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111-415: Similar to other earthquake early warning systems, ShakeAlert does not predict earthquakes , but rather it attempts to quickly identify a seismic event and issue an alert before widespread shaking is felt. It does this by detecting an earthquake's fast moving (but weak) P waves , then computes the event's location and estimated magnitude, after which it issues the warning. Depending on a person's distance from

222-573: A ground stop was enacted on the airport. The control tower was evacuated, and passengers in terminals and concourses were moved onto buses. Cars on the TRAX light rail system were held at their nearest stations. Roughly 55,000 electricity customers lost power throughout the Salt Lake Valley . Items were shaken off walls and shelves in homes and businesses, and bricks were shed off façades. The Granite School District cancelled its planned events for

333-729: A tsunami . Earthquakes can trigger landslides . Earthquakes' occurrence is influenced by tectonic movements along faults, including normal, reverse (thrust), and strike-slip faults, with energy release and rupture dynamics governed by the elastic-rebound theory . Efforts to manage earthquake risks involve prediction, forecasting, and preparedness, including seismic retrofitting and earthquake engineering to design structures that withstand shaking. The cultural impact of earthquakes spans myths, religious beliefs, and modern media, reflecting their profound influence on human societies. Similar seismic phenomena, known as marsquakes and moonquakes , have been observed on other celestial bodies, indicating

444-571: A depth of less than 70 km (43 mi) are classified as "shallow-focus" earthquakes, while those with a focal depth between 70 and 300 km (43 and 186 mi) are commonly termed "mid-focus" or "intermediate-depth" earthquakes. In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, deep-focus earthquakes may occur at much greater depths (ranging from 300 to 700 km (190 to 430 mi)). These seismically active areas of subduction are known as Wadati–Benioff zones . Deep-focus earthquakes occur at

555-488: A depth where the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure. Earthquakes often occur in volcanic regions and are caused there, both by tectonic faults and the movement of magma in volcanoes . Such earthquakes can serve as an early warning of volcanic eruptions, as during

666-521: A faster rate. A Bayesian framework was used with inputs of acceleration, velocity, and displacement. The last step required of all these algorithms is to come together in a decision module. This decision module broadcast the probability, size, and other characteristics of the earthquake. As of 2018, all three of these algorithms have been replaced with two new algorithms – earthquake point-source integrated code (EPIC) and finite-fault detector (FinDer). In 2024, Global Navigation Satellite System (GNSS) data

777-475: A few exceptions to this: Supershear earthquake ruptures are known to have propagated at speeds greater than the S wave velocity. These have so far all been observed during large strike-slip events. The unusually wide zone of damage caused by the 2001 Kunlun earthquake has been attributed to the effects of the sonic boom developed in such earthquakes. Slow earthquake ruptures travel at unusually low velocities. A particularly dangerous form of slow earthquake

888-603: A particular location in the Earth is the average rate of seismic energy release per unit volume. One of the most devastating earthquakes in recorded history was the 1556 Shaanxi earthquake , which occurred on 23 January 1556 in Shaanxi , China. More than 830,000 people died. Most houses in the area were yaodongs —dwellings carved out of loess hillsides—and many victims were killed when these structures collapsed. The 1976 Tangshan earthquake , which killed between 240,000 and 655,000 people,

999-511: A rural area near the California–Nevada border. Due to the remoteness of the area, there were few sensor stations near the earthquake and this resulted in the M W 6.0 earthquake incorrectly being split into "phantom quakes" by the system – a M W 4.8 near Lee Vining , M W 4.8 near Stockton , and M W 4.3 near Mammoth Lakes . Additionally, it took the system 25 seconds to declare an earthquake and issue an alert. While mobile apps received

1110-730: A single rupture) are approximately 1,000 km (620 mi). Examples are the earthquakes in Alaska (1957) , Chile (1960) , and Sumatra (2004) , all in subduction zones. The longest earthquake ruptures on strike-slip faults, like the San Andreas Fault ( 1857 , 1906 ), the North Anatolian Fault in Turkey ( 1939 ), and the Denali Fault in Alaska ( 2002 ), are about half to one third as long as

1221-583: A tank at Kennecott Utah Copper 's refinery in Magna due to the earthquake, which authorities said was confined to the facility and did not impact public safety. Radio station KMRI 1550 AM lost its transmitting tower located in West Valley City . The station was forced off air, and another station at the site KIHU 1010 AM was operating at reduced power. Both transmitters were very near the epicenter. KMRI filed for special temporary authority to go silent due to

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1332-515: Is a theory that earthquakes can recur in a regular pattern. Earthquake clustering has been observed, for example, in Parkfield, California where a long-term research study is being conducted around the Parkfield earthquake cluster. An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. Rapid changes of stress between rocks, and the stress from the original earthquake are

1443-410: Is called the hypocenter or focus, while the ground level directly above it is the epicenter . Earthquakes are primarily caused by geological faults , but also by volcanic activity , landslides, and other seismic events. The frequency, type, and size of earthquakes in an area define its seismic activity, reflecting the average rate of seismic energy release. Significant historical earthquakes include

1554-520: Is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior. There are three main types of fault, all of which may cause an interplate earthquake : normal, reverse (thrust), and strike-slip. Normal and reverse faulting are examples of dip-slip, where

1665-400: Is divided into 754 Flinn–Engdahl regions (F-E regions), which are based on political and geographical boundaries as well as seismic activity. More active zones are divided into smaller F-E regions whereas less active zones belong to larger F-E regions. Standard reporting of earthquakes includes its magnitude , date and time of occurrence, geographic coordinates of its epicenter , depth of

1776-532: Is probably a statistical fluctuation rather than a systematic trend. More detailed statistics on the size and frequency of earthquakes is available from the United States Geological Survey. A recent increase in the number of major earthquakes has been noted, which could be explained by a cyclical pattern of periods of intense tectonic activity, interspersed with longer periods of low intensity. However, accurate recordings of earthquakes only began in

1887-423: Is proportional to the area of the fault that ruptures and the stress drop. Therefore, the longer the length and the wider the width of the faulted area, the larger the resulting magnitude. The most important parameter controlling the maximum earthquake magnitude on a fault, however, is not the maximum available length, but the available width because the latter varies by a factor of 20. Along converging plate margins,

1998-410: Is the tsunami earthquake , observed where the relatively low felt intensities, caused by the slow propagation speed of some great earthquakes, fail to alert the population of the neighboring coast, as in the 1896 Sanriku earthquake . During an earthquake, high temperatures can develop at the fault plane, increasing pore pressure and consequently vaporization of the groundwater already contained within

2109-501: The 1556 Shaanxi earthquake in China, with over 830,000 fatalities, and the 1960 Valdivia earthquake in Chile, the largest ever recorded at 9.5 magnitude. Earthquakes result in various effects, such as ground shaking and soil liquefaction , leading to significant damage and loss of life. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause

2220-400: The 1980 eruption of Mount St. Helens . Earthquake swarms can serve as markers for the location of the flowing magma throughout the volcanoes. These swarms can be recorded by seismometers and tiltmeters (a device that measures ground slope) and used as sensors to predict imminent or upcoming eruptions. A tectonic earthquake begins as an area of initial slip on the fault surface that forms

2331-587: The 2004 Indian Ocean earthquake is simultaneously one of the deadliest earthquakes in history. Earthquakes that caused the greatest loss of life, while powerful, were deadly because of their proximity to either heavily populated areas or the ocean, where earthquakes often create tsunamis that can devastate communities thousands of kilometers away. Regions most at risk for great loss of life include those where earthquakes are relatively rare but powerful, and poor regions with lax, unenforced, or nonexistent seismic building codes. Tectonic earthquakes occur anywhere on

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2442-705: The Berkeley Seismological Laboratory at University of California, Berkeley , University of Washington , University of Oregon , and the Swiss Federal Institute of Technology in Zürich (ETHZ). Research and development of the West Coast system (initially called CISN ShakeAlert) began in August 2006, becoming demonstrable in August 2009. In 2011, test users (mostly other seismologists) were able to access

2553-678: The Federal Emergency Management Agency ), which then—through the WEA system—distributes messages to phone service providers who ultimately deliver the alert to their customers' devices. WEA alerts are simple text messages, unlike the alerts sent by some mobile apps (as select apps include graphics with estimated intensity and arrival time of shaking). WEA alerts may also arrive more slowly than alerts from apps. Although unlike apps which must be downloaded, phones can receive WEA alerts automatically as long as emergency alerts are turned on in

2664-490: The Himalayan Mountains . With the rapid growth of mega-cities such as Mexico City, Tokyo, and Tehran in areas of high seismic risk , some seismologists are warning that a single earthquake may claim the lives of up to three million people. While most earthquakes are caused by the movement of the Earth's tectonic plates , human activity can also produce earthquakes. Activities both above ground and below may change

2775-731: The Loma Prieta earthquake — Cal OES announced a statewide rollout of the alert distribution system in California. California refers to their system as the California Earthquake Early Warning System . On March 11, 2021, a statewide alert distribution system was rolled out in Oregon. Rollout of the alert system for the West Coast was completed when a statewide alert distribution system went live in Washington on May 4, 2021. Of

2886-609: The San Francisco Bay Area . By 2015, organizations enrolled in the beta test user program included: CalOES Warning Center, LA County Fire , LA City OEM , Amgen , LADWP , Metrolink , CalTrans and Disneyland . Additional institutional users were able to access alerts from the system, after ShakeAlert version 2.0 went live at the end of September 2018. As of 2023, there are two mobile apps licensed to work with ShakeAlert: MyShake , developed by UC Berkeley, and SD Emergency , developed by San Diego County . MyShake

2997-426: The brittle-ductile transition zone and upwards by the ground surface. The mechanics of this process are poorly understood because it is difficult either to recreate such rapid movements in a laboratory or to record seismic waves close to a nucleation zone due to strong ground motion. In most cases, the rupture speed approaches, but does not exceed, the shear wave (S wave) velocity of the surrounding rock. There are

3108-413: The least principal stress. Strike-slip faulting is intermediate between the other two types described above. This difference in stress regime in the three faulting environments can contribute to differences in stress drop during faulting, which contributes to differences in the radiated energy, regardless of fault dimensions. For every unit increase in magnitude, there is a roughly thirty-fold increase in

3219-516: The "ShakeReadySD" feature had been added to the county's SD Emergency app, which would provide ShakeAlert warnings throughout California. QuakeAlertUSA had been under development (and open to beta users), by Early Warning Labs, LLC, for several years before being publicly released on January 21, 2020 (at which time it only provided earthquake alerts in California). The app began providing earthquake alerts in Oregon on March 11, 2021. The QuakeAlertUSA app

3330-488: The $ 629 million in total economic losses, not including public infrastructure. Around 50,000 power outages were reported from customers across northern Utah following the earthquake from several damaged power lines , according to Rocky Mountain Power . The number of outages was down to 10,000 by 1:38 PM MDT , and down to 2,600 by the evening. The earthquake caused power outages near Salt Lake City International Airport , and

3441-417: The 1,675 seismic stations needed for full implementation of the West Coast system, only 1,115 had been built or funded by April 2018 (67% of the total needed). The project continues to solicit property owners for permission to place new seismic stations. Following the 2020 Salt Lake City earthquake , local media reported that Utah was the next state in line to get ShakeAlert. In 2014, USGS estimated that

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3552-541: The 20th century and has been inferred for older anomalous clusters of large earthquakes in the Middle East. It is estimated that around 500,000 earthquakes occur each year, detectable with current instrumentation. About 100,000 of these can be felt. Minor earthquakes occur very frequently around the world in places like California and Alaska in the U.S., as well as in El Salvador, Mexico, Guatemala, Chile, Peru, Indonesia,

3663-433: The 21st century. Seismic waves travel through the Earth's interior and can be recorded by seismometers at great distances. The surface-wave magnitude was developed in the 1950s as a means to measure remote earthquakes and to improve the accuracy for larger events. The moment magnitude scale not only measures the amplitude of the shock but also takes into account the seismic moment (total rupture area, average slip of

3774-399: The Earth's core was located in 1913 by Beno Gutenberg . S waves and later arriving surface waves do most of the damage compared to P waves. P waves squeeze and expand the material in the same direction they are traveling, whereas S waves shake the ground up and down and back and forth. Earthquakes are not only categorized by their magnitude but also by the place where they occur. The world

3885-481: The Earth. Also, the depth of the hypocenter can be computed roughly. P wave speed S waves speed As a consequence, the first waves of a distant earthquake arrive at an observatory via the Earth's mantle. On average, the kilometer distance to the earthquake is the number of seconds between the P- and S wave times 8. Slight deviations are caused by inhomogeneities of subsurface structure. By such analysis of seismograms,

3996-668: The Los Angeles County area, was made available to the general public at the end of 2018, but was retired after December 31, 2020. In the United States, the Wireless Emergency Alerts (WEA) system is used to disseminate emergency alerts (such as AMBER alerts ) to compatible mobile devices within a predefined area. ShakeAlert is capable of sending alerts to the Integrated Public Alert and Warning System (run by

4107-448: The P wave energy released during an earthquake. This energy, while given off quite early, does not usually cause damage. It was also the ElarmS that were responsible for roughly estimating the geographical location and size of the earthquake. Following these Elarms, empirical attenuation relations estimated how much the earth would shake in the specified region of the quake. The second algorithm

4218-558: The Philippines, Iran, Pakistan, the Azores in Portugal, Turkey, New Zealand, Greece, Italy, India, Nepal, and Japan. Larger earthquakes occur less frequently, the relationship being exponential ; for example, roughly ten times as many earthquakes larger than magnitude 4 occur than earthquakes larger than magnitude 5. In the (low seismicity) United Kingdom, for example, it has been calculated that

4329-593: The QuakeAlert mobile app received warnings on their phones. On average, the app's beta users received a warning of 45 seconds for both earthquakes. The only publicly available app (at the time), ShakeAlertLA, did not send an alert during the earthquakes. According to the City of Los Angeles, the system did not send alerts due to the estimated shaking in the Los Angeles area being below the activation threshold. On December 17, 2019,

4440-516: The West Coast system would cost $ 38 million to complete and $ 16 million per year (equivalent to $ 50 million and $ 20 million in 2023, respectively) to operate over and above the investment that had already been made in earthquake monitoring. By 2018, the estimates for the system's cost had grown to $ 39.4 million for the initial build out and $ 28.6 million for yearly maintenance and operation (equivalent to $ 47.1 million and $ 34.2 million in 2023, respectively). In December 2014, $ 5 million

4551-479: The aftershock pair led them to be a point of interest for Utah seismologists. It has been theorized that the first aftershock triggered the second. Coincidentally, the second aftershock occurred 2 hours before the Great Utah ShakeOut, one of many statewide earthquake preparedness drills. Though some minor injuries occurred, no major injuries or fatalities were reported as a result of the earthquake. After

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4662-586: 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. In its most general sense, the word earthquake is used to describe any seismic event that generates seismic waves. Earthquakes can occur naturally or be induced by human activities, such as mining , fracking , and nuclear tests . The initial point of rupture

4773-401: The alert, the warning was for an earthquake identified as M W 4.8 near Stockton (an incorrect magnitude and location). No Wireless Emergency Alert was transmitted because the system initially estimated the magnitude to be below the required M W 5.0 threshold (finalized reports showed the earthquake had actually exceeded the threshold for a WEA alert). About 270,000 phones were alerted during

4884-461: The alerts and stop public transport systems, prevent cars from entering bridges or tunnels, automatically shut down industrial systems and gas lines , and trigger specific protocols in hospitals and other sensitive work environments. Bay Area Rapid Transit (BART) was an early user of ShakeAlert, initially connecting to the system in 2012 (when it was still in development). BART uses the system to automatically brake its trains when shaking threatens

4995-463: The average recurrences are: an earthquake of 3.7–4.6 every year, an earthquake of 4.7–5.5 every 10 years, and an earthquake of 5.6 or larger every 100 years. This is an example of the Gutenberg–Richter law . The number of seismic stations has increased from about 350 in 1931 to many thousands today. As a result, many more earthquakes are reported than in the past, but this is because of

5106-404: The brittle crust. Thus, earthquakes with magnitudes much larger than 8 are not possible. In addition, there exists a hierarchy of stress levels in the three fault types. Thrust faults are generated by the highest, strike-slip by intermediate, and normal faults by the lowest stress levels. This can easily be understood by considering the direction of the greatest principal stress, the direction of

5217-555: The cause of other earthquakes in the past century. A Columbia University paper suggested that the 8.0 magnitude 2008 Sichuan earthquake was induced by loading from the Zipingpu Dam , though the link has not been conclusively proved. The instrumental scales used to describe the size of an earthquake began with the Richter scale in the 1930s. It is a relatively simple measurement of an event's amplitude, and its use has become minimal in

5328-534: The collapse. A preliminary survey of Salt Lake County government-owned buildings recorded at least $ 48.5 million worth of damage. Cyprus High School in Magna suffered some of the most significant damage, and West Lake Junior High in West Valley City was declared "a complete loss". Injuries in most schools were largely avoided due to the transition to online learning brought on by the COVID-19 pandemic . As this only covered government-owned buildings, actual damage

5439-444: The day to assess earthquake damage. The Salt Lake City School District also cancelled their lunch delivery program and device delivery services for the day, but resumed both on Thursday. The district reported little to no damage on all of their owned buildings. The earthquake took place during the COVID-19 pandemic in the United States , which had caused many residents to stay home from work or school to avoid infection. The day of

5550-430: The device's settings. ShakeAlert messages have been delivered via WEA in California since October 17, 2019, in Oregon since March 11, 2021, and in Washington since May 4, 2021. WEA alerts are only sent for M W 5.0 or larger earthquakes. On August 11, 2020, Google announced that it had partnered with USGS, allowing its Android operating system to distribute ShakeAlerts for California. The alerts are displayed using

5661-521: The dip angle of the rupture plane is very shallow, typically about 10 degrees. Thus, the width of the plane within the top brittle crust of the Earth can reach 50–100 km (31–62 mi) (such as in Japan, 2011 , or in Alaska, 1964 ), making the most powerful earthquakes possible. The majority of tectonic earthquakes originate in the Ring of Fire at depths not exceeding tens of kilometers. Earthquakes occurring at

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5772-678: The displacement along the fault is in the direction of dip and where movement on them involves a vertical component. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip. The topmost, brittle part of the Earth's crust, and the cool slabs of the tectonic plates that are descending into the hot mantle, are the only parts of our planet that can store elastic energy and release it in fault ruptures. Rocks hotter than about 300 °C (572 °F) flow in response to stress; they do not rupture in earthquakes. The maximum observed lengths of ruptures and mapped faults (which may break in

5883-439: The distance from the earthquake and the underlying rock or soil makeup. The first scale for measuring earthquake magnitudes was developed by Charles Francis Richter in 1935. Subsequent scales ( seismic magnitude scales ) have retained a key feature, where each unit represents a ten-fold difference in the amplitude of the ground shaking and a 32-fold difference in energy. Subsequent scales are also adjusted to have approximately

5994-543: The early 1900s, so it is too early to categorically state that this is the case. Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000-kilometre-long (25,000 mi), horseshoe-shaped zone called the circum-Pacific seismic belt, known as the Pacific Ring of Fire , which for the most part bounds the Pacific plate . Massive earthquakes tend to occur along other plate boundaries too, such as along

6105-403: The earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane . The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the fault surface that increases the frictional resistance. Most fault surfaces do have such asperities, which leads to a form of stick-slip behavior . Once

6216-430: The earthquake's epicenter , the alert may reach them before the earthquake's slower moving (but destructive) S waves do. These warnings can provide time for persons to take protective actions, such as "drop, cover, and hold," and for organizations to shut down transit systems, equipment, open fire station doors, and trigger specific protocols in hospitals and other sensitive work environments. Research and development of

6327-490: The earthquake, Governor Gary Herbert said, "This is extremely bad timing, because we already have the coronavirus issue going on right now causing a lot of anxiety." The earthquake disrupted some of the public health response to the pandemic. Testing at the Utah Public Health Laboratory was stopped, and the 24/7 coronavirus hotline went offline temporarily. Salt Lake City schools were already closed due to

6438-447: The earthquake, Utah Emergency Management said that serious damage was not expected, but there were reports of minor damage. Bricks fell off some buildings. The Salt Lake Temple was undergoing a seismic upgrade at the time of the earthquake, and sustained minor damage. The Angel Moroni statue that sits atop the highest spire lost its trumpet following the earthquake. Some stones were displaced as well. The construction crews working on

6549-426: The earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to aftershocks but on adjacent segments of fault, these storms occur over the course of years, with some of the later earthquakes as damaging as the early ones. Such a pattern was observed in the sequence of about a dozen earthquakes that struck the North Anatolian Fault in Turkey in

6660-771: The eastern boundary of the Basin and Range Province . The major active fault zone is the normal Wasatch Fault that throws down to the west. The footwall (upthrown part) is formed by the Wasatch Range with part of the Great Basin lying in the hanging-wall (downthrown part), at one time filled by Lake Bonneville , with the Great Salt Lake forming the largest remnant. The fault zone is broken up into six segments that appear to rupture separately. Paleoseismic investigations indicate that 19 surface rupturing earthquakes have occurred in

6771-498: The energy released. For instance, an earthquake of magnitude 6.0 releases approximately 32 times more energy than a 5.0 magnitude earthquake and a 7.0 magnitude earthquake releases 1,000 times more energy than a 5.0 magnitude earthquake. An 8.6-magnitude earthquake releases the same amount of energy as 10,000 atomic bombs of the size used in World War II . This is so because the energy released in an earthquake, and thus its magnitude,

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6882-535: The epicenter, geographical region, distances to population centers, location uncertainty, several parameters that are included in USGS earthquake reports (number of stations reporting, number of observations, etc.), and a unique event ID. 2020 Salt Lake City earthquake 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

6993-468: The epicenter. According to USGS, at least 26,000 people reported feeling the earthquake. More than 50 aftershocks were recorded within two hours of the main tremor. As of 11:00 MDT March 26, a total of 591 aftershocks have been observed and located by the University of Utah Seismograph Stations. The largest of the aftershocks were two M 4.6 events that occurred at 08:02 and 13:12 MDT on March 18. During

7104-458: The fact that no single earthquake in the sequence is the main shock, so none has a notably higher magnitude than another. An example of an earthquake swarm is the 2004 activity at Yellowstone National Park . In August 2012, a swarm of earthquakes shook Southern California 's Imperial Valley , showing the most recorded activity in the area since the 1970s. Sometimes a series of earthquakes occur in what has been called an earthquake storm , where

7215-462: The fault has locked, continued relative motion between the plates leads to increasing stress and, therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy . This energy is released as a combination of radiated elastic strain seismic waves , frictional heating of

7326-411: The fault plane that holds it in place, and fluids can exert a lubricating effect. As thermal overpressurization may provide positive feedback between slip and strength fall at the fault plane, a common opinion is that it may enhance the faulting process instability. After the mainshock, the pressure gradient between the fault plane and the neighboring rock causes a fluid flow that increases pore pressure in

7437-418: The fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory . It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or

7548-536: The fault, and rigidity of the rock). The Japan Meteorological Agency seismic intensity scale , the Medvedev–Sponheuer–Karnik scale , and the Mercalli intensity scale are based on the observed effects and are related to the intensity of shaking. The shaking of the earth is a common phenomenon that has been experienced by humans from the earliest of times. Before the development of strong-motion accelerometers,

7659-417: The focus. Once the rupture has been initiated, it begins to propagate away from the focus, spreading out along the fault surface. Lateral propagation will continue until either the rupture reaches a barrier, such as the end of a fault segment, or a region on the fault where there is insufficient stress to allow continued rupture. For larger earthquakes, the depth extent of rupture will be constrained downwards by

7770-406: The force that "pushes" the rock mass during the faulting. In the case of normal faults, the rock mass is pushed down in a vertical direction, thus the pushing force ( greatest principal stress) equals the weight of the rock mass itself. In the case of thrusting, the rock mass "escapes" in the direction of the least principal stress, namely upward, lifting the rock mass, and thus, the overburden equals

7881-540: The intensity and size of the earthquake than ElarmS did. The tradeoff of using these algorithms for the earliest detection possible meant having a less reliable approach than regional warning algorithms, however some argued that the added seconds to prepare are more important than reliability. Lastly, the Virtual Seismologist, known as the VS method, imitated the analysis of a human scientist in terms of capacity, but did so at

7992-410: The intensity of a seismic event was estimated based on the observed effects. Magnitude and intensity are not directly related and calculated using different methods. The magnitude of an earthquake is a single value that describes the size of the earthquake at its source. Intensity is the measure of shaking at different locations around the earthquake. Intensity values vary from place to place, depending on

8103-555: The last 6,000 years along the fault system. The earthquake's focal mechanism and depth were both consistent with displacement on the Wasatch fault system at depth. Significant shaking was felt in downtown Salt Lake City , and the earthquake was reportedly felt as far away as Wyoming and southern Idaho . The most distant report of shaking related to the earthquake occurred in Cokeville, Wyoming , over 110 miles (180 km) away from

8214-471: The lengths along subducting plate margins, and those along normal faults are even shorter. Normal faults occur mainly in areas where the crust is being extended such as a divergent boundary . Earthquakes associated with normal faults are generally less than magnitude 7. Maximum magnitudes along many normal faults are even more limited because many of them are located along spreading centers, as in Iceland, where

8325-449: The magnitude 6.4 December 2022 Ferndale earthquake . Earthquake 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

8436-402: The main causes of these aftershocks, along with the crust around the ruptured fault plane as it adjusts to the effects of the mainshock. An aftershock is in the same region as the main shock but always of a smaller magnitude, however, they can still be powerful enough to cause even more damage to buildings that were already previously damaged from the mainshock. If an aftershock is larger than

8547-414: The mainshock, the aftershock is redesignated as the mainshock and the original main shock is redesignated as a foreshock . Aftershocks are formed as the crust around the displaced fault plane adjusts to the effects of the mainshock. Earthquake swarms are sequences of earthquakes striking in a specific area within a short period. They are different from earthquakes followed by a series of aftershocks by

8658-515: The messages themselves could not be distributed until the various private and public distribution partners had completed mobile apps and made changes to various emergency alerting systems. The first publicly available alerting system was the ShakeAlertLA app, released on New Year's Eve 2018 (although it only alerted for shaking in the Los Angeles area ). On October 17, 2019—the thirtieth anniversary of

8769-519: The operating system's built-in notification feature, which does not require an app or a message from the WEA system. The feature was also rolled out on March 11, 2021, in Oregon, and in Washington in the days following May 4, 2021. As of 2021, Apple's iOS does not include a similar built-in notification system for ShakeAlert. Conversations between USGS and Apple have occurred, but no resolution has been reached. However, these devices can still receive earthquake alerts through WEA messaging, or, depending on

8880-473: The pandemic. The earthquake disrupted the operations of school districts throughout the Salt Lake Valley who were distributing food and learning materials to families. Salt Lake City International Airport was shut down and "60 to 70 flights" were diverted. Passengers were evacuated, which was easier because the airport already had fewer people than usual due to the COVID-19 pandemic (about 9,000 compared to 24,000 under normal circumstances). A water line

8991-576: The prototype to Oregon and Washington "pilot" users. (Until this time, the Oregon/Washington system had been developed and operated separately from the California system.) On September 28, 2018, version 2.0 went live, allowing the "sufficiently functional and tested" system to begin Phase 1 of alerting California, Oregon and Washington. Even though ShakeAlert could alert the public beginning in September 2018,

9102-518: The rock. In the coseismic phase, such an increase can significantly affect slip evolution and speed, in the post-seismic phase it can control the Aftershock sequence because, after the main event, pore pressure increase slowly propagates into the surrounding fracture network. From the point of view of the Mohr-Coulomb strength theory , an increase in fluid pressure reduces the normal stress acting on

9213-437: The rupture of geological faults but also by other events such as volcanic activity, landslides, mine blasts, fracking and nuclear tests . An earthquake's point of initial rupture is called its hypocenter or focus. The epicenter is the point at ground level directly above the hypocenter. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The seismicity at

9324-522: The same numeric value within the limits of the scale. Although the mass media commonly reports earthquake magnitudes as "Richter magnitude" or "Richter scale", standard practice by most seismological authorities is to express an earthquake's strength on the moment magnitude scale, which is based on the actual energy released by an earthquake, the static seismic moment. Every earthquake produces different types of seismic waves, which travel through rock with different velocities: Propagation velocity of

9435-462: The same time interval there were 33 events of M3 and greater. On the night of April 14, 2020, about a month after the main shock, a 4.2 magnitude aftershock occurred. Less than 2 days later on the morning of April 16, another aftershock of identical magnitude (4.2) occurred in the same location. Because data appeared to indicate dwindling of local seismicity, the prolonged mainshock-aftershock time period, and relative consecutiveness and similarity of

9546-486: The seismic upgrade were sent home. The historic Rio Grande Depot , St. Mark's Episcopal Cathedral , and dozens of mobile homes in West Valley City were damaged. As of December 2020, the Rio Grande Depot had still not re-opened due to damage being worse than initially thought, forcing a café that had occupied the building for 39 years to relocate. 8,200 U.S. gallons (31,000 L) hydrochloric acid leaked from

9657-464: The seismic waves through solid rock ranges from approx. 3 km/s (1.9 mi/s) up to 13 km/s (8.1 mi/s), depending on the density and elasticity of the medium. In the Earth's interior, the shock- or P waves travel much faster than the S waves (approx. relation 1.7:1). The differences in travel time from the epicenter to the observatory are a measure of the distance and can be used to image both sources of earthquakes and structures within

9768-404: 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. Salt Lake City lies at

9879-448: The state to continue being part of the crowdsourced global network. The app began providing earthquake alerts in Oregon on March 11, 2021 and in Washington state on January 26, 2022. MyShake only delivers alerts for earthquakes exceeding M W 4.5 and that will produce a shaking intensity greater than three. On August 26, 2021, officials from the County of San Diego and USGS announced that

9990-607: The state, through apps. The system issued alerts for several significant southern California earthquakes in 2014 including a M W 4.4 event in Encino , a M W 4.2 event in Westwood , and a M W 5.1 event in La Habra . It also issued a warning 5.4 seconds after the beginning of the M W 6.0 South Napa earthquake that hit the Napa region on August 24, 2014. Although it was initially reported that

10101-417: The stations send data to processing infrastructure in monitoring centers which, using various algorithms, are able to calculate the necessary information and generate alerts when needed. Initially, ShakeAlert processing centers were capable of detecting earthquakes at an early stage because of three specific algorithms. The first algorithm was ElarmS. Also known as Earthquake Alarm Systems, these signals detect

10212-422: The stresses and strains on the crust, including building reservoirs, extracting resources such as coal or oil, and injecting fluids underground for waste disposal or fracking . Most of these earthquakes have small magnitudes. The 5.7 magnitude 2011 Oklahoma earthquake is thought to have been caused by disposing wastewater from oil production into injection wells , and studies point to the state's oil industry as

10323-490: The surrounding fracture networks; such an increase may trigger new faulting processes by reactivating adjacent faults, giving rise to aftershocks. Analogously, artificial pore pressure increase, by fluid injection in Earth's crust, may induce seismicity . Tides may trigger some seismicity . Most earthquakes form part of a sequence, related to each other in terms of location and time. Most earthquake clusters consist of small tremors that cause little to no damage, but there

10434-588: The system began in 2006 and by the fall of 2018, the system was considered "sufficiently functional and tested" to enter phase 1 and begin issuing alerts for the West Coast states. While the warnings are generated by ShakeAlert, USGS does not send the alerts directly, instead relying on various private and public partners to distribute the messages through systems such as Wireless Emergency Alerts (WEA) and mobile apps . A statewide alert distribution system went online in California on October 17, 2019, in Oregon on March 11, 2021, and in Washington on May 4, 2021. Initially

10545-744: The system has been developed to monitor and alert the West Coast of the United States , an area with significant seismic risk due to the San Andreas fault zone and the Cascadia subduction zone . The West Coast system was developed by a consortium of institutions including the United States Geological Survey, the California Governor's Office of Emergency Services (Cal OES), the California Geological Survey , California Institute of Technology ,

10656-695: The system provided 10 seconds of warning before the S wave arrived in Berkeley , subsequent information showed that this was in error and the warning arrived 5 seconds before the S wave in Berkeley. This means the S waves had already arrived in Napa and Vallejo when the warning was issued. San Francisco received 8 seconds warning. ShakeAlert generated warnings for both the July 5 M W 6.4 and July 5 M W 7.1 Ridgecrest earthquakes . Although not yet publicly available, beta users of

10767-420: The system through the "UserDisplay" software. In January 2012, "beta" users were able to access the alerts in California. In February 2015, "beta" users were able to access the alerts in Oregon and Washington. In February 2016, the system moved from demonstrable to Production Prototype version 1.0 in California, providing alerts to "pilot" users. In April 2017, Production Prototype version 1.2 went live, expanding

10878-704: The system. In August 2024, the Canadian Earthquake Early Warning system was launched by Natural Resources Canada (NRCan); this system was developed in cooperation with USGS and is based on the same software as ShakeAlert. While the two systems are distinct, USGS and NRCan share processing software, algorithms and real-time data. Full implementation of ShakeAlert on the West Coast system will require 1,675 seismic stations —1,115 in California and 560 in Oregon and Washington. These stations include sensors, such as seismometers , which are part of USGS's Advanced National Seismic System . During an earthquake,

10989-502: The then recently released MyShake app sent its first alert for a M W 4.3 earthquake in the Cholame Valley. (Even though the earthquake was below the M W 4.5 threshold, a warning was still transmitted through the app, because preliminary readings measured the magnitude as 4.8.) No Wireless Emergency Alert was transmitted because the magnitude of the earthquake was below the 5.0 threshold. The 2021 Antelope Valley earthquake occurred in

11100-443: The thickness of the brittle layer is only about six kilometres (3.7 mi). Reverse faults occur in areas where the crust is being shortened such as at a convergent boundary . Reverse faults, particularly those along convergent boundaries, are associated with the most powerful earthquakes (called megathrust earthquakes ) including almost all of those of magnitude 8 or more. Megathrust earthquakes are responsible for about 90% of

11211-461: The total seismic moment released worldwide. Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Strike-slip faults, particularly continental transforms , can produce major earthquakes up to about magnitude 8. Strike-slip faults tend to be oriented near vertically, resulting in an approximate width of 10 km (6.2 mi) within

11322-505: The universality of such events beyond Earth. An earthquake is the shaking of the surface of Earth resulting from a sudden release of energy in the lithosphere that creates seismic waves . Earthquakes may also be referred to as quakes , tremors , or temblors . The word tremor is also used for non-earthquake seismic rumbling . In its most general sense, an earthquake is any seismic event—whether natural or caused by humans—that generates seismic waves. Earthquakes are caused mostly by

11433-436: The vast improvement in instrumentation, rather than an increase in the number of earthquakes. The United States Geological Survey (USGS) estimates that, since 1900, there have been an average of 18 major earthquakes (magnitude 7.0–7.9) and one great earthquake (magnitude 8.0 or greater) per year, and that this average has been relatively stable. In recent years, the number of major earthquakes per year has decreased, though this

11544-558: Was added to ShakeAlert to aid in the characterization of large magnitude earthquakes. The algorithm, GFAST (Geodetic First Approximation of Size and Timing), uses the peak ground displacement recorded at permanent GPS stations to determine magnitude. GFAST was developed by researchers from the Pacific Northwest Seismic Network at University of Washington . GFAST receives initial earthquake source information (origin time and epicenter) from EPIC or FinDer. Considerable logic

11655-495: Was added to ShakeAlert to combine magnitude estimates from all three ShakeAlert algorithms to ensure robustness of solutions. ShakeAlert warnings are sent to both institutional users and the general public through a variety of distribution methods; this includes messages via cell phones, television and radio. These alerts may give people time to take protective actions like " drop, cover and hold on ", preventing injuries caused by falling debris. Various automated systems can listen for

11766-555: Was added to the USGS budget for ShakeAlert development (equivalent to $ 10 million in 2023). This enabled USGS to purchase $ 1 million in seismic instrumentation and award $ 4 million in funding to the project partners to make the demonstration system more robust. In 2015, more than 30 Congress members signed a joint letter urging the President to add full funding for the system to his federal budget request. The Gordon and Betty Moore Foundation has invested more than $ 6 million in developing

11877-505: Was decommission on November 6, 2023, so that the company could focus on its commercial earthquake response services. QuakeAlertUSA delivered alerts for earthquakes exceeding M W 4.5 and that produced a shaking intensity greater than three. (Settings could be changed to require higher intensity earthquakes before alerting the user.) ShakeAlertLA, was developed by the City of Los Angeles and AT&T . This app, which only warned of shaking in

11988-500: Was expected to be much higher. Despite extensive damage to Magna's historic downtown core, city officials did not expect that any of the historic structures within Magna will need to be condemned. Despite damage to about 145 structures deemed as historic throughout the Salt Lake Valley, only 1 of them was damaged enough to require demolition. The cost for all building-related damages has been estimated to be about $ 62 million out of

12099-472: Was released in February 2016. Initially the app did not issue alerts, but instead used a phone's accelerometers to record shaking from an earthquake and send the data back to UC Berkeley for analysis, thereby creating a crowdsourced global seismic network. On October 17, 2019, a new version of the app was announced, which would also provide alerts from ShakeAlert to users in California, while allowing users outside

12210-471: Was the τ c {\displaystyle \tau _{c}} - P d {\displaystyle P_{d}} OnSite algorithm. By using displacement amplitude P d {\displaystyle P_{d}} and period τ c {\displaystyle \tau _{c}} of the first signs of shaking, the OnSite algorithm more accurately predicted

12321-626: Was the deadliest of the 20th century. The 1960 Chilean earthquake is the largest earthquake that has been measured on a seismograph, reaching 9.5 magnitude on 22 May 1960. Its epicenter was near Cañete, Chile. The energy released was approximately twice that of the next most powerful earthquake, the Good Friday earthquake (27 March 1964), which was centered in Prince William Sound , Alaska. The ten largest recorded earthquakes have all been megathrust earthquakes ; however, of these ten, only

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