203 Fun Facts About Earthquakes

Which scale, introduced in 1979, became the standard measure of total earthquake energy?

The moment magnitude scale, introduced in 1979, is computed from the seismic moment of the rupture and does not saturate for the largest quakes, which is why it replaced the older amplitude-based scales for reporting great earthquakes.

What is the geological term for the point within the Earth where an earthquake rupture first occurs?

The hypocenter, also called the focus, is the point where the rupture starts; plotting many hypocentres maps a fault plane in three dimensions.

Which type of plate boundary is most commonly associated with the deepest and most powerful earthquakes?

Convergent boundaries, where one plate subducts beneath another, host the deepest and largest earthquakes; their hypocentres trace a sloping plane that reaches hundreds of kilometres down.

Which seismic wave travels fastest and reaches a recording station first?

The P can stand for 'primary' or 'pressure', since the wave is a train of alternating compressions and rarefactions; the slower S-wave is usually the more destructive.

Which earthquake hazard turns saturated, loose soil into a slurry that cannot bear weight?

Liquefaction happens when shaking raises pore-water pressure in saturated loose sand until it flows; it tilted apartment blocks in Niigata, Japan, in 1964 and wrecked suburbs of Christchurch in 2011.

Roughly what share of the world's earthquakes, including most of the largest, occur along the Pacific Ring of Fire?

90% of quakes sit in the belt also called the Girdle of Fire, and plate tectonics has explained its layout since the early 1960s.

Which instrument records ground motion during an earthquake, classically a weight on a spring with a pen tracing a rotating drum?

The seismograph's trace is a seismogram, once inked onto paper by a pen on the swinging weight and now recorded digitally.

Which seismologist, working with Beno Gutenberg on a Southern California network, gave his name to the magnitude scale in his 1935 paper?

Charles Richter had been hired to measure seismograms from instruments strung across Southern California, and called his creation simply a magnitude scale.

Which country was devastated by the largest earthquake ever recorded, on 22 May 1960?

Chile's 1960 Valdivia earthquake, magnitude 9.5, is the largest ever instrumentally recorded; its tsunami crossed the Pacific and killed people in Hawaii, Japan and the Philippines.

What property of secondary seismic waves stops them passing through liquid?

Particles move at right angles to the direction of travel, and liquids and gases cannot sustain the shear stress that restores them.

The San Andreas Fault runs along the boundary between the North American plate and which other?

The San Andreas separates the Pacific plate from the North American plate; it is a right-lateral strike-slip transform fault whose two sides grind past each other horizontally rather than one diving beneath the other.

What does the Japanese word tsunami literally mean?

Tsunami means 'harbour wave', from tsu (harbour) and nami (wave): fishermen at sea felt nothing pass beneath them and came home to find their harbours wrecked.

What is the term for the point on the ground surface directly above where an earthquake begins?

News reports usually give this surface point, while the actual rupture starts kilometres below it.

If an aftershock is larger than the main shock, what is the original quake redesignated as?

The earlier quake becomes a foreshock: seismologists promote the larger later event to mainshock, as happened with the magnitude 7.3 shock two days before Japan's 2011 Tohoku earthquake.

In Japanese mythology, earthquakes are caused by Namazu, a giant example of which animal?

Namazu is a giant catfish said to lie beneath Japan, pinned down by the god Kashima with a stone; when Kashima's guard slips, the catfish thrashes and the earth shakes.

In Greek mythology, which god was held responsible for causing earthquakes?

Poseidon, god of the sea, was also the earth-shaker; Homer calls him Ennosigaios, and Greeks pictured his trident striking the ground to cause earthquakes.

On the Richter scale, each whole-number step corresponds to roughly how much more energy released?

Each whole magnitude step means about 31.6 times (10 to the power 1.5) more energy, so a magnitude 7 releases roughly 1,000 times the energy of a magnitude 5.

The AD 132 seismoscope dropped bronze balls from dragons' mouths into the mouths of which creatures?

Zhang Heng's device supposedly indicated the direction of a distant quake by which of eight dragons released its ball.

Which Han dynasty scholar is credited with inventing the first seismoscope?

Zhang Heng built his bronze seismoscope in AD 132; he was also an astronomer and mathematician who catalogued around 2,500 stars.

In December 2018, which mission became the first to place a seismometer on the surface of another planet?

InSight set its SEIS seismometer directly on the Martian ground on 19 December 2018, and the mission ended in December 2022 when dust smothered its solar panels.

Intensity scales such as the Modified Mercalli rate an earthquake by what?

Intensity scales like the Modified Mercalli rate observed effects at a given place, from I (not felt) to XII (total destruction), so one quake has many intensities but a single magnitude.

The law stating that aftershock frequency falls off with the reciprocal of time is named after which seismologist?

Fusakichi Omori published the law in 1894 from his aftershock studies in Japan; Tokuji Utsu's 1961 modification, which adds an exponent p, is the version used today.

Roughly how long is the Ring of Fire tectonic belt that surrounds most of the Pacific Ocean?

The Ring of Fire is about 40,000 km long, a horseshoe of subduction zones running from New Zealand up through Japan and the Aleutians and down the Americas to southern Chile.

Thomas C. Hanks and which Caltech seismologist defined the moment magnitude scale in 1979?

Hiroo Kanamori co-wrote the 1979 paper with Hanks; in 1977 he had already proposed an energy-based Mw for great earthquakes, which the 1979 scale generalised to all sizes.

The 1906 San Francisco earthquake struck at what time of day?

Fires that followed burned for days and caused most of the destruction, and the event remains the deadliest quake in US history.

What caused most of the destruction in San Francisco after the 1906 earthquake, levelling some 25,000 buildings within three days?

Gas-main fires did the damage: ruptured mains fed more than 30 blazes that destroyed roughly 25,000 buildings on 490 city blocks within three days.

The 2004 Indian Ocean earthquake struck off the west coast of which Indonesian province?

The epicentre lay off the west coast of Aceh, at Sumatra's northern tip; its capital Banda Aceh was the worst-hit city, and the tsunami killed about 228,000 people in 14 countries.

Roughly how long was the 2004 Sumatra–Andaman earthquake's fault rupture, the longest ever observed?

The 2004 rupture ran some 1,200 to 1,300 km along the Sunda subduction zone; the faulting lasted between eight and ten minutes and set the whole planet vibrating by up to 10 mm.

Ten-year-old Tilly Smith recognised the 2004 tsunami's warning signs on a Thai beach thanks to what?

She noticed the receding sea and frothing water and warned people to leave the beach.

How long did the shaking of the 1960 Valdivia earthquake last?

The Valdivia shaking lasted about 10 minutes; the magnitude 9.5 rupture ran some 1,000 km along the Chilean coast, and its tsunami reached Japan, 17,000 km away, killing more than 100 people there.

The 1960 Valdivia earthquake's tsunami devastated which Hawaiian city with 10.7-metre waves?

Hilo, on the Big Island, took waves up to 10.7 metres about 15 hours after the quake; 61 people died there, the city's second tsunami catastrophe after the 1946 Aleutian wave.

The 1964 Alaska earthquake, North America's strongest ever, is also named for which day?

It struck on Good Friday, 27 March 1964, at 5:36 p.m. local time, and the magnitude 9.2 shaking lasted four minutes and thirty-eight seconds.

The 2011 Tōhoku earthquake moved Japan's main island of Honshu about how far to the east?

GPS showed parts of Honshu moved about 2.4 metres east; the quake also shifted Earth's axis by an estimated 10 to 25 cm and shortened the day by about 1.8 microseconds.

The 2011 Tōhoku earthquake and tsunami, which triggered the Fukushima disaster, is known in Japan by which numerical shorthand for its date?

3.11 is read San ten Ichi-ichi: the quake struck on 11 March, and the tsunami it triggered led to the Fukushima Daiichi nuclear disaster.

The 1755 Lisbon earthquake struck on the morning of 1 November, which is which Christian holy day?

1 November is All Saints' Day; churches were packed with worshippers when the quake struck around 9:40 a.m., and fires and a tsunami together almost destroyed the city.

Which philosopher used the 1755 Lisbon earthquake in Candide to attack 'the best of all possible worlds'?

Voltaire mocked Leibnizian optimism through Dr Pangloss in Candide (1759), having already written a 'Poem on the Lisbon Disaster' in 1756; the quake became a landmark in debates about theodicy.

Asked what to do after the 1755 Lisbon earthquake, the Marquis of Pombal reportedly replied how?

Pombal's reported answer was 'Bury the dead and heal the living'; the Pombaline buildings he then commissioned, with timber-cage 'gaiola' frames, are among Europe's earliest earthquake-resistant constructions.

The 1556 Shaanxi earthquake killed so many partly because residents lived in yaodongs, which are what?

The dwellings collapsed and buried people as they slept, and modern estimates put direct deaths at roughly 100,000.

The 1556 Shaanxi earthquake, one of the deadliest in history, struck during which Chinese dynasty?

It struck Huaxian on 23 January 1556 in the Jiajing reign of the Ming dynasty; the population loss including migration and famine has been put at 830,000.

The 2010 Haiti earthquake was centred near which town, about 25 km west of Port-au-Prince?

The epicentre lay near Léogâne, about 25 km west of the capital; the magnitude 7.0 quake destroyed landmarks including the Presidential Palace and the National Assembly building.

Love waves are named after A. E. H. Love, a professor at which university?

Augustus Edward Hough Love was Oxford's Sedleian Professor of Natural Philosophy from 1899; he modelled these horizontally polarised surface waves in his 1911 book Some Problems of Geodynamics.

What is the branch of seismology that uses geology to study past earthquakes called?

Paleoseismology reads past earthquakes from geology, trenching across faults to date offset sediment layers; archaeoseismology does the same from damaged ancient buildings.

Which 17th-century scholar argued that earthquakes were caused by fire moving through channels inside the Earth?

Athanasius Kircher's Mundus Subterraneus (1665) pictured a network of fire-filled channels inside the Earth, with earthquakes and volcanoes breaking out where the fires surged.

A simple seismometer relies on which property of a suspended mass to measure ground motion?

Inertia keeps the suspended mass nearly still while the frame moves with the ground, so the relative motion between them traces the shaking.

Richter's original 1935 scale was later revised and given what name?

Richter's scale became the local magnitude, ML, because it was calibrated for Southern California quakes recorded on Wood–Anderson seismographs within about 600 km.

On the Richter scale, how much larger are seismometer readings for a magnitude 5 than a magnitude 3?

Each whole magnitude step is a tenfold increase in measured wave amplitude, so two steps from 3 to 5 means readings 100 times larger.

Shaking intensity can be amplified in which kind of geological setting?

Intensity generally falls off with distance from the epicentre.

Depending on definition, how many major tectonic plates make up Earth's lithosphere?

Seven or eight major plates are usually listed: African, Antarctic, Eurasian, North American, South American, Pacific and Indo-Australian, with the last sometimes split into Indian and Australian.

What is the typical maximum annual movement of tectonic plates?

Plates move at most about 10 cm a year, with the Pacific plate near the fast end, while the Atlantic opens only about 2.5 cm a year, roughly the rate fingernails grow.

What are the high-friction regions where a fault plane becomes locked called?

Asperities are the rough, locked patches on a fault plane where friction is highest; stress builds there until it exceeds the rock's strength and the patch ruptures.

Which term names the slow, steady fault slip that offsets kerbs in Hollister, California?

Aseismic creep is steady slip without earthquakes; the fault running through Hollister, California, creeps several millimetres a year, slowly offsetting kerbs and house foundations.

Roughly how long is the San Andreas Fault?

The San Andreas runs about 750 miles (1,200 km) through California, from the Salton Sea in the south to the Pacific coast north of San Francisco.

At which triple junction does the San Andreas Fault terminate in the north?

The Mendocino Triple Junction, off Cape Mendocino south of Eureka, is where the Pacific, North American and Gorda plates meet and the San Andreas gives way to the Cascadia subduction zone.

Near which Salton Sea community does the San Andreas Fault end in the south?

The fault's southern end lies near Bombay Beach on the Salton Sea's east shore, where motion passes into the Brawley Seismic Zone and the spreading of the Gulf of California.

Which UC Berkeley professor first identified the San Andreas Fault in 1895?

Andrew Lawson named the fault in 1895 after San Andreas Lake on the San Francisco peninsula, and chaired the state commission whose 1908 report analysed the 1906 quake.

What is the average annual slip rate along the San Andreas Fault?

The San Andreas slips about 20 to 35 mm a year on average, accounting for most of the roughly 50 mm a year of relative motion between the Pacific and North American plates.

The Ring of Fire holds roughly what share of the world's active or dormant volcanoes?

About two-thirds of the world's active or dormant volcanoes, some 750 to 915, sit on the Ring of Fire, among them Fuji, Krakatoa and Mount St Helens.

Which oceanic plate, subducting beneath South America, fuels the Andean stretch of the Ring of Fire?

The Nazca plate dives beneath the South American plate off Chile and Peru, feeding the Andean volcanoes and the great 1960 Valdivia earthquake.

Up to how wide is the Ring of Fire tectonic belt?

The belt is up to about 500 km wide, though its volcanoes and quake zones cluster in much narrower bands above each subducting slab.

When a main rupture happens in two or more steps of similar size, the quakes are known as what?

Doublet earthquakes are pairs of similar-sized shocks on the same fault system within hours to years, often with nearly identical waveforms; the two 2023 Kahramanmaraş quakes in Turkey were a doublet.

Foreshock activity has been detected before roughly what share of earthquakes over magnitude 7?

Studies find foreshock activity before about 70% of quakes above magnitude 7, compared with roughly 40% of moderate-to-large earthquakes overall.

The 2002 Sumatra quake is regarded as a foreshock of which later event?

The magnitude 7.3 Sumatra quake of November 2002 is treated as a foreshock of the 2004 Indian Ocean earthquake, despite a delay of more than two years.

The most famous claim of a successful earthquake prediction concerns which 1975 event?

A later study questioned whether a valid short-term prediction was made.

What stiff vertical panel do engineers build into a structure to resist sideways earthquake loads?

Shear walls are stiff vertical panels of reinforced concrete or braced timber that carry a building's sideways loads down to the ground; Chile's shear-wall apartment blocks mostly rode out the 2010 magnitude 8.8 quake.

What do base isolators, such as laminated rubber bearings, sit between?

Base isolators of laminated rubber or friction-pendulum bearings sit between a building and its foundation, letting the ground move beneath while the structure sways far less; San Francisco City Hall was retrofitted onto them in the 1990s.

Why do scientists dislike the term 'tidal wave' for a tsunami?

'Tidal wave' falsely implies tides cause them; tsunamis come from seafloor displacement, though the first arrival may look like a fast-rising tide rather than a breaking wave.

The term 'liquefied' was first used in soil mechanics after which 1918 event?

Allen Hazen coined the usage describing the 1918 failure of the Calaveras Dam in California, whose saturated hydraulic fill flowed as pore-water pressure rose.

A deep-focus earthquake has a hypocentre deeper than what?

Deep-focus earthquakes start below 300 km; shallow ones are above 70 km and intermediate ones between, and the deep ones occur almost only inside subducting slabs.

Which Japanese seismologist proved in 1928 that earthquakes occur well below the lithosphere?

Herbert Hall Turner had raised the idea in 1922.

Which California geothermal plant averaged two magnitude-4 quakes a year from 2004 to 2009?

The Geysers, north of San Francisco, is the world's largest geothermal field; injecting wastewater to replenish its steam reservoir has caused thousands of small quakes, including about two of magnitude 4 a year in 2004–2009.

A 2015 USGS study linked a surge of earthquakes in which state since 2010 to deep injection of oil-industry wastewater?

Oklahoma's quakes may go back further than 2010: the USGS suggested even the 1952 magnitude 5.7 El Reno earthquake may have been induced by wastewater injection.

How much bending did Harry Reid find along the San Andreas in the 50 years before 1906?

Comparing old and new surveys, Harry Reid found about 3.2 metres of gradual bending across the San Andreas in the fifty years before 1906, strain released all at once in the quake; this became his elastic-rebound theory.

Harry Fielding Reid, of elastic-rebound fame, was a professor at which university?

Reid taught geological physics at Johns Hopkins in his native Baltimore, where he was born in 1859, and published the elastic-rebound theory in his 1910 report on the 1906 earthquake.

Inge Lehmann discovered Earth's solid inner core in which year?

Inge Lehmann's 1936 paper, famously titled P', showed that waves reflecting off a solid inner core explained P-wave arrivals in the shadow zone; the Danish seismologist lived to 104.

The Lehmann discontinuity lies at roughly what depth?

The Lehmann discontinuity, an abrupt rise in P- and S-wave speeds roughly 190 to 250 km down in the upper mantle, is named for Inge Lehmann and is distinct from her far deeper inner-core boundary.

Beno Gutenberg earned his physics doctorate at Göttingen under which advisor?

Gutenberg took his 1911 Göttingen doctorate under Emil Wiechert, founder of the world's first geophysics institute; he later worked alongside Richter at Caltech.

In which state was Charles Richter born in 1900?

Richter was born on 26 April 1900 on a farm near Overpeck, Ohio, north of Cincinnati, and moved to Los Angeles with his mother and grandfather as a boy.

Andrija Mohorovičić, of Moho fame, was a scientist of which nationality?

Mohorovičić was Croatian, born in 1857 at Volosko near Opatija on the Istrian coast, and led the Zagreb meteorological observatory where he did his seismological work.

Which physicist taught Mohorovičić in Prague?

From 1875 Mohorovičić studied mathematics and physics at Prague, where Ernst Mach, later famous for the Mach number, was among his teachers.

British seismograph pioneer Milne, born in Liverpool, spent two decades working in which country?

He was hired by the Meiji government in 1876.

Luigi Palmieri, who improved the seismograph, took charge of which institution in 1854?

Palmieri directed the Vesuvius Observatory from 1854 and built an electromagnetic seismograph there in 1856 that registered the time and intensity of tremors.

Which element did Luigi Palmieri first detect on Earth?

Palmieri spotted helium's D3 spectral line in gases from Vesuvius lava in 1882, the first detection on Earth; the element had been seen in the Sun's spectrum in 1868.

Seismic wave velocity drops sharply at which boundary?

At the mantle–outer core boundary P-wave speed falls from about 13.7 to 8 km/s and S-waves stop entirely, since the liquid outer core cannot carry shear.

Which physicist predicted in 1885 the surface waves that now bear his name?

In Rayleigh waves surface particles move in retrograde ellipses.

Earthquake foci in a Wadati–Benioff zone can be as deep as roughly what?

Foci in a Wadati–Benioff zone follow the sinking slab down to about 670 km, the base of the mantle transition zone; no earthquakes are known much deeper.

Hugo Benioff, co-namesake of the Wadati–Benioff zone, worked at which institution?

Benioff spent his career at Caltech's Seismological Laboratory, where he designed the Benioff seismometer and strainmeter; his 1949 paper traced the dipping quake zones beneath island arcs.

What deep seafloor furrow forms where an oceanic plate bends down into a subduction zone?

An oceanic trench forms where the descending plate bends; the Mariana Trench reaches about 11 km below sea level at the Challenger Deep, the deepest point in the oceans.

Roughly how long is the Cascadia subduction zone?

It runs from Vancouver Island to Northern California.

The Explorer, Juan de Fuca and Gorda plates are remnants of which ancient plate?

They are the northern remnants of the Farallon plate, which has been sliding beneath North America for some 150 million years; the Cocos and Nazca plates are its southern remnants.

How much did the Juan de Fuca plate slip on average in the 1700 Cascadia earthquake?

The Juan de Fuca plate slipped an average of about 20 metres along a rupture some 1,000 km long, enough to put the 1700 quake's magnitude near 9.

On what date did the first great New Madrid earthquake strike?

The first great shock struck at about 2:15 a.m. on December 16, 1811, followed by others of similar size on January 23 and February 7, 1812.

The New Madrid quakes were the strongest recorded in the contiguous US east of which mountains?

The 1811–12 New Madrid shocks, estimated at magnitude 7 to 8, were the strongest ever recorded in the contiguous US east of the Rockies; the town of New Madrid sits in Missouri's bootheel.

Which Native American leader's alliance took the New Madrid quakes as a sign to support him?

Tecumseh had reportedly told southern tribes he would stamp his foot and shake the earth; when the New Madrid quakes struck in December 1811 many took it as proof, and his brother Tenskwatawa was the Prophet.

Reelfoot Lake, formed by the New Madrid earthquakes, lies in which state?

Reelfoot Lake lies in north-west Tennessee near Tiptonville, where land sank during the February 1812 shock and the Mississippi reportedly ran backwards to fill it; it is noted for bald cypress and nesting bald eagles.

The 1886 Charleston earthquake was felt as far away as which Caribbean island?

The magnitude-7-class Charleston shock of 31 August 1886 was felt as far away as Cuba, Bermuda and Chicago, and killed about 60 people in the city.

The 1933 Long Beach earthquake occurred on which fault?

The magnitude 6.4 shock of 10 March 1933 ruptured the Newport–Inglewood Fault; the collapse of unreinforced school buildings led to California's Field Act on school construction.

Which two hospitals collapsed in the 1971 San Fernando earthquake, causing most deaths?

The Veterans Administration Hospital in Sylmar collapsed, killing 49, and the new Olive View Medical Center was wrecked; the 9 February 1971 shock is also called the Sylmar earthquake.

The 1989 Loma Prieta earthquake was named after a peak in which mountain range?

Loma Prieta is a peak in the Santa Cruz Mountains south of San Jose; the magnitude 6.9 shock at 5:04 p.m. on 17 October 1989 interrupted the World Series at Candlestick Park.

Which San Francisco neighbourhood suffered heavy liquefaction damage in 1989?

The Marina District, built on sand and 1906 rubble dumped into the bay for the 1915 exposition, liquefied; buildings sank and a gas fire broke out, and the quake killed 63 people in all.

What peak ground acceleration did the 1994 Northridge earthquake reach?

Accelerometers at Tarzana recorded over 1.7 g during the 17 January 1994 shock, the highest ground acceleration ever measured in a North American urban area at the time.

The 1994 Northridge quake was what type of event?

Northridge was a blind thrust earthquake: the previously unknown thrust fault that slipped never breaks the surface, and its epicentre lay beneath Reseda in the San Fernando Valley.

The 1995 Kobe earthquake's hypocentre lay beneath the northern end of which land mass?

The rupture began beneath the northern tip of Awaji Island, about 20 km from central Kobe, on the Nojima Fault, whose surface break is now preserved in a museum.

The 1923 Great Kantō earthquake's fires were fanned by winds from what?

It struck at 11:58 am on September 1.

What share of Tangshan's buildings collapsed or became unusable within minutes in 1976?

About 85 percent of Tangshan's buildings collapsed or were left unusable within minutes of the 3:42 a.m. shock on 28 July 1976, in a city of a million people.

The 2008 Sichuan earthquake struck on which date, now China's Disaster Prevention and Reduction Day?

The Wenchuan quake struck at 2:28 p.m. on 12 May 2008; from 2009 China made the anniversary its National Disaster Prevention and Reduction Day.

The 2008 Sichuan earthquake's epicentre was about 80 km from which provincial capital?

The epicentre lay in Wenchuan County, about 80 km west-north-west of Chengdu, Sichuan's capital; the magnitude 7.9 quake killed more than 69,000 people.

Mexico City suffered badly in 1985 despite being over 350 km from the epicentre because it sits on what?

The quake struck along the Middle America Trench.

The 2017 Puebla quake struck on the anniversary of which disaster?

It struck on 19 September 2017, exactly 32 years after the 1985 Mexico City earthquake; a national drill marking that anniversary had been held just two hours earlier.

How is the 2010 Chile earthquake commonly known in Chile?

Chileans call it 27F for 27 February 2010, the date the magnitude 8.8 shock struck off central Chile before dawn.

The magnitude 8.8 Chilean earthquake of February 2010 is named for which region?

Seismologists call it the 2010 Maule earthquake: the rupture began off the Maule Region's coast near Curanipe and ran some 500 km along the subduction zone.

The 2015 Nepal earthquake caused the deadliest incident on record on which mountain?

Twenty-two people died at base camp.

The 2015 Nepal earthquake is also named for which district?

It is also called the Gorkha earthquake, after the district of its epicentre at the village of Barpak, about 80 km north-west of Kathmandu.

The 2005 Kashmir earthquake's epicentre was 19 km northeast of which city?

The epicentre lay about 19 km north-east of Muzaffarabad, capital of Pakistan-administered Azad Kashmir, which was largely destroyed; the 8 October 2005 quake killed at least 73,000.

Which building material worsened the 2003 Bam earthquake's death toll of 34,000?

Bam's houses and its ancient citadel, the Arg-e Bam, were largely mud brick, which crumbled in the 26 December 2003 shock; many newer buildings had ignored Iran's 1989 seismic code.

The 1999 İzmit earthquake was part of a westward-marching sequence on which structure since 1939?

Since 1939, ruptures on the North Anatolian Fault have stepped westward toward Istanbul, each loading the next segment; İzmit in August 1999 was followed by Düzce that November.

The first of the 2023 Turkey–Syria earthquakes had its epicentre 37 km from which city?

The epicentre lay about 37 km west-north-west of Gaziantep, near Pazarcık in Kahramanmaraş province; the Mw 7.8 shock struck at 4:17 a.m. on 6 February 2023 on the East Anatolian Fault.

Roughly how many aftershocks followed the 2023 Turkey–Syria earthquakes in three months?

More than 30,000 aftershocks were recorded in the three months after 6 February 2023; a second great shock of Mw 7.5–7.7 had struck near Elbistan the same afternoon.

The 1908 Messina earthquake is the deadliest in the history of which continent?

Messina, on 28 December 1908, killed more people than any other earthquake in European history; estimates of the dead in Sicily and Calabria run from about 75,000 to well over 100,000.

What share of Skopje was destroyed by the 1963 earthquake?

About 80 percent of Skopje, then in Yugoslavia, was destroyed by the 26 July 1963 quake, which killed over 1,000 people and left the old railway station's clock stopped at 5:17.

The 1977 Vrancea earthquake caused most of its deaths in which capital city?

Its hypocentre was unusually deep at 85 km.

How much silt did liquefaction produce in Christchurch's eastern suburbs in February 2011?

Liquefaction pushed around 400,000 tonnes of grey silt up through the eastern suburbs on 22 February 2011; the quake killed 185 people and closed the central city for years.

The 2010 Canterbury quake in New Zealand is also known by what name?

It is also called the Darfield earthquake, after the town nearest its epicentre west of Christchurch; the magnitude 7.1 shock at 4:35 a.m. on 4 September 2010 killed no one outright.

The 2016 Kaikōura quake has been described as what?

Geologists called Kaikōura the most complex earthquake ever studied: the magnitude 7.8 shock of 14 November 2016 ruptured at least 21 faults over about two minutes.

New Zealand's deadliest natural disaster, the 1931 quake, is named for which region?

The Hawke's Bay earthquake of 3 February 1931 killed 256 people, flattened Napier and Hastings, and lifted the seabed to turn a lagoon into dry land; it is also called the Napier earthquake.

Which capital city was devastated by an earthquake on 23 December 1972?

Managua, Nicaragua's capital, was wrecked just after midnight on 23 December 1972; between 4,000 and 11,000 people died, and Roberto Clemente was killed flying relief supplies there.

The 1970 Ancash earthquake in Peru triggered the world's deadliest example of what?

The shaking loosed ice and rock from Huascarán's north peak; the debris avalanche buried Yungay and Ranrahirca, killing about 20,000 of the quake's roughly 70,000 dead, the deadliest avalanche on record.

Which 1939 earthquake is tied as the most powerful ever instrumentally recorded in Turkey?

It killed 32,968 people.

The 1948 Ashgabat earthquake was little reported because of censorship by which government?

Casualty estimates range from 10,000 to 110,000.

The 1988 Armenian earthquake is also named for which town near its source?

It is the Spitak earthquake, after the town nearest the epicentre that was almost wholly destroyed on 7 December 1988; between 25,000 and 50,000 died, and Gyumri, then Leninakan, was badly hit too.

The 1990 Manjil–Rudbar earthquake in Iran struck near which sea?

The 21 June 1990 shock hit Gilan and Zanjan provinces just south of the Caspian Sea, killing between 35,000 and 50,000 and destroying the towns of Manjil and Rudbar.

The 2001 Gujarat earthquake struck on which Indian national holiday?

It struck at 8:46 a.m. on 26 January 2001, Republic Day, while crowds were at parades and school celebrations marking India's 1950 constitution.

Most deaths in the 2001 Gujarat earthquake occurred in which district?

Kutch district, around the epicentre near Bhuj, took the bulk of the 13,800 to 20,000 deaths; the towns of Bhuj, Anjar and Bhachau were largely flattened.

The 1935 Quetta earthquake was South Asia's deadliest until which year?

Quetta's toll of 30,000 to 60,000 on 31 May 1935 stood as South Asia's worst until the Kashmir earthquake of 8 October 2005 killed at least 73,000.

The 1897 Assam earthquake occurred on which structure at the edge of the Shillong Plateau?

Bilham and England's 2001 analysis put the rupture on the Oldham Fault, a steep reverse fault bounding the Shillong Plateau's northern edge, with slip of at least 11 metres.

The 1950 Assam–Tibet earthquake is the largest recorded quake caused by what?

The 15 August 1950 shock, magnitude 8.6 to 8.7, is the largest known earthquake caused by continental collision, where India pushes into Eurasia, rather than by oceanic subduction.

Russia's most powerful recorded earthquake struck off which peninsula in 1952?

The magnitude 9.0 quake of 4 November 1952 struck off Kamchatka's east coast; its tsunami destroyed Severo-Kurilsk on Paramushir Island, killing more than 2,000.

Between 1857 and 1966, Parkfield, California saw magnitude-6 quakes about every how many years?

Six magnitude-6 shocks between 1857 and 1966 came about every 22 years on average, so scientists forecast the next by 1993; it finally arrived in September 2004.

How long a stretch of the San Andreas ruptured in the 1857 Fort Tejon earthquake?

The 9 January 1857 rupture ran about 225 miles (360 km) along the San Andreas from Parkfield to Wrightwood, one of the largest quakes in California's recorded history.

Before 1906, which 1868 event was known as the 'Great San Francisco' quake?

The 21 October 1868 Hayward Fault earthquake was called the 'Great San Francisco earthquake' until 1906; it destroyed the Alameda County Courthouse in San Leandro and killed about 30 people.

The 1872 Owens Valley earthquake was centred near which town on the east side of the Sierra Nevada?

The 26 March 1872 shock centred near Lone Pine, where 27 people died in collapsed adobe houses; its magnitude, around 7.4 to 7.9, rivalled the 1906 San Francisco quake.

What new body of water did the 1959 Montana earthquake create by damming the Madison River?

The 17 August 1959 Hebgen Lake quake sent some 80 million tons of rock into Madison Canyon, burying a campground and damming the river to form Quake Lake, about 190 feet deep.

The 2002 Denali earthquake caused seiches on bodies of water as far away as which state?

Surface waves from the Mw 7.9 Denali quake of 3 November 2002 set water sloshing in lakes and pools as far as Texas and Louisiana, and damaged houseboats on Lake Union in Seattle.

What is Japan's JMA seismic intensity scale known as locally?

Shindo, 'degree of shaking', runs from 0 to 7 with levels 5 and 6 split into lower and upper; values come from ground acceleration and shaking duration, not from the quake's magnitude.

Japan's Earthquake Early Warning system began public nationwide alerts in which year?

The JMA began broadcasting Earthquake Early Warnings to the public on 1 October 2007; a P-wave detected by two or more stations triggers the analysis, and alerts go out by TV, radio and phone.

Over what timescale does a slow earthquake release its energy?

A slow earthquake, also called a silent earthquake, releases its energy over hours to months rather than seconds; slow-slip events beneath Cascadia recur roughly every 14 months.

Since 1900, every earthquake of magnitude 9.0 or greater has been what type?

They occur where one plate is forced beneath another.

An earthquake within a subducting plate is called what?

Intraslab quakes rupture inside the descending slab itself, as in the 2001 Nisqually quake some 50 km beneath Washington, rather than on the interface between plates.

A fault segment that has not slipped for an unusually long time is called a seismic what?

Loma Prieta filled a recognised gap in 1989.

Which Swiss hydrologist promoted the term 'seiche' in 1890 after observing Lake Geneva?

François-Alphonse Forel, the founder of limnology, popularised 'seiche' from 1890 in his studies of Lake Geneva; the word may derive from Latin siccus, 'dry', for the shoreline the oscillation exposes.

What distinguishes an earthquake swarm from a mainshock-aftershock sequence?

In a swarm no single quake is obviously the main shock; events of similar size cluster over weeks or months, as in the Vogtland and West Bohemia swarms recorded since the 16th century.

Which Austrian geologist coined 'Schwarmbeben', or swarm quake, in 1899?

Josef Knett, a geologist in the Austrian crown land of Bohemia, coined 'Schwarmbeben' in 1899 while analysing the 1824 swarm around Vogtland and western Bohemia.

Which mission first detected, but did not confirm, marsquakes in 1976?

Viking 2's deck-mounted seismometer registered one possible marsquake in 1976, but wind noise made it unconfirmable; InSight recorded the first confirmed marsquake in April 2019.

The Moho lies at what average depth beneath continental crust?

The Moho averages about 35 km down beneath the continents, deeper under mountain ranges, but only 5 to 10 km beneath the ocean floor.

In which year did Mohorovičić first identify the crust-mantle boundary named after him?

Analysing seismograms of the 8 October 1909 Pokupsko earthquake near Zagreb, Mohorovičić saw two sets of P and S arrivals and inferred a velocity jump about 50 km down.

Photographic examples of 'earthquake lights' came from which 1960s Japanese swarm?

The Matsushiro swarm of 1965–67 near Nagano produced tens of thousands of shocks, and Yutaka Yasui photographed glowing skies there, the best-known images of earthquake lights.

The 1975 Haicheng evacuation was based mainly on what warning sign?

A pronounced foreshock sequence in the days before 4 February 1975 drove the Haicheng evacuation; a 2006 study found the foreshocks, not a formal prediction, were the decisive trigger.

The Pacific Tsunami Warning Center is located where in Hawaii?

The PTWC moved from Ewa Beach to Ford Island in Pearl Harbor in 2012; the other US centre, the National Tsunami Warning Center, is at Palmer, Alaska.

How often do DART tsunami buoys log data in 'Event Mode'?

In Event Mode, triggered when the bottom pressure sensor detects a tsunami, a DART buoy reports every 15 seconds instead of the 15-minute readings of Standard Mode.

The 1946 Aleutian tsunami destroyed which lighthouse, killing all five keepers?

The Scotch Cap Lighthouse on Unimak Island was swept away by a wave of over 30 metres on 1 April 1946, killing its five Coast Guard keepers; the same tsunami killed 159 people in Hawaii.

The 1929 Grand Banks earthquake's submarine landslide snapped how many transatlantic cables?

The turbidity current from the 18 November 1929 slide snapped 12 transatlantic telegraph cables in sequence, and the timing of the breaks showed it raced downslope at speeds later estimated near 100 km/h.

The 526 Antioch earthquake struck during the reign of which Byzantine emperor?

Antioch burned and fell in May 526 under Justin I, whose nephew Justinian succeeded him the next year; chroniclers put the dead at about 250,000.

The tsunami from the 365 Crete earthquake hurled ships how far inland?

Alexandria and the Nile Delta were devastated.

The 1138 Aleppo earthquake's death toll of 230,000 was reported by which 15th-century historian?

Ibn Taghribirdi, writing in the 15th century, gave 230,000 dead; modern historians think the figure conflates the 1138 Aleppo quake with others of 1137 and 1139 in Mesopotamia and the Caucasus.

The 1693 Sicily earthquake killed almost two-thirds of the population of which city?

Catania lost some two-thirds of its people on 11 January 1693 and was rebuilt as a showpiece of Sicilian Baroque; at an estimated Mw 7.4 the quake is the most powerful in Italy's recorded history.

How many strong earthquakes struck Calabria over two months in 1783?

Five strong shocks hit Calabria between 5 February and 28 March 1783; the first two raised tsunamis, the second triggering the Scilla landslide wave that killed some 1,500 people on the beach.

Arica, struck by a great earthquake in 1868, was then part of which country?

Arica was Peruvian until Chile took it in the War of the Pacific of 1879–84; the 13 August 1868 tsunami carried the USS Wateree some 500 m inland and was recorded in Hawaii, Japan and New Zealand.

What is the largest known inland earthquake in the Japanese archipelago?

The 28 October 1891 Mino–Owari quake, also called the Nōbi earthquake, reached about magnitude 8.0 on the Neodani Fault, the largest inland shock known in Japan, and killed over 7,000 people.

The 1896 Sanriku tsunami set a wave-height record of 38.2 m that stood until when?

The 38.2 m run-up at Ryōri Bay in 1896 stood as Japan's record until the 2011 Tōhoku tsunami reached 40.5 m at Miyako in Iwate.

The 1707 Hōei earthquake was followed 49 days later by the eruption of which volcano?

The Hōei earthquake of 28 October 1707 ruptured the Nankai Trough; 49 days later, on 16 December, Mount Fuji began its Hōei eruption, which showered ash on Edo.

Great earthquakes along the Nankai Trough recur roughly every how many years?

Great Nankai Trough quakes recur roughly every 100 to 200 years; the record runs from the Hakuhō earthquake of 684 to the Shōwa Nankai quake of 1946.

Japan's 1948 Fukui earthquake devastated a city still recovering from what?

Some 3,769 people died.

The 2016 Kumamoto earthquakes struck which Japanese island?

Kumamoto is on Kyushu, Japan's south-western main island; a magnitude 6.2 foreshock on 14 April 2016 was followed two days later by the magnitude 7.0 mainshock that wrecked Kumamoto Castle's walls.

On what date did the 2024 Noto earthquake strike Japan's Ishikawa Prefecture?

It struck at 4:10 p.m. on New Year's Day, 1 January 2024, reaching the maximum JMA intensity of Shindo 7 in Shika and Wajima and killing more than 200 people.

Which Ecuadorian city's commercial district, Tarqui, was destroyed in the 2016 earthquake?

Manta, the port city in Manabí province, lost its Tarqui commercial district in the 16 April 2016 magnitude 7.8 quake, which killed at least 676 people across Ecuador.

The 2023 Morocco quake was the country's deadliest since which 1960 disaster?

The 8 September 2023 Al Haouz quake, centred in the High Atlas near Oukaïmeden, killed nearly 3,000, the most in Morocco since the 29 February 1960 Agadir earthquake killed some 12,000 to 15,000.

The 2021 Haiti earthquake struck which peninsula?

The magnitude 7.2 quake of 14 August 2021 hit Haiti's south-western Tiburon Peninsula around Les Cayes, on the Enriquillo–Plantain Garden fault zone, killing at least 2,248.

A localised tsunami from the 2018 Sulawesi earthquake struck which provincial capital?

Palu, capital of Central Sulawesi, sits at the head of a narrow bay that funnelled the 28 September 2018 tsunami; with liquefaction in Balaroa and Petobo, around 4,340 people died.

How many members of Italy's risk commission were accused after the 2009 L'Aquila quake?

Seven members of the Major Risks Commission, six scientists and one official, were convicted of manslaughter in 2012 for 'inexact, incomplete and contradictory' reassurances; all but the official were acquitted on appeal in 2014.

The August 2016 Central Italy earthquake's epicentre was close to which town?

The 24 August 2016 shock was centred near Accumoli, between Amatrice and Norcia, at a depth of only about 4 km; Amatrice was largely destroyed and 299 people died.

The 1980 Irpinia earthquake produced how many main shocks within 80 seconds?

Three main ruptures came about 20 seconds apart on 23 November 1980 in a magnitude 6.9 sequence that killed at least 2,483 and left some 250,000 homeless in Irpinia.

The 1915 Avezzano earthquake, which killed about 30,000, is also named after which basin?

It is also called the Fucino earthquake, after the drained lake basin where Avezzano stood; the 13 January 1915 shock killed about 30,000, wiping out most of Avezzano's population.

The 1976 Guatemala earthquake ruptured 240 km of which structure?

The 4 February 1976 quake ruptured some 240 km of the Motagua Fault, the boundary between the North American and Caribbean plates, at 3 a.m.; about 23,000 people died.

The original body-wave magnitude scale (mB) does not saturate until roughly what magnitude?

It is insensitive to events below about M5.5.

The surface-wave magnitude scale is based on which type of wave?

Ms is measured from the amplitude of Rayleigh waves with a period of about 20 seconds; China adopted it as a national standard for reporting magnitudes.

Homes built of which material may qualify for lower earthquake insurance rates, because they withstand shaking better?

Wood-frame houses flex with shaking and rarely collapse, so insurers rate them below brick or concrete-block homes, whose rigid walls crack and topple.

Japan's 'new seismic design' standard, the shin-taishin code, took effect in which year?

Japan's new seismic design standard took effect on 1 June 1981; buildings meeting it are called shin-taishin, and in the 1995 Kobe quake they collapsed far less often than older kyū-taishin structures.

A tuned mass damper reduces a building's sway by tuning its oscillation to what?

A tuned mass damper is tuned to the structure's own resonant frequency so it swings out of phase with the building and cancels its sway; Taipei 101's 660-tonne steel sphere is the best-known example.

Horizontal peak ground accelerations are generally larger than vertical ones, except where?

Close to large earthquakes the vertical component can rival or exceed the horizontal; the February 2011 Christchurch quake recorded vertical accelerations of about 2.2 g, well above the horizontal at the same site.

The European Macroseismic Scale is usually cited with which year?

The European Macroseismic Scale is cited as EMS-98 for the 1998 edition that replaced MSK-64; it rates intensity from I to XII using building vulnerability classes.

The MSK-64 intensity scale was proposed by scientists from the USSR, East Germany and where?

Medvedev, Sponheuer and Kárník gave it its name; Vít Kárník was a Czech seismologist in Prague, so the 1964 scale came from the USSR, East Germany and Czechoslovakia.

Which country used the Rossi–Forel scale until replacing it with its own scale in 1996?

The Philippines used Rossi–Forel until 1996, when PHIVOLCS introduced its own PHIVOLCS Earthquake Intensity Scale, running from I to X.

Besides being a volcanologist, Giuseppe Mercalli was what?

Mercalli was ordained a Catholic priest and taught in seminaries before his science career; he directed the Vesuvius Observatory from 1911 until he died in a fire at his home in 1914.

Fusakichi Omori sailed from Japan to study which 1906 disaster on site?

Omori travelled to California after the April 1906 San Francisco earthquake to survey its effects, and was assaulted in the street amid the anti-Japanese hostility of the time.

In 1969 Kiyoo Mogi warned of a possible magnitude-8 quake in which region of Japan?

Mogi identified a seismic gap along the Tōkai coast in 1969; Japan passed its Large-Scale Earthquake Countermeasures Act in 1978 to prepare Shizuoka and its neighbours for the expected shock.

Alfred Wegener proposed continental drift in which year?

Wegener presented continental drift in lectures in January 1912 and in his 1915 book The Origin of Continents and Oceans; mainstream geology accepted it only with plate tectonics in the 1960s.

The Alpide belt accounts for what share of the world's largest earthquakes?

About 17% of the world's largest earthquakes occur on the Alpide belt, second only to the Ring of Fire; it includes the 2005 Kashmir and 1999 İzmit quakes.

Roughly how long is the Alpide belt?

The Alpide belt runs more than 15,000 km from Java and Sumatra through the Himalayas, Iran and Turkey to the Alps and out into the Atlantic.

The 1958 Lituya Bay megatsunami stripped trees to what maximum elevation, a record for any tsunami?

The wave stripped trees to 524 m (1,720 ft) above the bay, a record run-up for any tsunami, after a magnitude 7.8 to 8.3 quake on the Fairweather Fault dropped 30 million cubic metres of rock into the inlet.

How was the time of the 1692 Port Royal disaster in Jamaica pinned down to about 11:43 a.m.?

A pocket watch recovered from the sunken harbour in 1959 had stopped at 11:43; most of the 'wickedest city in the world' sank, killing about 2,000 at once and 3,000 more from injury and disease.

Moonquakes are far weaker than earthquakes, but with little to damp the vibrations, their shaking can last up to how long?

An hour of shaking is possible because the Moon has fewer attenuating factors; Apollo seismometers listened from 1969 until they were switched off in 1977.

Roughly how many seismic events did NASA's InSight lander record on Mars between 2019 and 2022?

InSight logged 1,319 seismic events, over 1,300, before dust ended its mission in December 2022; several proved to be meteorite impacts, and the largest, in May 2022, was about magnitude 4.7.

Which ancient thinker's idea of winds trapped in caves gave rise to the 'sultry weather' quake myth?

Aristotle's Meteorologica blamed earthquakes on winds trapped in underground caves, so hot, still 'earthquake weather' was expected beforehand; geologists dismiss any link between weather and quakes.

In the open ocean a tsunami travels at roughly the speed of what?

In deep water a tsunami races along at 700 to 800 km/h, about the speed of a jet airliner, yet stands only tens of centimetres high until it slows and rears up in the shallows.