An earthquake – also called a quake, tremor, or temblor – is the shaking of the surface of Earth resulting from a sudden release of energy in the 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.
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.
The 1971 San Fernando earthquake occurred in the early morning of February 9 in the foothills of the San Gabriel Mountains in southern California. The unanticipated thrust earthquake had a magnitude of 6.5 on the scale and 6.6 on the scale, and a maximum Mercalli intensity of XI (Extreme). The event was one in a series that affected Los Angeles county in the late 20th century. Damage was locally severe in the northern San Fernando Valley and surface faulting was extensive to the south of the epicenter in the mountains, as well as urban settings along city streets and neighborhoods. Uplift and other effects affected private homes and businesses.
The New Madrid Seismic Zone, sometimes called the New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes in the Southern and Midwestern United States, stretching to the southwest from New Madrid, Missouri.
Induced seismicity is typically earthquakes and tremors that are caused by human activity that alters the stresses and strains on Earth's crust. Most induced seismicity is of a low magnitude. A few sites regularly have larger quakes, such as The Geysers geothermal plant in California which averaged two M4 events and 15 M3 events every year from 2004 to 2009. The Human-Induced Earthquake Database (HiQuake) documents all reported cases of induced seismicity proposed on scientific grounds and is the most complete compilation of its kind.
The 2005 Lake Tanganyika earthquake occurred at on 5 December with a moment magnitude of 6.8 and a maximum Mercalli intensity of X (Extreme). The shock occurred along the East African Rift, an active continental rift zone in East Africa that is characterized by normal faulting, and initiated at a depth of 22 kilometers (14 mi).
The 1959 Hebgen Lake earthquake occurred in the western United States on August 17 at 11:37 pm (MST) in southwestern Montana.
On February 4, 1975 at 19:36 CST, an earthquake of 7.5 and intensity (MMI) IX hit the city of Haicheng, Liaoning, China. Much of the city was evacuated before the earthquake, so few died from building collapse, however, many died from fire and hypothermia in the subsequent days. The evacuees lived during the deep winter in self-made tents made of tree branches, bed sheets, tarps and straw, 372 froze to death and 6,578 suffered frostbite, while a fire burned 341 to death and 980 suffered non-fatal burns. The fire was one of the most notable earthquake-induced fires in China, triggered from a combination of cooking, winter heating and lighting.
The 1967 Koynanagar earthquake occurred near Koynanagar town in Maharashtra, India on 11 December local time. The magnitude 6.6 shock hit with a maximum Mercalli intensity of VIII (Severe). It occurred near the site of Koyna dam, raising questions about induced seismicity, and claimed at least 177 lives and injured over 2,200.
The 1986 Chalfant Valley earthquake struck southern Mono County near Bishop and Chalfant, California at Pacific Daylight Time on July 21. With a moment magnitude of 6.2 and a maximum Mercalli intensity of VI (Strong), the shock injured two people and caused property damage estimated at $2.7 million in the affected areas. There was a significant foreshock and aftershock sequence that included a few moderate events, and was the last in a series of three earthquakes that affected southern California and the northern Owens Valley in July 1986.
The 1911 Sarez earthquake occurred at 18:41 UTC on 18 February in the central Pamir Mountains in the Rushon District of eastern Tajikistan. It had an estimated magnitude of 7.4 on the surface wave magnitude scale and a maximum felt intensity of about IX (Violent) on the Mercalli intensity scale. It triggered a massive landslide, blocking the Murghab River and forming the Usoi Dam, the tallest dam in the world, creating Sarez Lake. The earthquake and related landslides destroyed many buildings and killed about 100 people.
The Newmark's sliding block analysis method is an engineering that calculates permanent displacements of soil slopes during seismic loading. Newmark analysis does not calculate actual displacement, but rather is an index value that can be used to provide an indication of the structures likelihood of failure during a seismic event. It is also simply called Newmark's analysis or Sliding block method of slope stability analysis.
An earthquake occurred on 1 June 1786 in and around Kangding, in what is now China's Sichuan province. It had an estimated magnitude of about 7.75 and a maximum perceived intensity of X (Extreme) on the Mercalli intensity scale. The initial quake killed 435 people. After an aftershock ten days later, a further 100,000 died when a landslide dam collapsed across the Dadu river.
The 1979 Coyote Lake earthquake occurred at on August 6 with a moment magnitude of 5.7 and a maximum Mercalli Intensity of VII. The shock occurred on the Calaveras Fault near Coyote Lake in Santa Clara County, California and resulted in a number of injuries, including some that required hospitalization. Most of the $500,000 in damage that was caused was non-structural, but several businesses were closed for repairs. Data from numerous strong motion instruments was used to determine the type, depth, and extent of slip. A non-destructive aftershock sequence that lasted throughout the remainder of the month was of interest to seismologists, especially with regard to fault creep, and following the event local governments evaluated their response to the incident.
On May 4, 2018, an earthquake with a magnitude of 6.9 struck Hawaii island in the Hawaii archipelago at around 12:33 p.m. local time. The earthquake's epicenter was near the south flank of Kīlauea, which has been the site of seismic and volcanic activity since late April of that year. According to the United States Geological Survey the quake was related to the new lava outbreaks at the volcano, and it resulted in the Hilina Slump moving about two feet. It was the largest earthquake to affect Hawaii since the 1975 earthquake, which affected the same region, killing two people and injuring another 28.
On November 29, 1978 a moment magnitude 7.7–7.8 earthquake struck off the coast of the southern Mexican state Oaxaca. The thrust-faulting event caused severe damage in Oaxaca and Mexico City.
The 1968 Borrego Mountain earthquake occurred on April 8, at 18:28 PST in the geologically active Salton Trough of Southern California. The Salton Trough represents a pull-apart basin formed by movements along major faults. This region is dominated by major strike-slip faults one of them being the San Jacinto Fault which produced the 1968 earthquake. The mainshock's epicenter was near the unincorporated community of Ocotillo Wells in San Diego County. The moment magnitude (Mw ) 6.6 strike-slip earthquake struck with a focal depth of 11.1 km (6.9 mi). The zone of surface rupture was assigned a maximum Modified Mercalli intensity (MMI) of VII.
On 22 January 1988, a sequence of destructive earthquakes measuring 6.2, 6.3, and 6.6 struck southwest of Tennant Creek, Australia which was felt as far north as Darwin and in other regions of the country. The largest event of the sequence was the largest earthquake ever recorded in mainland Australia since records began in 1800. An intensity of IX (Violent) was observed. Despite the large magnitude of the earthquakes and a close proximity to a town, in a country where earthquakes of this size are not common, damages were limited. Thousands of aftershocks were reported and felt across Northern Territory.
The 1983 Kaoiki earthquake struck southern Hawaii Island on the morning of November 16, 1983. Measuring Mw 6.7, it was the largest to hit the island since 1975. The epicenter was located 50 km southeast of Hilo with an approximated depth of 12 km. The shallow strike-slip earthquake was assigned a maximum intensity of IX (Violent) on the Modified Mercalli scale. 6 people were injured, widespread damage and landslides were reported across the island.
The 1957 Sangchal earthquake struck northern Iran's Mazandaran province on 2 July 1957. It had a moment magnitude of 6.6 or 7.1 (Mw ), focal depth of 15 km (9.3 mi), and maximum Modified Mercalli intensity of IX (Violent). It devastated many communities in the Alborz Mountains and caused an estimated 1,500 fatalities. Damage was estimated at US$25 milion.
