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 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.
Seismology is the scientific study of earthquakes and the generation and propagation of elastic waves through the Earth or other planetary bodies. It also includes studies of earthquake environmental effects such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, glacial, fluvial, oceanic microseism, atmospheric, and artificial processes such as explosions and human activities. A related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of Earth motion as a function of time, created by a seismograph is called a seismogram. A seismologist is a scientist works in basic or applied seismology.
Earthquake prediction is a branch of the science of seismology concerned with the specification of the time, location, and magnitude of future earthquakes within stated limits, and particularly "the determination of parameters for the next strong earthquake to occur in a region". Earthquake prediction is sometimes distinguished from earthquake forecasting, which can be defined as the probabilistic assessment of general earthquake hazard, including the frequency and magnitude of damaging earthquakes in a given area over years or decades.
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 1976 Tangshan earthquake was a 7.6 earthquake that hit the region around Tangshan, Hebei, China, at 3:42 a.m. on 28 July 1976. The maximum intensity of the earthquake was XI (Extreme) on the Mercalli scale. In minutes, 85 percent of the buildings in Tangshan collapsed or were rendered unusable, all services failed, and most of the highway and railway bridges collapsed or were seriously damaged. The official report claimed 242,769 deaths and 164,851 serious injuries in Tangshan, but when taking into account the missing, the injured who later died and the deaths in nearby Beijing and Tianjin, scholars accepted at least 300,000 died, making it the deadliest earthquake in recorded history and one of the worst disasters in China by death toll.
James O. Berkland was an American geologist who controversially claimed to be able to predict earthquakes, including the 1989 Loma Prieta earthquake and 1994 Northridge Earthquake and who popularized the idea that some people are earthquake sensitive. He was profiled in a popular 2006 book as The Man Who Predicts Earthquakes. The book includes a chapter that notes "Many of Berkland's theories--based on tides, moons, disoriented pets, lost cats and dogs, and magnetic field changes--were factors in the great Indian Ocean quake-tsunami disaster on December 26, 2004." but neither his methods nor his predictions have been published in any scientific journals for peer review. His results have been disputed by peers, with other scientists going so far as calling him a crank and a clown.
Susan Elizabeth Hough is a seismologist at the United States Geological Survey in Pasadena, California, and scientist in charge of the office. She has served as an editor and contributor for many journals and is a contributing editor to Geotimes Magazine. She is the author of five books, including Earthshaking Science (Princeton).
Earthquake forecasting is a branch of the science of seismology concerned with the probabilistic assessment of general earthquake seismic hazard, including the frequency and magnitude of damaging earthquakes in a given area over years or decades. While forecasting is usually considered to be a type of prediction, earthquake forecasting is often differentiated from earthquake prediction, Earthquake forecasting estimates the likelihood of earthquakes in a specific timeframe and region, while earthquake prediction attempts to pinpoint the exact time, location, and magnitude of an impending quake, which is currently not reliably achievable.Wood & Gutenberg (1935). Kagan says: "This definition has several defects which contribute to confusion and difficulty in prediction research." In addition to specification of time, location, and magnitude, Allen suggested three other requirements: 4) indication of the author's confidence in the prediction, 5) the chance of an earthquake occurring anyway as a random event, and 6) publication in a form that gives failures the same visibility as successes. Kagan & Knopoff define prediction "to be a formal rule where by the available space-time-seismic moment manifold of earthquake occurrence is significantly contracted ...."</ref> Both forecasting and prediction of earthquakes are distinguished from earthquake warning systems, which, upon detection of an earthquake, provide a real-time warning to regions that might be affected.
Lucile M. Jones is an American seismologist and public voice for earthquake science and earthquake safety in California. One of the foremost and trusted public authorities on earthquakes, Jones is viewed by many in Southern California as "the Beyoncé of earthquakes" who is frequently called upon to provide information on recent earthquakes.
The San Jacinto Fault Zone (SJFZ) is a major strike-slip fault zone that runs through San Bernardino, Riverside, San Diego, and Imperial Counties in Southern California. The SJFZ is a component of the larger San Andreas transform system and is considered to be the most seismically active fault zone in the area. Together they relieve the majority of the stress between the Pacific and North American tectonic plates.
The Seismological Society of America (SSA) is an international scientific society devoted to the advancement of seismology and the understanding of earthquakes for the benefit of society. Founded in 1906, the society has members throughout the world representing seismologists and other geophysicists, geologists, engineers, insurers, and policy-makers in preparedness and safety.
The Brawley Seismic Zone (BSZ), also known as the Brawley fault zone, is a predominantly extensional tectonic zone that connects the southern terminus of the San Andreas Fault with the Imperial Fault in Southern California. The BSZ is named for the nearby town of Brawley in Imperial County, California, and the seismicity there is characterized by earthquake swarms.
The 1995 Gulf of Aqaba earthquake occurred on November 22 at 06:15 local time and registered 7.3 on the scale. The epicenter was located in the central segment of the Gulf of Aqaba, the narrow body of water that separates Egypt's Sinai Peninsula from the western border of Saudi Arabia. At least 8 people were killed and 30 were injured in the meizoseismal area.
Harry Oscar Wood (1879–1958) was an American seismologist who made several significant contributions in the field of seismology in the early twentieth-century. Following the 1906 earthquake in San Francisco, California, Wood expanded his background of geology and mineralogy and his career took a change of direction into the field of seismology. In the 1920s he co-developed the torsion seismometer, a device tuned to detect short-period seismic waves that are associated with local earthquakes. In 1931 Wood, along with another seismologist, redeveloped and updated the Mercalli intensity scale, a seismic intensity scale that is still in use as a primary means of rating an earthquake's effects.
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.
ShakeAlert is an earthquake early warning system (EEW) in the United States, developed and operated by the United States Geological Survey (USGS) and its partners. As of 2021, the system issues alerts for the country's West Coast. It is expected that the system will be expanded to other seismically active areas of the United States in the future. ShakeAlert is one of two EEW systems available in the United States, with Google's Android Earthquake Alerts System being the other.
The 1918 San Jacinto earthquake occurred in extreme eastern San Diego County in Southern California on April 21 at . The shock had a moment magnitude of 6.7 and a maximum Mercalli intensity of IX (Violent). Several injuries and one death occurred with total losses estimated to be $200,000.
The 2019 Ridgecrest earthquakes of July 4 and 5 occurred north and northeast of the town of Ridgecrest, California located in Kern County and west of Searles Valley. They included three initial main shocks of magnitudes 6.4, 5.4, and 7.1, and many perceptible aftershocks, mainly within the area of the Naval Air Weapons Station China Lake. Eleven months later, a Mw 5.5 aftershock took place to the east of Ridgecrest. The first main shock occurred on Thursday, July 4 at 10:33 a.m. PDT, approximately 18 km (11.2 mi) ENE of Ridgecrest, and 13 km (8.1 mi) WSW of Trona, on a previously unnoticed NE-SW trending fault where it intersects the NW-SE trending Little Lake Fault Zone. This quake was preceded by several smaller earthquakes, and was followed by more than 1,400 detected aftershocks. The M 5.4 and M 7.1 quakes struck on Friday, July 5 at 4:08 a.m. and 8:19 p.m. PDT approximately 10 km (6 miles) to the northwest. The latter, now considered the mainshock, was the most powerful earthquake to occur in the state in 20 years. Subsequent aftershocks extended approximately 50 km (~30 miles) along the Little Lake Fault Zone.
