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.
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.
Peak ground acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. PGA is equal to the amplitude of the largest absolute acceleration recorded on an accelerogram at a site during a particular earthquake. Earthquake shaking generally occurs in all three directions. Therefore, PGA is often split into the horizontal and vertical components. Horizontal PGAs are generally larger than those in the vertical direction but this is not always true, especially close to large earthquakes. PGA is an important parameter for earthquake engineering, The design basis earthquake ground motion (DBEGM) is often defined in terms of PGA.
In seismology, strong ground motion is the strong earthquake shaking that occurs close to a causative fault. The strength of the shaking involved in strong ground motion usually overwhelms a seismometer, forcing the use of accelerographs for recording. The science of strong ground motion also deals with the variations of fault rupture, both in total displacement, energy released, and rupture velocity.
An earthquake warning system or earthquake early warning system is a system of accelerometers, seismometers, communication, computers, and alarms that is devised for notifying adjoining regions of a substantial earthquake while it is in progress. This is not the same as earthquake prediction, which is currently incapable of producing decisive event warnings.
The 1868 Hayward earthquake occurred in the San Francisco Bay Area, California, United States on October 21. With an estimated moment magnitude of 6.3–6.7 and a maximum Mercalli intensity of IX (Violent), it was the most recent large earthquake to occur on the Hayward Fault Zone. It caused significant damage and a number of deaths throughout the region, and was known as the "Great San Francisco earthquake" prior to the 1906 San Francisco earthquake and fire.
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is an agency of the United States government with work spanning the disciplines of biology, geography, geology, and hydrology. The agency was founded on March 3, 1879 in order to study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The agency is also known to make maps of extraterrestrial planets and moons based of data from the U.S. space probes.
The 1984 San Pedro Basin earthquake occurred on June 24 at with a moment magnitude of 6.7 and a maximum Mercalli intensity of VII. The event occurred off the southern coast of the Dominican Republic and resulted in an estimated five fatalities.
The 1997 Chittagong earthquake occurred on 21 November at 11:23 UTC in the Bangladesh-India-Myanmar border region. It had a magnitude of 6.1. The epicenter was located in southern Mizoram, India. No fatalities were reported there, but 23 people were killed in Chittagong when a five-story building collapsed in Bangladesh. The shaking could also be felt in Dhaka.
Recent advances are improving the speed and accuracy of loss estimates immediately after earthquakes so that injured people may be rescued more efficiently. "Casualties" are defined as fatalities and injured people, which are due to damage to occupied buildings. After major and large earthquakes, rescue agencies and civil defense managers rapidly need quantitative estimates of the extent of the potential disaster, at a time when information from the affected area may not yet have reached the outside world. For the injured below the rubble every minute counts. To rapidly provide estimates of the extent of an earthquake disaster is much less of a problem in industrialized than in developing countries. This article focuses on how one can estimate earthquake losses in developing countries in real time.
The 2011 Guerrero earthquake struck with a moment magnitude of 5.7 in southern Mexico at on 5 May. It was positioned west of Ometepec, Guerrero, with a focal depth of 24 km (14.9 mi), and was lightly felt in many adjacent areas.
On August 23, 2011, a magnitude 5.8 earthquake hit the Piedmont region of the U.S. state of Virginia at 1:51:04 p.m. EDT. The epicenter, in Louisa County, was 38 mi (61 km) northwest of Richmond and 5 mi (8 km) south-southwest of the town of Mineral. It was an intraplate earthquake with a maximum perceived intensity of VIII (Severe) on the Mercalli intensity scale. Several aftershocks, ranging up to 4.5 in magnitude, occurred after the main tremor.
The Oklahoma earthquake swarms are an ongoing series of human activity-induced earthquakes affecting central Oklahoma, southern Kansas, northern Texas since 2009. Beginning in 2009, the frequency of earthquakes in the U.S. state of Oklahoma rapidly increased from an average of fewer than two 3.0+ magnitude earthquakes per year since 1978 to hundreds each year in the 2014–17 period. Thousands of earthquakes have occurred in Oklahoma and surrounding areas in southern Kansas and North Texas since 2009. Scientific studies attribute the rise in earthquakes to the disposal of wastewater produced during oil extraction that has been injected more deeply into the ground.
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.
At 7:09 AM MDT on March 18, 2020, a 5.7 magnitude earthquake hit Salt Lake City, Utah, United States, with an epicenter 6 km (3.7 mi) north-northeast of Magna, Utah, beneath the site of the planned Utah Inland Port. It was the first major earthquake to occur within the Salt Lake Valley since the city was founded, the state's strongest earthquake since the 1992 St. George earthquake, and the first earthquake of comparable magnitude to occur near Salt Lake City since 1962, when a magnitude 5.0 earthquake struck a similar location in Magna.
On December 20, 2022, a magnitude 6.4 earthquake struck Ferndale, California in Humboldt County, United States at 10:34:25 UTC, or 2:34 a.m. PST.
David Jay Wald is a seismologist with the U.S. Geological Survey (USGS) at the National Earthquake Information Center (NEIC) in Golden, Colorado. He is an affiliated faculty member at the Colorado School of Mines, and served as the editor-in-chief of the Earthquake Engineering Research Institute's (EERI) journal, Earthquake Spectra, from 2018–2022. He also served on the Southern California Earthquake Center Science Planning Committee, 2014–2020.
ShakeMap is a product of the U.S. Geological Survey (USGS) to map the shaking of earthquakes. According to the USGS, "ShakeMaps provide near-real-time maps of ground motion and shaking intensity following significant earthquakes. These maps are used by federal, state, and local organizations, both public and private, for post-earthquake response and recovery, public and scientific information, as well as for preparedness exercises and disaster planning." The system's development was lead largely by USGS seismologist David J. Wald with others.
