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.
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. Not all scientists distinguish "prediction" and "forecast", but the distinction is useful.
The moment magnitude scale is a measure of an earthquake's magnitude based on its seismic moment. Mw was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori. Similar to the local magnitude/Richter scale (ML ) defined by Charles Francis Richter in 1935, it uses a logarithmic scale; small earthquakes have approximately the same magnitudes on both scales. Despite the difference, news media often use the term "Richter scale" when referring to the moment magnitude scale.
An interplate earthquake is an earthquake that occurs at the boundary between two tectonic plates. Earthquakes of this type account for more than 90 percent of the total seismic energy released around the world. If one plate is trying to move past the other, they will be locked until sufficient stress builds up to cause the plates to slip relative to each other. The slipping process creates an earthquake with relative displacement on either side of the fault, resulting in seismic waves which travel through the Earth and along the Earth's surface. Relative plate motion can be lateral as along a transform fault boundary, vertical if along a convergent boundary or a divergent boundary, and oblique, with horizontal and lateral components at the boundary. Interplate earthquakes associated at a subduction boundary are called megathrust earthquakes, which include most of the Earth's largest earthquakes.
The 1933 Long Beach earthquake took place on March 10 at south of downtown Los Angeles. The epicenter was offshore, southeast of Long Beach, California, on the Newport–Inglewood Fault. The earthquake had a magnitude estimated at 6.4 , and a maximum Mercalli intensity of VIII (Severe). Damage to buildings was widespread throughout Southern California. It resulted in 115 to 120 fatalities and an estimated $40 million worth of property damage, equivalent to $941 million in 2023. The majority of the fatalities resulted from people running out of buildings exposing themselves to the falling debris.
The 1999 Hector Mine earthquake occurred in Southern California, United States, on October 16 at 02:46:50 PDT. Its moment magnitude was 7.1 and the earthquake was preceded by 12 foreshocks, the largest of which had a magnitude of 3.8. The event is thought to have been triggered by the 1992 Landers earthquake which occurred seven years earlier. It also deformed nearby faults vertically and horizontally. The earthquake's hypocenter was at a depth of 20 kilometers and its epicenter at 34.603° N 116.265° W.
Kate Hutton, nicknamed the Earthquake Lady, Dr. Kate, or Earthquake Kate, is a former staff seismologist at the California Institute of Technology in Pasadena, California, where she monitored Southern California's earthquake activity for 37 years.
The 1938 Banda Sea earthquake occurred on February 2 with an estimated magnitude of 8.5–8.6 on the moment magnitude scale and a Rossi–Forel intensity of VII. This oblique-slip event generated destructive tsunamis of up to 1.5 metres in the Banda Sea region, but there were no deaths.
Lucile M. Jones is a 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 up on to provide information on recent earthquakes.
Seismotectonics is the study of the relationship between the earthquakes, active tectonics and individual faults of a region. It seeks to understand which faults are responsible for seismic activity in an area by analysing a combination of regional tectonics, recent instrumentally recorded events, accounts of historical earthquakes and geomorphological evidence. This information can then be used to quantify the seismic hazard of an area.
The 2002 Kalehe earthquake occurred on October 24 at 06:08 UTC. This earthquake had a magnitude 6.2, and the epicenter was located in Democratic Republic of the Congo, near Lake Kivu. Two people were reported dead. Building damage was reported in Goma, Lwiro, Kalehe, and Mugeri. The seismicity, volcanism, and uplift in the basin of Lake Kivu delimits the rift of a tectonic plate. Lake Kivu belongs to the western branch of the East African Rift System (EARS). The western branch is usually divided into several segments, and Lake Kivu belongs to the northern segment.
A deep-focus earthquake in seismology is an earthquake with a hypocenter depth exceeding 300 km. They occur almost exclusively at convergent boundaries in association with subducted oceanic lithosphere. They occur along a dipping tabular zone beneath the subduction zone known as the Wadati–Benioff zone.
The Advanced National Seismic System (ANSS) is a collaboration of the U.S. Geological Survey (USGS) and regional, state, and academic partners that collects and analyzes data on significant earthquakes to provide near real-time information to emergency responders and officials, the news media, and the public. Such information is used to anticipate the likely severity and extent of damage, and to guide decisions on the responses needed.
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.
The 2020 Central Idaho earthquake occurred in the western United States on March 31, 2020, at 5:52 PM MDT, near Ruffneck Peak in the Sawtooth Mountains of central Idaho, 72 miles (116 km) northeast of Boise and 19 miles (31 km) northwest of Stanley. It had a magnitude of 6.5 and was felt with a maximum intensity of VIII.
Donna Eberhart-Phillips is a geologist known for her research on subduction zones, especially in Alaska and New Zealand.
Ruth Harris is a scientist at the United States Geological Survey known for her research on large earthquakes, especially on how they begin, end, and cause the ground to shake. In 2019, Harris was elected a fellow of the American Geophysical Union who cited her "for outstanding contributions to earthquake rupture dynamics, stress transfer, and triggering".
The 1955 Lanao earthquake struck Lanao del Sur on April 1 at 02:17 local time. The earthquake measuring 7.4 on the moment magnitude scale and assigned a maximum intensity of VIII (Severe) on the Modified Mercalli intensity scale was one of the largest to hit Mindanao. It caused immense damage around Lake Lanao and the southern reaches of the Visayan islands. It killed at least 465 individuals and injured a further 898.
The 1968 Aegean Sea earthquake was a 7.0 earthquake that occurred in the early morning hours of February 20, 1968 local time about 57.1 km (35.5 mi) away from Myrina, Greece. This earthquake occurred between mainland Greece and Turkey, meaning both countries were impacted. 20 people died, and 39 people were injured to various degrees. It was the deadliest Greek earthquake since the 1956 Amorgos earthquake.
