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An earthquake – also called a quake, tremor, or temblor – is the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak 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 San Andreas Fault is a continental right-lateral strike-slip transform fault that extends roughly 1,200 kilometers (750 mi) through the U.S. state of California. It forms part of the tectonic boundary between the Pacific plate and the North American plate. Traditionally, for scientific purposes, the fault has been classified into three main segments, each with different characteristics and a different degree of earthquake risk. The average slip rate along the entire fault ranges from 20 to 35 mm per year.
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 Ms scale and 6.6 on the Mw scale, and a maximum Mercalli intensity of XI (Extreme). The event was one in a series that affected Los Angeles County during 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 (NMSZ), 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.
The Calaveras Fault is a major branch of the San Andreas Fault System that is located in northern California in the San Francisco Bay Area. Activity on the different segments of the fault includes moderate and large earthquakes as well as aseismic creep. The last large event was the magnitude 6.2 1984 Morgan Hill event. The most recent moderate earthquakes were the magnitude 5.1 event on 25 October 2022, and the magnitude 5.6 2007 Alum Rock event.
The 2008 Illinois earthquake was one of the largest earthquakes ever recorded in the Midwest state of Illinois. This moderate strike-slip shock measured 5.2 on the moment magnitude scale and had a maximum Mercalli intensity of VII (Very strong). It occurred at 04:36:59 local time on April 18 near Bellmont and Mount Carmel, Illinois, within the Wabash Valley seismic zone. Earthquakes in this part of the country are often felt at great distances.
The Wabash Valley seismic zone is a tectonic region located in the Midwestern United States, centered on the valley of the lower Wabash River, along the state line between southeastern Illinois and southwestern Indiana.
The 1888 North Canterbury earthquake occurred at 4:10 am on 1 September following a sequence of foreshocks that started the previous evening, and whose epicentre was in the North Canterbury region of the South Island of New Zealand. The epicentre was approximately 35 kilometres (22 mi) west of Hanmer.
The 1968 Illinois earthquake was the largest recorded earthquake in the U.S. Midwestern state of Illinois. Striking at 11:02 a.m. on November 9, it measured 5.3 on the Richter scale. Although no fatalities occurred, the event caused considerable structural damage to buildings, including the toppling of chimneys and shaking in Chicago, the region's largest city. The earthquake was one of the most widely felt in U.S. history, largely affecting 23 states over an area of 580,000 sq mi (1,500,000 km2). In studying its cause, scientists discovered the Cottage Grove Fault in the Southern Illinois Basin.
The 1867 Manhattan earthquake struck Riley County, Kansas, in the United States on April 24, 1867, at 20:22 UTC, or about 14:30 local time. The strongest earthquake to originate in the state, it measured 5.1 on a seismic scale that is based on an isoseismal map or the event's felt area. The earthquake's epicenter was near the town of Manhattan.
The 2010 Baja California earthquake occurred on April 4 with a moment magnitude of 7.2 and a maximum Mercalli intensity of VII. The shock originated at 15:40:41 local time south of Guadalupe Victoria, Baja California, Mexico.
At 04:56 and 06:19 UTC on October 2, 1969, a pair of earthquakes of magnitude 5.6 and 5.7, respectively, struck the city of Santa Rosa, California, killing one person and damaging buildings. The maximum felt intensity for the two events was VII and VIII (Severe) respectively on the Mercalli intensity scale. The $8.35 million cost of the earthquakes went mostly to replace buildings damaged beyond repair. There were at least 200 aftershocks after the initial pair of earthquakes. At the time they were the largest earthquakes to affect the northern San Francisco Bay Area since the 1906 San Francisco earthquake.
The 1916 Irondale earthquake struck in the north-central region of the U.S. state of Alabama on October 18. The strongest earthquake in state history, it registered an estimated Richter scale magnitude of 5.1 and resulted in minor damage. Damage was limited to Shelby and Jefferson counties and reached its maximum severity near the epicenter in the city of Irondale, including cracked windows, fallen chimneys, and dried-up wells. While there were no fatalities, the earthquake spawned widespread panic, prompting alarmed workers to evacuate tall buildings.
The 1892 Laguna Salada earthquake occurred at 23:20 Pacific Standard Time on February 23. It had an estimated moment magnitude of 7.1–7.2 and a maximum perceived intensity of VIII (Severe). The shock was centered near the Mexico–United States border and takes its name from a large dry lake bed in Baja California, Mexico. There were no reported casualties, but the event affected the then largely-uninhabited areas of northern Mexico and Southern California.
The 1979 Imperial Valley earthquake occurred at 16:16 Pacific Daylight Time on 15 October just south of the Mexico–United States border. It affected Imperial Valley in Southern California and Mexicali Valley in northern Baja California. The earthquake had a relatively shallow hypocenter and caused property damage in the United States estimated at US$30 million. The irrigation systems in the Imperial Valley were badly affected, but no deaths occurred. It was the largest earthquake to occur in the contiguous United States since the 1971 San Fernando earthquake eight years earlier.
The 2000 Yountville earthquake occurred with a moment magnitude of 5 on a previously unmapped fault, about 3 miles (4.8 km) south southwest of Yountville, California in the Mayacamas Mountain Range under Mount Veeder and about 9 miles (14 km) south northwest of Napa, California. It occurred at 01:36 PDT on September 3.
The 1838 San Andreas earthquake is believed to be a rupture along the northern part of the San Andreas Fault in June 1838. It affected approximately 100 km of the fault, from the San Francisco Peninsula to the Santa Cruz Mountains. It was a strong earthquake, with an estimated moment magnitude of 6.8 to 7.2, making it one of the largest known earthquakes in California. The region was lightly populated at the time, although structural damage was reported in San Francisco, Oakland, and Monterey. It is unknown whether there were fatalities. Based on geological sampling, the fault created approximately 1.5 meters of slip.
On July 17, 2017, an earthquake struck near the Komandorski Islands, east of the Kamchatka Peninsula in the Bering Sea at. Although there were no casualties from this earthquake, it was notable for a rare characteristic known as supershear, and is one of the few times a large supershear earthquake has been observed. It was preceded by a few foreshocks months earlier, and aftershocks that continued for nearly six months.
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.
An earthquake occurred off the coast of the Alaska Peninsula on July 28, 2021, at 10:15 p.m. local time. The large megathrust earthquake had a moment magnitude of 8.2 according to the United States Geological Survey (USGS). A tsunami warning was issued by the National Oceanic and Atmospheric Administration (NOAA) but later cancelled. The mainshock was followed by a number of aftershocks, including three that were of magnitude 5.9, 6.1 and 6.9 respectively.
References
- Kolata, Dennis R.; Buschbach, T. C.; Treworgy, Janis D. (1978). The Sandwich Fault Zone of Northern Illinois. Vol. Information circular / Illinois State Geological Survey, [no. 505]. Urbana: Illinois State Geological Survey. hdl:10111/UIUCOCA:sandwichfaultzon505kola.
