities along the coast, especially Aomori and Akita Prefectures and the east coast of Noto Peninsula. Images of the tsunami hitting the fishing harbor of Wajima on Noto Peninsula were broadcast on TV. The waves exceeded 10 meters (33 ft) in some areas. Three of the fatalities were along the east coast of South Korea. The tsunami also hit Okushiri Island, the site of a more deadly tsunami 10 years later.
The 1935 Helena earthquake occurred at in Montana, with an epicenter near Helena. It had a magnitude of 6.2 on the surface wave magnitude scale and a maximum perceived intensity of VIII (Severe) on the Mercalli intensity scale. The temblor on that date was the largest of a series of earthquakes that also included a large aftershock on October 31 of magnitude 6.0 and a maximum intensity of VIII. Two people died in the mainshock and two others died as a result of the October 31 aftershock. Property damage was over $4 million.
The 1805 Molise earthquake occurred on July 26 at 21:01 UTC. It has an estimated magnitude of 6.6 on the equivalent magnitude scale (Me) and a maximum perceived intensity of X on the Mercalli intensity scale. The area of greatest damage was between the towns of Isernia and Campobasso, while the area of intense damage extended over about 2,000 square kilometres. There were an estimated 5,573 deaths resulting from this earthquake and two of the aftershocks.
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.
In early 1981 the eastern Gulf of Corinth, Greece was struck by three earthquakes with a magnitude greater than 6 over a period of 11 days. The earthquake sequence caused widespread damage in the Corinth–Athens area, destroying nearly 8,000 houses and causing 20–22 deaths.
The 1739 Yinchuan–Pingluo earthquake rocked the northern Ningxia Hui Autonomous Region on January 3 with an epicenter in the prefecture-level city Shizuishan. The estimated magnitude 7.1–7.6 earthquake had a maximum intensity of XI on the Mercalli intensity scale, and killed about 50,000 residents and officials. It was widely felt; perceived in Shanxi, Shaanxi and Hebei provinces. Aftershocks persisted for more than two years with the largest being a 5.5 on February 13 that same year.
The 1900 Venezuelan earthquake, occurred on October 28 at between 4:30 and 4:45 am local time. This earthquake had an epicenter off Miranda State or near the Venezuelan capital Caracas, in the Cariaco Basin. It had an estimated moment magnitude of 7.6–7.7 and a surface-wave magnitude of 7.7–8.4. It had a maximum Mercalli intensity assigned VIII–X, causing landslides and liquefaction events. Many buildings were severely damaged or collapsed during the earthquake. It is thought to be the last great earthquake of the 19th century and the largest instrumentally recorded in the republic, having been felt throughout.
The 1852 Banda Sea earthquake struck on 26 November at 07:40 local time, affecting coastal communities on the Banda Islands. It caused violent shaking lasting five minutes, and was assigned XI on the Modified Mercalli intensity scale in the Maluku Islands. A tsunami measuring up to 8 m (26 ft) slammed into the islands of Banda Neira, Saparua, Haruku and Ceram. The tsunami caused major damage, washing away many villages, ships and residents. At least 60 people were killed in the earthquake and tsunami. The earthquake had an estimated moment magnitude of 7.5 or 8.4–8.8, according to various academic studies.
The 1889 Chilik earthquake occurred on July 11 on the Gregorian calendar, or June 30 on the Julian calendar at 15:14 local time in the Tien Shan mountains. The earthquake measured an estimated Mw 7.9–8.0 on the moment magnitude scale and was assigned a maximum intensity of X (Devastating) on the MSK 64 and Rossi-Forel scales. Over 92 people across Kazakhstan, Kyrgyzstan and China were killed.
The 1790 Oran earthquake occurred on October 10, striking near the coastal city of Oran in Algeria. The earthquake had an evaluated maximum seismic intensity of VIII–X on the European macroseismic scale (EMS-98). An estimated 3,000 people died during the earthquake and accompanying tsunami. The magnitude of this earthquake has been disputed among members of the paleoseismology field, with estimates ranging from 7.5 to even as small as 5.5.
The 1850 Xichang earthquake rocked Sichuan Province of Qing China on September 12. The earthquake which caused major damage in Xichang county had an estimated moment magnitude of 7.6–7.9 Mw and a surface wave magnitude of 7.5–7.7 Ms . An estimated 20,650 people died.
The 1885 Kashmir earthquake, also known as the Baramulla earthquake occurred on 30 May in Srinagar. It had an estimated moment magnitude of Mw 6.3–6.8 and maximum Medvedev–Sponheuer–Karnik scale intensity of VIII (Damaging). At least 3,081 people died and severe damage resulted.
The 1887 Verny earthquake occurred on June 8 at 04:35 local time in the Turkestan region of present-day Kazakhstan. It had an epicenter in the northern foothills of the Trans-Ili Alatau mountain range, or just south of the city of Verny,. This earthquake destroyed the city of Verny, killing at least 330 people. A moment magnitude of 7.3–7.7 and MSK 64 intensity of X (Devastating) has been estimated for the earthquake.
The 1879 Surigao earthquake occurred on June 30 at 18:38 02:55 local time on the northeastern tip of Mindanao. The earthquake with a moment magnitude (Mw ) of 7.4 struck with an epicenter just south of Lake Mainit. Extensive damage occurred but there were no reports of casualties.
